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fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.4.1 General | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.4.1.1 UE Network Slice configuration | The Network Slice configuration information contains one or more Configured NSSAI(s). A Configured NSSAI may either be configured by a Serving PLMN and apply to the Serving PLMN, or may be a Default Configured NSSAI configured by the HPLMN and that applies to any PLMNs for which no specific Configured NSSAI has been provided to the UE. There is at most one Configured NSSAI per PLMN.
NOTE 1: The value(s) used in the Default Configured NSSAI are expected to be commonly decided by all roaming partners, e.g. by the use of values standardized by 3GPP or other bodies.
The Default Configured NSSAI, if it is configured in the UE, is used by the UE in a Serving PLMN only if the UE has no Configured NSSAI for the Serving PLMN.
The Configured NSSAI of a PLMN may include S-NSSAIs that have standard values or PLMN-specific values.
The Configured NSSAI for the Serving PLMN includes the S-NSSAI values which can be used in the Serving PLMN and may be associated with mapping of each S-NSSAI of the Configured NSSAI to one or more corresponding HPLMN S-NSSAI values. The following applies:
- In the non-roaming case and if the Serving PLMN ID is the same as the PLMN ID of the SUPI, the network shall not provide any mapped S-NSSAI to the UE with the Configured NSSAI.
- In the non-roaming case and if the Serving PLMN ID is not the same as the PLMN ID of the SUPI, when the Configured NSSAI of Serving PLMN is provided to the UE the network shall provide the mapped S-NSSAI(s) of the HPLMN to the UE if different values are used for S-NSSAI in Serving PLMN and mapped S-NSSAI in HPLMN.
NOTE 2: It is recommended that the Serving PLMN and the HPLMN use the same S-NSSAI values in this case.
- In the roaming case, the AMF shall provide to the UE the mapping of each S-NSSAI of the Configured NSSAI for the Serving PLMN to the corresponding S-NSSAI values of the HPLMN when providing NSSAI information, as described in TS 24.501 [47].
A UE subscription may contain Network Slice Simultaneous Registration Group (NSSRG) information. If so, the UE configuration is performed as described in clause 5.15.12.2.
The UE may be pre-configured with a Default Configured NSSAI associated with the SUPI. The UE may be provisioned/updated by the HPLMN with a Default Configured NSSAI, determined by the UDM in the HPLMN, by using the UE Parameters Update via UDM Control Plane procedure defined in clause 4.20 of TS 23.502 [3]. If the HPLMN configures a UE with the Default Configured NSSAI, each S-NSSAI in the Default Configured NSSAI shall also be one of the Subscribed S-NSSAI(s). If the Subscribed S-NSSAI(s) which are also present in the Default Configured NSSAI are updated (i.e. a Subscribed S-NSSAI is added or removed from the UE subscription or a Subscribed S-NSSAI is added to (or removed from) the Default Configured NSSAI), the UDM should update the Default Configured NSSAI in the UE.
NOTE 2: The Subscribed S-NSSAIs marked as default S-NSSAI are not required to be part of the Default Configured NSSAI if one is configured for the UE.
In the HPLMN, the S-NSSAIs in the Configured NSSAI provided as described in clause 5.15.4.2, at the time when they are provided to the UE, shall match the Subscribed S-NSSAIs for the UE except a case when Alternative S-NSSAI(s) that are not subscribed S-NSSAI(s) are temporarily used and provided to the UE in the Configured NSSAI as described in clause 5.15.19.
When the Subscribed S-NSSAI(s) are updated (i.e. some existing S-NSSAIs are removed and/or some new S-NSSAIs are added) and one or more are applicable to the Serving PLMN the UE is registered in, as described in clause 5.15.3, or when the associated mapping is updated the AMF shall update the UE with the Configured NSSAI for the Serving PLMN and/or Allowed NSSAI and Partially Allowed NSSAI and/or the associated mapping to HPLMN S-NSSAIs (see clause 5.15.4.2). When there is the need to update the Allowed NSSAI or Partially Allowed NSSAI, the AMF shall provide the UE with the new Allowed NSSAI or Partially Allowed NSSAI and the associated mapping to HPLMN S-NSSAIs, unless the AMF cannot determine the new Allowed NSSAI (e.g. all S-NSSAIs in the old Allowed NSSAI have been removed from the Subscribed S-NSSAIs), in which case the AMF shall not send any Allowed NSSAI to the UE but indicate to the UE to perform a Registration procedure. If the UE is in a CM-IDLE state, the AMF may trigger Network Triggered Service Request or wait until the UE is in a CM-CONNECTED state as described in clause 4.2.4.2, TS 23.502 [3].
When providing a Requested NSSAI to the network upon registration, the UE in a given PLMN only includes and uses S-NSSAIs applying to this PLMN. The mapping of S-NSSAIs of the Requested NSSAI to HPLMN S-NSSAIs may also be provided (see clause 5.15.4.1.2 for when this is needed). The S-NSSAIs in the Requested NSSAI are part of the Configured and/or Allowed NSSAIs applicable for this PLMN, when they are available. If the UE has received NSSRG information together with the Configured NSSAI, it only includes in the Requested NSSAI S-NSSAIs that all share a common NSSRG. If the UE has stored Pending NSSAI and the UE is still interested in the Pending NSSAI then all the S-NSSAIs in the Requested NSSAI and the Pending S-NSSAI shall share a common NSSRG. If no Configured NSSAI and Allowed NSSAI for the PLMN are available, the S-NSSAIs in the Requested NSSAI correspond to the Default Configured NSSAI, if configured in the UE. Upon successful completion of a UE's Registration procedure over an Access Type, the UE obtains from the AMF an Allowed NSSAI or Partially Allowed NSSAI for this Access Type, which includes one or more S-NSSAIs and, if needed (see clause 5.15.4.1.2 for when this is needed), their mapping to the HPLMN S-NSSAIs. These S-NSSAIs are valid for the current Registration Area and Access Type provided by the AMF the UE has registered with and can be used simultaneously by the UE (up to the maximum number of simultaneous Network Slice instances or PDU Sessions).
The UE might also obtain from the AMF, one or more rejected S-NSSAIs with cause and validity of rejection. An S-NSSAI may be rejected:
- for the entire PLMN;
- for the current Registration Area; or
- partially in the current Registration Area. Such S-NSSAI rejected partially in the current Registration area is associated with a list of TAs where the S-NSSAI is not supported.
The AMF may also reject the use of an S-NSSAI due to congestion as described in clause 5.19.7.4.
While the UE remains RM-REGISTERED in the PLMN and regardless of the Access Type, the UE shall not re-attempt to register to an S-NSSAI rejected for the entire PLMN until this rejected S-NSSAI is deleted as specified below.
While the UE remains RM-REGISTERED in the PLMN, the UE shall not re-attempt to register to an S-NSSAI rejected in the current Registration Area until it moves out of the current Registration Area.
While the UE remains RM-REGISTERED in the PLMN, the UE shall not re-attempt to register to an S-NSSAI rejected partially in the RA until the UE moves into a TA which is not part of the list of TAs associated with the S-NSSAI.
NOTE 3: The details and more cases of S-NSSAI rejection are described in TS 24.501 [47].
The S-NSSAIs that the UE provides in the Requested NSSAI which are neither in the Allowed NSSAI nor in the Partially Allowed NSSAI, nor provided as a rejected S-NSSAI, shall, by the UE, not be regarded as rejected, i.e. the UE may request to register these S-NSSAIs again next time the UE sends a Requested NSSAI.
The UE stores (S-)NSSAIs as follows:
- When provisioned with a Configured NSSAI for a PLMN and/or a mapping of Configured NSSAI to HPLMN S-NSSAIs and possibly NSSRG information for each S-NSSAI in the Configured NSSAI (if applicable and supported by the UE), or when requested to remove the configuration due to network slicing subscription change, the UE shall:
- replace any stored (old) Configured NSSAI for this PLMN with the new Configured NSSAI for this PLMN (if applicable); and
- delete any stored associated mapping of this old Configured NSSAI for this PLMN to HPLMN S-NSSAIs and, if present and applicable, store the mapping of Configured NSSAI to HPLMN S-NSSAIs; and
- delete any stored associated NSSRG information for each S-NSSAI of the Configured NSSAI and, if present, store the associated NSSRG information for each S-NSSAI of the Configured NSSAI; and
- delete any stored rejected S-NSSAI for this PLMN;
- keep the received Configured NSSAI for a PLMN (if applicable) and associated mapping to HPLMN S-NSSAIs (if applicable) and associated NSSRG information for each S-NSSAI of the Configured NSSAI (if applicable and supported by the UE) stored in the UE, even when registering in another PLMN, until a new Configured NSSAI for this PLMN and/or associated mapping are provisioned in the UE, or until the network slicing subscription changes, as described in clause 5.15.4.2. The number of Configured NSSAIs and associated mapping to be kept stored in the UE for PLMNs other than the HPLMN is up to UE implementation. A UE shall at least be capable of storing a Configured NSSAI for the serving PLMN including any necessary mapping of the Configured NSSAI for the Serving PLMN to HPLMN S-NSSAIs and the Default Configured NSSAI.
- The Allowed NSSAI received in a Registration Accept message or a UE Configuration Update Command applies to a PLMN when at least a TAI of this PLMN is included in the RA/TAI list included in this Registration Accept message or UE Configuration Update Command. If the UE Configuration Update Command contains an Allowed NSSAI but not a TAI List, then the last received RA/TAI list applies for the decision on which PLMN(s) the Allowed NSSAI is applicable. If received, the Allowed NSSAI for a PLMN and Access Type and any associated mapping of this Allowed NSSAI to HPLMN S-NSSAIs shall be stored in the UE. The UE should store this Allowed NSSAI and any associated mapping of this Allowed NSSAI to HPLMN S-NSSAIs also when the UE is turned off, or until the network slicing subscription changes, as described in clause 5.15.4.2:
NOTE 4: Whether the UE stores the Allowed NSSAI and any associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs also when the UE is turned off is left to UE implementation.
- When a new Allowed NSSAI for a PLMN and any associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs are received over an Access Type, the UE shall:
- replace any stored (old) Allowed NSSAI and any associated mapping for these PLMN and Access Type with this new Allowed NSSAI; and
- delete any stored associated mapping of this old Allowed NSSAI for this PLMN to HPLMN S-NSSAIs and, if present, store the associated mapping of this new Allowed NSSAI to HPLMN S-NSSAIs;
- If received, a Partially Allowed NSSAI received in a Registration Accept message or a UE Configuration Update Command message applies to the current Registration Area. The UE stores the Partially Allowed NSSAI in the same way as described for the Allowed NSSAI (see also clause 5.15.17).
- If received, an S-NSSAI rejected for the entire PLMN shall be stored in the UE while RM-REGISTERED in this PLMN regardless of the Access Type or until it is deleted.
- If received, an S-NSSAI rejected for the current Registration Area shall be stored in the UE while RM-REGISTERED until the UE moves out of the current Registration Area or until the S-NSSAI is deleted.
- If received, an S-NSSAI rejected partially in the RA shall be stored in the UE while RM-REGISTERED until the UE moves out of the current Registration Area or until the S-NSSAI is deleted (see also clause 5.15.17).
NOTE 5: The storage aspects of rejected S-NSSAIs are described in TS 24.501 [47].
- If received, the Pending NSSAI shall be stored in the UE as described in TS 24.501 [47].
- If received, the S-NSSAI validity time information shall be stored in the UE in the UE as described in TS 24.501 [47].
- If received, the S-NSSAI location availability information shall be stored in the UE as described in TS 24.501 [47].
- If received, the mapping of old S-NSSAI to the Alternative S-NSSAI and associated Access Type shall be stored in the UE as described in TS 24.501 [47].
UE configuration to guide UE selection of a N3IWF/TNGF that supports the S-NSSAIs needed by the UE is defined in clause 6.3.6 and clause 6.3.12 respectively. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.4.1.2 Mapping of S-NSSAIs values in the Allowed NSSAI and in the Requested NSSAI to the S-NSSAIs values used in the HPLMN | For the roaming case, one or more S-NSSAIs in an Allowed NSSAI provided to the UE can have values which are not part of the UE's current Network Slice configuration information for the Serving PLMN. In this case, the network provides the Allowed NSSAI together with the mapping of each S-NSSAI of the Allowed NSSAI to the corresponding S-NSSAI of the HPLMN. This mapping information allows the UE to associate Applications to S-NSSAIs of the HPLMN as per NSSP of the URSP rules or as per the UE Local Configuration, as defined in clause 6.1.2.2.1 of TS 23.503 [45] and to the corresponding S-NSSAI from the Allowed NSSAI.
In the non-roaming case and if the Serving PLMN ID is the same as the PLMN ID of the SUPI, the network shall not provide any mapped S-NSSAI to the UE with the Allowed NSSAI. In the non-roaming case and if the Serving PLMN ID is not the same as the PLMN ID of the SUPI, the network shall provide the mapped S-NSSAI of the HPLMN to the UE with the Allowed NSSAI if different values are used for S-NSSAI in Serving PLMN and mapped S-NSSAI in HPLMN.
NOTE: It is recommended that the Serving PLMN and the HPLMN use the same S-NSSAI values in this case.
The UE shall provide in the Requested NSSAI the mapping of S-NSSAIs of the Serving PLMN values to the corresponding S-NSSAI values of the HPLMN, for each S-NSSAI in the Requested NSSAI for which a mapping is available. These values are found in the mapping previously received from the Serving PLMN of the S-NSSAIs of the Configured NSSAI for the Serving PLMN or of the S-NSSAIs of the Allowed NSSAI for the Serving PLMN and Access Type to the corresponding S-NSSAIs values used in the HPLMN.
If the AMF provides Partially Allowed NSSAI to the UE, in roaming case the AMF may provide the mapping information of each S-NSSAI of the Partially Allowed NSSAI to the corresponding HPLMN S-NSSAI as described in clause 5.15.17. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.4.2 Update of UE Network Slice configuration | At any time, the AMF may provide the UE with a new Configured NSSAI for the Serving PLMN, associated with mapping of the Configured NSSAI to HPLMN S-NSSAIs as specified in clause 5.15.4.1. The Configured NSSAI for the Serving PLMN and the mapping information is either determined in the AMF (if based on configuration, the AMF is allowed to determine the Network Slice configuration for the whole PLMN) or by the NSSF. The AMF provides an updated Configured NSSAI as specified in clause 4.2.4 of TS 23.502 [3], UE Configuration Update procedure.
If an S-NSSAI is to be stopped to be used, e.g. due to the network slice is to be deleted as described in TS 28.541 [149], the AMFs may reject UE requests for the S-NSSAI based on the OAM state before the network slice becomes unavailable. The AMF may based on operator policies (e.g. when there is no timing information related to the termination or the AMF or UE does not support the timing information as described in in clause 5.15.16), release PDU Sessions associated with the S-NSSAI and remove the S-NSSAI from e.g. the Allowed NSSAI and the Configured NSSAI before the Network Slice becomes unavailable. The AMF may use the timing information as described in clause 5.15.16 if it supports this feature and set validity time of the S-NSSAI accordingly.
The AMF shall provide the UE with NSSRG information alongside the Configured NSSAI if NSSRG information is included in the subscription information received from the UDM and if the UE has indicated support for the feature as part of the registration request, see clause 5.15.12.
The AMF may provide the UE with the mapping of old S-NSSAI to the Alternative S-NSSAI if the UE has indicated support for the feature as part of the registration request, see clause 5.15.19.
If the HPLMN performs the configuration update of a UE registered in the HPLMN (e.g. due to a change in the Subscribed S-NSSAI(s) or due to a change of NSSRG information), this results in updates to the Configured NSSAI for the HPLMN and, if applicable, NSSRG information for each S-NSSAI of the Configured NSSAI. Updates to the Allowed NSSAI and/or, if present, to the associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs are also possible if the configuration update affects S-NSSAI(s) in the current Allowed NSSAI.
If the VPLMN performs the configuration update of a UE registered in the VPLMN (e.g. due to a change in the Subscribed S-NSSAI(s), the associated mapping is updated, or due to a change of NSSRG information), this results in updates to the Configured NSSAI for the Serving PLMN and/or to the associated mapping of the Configured NSSAI for the Serving PLMN to HPLMN S-NSSAIs and, if applicable, NSSRG information for each S-NSSAI of the Configured NSSAI. Updates to the Allowed NSSAI and/or to the associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs are also possible if the configuration update affects S-NSSAI(s) in the current Allowed NSSAI.
A UE for which the Configured NSSAI for the Serving PLMN has been updated as described in clause 5.15.4.1 and has been requested to perform a Registration procedure, shall initiate a Registration procedure to receive a new valid Allowed NSSAI (see clause 5.15.5.2.2).
When the subscribed S-NSSAIs change, a UDR flag is set in the HPLMN to make sure the current PLMN (or, if the UE was not reachable, the next serving PLMN) is informed by the UDM that the subscription data for network slicing has changed. The AMF, when it receives the indication from the UDM subscription has changed, indicates the UE that subscription has changed and uses any updated subscription information from the UDM to update the UE. Once the AMF updates the UE and obtains an acknowledgment from the UE, the AMF informs the UDM that the configuration update was successful and the UDM clears the flag in the UDR. If the UE is in a CM-IDLE state, the AMF may trigger Network Triggered Service Request or wait until the UE is in a CM-CONNECTED state as described in clause 4.2.4.2, TS 23.502 [3].
If the UE receives indication from the AMF that Network Slicing subscription has changed, the UE locally deletes the network slicing information it has for all PLMNs, except the Default Configured NSSAI (if present). It also updates the current PLMN network slicing configuration information with any received values from the AMF.
The update of URSP rules (which include the NSSP), if necessary at any time, is described in TS 23.503 [45]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5 Detailed Operation Overview | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.1 General | The establishment of User Plane connectivity to a Data Network via a Network Slice instance(s) comprises two steps:
- performing a RM procedure to select an AMF that supports the required Network Slices.
- establishing one or more PDU Session to the required Data network via the Network Slice instance(s). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.2 Selection of a Serving AMF supporting the Network Slices | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.2.1 Registration to a set of Network Slices | When a UE registers over an Access Type with a PLMN, if the UE has either or both of:
- a Configured NSSAI for this PLMN;
- an Allowed NSSAI for this PLMN and Access Type;
the UE shall provide to the network, in AS layer under the conditions described in clause 5.15.9 and in NAS layer, a Requested NSSAI containing the S-NSSAI(s) corresponding to the Network Slice(s) to which the UE wishes to register, unless they are stored in the UE in the Pending NSSAI.
The Requested NSSAI shall be one of:
- the Default Configured NSSAI, i.e. if the UE has no Configured NSSAI nor an Allowed NSSAI for the serving PLMN;
- the Configured-NSSAI, or a subset thereof as described below, e.g. if the UE has no Allowed NSSAI for the Access Type for the serving PLMN;
- the Allowed-NSSAI for the Access Type over which the Requested NSSAI is sent, or a subset thereof; or
- the Allowed-NSSAI for the Access Type over which the Requested NSSAI is sent, or a subset thereof, plus one or more S-NSSAIs from the Configured-NSSAI not yet in the Allowed NSSAI for the Access Type as described below.
NOTE 1: If the UE wishes to register only a subset of the S-NSSAIs from the Configured NSSAI or the Allowed NSSAI, to be able to register with some Network Slices e.g. to establish PDU Sessions for some application(s) and the UE uses the URSP rules (which includes the NSSP) or the UE Local Configuration as defined in clause 6.1.2.2.1 of TS 23.503 [45], then the UE uses applicable the URSP rules or the UE Local Configuration to ensure that the S-NSSAIs included in the Requested NSSAI are not in conflict with the URSP rules or with the UE Local Configuration.
The subset of S-NSSAIs in the Configured-NSSAI provided in the Requested NSSAI consists of one or more S-NSSAI(s) in the Configured NSSAI applicable to this PLMN, if one is present and for which no corresponding S-NSSAI is already present in the Allowed NSSAI for the access type for this PLMN. The UE shall not include in the Requested NSSAI any S-NSSAI that is currently rejected by the network (i.e. rejected in the current registration area or rejected in the PLMN). For the registration to a PLMN for which neither a Configured NSSAI applicable to this PLMN or an Allowed NSSAI are present, the S-NSSAIs provided in the Requested NSSAI correspond to the S-NSSAI(s) in the Default Configured NSSAI unless the UE has HPLMN S-NSSAI for established PDU Session(s) in which case the HPLMN S-NSSAI(s) shall be provided in the mapping of Requested NSSAI in the NAS Registration Request message, with no corresponding VPLMN S-NSSAI in the Requested NSSAI. If the UE has been provided with NSSRG information together with the Configured NSSAI, the UE only includes in the Requested NSSAI S-NSSAIs that share a common NSSRG, see clause 5.15.12.2. If the UE has stored Pending NSSAI and the UE is still interested in the Pending NSSAI then all the S-NSSAIs in the Requested NSSAI and the Pending S-NSSAI shall share a common NSSRG.
When a UE registers over an Access Type with a PLMN, the UE shall also indicate in the Registration Request message when the Requested NSSAI is based on the Default Configured NSSAI.
The UE shall include the Requested NSSAI in the RRC Connection Establishment and in the establishment of the connection to the N3IWF/TNGF (as applicable) and in the NAS Registration procedure messages subject to conditions set out in clause 5.15.9. However, the UE shall not indicate any NSSAI in RRC Connection Establishment or Initial NAS message unless it has either a Configured NSSAI for the corresponding PLMN, an Allowed NSSAI for the corresponding PLMN and Access Type, or the Default Configured NSSAI. If the UE has HPLMN S-NSSAI(s) for established PDU Session(s), the HPLMN S-NSSAI(s) shall be provided in the mapping of Requested NSSAI in the NAS Registration Request message, independent of whether the UE has the corresponding VPLMN S-NSSAI. The (R)AN shall route the NAS signalling between this UE and an AMF selected using the Requested NSSAI obtained during RRC Connection Establishment or connection to N3IWF/TNGF respectively. If the (R)AN is unable to select an AMF based on the Requested NSSAI, it routes the NAS signalling to an AMF from a set of default AMFs. In the NAS signalling, if the UE is roaming, the UE provides the mapping of each S-NSSAI of the Requested NSSAI to a corresponding HPLMN S-NSSAI.
When a UE registers with a PLMN, if for this PLMN the UE has not included a Requested NSSAI nor a GUAMI while establishing the connection to the (R)AN, the (R)AN shall route all NAS signalling from/to this UE to/from a default AMF. When receiving from the UE a Requested NSSAI and a 5G-S-TMSI or a GUAMI in RRC Connection Establishment or in the establishment of connection to N3IWF/TNGF, if the 5G-AN can reach an AMF corresponding to the 5G-S-TMSI or GUAMI, then 5G-AN forwards the request to this AMF. Otherwise, the 5G-AN selects a suitable AMF based on the Requested NSSAI provided by the UE and forwards the request to the selected AMF. If the 5G-AN is not able to select an AMF based on the Requested NSSAI, then the request is sent to a default AMF.
When the AMF selected by the AN during Registration Procedure receives the UE Registration request, or after an AMF selection by MME (i.e. during EPS to 5GS handover) the AMF receives S-NSSAI(s) from SMF+PGW-C in 5GC:
- As part of the Registration procedure described in clause 4.2.2.2.2 of TS 23.502 [3], or as part of the EPS to 5GS handover using N26 interface procedure described in clause 4.11.1.2.2 of TS 23.502 [3], the AMF may query the UDM to retrieve UE subscription information including the Subscribed S-NSSAIs.
- The AMF verifies whether the S-NSSAI(s) in the Requested NSSAI or the S-NSSAI(s) received from SMF+PGW-C are permitted based on the Subscribed S-NSSAIs (to identify the Subscribed S-NSSAIs the AMF may use the mapping to HPLMN S-NSSAIs provided by the UE, in the NAS message, for each S-NSSAI of the Requested NSSAI).
- When the UE context in the AMF does not yet include an Allowed NSSAI for the corresponding Access Type, the AMF queries the NSSF (see (B) below for subsequent handling), except in the case when, based on configuration in this AMF, the AMF is allowed to determine whether it can serve the UE (see (A) below for subsequent handling). The discovery and selection of the NSSF is defined in clause 6.3.28.
NOTE 2: The configuration in the AMF depends on operator's policy.
- When the UE context in the AMF already includes an Allowed NSSAI for the corresponding Access Type, based on the configuration for this AMF, the AMF may be allowed to determine whether it can serve the UE (see (A) below for subsequent handling).
- AMF or NSSF may have previously subscribed to slice load level and/or Observed Service Experience and/or Dispersion Analytics related network data analytics for a Network Slice from NWDAF, optionally for an Area of Interest composed of one or several TAIs. If AMF subscribes to analytics, AMF may determine that it cannot serve the UE based on received analytics (see (A) below). If AMF subscribes to notifications on changes on the Network Slice or Network Slice instance availability information from NSSF optionally indicating a list of supported TAIs, it may determine that it cannot serve the UE after the restriction notification is received (see (A) below). If AMF does not subscribe to notifications on changes on the availability information from NSSF, NSSF may take the analytics information into account when AMF queries NSSF (see (B) below).
NOTE 3: The configuration in the AMF depends on the operator's policy.
(A) Depending on fulfilling the configuration as described above, the AMF may be allowed to determine whether it can serve the UE and the following is performed:
- For the mobility from EPS to 5GS, the AMF first derives the serving PLMN value(s) of S-NSSAI(s) based on the HPLMN S-NSSAI(s) in the mapping of Requested NSSAI (in CM-IDLE state) or the HPLMN S-NSSAI(s) received from SMF+PGW-C (in CM-CONNECTED state). After that the AMF regards the derived value(s) as the Requested NSSAI.
- For the inter PLMN within 5GC mobility, the new AMF derives the serving PLMN value(s) of S-NSSAI(s) based on the HPLMN S-NSSAI(s) in the mapping of Requested NSSAI. After that the AMF regards the derived value(s) as the Requested NSSAI.
- AMF checks whether it can serve all the S-NSSAI(s) from the Requested NSSAI present in the Subscribed S-NSSAIs (potentially using configuration for mapping S-NSSAI values between HPLMN and Serving PLMN), or all the S-NSSAI(s) marked as default in the Subscribed S-NSSAIs in the case that no Requested NSSAI was provided or none of the S-NSSAIs in the Requested NSSAI are permitted, i.e. do not match any of the Subscribed S-NSSAIs (see clause 5.15.3) or not available at the current UE's Tracking Area (see clause 5.15.8). If the AMF is configured with a local policy to include in the Allowed NSSAI subscribed S-NSSAIs that are not in the Requested NSSAI and some of the Subscribed S-NSSAIs are not supported by the AMF, the AMF queries the NSSF (see (B) below).
- If AMF has subscribed to slice load level and/or Observed Service Experience and/or Dispersion Analytics related network data analytics for a Network Slice from NWDAF, or if AMF had received a Network Slice restriction from NSSF that applies to the list of TAIs supported by the AMF, it may use that information to determine whether the AMF can serve the UE on the S-NSSAI(s) in the Requested NSSAI.
- If the AMF can serve the S-NSSAIs in the Requested NSSAI and any additional S-NSSAI added due to local policy as described below, the AMF remains the serving AMF for the UE. The Allowed NSSAI is then determined by taking into account the list of S-NSSAI(s) in the Requested NSSAI permitted based on the Subscribed S-NSSAIs and/or the list of S-NSSAI(s) for the Serving PLMN which are mapped to the HPLMN S-NSSAI(s) provided in the mapping of Requested NSSAI permitted based on the Subscribed S-NSSAIs, or, if neither Requested NSSAI nor the mapping of Requested NSSAI was provided or none of the S-NSSAIs in the Requested NSSAI are permitted, all the S-NSSAI(s) marked as default in the Subscribed S-NSSAIs and taking also into account the availability of the Network Slice instances as described in clause 5.15.8 that are able to serve the S-NSSAI(s) in the Allowed NSSAI in the current UE's Tracking Areas in addition to any Network Slice instance restriction for the S-NSSAI(s) in the Allowed NSSAI provided by the NSSF. The AMF based on local policy may determine to include in the Allowed NSSAI additional Subscribed S-NSSAIs e.g. Subscribed S-NSSAIs not marked as default and/or Subscribed S-NSSAIs that were not provided in the Requested NSSAI (See NOTE 4). If the AMF has received NSSRG Information for the Subscribed S-NSSAIs as part of the UE subscription information, it shall only include in the Allowed NSSAI S-NSSAIs that all share a common NSSRG (see clause 5.15.12). If at least one S-NSSAI in the Requested NSSAI is not available in the current UE's Tracking Area, then either the AMF may determine a Target NSSAI or step (B) is executed. The AMF also determines the mapping if the S-NSSAI(s) included in the Allowed NSSAI needs to be mapped to Subscribed S-NSSAI(s) values. If no Requested NSSAI is provided, or the mapping of the S-NSSAIs in Requested NSSAI to HPLMN S-NSSAIs is incorrect, or the Requested NSSAI includes an S-NSSAI that is not valid in the Serving PLMN, or the UE indicated that the Requested NSSAI is based on the Default Configured NSSAI, the AMF, based on the Subscribed S-NSSAI(s) and operator's configuration, may also determine the Configured NSSAI for the Serving PLMN and, if applicable, the associated mapping of the Configured NSSAI to HPLMN S-NSSAIs, so these can be configured in the UE. Then Step (C) is executed.
NOTE 4: The ability for the AMF to construct the Allowed NSSAI with values not contained in Requested NSSAI but permitted by subscribed NSSAI can be used to allow the UE to use newly-added S-NSSAI(s) in the case of Network Slicing Subscription Change (see clause 4.2.2.2.2 of TS 23.502 [3]).
- Else, the AMF queries the NSSF (see (B) below).
(B) When required as described above, the AMF needs to query the NSSF and the following is performed:
- The AMF queries the NSSF, with Requested NSSAI, Default Configured NSSAI Indication, mapping of Requested NSSAI to HPLMN S-NSSAIs, the Subscribed S-NSSAIs (with an indication if marked as default S-NSSAI), NSSRG Information (if provided by the UDM, see clause 5.15.12), any Allowed NSSAI it might have for the other Access Type (including its mapping to HPLMN S-NSSAIs), PLMN ID of the SUPI and UE's current Tracking Area. If the AMF has pending NSSAI for the UE then the AMF includes pending NSSAI in the Requested NSSAI.
NOTE 5: The Default Configured NSSAI Indication is provided when received from the UE or when the AMF indicates to the NSSF to return Configured NSSAI in case of the Network Slicing Subscription Change Indication is received from UDM.
- Based on this information, local configuration and other locally available information including RAN capabilities in the current Tracking Area for the UE or load level information for a Network Slice instance provided by the NWDAF, the NSSF does the following:
- It verifies which S-NSSAI(s) in the Requested NSSAI are permitted based on comparing the Subscribed S-NSSAIs with the S-NSSAIs in the mapping of Requested NSSAI to HPLMN S-NSSAIs. It considers the S-NSSAI(s) marked as default in the Subscribed S-NSSAIs in the case that no Requested NSSAI was provided or no S-NSSAI from the Requested NSSAI are permitted i.e. are not present in the Subscribed S-NSSAIs or not available e.g. at the current UE's Tracking Area. If NSSRG information is provided, the NSSF only selects S-NSSAIs that share a common NSSRG (see clause 5.15.12).
- If AMF has not subscribed to notifications on changes on the Network Slice or Network Slice instance availability information from NSSF and NSSF has subscribed to slice load level and/or Observed Service Experience and/or Dispersion Analytics related network data analytics for a Network Slice from NWDAF, NSSF may use the analytics information for the determination of the (Network Slice instance(s) and the) list of S-NSSAI(s) in the Allowed NSSAI(s) to serve the UE.
- It selects the Network Slice instance(s) to serve the UE. When multiple Network Slice instances in the UE's Tracking Area are able to serve a given S-NSSAI, based on operator's configuration, the NSSF may select one of them to serve the UE, or the NSSF may defer the selection of the Network Slice instance until a NF/service within the Network Slice instance needs to be selected.
- It determines the target AMF Set to be used to serve the UE, or, based on configuration, the list of candidate AMF(s), possibly after querying the NRF.
