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fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.2 Multi Access PDU Sessions | A Multi-Access PDU (MA PDU) Session is managed by using the session management functionality specified in clause 5.6, with the following additions and modifications:
- When the UE wants to request a new MA PDU Session:
- If the UE is registered to the same PLMN over 3GPP and non-3GPP accesses, then the UE shall send a PDU Session Establishment Request over any of the two accesses. The UE also provides Request Type as "MA PDU Request" in the UL NAS Transport message. The AMF informs the SMF that the UE is registered over both accesses and this triggers the establishment of user-plane resources on both accesses and two N3/N9 tunnels between PSA and the RAN/AN.
- If the UE is registered to different PLMNs over 3GPP and non-3GPP accesses, then the UE shall send a PDU Session Establishment Request over one access. The UE also provides Request Type as "MA PDU Request" in the UL NAS Transport message. After this PDU Session is established with one N3/N9 tunnel between the PSA and (R)AN established, the UE shall send another PDU Session Establishment Request over the other access. The UE also provides the same PDU Session ID and Request Type as "MA PDU Request" in the UL NAS Transport message. Two N3/N9 tunnels and User-plane resources on both accesses are established.
- If the UE is registered over one access only, then the UE shall send a PDU Session Establishment Request over this access. The UE also provides Request Type as "MA PDU Request" in the UL NAS Transport message. One N3/N9 tunnel between the PSA and (R)AN and User-plane resources on this access only are established. After the UE is registered over the second access, the UE shall establish user-plane resources on the second access.
- In the PDU Session Establishment Request that is sent to request a new MA PDU Session, the UE shall provide also its ATSSS capabilities, which indicate the steering functionalities and the steering modes supported in the UE. These functionalities are defined in clause 5.32.6.
- If the UE indicates it is capable of supporting:
- the "ATSSS-LL functionality with any steering mode" (as specified in clause 5.32.6.1);
and the network accepts to activate this functionality, then the network may provide to UE Measurement Assistance Information (see details in clause 5.32.5) and shall provide to UE one or more ATSSS rules.
NOTE 1: As specified in Table 5.32.8-1 and in Table 5.8.5.8-1, the ATSSS-LL functionality cannot be used together with the Redundant steering mode. When the UE indicates it is capable of supporting the ATSSS-LL functionality with any steering mode, it is implied that the UE can support the ATSSS-LL functionality with any steering mode except the Redundant steering mode.
- If the UE indicates it is capable of supporting:
- the "MPTCP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode (as specified in clause 5.32.6.1);
and the network accepts to activate these functionalities, then the network provides MPTCP proxy information to UE and allocates to UE (a) one IP address/prefix for the MA PDU session (as defined in clause 5.8.2.2) and (b) two additional IP addresses/prefixes, called "MPTCP link-specific multipath" addresses. Further details are provided in clause 5.32.6.2.1. In addition, the network may provide to UE Measurement Assistance Information and shall provide to UE one or more ATSSS rules. The network shall provide to UE ATSSS rule(s) for non-MPTCP traffic. The ATSSS rule(s) for non-MPTCP traffic shall use the ATSSS-LL, MPQUIC-UDP and/or MPQUIC-IP steering functionality(ies) depending on what is supported and selected for the MA PDU Session.
If the network accepts to activate only ATSSS-LL functionality with only the Active-Standby steering mode, the network shall provide to the UE an ATSSS rule that uses the ATSSS-LL functionality and the Active-Standby Steering Mode, to indicate how the traffic shall be transferred across the 3GPP access and the non-3GPP access in the uplink direction.
- If the UE indicates it is capable of supporting
- the "MPQUIC-UDP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode" (as specified in clause 5.32.6.1);
and the network accepts to activate these functionalities, then the network provides MPQUIC-UDP proxy information to UE and allocates to UE (a) one IP address/prefix for the MA PDU session (as defined in clause 5.8.2.2) and (b) two additional IP addresses/prefixes, called "MPQUIC link-specific multipath" addresses. Further details are provided in clause 5.32.6.2.2. In addition, the network may provide to UE Measurement Assistance Information and shall provide to UE one or more ATSSS rules. The network shall provide to UE an ATSSS rule(s) for non-MPQUIC-UDP traffic. The ATSSS rule(s) for non-MPQUIC-UDP traffic shall use the ATSSS-LL, MPTCP and/or MPQUIC-IP steering functionality(ies) depending on what is supported and selected for the MA PDU Session.