NOTE 6: If the target AMF(s) returned from the NSSF is the list of candidate AMF(s), the Registration Request message can only be redirected via the direct signalling between the initial AMF and the selected target AMF as described in clause 5.15.5.2.3. The NSSF does not provide the target AMF(s), when it provides a Target NSSAI in order to redirect or handover the UE to a cell of another TA as described in clause 5.3.4.3.3.
- It determines the Allowed NSSAI(s) for the applicable Access Type, by taking into account the list of S-NSSAI(s) in the Requested NSSAI permitted based on the Subscribed S-NSSAIs and/or the list of S-NSSAI(s) for the Serving PLMN which are mapped to the HPLMN S-NSSAIs provided in the mapping of Requested NSSAI permitted based on the Subscribed S-NSSAIs, or, if neither Requested NSSAI nor the mapping of Requested NSSAI was provided or none of the S-NSSAIs in the Requested NSSAI are permitted, all the S-NSSAI(s) marked as default in the Subscribed S-NSSAIs and taking also into account the availability of the Network Slice instances as described in clause 5.15.8 that are able to serve the S-NSSAI(s) in the Allowed NSSAI in the current UE's Tracking Areas and taking also into account local policy in the NSSF that may determine to include in the Allowed NSSAI additional Subscribed S-NSSAIs e.g. Subscribed S-NSSAIs not marked as default and/or Subscribed S-NSSAIs that were not provided in the Requested NSSAI (see NOTE 7). If NSSRG information applies, the NSSF only selects S-NSSAIs that share a common NSSRG (see clause 5.15.12).
NOTE 7: The ability for the NSSF to construct the Allowed NSSAI with values not contained in Requested NSSAI but permitted by Subscribed NSSAIs can be used to allow the UE to use newly-added S-NSSAI(s) in the case of Network Slicing Subscription Change (see clause 4.2.2.2.2 of TS 23.502 [3]).
- It also determines the mapping of each S-NSSAI of the Allowed NSSAI(s) to the Subscribed S-NSSAIs if necessary.
- Based on operator configuration, the NSSF may determine the NRF(s) to be used to select NFs/services within the selected Network Slice instance(s).
- Additional processing to determine the Allowed NSSAI(s) in roaming scenarios and the mapping to the Subscribed S-NSSAIs, as described in clause 5.15.6.
- If no Requested NSSAI is provided or the Requested NSSAI includes an S-NSSAI that is not valid in the Serving PLMN, or the mapping of the S-NSSAIs in Requested NSSAI to HPLMN S-NSSAIs is incorrect, the NSSF based on the Subscribed S-NSSAI(s) and operator configuration may also determine the Configured NSSAI for the Serving PLMN and, if applicable, the associated mapping of the Configured NSSAI to HPLMN S-NSSAIs, so these can be configured in the UE. The NSSF shall return a Configured NSSAI when receiving Default Configured NSSAI Indication from the AMF.
- If at least one S-NSSAI in the Requested NSSAI is not available in the current UE's Tracking Area, the NSSF may provide a Target NSSAI for the purpose of allowing the NG-RAN to redirect the UE to a cell of a TA in another frequency band supporting network slices not available in the current TA as described in clause 5.3.4.3.3.
- The NSSF returns to the current AMF the Allowed NSSAI for the applicable Access Type, the mapping of each S-NSSAI of the Allowed NSSAI to the Subscribed S-NSSAIs if determined and the target AMF Set, or, based on configuration, the list of candidate AMF(s). The NSSF may return the NRF(s) to be used to select NFs/services within the selected Network Slice instance(s) and the NRF to be used to determine the list of candidate AMF(s) from the AMF Set. The NSSF may return NSI ID(s) to be associated to the Network Slice instance(s) corresponding to certain S-NSSAIs. NSSF may return the rejected S-NSSAI(s) as described in clause 5.15.4.1. The NSSF may return the Configured NSSAI for the Serving PLMN and the associated mapping of the Configured NSSAI to HPLMN S-NSSAIs. The NSSF may return Target NSSAI as described in clause 5.3.4.3.3.
- Depending on the available information and based on configuration, the AMF may query the appropriate NRF (e.g. locally pre-configured or provided by the NSSF) with the target AMF Set. The NRF returns a list of candidate AMFs.
- If AMF Re-allocation is necessary, the current AMF reroutes the Registration Request or forwards the UE context to a target serving AMF as described in clause 5.15.5.2.3.
- Step (C) is executed.
(C) The serving AMF shall determine a Registration Area such that all S-NSSAIs of the Allowed NSSAI for this Registration Area are available in all Tracking Areas of the Registration Area (and also considering other aspects as described in clause 5.3.2.3 and clause 5.3.4.3.3) and then return to the UE this Allowed NSSAI and the mapping of the Allowed NSSAI to the Subscribed S-NSSAIs if provided. The AMF may return the rejected S-NSSAI(s) as described in clause 5.15.4.1.
NOTE 8: The S-NSSAIs in the Allowed NSSAI for Non-3GPP access are available homogeneously "in the PLMN" for the N3IWF case since a N3IWF providing access to a 5GC can be reached from any IP location. For other types of Non-3GPP access the S-NSSAIs in the Allowed NSSAI for Non-3GPP access can be not available homogeneously, for example different W-AGFs/TNGF(s) can be deployed in different locations and support different TAIs that support different network slices.
When either no Requested NSSAI was included, or the mapping of the S-NSSAIs in Requested NSSAI to HPLMN S-NSSAIs is incorrect, or a Requested NSSAI is not considered valid in the PLMN and as such at least one S-NSSAI in the Requested NSSAI was rejected as not usable by the UE in the PLMN, or the UE indicated that the Requested NSSAI is based on the Default Configured NSSAI, the AMF may update the UE slice configuration information for the PLMN as described in clause 5.15.4.2.
If the Requested NSSAI does not include S-NSSAIs which map to S-NSSAIs of the HPLMN subject to Network Slice-Specific Authentication and Authorization and the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE in the current UE's Tracking Area and if no default S-NSSAI(s) could be added as described in step (A), the AMF shall reject the UE Registration and shall include in the rejection message the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value.
If the Requested NSSAI includes S-NSSAIs which map to S-NSSAIs of the HPLMN subject to Network Slice-Specific Authentication and Authorization, the AMF shall include in the Registration Accept message an Allowed NSSAI containing only those S-NSSAIs that are not to be subject to Network Slice-Specific Authentication and Authorization and, based on the UE Context in AMF, those S-NSSAIs for which Network Slice-Specific Authentication and Authorization for at least one of the corresponding HPLMN S-NSSAIs succeeded previously regardless the Access Type, if any.
The AMF shall also provide the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value.
If the AMF determined the Target NSSAI or received a Target NSSAI from the NSSF, the AMF should provide the Target NSSAI to the PCF for retrieving a corresponding RFSP as described in clause 5.3.4.3.1 or, if the PCF is not deployed, the AMF should determine a corresponding RFSP based on local configuration. Then the AMF provides the Target NSSAI and the corresponding RFSP to the NG-RAN as described in clause 5.3.4.3.3. The S-NSSAIs which map to S-NSSAIs of the HPLMN subject to an ongoing Network Slice-Specific Authentication and Authorization shall be included in the Pending NSSAI and removed from Allowed NSSAI. The Pending NSSAI may contain a mapping of the S-NSSAI(s) for the Serving PLMN to the HPLMN S-NSSAIs, if applicable. The UE shall not include in the Requested NSSAI any of the S-NSSAIs from the Pending NSSAI the UE stores, regardless of the Access Type.
If:
- all the S-NSSAI(s) in the Requested NSSAI are still to be subject to Network Slice-Specific Authentication and Authorization; or
- no Requested NSSAI was provided or none of the S-NSSAIs in the Requested NSSAI matches any of the Subscribed S-NSSAIs and all the S-NSSAI(s) marked as default in the Subscribed S-NSSAIs are to be subject to Network Slice-Specific Authentication and Authorization;
the AMF shall provide a "NSSAA to be performed" indicator and no Allowed NSSAI to the UE in the Registration Accept message. Upon receiving the Registration Accept message, the UE is registered in the PLMN but shall wait for the completion of the Network Slice-Specific Authentication and Authorization without attempting to use any service provided by the PLMN on any access, except e.g. emergency services (see TS 24.501 [47]), until the UE receives an allowed NSSAI.
Then, the AMF shall initiate the Network Slice-Specific Authentication and Authorization procedure as described in clause 5.15.10 for each S-NSSAI that requires it, except, based on Network policies, for those S-NSSAIs for which Network Slice-Specific Authentication and Authorization have been already initiated on another Access Type for the same S-NSSAI(s). At the end of the Network Slice-Specific Authentication and Authorization steps, the AMF by means of the UE Configuration Update procedure shall provide a new Allowed NSSAI to the UE which also contains the S-NSSAIs subject to Network Slice-Specific Authentication and Authorization for which the authentication and authorization is successful. The AMF may perform AMF selection when NSSAA completes for the S-NSSAIs subject to NSSAA. If an AMF change is required, this shall be triggered by the AMF using the UE Configuration Update procedure indicating a UE re-registration is required. The S-NSSAIs which were not successfully authenticated and authorized are not included in the Allowed NSSAI and are included in the list of Rejected S-NSSAIs with a rejection cause value indicating Network Slice-Specific Authentication and Authorization failure.
Once completed the Network Slice-Specific (re-)Authentication and (re-)Authorization procedure, if the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE, which is already authenticated and authorized successfully by a PLMN and if no default S-NSSAI(s) could be added as described in step (A), the AMF shall execute the Network-initiated Deregistration procedure described in clause 4.2.2.3.3 of TS 23.502 [3] and shall include in the explicit De-Registration Request message the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value.
If an S-NSSAI is rejected with a rejection cause value indicating Network Slice-Specific Authentication and Authorization failure or revocation, the UE can re-attempt to request the S-NSSAI based on policy, local in the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.2.2 Modification of the Set of Network Slice(s) for a UE | The set of Network Slices for a UE can be changed at any time while the UE is registered with a network and may be initiated by the network, or by the UE, under certain conditions as described below.
The network, based on local policies, subscription changes and/or UE mobility and/or UE Dispersion data classification, operational reasons (e.g. a Network Slice instance is no longer available or load level information or service experience for a Network Slice or network slice instance provided by the NWDAF), may change the set of Network Slice(s) to which the UE is registered and provide the UE with a new Registration Area and/or Allowed NSSAI and the mapping of this Allowed NSSAI to HPLMN S-NSSAIs, for each Access Type over which the UE is registered. In addition, the network may provide the Configured NSSAI for the Serving PLMN, the associated mapping information and the rejected S-NSSAIs. The network may perform such a change over each Access Type during a Registration procedure or trigger a notification towards the UE of the change of the Network Slices using a UE Configuration Update procedure as specified in clause 4.2.4 of TS 23.502 [3]. The new Allowed NSSAI(s) and the mapping to HPLMN S-NSSAIs are determined as described in clause 5.15.5.2.1 (an AMF Re-allocation may be needed). The AMF provides the UE with:
- an indication that the acknowledgement from UE is required;
- Configured NSSAI for the Serving PLMN (if required), rejected S-NSSAI(s) (if required) and TAI list and
- the new Allowed NSSAI with the associated mapping of Allowed NSSAI for each Access Type (as applicable) unless the AMF cannot determine the new Allowed NSSAI (e.g. all S-NSSAIs in the old Allowed NSSAI have been removed from the Subscribed S-NSSAIs).
Furthermore:
- If the changes to the Allowed NSSAI require the UE to perform immediately a Registration procedure because they affect the existing connectivity to AMF (e.g. the new S-NSSAIs require a separate AMF that cannot be determined by the current serving AMF, or the AMF cannot determine the Allowed NSSAI) or due to AMF local policies also when the changes does not affect the existing connectivity to AMF:
- The serving AMF indicates to the UE the need for the UE to perform a Registration procedure without including the GUAMI or 5G-S-TMSI in the access stratum signalling after entering CM-IDLE state. The AMF shall release the NAS signalling connection to the UE to allow to enter CM-IDLE after receiving the acknowledgement from UE.
- When the UE receives indications to perform a Registration procedure without including the GUAMI or 5G-S-TMSI in the access stratum signalling after entering CM-IDLE state, then:
- The UE deletes any stored (old) Allowed NSSAI and associated mapping as well as any (old) rejected S-NSSAI.
- The UE shall initiate a Registration procedure with the registration type Mobility Registration Update after the UE enters CM-IDLE state as specified in as described in step 4 of clause 4.2.4.2 of TS 23.502 [3]. The UE shall include a Requested NSSAI (as described in clause 5.15.5.2.1) with the associated mapping of Requested NSSAI in the Registration Request message. Also, the UE shall include, subject to the conditions set out in clause 5.15.9, a Requested NSSAI in access stratum signalling but no GUAMI.
- If the AMF determines that the S-NSSAI in the Allowed NSSAI is replaced with Alternative S-NSSAI over an Access Type, the AMF provides the mapping of old S-NSSAI to the Alternative S-NSSAI to the UE over the same Access Type (as described in clause 5.15.19).
If there is an established PDU Session associated with emergency services, then the serving AMF indicates to the UE the need for the UE to perform a Registration procedure but does not release the NAS signalling connection to the UE. The UE performs the Registration procedure only after the release of the PDU Session used for the emergency services.
In addition to sending the new Allowed NSSAI to the UE, when a Network Slice used for a one or multiple PDU Sessions is no longer available for a UE, the following applies:
- If the Network Slice becomes no longer available under the same AMF and the Network Slice Replacement is not used (e.g. due to UE subscription change), the AMF indicates to the SMF(s) which PDU Session ID(s) corresponding to the relevant S-NSSAI shall be released. SMF releases the PDU Session according to clause 4.3.4.2 of TS 23.502 [3]. If the Network Slice Replacement is used, the AMF performs Network Slice Replacement as described in clause 5.15.19.
- If the Network Slice becomes no longer available upon a change of AMF (e.g. due to Registration Area change), the new AMF indicates to the old AMF that the PDU Session(s) corresponding to the relevant S-NSSAI shall be released. The old AMF informs the corresponding SMF(s) to release the indicated PDU Session(s). The SMF(s) release the PDU Session(s) as described in clause 4.3.4 of TS 23.502 [3]. Then the new AMF modifies the PDU Session Status correspondingly. The PDU Session(s) context is locally released in the UE after receiving the PDU Session Status in the Registration Accept message.
The UE uses either the URSP rules (which includes the NSSP) or the UE Local Configuration as defined in clause 6.1.2.2.1 of TS 23.503 [45] to determine whether ongoing traffic can be routed over existing PDU Sessions belonging to other Network Slices or establish new PDU Session(s) associated with same/other Network Slice.
In order to change the set of S-NSSAIs the UE is registered to over an Access Type, the UE shall initiate a Registration procedure over this Access Type as specified in clause 5.15.5.2.1.
If, for an established PDU Session:
- none of the values of the S-NSSAIs of the HPLMN in the mapping of the Requested NSSAI to S-NSSAIs of the HPLMN included in the Registration Request matches the S-NSSAI of the HPLMN associated with the PDU Session; or
- none of the values of the S-NSSAIs in the Requested NSSAI matches the value of the S-NSSAI of HPLMN associated with the PDU Session and the mapping of the Requested NSSAI to S-NSSAIs of the HPLMN is not included in the Registration Request,
the network shall release this PDU Session as follows.
- the AMF informs the corresponding SMF(s) to release the indicated PDU Session(s). The SMF(s) release the PDU Session(s) as described in clause 4.3.4 of TS 23.502 [3]. Then the AMF modifies the PDU Session Status correspondingly. The PDU Session(s) context is locally released in the UE after receiving the PDU Session Status from the AMF.
A change of the set of S-NSSAIs (whether UE or Network initiated) to which the UE is registered may, subject to operator policy, lead to AMF change, as described in clause 5.15.5.2.1.
If the AMF supports the Network Slice Replacement feature and is configured to use the NSSF to trigger the Network Slice Replacement, the AMF subscribes with the NSSF for notifications when any of the S-NSSAIs served by the AMF (e.g. the S-NSSAI in the Serving PLMN and the HPLMN S-NSSAI in roaming case) has to be replaced as described in clause 5.15.19.
If the AMF supports the Network Slice Instance Replacement and configured to use Network Slice Instance Replacement, the AMF subscribes with the NSSF for notifications when a Network Slice instances served by the AMF is congested or no longer available as described in clause 5.15.20.
The AMF may perform Network Slice Replacement for the PDU Session as described in clause 5.15.19.
5.15.5.2.2a AF Requested modification of the Set of Network Slice(s) for a UE
In non-roaming cases, an authorized AF or an AF subject to authorization via the NEF, may request to replace a certain S-NSSAI (Replaced S-NSSAI) for a UE with another S-NSSAI (Alternative S-NSSAI) which is part of the UE subscription. The request in either case is sent to the PCF for the UE handling the impacted subscriber. Similarly, an authorized AF or an AF subject to authorization via the NEF, may request to terminate the replacement then request to use the Replaced S-NSSAI instead of the Alternative S-NSSAI for a UE again. The PCF notifies the AF may subscribe to Notification on the outcome of the AF requested Network Slice Replacement. The network slice associated with the Alternative S-NSSAI is assumed in this specification to have NS-AoS to be covering at least the NS-AoS of the network slice associated with the Replaced S-NSSAI.
Only a single AF can request the modification of the Set of Network Slice(s) for one replaced S-NSSAI.
NOTE 1: It is assumed that in the area where the AF requested Network Slice Replacement feature described in this clause is expected to operate, the AMFs supports AF requested Network Slice Replacement notifications handling from the PCF. How the AF obtains the S-NSSAI to be replaced and the Alternative S-NSSAI is out of scope of this specification.
NOTE 2: Application of this feature over non-3GPP access is not further specified.
The PCF for the UE based on operator policies considers the AF request. Consequently the PCF for the UE triggers the Network Slice Replacement at the AMF as defined in TS 23.503 [45].The PCF sends Slice replacement management in the access and mobility management policies to the AMF per implicitly subscription, as described in TS 23.503 [45]. The Slice replacement management policy includes the Replaced S-NSSAI and the corresponding Alternative S-NSSAI as provided in the AF request, PCRT to request Notification on outcome of Network Slice Replacement request, together with a Network Slice Replacement Type. The Network Slice Replacement Type indicates that the Network Slice Replacement is requested by an AF. The AMF handles the procedure as following:
- The AMF shall not handle the Network Slice Replacement procedure as described in clause 5.15.19.
- If the Alternative S-NSSAI is not within the UE subscription, or is not supported in the UE Registration Area, the AMF shall notify the PCF that the Network Slice Replacement is not triggered with a cause value. The PCF further notifies the AF.
- If the Alternative S-NSSAI is within the UE subscription and is supported uniformly in the UE Registration Area, the replacement is successful and AMF includes the Alternative S-NSSAI in the Allowed NSSAI (if not present). In addition:
a) The AMF removes the Replaced S-NSSAI from the Allowed NSSAI and add the Replaced S-NSSAI into the Rejected S-NSSAI by a UE Configuration Update procedure.
Editor's note: It is FFS whether the Replaced S-NSSAI should be removed from the Configured NSSAI.
b) The AMF and UE release the PDU sessions that were using the Replaced S-NSSAI.
c) The AMF stores in the UE context the access and mobility management policy information as received from PCF and transfers to new AMF during inter AMF mobility.
d) After performing the above steps a) to c), the AMF reports to the PCF the outcome of the network slice replacement (e.g. the S-NSSAI has been replaced by an Alternative S-NSSAI) as defined in TS 23.503 [45]. The PCF further notifies the AF.
NOTE 2: Operator policies in the PCF ensures that the UE is configured with a URSP rule that contains the Alternative S-NSSAI to establish a new PDU Session. These policies should not cause the selection of the RSDs with the Alternative S-NSSAI with priority over the RSDs with the Replaced S-NSSAI for the same traffic (i.e. for traffic matching the same TD).
The trusted AF or a NEF may send request to PCF for the UE to terminate the Network Slice Replacement. In this case the PCF for the UE sends access and mobility management policies to the AMF, as described in TS 23.503 [45]. The AMF updates the Allowed NSSAI to include the Replaced S-NSSAI and remove the Replaced S-NSSAI from the Rejected S-NSSAI by a UE Configuration Update procedure. The UE may request to register the Replaced S-NSSAIs again next time the UE sends a Requested NSSAI. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.2.3 AMF Re-allocation due to Network Slice(s) Support | During a Registration procedure in a PLMN, if the network decides that the UE should be served by a different AMF based on Network Slice(s) aspects, then the AMF that first received the Registration Request shall redirect the Registration request to target AMF via the 5G-AN or via direct signalling between the initial AMF and the target AMF. If the target AMF(s) are returned from the NSSF and identified by a list of candidate AMF(s), the redirection message shall only be sent via the direct signalling between the initial AMF and the target AMF. If the redirection message is sent by the AMF via the 5G-AN, the message shall include information for selection of a new AMF to serve the UE.
When during a Registration procedure the UE requests a new S-NSSAI which is not supported in the UE's current Tracking Area, the serving AMF itself or by interacting with the NSSF as described in clause 5.15.5.2.1 may determine a Target NSSAI. The AMF provides the Target NSSAI to the NG-RAN and the NG-RAN may apply redirection or handover of the UE to a cell in another TA supporting the Target NSSAI as described in clause 5.3.4.3.3.
During a EPS to 5GS handover using N26 interface procedure, if the network decides that the UE should be served by a different AMF based on Network Slice(s) aspects, then the AMF, which received the Forward Relocation Request from MME, shall forward the UE context to target AMF via direct signalling between the initial AMF and the target AMF as described in clause 4.11.1.2.2 of TS 23.502 [3].
For a UE that is already registered, the system shall support a redirection initiated by the network of a UE from its serving AMF to a target AMF due to Network Slice(s) considerations (e.g. the operator has changed the mapping between the Network Slice instances and their respective serving AMF(s)). Operator policy determines whether redirection between AMFs is allowed. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.5.3 Establishing a PDU Session in a Network Slice | The PDU Session Establishment in a Network Slice instance to a DN allows data transmission in a Network Slice instance. A PDU Session is associated to an S-NSSAI and a DNN. A UE that is registered in a PLMN over an Access Type and has obtained a corresponding Allowed NSSAI, shall indicate in the PDU Session Establishment procedure the S-NSSAI according to the NSSP in the URSP rules or according to the UE Local Configuration as defined in clause 6.1.2.2.1 of TS 23.503 [45] and, if available, the DNN the PDU Session is related to. The UE includes the appropriate S-NSSAI from this Allowed NSSAI and, if mapping of the Allowed NSSAI to HPLMN S-NSSAIs was provided, an S-NSSAI with the corresponding value from this mapping.
If the UE cannot determine any S-NSSAI after performing the association of the application to a PDU Session according to clause 6.1.2.2.1 of TS 23.503 [45], the UE shall not indicate any S-NSSAI in the PDU Session Establishment procedure.
The network (HPLMN) may provision the UE with Network Slice selection policy (NSSP) as part of the URSP rules, see clause 6.6.2 of TS 23.503 [45]. When the Subscription Information contains more than one S-NSSAI and the network wants to control/modify the UE usage of those S-NSSAIs, then the network provisions/updates the UE with NSSP as part of the URSP rules. When the Subscription Information contains only one S-NSSAI, the network needs not provision the UE with NSSP as part of the URSP rules. The NSSP rules associate an application with one or more HPLMN S-NSSAIs. A default rule which matches all applications to a HPLMN S-NSSAI may also be included.
The UE shall store and use the URSP rules, including the NSSP, as described in TS 23.503 [45]. When a UE application associated with a specific S-NSSAI requests data transmission:
- if the UE has one or more PDU Sessions established corresponding to the specific S-NSSAI, the UE routes the user data of this application in one of these PDU Sessions, unless other conditions in the UE prohibit the use of these PDU Sessions. If the application provides a DNN, then the UE considers also this DNN to determine which PDU Session to use. This is further described in clause 6.6.2 of TS 23.503 [45].
- If the UE does not have a PDU Session established with this specific S-NSSAI, the UE requests a new PDU Session corresponding to this S-NSSAI and with the DNN that may be provided by the application. In order for the RAN to select a proper resource for supporting network slicing in the RAN, RAN needs to be aware of the Network Slices used by the UE. This is further described in clause 6.6.2 of TS 23.503 [45].
If the AMF is not able to determine the appropriate NRF to query for the S-NSSAI provided by the UE, the AMF may query the NSSF with this specific S-NSSAI, location information, PLMN ID of the SUPI. The NSSF determines and returns the appropriate NRF to be used to select NFs/services within the selected Network Slice instance. The NSSF may also return an NSI ID to be used to select NFs within the selected Network Slice instance to use for this S-NSSAI.
The AMF or NSSF may select an S-NSSAI (if the UE does not provide an S-NSSAI for the PDU session establishment) and a Network Slice instance, based on load level and/or Observe Service Experience and/or Dispersion analytics from NWDAF, as described in TS 23.288 [86].
The discovery and selection of the NSSF is defined in clause 6.3.28.
SMF discovery and selection within the selected Network Slice instance is initiated by the AMF when a SM message to establish a PDU Session is received from the UE. The appropriate NRF is used to assist the discovery and selection tasks of the required network functions for the selected Network Slice instance.
The AMF queries the appropriate NRF to select an SMF in a Network Slice instance based on S-NSSAI, DNN, NSI-ID (if available) and other information e.g. UE subscription and local operator policies, when the UE triggers PDU Session Establishment. The AMF may select the SMF among the set of the SMF instance(s) returned by the NRF or locally configured in the AMF, based on network data analytics (NF load, etc.) from the NWDAF as described in TS 23.288 [86]. The selected SMF establishes a PDU Session based on S-NSSAI and DNN.
When the AMF belongs to multiple Network Slice instances, based on configuration, the AMF may use an NRF at the appropriate level for the SMF selection.
For further details on the SMF selection, refer to clause 4.3.2.2.3 of TS 23.502 [3].
When a PDU Session for a given S-NSSAI is established using a specific Network Slice instance, the CN provides to the (R)AN the S-NSSAI corresponding to this Network Slice instance to enable the RAN to perform access specific functions.
The UE shall not perform PDU Session handover from one Access Type to another if the S-NSSAI of the PDU Session is not included in the Allowed NSSAI of the target Access Type.
In non-roaming case, if the Serving PLMN ID is not the same as the PLMN ID of the SUPI and a mapped S-NSSAI value of the HPLMN is present in the Allowed NSSAI, the procedures as defined in clause 4.23.5 of TS 23.502 [3] is used for PDU Session Management, with the following differences:
- In PDU Session Establishment procedure the AMF selects the SMF according to the S-NSSAI of the mapped S-NSSAI value of the HPLMN and selects I-SMF according to the S-NSSAI of the S-NSSAI value of the Serving PLMN and provides the S-NSSAI of the Serving PLMN and the mapped S-NSSAI of the HPLMN as received from the UE to the selected (I-)SMF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.6 Network Slicing Support for Roaming | For roaming scenarios:
- If the UE only uses standard S-NSSAI values, then the same S-NSSAI values can be used in VPLMN as in the HPLMN.
- If the VPLMN and HPLMN have an SLA to support non-standard S-NSSAI values in the VPLMN, the NSSF of the VPLMN maps the Subscribed S-NSSAIs values to the respective S-NSSAI values to be used in the VPLMN. The S-NSSAI values to be used in the VPLMN are determined by the NSSF of the VPLMN based on the SLA. The NSSF of the VPLMN need not inform the HPLMN of which values are used in the VPLMN.
Depending on operator's policy and the configuration in the AMF, the AMF may decide the S-NSSAI values to be used in the VPLMN and the mapping to the Subscribed S-NSSAIs.
For the home routed case, the AMF or NSSF may select an S-NSSAI (if the UE does not provide an S-NSSAI for the PDU session establishment) and a Network Slice instance, based on load level and/or Observe Service Experience and/or Dispersion analytics of the VPLMN and/or that of the HPLMN from NWDAF as described in TS 23.288 [86].
- The UE constructs Requested NSSAI and provides the mapping of S-NSSAIs of the Requested NSSAI to HPLMN S-NSSAIs if the mapping is stored in the UE, as described in clause 5.15.5.2.1.
- The NSSF in the VPLMN determines the Allowed NSSAI without interacting with the HPLMN.
- the HPLMN may provide NSSRG Information as part of the Subscription information as described in clause 5.15.12.
- The Allowed NSSAI in the Registration Accept includes S-NSSAI values used in the VPLMN. The mapping information described above is also provided to the UE with the Allowed NSSAI as described in clause 5.15.4.
- If the S-NSSAI values are subject to NSAC, depending on operator's policy, a roaming agreement or an SLA between VPLMN and HPLMN, the AMF or SMF in VPLMN triggers a request for NSAC for these S-NSSAI values as described in clause 5.15.11.3.
- In PDU Session Establishment procedure, the UE includes both:
(a) the S-NSSAI that matches the application (that is triggering the PDU Session Request) within the NSSP in the URSP rules or within the UE Local Configuration as defined in clause 6.1.2.2.1 of TS 23.503 [45]; the value of this S NSSAI is used in the HPLMN; and
(b) an S-NSSAI belonging to the Allowed NSSAI that maps to (a) using the mapping of the Allowed NSSAI to HPLMN S-NSSAIs; the value of this S-NSSAI is used in the VPLMN.
For the home routed case, the AMF may select the V-SMF and the H-SMF based on network data analytics (NF load, etc.) of the VPLMN and that of the HPLMN from the NWDAF as described in TS 23.288 [86]. The V-SMF sends the PDU Session Establishment Request message to the H-SMF along with the S-NSSAI with the value used in the HPLMN (a). If the S-NSSAI values are subject to NSAC, the V-SMF or H-SMF triggers a request for NSAC for these S-NSSAI values as described in clause 5.15.11.3.
- When a PDU Session is established, the CN provides to the AN the S-NSSAI with the value from the VPLMN corresponding to this PDU Session, as described in clause 5.15.5.3.
- The Network Slice instance specific network functions in the VPLMN are selected by the VPLMN by using the S-NSSAI with the value used in the VPLMN and querying an NRF that has either been pre-configured, or provided by the NSSF in the VPLMN. The Network Slice specific functions of the HPLMN (if applicable) are selected by the VPLMN by using the related S-NSSAI with the value used in the HPLMN via the support from an appropriate NRF in the HPLMN, identified as specified in clause 4.17.5 of TS 23.502 [3] and, for SMF in clause 4.3.2.2.3.3 of TS 23.502 [3].
- If the serving AMF supports the Network Slice Replacement feature and is configured to use the NSSF for Network Slice Replacement triggering, the AMF subscribes with the NSSF of the VPLMN for notifications when an HPLMN S-NSSAI needs to be replaced with an Alternative S-NSSAI, in addition to notifications for the Serving PLMN S-NSSAIs. The NSSF of the VPLMN shall subscribe with the NSSF of the HPLMN for notifications when an HPLMN S-NSSAI needs to be replaced with an Alternative S-NSSAI.
- If the serving AMF support the Network Slice Instance Replacement and configured to use Network Slice Instance Replacement, the AMF subscribes with the NSSF of the VPLMN for notifications when a Network Slice instance is congested or no longer available as described in clause 5.15.20. The NSSF of the VPLMN shall subscribe with the NSSF of the HPLMN for notifications when the Network Slice instance is congested or no longer available. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.7 Network slicing and Interworking with EPS | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.7.1 General | A 5GS supports Network Slicing and might need to interwork with the EPS in its PLMN or in other PLMNs as specified in clause 5.17.2. The EPC may support the Dedicated Core Networks (DCN). In some deployments, the MME selection may be assisted by a DCN-ID provided by the UE to the RAN (see TS 23.401 [26]).
Mobility between 5GC to EPC does not guarantee all active PDU Session(s) can be transferred to the EPC.
During PDN connection establishment in the EPC, the UE allocates the PDU Session ID . A UE that supports selecting S-NSSAI based on URSP rules while in EPS and that is provisioned with URSP rules may select, if available, an S-NSSAI for the APN based on evaluation of the Traffic descriptor as defined in TS 24.526 [110] clause 4.4.2. The selected S-NSSAI and PDU Session ID are sent to the SMF+PGW-C via PCO. As described in clause 4.11.0a.5 of TS 23.502 [3], an S-NSSAI associated with the PDN connection is determined based on the S-NSSAI(s) supported by the SMF+PGW-C, the Subscribed S-NSSAI from UDM, whether interworking with EPS is supported for the DNN and S-NSSAI in the Session Management Subscription data and the operator policy by the SMF+PGW-C, (e.g. based on a combination of SMF+PGW-C address and APN and taking into account the S-NSSAI provided by the UE if any) and is sent to the UE in PCO together with a PLMN ID that the S-NSSAI relates to. In Home Routed roaming case, the UE receives a HPLMN S-NSSAI value from the SMF+PGW-C. If the SMF+PGW-C supports more than one S-NSSAI and the APN is valid for more than one S-NSSAI, the SMF+PGW-C should take into account the S-NSSAI provided by the UE and only select an S-NSSAI that is mapped to the subscribed S-NSSAI of the UE and this subscribed S-NSSAI is not subject to Network Slice-Specific Authentication and Authorization. The UE stores this S-NSSAI and the PLMN ID associated with the PDN connection. The UE derives Requested NSSAI by taking into account of the received PLMN ID. The Requested NSSAI is included in the NAS Registration Request message and, subject to the conditions in clause 5.15.9, the RRC message carrying this Registration Request when the UE registers in 5GC if the UE is non-roaming or the UE has Configured NSSAI for the VPLMN in roaming case. If the UE has no Configured NSSAI of the VPLMN, the UE includes the HPLMN S-NSSAIs in the NAS Registration Request message as described in clause 5.15.5.2.1.
If the PCO received by the SMF+PGW-C contains an S-NSSAI that is not supported by the SMF+PGW-C, then the SMF+PGW-C may determine another SMF+PGW-C that supports the DNN and the S-NSSAI received in the PCO, based on operator policies and follows the PGW selection in case of PGW mismatch with network slice subscribed by the UE as specified in clause 7.2.1 and clause 7.2.2 of TS 29.274 [101].
When UE moves from EPS to 5GS, AMF reallocation may happen as described in clause 5.15.7.2 and clause 5.15.7.3.
NOTE: It is assumed that if a MME is configured with a N26 interface towards an AMF, the MME has N26 interfaces with all AMFs serving the same area than the initial AMF and that can serve UE subject to EPS to 5GS mobility. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.7.2 Idle mode aspects | In addition to the interworking principles documented in clause 5.17.2 the following applies for interworking with N26:
- When UE moves from 5GS to EPS, the UE context information sent by AMF to MME includes the UE Usage type, which is retrieved from UDM by AMF as part of subscription data.
- When UE moves from EPS to 5GS, then the UE includes the S-NSSAIs (with values for the Serving PLMN of the target 5GS, if available) associated with the established PDN connections in the Requested NSSAI in RRC Connection Establishment (subject to the conditions set out in clause 5.15.9) and NAS. The UE also provides to the AMF in the Registration Request message the mapping information as described in clause 5.15.6. The UE derives the S-NSSAIs values for the Serving PLMN by using the latest available information from EPS (if received in PCO) and from 5GS (e.g. based on URSP, Configured NSSAI, Allowed NSSAI). In the home-routed roaming case, the AMF selects default V-SMFs. The SMF+PGW-C sends PDU Session IDs and related S-NSSAIs to AMF. The AMF derives S-NSSAI values for the Serving PLMN as described in clause 5.15.5.2.1 and determines whether the AMF is the appropriate AMF to serve the UE. If not, the AMF reallocation may need be triggered. For each PDU Session the AMF determines whether the V-SMF need be reselected based on the associated S-NSSAI value for the Serving PLMN. If the V-SMF need be reallocated, i.e. change from the default V-SMF to another V-SMF, the AMF trigger the V-SMF reallocation as described in clause 4.23.3 of TS 23.502 [3].
In addition to the interworking principles documented in clause 5.17.2 the following applies for interworking without N26:
- When the UE initiates the Registration procedure and subject to the conditions set out in clause 5.15.9, the UE includes the S-NSSAI (with values for the Serving PLMN of the target 5GS) associated with the established PDN connections in the Requested NSSAI in the RRC Connection Establishment.
- The UE includes the S-NSSAIs (with values for the Serving PLMN of the target 5GS, if available) and the HPLMN S-NSSAI received in the PCO for the PDN connections as mapping information when moving PDN connections to 5GC using PDU Session Establishment Request message. The UE derives the S-NSSAIs values for the Serving PLMN by using, the latest available information from EPS (if received in PCO) and from 5GS (e.g. based on URSP, Configured NSSAI, Allowed NSSAI). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.7.3 Connected mode aspects | In addition to the interworking principles documented in clause 5.17.2 the following applies for interworking with N26:
- When a UE is CM-CONNECTED in 5GC and a handover to EPS occur, the AMF selects the target MME based on the source AMF Region ID, AMF Set ID and target location information. The AMF forwards the UE context to the selected MME over the N26 Interface. In the UE context, the AMF also includes the UE Usage type, if it is received as part of subscription data. The Handover procedure is executed as documented in TS 23.502 [3]. When the Handover procedure completes successfully the UE performs a Tracking Area Update. This completes the UE registration in the target EPS. As part of this the UE obtains a DCN-ID if the target EPS uses it.
- When a UE is ECM-CONNECTED in EPC and performs a handover to 5GS, the MME selects the target AMF based on target location information, e.g. TAI and any other available local information (including the UE Usage Type if one is available for the UE in the subscription data) and forwards the UE context to the selected AMF over the N26 interface. In the home-routed roaming case, the AMF selects default V-SMFs. The Handover procedure is executed as documented in TS 23.502 [3]. The SMF+PGW-C sends PDU Session IDs and related S-NSSAIs to AMF. Based on the received S-NSSAIs values the target AMF derives the S-NSSAI values for the Serving PLMN, the target AMF reselects a final target AMF if necessary as described in clause 5.15.5.2.1, the AMF reallocation procedure is triggered. For each PDU Session based on the associated derived S-NSSAI values if the V-SMF need be reallocated, the final target AMF triggers the V-SMF reallocation as described in clause 4.23.2 of TS 23.502 [3]. When the Handover procedure completes successfully the UE performs a Registration procedure. This completes the UE registration in the target 5GS and as part of this the UE obtains an Allowed NSSAI. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.7.4 Support of Network Slice usage control and Interworking with EPC | As described in clause 5.15.15, if Network Slice usage control is required for a PDN Connection, the SMF+PGW-C configures PDU Session inactivity timer to the UPF+PGW-U. When the SMF+PGW-C receives inactivity report of the PDN Connection from the UPF+PGW-U, the SMF+PGW-C releases the PDN Connection. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.8 Configuration of Network Slice support and availability in a PLMN | A Network Slice may be supported in the whole PLMN or in one or more Tracking Areas of the PLMN. A Network Slice is supported within a TA if the 5G-AN has been configured to support the S-NSSAI in the TA.
Network Slices are defined to be available within an NS-AoS when the Network Slice is supported in the set of TAs which the NS-AoS comprises and more than zero resources are allocated to the Network Slice in the NG-RAN cells of the NS-AoS. An NS-AoS can be defined on a per cell level granularity when the NS-AoS is not matching deployed Tracking Areas as defined in clause 5.15.18.
The availability of a Network Slice S-NSSAI in an NS-AoS requires the support of the S-NSSAI in the involved NFs and in the NG-RAN in the TAs which the NS-AoS comprises. Hence, the cells of a TA need to be configured to support a S-NSSAI if the S-NSSAI needs to be available in at least a cell of the TA. A Network Slice is considered available in a TA if the Network Slice is supported within the TA and available in all cells of the TA. In addition, policies in the NSSF may further restrict from using certain Network Slices in a particular TA, e.g. depending on the HPLMN of the UE. The UE can receive, for a Network Slice where the NS-AoS does not match the whole set of cells in one or more TAs, S-NSSAI location availability information as described in clause 5.15.18.
The support of a Network Slice in a TA is established end-to-end using a combination of OAM and signalling among network functions. It is derived by using the S-NSSAIs supported per TA in 5G-AN, the S-NSSAIs supported in the AMF and operator policies per TA in the NSSF.
The AMF learns the S-NSSAIs supported per TA by the 5G-AN when the 5G-AN nodes establish or update the N2 connection with the AMF (see TS 38.413 [34]) and TS 38.300 [27]). One or all AMF per AMF Set provides and updates the NSSF with the S-NSSAIs support per TA. The 5G-AN learns the S-NSSAIs per PLMN ID the AMFs it connects to support when the 5G-AN nodes establishes the N2 connection with the AMF or when the AMF updates the N2 connection with the 5G-AN (see TS 38.413 [34] and TS 38.300 [27]).
The NSSF may be configured with operator policies specifying under what conditions the S-NSSAIs can be restricted per TA and per HPLMN of the UE.
The per TA restricted S-NSSAIs may be provided to the AMFs of the AMF Sets at setup of the network and whenever changed.
The AMF may be configured for the S-NSSAIs it supports with operator policies specifying any restriction per TA and per HPLMN of the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.9 Operator-controlled inclusion of NSSAI in Access Stratum Connection Establishment | The Serving PLMN can control per Access Type which (if any) NSSAI the UE includes in the Access Stratum when establishing a connection caused by Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities. In addition, the Home and Visited PLMNs can also instruct the UE to never include NSSAI in the Access Stratum, regardless of the procedure that causes a RRC Connection to be established, i.e. to always enable privacy for the NSSAI).
During the Registration procedure, the AMF may provide to the UE in the Registration Accept message, an Access Stratum Connection Establishment NSSAI Inclusion Mode parameter, indicating whether and when the UE shall include NSSAI information in the Access Stratum Connection Establishment (e.g. an RRC connection Establishment defined in TS 38.331 [28]) according to one of these modes:
a) The UE shall include an NSSAI set to the Allowed NSSAI, if available, in the Access Stratum Connection Establishment caused by a Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities;
b) The UE shall include a NSSAI with the following content:
- for the case of Access Stratum Connection Establishment caused by a Service Request: an NSSAI including the S-NSSAI(s) of the Network Slice(s) that trigger the Access Stratum Connection Establishment; i.e. all the S-NSSAIs of the PDU sessions that have the User Plane reactivated by the Service Request, or the S-NSSAIs of the Network Slices a Control Plane interaction triggering the Service Request is related to, e.g. for SM it would be the S-NSSAI of the PDU Session the SM message is about;
- for the case of Access Stratum Connection Establishment caused by a Periodic Registration Update or Registration procedure used to update the UE capabilities, an NSSAI set to the Allowed NSSAI;
c) The UE shall not include any NSSAI in the Access Stratum Connection Establishment caused by Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities; or
d) The UE shall not provide NSSAI in the Access stratum.
For the case of Access Stratum Connection Establishment caused by Mobility Registration Update or Initial Registration in modes a), b) or c) the UE shall include the Requested NSSAI provided by the NAS layer and defined in clause 5.15.5.2.1.
For all UEs that are allowed to use modes a), b) or c), the Access Stratum Connection Establishment NSSAI Inclusion Mode should be the same over the same Registration Areas.The UE shall store and comply to the required behaviour for a PLMN per Access Type as part of the network slicing configuration. The Serving PLMN AMF shall not instruct the UE to operate in any other mode than mode d) in 3GPP Access Type unless the HPLMN provides an indication that it is allowed to do so (i.e. if a PLMN allows behaviours a,b,c, then its UDM sends to the serving AMF an explicit indication that the NSSAI can be included in RRC as part of the subscription data).
The UE default mode of operation is the following:
- For 3GPP access the UE shall by default operate in mode d) unless it has been provided with an indication to operate in mode a), b) or c).
- For untrusted non-3GPP access the UE shall operate by default in mode b) unless it has been provided with an indication to operate in mode a), c) or d).
- For trusted non-3GPP access the UE shall operate by default in mode d) unless it has been provided with an indication to operate in mode a), b) or c).
- For W-5GAN access the 5G-RG shall operate by default in mode b) unless it has been provided with an indication to operate in mode a), c) or d).
An operator may pre-configure the UE to operate by default according to mode c) in the HPLMN (i.e. the UE by default includes NSSAI in the access stratum when it performs an Initial Registration and Mobility Registration Update with the HPLMN until the HPLMN changes the mode as described above). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.10 Network Slice-Specific Authentication and Authorization | A serving PLMN or SNPN shall perform Network Slice-Specific Authentication and Authorization for the S-NSSAIs of the HPLMN or SNPN which are subject to it based on subscription information. The UE shall indicate in the Registration Request message in the UE 5GMM Core Network Capability whether it supports NSSAA feature. If the UE does not support NSSAA feature and if the UE requests any of these S-NSSAIs that are subject to Network Slice-Specific Authentication and Authorization, the AMF shall not trigger this procedure for the UE and they are rejected for the PLMN or SNPN. If the UE supports NSSAA feature and if the UE requests any of these S-NSSAIs that are subject to Network Slice-Specific Authentication and Authorization, they are included in the list of Pending NSSAI for the PLMN or SNPN, as described in clause 5.15.5.2.1.
If a UE is configured with S-NSSAIs, which are subject to Network Slice-Specific Authentication and Authorization, the UE stores an association between the S-NSSAI and corresponding credentials for the Network Slice-Specific Authentication and Authorization.
NOTE 1: How the UE is aware that an S-NSSAI is subject to Network Slice-Specific Authentication and Authorization (e.g. based on local configuration) is out of scope of this specification.
The UE may support remote provisioning of credentials for NSSAA, specified in clause 5.39.
A UE that supports to be provisioned with the credentials used for NSSAA over UP remote provisioning shall use connectivity over an S-NSSAI/DNN which can access the provisioning server to establish a PDU session for remote provisioning as defined in clause 5.39.
NOTE 2: The credentials for Network Slice-Specific Authentication and Authorization are not specified.
To perform the Network Slice-Specific Authentication and Authorization for an S-NSSAI, the AMF invokes an EAP- based Network Slice-Specific authorization procedure documented in clause 4.2.9 of TS 23.502 [3] (see also TS 33.501 [29]) for the S-NSSAI. When an NSSAA procedure is started and is ongoing for an S-NSSAI, the AMF stores the NSSAA status of the S-NSSAI as pending and when the NSSAA is completed the S-NSSAI becomes either part of the Allowed NSSAI or a Rejected S-NSSAI. The NSSAA status of each S-NSSAI, if any is stored, is transferred when the AMF changes.
This procedure can be invoked for a supporting UE by an AMF at any time, e.g. when:
a. The UE registers with the AMF and one of the S-NSSAIs of the HPLMN or SNPN which maps to an S-NSSAI in the Requested NSSAI is requiring Network Slice-Specific Authentication and Authorization (see clause 5.15.5.2.1 for details) and the S-NSSAI in the Requested NSSAI can be added to the Allowed NSSAI by the AMF once the Network Slice-Specific Authentication and Authorization for the HPLMN or SNPN S-NSSAI succeeds; or
b. The Network Slice-Specific AAA Server triggers a UE re-authentication and re-authorization for an S-NSSAI; or
c. The AMF, based on operator policy or a subscription change, decides to initiate the Network Slice-Specific Authentication and Authorization procedure for a certain S-NSSAI which was previously authorized.
In the case of re-authentication and re-authorization (b. and c. above) the following applies:
- If S-NSSAIs that are requiring Network Slice-Specific Authentication and Authorization map to S-NSSAIs that are included in the Allowed NSSAI for each Access Type, AMF selects an Access Type to be used to perform the Network Slice Specific Authentication and Authorization procedure based on network policies.
- If the Network Slice-Specific Authentication and Authorization for some S-NSSAIs mapped to some S-NSSAIs in the Allowed NSSAI is unsuccessful, the AMF shall update the Allowed NSSAI for each Access Type to the UE via UE Configuration Update procedure.
- If the Network Slice-Specific Authentication and Authorization fails for all S-NSSAIs mapped to all S-NSSAIs in the Allowed NSSAI, the AMF determines a new Allowed NSSAI including default S-NSSAI(s). If no default S-NSSAI(s) could be added, the AMF shall execute the Network-initiated Deregistration procedure described in clause 4.2.2.3.3 of TS 23.502 [3] and shall include in the explicit De-Registration Request message the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value.
After a successful or unsuccessful UE Network Slice-Specific Authentication and Authorization, the UE context in the AMF shall retain the authentication and authorization status for the UE for the related specific S-NSSAI of the HPLMN or SNPN while the UE remains RM-REGISTERED in the PLMN or SNPN, so that the AMF is not required to execute a Network Slice-Specific Authentication and Authorization for a UE at every Periodic Registration Update or Mobility Registration procedure with the PLMN or SNPN.
A Network Slice-Specific AAA server may revoke the authorization or challenge the authentication and authorization of a UE at any time. When authorization is revoked for an S-NSSAI that maps to an S-NSSAI in the current Allowed NSSAI for an Access Type, the AMF shall provide a new Allowed NSSAI to the UE and trigger the release of all PDU sessions associated with the S-NSSAI, for this Access Type.
The AMF provides the GPSI of the UE related to the S-NSSAI to the AAA Server to allow the AAA server to initiate the Network Slice-Specific Authentication and Authorization, or the Authorization revocation procedure, where the current AMF serving the UE needs to be identified by the system, so the UE authorization status can be challenged or revoked.
The Network Slice-Specific Authentication and Authorization requires that the UE Primary Authentication and Authorization of the SUPI has successfully completed. If the SUPI authorization is revoked, then also the Network Slice-Specific authorization is revoked. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11 Network Slice Admission Control | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.0 General | The Network Slice Admission Control Function (NSACF) monitors and controls the number of registered UEs per network slice and/or the number of PDU Sessions per network slice for the network slices that are subject to Network Slice Admission Control (NSAC). The NSACF is configured with the maximum number of UEs and/or the maximum number of PDU Sessions allowed to be served per S-NSSAI subject to NSAC. The NSACF is also configured with information indicating applicable access type(s) for the S-NSSAI (i.e. 3GPP Access Type, Non-3GPP Access Type, or both).
The NSACF also provides event-based Network Slice status notifications and reports to the consumer NFs (e.g. AF).
A NSACF can be configured with the NSAC Service Area(s) it serves. The NSAC Service Area Identifier is a unique identifier in a PLMN or SNPN. The consumer NFs which use the NSAC services are configured with a single and network slice independent value of the NSAC Service Area Identifier so they can discover the correct NSACF (see clause 6.3.22).
The NSACF may be responsible for one or more S-NSSAIs. For one S-NSSAI there may be one or multiple NSACFs deployed in a network (a PLMN or a SNPN) as follows:
- If a PLMN or SNPN is configured with a single NSAC service area, there is a single NSACF configured with the maximum number of UEs per network slice and/or the maximum number of PDU Sessions per network slice, which are valid in the network. In this case there is no need to provision any NSAC Service Area Identifier value in the PLMN or SNPN.
- If a PLMN or SNPN is configured with multiple NSAC service areas, an NSACF may be deployed on a NSAC service area basis, which can be one NSACF instance or one NSACF Set. There are three NSAC architecture options:
- Option 1: non-Hierarchical NSAC architecture. In this architecture, independent NSACFs are deployed in every NSAC service area. There is no interaction between the NSACFs deployed in different NSAC service areas. Each NSACF is configured with the maximum number of UEs per network slice and/or the maximum number of PDU Sessions which are valid in the NSAC service area (see clauses 5.15.11.1.1 and 5.15.11.2.1 for more details).
- Option 2: Centralized NSAC architecture. In this architecture, a single centralized NSACF is deployed in the network to handle admissions in all NSAC service areas. The centralized NSACF is configured with the total number of UEs per network slice and the maximum number of PDU Sessions for the entire PLMN. NSAC Requests from AMF or SMF to the single centralized NSCAF in this case includes the NSAC service area of the NF consumer if multiple NSAC service areas are deployed in PLMN.
NOTE 1: It is possible to configure in the centralized architecture the maximum number of registered UEs and/or the maximum number of PDU sessions per NSAC service area if required by the operator. In this case, NSAC can be performed on a per NSAC service area.
- Option 3: Hierarchical NSAC architecture is deployed in the network. There are two roles of NSACF and interaction between them may be required (see clauses 5.15.11.1.2 and 5.15.11.2.2 for more details):
- Primary NSACF, controls and distributes of the maximum number of UEs and/or the maximum number of PDU Sessions for other NSACF(s) deployed in different NSAC service Area. The Primary NSACF handles overall NSAC for an S-NSSAI at the global level (i.e. it is ultimately responsible for the NSAC for an S-NSSAI).
‐ NSACF is responsible for one or multiple NSAC service Area. And one NSAC service area is only associated with one NSACF instance or one NSACF Set.
NOTE 2: When multiple NSACFs are deployed, how the maximum number of UEs per network slice and the maximum number of PDU Sessions per network slice is distributed (by OAM for Option 1 and by the primary NSACF for Option 3) among multiple NSACFs, i.e. the algorithm of the maximum number distribution, is implementation specific.
NOTE 3: When multiple NSACFs are deployed based on option 1, the UE moves to new NSAC service area with a different NSACF and if the number of UE or PDU Sessions in the target NSACF has reached the maximum number, whether the session continuity can be guaranteed is left to implementation.
NOTE 4: When multiple NSACFs are deployed based on Hierarchical NSAC architecture, it is possible that the role of Primary NSACF and the role of NSACF are co-located at the same NSACF instance.
Subject to operator policy and national/regional regulations, the AMF may exempt UEs and the SMF may exempt PDU sessions from NSAC when the UE and/or PDU Session is used for Emergency service or for Critical and Priority services (e.g. MCX, MPS).
When the AMF receives a Registration Request for an Emergency Registration, or with a Registration Request with an Establishment Cause indicating a priority service (e.g. MCX, MPS) or when the AMF determines that there is a priority subscription (e.g. MPS, MCX) in the UDM, the AMF may accept the registration request without applying NSAC, i.e. the AMF triggers the NSAC procedure, but the response from the NSACF is ignored at the AMF.
When the SMF receives a PDU Session Establishment Request for an emergency PDU Session or a PDU Session Establishment Request with a priority header, the SMF may accept the PDU Session Establishment Request without applying NSAC, i.e. the SMF triggers the NSAC procedure, but the response from the NSACF is ignored at the SMF.
Alternatively, when NSAC is exempted for the UE and/or PDU Session, the AMF and the SMF skip the corresponding NSAC procedure, i.e. this UE (respectively PDU Session) is not counted towards the maximum number of UEs (respectively PDU Sessions).
The support of NSAC for the S-NSSAI used for onboarding as described in clause 5.30.2.10 is optional and subject to Onboarding Network operator policies. However, NSAC for S-NSSAI used for onboarding is not applicable to UEs that registered in ON-SNPN with Registration Type "SNPN Onboarding".
In the case of NSAC for maximum number of PDU Sessions, when the NSACF rejects the request from the SMF to increase the number of PDU Sessions, the SMF may provide to the UE a back-off timer associated with reject cause set to 'Maximum number of PDU Sessions per S-NSSAI reached' for an Access Type as described in clause 4.2.11.4 of TS 23.502 [3]. If the UE receives from the SMF a back-off timer associated with the reject cause set to 'Maximum number of PDU Sessions per S-NSSAI reached' for an Access Type, the UE shall not request the establishment of a PDU Session for this S-NSSAI on the indicated Access Type until the back-off timer expires. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.1 Network Slice Admission Control for maximum number of UEs | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.1.1 Non-Hierarchical NSAC architecture | The NSACF keeps track of the current number of UEs registered for a network slice so that it can ensure it does not exceed the maximum number of UEs allowed to register with the network slice. The NSACF also maintains a list of UE IDs registered with a network slice that is subject to NSAC. When an event related to a UE causes the current number of UEs registered with a network slice to increase, the NSACF first checks whether the UE Identity is already in the list of UEs registered with that network slice. If not, the NSACF checks whether the maximum number of UEs per network slice for that network slice has already been reached and if it has, the NSACF applies admission control policies.
The AMF triggers a request to NSACF for NSAC for maximum number of UEs when the UE's registration status for a network slice subject to NSAC is changing, i.e. during the UE Registration procedure in clause 4.2.2.2.2 of TS 23.502 [3], UE Deregistration procedure in clause 4.2.2.3 of TS 23.502 [3], Network Slice-Specific Authentication and Authorisation procedure in clause 4.2.9.2 of TS 23.502 [3], AAA Server triggered Network Slice-Specific Re-authentication and Re-authorization procedure in clause 4.2.9.3 of TS 23.502 [3], AAA Server triggered Slice-Specific Authorization Revocation in clause 4.2.9.4 of TS 23.502 [3] and UE Configuration Update procedure in clause 4.2.4.2 of TS 23.502 [3].
NOTE 1: Early Admission Control (EAC) mode is applicable for Number of UEs per network slice admission control. The use of EAC in relation to the number of registered UEs is described in clauses 4.2.11.2 and 4.2.11.3 of TS 23.502 [3].
Since the UE may register or deregister for an S-NSSAI via 3GPP access and/or non-3GPP access as described in clause 5.15.5.2.1. The Allowed NSSAI for the access type may change while the UE is registering to a network. The AMF provides the Access Type to the NSACF when triggering a request to increase or decrease the current number of UEs registered with a S-NSSAI. The NSACF may take the Access Type into account for increasing and decreasing the number of UEs per network slice by storing the UE ID with the associated one or more Access Type(s), i.e. the NSACF is able to add or remove a registration for the UE ID for each Access Type and trigger the increase or decrease of the current number of UEs registered with a S-NSSAI based on a policy that takes the access type into account. If the Access Type provided by the AMF is not configured for NSAC in the NSACF, the NSACF always accepts the request from the AMF without increasing or decreasing the number of UEs. If the Access Type provided by the AMF is configured for NSAC in the NSACF and the maximum number is reached, the NSACF sends a reject response to the AMF including the access type.
NOTE 2: For example, if the NSACF is configured to apply NSAC for 3GPP Access Type only, the NSACF counts registration via 3GPP access type only. If the NSACF is configured to apply NSAC for both Access Types and the UE newly registers via 3GPP access while the UE is already registered via non-3GPP access (or vice versa), the NSACF updates the UE ID entry with both 3GPP Access Type and non-3GPP Access Type and the NSACF may count the UE once or twice based on its policy. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.1.2 Hierarchical NSAC architecture | In the Hierarchical NSAC architecture, the NSACFs deployed in the NSAC service areas interacts with the Primary NSACF when needed and as explained below.
The main differences between the non-Hierarchical architecture and the Hierarchical architecture is that the AMFs and the NSACFs deployed in the Hierarchical architecture support the following:
- When the AMF triggers an NSAC request to the NSACF, the AMF includes the UE already Registered indication if the AMF can determine that the UE has been registered with the S-NSSAI in one NSAC service area before. If the AMF does not include the UE already Registered indication, the registration request to the indicated S-NSSAI is determined as initial registration, i.e. the UE has not been registered in any service area before. The AMF determines the UE already Registered indication based on the received Allowed NSSAI information from the source AMF (in case of inter AMF handover) or from SMF+PGW-C (in case of mobility from EPS to 5GS).
- There are two types of UE admission control: quota-based control or threshold-based control. A PLMN is configured to deploy only one type of UE admission control. Based on the type of UE admission control configured for the PLMN, the NSACF handles the NSAC request as described below:
- For NSACFs supporting quota-based control, if the NSACF receives a request to increase the number of UEs and the number of UEs registered for a network slice has reached the local maximum number of UEs provisioned in the NSACF, or upon receiving a request to decrease the number of UEs and no UE entry is present in the NSACF, the NSACF interacts with the Primary NSACF for the handling of the NSAC request for the UE. The Primary NSACF may return in the response an updated local maximum number of registered UEs value to the NSACF based on the status of registered UEs for the Network Slice and which enables the NSACF to handle locally the request. Alternatively and if the request to increase the number of UEs includes the UE already Registered indication, the Primary NSACF may admit the UE request and store the UE entry which allows for service continuity. The Primary NSACF may also reject the request. If the NSACF receives a request to increase the number of UEs and the local maximum number of UEs is not reached, the NSACF handles the request locally and sends a response to the AMF without interaction with the Primary NSACF.
- For NSACF supporting threshold-based control, the NSACF is initially configured with a UE admission threshold and a local maximum number of Registered UEs to be admitted. Threshold-based control refers to an admission threshold, defined in percentage, against provisioned local maximum number in NSACF (e.g. an admission threshold of 80% refers to the case when 80% of the provisioned local maximum number should be used). If upon a receiving a request to increase the number of UEs without a UE already Registered indication and if UE admission threshold is at or above the threshold level configured at the NSACF, the NSACF immediately rejects the NSAC request. If the received request includes the UE already Registered indication and if UE admission is at or above the threshold level configured at the NSACF, the NSACF accepts the request to enable UE admission and allow for service continuity as long as the local maximum number of Registered UEs have not been reached. If the local maximum number of registered UEs value have been reached, the NSACF interacts with the Primary NSACF for the handling of the NSAC request for the UE. The NSACF does not include the UE already Registered indication in this case. The Primary NSACF may return an updated UE admission threshold value to the NSACF in the response which enables the NSACF to handle the request locally. Alternatively, the Primary NSACF may handle and store the UE entry. The Primary NSACF may also reject the request.
- For both options, the Primary NSACF supports the following capabilities depending on the NSACF configuration:
- Returning a new updated local maximum number of Registered UEs for the NSACF to admit if the NSACF is configured to support the quota-based UE admission control; or
- Returning a new updated UE admission threshold for the NSACF to apply if the NSACF is configured to support the threshold-based UE admission control;
- The Primary NSACF handles, stores entries only related to UEs which the NSAC request includes the UE already Registered indication, that are already admitted in an existing NSAC service area but cannot be admitted in the new NSAC service area due to no remaining local maximum number of registered UEs, as long as the overall PLMN number of registered UEs at the Primary NSACF is not exhausted. The Primary NSACF informs the NSACF in its response;
- Based on the response from the Primary NSACF, the NSACF determines whether to accept or reject the NSAC request for UE registration. In addition, the NSACF may also update the local maximum number of Registered UEs or admission threshold respectively if the related updated value is received;
- At any time, the Primary NSACF can update the NSACFs local maximum number of Registered UEs or admission threshold through the Nnsacf_NSAC_LocalNumberUpdate operation as described in clause 4.2.11.6 of TS 23.502 [3]. The updated values provided from the Primary NSACF to the NSACFs may directly apply to current NSAC pending request in NSACF and are used for all future requests.
- The Primary NSACF subscribes with all NSACFs to obtain the number of currently registered UEs at all NSACFs. Based on the obtained information, the Primary NSACF can update the NSACF with local maximum number of registered UEs. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.1.3 Centralized NSAC architecture | The main differences between the NSACFs deployed in a non-Hierarchical architecture and NSACFs deployed in a Centralized NSAC architecture is as follows:
- If multiple NSAC service areas are deployed in PLMN, the AMF provides the NSAC Service Area Identifier information to the centralized NSACF. The centralized NSACF also stores the NSAC Service Area Identifier of the AMF the UE is registered with. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.2 Network Slice Admission Control for maximum number of PDU sessions | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.2.1 Non- Hierarchical NSAC architecture | The NSACF keeps track of the current number of PDU Sessions per network slice so that it can ensure it does not exceed the maximum number of PDU session allowed to be served by the network slice. When an event related to a UE causes the current number of PDU sessions established within the network slice is to increase, the NSACF checks whether the maximum number of PDU sessions per network slice for that network slice has already been reached and if it has, the NSACF applies admission control policies.
The anchor SMF triggers a request to NSACF for maximum number of PDU sessions per network slice control during PDU session establishment/release procedures in clauses 4.3.2 and 4.3.4 of TS 23.502 [3].
The SMF provides the Access Type to the NSACF when triggering a request to increase or decrease the number of PDU Sessions. The NSACF takes Access Type into account for increasing and decreasing the current number of PDU Sessions depending on the applicability of the Access Type for the NSAC for maximum number of PDU Sessions for the S-NSSAI.