If the network accepts to activate only ATSSS-LL functionality with only the Active-Standby steering mode, the network shall provide to the UE an ATSSS rule that uses the ATSSS-LL functionality and the Active-Standby Steering Mode, to indicate how the traffic shall be transferred across the 3GPP access and the non-3GPP access in the uplink direction.
- If the UE indicates it is capable of supporting:
- the "MPQUIC-IP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1);
and the network accepts to activate these functionalities, then the network provides MPQUIC proxy information to UE and allocates to UE (a) one IP address/prefix for the MA PDU session (as defined in clause 5.8.2.2) and (b) two additional IP addresses/prefixes, called "MPQUIC link-specific multipath" addresses. Further details are provided in clause 5.32.6.2.2. In addition, the network may provide to UE Measurement Assistance Information and shall provide to UE one or more ATSSS rules.
If the network accepts to activate only ATSSS-LL functionality with only the Active-Standby steering mode, the network shall provide to the UE an ATSSS rule that uses the ATSSS-LL functionality and the Active-Standby Steering Mode, to indicate how the traffic shall be transferred across the 3GPP access and the non-3GPP access in the uplink direction.
- If the UE indicates it is capable of supporting:
- the "MPQUIC-E functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1);
and the network accepts to activate MPQUIC-E functionality, then the network provides MPQUIC proxy information to UE and allocates to UE two IP addresses/prefixes, called "MPQUIC link-specific multipath" addresses. Further details are provided in clause 5.32.6.2.2. In addition, the network shall provide to UE one or more ATSSS rules.
If the network accepts to activate only ATSSS-LL functionality with only the Active-Standby steering mode, the network shall provide to the UE an ATSSS rule that uses the ATSSS-LL functionality and the Active-Standby Steering Mode, to indicate how the traffic shall be transferred across the 3GPP access and the non-3GPP access in the uplink direction. In addition, the network may provide to UE Measurement Assistance Information.
- If the UE indicates it is capable of supporting:
- the "MPQUIC-IP functionality with any steering mode without any ATSSS-LL functionality" (as specified in clause 5.32.6.1);
and the network accepts to activate MPQUIC-IP functionality, then the network provides MPQUIC proxy information to UE and allocates to UE (a) one IP address/prefix for the MA PDU session (as defined in clause 5.8.2.2) and (b) two additional IP addresses/prefixes, called "MPQUIC link-specific multipath" addresses. In addition, the network shall provide to UE one or more ATSSS rules.
NOTE 2: The "MPTCP link-specific multipath" addresses and the "MPQUIC link-specific multipath" addresses can be the same.
- If the UE requests an S-NSSAI, this S-NSSAI should be allowed on both accesses. Otherwise, the MA PDU Session shall not be established.
- The SMF determines the ATSSS capabilities supported for the MA PDU Session taking into consideration one or more of the following aspects based on the ATSSS capabilities provided by the UE and per DNN configuration on SMF:
a) If the UE includes in its ATSSS capabilities "MPTCP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1), then:
i) If the DNN configuration allows MPTCP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL), including RTT measurement without using PMF protocol, the MA PDU Session is capable of (1) MPTCP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL) in the downlink and (2) MPTCP and ATSSS-LL with Active-Standby mode in the uplink.