NOTE 1: For MA PDU Session, the SMF provides the Access Type to NSACF when the user plane connection is about to be established or released in the corresponding access network. With this, the SMF provides one or two Access Types for the MA PDU Session in the same request message to the NSACF. The NSACF can reject a single or both Access Types depending on the applicability of the Access Type for the NSAC.
NOTE 2: I-SMF does not interact with NSCAF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.2.2 Hierarchical NSAC architecture | The main differences between the NSACFs deployed in a non-Hierarchical architecture and NSACFs deployed in a Hierarchical architecture is as follows:
- The NSCAF is enhanced to support PDU session admission quota-based control.
- When the local maximum number of PDU sessions is reached, the NSACF interacts with the Primary NSACF to handle the request. The Primary NSACF either return an increased local maximum number to the NSACF, or reject the local maximum number value update request if all the global maximum number are consumed based on the status of established PDU sessions to the network slice.
NOTE: For Hierarchical NSAC architecture global maximum number used within this specification is synonymous with the maximum number of allowed registered UEs or established PDU Sessions for an S-NSSAI subject to Network Slice Admission Control (NSAC) for the entire PLMN and outbound roamers.
- Based on the response from Primary NSACF, the NSACF updates the local maximum number if updated value is received from the Primary NSACF. The NSACF updates local maximum number value (if received) and determines whether to accept or reject the NSAC request for PDU session establishment based on the local maximum number value.
- The update of local maximum number value by the Primary NSACF can also happen at any time through the Nnsacf_NSAC_LocalNumberUpdate service operation as described in clause 4.2.11.6 TS 23.502 [3]. The updated values provided from the Primary NSACF to NSACFs may directly apply to current NSAC pending request in NSACF and are used for all future requests.
- The Primary NSACF subscribes with all NSACFs to obtain the number of currently established PDU sessions at all NSACFs. Based on the obtained information, the Primary NSACF can update the NSACF with local maximum number of established PDU sessions. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.2.3 Centralized NSAC architecture | The main differences between the NSACFs deployed in a non-Hierarchical NSAC architecture and NSACFs deployed in a Centralized NSAC architecture is as follows
- If multiple NSAC service areas are deployed in a PLMN, the SMF provides the NSAC Service Area Identifier to the centralized NSACF. The centralized NSACF also stores the NSAC Service Area Identifier of the SMF the PDU session is established on. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.3 Network Slice Admission Control for Roaming | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.3.0 General | In the case of roaming, depending on operator's policy, a roaming agreement or an SLA between the VPLMN and the HPLMN, NSAC of roaming UEs is performed by one of the following modes of NSAC admission:
- VPLMN NSAC Admission; or
- VPLMN with HPLMN assistance NSAC Admission; or
- HPLMN NSAC Admission.
The VPLMN (AMF and SMF) identifies the mode to apply from the AMF subscription data at UE registration and from the SMF subscription data at PDU session establishment.
For all the above modes, for NSAC of roaming UEs for maximum number of UEs per network slice and/or maximum number of PDU Sessions per network slice managed by the VPLMN, each S-NSSAI of the HPLMN that is subject to NSAC is mapped to a corresponding S-NSSAI of the VPLMN subject to NSAC.
For both VPLMN NSAC Admission and VPLMN with HPLMN assistance NSAC Admission modes, each configured S-NSSAI that is subject to NSAC and that is mapped from the HPLMN S-NSSAI, the SMF performs NSAC for home routed PDU sessions according to the principles described in clause 5.15.11.2. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.3.1 VPLMN NSAC Admission Mode | For NSAC of roaming UEs for maximum number of UEs per network slice and/or maximum number of PDU Sessions per network slice managed by the VPLMN, the following principles shall be used:
- For NSAC for the maximum number of UEs for S-NSSAI of the HPLMN, a NSACF in the VPLMN can be configured with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN for a S-NSSAI of the HPLMN that is subject to NSAC. In such a case, the AMFs trigger a request to a NSACF of the VPLMN.
- For NSAC for the maximum number of PDU Sessions for S-NSSAI of the HPLMN, a NSACF in the VPLMN can be configured with the maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI of the HPLMN for a S-NSSAI of the HPLMN that is subject to NSAC. In such a case, the anchor SMF in the VPLMN triggers a request to a NSACF of the VPLMN.
- For NSAC for the maximum number of UEs for S-NSSAI of the VPLMN, AMFs trigger a request to a NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved.
- For NSAC for the maximum number of PDU Sessions for S-NSSAI of the VPLMN in the LBO roaming case, the SMF triggers a request to a NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved.
‐ The AMF or SMF (in LBO roaming case) in the VPLMN provides both the S-NSSAI in the VPLMN and the corresponding mapped S-NSSAI in the HPLMN to the NSACF in the VPLMN. The NSACF in the VPLMN performs NSAC for both S-NSSAI of the VPLMN and the corresponding mapped S-NSSAI of the HPLMN based on the SLA between the VPLMN and the HPLMN.
In addition to configuring the VPLMN NFs with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN subject to NSAC and the maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI of the HPLMN subject to NSAC, the VPLMN can optionally fetch this information from the HPLMN primary NSACF in a hierarchal architecture or centralized NSACF in a centralized architecture. If the NSACF in VPLMN does not have quota configured but can receive quota from the HPLMN, the NSACF in VPLMN may interact with the HPLMN for retrieving the quota before processing any incoming request. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval. However, in this case, the VPLMN rejects any additional requests exceeding the received information. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.3.2 VPLMN with HPLMN assistance NSAC Admission | In this admission mode HPLMN delegates NSAC for S-NSSAIs subject to NSAC to the VPLMN, both for number of registered UEs and the number of LBO PDU sessions.
Every NSACF performing admission in the VPLMN for each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, fetches from the VPLMN primary NSACF in a hierarchal architecture the maximum number of registered UEs to be admitted and/or the maximum number of LBO PDU sessions to be allowed. The VPLMN primary or central NSACF, in turn, acquires the information from the HPLMN central or primary NSACF depending on the deployed architecture. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval.
If re-distribution of quota is required in the VPLMN in a hierarchal architecture, amongst multiple NSACFs than this is handled by the primary NSACF in VPLMN with no involvement from the HPLMN. The VPLMN NSACF discovers the HPLMN primary or central NSACF or be configured with the needed information.
For any request(s) received in any NSACF in the VPLMN exceeding the received maximum number information, the NSACF interacts with the VPLMN primary NSACF which in turn interacts with HPLMN primary or central NSACF to receive an updated roaming quota for the corresponding mapped S-NSSAI, which is used to determine whether admission request is accepted or rejected, unless forbidden by the SLA. If an admission request is accepted, the UE entry is stored in the NSACF performing admission in the VPLMN. This applies to the number of registered UEs as well as the number of LBO PDU sessions. The primary NSACF in VPLMN may re-distribute the received updated roaming quota to the NSACFs in VPLMN to perform NSAC for Roaming UEs according to the principles described in clauses 5.15.11.1 and 5.15.11.2. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.3.3 HPLMN NSAC Admission Mode | In this admission mode the AMF or SMF in VPLMN interacts with HPLMN for admission, both for number of registered UEs or the number of LBO PDU sessions respectively.
For each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, AMF performs NSAC admission for the number of registered UEs with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they register in this VPLMN. The AMF discovers the HPLMN primary or central NSACF or be configured with the needed information.
For each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, every SMF in this VPLMN performs NSAC admission for the number of LBO PDU sessions with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they initiate an LBO PDU session. The SMFs discover the HPLMN primary or central NSACF or be configured with the needed information. For each S-NSSAI of the HPLMN that is subject to NSAC, the SMF performs NSAC according to the principles described in clause 5.15.11.2 for home routed PDU sessions.
In the HPLMN NSAC admission mode, the primary NSACF or central NSACF in HPLMN determines whether the NSAC admission request for a roaming UE is accepted or rejected. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.4 Network Slice status notifications and reports to a consumer NF | A consumer NF (e.g. AF, Primary NSACF) can subscribe with the NSACF for Network Slice status notifications and reports. Upon such subscription, the corresponding NSACF in different NSAC architecture as defined in clause 5.15.11.0 can provide event based notifications and reports to the consumer NF (e.g. to AF via NEF) related to the current number of UEs registered for a network slice or the current number of UEs with at least one PDU Session/PDN Connection in the case of EPC interworking or the current number of PDU Sessions established on a network slice.
NOTE: The Primary NSACF subscribes Network Slice status from all the NSACF(s) it contacts with for the update of the maximum number of UE or PDU session configured at the NSACF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.11.5 Support of Network Slice Admission Control and Interworking with EPC | This clause describes the NSAC for maximum number of registered UEs and for maximum number of PDU Sessions for network slice subjected to EPS interworking. The NSAC for maximum number of UE with at least one PDU Session/PDN Connection is described in clause 5.15.11.5a. A network slice subject to both NSAC and EPS counting shall be configured with only one of the options:
- Maximum number of registered UEs and/or maximum number of PDU Session; or
- Maximum number of UEs with at least one PDU Session/PDN Connection and/or maximum number of PDU Session.
If EPS counting is required for a network slice, the NSAC for maximum number of UEs and/or for maximum number of PDU Sessions per network slice is performed at the time of PDN connection establishment in case of EPC interworking. To support the NSAC for maximum number of UEs and/or for maximum number of PDU Sessions per network slice in EPC, the SMF+PGW-C is configured with the information indicating which network slice is subject to NSAC. During PDN connection establishment in EPC, the SMF+PGW-C selects an S-NSSAI associated with the PDN connection as described in clause 5.15.7.1. If the selected S-NSSAI by the SMF+PGW-C is subject to the NSAC, the SMF+PGW-C triggers interaction with NSACF to check the availability of the network slice by invoking separate NSAC procedures for number of UE and number of PDU Session (as described in clause 4.11.5.9 of TS 23.502 [3]), before the SMF+PGW-C provides the selected S-NSSAI to the UE. If the network slice is available, the SMF+PGW-C continues to proceed with the PDN connection establishment procedure.
The NSACF performs the following for checking network slice availability prior to returning a response to the SMF+PGW-C:
- For NSAC for number of UEs, if the UE identity is already included in the list of UE IDs registered with a network slice, or the UE identity is not included in the list of UE IDs registered with a network slice and the current number of UE registration did not reach the maximum number, the NSACF responds to the SMF+PGW-C with the information that the network slice is available. The NSACF includes the UE identity in the list of UE IDs if not already on the list and increases the current number of UE registration. Otherwise, the NSACF returns a response indicating that the maximum number with the network slice has been reached.
If hierarchical NSAC architecture is deployed, when the local maximum number or local threshold is reached the NSACF may interact with the Primary NSACF before it returns the response back to the SMF+PGW-C. For more details on handling at the NSACF and Primary NSACF see clause 5.15.11.1.2.
- For NSAC for number of PDU Sessions, if the current number of PDU sessions is below the maximum number, the NSACF responds to the SMF+PGW-C with the information that the network slice is available. The NSACF increases the current number of PDU sessions. Otherwise, the NSACF returns the response indicating that the maximum number with the network slice has been reached.
If hierarchical NSAC architecture is deployed, when the local maximum number is reached the NSACF may interact with the Primary NSACF before it returns the response back to the SMF+PGW-C. For more details on handling at the NSACF and Primary NSACF see clause 5.15.11.2.2.
If the maximum number of UEs and/or the maximum number of PDU sessions has already been reached, unless operator policy implements a different action, the SMF+PGW-C rejects the PDN connection.
NOTE 1: As an implementation option, if the APN is mapped to more than one S-NSSAI and the first selected S-NSSAI is not available (e.g. either current number of UE registration reached maximum or current number of PDU sessions reached maximum), then based on the operator policy the PGW-C+SMF can try another mapped S-NSSAI for the PDN connection establishment procedure.
If the establishment of a new PDN Connections is with a different SMF+PGW-C from the SMF+PGW-C used for already existing PDN connection associated with the same S-NSSAI, each SMF+PGW-C will send a request for update (e.g. increase or decrease) to the NSACF. The NSACF may maintain a registration entry per SMF+PGW-C for the same UE ID.
The SMF+PGW-C provides the Access Type to the NSACF when triggering a request to increase or decrease the number of UEs and/or the number of PDU Sessions for an S-NSSAI.
NOTE 2: The SMF+PGW-C determines the Access Type based on the RAT type parameter in the PMIP or GTP message received from the ePDG; or alternatively it can internally determine the Access Type based on the source node (e.g. SGW) sending the request for the PDN Connection establishment.
When the UE with ongoing PDN connection(s) moves from EPC to 5GC, the SMF+PGW-C triggers a request to decrease the number of the UE registration in NSACF and the AMF triggers a request to increase the number of the UE registration in NSACF when the UE is registered in the new AMF. If there are more than one PDN connections associated with the S-NSSAI, the NSACF may receive multiple requests for the same S-NSSAI from different SMF+PGW-Cs. When the UE with ongoing PDU session(s) moves from 5GC to EPC, the SMF+PGW-C triggers a request to increase the number of the UE registration in NSACF and the old AMF triggers a request to decrease the number of the UE registration in NSACF when the UE is deregistered in old AMF. If there are more than one PDU sessions associated with the S-NSSAI, the NSACF may receive multiple requests for the same S-NSSAI from different SMF+PGW-Cs. The NSACF maintains a list of UE IDs based on the requests from SMF+PGW-C(s) and AMF and adjusts the current number of registrations accordingly.
When EPS counting is performed for a network slice and the UE with ongoing PDN connection(s) moves from EPC to 5GC, session continuity is guaranteed from NSAC standpoint, as the admission was granted at the time of PDN connection establishment, i.e. the number of PDU session is not counted again in 5GC. Similarly, when the UE with ongoing PDU session(s) moves from 5GC to EPC, session continuity is guaranteed from NSAC standpoint as the admission of the PDN Connection(s) to the network slice was already granted at the time of PDU Session establishment in 5GC.
If the PDN connection associated with S-NSSAI is released in EPC, the SMF+PGW-C triggers a request (i.e. decrease) to NSACF for maximum number of UEs and/or maximum number of PDU sessions per network slice control. The NSACF decreases the current number of registrations and removes the UE identity from the list of UE IDs if the PDN connection(s) associated with the S-NSSAI are all released in EPC.
NOTE 3: NSAC in EPC is not performed for the attachment without PDN connectivity.
If EPS counting is not required for a network slice, the NSAC for maximum number of UEs and/or for maximum number of PDU Sessions per network slice is performed when the UE moves from EPC to 5GC, i.e. when the UE performs mobility Registration procedure from EPC to 5GC (NSAC for maximum number of UEs per network slice) and/or when the PDN connections are handed over from EPC to 5GC (NSAC for maximum number of PDU Sessions per network slice). The SMF+PGW-C is configured with the information indicating the network slice is subject to NSAC only in 5GS. The PDN connection interworking procedure is performed as described in clause 5.15.7.1. Mobility from EPC to 5GC does not guarantee all active PDU Session(s) can be transferred to the 5GC in certain circumstances when either the current number of UE registration or the current number of PDU sessions would exceed the maximum number when the UE moves from EPC to 5GC. When the UE with ongoing PDU session(s) moves from 5GC to EPC, the SMF+PGW-C triggers a request to decrease the number of PDU Session to NSACF. If there are more than one PDU sessions associated with the S-NSSAI, the NSACF may receive multiple requests for the same S-NSSAI from different SMF+PGW-Cs and NSACF removes the PDU Session ID(s) while decreasing the number of PDU Session(s).
NOTE 4: Given that session continuity is not guaranteed when EPS counting is not required, it is recommended for services which require the session continuity to support EPS counting.
NOTE 5: When multiple NSACFs are deployed and if the number of UE in target NSACF has reached the maximum number, whether session continuity can be guaranteed is left to implementation.
NOTE 6: When a centralized architecture is deployed, UE admission is guaranteed at inter-system and inter-AMF mobility if the same NSACF is selected. This is the case for non-roaming scenarios and for roaming scenarios with HPLMN NSAC Admission Mode described in clause 5.15.11.3.
5.15.11.5a Support of Network Slice Admission Control in 5GS for maximum number of UEs with at least one PDU Session/PDN Connection
When EPS counting is required for a network slice and NSACF is configured with maximum number of UEs with at least one PDU Session/PDN Connection, the NSACF keeps track of the current number of UEs with at least one PDU session/PDN connection established on a network slice to ensure it does not exceed the maximum configured number.
To support the NSAC for maximum number of UEs with at least one PDU Session/PDN Connection, the SMF+PGW-C may be configured with one of the following options:
- Option 1: Triggering an Nnsacf_NSAC_NumOfUEsUpdate_Request to NSACF for NSAC for maximum number of UEs when the UE establishes first PDU Session/PDN connection associated with the network slice in the SMF+PGW-C, or when the last PDU Session/PDN connection associated with the network slice is released. The NSACF performs admission control as described in clause 5.15.11.5 and the number of registered UE is replaced with number of UE with at least one PDU session/PDN connection. Also, if the maximum number of UEs with at least one PDU Session/PDN connection has already been reached and SMF+PGW-C receives the rejection from NSACF, unless operator policy implements a different action, the SMF+PGW-C rejects the PDU Session/PDN connection indicating the cause being the number of UEs in the network slice has been exceeded. The AMF is not configured for this S-NSSAI to be subject to NSAC; or
- Option 2: Triggering an Nnsacf_NSAC_NumOfPDUsUpdate_Request as described in clause 5.15.11.5 to NSACF and the NSACF performs admission control for the number of UEs with at least one PDU Session/PDN connection as follows:
- The NSACF supports handling both for the number of UEs with at least one PDU Session/PDN Connection and number of PDU session for the S-NSSAI that is subject to EPC interworking and NSAC. In this case the AMF is not configured for this S-NSSAI to be subject to NSAC. As an optimization option, the SMF+PGW-C can be configured not to trigger the Nnsacf_NSAC_NumOfUEsUpdate_Request to NSACF.
- When the NSACF receives request to increase the current number of PDU Session/PDN Connection established for the network slice, the NSACF checks whether this is the first PDU Session/PDN Connection associated with the network slice. If this is the first PDU Session/PDN Connection associated with the network slice the NSACF checks whether the maximum number of UEs with at least one PDU Session/PDN Connection has been reached. If the maximum number has not been reached then the NSACF increases the number of UE with at least one PDU session/PDN connection and add an entry for UE ID. If the maximum number of UEs has already been reached, unless operator policy implements a different action, the SMF+PGW-C rejects the PDU Session/PDN connection indicating the cause being the number of UEs in the network slice has been exceeded.
- When the NSACF receives request to decrease the current number of PDU Session/PDN Connection established for the network slice, the NSACF locates the UE entry, checks whether this is the last PDU Session/PDN Connection associated with the network slice for the UE. If it is the last PDU Session/PDN Connection the NSACF decreases the number of UE with at least one PDU session/PDN connection and remove the associated UE entry.
NOTE 1: A PLMN can deploy one of the above two options for a slice when EPS counting is required for a network slice and NSACF is configured with maximum number of UEs with at least one PDU Session/PDN Connection.
NSACF is configured with the information of whether the NSAC for number of UEs with at least one PDU session/PDN connection is based on Option1 or Option 2.
In both options, the SMF+PGW-C provides the Access Type to the NSACF when triggering a request to increase or decrease or update the number of UEs with at least one PDU Session/PDN Connection and/or the number of PDU Sessions for an S-NSSAI.
In the case of roaming, same mechanisms in clause 5.15.11.3 are used and number of registered UE is replaced with number of UE with at least one PDU Session/PDN Connection. For home routed PDU Session/PDN Connection only HPLMN admission mode can be used in this case.
If hierarchical NSAC architecture is deployed, when the local maximum number or local threshold is reached the NSAC may interact with the Primary NSACF before it returns the response back to the SMF+PGW-C. For more details on handling at the NSACF and Primary NSACF see clause 5.15.11.1.2.
NOTE 2: When NSAC for number of UEs with at least one PDU session or one PDN connection is used, the session continuity is guaranteed at inter-system mobility as the admission is granted during the establishment of the PDU Session/PDN Connection. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.12 Support of subscription-based restrictions to simultaneous registration of network slices | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.12.1 General | The subscription information for a UE may include for each S-NSSAI Network Slice Simultaneous Registration Group (NSSRG) information constraining which S-NSSAIs can be simultaneously provided to the UE in the Allowed NSSAI.
When S-NSSAIs have associated NSSRG information, then the S-NSSAIs in the Allowed NSSAI shall share at least one NSSRG.
The NSSRG information, defining the association of S-NSSAIs to NSSRG, is provided as an additional and separate information.
If the optional NSSRG information is not present for the S-NSSAIs of a subscription and other restrictions do not apply e.g. availability at a specific location, then it is assumed that all the S-NSSAIs in the subscription information can be simultaneously provided to the UE in the Allowed NSSAI. However, if NSSRG information is present in the subscription information, at least one NSSRG shall be associated with each of the S-NSSAIs in the subscription information. At any time, if the AMF has received subscription information for a UE that includes NSSRG information, the Allowed NSSAI for the UE can only include S-NSSAIs which share a common NSSRG.
NOTE 1: The AMF enforces NSSRG only for the access(es) the UE registered to the AMF. When the UE is registered to different PLMNs over 3GPP access and non-3GPP access, the AMF in one access cannot enforce a common NSSRG over both accesses.
The default S-NSSAIs, if more than one is present, are associated with the same NSSRGs, i.e. the UE is always allowed to be registered with all the default S-NSSAIs simultaneously. The HPLMN only sends S-NSSAIs sharing all the NSSRGs of the Default S-NSSAIs to a non-supporting VPLMN as part of the subscription information, i.e. in addition to the default S-NSSAI(s), the HPLMN may send any other subscribed S-NSSAI which shares at least all the NSSRG defined for the default S-NSSAI(s) and the HPLMN sends no NSSRG information to the VPLMN. A subscription information that includes NSSRG information shall include at least one default S-NSSAI.
A supporting AMF/NSSF, when it receives a Requested NSSAI, evaluates the S-NSSAIs of the HPLMN (in the mapping information of the Requested NSSAI, when a mapping information is applicable) based on any received NSSRG information for these S-NSSAIs, to determines whether they can be provided together in the Allowed NSSAI.
NOTE 2: An HPLMN enabling support of subscription-based restrictions to simultaneous registration of network slices for a Subscriber, can set the subscribed S-NSSAI(s) already in the subscription information before the NSSRG information was added to the subscription information, to have the same NSSRGs defined for the default S-NSSAI(s) if it has to continue to support the same service behaviour for these S-NSSAIs. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.12.2 UE and UE configuration aspects | A UE may support the subscription-based restrictions to simultaneous registration of network slices feature. In this case, the UE indicates its support in the Registration Request message in the Initial Registration and the Mobility Registration Update as part of the UE 5GMM Core Network Capability.
When the serving AMF provides the Configured NSSAI to the UE and the UE has indicated it supports the subscription-based restrictions to simultaneous registration of network slices feature, the AMF also provides the UE with the NSSRG information related to the S-NSSAIs of the HPLMN which are in the mapping information of the Configured NSSAI. A UE which receives the NSSRG values in the network slicing configuration information shall only include in the Requested NSSAI S-NSSAIs that share a common NSSRG as per the received information. If the UE has stored Pending NSSAI and the UE is still interested in the Pending NSSAI then all the S-NSSAIs in the Requested NSSAI and the Pending S-NSSAI shall share a common NSSRG. If the HPLMN changes NSSRG information in the subscription information for a UE, the UDM updates the supporting AMF serving the UE with the new NSSRG information and the AMF, possibly after interaction with the NSSF (see clause 5.2.16.2.1 of TS 23.502 [3]), updates the UE as necessary with network slicing configuration by means of the UE Configuration Update procedure (this may include changes in the Configured NSSAI (and related mapping information) and changes in the Allowed NSSAI as applicable). The UE acknowledges this UE Configuration Update according to clause 4.2.4.2 of TS 23.502 [3].
At any time, a UE supporting subscription-based restrictions to simultaneous registration of network slices feature and that has received NSSRG information together with the Configured NSSAI shall only request S-NSSAIs, across all Access Type(s) regardless of whether the same PLMN or different PLMNs are used, that share one or more common NSSRG.
NOTE: In Requested NSSAI across all Access Type(s), the UE needs to include S-NSSAIs that share at least one common NSSRG.
An AMF which supports the subscription-based restrictions to simultaneous registration of network slice feature configures a non-supporting UE with a Configured NSSAI including only the S-NSSAIs sharing all the NSSRG values of the default S-NSSAI(s), except if it has been instructed otherwise by the UDM. In addition to the default S-NSSAI(s), the AMF sends to the UE in the Configured NSSAI any other subscribed S-NSSAI whose NSSRG match at least those defined for the default S-NSSAI(s).
The UDM in a supporting HPLMN may optionally keep a record of the PEIs or Type Allocation Codes values regarding UE ability to handle network slices that cannot be provided simultaneously in Allowed NSSAI.
The UDM may, based on configuration or the optional PEI records, indicate the AMF to provide the non-supporting UEs with the full set of subscribed S-NSSAIs even if they do not share a common NSSRG. The UDM instructs the supporting AMFs of a PLMN to do so by indicating that the UE can be given a Configured NSSAI with all the S-NSSAIs in the subscription information. If this indication is received from the UDM by the AMF, this is included in the UE context.
Based on its policy (including configuration or optionally checking the specific PEI or Type Allocation Code used by the UE and subject to roaming agreement) the UDM may also provide the serving AMF in a non-supporting VPLMN with all the S-NSSAI in the subscription information. In this case the AMF provides the UE with a Configured NSSAI including all the S-NSSAIs in the subscription information the AMF receives.
The AMF provides no NSSRG information to a non-supporting UE.
When an AMF which supports the subscription-based restrictions to simultaneous registration of network slice feature, receives from a UE a Requested NSSAI including S-NSSAIs that are supported in the Tracking Area but do not share a common NSSRG, or the AMF has pending NSSAI stored for the UE and the S-NSSAI(s) of the requested NSSAI and the pending NSSAI do not share a common NSSRG, the AMF assumes the UE configuration is not up-to-date and provides the following:
- a supporting UE with an updated configuration including the up-to-date NSSRG information for the S-NSSAIs in the Configured NSSAI as described above.
- a non-supporting UE with an updated Configured NSSAI including only the S-NSSAIs sharing all the NSSRG values of the default S-NSSAI(s), only for the case where the UE context does not include an indication to provide all the subscribed S-NSSAIs in the subscription information in the Configured NSSAI for the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.13 Support of data rate limitation per Network Slice for a UE | A UE subscription information may include an optional Slice Maximum Bit Rate for the UE (Subscribed UE-Slice-MBR) for an S-NSSAI, which applies for 3GPP access type only. The Subscribed UE-Slice-MBR includes a UL and a DL value. If a Subscribed UE-Slice-MBR is associated to an S-NSSAI in the subscription information, it is provided by the AMF to the NG-RAN when the AMF provides the Allowed NSSAI for the UE to the NG-RAN as UE-Slice-MBR QoS parameter. The UE-Slice-MBR QoS parameter is defined in clause 5.7.2.6. If the Subscribed UE-Slice-MBR for a UE changes, the AMF updates UE-Slice-MBR in the NG-RAN accordingly.
In roaming case, the UE-Slice-MBR is provided for the S-NSSAI of the VPLMN which maps to the S-NSSAI of the HPLMN and the AMF may first interact with the PCF for authorization of the Subscribed UE-Slice-MBR. If the AMF interacts with the PCF, the PCF may provide the Authorized UE-Slice-MBR that is used as UE-Slice-MBR by the AMF as described in clause 6.1.2.1 of TS 23.503 [45].
For a roaming UE, the S-NSSAI of the VPLMN maps to only one S-NSSAI of the HPLMN for which an UE-Slice-MBR is applied.
The enforcement of the UE-Slice-MBR value, if present in the UE context in the NG-RAN for an S-NSSAI, is described in clause 5.7.1.10.
NOTE: The PCF for the PDU Session may in addition be configured to monitor the data rate per Network Slice for a UE and to strengthen or relax the traffic restrictions for individual PDU Sessions or PCC rules accordingly, as described in TS 23.503 [45] clause 6.2.1.9. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.14 Network Slice AS Groups support | The NG-RAN may support Network Slice AS Groups (NSAGs) which are used as specified in TS 38.300 [27], TS 38.331 [28], TS 38.321 [143] and TS 38.304 [50]. A Network Slice AS Group is an identifier of a group of network slices which are associated with it. A Network Slice AS Group association with a group of network slices may be valid in one or more Tracking Areas. An S-NSSAI can be associated with at most one NSAG values for Random Access and at most one NSAG value for Cell Reselection within a Tracking Area. An S-NSSAI can be associated with different NSAG values in different Tracking Areas.
The NG-RAN provides (and updates) the AMF with the values of the NSAG(s) an S-NSSAI is associated with in a TA using the NG Set Up and RAN Configuration Update procedures (see TS 38.413 [34]). The AMF in turn provides this information to the NSSF. In deployments where the total number of groups does not exceed the number of groups associated with the NSAG size limit defined in TS 38.331 [28]), all the NSAGs configured in the NG-RAN may be unique per PLMN or SNPN. If the UE has indicated that the UE supports NSAG in the 5GMM Core Network Capability (see clause 5.4.4a), the AMF may, with or without NSSF assistance, configure the UE with NSAG Information for one or more S-NSSAIs in the Configured NSSAI, by including this NSAG Information in the Registration Accept message or the UE Configuration Command message. The UE uses the NSAG Information as defined in clause 5.3.4.3.1. The AMF shall indicate in the NSAG Information in which TA a specific NSAG association to S-NSSAI(s) is valid if the AMF provides in the UE configuration a NSAG value which is used in different TAs with a different association with NSSAIs. The configuration the AMF provides includes at least the NSAGs for the UE for the TAs of the Registration Area. If the AMF does not include the list of TAIs in association with an NSAG in the NSAG Information, the NSAG is valid in the Registered PLMN and equivalent PLMNs, or SNPN.
NOTE: If the NSAGs for the PLMN and equivalent PLMNs have different associations to S-NSSAIs, then the AMF includes the list of TAIs in the NSAG information.
The UE shall store and consider the received NSAG Information, valid for the Registered PLMN and equivalent PLMNs, or SNPN until:
- the UE receives new NSAG information in a Registration Accept message or UE Configuration Command message in this PLMN or SNPN; or
- the UE receives a Configured NSSAI without any NSAG information in this PLMN or SNPN.
The UE shall store the currently valid NSAG information received in the Registered PLMN or SNPN when registered in this PLMN or SNPN and:
- The UE should be able to store the NSAG information for at least the Registered-PLMN and equivalent PLMNs, or the Registered-SNPN and equivalent SNPNs.
- The Registered-PLMN can provide NSAG information to the UE for the PLMN and the equivalent PLMNs and the Registered-SNPN can provide NSAG information to the UE for the SNPN.
- There can be at most 32 NSAGs configured in the UE at a time for a PLMN or SNPN.
- At most 4 NSAGs can have an optional TAI associated with it.
The NSAG information is not required to be stored after power off or after the UE becomes Deregistered as it is not used for cell selection. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.15 Support of Network Slice usage control | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.15.1 General | Network Slice usage control is achieved as follows:
1) Configuring network-controlled Slice Usage Policy to supporting UEs (see clause 5.15.15.2).
2) Configuring PDU Sessions inactivity timers and Network Slice deregistration inactivity timers (see clause 5.15.15.3).
NOTE: The use of Network Slice Usage Control while roaming is not supported in UE and VPLMN, i.e. no timers are configured in the UE and VPLMN in this Release of the specification. However, for Home Routed PDU sessions, PDU Session inactivity timer can be configured in the H-UPF based on operator policy.
Subject to operator policy and national/regional regulations, the AMF ensures that Network Slice usage control does not apply to a Network Slice used for Emergency services. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.15.2 UE Configuration of network-controlled Slice Usage Policy | The UE during the Registration procedure may indicate in UE MM Core Network Capability that it supports UE configuration of network-controlled Slice Usage Policy. If so, the AMF determines Slice Usage Policy for one (or more) Network Slice(s) for the UE and configures the UE with this information together with Configured NSSAI to control the usage of this (or these) Network Slice(s). The AMF may be locally configured with network Slice Usage Policy, or receive the policy from the AM-PCF, or per the information received from UDM for AF managed timer values (see clause 5.15.15.3 for more details).
The network-controlled Slice Usage Policy is provided to the UE in the Registration Accept or the UE Configuration Update Command and may include:
- An indication, for one or more of S-NSSAI(s) of the HPLMN in the Configured NSSAI, whether the UE only registers with the Network Slice with the network when applications in the UE require data transmission in the Network Slice (i.e. the UE can only register the Network Slice only on demand and consider the Network Slice as on demand S-NSSAI).
NOTE: All Other Network Slices in the Configured NSSAI are handled by the UE using UE specific policies (e.g. they may be registered irrespective of applications need).
- Optionally, for on demand S-NSSAI(s) of the HPLMN in the Configured NSSAI, a slice deregistration inactivity timer per access type that causes the UE to deregister the Network Slice. Regarding the slice deregistration inactivity timer, following applies:
a. The UE and AMF start the timer when one of the following conditions occur:
1) the Network Slice is added to the Allowed NSSAI and there are no PDU Sessions associated with the Network Slice over the corresponding access type; and
2) the last PDU Session associated with the Network Slice over the same access type is released.
b. The UE and AMF stop the timer and reset when at least one PDU Session associated with the Network Slice is successfully established or the Network Slice is removed from the Allowed NSSAI.
c. When the slice deregistration inactivity timer for a Network Slice over an access type expires, the UE and AMF locally remove the S-NSSAI from the Allowed NSSAI.
If the UE and network state became misaligned, the UE may, for example, request connectivity in a Network Slice which is no longer allowed. In this case, the AMF shall provide the updated Allowed NSSAI in a UE Configuration Update Command after rejecting the PDU Session establishment. The UE may then re-register with the Network Slice if needed.
The UE stores the received Slice Usage Policy with the Configured NSSAI for the serving PLMN and this is kept stored for as long as a Configured NSSAI remains stored for the PLMN. When the Configured NSSAI is updated, the AMF may also provide a new Slice Usage Policy to the UE.
The AMF receives slice deregistration inactivity timer values, i.e. the configured slice deregistration inactivity timer, as described in clause 5.15.15.3.
At mobility between AMFs, the old AMF provides both the ongoing slice deregistration inactivity timer information, if it is started, to enable the new AMF know when the timer expires and the configured slice deregistration inactivity timer value(s) in the UE context to the new AMF if the slice deregistration inactivity timer is received from the AM-PCF. If the configured slice deregistration inactivity timer value(s) have been updated at the old AMF but not notified to the UE, the old AMF provides the new configured slice deregistration inactivity timer value(s) as the configured slice deregistration inactivity timer value(s) to the new AMF. The new AMF includes the slice deregistration inactivity timer in Registration Accept Message sent to the UE.
If the slice deregistration inactivity timer value is updated and the AMF determines to provide the timer to the UE, the AMF provides the updated value to the UE, if the UE supports UE configuration of network-controlled Slice Usage Policy, during the registration procedure or any subsequent registration if there is no ongoing registration procedure. The AMF and the UE, if the update been provided to the UE successfully, use the updated slice deregistration inactivity timer value next time the slice deregistration inactivity timer starts. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.15.3 Network-based per UE Network Slice usage behaviour control | The 5GC performs Network Slice usage monitoring to be able to enforce the release of inactive PDU Sessions and deregistering of UEs from Network Slices with no PDU Sessions on them according to its own policies. In order to support usage monitoring for a Network Slice:
- The AMF runs a slice deregistration inactivity timer per S-NSSAI and access type to deregister the Network Slice. Regarding the slice deregistration inactivity timer, following applies:
a. The AMF starts the timer when one of the following conditions occur:
1) the Network Slice is added to the Allowed NSSAI and there are no PDU Sessions associated with the Network Slice over the corresponding access type; and
2) the last PDU Session associated with the Network Slice over the same access type is released.
b. The AMF stops the timer and reset when at least one PDU Session associated with the Network Slice is successfully established or the Network Slice is removed from the Allowed NSSAI.
c. When the slice deregistration inactivity timer for a Network Slice over an access type expires, the AMF removes the Network Slice from the Allowed NSSAI over the access type by sending the UE Configuration Update Command to impacted UE(s).
- The SMFs provide to UPFs that handle the PDU sessions in the Network Slice a PDU Session inactivity timer. The PDU Session inactivity timer is started after no data packet is transmitted or received and runs until the next data packet is transmitted or received which restarts the timer again. If the PDU Session inactivity timer expires before any packet is received or transmitted, the UPF reports this PDU Session inactivity event to the SMF to cause the SMF to release the PDU Session. While releasing the PDU session the SMF may indicate the release cause because of slice inactivity. When the AMF receives the notification of PDU Session release and it includes the release cause of slice inactivity and if the Network Slice of the released PDU Session is not used by other PDU Sessions (i.e. the last PDU Session using the Network Slice is released) over the corresponding access type, the AMF may trigger the UE Configuration Update procedure to remove the Network Slice from the Allowed NSSAI over that corresponding access type or start slice deregistration inactivity timer for the Network Slice.
If the PDU Session inactivity timer value is updated, the SMF provides the updated PDU Session inactivity timer value to the UPF. The UPF uses the updated PDU Session inactivity timer value immediately or next time the PDU Session inactivity timer starts.
NOTE: For MA PDU Session, the PDU Session inactivity timer is independent of Access Type.
If an S-NSSAI is dedicated for a single AF and if authorized by operator policy to provide deregistration inactivity/PDU Session inactivity timer values for the S-NSSAI, the AF uses external parameter provisioning procedure to provide deregistration inactivity and PDU session inactivity timer values as described in clause 4.15.6.3g of TS 23.502 [3]. In this case, the AF provided timer values are stored in the UDM and provided to the AMF/SMF as part of subscription data for the corresponding S-NSSAI. If no AF is authorized to provide deregistration inactivity/PDU Session inactivity timer values for the S-NSSAI, i.e. no timer value received from UDM, the slice deregistration inactivity timer value and PDU Session inactivity timer value are either pre-configured in the AMF/SMF or received by the AMF/SMF during the AM Policy Association / SM Policy Association procedure respectively.
To enable a serving network to direct UEs to a preferred Network Slice, the AMF may request the UE to transfer a PDU Session from one S-NSSAI to another S-NSSAI as described in clause 5.15.19. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.16 Optimized handling of temporarily available network slices | A network slice may be available for all UEs or a limited number of UEs only for a limited time that is known at the network in advance e.g. by OAM or subscription. The limited time duration may be due to, for example, the fact that network slice is only temporarily or periodically active in the deployment (e.g. for a limited time to serve an event or a UE may be only authorized to access the network slice for a limited time known in advance), or the network slice is being decommissioned at a known future time. This feature is enabled by S-NSSAI validity time that the network and the UE can handle to reduce the signalling load associated to the transitions in RM and SM states for the network slice.
The UE may indicate its support for temporarily available network slices in the UE MM Core Network Capability (see clause 5.4.4a) in the Registration Request. The AMF, based on OAM configuration or information received from the UDM or NSSF, may indicate to a supporting UE the validity time for one or more S-NSSAIs in the Configured NSSAI in the Registration Accept message or via the UE Configuration Update procedure. In roaming case, the AMF my include the validity time for an S-NSSAI in the Configured NSSAI either because of limited availability of the VPLMN S-NSSAI or the mapped S-NSSAI of the HPLMN.
If the validity time value from the OAM, UDM or NSSF are different (including the roaming case), how to select which of the validity time values is applicable for the UE is based on operator's policy.
NOTE 1: When the validity time changes or a validity time is determined for a S-NSSAI in the configured NSSAI, the PLMN provides the new validity time for the S-NSSAIs in the Configured NSSAI to a supporting UE.
If a supporting UE is configured with validity time for an S-NSSAI:
a) If the validity time indicates the S-NSSAI is available, the UE may request the S-NSSAI in a Requested NSSAI in a Registration request and, if the S-NSSAI is included in the Allowed NSSAI or in the Partially Allowed NSSAI, the UE may establish PDU sessions associated with the S-NSSAI.
b) If the validity time indicates the S-NSSAI is not available
- The UE shall not include the S-NSSAI in the Requested NSSAI for any Access Types regardless of the validity time information was received;
- If the S-NSSAI is already part of the Allowed NSSAI or Partially Allowed NSSAI, the UE shall remove the S-NSSAI from the locally stored Allowed NSSAI or Partially Allowed NSSAI and the UE shall also locally release any PDU sessions associated with the S-NSSAI.
- If the validity time indicates the S-NSSAI will not be available again, the UE shall remove the S-NSSAI from the locally stored Configured NSSAI.
NOTE 2: Subject to implementation decisions outside 3GPP scope, the UE may also use the validity time information to e.g. attempt to use another PDU sessions to continue supporting the connectivity with another connectivity option if possible according to the URSP rules, or, if not possible, e.g. provide implementation-dependent information on the availability of connectivity for specific applications affected by an impending connectivity loss, so the UE can let the end user prepare for the loss of connectivity.
NOTE 3: The AMF will add an S-NSSAI to the Allowed NSSAI before an S-NSSAI validity time of a single S-NSSAI in the Allowed NSSAI expires.
- If a UE supporting temporary available network slices only got one S-NSSAI in the Allowed NSSAI with a validity time that is about to expire and does not have any Pending NSSAI, then the UE may trigger a Mobility Registration Update to register with any other S-NSSAI in the Configured NSSAI which is still available, if any and if UE does not trigger Mobility Registration Update and Allowed NSSAI becomes empty after expiry of validity time, then the UE shall enter RM-DEREGISTERED state implicitly.
For a supporting UE, if validity time applies to an S-NSSAI, an AMF supporting temporarily available network slices shall:
- If the S-NSSAI is provided in a Requested NSSAI in a Registration Request by the UE and the validity time indicates the S-NSSAI is not available, but it is going to become available again (i.e. the UE is detected as not having up to date validity time), then the AMF sends the Configured NSSAI to the UE including the validity time for the S-NSSAI in the Registration Accept message. If the validity time indicates the S-NSSAI is not available and will not become available again, then the AMF sends the Configured NSSAI to the UE, excluding the S-NSSAI from the Configured NSSAI.
- If the S-NSSAI is in the Allowed NSSAI or the Partially Allowed NSSAI for the UE and the validity time indicates that the S-NSSAI is not available, then locally remove (i.e. without sending any signalling to the UE) the S-NSSAI from the Allowed NSSAI or Partially Allowed NSSAI. If there is any PDU session established for the S-NSSAI, the AMF requests the SMF to release the PDU session:
- If the UE is in CM-CONNECTED state, the AMF releases the PDU session for the S-NSSAI by sending to the SMF, as per step 1f in clause 4.3.4.2 of TS 23.502 [3], a Nsmf_PDUSession_UpdateSMContext Request with a release indication to request the release of the PDU Session and then the AMF forwards the N2 SM request to release the AN resources associated with the PDU session
- If the UE is in CM-IDLE state, the AMF locally releases the PDU session without paging the UE and causes the SMF to locally release the SM context for the UE by a Nsmf_PDUSession_ReleaseSMContext, as in step 1c in clause 4.3.4.2 of TS 23.502 [3]. The PDU Session status is synchronized at next time when the UE connects to the network.
- If there is no S-NSSAI present in the Allowed NSSAI or Partially Allowed NSSAI after AMF removes the S-NSSAI locally after expiry of validity time, the AMF shall enter RM-DEREGISTERED state for the UE implicitly.
For a non-supporting UE, if validity time applies to an S-NSSAI, an AMF supporting temporarily available network slices shall:
- If the validity time indicates the S-NSSAI is available, allow or partially allow the network slice when requested, establish PDU sessions when requested.
- If the S-NSSAI is provided in a Requested NSSAI in a Registration Request by the UE and the validity time indicates the S-NSSAI is not available, reject the S-NSSAI and remove the S-NSSAI from the Configured NSSAI by providing an updated Configured NSSAI in the Registration Accept message.
- If the S-NSSAI is in the UE in the Allowed NSSAI or Partially Allowed NSSAI and the validity time indicates the S-NSSAI is not available, remove the S-NSSAI from the Configured NSSAI and the Allowed NSSAI or Partially Allowed NSSAI by a UE Configuration Update procedure. If there is any PDU session established for the S-NSSAI, the AMF requests the SMF to release the PDU session in the network:
- If the UE is in CM-CONNECTED state, the AMF releases the PDU session for the S-NSSAI by sending to the SMF, as in step 1f in clause 4.3.4.2 of TS 23.502 [3], a Nsmf_PDUSession_UpdateSMContext Request with a release indication to request the release of the PDU Session and then the AMF forwards the N2 SM request to release the AN resources associated with the PDU session
- If the UE is in CM-IDLE, the AMF locally releases the PDU session without paging the UE and causes the SMF to locally release the SM context for the UE by a Nsmf_PDUSession_ReleaseSMContext, as in step 1c in clause 4.3.4.2 of TS 23.502 [3]. The PDU Session status is synchronized at next time when the UE connects to the network
NOTE 4: If the network slice becomes unavailable and a large number of UEs are impacted, the AMF can send the updates to the non-supporting UEs in a manner that avoids surge in signalling (e.g. next time the UE becomes connected).
- If the AMF detects from the validity time of a S-NSSAI that it is available again, then update the Configured NSSAI to include the S-NSSAI via a UE Configuration Update procedure.
NOTE 5: The AMF, for the case of UE not performing any actions despite the validity timing information provided by the network, can terminate PDU Session(s) associated with S-NSSAI subject to be terminated according to the validity time by explicitly releasing the PDU Sessions associated with the S-NSSAI. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.17 Partial Network Slice support in a Registration Area | A Network Slice may be supported in one or more TAs in a PLMN/SNPN. The Partial Network Slice support in a Registration Area for a UE includes configuring the UE with a Partially Allowed NSSAI and/or S-NSSAI(s) rejected partially in the RA.
When creating a Registration Area for UEs registering over the 3GPP access and supporting the Partial Network Slice support in a Registration Area, the AMF may consider the trade-off between signalling for paging in TAs where the S-NSSAI is not supported versus the signalling for Mobility Registration Updates to register with the S-NSSAI in the TA(s) where the S-NSSAI is supported, so that the AMF may create a Registration Area including the TA(s) where a requested S-NSSAI is not supported. For supporting UEs, whether the AMF uses the Partially Allowed NSSAI or rejects the S-NSSAIs partially in the RA, or whether the AMF rejects the S-NSSAI for the current RA, is a per S-NSSAI decision which is based on AMF local policy. If supported and allowed by local policy, the Partially Allowed NSSAI and S-NSSAIs rejected partially in the RA may be applied simultaneously for one UE for different S-NSSAIs.
For such S-NSSAI:
- If requested by the UE from a TA where the S-NSSAI is not supported (including the case when the S-NSSAI is provided as a rejected S-NSSAI for the TA from the NSSF):
- the S-NSSAI is included either in the Partially Allowed NSSAI or the AMF rejects the S-NSSAI partially in the RA; or
- if the S-NSSAI is subject to NSAC for maximum number of UEs, then the AMF should send this S-NSSAI as rejected partially in the RA, in the Registration Accept message.
- If the S-NSSAI is subject to NSSAA and successful NSSAA status for the S-NSSAI is not present in the AMF, then the AMF either sends this S-NSSAI as rejected partially in the RA in the Registration Accept message, or the AMF starts executing NSSAA and includes the S-NSSAI in the Pending NSSAI in the Registration Accept message. If the S-NSSAI is subject to NSSAA and successful NSSAA status for the S-NSSAI is present, then the AMF may include the S-NSSAI either in the Partially Allowed NSSAI or the AMF rejects the S-NSSAI partially in the RA.
NOTE 1: In roaming case the NSSAA requirement is based on the mapped S-NSSAI of the HPLMN.
- if the slice deregistration inactivity timer is configured for the S-NSSAI (see clause 5.15.15.3), then AMF should send this S-NSSAI as rejected partially in the RA.
- If requested by the UE from a TA where the S-NSSAI is supported (including the case when the S-NSSAI is provided in the Allowed NSSAI from the NSSF):
- the S-NSSAI is included in the Partially Allowed NSSAI; or
- if the S-NSSAI is subjected to NSAC for maximum number of UEs, then the AMF should restrict the RA so that the S-NSSAI is supported in all the TAs of the RA and includes the S-NSSAI in the Allowed NSSAI.
- If the S-NSSAI is subject to NSSAA, then the AMF starts executing NSSAA and sends this S-NSSAI in the Pending NSSAI in the Registration Accept message, unless successful NSSAA status is present in the AMF for this S-NSSAI (in which case it can be sent in the Partially Allowed NSSAI).
NOTE 2: In roaming case the NSSAA requirement is based on the mapped S-NSSAI of the HPLMN.
- if the S-NSSAI is included in neither the Partially Allowed NSSAI nor the Allowed NSSAI, the AMF may reject the S-NSSAI as described in clause 5.15.4.1.1.
While the S-NSSAIs of the Allowed NSSAI are supported in all the TAs of the Registration Area, the S-NSSAIs of the Partially Allowed NSSAI are supported only in the TAs corresponding to the list of TAs (which are subset of the list of TAIs forming the Registration Area) associated with the S-NSSAI.
If the UE supports Partial Network Slice support in a Registration Area, the AMF may create a Registration Area for the UE considering the support of the S-NSSAIs of the Requested NSSAI in the current TA and in the neighbouring TAs and provides to the UE in the Registration Accept message or in the UE Configuration Update Command message the Partially Allowed NSSAI or the S-NSSAIs rejected partially in the RA as follows:
- If one or more of the requested S-NSSAI(s) are supported in a subset of the TAs of the (potential) Registration Area, the AMF may include such S-NSSAI(s) in the Partially Allowed NSSAI and corresponding mapping information of the S-NSSAI(s) of the Partially Allowed NSSAI to the HPLMN S-NSSAI(s). For each S-NSSAI of the Partially Allowed NSSAI the AMF provides a list of TAs where the S-NSSAI is supported. The UE is considered registered with the S-NSSAI in the whole Registration Area. The AMF also provides the Partially Allowed NSSAI (without indication of the TA list where the partially allowed S-NSSAIs are supported) to the NG-RAN together with the UE's context.
- Alternatively, the AMF may reject the S-NSSAI(s) with reject cause indicating "partially in the RA". For each S-NSSAI of the S-NSSAIs rejected partially in the RA the AMF provides a list of TAs where the S-NSSAI is not supported.
NOTE 3: If the UE requests an S-NSSAI in a cell of a TA where the NS-AoS of the S-NSSAI does not match deployed Tracking Areas (see clause 5.15.18), the AMF includes the S-NSSAI in the Allowed NSSAI or Partially Allowed NSSAI.
For Partially Allowed NSSAI the following applies:
- The UE is considered registered with an S-NSSAI of the Partially Allowed NSSAI in the whole Registration Area. The UE does not trigger registration when moving between the TAs of support and non-support for the S-NSSAI within the RA.
- The UE is allowed to initiate PDU Session establishment for the S-NSSAI only when the UE is in a TA where the S-NSSAI is supported. If the UE has overlapping areas between non-allowed area, area where the S-NSSAI is supported, then the non-allowed area restriction applies.
- If the AMF determines a PDU Session is associated with S-NSSAI present in the Partially Allowed NSSAI, the AMF indicates to the SMF that the PDU Session is subject to area restrictions for the S-NSSAI. As a result, the SMF subscribes to "UE mobility event notification" event for reporting UE presence in Area of Interest by providing S-NSSAI to the AMF as described in clauses 5.6.11 and 5.3.4.4 if this event has not been subscribed before. The supporting AMF shall provide this indication in all the subsequent PDU Session update message to the SMF as long as the S-NSSAI of the PDU Session is subject to area restriction. When the AMF does not indicate to the SMF that the PDU Session is subject to area restriction for the S-NSSAI, the SMF may unsubscribe "UE mobility event notification" event in the AMF and if this event has been subscribed before.
- When the UE has already established a PDU Session with an S-NSSAI part of the Partially Allowed NSSAI, the UE is allowed to activate the User Plane resources of the PDU Session only when the UE is in a TA part of the list of TAs associated with the S-NSSAI. The UE shall not request User Plane resources when the UE is in a TAI where the S-NSSAI of the PDU Session is not supported based on the Partially Allowed NSSAI as a result the always-on PDU Session is also not re-activated during the Service Request or registration procedure.
- When the User Plane resources are activated for a PDU Session of an S-NSSAI part of the Partially Allowed NSSAI and the UE moves to a TA which is not part of the list of TAs associated with the S-NSSAI, the NG-RAN releases the User Plane resources for the PDU Session as described in step 1d in clause 4.3.4.2 of TS 23.502 [3] and the SMF deactivates the PDU Session as described in step 3a in clause 4.3.4.2 of TS 23.502 [3], but the PDU Session context in UE and SMF is not released. The User Plane resources for the PDU Session shall not be activated as long as the UE is located in a TA which is not part of the list of TAs associated with the S-NSSAI of the Partially Allowed NSSAI. The UE shall not send user data as payload of a NAS message (see clause 5.31.4.1) in uplink directions. The AMF determines the UE presence in Area of Interest as described in Annex D, clauses D.1 and D.2 of TS 23.502 [3] and notifies the result to the SMF. When the SMF is notified by the AMF that the UE location is outside of the Area of Interest, the SMF shall not send user data as payload of NAS message (see clause 5.31.4.1) in downlink directions and disable data notification. When the SMF is notified by the AMF that the UE location is UNKNOWN as defined in Annex D, clauses D.1 and D.2 of TS 23.502 [3], then based on operator policy SMF may enable downlink data notification and trigger the Network triggered Service Request procedure to active the UP connection or send user data as payload of a NAS message (see clause 5.31.4.1) when the SMF receives downlink data or Data Notification from UPF.
NOTE 4: When I-SMF/V-SMF is inserted for the PDU session it is the I-SMF/V-SMF to handle the area restrictions for the S-NSSAI. The SMF/H-SMF is not involved in this procedure.
For an already established PDU Session associated with an S-NSSAI included in the Partially Allowed NSSAI, even when the supporting UE is in a TA where the S-NSSAI is not supported, the supporting UE may initiate a PDU Session release procedure or PDU Session modification procedure (i.e. for PS data off status change reporting).
When the UE stores a S-NSSAI rejected partially in the RA with the associated list of TAs, the UE is allowed to initiate a Mobility Registration Update procedure to request registration with the S-NSSAI only when the UE is in a TA which is not part of the list of TAs associated with this S-NSSAI.
For a UE in CM-CONNECTED state, when a PDU Session is established on an S-NSSAI included in the Partially Allowed NSSAI, the User Plane resources are activated and the UE moves to a TA where the S-NSSAI is not supported, the NG-RAN releases the User Plane resources of the PDU sessions associated with the S-NSSAIs, as described in step 1d of clause 4.3.4.2 of TS 23.502 [3] and the SMF deactivates the PDU session as described in step 3a of clause 4.3.4.2 of TS 23.502 [3]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.18 Support for Network Slices with Network Slice Area of Service not matching deployed Tracking Areas | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.18.1 General | The network support for a Network Slice is defined on a per Tracking Area granularity. It may be beneficial to deploy some Network Slices such that the Network Slice have a limited geographical availability that is not matching existing Tracking Area boundaries.
The operator can in this case decide to change the topology of the Tracking Areas so they match the boundaries of the Network Slice, or the operator may configure resources for the Network Slices in the cells of TAs where the Network Slices are to be available and in cells of the TAs where the network slice is defined to be not available the cells are configured with zero resources. If a Network Slice is considered available in a cell, the Network Slice is also supported by the TA comprising the cell.
The AMF receives from the OAM the information on availability of a network slice when the granularity is smaller than TA, i.e. if the NS-AoS includes TAs where the network slice is not available in some cells of the TA.
In order to optimize the end-to-end behaviour, the AMF can, based on NS-AoS information received from OAM, configure supporting UEs with S-NSSAI location availability information and the network may need to monitor the S-NSSAI usage and enforce the NS-AoS e.g. if the UE does not support the S-NSSAI location availability information. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.18.2 S-NSSAI location availability information | S-NSSAI location availability information defines additional restrictions to the usage of an S-NSSAI in TAs where the Network Slice availability does not match the TA boundaries. The AMF is configured per S-NSSAI whether to send the S-NSSAI location availability information to supporting UEs.
The S-NSSAI location availability information sent to the UE includes, for each applicable S-NSSAI of the Configured NSSAI, Location information indicating the cells of TAs in the RA where the related S-NSSAI is available if the S-NSSAI is not available in all the cells of the TA.
If the UE has indicated that the UE supports S-NSSAI location availability information in the 5GMM Core Network Capability (see clause 5.4.4a), the AMF may, based on OAM configuration, configure the UE with S-NSSAI location availability information for one or more S-NSSAIs when the AMF allocates an RA where the Network Slice availability does not match whole TAs, by including the S-NSSAI location availability information in the Registration Accept message or the UE Configuration Command message. A UE that receives S-NSSAI location availability information applies the information as follows.
1. If the S-NSSAI is rejected in the RA or rejected partially in the RA or rejected with a cause code that allows attempting to register the S-NSSAI again, the UE can request the S-NSSAI only if the S-NSSAI location availability information indicates that the S-NSSAI is available at the cell where the UE is camping.
2. If the S-NSSAI is in the Partially Allowed NSSAI or in the Allowed NSSAI and the UE is in a cell within the RA but outside the NS-AoS of the S-NSSAI, the following applies:
a. The UE shall not activate User Plane resources for any already established PDU Session with that S-NSSAI including the case of always-on PDU Session.
b. The UE shall not send user data as payload of a NAS message (see clause 5.31.4.1) in uplink direction.
c. For an already established PDU Session, the supporting UE may initiate signalling for PDU Session release procedure or PDU Session modification procedure (i.e. for PS data off status change reporting).
3 If the UE has overlapping areas between non-allowed area, a cell inside the NS-AoS, then the non-allowed area restriction applies.
4. If the S-NSSAI is in the Partially Allowed NSSAI or in the Allowed NSSAI and the UE in CM-CONNECTED state moves from a cell inside the NS-AoS to a cell outside the NS-AoS and the User Plane resources are active for a PDU Session on that S-NSSAI, the NG-RAN releases the User Plane resources as described in step 1d of the AN initiated Release of a PDU Session in clause 4.3.4.2 of TS 23.502 [3]. The SMF also deactivates the PDU Session as described in step 3a in clause 4.3.4.2 of TS 23.502 [3].
NOTE 1: By Radio Resource Management and existing mechanisms in NG-RAN, handover can be used to keep the UE in the NS-AoS or steer the UE to enter the NS-AoS as long as radio conditions allow it.
NOTE 2: Since the S-NSSAI location availability information is not a used as a trigger for the UE to perform MRU due to mobility, i.e. the UE performs MRU due to mobility upon changing to a new TA outside the UE's Registration Area, the S-NSSAI remains registered and is included in the Allowed NSSAI when the UE exits the NS-AoS. If the S-NSSAI is subject for NSAC, the S-NSSAI is counted towards NSAC as described in clause 5.15.11 also when the UE is outside the NS-AoS. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.18.3 Network based monitoring and enforcement of Network Slice Area of Service not matching deployed Tracking Areas | OAM may configure RRM policies for S-NSSAIs on a per cell basis as defined in TS 28.541 [149], i.e. cells outside the Network Slice Area of Service while in a TA supporting the S-NSSAI are allocated with no RRM resources for the S-NSSAI.
The network may enforce the NS-AoS for an S-NSSAI as follows:
1. The network may monitor the validity of the S-NSSAI for UE in CM-CONNECTED state, i.e. the AMF subscribes to the AoI using the Location information of the S-NSSAI location availability information as described in TS 38.413 [34].
2. If the non-supporting UE makes a PDU Session establishment request with an S-NSSAI that is not valid as per the S-NSSAI location availability information, the AMF may reject the NAS Transport message with a back-off timer using S-NSSAI based congestion control as described in clause 5.19.7.4.
3. If the AMF determines that the UE in CM-CONNECTED has moved outside the NS-AoS, the AMF performs the following logic:
a) If the non-supporting UE has other S-NSSAI(s) in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI and optionally removing the S-NSSAI from the Configured NSSAI and then, the AMF requests the SMF to release any PDU Sessions with that S-NSSAI as per step 1f in clause 4.2.3.4 in TS 23.502 [3].
b) If the non-supporting UE does not have any other S-NSSAI in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI and optionally removing the S-NSSAI from the Configured NSSAI and adding a default S-NSSAI to the Allowed NSSAI and then, the AMF requests the SMF to release any PDU Sessions with the removed S-NSSAI as per step 1f in clause 4.3.4.2 in TS 23.502 [3].
NOTE 1: Whether the AMF removes the S-NSSAI only from Allowed NSSAI, or from both Allowed NSSAI and Configured NSSAI, or only releases the associated PDU Sessions when the AMF enforces the NS-AoS is up to AMF configuration.
c) For a non-supporting UE that does not have any other S-NSSAI in the Allowed NSSAI nor in the Configured NSSAI, then the AMF indicates to the SMF to release the PDU Session.
4. If the AMF determines that the S-NSSAI becomes valid e.g. the UE has moved into the NS-AoS, the AMF may update the UE with a UCU e.g. including the S-NSSAI in the Configured NSSAI.
5. When the AMF determines that the S-NSSAI of a PDU Session is restricted to an NS-AoS in the PDU session, the AMF indicates to the SMF that the PDU Session is subject to area restriction for the S-NSSAI. As a result, the SMF subscribes to "UE mobility event notification" event for reporting UE presence in Area of Interest by providing S-NSSAI to the AMF as described in clauses 5.6.11 and 5.3.4.4 if this event has not been subscribed before. The supporting AMF shall provide this indication in all the subsequent PDU Session update message to the SMF as long as the S-NSSAI of the PDU Session is subject to area restriction. The AMF determines the UE presence in Area of Interest as described in Annex D, clauses D.1 and D.2 of TS 23.502 [3] and notifies the result to the SMF. When SMF is notified that the UE location is outside of Area of Interest, SMF shall not send user data as payload of NAS message (see clause 5.31.4.1) in downlink directions and disable data notification. When the AMF does not indicate to the SMF that the PDU Session is subject to area restriction for the S-NSSAI, based on local configuration, the SMF may unsubscribe the "UE mobility event notification" event in AMF if this event has been subscribed before.
6. When the SMF is notified by the AMF that the UE location is UNKNOWN as defined in Annex D, clauses D.1 and D.2 of TS 23.502 [3], then based on operator policy SMF may enable downlink data notification and trigger the Network triggered Service Request procedure to active the UP connection or send user data as payload of a NAS message (see clause 5.31.4.1) when the SMF receives downlink data or Data Notification from UPF.
NOTE 2: When I-SMF/V-SMF is inserted for the PDU session it is the I-SMF/V-SMF to handle the area restrictions for the S-NSSAI. The SMF/H-SMF is not involved in this procedure. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.19 Support of Network Slice Replacement | The Network Slice Replacement feature is used to temporarily replace an S-NSSAI with an Alternative S-NSSAI when an S-NSSAI becomes unavailable or congested in the 5GC. The Network Slice Replacement may be triggered in the following cases:
- If the NSSF detects that an S-NSSAI becomes unavailable or congested (e.g. based on OAM or NWDAF analytics output), the NSSF sends network slice availability notification for the S-NSSAI to the AMF. The notification may include an Alternative S-NSSAI which can be used by the AMF to replace the S-NSSAI and congestion mitigation information if the S-NSSAI is congested. The NSSF notifies the AMF when the S-NSSAI is available again.
- If the PCF detects that an S-NSSAI becomes unavailable or congested for a UE (e.g. based on OAM or NWDAF analytics output), the PCF sends access and mobility related policy notification to the AMF. The notification may include an Alternative S-NSSAI which can be used by the AMF to replace the S-NSSAI. The PCF notifies the AMF when the S-NSSAI is available again for the UE.
- The OAM sends notification to AMF when an S-NSSAI becomes unavailable or congested (and also when this S-NSSAI becomes available again) and provides the Alternative S-NSSAI to AMF and the OAM may provide congestion mitigation information if the S-NSSAI is congested.