NOTE 3: In this case, it is assumed that ATSSS-LL with "Smallest Delay" steering mode is selected for the downlink only when the UPF can measure RTT without using the PMF protocol, e.g. by using other means not defined by 3GPP such as using the RTT measurements of MPTCP.
ii) If the DNN configuration allows MPTCP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL), but not RTT measurement without using PMF protocol, the MA PDU Session is capable of (1) MPTCP in the downlink (2) ATSSS-LL with any steering mode except Smallest Delay steering mode (i.e. any Steering Mode allowed for ATSSS-LL except Smallest Delay steering mode) in the downlink and (3) MPTCP and ATSSS-LL with Active-Standby mode in the uplink.
iii) If the DNN configuration allows MPTCP with any steering mode and ATSSS-LL with only Active-Standby steering mode, the MA PDU Session is capable of MPTCP and ATSSS-LL with Active-Standby mode in the uplink and in the downlink.
iv) If the DNN configuration does not allow MPTCP steering functionality and the DNN configuration allows ATSSS-LL functionality with at least the Active-Standby steering mode, then the MA PDU Session is capable of ATSSS-LL with only Active-Standby steering mode in the uplink and in the downlink.
b) If the UE includes in its ATSSS capabilities "MPQUIC-UDP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1), then:
i) If the DNN configuration allows MPQUIC-UDP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL), including RTT measurement without using PMF protocol, the MA PDU Session is capable of (1) MPQUIC-UDP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL) in the downlink and (2) MPQUIC-UDP and ATSSS-LL with Active-Standby mode in the uplink.
NOTE 4: In this case, it is assumed that ATSSS-LL with "Smallest Delay" steering mode is selected for the downlink only when the UPF can measure RTT without using the PMF protocol, e.g. by using other means not defined by 3GPP such as using the RTT measurements of MPQUIC.
ii) If the DNN configuration allows MPQUIC-UDP and ATSSS-LL with any steering mode (i.e. any Steering Mode allowed for ATSSS-LL), but not RTT measurement without using PMF protocol, the MA PDU Session is capable of (1) MPQUIC-UDP in the downlink (2) ATSSS-LL with any steering mode except Smallest Delay steering mode (i.e. any Steering Mode allowed for ATSSS-LL except Smallest Delay steering mode) in the downlink and (3) MPQUIC-UDP and ATSSS-LL with Active-Standby mode in the uplink.
iii) If the DNN configuration allows MPQUIC-UDP with any steering mode and ATSSS-LL with only Active-Standby steering mode, the MA PDU Session is capable of MPQUIC-UDP and ATSSS-LL with Active-Standby mode in the uplink and in the downlink.
iv) If the DNN configuration does not allow MPQUIC-UDP steering functionality and the DNN configuration allows ATSSS-LL functionality with at least the Active-Standby steering mode, then the MA PDU Session is capable of ATSSS-LL with only Active-Standby steering mode in the uplink and in the downlink.
c) If the UE includes in its ATSSS capabilities "ATSSS-LL functionality with any steering mode" (as specified in clause 5.32.6.1) and the DNN configuration allows ATSSS-LL with any steering mode allowed for ATSSS-LL, the MA PDU Session is capable of ATSSS-LL with any steering mode allowed for ATSSS-LL in the uplink and in the downlink.
d) If the UE includes in its ATSSS capabilities "MPQUIC-IP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1) and the DNN configuration allows MPQUIC-IP functionality with any steering mode, the MA PDU Session is capable of MPQUIC-IP functionality with any steering mode in the uplink and in the downlink. If the DNN configuration does not allow MPQUIC-IP steering functionality and the DNN configuration allows ATSSS-LL functionality with at least the Active-Standby steering mode, then the MA PDU Session is capable of ATSSS-LL with only Active-Standby steering mode in the uplink and in the downlink.
e) If the UE includes in its ATSSS capabilities "MPQUIC-E functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" (as specified in clause 5.32.6.1) and the DNN configuration allows MPQUIC-E functionality with any steering mode, the MA PDU Session is capable of MPQUIC-E functionality with any steering mode in the uplink and in the downlink. If the DNN configuration does not allow MPQUIC-E steering functionality and the DNN configuration allows ATSSS-LL functionality with at least the Active-Standby steering mode, then the MA PDU Session is capable of ATSSS-LL with only Active-Standby steering mode in the uplink and in the downlink.
f) If the UE includes in its ATSSS capabilities "MPQUIC-IP functionality with any steering mode without any ATSSS-LL functionality" (as specified in clause 5.32.6.1) and the DNN configuration allows MPQUIC-IP functionality with any steering mode, the MA PDU Session is capable of MPQUIC-IP functionality with any steering mode in the uplink and in the downlink. If the DNN configuration does not allow MPQUIC-IP steering functionality, then the SMF rejects the MA PDU Session request.