The network slice associated with the Alternative S-NSSAI is assumed in this specification to have NS-AoS to be covering at least the NS-AoS of the replaced network slice. If the UE moves to a cell where the replaced S-NSSAI is not supported, but still within the NS-AoS of the Alternative S-NSSAI, the AMF removes the replaced S-NSSAI from the Allowed NSSAI (if the S-NSSAI was in the Allowed NSSAI) and from the Partially Allowed NSSAI (if the UE moves out of the RA also).
If the replaced S-NSSAI is subject to area restrictions, the AMF indicates to the SMF that the PDU Session is subject to area restrictions for the replaced S-NSSAI and the AMF and the SMF then apply the area restriction for the replaced S-NSSAI as described in clause 5.15.17 or clause 5.15.18 and the SMF additionally deactivates the PDU Session when the UE is OUT of AoI.
NOTE 1: It is recommended to use a network slice associated with the Alternative S-NSSAI that is able to support requirements for the services that the replaced network slice supports. It is further recommended in particular that the Alternative S-NSSAI supports at least the DNNs supported in the replaced S-NSSAI.
NOTE 2: The AMF can, by using the UE's presence in the AoI for the replaced S-NSSAI, prevent the UE from obtaining service in the Alternative network slice in cells outside the NS-AoS of the replaced network slice but within the NS-AoS of the Alternative network slice if the Alternative network slice NS-AoS exceeds the NS-AoS of the replaced network slice.
Based on the notification above from NSSF or PCF or OAM, the AMF may determine that an S-NSSAI is to be replaced with Alternative S-NSSAI. For roaming case, the AMF subscribes the network slice availability notification of the HPLMN S-NSSAI from the NSSF in VPLMN and the NSSF in VPLMN subscribes the notification from NSSF in the HPLMN as described in clause 5.15.6.
If the notification is from NSSF or OAM and reason for the replacement is due to congestion, the notification includes additional congestion mitigation information. The details of the congestion mitigation information from NSSF and how the congestion mitigation information is used by the AMF is described in clause 5.2.16.3.3 of TS 23.502 [3].
NOTE 3: It is recommended that, the operator configures to use only one option, i.e. OAM, PCF or NSSF, for determining an Alternative S-NSSAI and triggering the Network Slice Replacement for S-NSSAI.
The AMF uses the Alternative S-NSSAI received in the notification from the NSSF, or from OAM or from the PCF. If the NSSF or PCF or OAM do not provide an Alternative S-NSSAI in the notification, the AMF uses an Alternative S-NSSAI based on local configuration. The Alternative S-NSSAI shall be supported in the UE Registration Area. If AMF cannot determine the Alternative S-NSSAI for the S-NSSAI, e.g. OAM or NSSF doesn't provide Alternative S-NSSAI and there is no Alternative S-NSSAI in the AMF local configuration, the AMF may further interact with the PCF to determine the Alternative S-NSSAI. The event trigger in AMF for interacting with PCF is described in clause 6.1.2.5 of TS 23.503 [45].
If the Alternative S-NSSAI is subject to NSSAA, the Alternative S-NSSAI shall only be used for UEs for which the Alternative S-NSSAI is included in the Subscribed S-NSSAIs. In this case, the AMF performs the NSSAA procedure for the Alternative S-NSSAI as described in clause 5.15.10 before the AMF triggers Network Slice Replacement as specified below.
The UE indicates the support of Network Slice Replacement feature during the UE Registration procedure. For supporting UE in CM-CONNECTED state and if there is a PDU Sessions in the UE context associated with the S-NSSAI that needs to be replaced over an Access Type, the AMF additionally provides the Alternative S-NSSAI for this S-NSSAI in the Allowed NSSAI over the same Access Type and in the Configured NSSAI, if not included yet and the mapping between S-NSSAI(s) to Alternative S-NSSAI(s) to the UE in UE Configuration Update message as follows:
- for non-roaming UEs, the AMF provides the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE.
NOTE 4: In the non-roaming case, the Alternative S-NSSAI does not have to be a Subscribed S-NSSAIs, as the replaced S-NSSAI is always a subscribed S-NSSAI.
- for roaming UEs when the VPLMN S-NSSAI has to be replaced by a VPLMN Alternative S-NSSAI, the AMF provides the mapping of the VPLMN S-NSSAI to the Alternative VPLMN S-NSSAI to the UE.
- for roaming UEs when the HPLMN S-NSSAI has to be replaced by an Alternative HPLMN S-NSSAI, the AMF provides the mapping of the HPLMN S-NSSAI to the Alternative HPLMN S-NSSAI to the UE.
NOTE 5: In the roaming cases, the Alternative HPLMN S-NSSAI does not have to be one of the Subscribed S-NSSAIs as the replaced HPLMN S-NSSAI is always part of the Subscribed S-NSSAIs.
The AMF provides the mapping of the S-NSSAI to the Alternative S-NSSAI over the access the AMF wants to trigger Network Slice Replacement. The UE stores the received mapping information together with the received Access Type and only uses it over that access.
Since Network Slice Replacement applies independent of Access Type, when the replacement occurs, the same Alternative S-NSSAI mapping to the replaced S-NSSAI is provided over the Access Types where the replaced S-NSSAI is in the Allowed NSSAI.
If the replaced S-NSSAI cannot be kept in the Allowed NSSAI or Partially Allowed NSSAI, the AMF additionally removes the Alternative S-NSSAI from the Allowed NSSAI or Partially Allowed NSSAI if the Alternative S-NSSAI is only used for Network Slice Replacement.
At mobility between AMFs, the source AMF provides, to the new AMF, the Alternative S-NSSAI and the mapping of the replaced S-NSSAI to the Alternative S-NSSAI in the UE context. When an S-NSSAI is subject to Network Slice Replacement, the new AMF compares the Requested NSSAI with the received UE context and updates the UE which misses the mapping of the replaced S-NSSAI to the Alternative S-NSSAI.
For the supporting UE when the UE has a NAS signalling connection, i.e. it is CM-CONNECTED or it has become CM-CONNECTED, e.g. through a Service Request procedure or through a UE registration procedure, if the AMF determines that the S-NSSAI is to be replaced and there is a PDU Session associated with the S-NSSAI in the UE context (see also NOTE 3), the AMF sends the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE in the UE Configuration Update message or in the Registration Accept message.
NOTE 6: It is left to AMF local policy whether to send the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE when there is no PDU session associated with the S-NSSAI or wait and send the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE when the UE establishes a PDU Session associated with the S-NSSAI.
When the S-NSSAI is replaced by the Alternative S-NSSAI, the UE associates both of the replaced S-NSSAI and the Alternative S-NSSAI with the PDU session. The UE procedure for associating applications to PDU session based on URSP described in clause 6.6.2.3 of TS 23.503 [45] and establishing a PDU session described in clause 5.15.5.3 is based on the replaced S-NSSAI (not based on Alternative S-NSSAI).
During a new PDU Session establishment procedure for a S-NSSAI,
- if the UE has received together with the Allowed NSSAI a mapping of the S-NSSAI to an Alternative S-NSSAI, the UE shall provide both the Alternative S-NSSAI and the S-NSSAI in the PDU Session Establishment message. When the AMF receives the Alternative S-NSSAI and the S-NSSAI in the PDU Session Establishment message, the AMF uses SMF Selection Subscription data of the replaced S-NSSAI and selects a suitable SMF supporting Network Slice Replacement and the Alternative S-NSSAI and verifies the Alternative S-NSSAI and the S-NSSAI based on the UE context and includes both the Alternative S-NSSAI and the S-NSSAI to the SMF in Nsmf_PDUSession_CreateSMContext service operation.
- if the UE has not yet received with the Allowed NSSAI a mapping of the S-NSSAI to the Alternative S-NSSAI, the UE provides only the S-NSSAI in the PDU Session Establishment message. If the AMF determines that the requested S-NSSAI is to be replaced with the Alternative S-NSSAI and if the UE supports Network Slice Replacement, the AMF performs UE Configuration Update procedure to reconfigure the UE with the Alternative S-NSSAI. The AMF continues the PDU Session establishment procedure with the Alternative S-NSSAI and uses SMF Selection Subscription data of the replaced S-NSSAI and selects a suitable SMF supporting Network Slice Replacement and the Alternative S-NSSAI. The AMF provides both the Alternative S-NSSAI and the S-NSSAI to the SMF in Nsmf_PDUSession_CreateSMContext service operation.
The SMF proceeds with the PDU Session establishment using the Alternative S-NSSAI and the received DNN. The SMF retrieves subscription data by using the replaced S-NSSAI and the DNN. The SMF uses replaced S-NSSAI value when the SMF registers the PDU Session to the UDM. The SMF sends the Alternative S-NSSAI to NG-RAN in N2 SM information and to UE in PDU Session Establishment Accept message.
NOTE 7: It is assumed that the operator configures their network so that the Alternative S-NSSAI is selected to ensure that the selected SMF by using the Alternative S-NSSAI supports necessary capabilities according to the replaced S-NSSAI subscription data.
For existing PDU Session associated with an S-NSSAI that is replaced with the Alternative S-NSSAI, after the AMF sends mapping of the S-NSSAI to the Alternative S-NSSAI to the supporting UE in UE Configuration Update message, the AMF sends updates to the SMF of the PDU Session, e.g. triggering Nsmf_PDUSession_UpdateSMContext service operation, that the PDU Session is to be transferred to Alternative S-NSSAI and includes the Alternative S-NSSAI as follows (see details in clause 4.3.3 of TS 23.502 [3]):
- If the SMF determines that the PDU Session is to be retained (e.g. if the anchor UPF can be reused with the alternative S-NSSAI and SSC mode 1), the SMF sends the Alternative S-NSSAI to the UPF in the N4 message, to the NG-RAN in N2 message and to the supporting UE in PDU Session Modification Command message. The S-NSSAI provided to the (R)AN and to the UPF is the Alternative S-NSSAI.
- If the SMF determines that the PDU Session is to be re-established, the SMF sends the Alternative S-NSSAI to the supporting UE either in PDU Session Modification Command if the PDU Session is of SSC mode 3, or in PDU Session Release if the PDU Session is of SSC mode 2 or SSC mode 1, to trigger the re-establishment of the PDU Session. The UE includes both, the S-NSSAI and the Alternative S-NSSAI in the PDU Session Establishment message.
During registration procedure, the Requested NSSAI may include Alternative S-NSSAI(s) that are not subscribed S-NSSAI(s). In addition to the behaviour described in clause 5.15.5.2.1, the AMF verifies if S-NSSAI(s) in the Requested NSSAI are either subscribed S-NSSAI(s) or Alternative S-NSSAI(s) in UE context and based on the verification, the AMF determines whether to update the UE configuration.
When the AMF is notified that the S-NSSAI is available again (e.g. the congestion of the S-NSSAI has been mitigated), if the AMF has configured the supporting UE with the Alternative S-NSSAI and the AMF determines for the UE in CM-CONNECTED state to use the replaced S-NSSAI again, the AMF reconfigures the supporting UE (e.g. by using UE Configuration Update procedure or in the next registration procedure) to use the replaced S-NSSAI again by removing the mapping of the replaced S-NSSAI to Alternative S-NSSAI and removing the Alternative S-NSSAI from the Allowed NSSAI if the Alternative S-NSSAI is only used for the Network Slice Replacement. The AMF also removes the Alternative S-NSSAI from the Configured NSSAI if the Alternative S-NSSAI is not one of the Subscribed S-NSSAIs and the Alternative S-NSSAI is not used in any Access Type. If the UE is in CM-IDLE, the AMF can wait until the UE in CM-CONNECTED state as described in clause 5.23. When the UE establishes a NAS signalling connection, e.g. through a Service Request procedure or through a UE registration procedure, the AMF reconfigures the UE.
If there is an existing PDU Session associated with the Alternative S-NSSAI for the S-NSSAI being available again or not congested anymore, the AMF updates the SMF(s) of the PDU Session(s), by Nsmf_PDUSession_UpdateSMContext service operation, causing the PDU Session to be transferred to the replaced S-NSSAI. The event trigger in SMF for interacting with PCF is described in clause 6.1.3.5 of TS 23.503 [45].
- If the SMF determines that the PDU Session is to be retained (e.g. if the anchor UPF can be reused with the replaced S-NSSAI and SSC mode 1), the SMF sends the replaced S-NSSAI i.e. does not include Alternative S-NSSAI to the UPF in the N4 message, to the NG-RAN in N2 message and to the supporting UE in PDU Session Modification Command message. The S-NSSAI provided to the (R)AN and to the UPF is the replaced S-NSSAI.
- If the SMF determines that the PDU Session is to be re-established, the SMF sends the replaced S-NSSAI (i.e. does not include Alternative S-NSSAI) to the supporting UE either in PDU Session Modification Command if the PDU Session is of SSC mode 3, or in PDU Session Release if the PDU Session is of SSC mode 2 or SSC mode 1, to trigger the re-establishment of the PDU Session. The UE includes the replaced S-NSSAI in the PDU Session Establishment message.
During a handover procedure, if an S-NSSAI has to be replaced with an Alternative S-NSSAI, the handover procedure (including any PDU session associated with the S-NSSAI to be replaced) shall continue unaffected by the Network Slice Replacement. Any Network Slice Replacement for the S-NSSAI shall not take place during the handover.
During NSSAA re-authentication procedure for an S-NSSAI, if the S-NSSAI has to be replaced with Alternative S-NSSAI, the AMF shall continue with the NSSAA procedure unaffected by the Network Slice Replacement and the AMF executes the Network Slice Replacement after the NSSAA procedure is completed.
If NSAC for maximum number of PDU sessions is configured for the replaced S-NSSAI and/or the Alternative S-NSSAI, the SMF performs NSAC by interacting with the NSACF of the replaced S-NSSAI and/or the NSACF of the Alternative S-NSSAI based on operator determined policies configured in the SMF (e.g. for the increase of Alternative S-NSSAI and the decrease of replaced S-NSSAI).
The UE and the AMF locally removes the mapping of the replaced S-NSSAI and the Alternative S-NSSAI in an access type when the replaced S-NSSAI or alternative S-NSSAI is removed from the allowed NSSAI due to slice deregistration inactivity timer expiry over corresponding access type as described in clause 5.15.15. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.15.20 Support of Network Slice Instance Replacement | The Network Slice Instance Replacement is used when a PDU Session for a given S-NSSAI is established using a selected Network Slice instance and the S-NSSAI corresponding to this Network Slice instance is associated with multiple Network Slice instances. In this case, the network may change the Network Slice instance for the S-NSSAI if the selected Network Slice instance is no longer available (e.g. due to overload). The AMF may subscribe with the NSSF for notifications when any of the Network Slice instances served by the AMF is congested or no longer available. In case of roaming, the NSSF of VPLMN subscribes with the NSSF of the HPLMN for notifications. When the NSSF notifies the AMF that a Network Slice instance is congested or no longer available, for some of PDU Sessions associated with the Network Slice instance that is no longer available, the AMF may delete old NSI ID corresponding to the Network Slice instance that is no longer available and the SMF of the PDU Session(s) selected by using such old NSI ID is informed by the AMF to release the PDU Session(s). Subsequently, the SMF triggers the impacted UE(s) to establish new PDU session(s) associated with the same S-NSSAI as described in clause 5.6.9.2 for PDU Session(s) of SSC Mode 2 and SSC Mode 3. The AMF selects a new Network Slice instance for the given S-NSSAI during PDU Session Establishment. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16 Support for specific services | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.1 Public Warning System | The functional description for supporting Public Warning System for 5G System can be found in TS 23.041 [46]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.2 SMS over NAS | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.2.1 General | This clause includes feature description for supporting SMS over NAS in 5G System. Support for SMS incurs the following functionality:
- Support for SMS over NAS transport between UE and AMF. This applies to both 3GPP and Non 3GPP accesses.
- Support for AMF determining the SMSF for a given UE.
- Support for subscription checking and actual transmission of MO/MT-SMS transfer by the SMSF.
- Support for MO/MT-SMS transmission for both roaming and non-roaming scenarios.
- Support for selecting proper domains for MT SMS message delivery including initial delivery and re-attempting in other domains. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.2.2 SMS over NAS transport | 5G System supports SMS over NAS via both 3GPP access and non-3GPP access.
During Registration procedure, a UE that wants to use SMS provides an "SMS supported" indication over NAS signalling indicating the UE's capability for SMS over NAS transport. "SMS supported" indication indicates whether UE can support SMS delivery over NAS. If the core network supports SMS functionality, the AMF includes "SMS allowed" indication to the UE and whether SMS delivery over NAS is accepted by the network.
SMS is transported via NAS transport message, which can carry SMS messages as payload. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3 IMS support | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.1 General | IP-Connectivity Access Network specific concepts when using 5GS to access IMS can be found in TS 23.228 [15].
5GS supports IMS with the following functionality:
- Indication toward the UE if IMS voice over PS session is supported.
- Capability to transport the P-CSCF address(es) to UE.
- Paging Policy Differentiation for IMS as defined in TS 23.228 [15].
- IMS emergency service as defined in TS 23.167 [18].
- Domain selection for UE originating sessions.
- Terminating domain selection for IMS voice.
- Support of P-CSCF restoration procedure (clause 5.16.3.9).
- NRF based P-CSCF discovery (clause 5.16.3.11).
NOTE: The NRF based P-CSCF discovery has no impact on the UE, i.e. the UE does not need to know how P-CSCF IP address(es) is discovered in the network.
- NRF based HSS discovery (clause 5.16.3.12). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.2 IMS voice over PS Session Supported Indication over 3GPP access | The serving PLMN AMF shall send an indication toward the UE during the Registration procedure over 3GPP access to indicate if an IMS voice over PS session is supported or not supported in 3GPP access and non-3GPP access. A UE with "IMS voice over PS" voice capability over 3GPP access should take this indication into account when performing voice domain selection, as described in clause 5.16.3.5.
The serving PLMN AMF may only indicate IMS voice over PS session supported over 3GPP access in one of the following cases:
- If the network and the UE are able to support IMS voice over PS session in the current Registration Area with a 5G QoS Flow that supports voice as specified in clause 5.7.
- If the network or the UE are not able to support IMS voice over PS session over NR connected to 5GC, but is able for one of the following:
- If the network and the UE are able to support IMS voice over PS session over E-UTRA connected to 5GC and the NG-RAN supports a handover or redirection to E-UTRA connected to 5GC for this UE at QoS Flow establishment for IMS voice;
- If the UE supports handover to EPS, the EPS supports IMS voice and the NG-RAN supports a handover to EPS for this UE at QoS Flow establishment for IMS voice; or
- If the UE supports redirection to EPS, the EPS supports IMS voice and the NG-RAN supports redirection to EPS for this UE at QoS Flow establishment for IMS voice.
- If the network is not able to provide a successful IMS voice over PS session over E-UTRA connected to 5GC, but is able for one of the following:
- If the UE supports handover to EPS, the EPS supports IMS voice and the NG-RAN supports a handover to EPS for this UE at QoS Flow establishment for IMS voice; or
- If the UE supports redirection to EPS, the EPS supports IMS voice and the NG-RAN supports redirection to EPS for this UE at QoS Flow establishment for IMS voice.
The serving PLMN provides this indication based e.g. on local policy, UE capabilities, HPLMN, whether IP address preservation is possible, whether NG-RAN to UTRAN SRVCC is supported and how extended NG-RAN coverage is and the Voice Support Match Indicator from the NG-RAN (see clause 4.2.8a of TS 23.502 [3]).
NOTE 1: The terms "UE supports handover to EPS" or "UE supports redirection to EPS" used above also consider the case that the UE has signalled that S1 mode is enabled. In case the UE has signalled that S1 mode is disabled for a network that only supports IMS voice via EPS Fallback, the AMF will not indicate that IMS voice over PS session is supported over 3GPP access. A voice centric UE ensures its voice service as described in clauses 5.16.3.5 and 5.16.3.6.
The AMF in serving PLMN shall indicate that IMS voice over PS is supported only if the serving PLMN has a roaming agreement that covers support of IMS voice with the HPLMN. This indication is per Registration Area.
NOTE 2: If the network supports EPS fallback for voice the 5GC can be configured not to perform the Voice Support Match Indicator procedure in order to set the IMS voice over PS session Supported Indication.
The serving SNPN provides the IMS voice over PS indication based e.g. on local policy, UE capabilities, whether IP address preservation is possible and how extended NR coverage is. This indication is per Registration Area.
NOTE 3: Since over 3GPP access, in SNPN access mode there is only support for NR and the "voice centric" UE cannot reselect to another RAT in the same registered SNPN if the first Registration Area that the UE tries to register from cannot support IMS voice, it is recommended that support for IMS voice is provided homogeneously in the whole SNPN if at all.
5.16.3.2a IMS voice over PS Session Supported Indication over non-3GPP access
The serving PLMN AMF shall send an indication toward the UE during the Registration procedure over non-3GPP access to indicate whether an IMS voice over PS session is supported or not supported via non-3GPP access. A UE with "IMS voice over PS" voice capability over non-3GPP access should take this indication (received in the Registration procedure performed over either 3GPP access or Non-3GPP access) into account when performing the selection between N3IWF/TNGF and ePDG described in clause 6.3.6.
The serving PLMN AMF may only indicate IMS voice over PS session supported over non-3GPP access if the network is able to provide a successful IMS voice over PS session over N3IWF/TNGF connected to 5GC with a 5G QoS Flow that supports voice as specified in clause 5.7. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.3 Homogeneous support for IMS voice over PS Session supported indication | 5GC shall support the usage of "Homogeneous Support of IMS Voice over PS Sessions" indication between AMF and UDM.
When the AMF initiates Nudm_UECM_Registration operation to the UDM, it shall:
- if "IMS Voice over PS Sessions" is supported homogeneously in all TAs in the serving AMF for the UE, include the "Homogeneous Support of IMS Voice over PS Sessions" indication set to "Supported";
- if none of the TAs of the serving AMF supports "IMS Voice over PS Sessions" for the UE, include the "Homogeneous Support of IMS Voice over PS Sessions" indication set to "Not supported";
- if "IMS Voice over PS Sessions" support is either non-homogeneous or unknown, not include the "Homogeneous Support of IMS Voice over PS Sessions" indication.
The AMF shall be able to provide the "Homogeneous Support of IMS Voice over PS Sessions" indication as described above to the UDM using Nudm_UECM_Update operation as specified in clause 4.2.2.2.2 of TS 23.502 [3].
The UDM shall take this indication into account when doing Terminating Access Domain Selection (T-ADS) procedure for IMS voice.
NOTE: A TA supports "IMS Voice over PS Sessions" if the serving AMF indicates IMS voice over PS Session Supported Indication over 3GPP access to the UE, as described in clause 5.16.3.2. In order to support routing of incoming IMS voice calls to the correct domain, the network-based T-ADS (see TS 23.292 [63] and TS 23.221 [23]) requires that the "Homogeneous Support of IMS Voice over PS Sessions" indication is set to "Supported" for all registered TAs of the UE or "Not supported" for all registered TAs of the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.4 P-CSCF address delivery | At PDU Session Establishment procedure related to IMS, SMF shall support the capability to send the P-CSCF address(es) to UE. The SMF is located in VPLMN if LBO is used. This is sent by visited SMF if LBO is used. For Home routed, this information is sent by the SMF in HPLMN. P-CSCF address(es) shall be sent transparently through AMF and in the case of Home Routed also through the SMF in VPLMN. The P-CSCF IP address(es) may be locally configured in the SMF, or discovered using NRF as described in clause 5.16.3.11.
NOTE 1: Other options to provide P-CSCF to the UE as defined in TS 23.228 [15] is not excluded.
NOTE 2: PDU Session for IMS is identified by "APN" or "DNN".
In the case of SNPN access the SMF is always located in the serving SNPN (no support for Home Routed traffic); therefore, the serving SMF sends the P-CSCF address(es) to the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.5 Domain selection for UE originating sessions / calls | For UE originating calls, the 5GC capable UE performs access domain selection. The UE shall be able to take following factors into account for access domain selection decision:
- The state of the UE in the IMS. The state information shall include: Registered, Unregistered.
- The "IMS voice over PS session supported indication" as defined in clause 5.16.3.2.
- Whether the UE is expected to behave in a "voice centric" or "data centric" way for 5GS.
- UE capability of supporting IMS PS voice.
- UE capability for operating in dual-registration mode with selective PDU Session transfer as defined in clause 5.17.2.3.3.
- Whether 3GPP PS Data Off is active or not and whether IMS voice is included in 3GPP PS Data Off Exempt Services or not as defined in clause 5.24.
NOTE 1: In this release of the specification, the exact logic of which PDU sessions are kept in which system for Dual Registration UE with selective transfer of certain PDU Sessions as defined in clause 5.17.2.3.3, is left up to UE implementation. The voice centric UE will keep the PDU Session used for IMS services to a system that supports voice over IMS. The voice centric UE can re-register with the IMS (if needed) when the IMS PDU session is transferred between 5GS and EPS.
To allow for appropriate domain selection for originating voice calls, the UE shall attempt Initial Registration in 5GC. If the UE fails to use IMS for voice, e.g. due to "IMS voice over PS session supported indication" indicates voice is not supported in 5G System, the UE behaves as described below for "voice centric" for 5GS or "data centric" for 5GS:
- A UE set to "voice centric" for 5GS shall always try to ensure that Voice service is possible. A voice centric 5GC capable and EPC capable UE unable to obtain voice service in 5GS shall not select a cell connected only to 5GC. By disabling capabilities to access 5GS, the UE re-selects to E‑UTRAN connected to EPC first (if available). When the UE selects E-UTRAN connected to EPC, the UE performs Voice Domain Selection procedures as defined in TS 23.221 [23].
- A UE set to "data centric" for 5GS does not need to perform any reselection if voice services cannot be obtained.
NOTE 2: The related radio capabilities in order for the voice centric UE to not reselect to NR or E-UTRA cell connected to 5GC (i.e. avoid ping pong) will be defined by RAN WGs. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.6 Terminating domain selection for IMS voice | When requested by IMS, the UDM/HSS shall be able to query the serving AMF for T-ADS related information. T-ADS is a functionality located in the IMS and is performed as specified in TS 23.221 [23].
The AMF shall respond to the query with the following information unless the UE is detached:
- whether or not IMS voice over PS Session is supported in the registration area (s) where the UE is currently registered;
- whether or not IMS voice over PS Session Supported Indication over non-3GPP access is supported in the WLAN where the UE is currently registered;
- the time of the last radio contact with the UE; and
- the current Access Type and RAT type. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.7 UE's usage setting | If the UE is configured to support IMS voice, the UE shall include the information element "UE's usage setting" in Registration Request messages. The UE's usage setting indicates whether the UE behaves in a "voice centric" or "data centric" way (as defined in clause 5.16.3.5).
A UE supporting IMS voice over 3GPP access connected to 5GC and that is EPS capable shall also support IMS voice over E-UTRA connected to EPC.
NOTE: Depending on operator's configuration, the UE's usage setting can be used by the network to choose the RFSP Index in use (see clause 5.3.4.3). As an example, this enables the enforcement of selective idle mode camping over E-UTRA for voice centric UEs. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.8 Domain and Access Selection for UE originating SMS | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.8.1 UE originating SMS for IMS Capable UEs supporting SMS over IP | To allow for appropriate domain selection for SMS delivery, it should be possible to provision UEs with the following HPLMN operator preferences on how an IMS enabled UE is supposed to handle SMS services:
- SMS is not to be invoked over IP networks: the UE does not attempt to deliver SMS over IP networks. The UE attempts to deliver SMS over NAS signalling.
- SMS is preferred to be invoked over IP networks: the UE attempts to deliver SMS over IP networks. If delivery of SMS over IP networks is not available, the UE attempts to deliver SMS over NAS signalling. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.8.2 Access Selection for SMS over NAS | It should be possible to provision UEs with the HPLMN SMS over NAS operator preferences on access selection for delivering SMS over NAS signalling.
Based on the SMS over NAS preference:
- SMS is preferred to be invoked over 3GPP access for NAS transport: the UE attempts to deliver MO SMS over NAS via 3GPP access if the UE is both registered in 3GPP access and non-3GPP access.
- SMS is preferred to be invoked over non-3GPP access for NAS transport: the UE attempts to deliver MO SMS over NAS via non-3GPP access if the UE is both registered in 3GPP access and non-3GPP access. If delivery of SMS over NAS via non-3GPP access is not available, the UE attempts to deliver SMS over NAS via 3GPP access. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.9 SMF support for P-CSCF restoration procedure | For the support of P-CSCF restoration the SMF behaves as described in TS 23.380 [61]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.10 IMS Voice Service via EPS Fallback or RAT fallback in 5GS | In order to support various deployment scenarios for obtaining IMS voice service, the UE and NG-RAN may support the mechanism to direct or redirect the UE from NG-RAN either towards E-UTRA connected to 5GC (RAT fallback) or towards EPS (E-UTRAN connected to EPC System fallback).
Following principles apply for IMS Voice Service:
- The serving AMF indicates toward the UE during the Registration procedure that IMS voice over PS session is supported.
- If a request for establishing the QoS Flow for IMS voice reaches the NG-RAN, the NG-RAN responds indicating rejection of the establishment request and the NG-RAN may trigger one of the following procedures depending on UE capabilities, N26 availability, network configuration and radio conditions:
- Redirection to EPS;
- Handover procedure to EPS;
- Redirection to E-UTRA connected to 5GC; or
- Handover to E-UTRA connected to 5GC.
- If needed, Network Provided Location Information is provided as described in clauses 4.13.6.1 and 4.13.6.2 of TS 23.502 [3].
- The ongoing IMS voice session is not impacted by a change of the IMS voice over PS session indicator from supported to unsupported (e.g. the UE receives during RAT Fallback or EPS Fallback the IMS voice over PS session indicator indicating that IMS voice over PS sessions are not supported).
NOTE: Any change in IMS voice over PS session indicator applies to new IMS sessions initiated only after the ongoing IMS voice session is terminated.
During any release of RRC connection including after EPS/RAT fallback is performed, the eNB or NG-RAN node may provide to the UE dedicated idle mode priorities for NR as defined in TS 36.331 [51] taking into account RFSP, PLMNs contained in Handover Restriction List and local operator policy. If the UE remains ECM/CM-CONNECTED after the voice call has ended, the eNB or NG-RAN node may trigger handover to NR connected to 5GC, if configured to do so, taking into account local operator policy and Handover Restriction List. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.11 P-CSCF discovery and selection | P-CSCF selection functionality may be used by the SMF to select the P-CSCF for an IMS PDU Session of the UE.
The SMF can utilize the Network Repository Function to discover the P-CSCF instance(s). The NRF provides the IP address or the FQDN of P-CSCF instance(s) to the SMF. The P-CSCF selection function in the SMF selects the P-CSCF instance(s) based on the available P-CSCF instances obtained from NRF or based on the configured P-CSCF information in the SMF. If the SMF receives FQDN(s) from the NRF or is configured with FQDN(s) the SMF shall resolve these to IP addresses for sending to the UE in the PDU session response.
The following factors may be considered during the P-CSCF discovery and selection:
- S-NSSAI of the PDU Session.
- UE location information.
- Local operator policies.
- Availability of candidate P-CSCFs.
- UE IP address.
- Access Type.
- Proximity to location of selected UPF.
- Selected Data Network Name (DNN). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.3.12 HSS discovery and selection | HSS discovery and selection functionality is used by the I-CSCF/S-CSCF/IMS-AS to select an HSS that manages the user's IMS subscriptions and has the ability to serve the IMS services for the UE, see clause AA.3.3 of TS 23.228 [15] and clause 6.3.1 for details. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4 Emergency Services | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.1 Introduction | Emergency Services are provided to support IMS emergency sessions. "Emergency Services" refers to functionalities provided by the serving network when the network is configured to support Emergency Services. Emergency Services are provided to normally registered UEs and to Emergency Registered UEs, that can be either normally registered or in limited service state. Depending on local regulation, receiving Emergency Services in limited service state does not require a valid subscription. Depending on local regulation and on operator's policy, the network may allow or reject a registration request for Emergency Services (i.e. Emergency Registration) from UEs that have been identified to be in limited service state. Four different behaviours of Emergency Services as defined in clause 4.3.12.1 of TS 23.401 [26] are supported.
Emergency Services shall not be provided to a UE over 3GPP access and non-3GPP access concurrently. Transfer from one Access Type to the other takes place as follows:
- a UE may be Emergency or normally Registered and have an emergency PDU session over non-3GPP access or may be attached with an emergency session to ePDG over untrusted WLAN (as defined in TS 23.402 [43]) when 3GPP access becomes available. In which case the UE may have to register over 3GPP access and check first the support for Emergency Services over the 3GPP RAT it has selected (e.g. based on Emergency Services Support indication, Emergency Services Fallback, AS broadcast indicator). If there is native support for Emergency Services in the selected 3GPP RAT the UE will attempt to transfer the emergency PDU session from non-3GPP access to 3GPP access (see clause 4.9.2 or clause 4.9.3 of TS 23.502 [3]). If there is no native support for Emergency Services in the selected RAT, but Emergency Services Fallback to another RAT in 5GS or to another System where Emergency Services is supported (based on the conditions defined in clause 5.16.4.11), the UE may trigger first Emergency Services Fallback (see clause 4.13.4.2 of TS 23.502 [3]) and then attempt to transfer the emergency PDU session from non-3GPP access to 3GPP access (see clause 4.9.2 of TS 23.502 [3]). During the session transfer the UE may be registered to receive emergency services over both 3GPP access and non-3GPP access concurrently.
NOTE 1: The conditions upon which the UE determines that 3GPP access becomes available are implementation dependent.
A UE may only attempt to use Emergency Services over non-3GPP access if it is unable to use Emergency Services over 3GPP access as specified in TS 23.167 [18].
The UE is only allowed to have one PDU session for Emergency services at a time. A PDU Session cannot be changed between a PDU Session for Non-Emergency services and a PDU Session for Emergency services. PDU session for emergency services can be transferred from one Access Type to another as specified in clause 5.16.4.9.
To provide Emergency Services, the AMF is configured with Emergency Configuration Data that are applied to Emergency Services that are established by an AMF based on request from the UE. The AMF Emergency Configuration Data contains the S-NSSAI and Emergency DNN which is used to derive an SMF. In addition, the AMF Emergency Configuration Data contains UE-AMBR and may also contain the statically configured SMF for the Emergency DNN. The SMF may also store Emergency Configuration Data that contains statically configured UPF information for the Emergency DNN.
NOTE 2: The Network slices associated with emergency services are assumed to be configured consistently in the AMF (i.e. emergency configuration data) and NG-RAN nodes within the corresponding Registration Area where emergency services are to be supported.
When the UE is camped normally in the cell, i.e. not in limited service state, during Registration procedure described in clause 4.2.2.2 of TS 23.502 [3], the serving AMF includes an indication for Emergency Services Support within the Registration Accept to the UE. For 3GPP access, the Emergency Services Support indication is valid within the current Registration Area per RAT (i.e. this is to cover cases when the same registration area supports multiple RATs and they have different capability).
The Emergency Services Support is configured in the AMF according to local regulations and network capabilities. AMF includes Emergency Services Support indicator in the Registration Accept message to indicate that the UE can setup emergency PDU Session to obtain emergency services. The AMF may include additional local emergency numbers associated with the serving network for the UE, further defined in TS 24.501 [47].
During Registration procedures over 3GPP access in a PLMN, the 5GC includes the Emergency Services Support indicator, valid for the current Registration Area and indicating per RAT that Emergency Services are supported if any of the following conditions is true within the current Registration Area:
- the Network is able to support Emergency Services natively over 5GS;
- E-UTRA connected to 5GC supports IMS Emergency Services (e.g. voice) and the NG-RAN is able to trigger handover or redirection from NR to E-UTRA connected to 5GC at QoS Flow establishment for IMS Emergency Services (e.g. voice);
- NG-RAN is able to trigger handover to EPS at QoS Flow establishment for IMS Emergency Services (e.g. voice);
- NG-RAN is able to trigger redirection to EPS at QoS Flow establishment for IMS Emergency Services (e.g. voice); or
- NG-RAN is able to trigger 5G SRVCC handover to UTRAN for IMS Emergency Services (i.e. voice).
During Registration procedures over non-3GPP access, the 5GC indicates that Emergency Services are supported if the Network is able to support Emergency Services natively over 5GS.
In the case of SNPN, during Registration procedures over 3GPP access, the 5GC includes the Emergency Services Support indicator, valid for the current Registration Area indicating that Emergency Services are supported if the following condition is true within the current Registration Area:
- the Network is able to support Emergency Services natively over 5GS.
The 5GC includes an indication per RAT whether it supports Emergency Services Fallback (as defined in clause 5.16.4.11) to another RAT in 5GS or to another System where Emergency Services are supported natively. The Emergency Services Fallback support indicator is valid within the current Registration Area per RAT.
NOTE 3: If a certain RAT is restricted for Emergency Services, the restriction of the corresponding RAT for Emergency Services Support is configured in the RAN Node. This helps the RAN node to determine whether to set up Dual Connectivity for Emergency Services.
UEs that are in limited service state, as specified in TS 23.122 [17], or that camp normally on a cell but failed to register successfully to the network under conditions specified in TS 24.501 [47], initiate the Registration procedure by indicating that the registration is to receive Emergency Services, referred to as Emergency Registration and a Follow-on request is included in the Registration Request to initiate PDU Session Establishment procedure with a Request Type indicating "Emergency Request". UEs that had registered for normal services and do not have emergency PDU Session established and that are subject to Mobility Restriction in the present area or RAT (e.g. because of restricted tracking area) shall initiate the UE Requested PDU Session Establishment procedure to receive Emergency Services, i.e. with a Request Type indicating "Emergency Request". Based on local regulation, the network supporting Emergency Services for UEs in limited service state provides Emergency Services to these UE, regardless whether the UE can be authenticated, has roaming or Mobility Restrictions or a valid subscription.
For Emergency Services over 3GPP access via PLMN, other than eCall over IMS, the UEs in limited service state that do not operate in SNPN access mode determine that the cell supports Emergency Services over NG-RAN from a broadcast indicator in AS. The cell connected to EPC and 5GC broadcasts separate broadcast indicator for EPC and 5GC to indicate support of emergency services by the EPC and 5GC. If the UE supports SNPN access mode, is in limited service state, is not operating in SNPN access mode, needs to make an emergency call and cannot find an acceptable cell in any PLMN, the UE may activate SNPN access mode and attempt to camp on an acceptable cell of any available SNPN supporting emergency calls (irrespective of SNPN ID or GIN) as defined in TS 23.122 [17]. For Emergency Services over untrusted non-3GPP access, other than eCall over IMS, the UE in limited service state selects any N3IWF as specified in clause 6.3.6. Emergency calls for eCall Over IMS may only be performed if the UE has a USIM.
For Emergency Services over NR via SNPN, other than eCall over IMS, the UEs in limited service state that operate in SNPN access mode determine that the cell supports Emergency Services over NR from a broadcast indicator in AS and indication that the SNPN supports Emergency Services. If the UE operates in SNPN access mode and is in limited service state, the UE shall attempt to camp on an acceptable cell of any available SNPN supporting emergency calls (irrespective of SNPN ID or GIN). If the UE cannot find acceptable cell on any available SNPN, the UE shall deactivate SNPN access mode and camp on any available PLMN cell supporting emergency calls (irrespective of PLMN ID) as defined in TS 23.122 [17].
For NR satellite access, if a UE in limited service state is aware of its location, the UE selects a PLMN that is allowed to operate in the UE location as specified in TS 23.122 [17]. The network may be configured to verify the location of a UE that is registering for emergency services as specified in clause 5.4.11.4.
There is no support for eCall over IMS for SNPNs in this Release.
A serving network shall provide an Access Stratum broadcast indication from NG-RAN (NR or E-UTRA connected to 5GC) to UEs indicating whether eCall Over IMS is supported:
- When an E-UTRA cell is connected to EPC and 5GC, the cell broadcasts separate Access stratum broadcast indication for 5GC and EPC to indicate support of eCall over IMS by 5GC and EPC.
- A UE that is not in limited service state determines that the NG-RAN cell supports eCall Over IMS via 5GC using the broadcast indicator for eCall over IMS. Emergency calls for eCall over IMS are not supported over non-3GPP access.
NOTE 4: The Access Stratum broadcast indicator is determined according to operator policies and minimally indicates that the PLMN, or all of the PLMNs in the case of network sharing and at least one emergency centre or PSAP to which an eCall Over IMS can be routed, support eCall Over IMS.
- A UE in limited service state determines that the cell supports eCall Over IMS using both the broadcast indicator for support of Emergency Services over NG-RAN and the broadcast indicator of NG-RAN for eCall over IMS. Emergency calls for eCall Over IMS are not supported over Non-3GPP access and NR via SNPN.
NOTE 5: The broadcast indicator for eCall Over IMS does not indicate whether UEs in limited service state are supported. So, the broadcast indicator for support of Emergency Services over NG-RAN that indicates limited service state support needs to be applied in addition.
For a UE that is Emergency Registered, if it is unauthenticated the security context is not set up on UE.
In order to receive Emergency Services, UEs that camp on a suitable cell in RM-DEREGISTERED state (i.e. without any conditions that result in limited service state), or that decide to access 5GC via non-3GPP access (and not in limited service state over non-3GPP access), initiate the Initial Registration procedure for normal service instead of Emergency Registration. Upon successful registration, such UEs shall initiate the UE Requested PDU Session Establishment procedure with a Request Type indicating "Emergency Request" to receive Emergency Services if the AMF indicated support for Emergency Services in 5GC (for the RAT the UE is currently camped on when UE is camping on 3GPP access). The UEs that camp normally on a cell or that are connected via Non-3GPP access are informed that the PLMN supports Emergency Services over 5G-AN from the Emergency Services Support indicator in the Registration procedure. This applies to both 3GPP and non-3GPP Access Types. There is no support for Emergency Services for SNPN that is accessed via NWu from a PLMN.
NOTE 6: The Emergency Services Support indicator in the Registration procedures does not indicate support for eCall Over IMS.
For a UE that is Emergency Registered, normal PLMN or SNPN selection principles apply after the end of the IMS emergency session.
NOTE 7: For Emergency Services, there is no support for inter PLMN mobility thus there is a risk of service disruption due to failed inter PLMN mobility attempts when there is no session continuity (e.g. change of anchor SMF/UPF due to mobility) for the PDU Session and/or based on operator policies.
NOTE 8 Based on operator policies, Inter PLMN mobility with session continuity can be supported for Emergency Services if the anchor SMF/UPF for PDU Session supporting Emergency Services does not change.
The UE shall set the RRC establishment cause to emergency as defined in TS 38.331 [28] when it requests an RRC Connection in relation to an emergency session.
In the case of Limited Service state, UE shall not include any Network Slice related parameters when communicating with the network.
When a PLMN or SNPN supports IMS and Emergency Services:
- all AMFs in that PLMN or SNPN shall have the capability to support Emergency Services.
- at least one SMF shall have this capability.
For other emergency scenarios (e.g. UE autonomous selection for initiating Emergency Services), refer to TS 23.167 [18] for domain selection principles.
For emergency service support in Public network integrated NPNs, refer to clause 5.30.3.5.
For emergency support via 5G ProSe UE-to-Network Relaying, refer to TS 23.304 [128]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.2 Architecture Reference Model for Emergency Services | According to clause 4.2, the non-roaming architectures (Figure 4.2.3-1 and Figure 4.2.3-2) and roaming architecture with the visited operator's application function (Figure 4.2.4-1 and Figure 4.2.4-4) apply for Emergency Services. The other non-roaming and roaming architectures with services provided by the home network do not apply for Emergency Services. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.3 Mobility Restrictions and Access Restrictions for Emergency Services | When Emergency Services are supported and local regulation requires IMS Emergency Sessions to be provided regardless of Mobility Restrictions or Access Restrictions, the Mobility Restrictions or Access Restrictions (see clause 5.3.4.1) should not be applied to UEs receiving Emergency Services. Additionally, due to Mobility Restrictions or Access Restrictions (e.g. CAG restrictions) for normally registered UEs, that have established both non-emergency PDU Sessions and emergency PDU Session, the AMF indicates to the SMF to perform a local release of all non-emergency PDU Sessions via PDU Session Release procedure as specified in clause 4.3.4 of TS 23.502 [3]. The UE locally releases non-emergency PDU Sessions. The AMF and the UE behave as if the UE is emergency registered as described in TS 24.501 [47].
When the (R)AN resources for Emergency Services are established, the ARP value for Emergency Services indicates the usage for Emergency Services to the 5G-AN.
During handover, the source NG-RAN and source AMF ignore any UE related restrictions during handover evaluation when there is an active PDU Session associated with emergency service.
During Mobility Registration Update procedures, including a Mobility Registration Update as part of a handover, the target AMF ignores any Mobility Restrictions or access restrictions for UE with emergency services where required by local regulation. Any non-emergency services are not allowed, by the target network when not allowed by the subscription for the target location. To allow the UE in limited service state (either Emergency Registered or registered for normal service) over a given Access Type to get access to normal services over this Access Type after the Emergency Session has ended and when it has moved to a new area that is not stored by the UE as a forbidden area, after allowing a period of time for subsequent Emergency Services, the UE may explicitly deregister and register for normal services over this Access Type without waiting for the emergency PDU Session Release by the SMF.
This functionality applies to all mobility procedures. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.4 Reachability Management | Over 3GPP access, an Emergency Registered UE when its Periodic Registration Update timer expires shall not initiate a Periodic Registration Update procedure but shall enter the RM-DEREGISTERED state. For such UEs, the AMF runs a mobile reachable timer with a similar value to the UE's Periodic Registration Update timer. After expiry of this timer the AMF may change the UE RM state for 3GPP Access in the AMF to RM-DEREGISTERED. The AMF assigns the Periodic Registration Update timer value to Emergency Registered UEs. This timer keeps the Emergency Registered UE registered for Emergency Services after change to CM-IDLE state to allow for a subsequent Emergency Service without a need for a new Emergency Registration.
Over non-3GPP access, an Emergency Registered UE is only reachable in CM-CONNECTED state: since the UE may only use Emergency Services over Non-3GPP access when it is not possible over 3GPP access, 3GPP access is assumed to be unavailable for paging the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.5 SMF and UPF selection function for Emergency Services | When a SMF is selected for Emergency Services, the SMF selection function described in clause 6.3.2 for normal services is applied to the Emergency DNN or the AMF selects the SMF directly from the AMF Emergency Configuration Data. If the SMF selection function described in clause 6.3.2 is used it shall always derive a SMF in the Serving PLMN or SNPN, which guarantees that the IP address is also allocated by the Serving PLMN or SNPN. When a UPF is selected for Emergency Services, the UPF selection function described in clause 6.3.3 for normal services is applied to the Emergency DNN or the SMF selects the UPF directly from the SMF Emergency Configuration Data. The information in the AMF Emergency Configuration Data and the SMF Emergency Configuration Data is specified in clause 5.16.4.1. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.6 QoS for Emergency Services | Local regulation may require supporting emergency calls from an unauthorised UE. In such a case, the SMF may not have subscription data. Additionally, the local network may want to provide Emergency Services support differently than what is allowed by a UE subscription. Therefore, the initial QoS parameters used for establishing Emergency Services are configured in the V-SMF (local network) in the SMF Emergency Configuration Data.
This functionality is used by the UE Requested PDU Session Establishment procedure when establishing Emergency Services. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.7 PCC for Emergency Services | Dynamic PCC is used for UEs establishing emergency service and shall be used to manage IMS emergency sessions when an operator allows IMS emergency sessions. When establishing Emergency Services with a SMF, the PCF provides the SMF with the QoS parameters, including an ARP value reserved for the Emergency Services to prioritize the QoS Flows when performing admission control, as defined in TS 23.503 [45].
The PCF rejects an IMS session established via the emergency PDU Session if the AF (i.e. P-CSCF) does not provide an emergency indication to the PCF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.8 IP Address Allocation | Emergency service is provided by the serving PLMN or SNPN. The UE and serving PLMN or SNPN must have compatible IP address versions in order for the UE to obtain a local emergency PDU Session. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.9 Handling of PDU Sessions for Emergency Services | The QoS Flows of a PDU Session associated with the emergency DNN shall be dedicated for IMS emergency sessions and shall not allow any other type of traffic. The emergency contexts shall not be changed to non-emergency contexts and vice versa. The UPF shall block any traffic that is not from or to addresses of network functions (e.g. P-CSCF) providing Emergency Services.
If there is already an emergency PDU Session over a given Access Type (3GPP access or non-3GPP access), the UE shall not request another emergency PDU Session over any Access Type except for handing over the existing emergency PDU Session to the other Access Type.
If the SMF receives a new emergency PDU session establishment request and an emergency PDU Session exists for the same UE over any Access Type, the SMF shall remove the existing SM context locally and clear the associated resources in the network and proceed with the new request.
NOTE: If the UE releases emergency PDU session locally and requests for establishment of a new one before the SMF has released the emergency PDU session due to PDU session inactivity as specified in clause 4.3.4.2 of TS 23.502 [3], the above duplicate emergency PDU session handling in the network removes the old emergency PDU session as part of establishing a new one. This releases all emergency call back resources related with the old emergency PDU Session.
The ARP reserved for emergency service shall only be assigned to QoS Flows associated with an emergency PDU Session. If the UE is Emergency Registered over a given access, it shall not request a PDU Session to any other DNN over this access.
5.16.4.9a Handling of PDU Sessions for normal services for Emergency Registered UEs
For an Emergency Registered UE over a given Access Type:
- the UE shall not initiate the UE Requested PDU Session Establishment procedure for normal service over this Access Type; and
- the network shall reject any PDU Session Establishment request for normal service from the UE on this Access Type;
- the UE may attempt to receive normal service over another Access Type if not otherwise prevented by the present document. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.10 Support of eCall Only Mode | For service requirements for eCall only mode, refer to TS 22.101 [33].
A UE configured for eCall Only Mode shall remain in RM-DEREGISTERED state, shall camp on a network cell when available but shall refrain from any Registration Management, Connection Management or other signalling with the network. The UE may instigate Registration Management and Connection Management procedures in order to establish, maintain and release an eCall Over IMS session or a session to any non-emergency MSISDN(s) or URI(s) configured in the USIM for test and/or terminal reconfiguration services. Following the release of either session and after the UE has left RRC_CONNECTED state, the UE starts a timer whose value depends on the type of session (i.e. whether eCall or a session to a non-emergency MSISDN or URI for test/reconfiguration). While the timer is running, the UE shall perform normal RM/CM procedures and is permitted to respond to paging to accept and establish an incoming session (e.g. from an emergency centre, PSAP or HPLMN operator). When the timer expires, once the UE is not in RRC_CONNECTED state, the UE shall perform a UE-initiated Deregistration procedure if still registered and enter RM-DEREGISTERED state.
NOTE 1: An HPLMN operator can change the eCall Only Mode configuration state of a UE in the USIM. An HPLMN operator can also instead add, modify or remove a non-emergency MSISDN or URI in the USIM for test and/or terminal reconfiguration services. This can occur following a UE call to a non-emergency MSISDN or URI configured for reconfiguration. When the eCall Only Mode configuration is removed, the UE operates as a normal UE that can support eCall over IMS.
NOTE 2: A test call and a reconfiguration call can be seen as normal (non-emergency) call by a serving PLMN and normal charging rules can apply depending on operator policy.
NOTE 3: An MSISDN configured in the USIM for test and/or terminal reconfiguration services for eCall Over IMS can differ from an MSISDN configured in the USIM for test services for eCall over the CS domain. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.4.11 Emergency Services Fallback | In order to support various deployment scenarios for obtaining Emergency Services, the UE and 5GC may support the mechanism to direct or redirect the UE either towards E-UTRA connected to 5GC (RAT fallback) when only NR does not support Emergency Services or towards EPS (E-UTRAN connected to EPC System fallback) when the 5GC does not support Emergency Services. Emergency Services fallback may be used when the 5GS does not indicate support for Emergency Services (see clause 5.16.4.1) and indicates support for Emergency Services fallback.
Following principles apply for Emergency Services Fallback:
- If the AMF indicates support for Emergency Services fallback in the Registration Accept message, then in order to initiate Emergency Service, normally registered UE supporting Emergency Services fallback shall initiate a Service Request with Service Type set to Emergency Services fallback as defined in clause 4.13.4.1 of TS 23.502 [3].
- AMF uses the Service Type Indication within the Service Request to redirect the UE towards the appropriate RAT/System. The 5GS may, for Emergency Services, trigger one of the following procedures:
- Handover or redirection to EPS.
- Handover or redirection to E-UTRA connected to 5GC.
- After receiving the Service Request for Emergency Fallback, the AMF triggers N2 procedure resulting in either CONNECTED state mobility (Handover procedure) or IDLE state mobility (redirection) to either E-UTRA/5GC or to E-UTRAN/EPC depending on factors such as N26 availability, network configuration and radio conditions. In the N2 procedure, the AMF based on support for Emergency Services in 5GC or EPC may indicate the target CN for the RAN node to know whether inter-RAT fallback or inter-system fallback is to be performed. The target CN indicated in the N2 procedure is also conveyed to the UE in order to be able to perform the appropriate NAS procedures (S1 or N1 Mode).
- When the AS re-keying procedure and the Emergency Fallback procedure collides, the AMF gives up the AS re-keying procedure and only initiates the Emergency Fallback procedure.
NOTE 1: Emergency Services Fallback to EPS can be followed by an onward movement to GERAN or UTRAN via CSFB procedures if the PLMN does not support IMS emergency services.
NOTE 2: If the UE has signalled that S1 mode is disabled for a network that only supports IMS voice via EPS Fallback, the AMF will not indicate that Emergency Services Fallback is supported over 3GPP access.
Emergency Services fallback is supported only in case of PLMN. Emergency Services Fallback is not supported for SNPN. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.5 Multimedia Priority Services | TS 22.153 [24] specifies the service requirements for Multimedia Priority Service (MPS). MPS allows Service Users (as per TS 22.153 [24]) priority access to system resources in situations such as during congestion, creating the ability to deliver or complete sessions of a high priority nature. Service Users are government-authorized personnel, emergency management officials and/or other authorized users. MPS supports priority sessions on an "end-to-end" priority basis.
MPS is based on the ability to invoke, modify, maintain and release sessions with priority and deliver the priority media packets under network congestion conditions. MPS is supported in a roaming environment when roaming agreements are in place and where regulatory requirements apply.
NOTE 1: If a session terminates on a server in the Internet (e.g. web-based service), then the remote end and the Internet transport are out of scope for this specification.
MPS is supported for Service Users using UEs connecting via 3GPP access. MPS is also supported for Service Users using UEs that connect via Trusted or Untrusted non-3GPP access for MPS. N3IWF selection is according to clause 6.3.6 for PLMN access.
A Service User may use an MPS-subscribed UE or any other UE to obtain MPS. An MPS-subscribed UE obtains priority access to the Radio Access Network by using the Unified Access Control mechanism according to TS 22.261 [2]. This mechanism provides preferential access to UEs based on its assigned Access Identity. If an MPS-subscribed UE belongs to the special Access Identity as defined in TS 22.261 [2], the UE has preferential access to the network compared to ordinary UEs in periods of congestion.
In the RRC Connection Establishment procedure and the RRC Connection Resume procedure, an MPS subscribed UE connected to NG-RAN shall use a high priority access Establishment or Resume Cause with values according to TS 24.501 [47], TS 36.331 [51] and TS 38.331 [28].
MPS subscription allows users to receive priority services, if the network supports MPS. The same MPS subscription applies to access via 3GPP access and Trusted or Untrusted non-3GPP access. MPS subscription entitles a USIM with special Access Identity. MPS subscription includes indication for support of priority PDU connectivity service including MPS for Data Transport Service, IMS priority service support and MPS for Messaging support for the end user. Priority Level regarding QoS Flows and IMS are also part of the MPS subscription information. The usage of Priority Level is defined in TS 22.153 [24], TS 23.503 [45] and TS 23.228 [15].
The UE determines whether to apply MPS exceptions for Non-Allowed Areas based on MPS subscription i.e. USIM with special Access Identity or MPS priority received from the AMF as defined in TS 23.502 [3] over 3GPP or Trusted or Untrusted non-3GPP access.
NOTE 2: The same MPS subscription in the UDM and/or on the USIM is used for priority treatment of 3GPP procedures when the access is Trusted or Untrusted non-3GPP.
NOTE 3: The term "Priority PDU connectivity services" is used to refer to 5G System functionality that corresponds to the functionality as provided by LTE/EPC Priority EPS bearer services in clause 4.3.18.3 of TS 23.401 [26].
MPS includes signalling priority and media priority. All MPS-subscribed UEs get priority for QoS Flows (e.g. used for IMS signalling) when established to the DN that is configured to have priority for a given Service User by setting MPS-appropriate values in the QoS profile in the UDM.
Service Users are treated as On Demand MPS subscribers or not, based on regional/national regulatory requirements. On Demand service is based on Service User invocation/revocation explicitly and applied to the media QoS Flows being established. When not On Demand MPS service does not require invocation and provides priority treatment for all QoS Flows only to the DN that is configured to have priority for a given Service User after attachment to the 5G network.
MPS for Data Transport Service is an on-demand service that may be invoked/revoked by an authorized Service User using a UE with a subscription for MPS (i.e. according to its MPS profile), or using a UE that does not have a subscription for MPS (using methods not in scope of this specification).
MPS for Data Transport Service requires explicit invocation. The Service User invokes the service by communicating with an AF. The authorization of an MPS for Data Transport Service request is done by the AF or the PCF according to clause 6.1.3.11 of TS 23.503 [45]. Upon successful authorization, the PCF performs the necessary actions to achieve appropriate ARP and 5QI settings for the QoS Flows (see clause 6.1.3.11 of TS 23.503 [45]).
MPS for Data Transport Service enables the prioritization of all traffic on the QoS Flow associated with the default QoS rule and other QoS Flows upon AF request. The QoS modification to the QoS Flow associated with the default QoS rule and other QoS Flows is done based on operator policy and regulatory rules by means of local PCF configuration.
NOTE 4: According to regional/national regulatory requirements and operator policy, On-Demand MPS (including MPS for Data Transport Service) Service Users can be assigned the highest priority.
NOTE 5: If no configuration is provided, MPS for Data Transport Service applies only to the QoS Flow associated with the default QoS rule.
NOTE 6: MPS for DTS controls the priority of traffic on QoS Flows independent of the application(s) being used. Other mechanisms (e.g. Priority PDU connectivity service) can be used to control the priority of traffic on other QoS Flows under the control of specific data application(s), based on operator policy.
NOTE 7: MPS for Data Transport Service can be applied to any DNN other than the well-known DNN for IMS.
For MPS for Data Transport Service, the AF may also create an SDF for priority signalling between the UE and the AF (see clause 6.1.3.11 of TS 23.503 [45]).
Priority treatment is applicable to IMS based multimedia services and Priority PDU connectivity service including MPS for Data Transport Service.
Priority treatment for MPS includes priority message handling, including priority treatment during authentication, security and Mobility Management procedures.
Priority treatment for MPS session requires appropriate ARP and 5QI (plus 5G QoS characteristics) setting for QoS Flows according to the operator's policy.
NOTE 8: Use of QoS Flows for MPS with QoS characteristics signalled as part of QoS profile enables the flexible assignment of 5G QoS characteristics (e.g. Priority Level) for MPS.
When an MPS session is requested by a Service User, the following principles apply in the network:
- QoS Flows employed in an MPS session shall be assigned ARP value settings appropriate for the priority of the Service User.
- Setting ARP pre-emption capability and vulnerability for MPS QoS Flows, subject to operator policies and depending on national/regional regulatory requirements.
- Pre-emption of non-Service Users over Service Users during network congestion situation, subject to operator policy and national/regional regulations.
The terminating network identifies the priority of the MPS session and applies priority treatment, including paging with priority, to ensure that the MPS session can be established with priority to the terminating user (either a Service User or normal user).
MPS priority mechanisms can be classified as subscription-related, invocation-related and those applied to existing QoS Flows. Subscription related mechanisms, as described in clause 5.22.2, are further divided into two groups: those which are always applied and those which are conditionally applied. Invocation-related mechanisms, as described in clause 5.22.3, are further divided into three groups: those that apply for mobile originated SIP call/sessions, those that apply for mobile terminated SIP call/sessions and those that apply for the Priority PDU connectivity services including MPS for Data Transport Service. Methods applied to existing QoS Flows focus on handover and congestion control and are described in clause 5.22.4.
NOTE 9: The network can hide its topology from the AF supporting MPS for Data Transport Service. At the same time, the UE needs to provide its locally known IP address to the AF supporting MPS for Data Transport Service to support interactions with the applicable PCF. Thus, there can be no NAT of the UE IP address between the UPF and the AF supporting MPS for Data Transport Service.
For WLAN access, the UE may notify the TNAN/N3IWF of its MPS subscription before the NAS Registration Request. Based on operator policy, the TNAN/N3IWF may use this indication to provide this UE with priority treatment in the case of congestion/overload before receipt of the NAS Registration Request with an MPS priority establishment cause.
An MPS subscription supports setting (enabling)/clearing (disabling) priority treatment of the Messaging service (i.e. SMS over NAS, SMS over IP and messaging over IMS) for an MPS-subscribed UE. The usage of the MPS for Messaging indication in the subscription data is further specified in clause 5.22. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.16.6 Mission Critical Services | According to TS 22.280 [37], a Mission Critical Service (MCX Service) is a communication service reflecting enabling capabilities Mission Critical Applications and provided to end users from Mission Critical Organizations and mission critical applications for other businesses and organizations (e.g. utilities, railways). An MCX Service is either Mission Critical Push To Talk (MCPTT) as defined in TS 23.379 [38], Mission Critical Video (MCVideo) as defined in TS 23.281 [39], or Mission Critical Data (MCData) as defined in TS 23.282 [40] and represents a shared underlying set of requirements between two or more MCX Service types. MCX Services are not restricted only to the ones defined in this clause and such services can also have priority treatment, if defined via operator's policy and/or local regulation.
MCX Services are based on the ability to invoke, modify, maintain and release sessions with priority and deliver the priority media packets under network congestion conditions. As specified in clause 6.8 of TS 22.261 [2], MCX Users require 5GS functionality that allows for real-time, dynamic, secure and limited interaction with the QoS and policy framework for modification of the QoS and policy framework by authorized users. The limited interaction is based on operator policy and provides specific limitations on what aspects of the QoS and policy framework an authorized MCX User can modify. MCX Services are supported in a roaming environment when roaming agreements are in place and where regulatory requirements apply.
An MCX-subscribed UE obtains priority access to the Radio Access Network by using the Unified Access Control mechanism according to TS 22.261 [2]. This mechanism provides preferential access to UEs based on its assigned Access Identity. If an MCX-subscribed UE belongs to the special Access Identity as defined in TS 22.261 [2], the UE has preferential access to the network compared to ordinary UEs in periods of congestion. MCX subscription allows users to receive priority services, if the network supports MCX. MCX subscription entitles a USIM with special Access Identity.
NOTE 1: For Mission Critical Services that require low latency and zero packet loss even for the first downlink packet(s), periodic keep-alive packets during interruptions of media transmission (e.g. Floor Idle as specified in TS 23.379 [38], referenced by TS 23.289 [184]), which is sent over user plane of PDU session, can be used so that the UE is kept in RRC_CONNECTED state without being paged when unicast transmission is used. It is up to the implementation, the periodicity of the keep-alive packets configured in the AF can consider NG-RAN's configuration.
NOTE 2: For support of Mission Critical Services that require low latency and zero packet loss when using MBS, see TS 23.247 [121].
MCX Services leverage the foundation of the 5G QoS Model as defined in clause 5.7 and 5G Policy Control as defined in clause 5.14. It requires that the necessary subscriptions are in place for both the 5G QoS Profile and the necessary Policies. In addition, MCX Services leverage priority mechanism as defined in clause 5.22.
The terminating network identifies the priority of the MCX Service session and applies priority treatment, including paging with priority, to ensure that the MCX Service session can be established with priority to the terminating user (either an MCX User or normal user).
Priority treatment for MCX Service includes priority message handling, including priority treatment during authentication, security and Mobility Management procedures.
Priority treatment for MCX Service sessions require appropriate ARP and 5QI (plus 5G QoS characteristics) setting for QoS Flows according to the operator's policy.
NOTE 3: Use of QoS Flows for MCX Service sessions with non-standardized 5QI values enables the flexible assignment of 5G QoS characteristics (e.g. Priority Level).
When a MCX Service session is requested by an MCX User, the following principles apply in the network:
- QoS Flows employed in a MCX Service session shall be assigned ARP value settings appropriate for the priority of the MCX User.
- Setting ARP pre-emption capability and vulnerability of QoS Flows related to a MCX Service session, subject to operator policies and depending on national/regional regulatory requirements.
- Pre-emption of non-MCX Users over MCX Users during network congestion situations, subject to operator policy and national/regional regulations.
Priority treatment is applicable to IMS based multimedia services and priority PDU connectivity services.
Relative PDU priority decisions for MCX Service sessions are based on real-time data of the state of the network and/or based on modification of the QoS and policy framework by authorized users as described in clause 6.8 of TS 22.261 [2]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17 Interworking and Migration | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.1 Support for Migration from EPC to 5GC | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.1.1 General | Clause 5.17.1 describes the UE and network behaviour for the migration from EPC to 5GC.
Deployments based on different 3GPP architecture options (i.e. EPC based or 5GC based) and UEs with different capabilities (EPC NAS and 5GC NAS) may coexist at the same time within one PLMN.
It is assumed that a UE that is capable of supporting 5GC NAS procedures may also be capable of supporting EPC NAS (i.e. the NAS procedures defined in TS 24.301 [13]) to operate in legacy networks e.g. in the case of roaming.
The UE will use EPC NAS or 5GC NAS procedures depending on the core network by which it is served.
In order to support smooth migration, it is assumed that the EPC and the 5GC have access to a common subscriber database, that is HSS in the case of EPC and the UDM in the case of 5GC, acting as the master data base for a given user as defined in TS 23.002 [21]. The PCF has access to the UDR that acts as a common subscriber database for a given user identified by a SUPI using the Nudr services defined in TS 23.502 [3].
Figure 5.17.1.1-1: Architecture for migration scenario for EPC and 5G CN
A UE that supports only EPC based Dual Connectivity with secondary RAT NR:
- always performs initial access through E-UTRA (LTE-Uu) but never through NR;
- performs EPC NAS procedures over E-UTRA (i.e. Mobility Management, Session Management etc) as defined in TS 24.301 [13].
A UE that supports camping on 5G Systems with 5GC NAS:
- performs initial access either through E-UTRAN that connects to 5GC or NR towards 5GC;
- performs initial access through E-UTRAN towards EPC, if supported and needed;
- performs EPC NAS or 5GC NAS procedures over E-UTRAN or NR respectively (i.e. Mobility Management, Session Management etc) depending on whether the UE requests 5GC access or EPC access, if the UE also supports EPC NAS.
When camping on an E-UTRA cell connected to both EPC and 5GC, a UE supporting EPC NAS and 5GC NAS shall select a core network type (EPC or 5GC) and initiate the corresponding NAS procedure as specified in TS 23.122 [17].
In order to support different UEs with different capabilities in the same network, i.e. both UEs that are capable of only EPC NAS (possibly including EPC based Dual Connectivity with NR as secondary RAT) and UEs that support 5GC NAS procedures in the same network:
- eNB that supports access to 5GC shall broadcast that it can connect to 5GC. Based on that, the UE AS layer indicates "E-UTRA connected to 5GC" capability to the UE NAS layer. In addition the eNB broadcasts the supported CIoT 5GS Optimisations that the UE uses for selecting a core network type.
- It is also expected that the UE AS layer is made aware by the UE NAS layer whether a NAS signalling connection is to be initiated to the 5GC. Based on that, UE AS layer indicates to the RAN whether it is requesting 5GC access (i.e. "5GC requested" indication). The RAN uses this indication to determine whether a UE is requesting 5GC access or an EPC access. RAN routes NAS signalling to the applicable AMF or MME accordingly.
NOTE: The UE that supports EPC based Dual Connectivity with secondary RAT only does not provide this "5GC requested" indication at Access Stratum when it performs initial access and therefore eNB uses the "default" CN selection mechanism to direct this UE to an MME
The 5GC network may steer the UE from 5GC based on:
- Core Network type restriction (e.g. due to lack of roaming agreements) described in clause 5.3.4.1.1;
- Availability of EPC connectivity;
- UE indication of EPC Preferred Network Behaviour; and
- Supported Network Behaviour.
The UE that wants to use one or more of these functionalities not supported by 5G System, when in CM-IDLE may disable all the related radio capabilities that allow the UE to access 5G System. The triggers to disable and re-enable the 5GS capabilities to access 5G System in this case are left up to UE implementation. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.1.2 User Plane management to support interworking with EPS | In order to support the interworking with EPC, the SMF+PGW-C provides information over N4 to the UPF+PGW-U related to the handling of traffic over S5-U. Functionality defined in TS 23.503 [45] for traffic steering control on SGi-LAN/N6 can be activated in UPF+PGW-U under consideration of whether the UE is connected to EPC or 5GC.
When the UE is connected to EPC and establishes/releases PDN connections, the following differences apply to N4 compared to when the UE is connected to 5GC:
- The CN Tunnel Info is allocated for each EPS Bearer.
- In addition to the Service Data Flow related information, the SMF+PGW-C shall be able to provide the GBR and MBR values for each GBR bearer of the PDN connection to the UPF+PGW-U.
If the UE does not have preconfigured rules for associating an application to a PDN connection (i.e. the UE does not have rules in UE local configuration and is not provisioned with ANDSF rules), the UE should use a matching URSP rule as defined in TS 23.503 [45], if available, to derive the parameters, e.g. APN, for the PDN connection establishment and associating an application to the PDN connection.
NOTE: The mapping between the parameters in the URSP rules and the parameters used for PDN connection establishment is defined in TS 24.526 [110]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.1.3 QoS handling for home routed roaming | During mobility from EPS to 5GS, the handling of QoS constraints in V-SMF is specified in clauses 4.11.1.2.2 and 4.11.1.3.3 of TS 23.502 [3] and follows the same principle as described in clause 5.7.1.11. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2 Interworking with EPC | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.1 General | Interworking with EPC in this clause refers to mobility procedures between 5GC and EPC/E-UTRAN, except for clause 5.17.2.4. Network slicing aspects for EPS Interworking are specified in clause 5.15.7
In order to interwork with EPC, the UE that supports both 5GC and EPC NAS can operate in single-registration mode or dual-registration mode:
- In single-registration mode, UE has only one active MM state (either RM state in 5GC or EMM state in EPC) and it is either in 5GC NAS mode or in EPC NAS mode (when connected to 5GC or EPC, respectively). UE maintains a single coordinated registration for 5GC and EPC. Accordingly, the UE maps the EPS-GUTI to 5G GUTI during mobility between EPC and 5GC and vice versa following the mapping rules in Annex B. To enable re-use of a previously established 5G security context when returning to 5GC, the UE also keeps the native 5G-GUTI and the native 5G security context when moving from 5GC to EPC.
- In dual-registration mode, UE handles independent registrations for 5GC and EPC using separate RRC connections. In this mode, UE maintains 5G-GUTI and EPS-GUTI independently. In this mode, UE provides native 5G-GUTI, if previously allocated by 5GC, for registrations towards 5GC and it provides native EPS-GUTI, if previously allocated by EPC, for Attach/TAU towards EPC. In this mode, the UE may be registered to 5GC only, EPC only, or to both 5GC and EPC.
Dual-registration mode is intended for interworking between EPS/E-UTRAN and 5GS/NR. A dual-registered UE should not send its E-UTRA connected to 5GC and E-UTRAN radio capabilities to NR access when connected to 5GS/NR to avoid being handed over to 5GC-connected E-UTRA or to E-UTRAN.
NOTE 1: This is to prevent the dual registered UE from being connected to the same E-UTRA cell either connected to EPC or 5GC simultaneously using separate RRC connections via single RAN node as a result of handover. If a dual- registered UE implementation chooses to send its E-UTRA capability when connected to 5GS/NR, the UE and the network behaviour when UE enters a 5GC-connected E-UTRA is not further specified. If however the UE is registered with 5GS/NR only, the UE can send its E-UTRA capability in order to allow inter-RAT handover to E-UTRA/5GC and Dual Connectivity with multiple RATs.
If a dual-registered UE had not sent its E-UTRA connected to 5GC and E-UTRAN radio capabilities to 5GS and the UE needs to initiate emergency services, it shall locally re-enable its E-UTRA connected to 5GC and E-UTRAN radio capabilities in order to perform domain selection for emergency services as defined in TS 23.167 [18].
NOTE 2: However even in this case, the UE is still not expected to connect to E-UTRAN/EPC and E-UTRA/5GC simultaneously using separate RRC connection via single RAN node as a result of the domain selection for emergency services.
The support of single registration mode is mandatory for UEs that support both 5GC and EPC NAS.
During E-UTRAN Initial Attach, UE supporting both 5GC and EPC NAS shall indicate its support of 5G NAS in UE Network Capability described in clause 4.11.1.5.2 of TS 23.502 [3].
During registration to 5GC, UE supporting both 5GC and EPC NAS shall indicate its support of EPC NAS.
NOTE 3: This indication may be used to give the priority towards selection of SMF+PGW-C for UEs that support both EPC and 5GC NAS.
If the UE supports 5GC NAS, at PDN connection establishment in EPC, the UE may allocate a PDU Session ID and sends it via PCO, regardless of N1 mode status (i.e. enabled or disabled) in the UE.
NOTE 4: UE providing a PDU Session ID at PDN connection establishment even when N1 mode is disabled allows for IP address preservation during EPC to 5GC mobility once the UE re-enables N1 mode.
NOTE 5: For the case the MME has selected a standalone PGW for a PDN connection, if the UE re-enables N1 mode and reports the change in UE Network Capability, the MME can initiate PDN disconnection with reactivation required as described in clause 4.11.0a.8 of TS 23.502 [3] to allow selection of SMF+PGW-C thus session continuity at EPC to 5GC mobility.
If the EPC supports "Ethernet" PDU Session Type and the 5GSM Capabilities indicate that the UE supports Ethernet PDN type in EPC, then PDU Session type "Ethernet" is transferred to EPC as "Ethernet". Otherwise, PDU Session types "Ethernet" and "Unstructured" are transferred to EPC as "non-IP" PDN type (when supported by UE and network). If the UE or EPC does not support Ethernet PDN type in EPC, the UE sets the PDN type to non-IP when it moves from 5GS to EPS and after the transfer to EPS and the UE and the SMF shall maintain information about the PDU Session type used in 5GS, i.e. information indicating that the PDN Connection with "non-IP" PDN type corresponds to PDU Session type Ethernet or Unstructured respectively. This is done to ensure that the appropriate PDU Session type will be used if the UE transfers to 5GS.
PDN type "non-IP" is transferred to 5GS as "Unstructured" PDU Session type if it is successfully transferred.
It is assumed that if a UE supports Ethernet PDU Session type and/or Unstructured PDU Session type in 5GS it will also support non-IP PDN type in EPS. If this is not the case, the UE shall locally delete any EBI(s) corresponding to the Ethernet/Unstructured PDU Session(s) to avoid that the Ethernet/Unstructured PDU Session(s) are transferred to EPS.
MTU size consideration for PDU Sessions and PDN Connections towards a SMF+PGW-C follows the requirements in clause 5.6.10.4.
Networks that support interworking with EPC, may support interworking procedures that use the N26 interface or interworking procedures that do not use the N26 interface. Interworking procedures with N26 support provides IP address continuity on inter-system mobility to UEs that support 5GC NAS and EPC NAS and that operate in single registration mode. Networks that support interworking procedures without N26 shall support procedures to provide IP address continuity on inter-system mobility to UEs operating in both single-registration mode and dual-registration mode. In such networks, AMF shall provide the indication that interworking without N26 is supported to UEs during initial Registration in 5GC or MME may optionally provide the indication that interworking without N26 is supported in the Attach procedure in EPC as defined in TS 23.401 [26].
If the network does not support interworking with EPC, network shall not indicate support for "interworking without N26" to the UE.
When the HSS+UDM is required to provide the subscription data to the MME, for each APN, only one SMF+PGW-C FQDN and associated APN is provided to the MME according to TS 23.401 [26].
For interworking without N26 interface:
- if the PDU session supports interworking, the SMF+PGW-C stores the SMF+PGW-C FQDN to SMF context in HSS+UDM when the SMF is registered to HSS+UDM.
- For an APN, the HSS+UDM selects one of the stored SMF+PGW-C FQDN based on operator's policy.
For interworking with N26 interface:
- For a DNN, AMF determines PDU session(s) associated with 3GPP access in only one SMF+PGW-C supporting EPS interworking via EBI allocation procedure as described in clause 4.11.1.4.1 of TS 23.502 [3].
- If the network supports EPS interworking of non-3GPP access connected to 5GC, the AMF serving 3GPP access notifies the UDM to store the association between DNN and SMF+PGW-C FQDN which supports EPS interworking as Intersystem continuity context, to avoid MME receiving inconsistent SMF+PGW-C FQDN from AMF and HSS+UDM.
- The AMF updates Intersystem continuity context if the SMF+PGW-C and DNN association is changed due to the AMF selecting another SMF+PGW-C for EPS interworking for the same DNN.
- If the SMF+PGW-C FQDN and associated DNN exists in Intersystem continuity context, the HSS+UDM provides MME with SMF+PGW-C FQDN and associated APN.
It does not assume that the HSS+UDM is aware of whether N26 is deployed in the serving network. The HSS+UDM check the Intersystem continuity context first. If no SMF+PGW-C FQDN associated with an DNN exists in Intersystem continuity context, the HSS+UDM selects one of the SMF+PGW-C FQDN for the APN from SMF context based on operator's policy.
In entire clause 5.17.2 the terms "initial attach", "handover attach" and "TAU" for the UE procedures in EPC can alternatively be combined EPS/IMSI Attach and combined TA/LA depending on the UE configuration defined in TS 23.221 [23].
If a UE in MICO mode moves to E-UTRAN connected to EPC and any of the triggers defined in clause 5.4.1.3 occur, then the UE shall locally disable MICO mode and perform the TAU or Attach procedure as defined in clause 5.17.2. The UE can renegotiate MICO when it returns to 5GS during (re-)registration procedure.
IP address preservation for IP PDU sessions cannot be ensured on subsequent mobility from EPC/E-UTRAN to GERAN/UTRAN to a UE that had initially registered in 5GS and moved to EPC/E-UTRAN.
NOTE 6: The SMF+PGW-C might not include the GERAN/UTRAN PDP Context anchor functionality. Also, 5GC does not provide GERAN/UTRAN PDP Context parameters to the UE when QoS Flows of PDU Session are setup or modified in 5GS. Hence, the UE might not be able to activate the PDP contexts when it transitions to GERAN/UTRAN.
IP address preservation for IP PDU sessions cannot be ensured on subsequent mobility from EPC/E-UTRAN to 5GS for a 5GS NAS capable UE that had initially established a PDP context via GERAN/UTRAN and moved to EPC/E-UTRAN. IP address preservation for IP PDU session mobility between EPC/E-UTRAN and 5GS may be re-ensured as specified in clause 5.17.2.4 when UE moves from GERAN/UTRAN into EPC/E-UTRAN.
NOTE 7: The PGW acting as a GGSN might not support SMF+PGW-C functionality. GPRS does not support 5GS parameters transfer between UE and SMF+PGW-C (e.g. providing of PDU session ID and 5GS QoS information).
When a PDU session is moved from 5GS to EPS, the SMF+PGW-C keeps the registration and subscription in HSS+UDM until the corresponding PDN connection is released.
The SMF+PGW-C receives notification of subscription update regarding the 5G parameters (e.g. DNNs, S-NSSAIs) which are associated with the established PDN connection(s) connecting via EPS. If the subscription regarding DNN, QoS profile or PDN connection type associated with the PDN connection is updated, then the MME receives the subscription update and triggers corresponding actions according to TS 23.401 [26]. If the SMF+PGW-C receives subscription updates (e.g. change of 5GS Subscribed NSSAI) from the UDM the SMF+PGW-C triggers corresponding actions for the PDN connection. This may include (depending on the modified parameter) to:
- update the UPF (e.g. for a change of Framed Route information); or
- release the PDN connection with an appropriate cause (e.g. for change of EPS/5GS interworking support, for subscription removal of S-NSSAI associated with the PDN connection);
- do nothing about changes to DNN and/or PDU Session type that are handled by the MME.
If header compression is used for Control Plane CIoT EPS/5GS Optimisations and when the UE moves from EPS to 5GS or from 5GS to EPS, the UE may initiate the PDU Session Modification Procedure or UE requested bearer resource modification procedure to renegotiate the header compression configuration and to establish the compression context between the UE and MME/SMF, see TS 23.401 [26] and TS 24.501 [47].
If the UE is moving from 5GS to EPS and the RAT type is also moving from a "broadband" RAT (e.g. NR or WB-E-UTRA) to NB-IoT in EMM-IDLE state, the UE should set the mapped EPS bearer context for which the EPS bearer is a dedicated EPS bearer to state BEARER CONTEXT INACTIVE as for NB-IoT UEs in EPS only support the default bearers. In addition, UE shall locally deactivate the related bearers according to the maximum number of supported UP resources and send the latest bearer context status in the TAU Request.
If APN Rate Control is used when the UE moves from EPC to 5GC then the P-GW/SCEF and UE store the current APN Rate Control Status for an APN. If while connected to 5GC the last PDU Session to a DNN that is the same as the APN identified in the APN Rate Control Status is released then the APN Rate Control Status may be stored in the AMF in addition to the Small Data Rate Control Status and the UE discards the APN Rate Control Status. The APN Rate Control Status is stored in the AMF so it can be provided to the MME during mobility to EPC and subsequently applied at establishment of a new first PDN Connection to the same APN, if valid. The APN Rate Control Status is provided to the UPF+PGW-U if a first new PDU Session is established towards the DNN that is the same as the APN identified in the APN Rate Control Status if the UE moves back to EPC, taking into account its validity period.
The UE may be provided with initial APN Rate Control parameters by the SMF when a first new PDU Session is established for a DNN and S-NSSAI that supports interworking with EPS and the DNN matches an APN. The SMF provides the APN Rate Control Status for the APN that matches the DNN, if available at the SMF, otherwise the configured APN Rate Control parameters for the APN that matches the DNN are provided as the initially applied parameters. If the initially applied parameters differ from the configured APN Rate Control parameters and the first APN Rate Control validity period expires, the UE is updated with the configured APN Rate Control parameters once the UE has moved to EPC.
NOTE 8: If the APN Rate Control Status is provided to a UPF+PGW-U it is not used for Small Data Rate Control while the UE is connected to 5GC, it is only used as the APN Rate Control Status if the UE moves to EPC.
NOTE 9: Encoding of APN and DNN specified in TS 23.003 [19] allows the comparison of EPS APN and 5GS DNN.
If a Service Gap timer is running in the AMF when the UE moves from 5GC to EPC, the AMF stops the running Service Gap timer. If the UE returns to 5GC from EPC the AMF provides the Service Gap Time to the UE as described in clause 5.31.16.
If a Service Gap timer is running in the MME when the UE moves from EPC to 5GC, the MME stops the running Service Gap timer. If the UE returns to E-UTRAN connected to EPC from 5GC the MME provides the Service Gap Time to the UE as described in TS 23.401 [26].
If a Service Gap timer is running in the UE when the UE moves to from 5GC to EPC and if Service Gap Time is received from the MME, the UE stores the received Service Gap Time for later use when the timer needs to be started next time and the Service Gap timer that was started before the system change is kept running in the UE and applied for EPC. If a Service Gap timer is running in the UE when the UE moves to 5GC and if Service Gap Time is received from the AMF, the UE stores the received Service Gap Time for later use when the timer needs to be started next time and the Service Gap timer that was started before the system change is kept running in the UE and applied in 5GS.
For UE currently served by EPC, a SMF+PGW-C may support L2TP tunnelling on N6, as described in clause 5.8.2.16. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.2 Interworking Procedures with N26 interface | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.2.1 General | NOTE 1: Additional network slicing and Interworking with EPS with N26 aspects are specified in clause 5.15.7.
Interworking procedures using the N26 interface, enables the exchange of MM and SM states between the source and target network. The N26 interface may be either intra-PLMN or inter-PLMN (e.g. to enable inter-PLMN mobility). When interworking procedures with N26 is used, the UE operates in single-registration mode. For the 3GPP access, the network keeps only one valid MM state for the UE, either in the AMF or MME. For the 3GPP access, either the AMF or the MME is registered in the HSS+UDM.
The support for N26 interface between AMF in 5GC and MME in EPC is required to enable seamless session continuity (e.g. for voice services) for inter-system change.
The UE's subscription may include restriction for Core Network Type (EPC) and RAT restriction for E-UTRA. If so, the UDM provides these restrictions to the AMF. The AMF includes RAT and Core Network type restrictions in the Handover Restriction List to the NR. The AMF and NR use these restrictions to determine if mobility of the UE to EPS or E-UTRA connected to EPS should be permitted. When the UE moves from 5GS to EPS, the SMF determines which PDU Sessions can be relocated to the target EPS, e.g. based on capability of the deployed EPS, operator policies for which PDU Session, seamless session continuity should be supported etc. The SMF can release the PDU Sessions that cannot be transferred as part of the handover or Idle mode mobility. However, whether the PDU Session is successfully moved to the target network is determined by target EPS.
Similarly, the UE's subscription may include restriction for Core Network Type (5GC) and RAT restriction for NR. If so, the HSS provides these restrictions to the MME. The MME includes RAT and Core Network type restrictions in the Handover Restriction List to the E-UTRAN. The MME and E-UTRAN use these restrictions to determine if mobility of the UE to 5GS or NR connected to 5GS should be permitted. If the SMF+PGW-C receives the PDU session ID from UE via PCO and know 5GC is not restricted for the PDN connection by user subscription, the SMF+PGW-C sends the mapped QoS parameters to UE. When the UE moves from EPS to 5GS, for the case when the MME has selected SMF+PGW-C even for PDN connections that cannot be relocated to the target 5GS, the SMF+PGW-C determines which PDN Connections can be relocated to the target 5GS, e.g. based on capability of the deployed 5GS, subscription and operator policies for which PDN Connection, seamless session continuity should be supported etc. The SMF+PGW-C and NG-RAN can reject the PDN Connections that cannot be transferred as part of the handover or Idle mode mobility.
NOTE 2: At inter-PLMN scenarios, in case the V-SMF receives an operator specific QCI value, whether/how the remapping is done is implementation specific according to the local policy and according to an inter-PLMN agreement between the involved operators. If remapping at inter-PLMN mobility between HPLMN and VPLMN is to be performed, the V-SMF chooses a 5QI value based on inter-PLMN agreement between the VPLMN and the HPLMN and updates the QoS Flows accordingly. The remapping can result in service degradation.
For the case when the MME has selected standalone P-GW for a PDN connection for which session continuity is not supported and the AMF cannot retrieve the address of the corresponding SMF during EPS to 5GS mobility, the AMF does not move the PDN connection to 5GS.
NOTE 2: When applying the AMF planned removal procedure or the procedure to handle AMF failures (see clause 5.21.2) implementations are expected to update the DNS configuration to enable MMEs to discover alternative AMFs if the MME tries to retrieve a UE context from an AMF that has been taken out of service or has failed. This addresses the scenario of UEs performing 5GS to EPS Idle mode mobility and presenting a mapped GUTI pointing to an AMF that has been taken out of service or has failed.
In the case of mobility from 5GS to EPS, if the MME lacks certain capability, e.g. MME not supporting 15 EPS bearers, the 5GC shall not transfer the UE EPS bearers and/or EPS PDN connections that are not supported by the EPC network. If the MME does not support 15 EPS bearers, the AMF determines which EBIs cannot be transferred to EPS and retrieves the EPS bearer contexts from the SMF+PGW-C for the EBIs that can be transferred to EPS.
NOTE 3: How the AMF determines which EBIs can be transferred to EPS is according to local configuration, e.g. according to DNN, S-NSSAI, ARP associated with an EBI.
In the case of mobility from 5GS to EPS, if the mobility is a result of the PCF modifying the RFSP Index value for the UE to indicate that EPC/E-UTRAN access is prioritized over the 5GS access, the AMF may be sent with a RFSP Index in Use Validity Time by the PCF as specified in TS 23.503 [45]. If the AMF receives RFSP Index in Use Validity Time and selects the RFSP Index in use identical to the authorized RFSP Index as specified in clause 5.3.4.3, then the AMF provides the MME with the RFSP Index in use and the RFSP Index in Use Validity Time, which indicates the time by which the RFSP Index in use will be used in the MME as specified in clause 4.11.1.5.8 of TS 23.502 [3].
NOTE 4: The RFSP Index in Use Validity Time is to allow the UE to stay in EPS for a period of time to avoid the potential ping-pong issue (i.e. 5GS keeps sending the UE to EPS based on authorized RFSP Index from PCF and the EPS keeps sending the UE back to 5GS immediately based on the subscribed RFSP Index.
NOTE 5: The RFSP Index in Use Validity Time applies only to EPS but not to 5GS, therefore in the case of mobility from EPS to 5GS, the RFSP Index in Use Validity Time if received from MME is ignored by the AMF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.2.2 Mobility for UEs in single-registration mode | When the UE supports single-registration mode and network supports interworking procedure with the N26 interface:
- For idle mode mobility from 5GS to EPS, the UE performs either TAU or Attach procedure with EPS GUTI mapped from 5G-GUTI sent as old Native GUTI, as described in clause 4.11.1.3.2.1 of TS 23.502 [3] and indicates that it is moving from 5GC. The UE includes in the RRC message a GUMMEI mapped from the 5G-GUTI and indicates it as a native GUMMEI and should in addition indicate it as "Mapped from 5G-GUTI". The MME retrieves the UE's MM and SM context from 5GC. For connected mode mobility from 5GS to EPS, either inter-system handover or RRC Connection Release with Redirection to E-UTRAN is performed. At inter-system handover, the AMF selects target MME based on 2 octet TAC format used in the Target ID as specified in TS 38.413 [34]. During the TAU or Attach procedure the HSS+UDM cancels any AMF registration associated with the 3GPP access (but not AMF registration associated with the non-3GPP access): an AMF that was serving the UE over both 3GPP and non-3GPP accesses does not consider the UE as deregistered over non 3GPP access.
- For the first TAU after 5GC initial Registration, the UE and MME for the handling of UE Radio Capabilities follow the procedures as defined in clause 5.11.2 of TS 23.401 [26] for first TAU after GERAN/UTRAN Attach.
NOTE 1: MMEs supporting interworking with N26 interface are not required to process the indication from the UE that it is moving from 5GC and will assume that the UE is moving from another MME.
- For idle mode mobility from EPC to 5GC, the UE performs mobility Registration procedure with the 5G GUTI mapped from EPS GUTI and indicates that it is moving from EPC. The UE derives GUAMI from the native 5G-GUTI and includes GUAMI in the RRC message to enable RAN to route to the corresponding AMF (if available). If the UE holds no native 5G-GUTI, then the UE provides in the RRC message a GUAMI mapped from the EPS GUTI and indicates it as "Mapped from EPS". The AMF and SMF retrieve the UE's MM and SM context from EPC. For connected mode mobility from EPC to 5GC, either inter-system handover or RRC Connection Release with Redirection to NG-RAN is performed. At inter-system handover, the MME selects target AMF based on TAC used in the Target ID as specified in TS 38.413 [34]. During the Registration procedure, the HSS+UDM cancels any MME registration.
NOTE 2: During a transition period, the source eNB may be configured via O&M to know that the MME is not upgraded and thus supports only 2 octet TAC. The Target ID for the NG-RAN node is set as "Target eNB ID" in the existing IEs as defined in TS 38.413 [34].
For both idle mode and connected mode mobility from EPC to 5GC:
- The UE includes the native 5G-GUTI as an additional GUTI in the Registration request; the AMF uses the native 5G-GUTI to retrieve MM context identified by the 5G-GUTI from old AMF or from UDSF (if UDSF is deployed and the old AMF is within the same AMF set).
- If this is the first mobility event for a PDU Session that was established while being connected to EPC, the UE shall trigger the PDU Session Modification procedure and:
- should indicate the support of Reflective QoS to the network (i.e. SMF) if the UE supports Reflective QoS functionality. If the UE indicated support of Reflective QoS, the network may provide a Reflective QoS Timer (RQ Timer) value to the UE;
- shall indicate the number of supported packet filters for signalled QoS rules, if the UE supports more than 16 packet filters for the PDU Session. The network shall store this information so that subsequent mobility events do not require another signalling of it.
- should indicate the support of Multi-homed IPv6 PDU session to the network (i.e. SMF) if the UE supports Multi-homed IPv6 PDU session. If the UE indicated support of Multi-homed IPv6 PDU session, the network shall consider that this PDU session is supported to use multiple IPv6 prefixes.
- should provide the UE Integrity Protection Maximum Data Rate to the network (i.e. SMF). The network shall consider that the maximum data rate per UE for user-plane integrity protection supported by the UE is valid for the lifetime of the PDU session. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.3 Interworking Procedures without N26 interface | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.17.2.3.1 General | For interworking without the N26 interface, IP address preservation is provided to the UEs on inter-system mobility by storing and fetching SMF+PGW-C and corresponding APN/DNN information via the HSS+UDM. In such networks AMF also provides an indication that interworking without N26 is supported to UEs during Initial Registration in 5GC or MME may optionally provide an indication that interworking without N26 is supported in the Attach procedure in EPC as defined in TS 23.502 [3] and TS 23.401 [26]. The UE provides an indication that it supports Request Type flag "handover" for PDN connectivity request during the attach procedure as described in clause 5.3.2.1 of TS 23.401 [26] and during initial Registration and Mobility Registration Update in 5GC.
NOTE 1: The UE support of Request Type flag "handover" for PDN connectivity request during the attach procedure is needed for IP address preservation in the case of interworking without N26.
The indication that interworking without N26 is valid for the entire Registered PLMN and for PLMNs equivalent to the Registered PLMN that are available in the Registration Area. The same indication is provided to all UEs served by the same PLMN. UEs that operate in interworking without N26 may use this indication to decide whether to register early in the target system. UEs that only support single registration mode may use this indication as described in clause 5.17.2.3.2. UE that support dual registration mode uses this indication as described in clause 5.17.2.3.3.
Interworking procedures without N26 interface use the following two features:
1. When UE performs Initial Attach in EPC (with or without "Handover" indication in PDN CONNECTIVITY Request message) and indicates that it is moving from 5GC, the MME indicates to the HSS+UDM not to cancel the registration of AMF, if any.
2. When UE performs Initial Registration in 5GC and indicates that it is moving from EPC, the AMF indicates to the HSS+UDM not to cancel the registration of MME, if any.
To support mobility both for single and dual registration mode UEs, the following also are supported by the network:
3. When PDU Session are created in 5GC, the SMF+PGW-C which supports EPS interworking stores the SMF+PGW-C FQDN along with DNN in the HSS+UDM.
4. The HSS+UDM provides the information about dynamically allocated SMF+PGW-C and APN/DNN information to the target CN network. If there are multiple SMF+PGW-C serving the UE for the same DNN which support EPS interworking in 5GS, the HSS+UDM select one of them according to operator's policy and provides together with the associated APN to the MME.
5. When PDN connections are created in EPC, the MME stores the SMF+PGW-C and APN information in the HSS+UDM.
NOTE 2: Items 3, 4 and 5 are also supported in networks that support interworking with N26 procedures. This enables a VPLMN that does not deploy N26 interface to provide IP address preservation to roamed-in single-registration mode UEs from a HPLMN that only supports interworking with N26 procedures.
When the network serving the UE supports 5GS-EPS interworking procedures without N26 interface, the SMF shall not provide the UEs with mapped target system parameters of the target system when UE is in the source network.
A UE that operates in dual registration mode ignores any received mapped target system parameters (e.g. QoS parameters, bearer IDs/QFI, PDU Session ID, etc.). |
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