NOTE 5: As described above, an example of how SMF determines the ATSSS capabilities of a MA PDU Session is as follows:
- If the UE indicates that it supports "MPTCP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" and "MPQUIC-UDP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" and "MPQUIC-IP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode" and the DNN configuration allows only MPTCP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode, then the MA PDU Session is capable of MPTCP and ATSSS-LL with Active-Standby mode in the uplink and in the downlink.
NOTE 6: MPQUIC-E functionality is enabled only when the type of the MA PDU Session is Ethernet. The MPTCP, MPQUIC-UDP and MPQUIC-IP functionalities are not enabled when the type of the MA PDU Session is Ethernet.
For ATSSS-LL with only Active-Standby steering mode, the UE and the UPF needs to support Access Availability/Unavailability Report as specified in clause 5.32.5.3.
The SMF provides the ATSSS capabilities of the MA PDU Session to the PCF during PDU Session Establishment.
- The PCC rules provided by PCF include MA PDU Session Control information (see TS 23.503 [45]). They are used by SMF to derive ATSSS rules for the UE and N4 rules for the UPF. When dynamic PCC is not used for the MA PDU Session, the SMF shall provide ATSSS rules and N4 rules based on local configuration (e.g. based on DNN or S-NSSAI).
- The UE receives ATSSS rules from SMF, which indicate how the uplink traffic should be routed across 3GPP access and non-3GPP access. Similarly, the UPF receives N4 rules from SMF, which indicate how the downlink traffic should be routed across 3GPP access and non-3GPP access.
- When the SMF receives a PDU Session Establishment Request and a "MA PDU Request" indication and determines that UP security protection (see clause 5.10.3) is required for the PDU Session, the SMF shall only confirm the establishment of the MA PDU session if the 3GPP access network can enforce the required UP security protection. The SMF needs not confirm whether the non-3GPP access can enforce the required UP security protection.
- The UE indicates during MA PDU Session Establishment to the AMF whether it supports non-3GPP access path switching, i.e. whether the UE can transfer the non-3GPP access path of the MA PDU Session from a source non-3GPP access (N3IWF/TNGF) to a target non-3GPP access (a different N3IWF/TNGF). If the UE has indicated support for non-3GPP access path switching and the AMF supports non-3GPP access path switching, the AMF selects an SMF that supports non-3GPP access path switching, if such an SMF is available. If the AMF supports to maintain two N2 connections for non-3GPP access during the Registration procedure and the selected SMF supports non-3GPP path switching, the AMF indicates whether the UE supports non-3GPP path switching to the SMF. The SMF indicates support for non-3GPP path switching to the UE in the PDU Session Establishment Accept message.
NOTE 7: If the AMF selects an SMF not supporting non-3GPP access path switching, the non-3GPP access path switching can still be performed with the AMF triggering release of the old user plane resources before new user plane resources are established.
- After the MA PDU Session establishment:
- At any given time, the MA PDU session may have user-plane resources on both 3GPP and non-3GPP accesses, or on one access only, or may have no user-plane resources on any access.
- The AMF, SMF, PCF and UPF maintain their MA PDU Session contexts, even when the UE deregisters from one access (but remains registered on the other access).
- When the UE deregisters from one access (but remains registered on the other access), the AMF informs the SMF to release the resource of this access type in the UPF for the MA PDU Session. Subsequently, the SMF notifies the UPF that the access type has become unavailable and the N3/N9 tunnel for the access type are released.
- If the UE wants to add user-plane resources on one access of the MA PDU Session, e.g. based on access network performance measurement and/or ATSSS rules, then the UE shall send a PDU Session Establishment Request over this access containing PDU Session ID of the MA PDU Session. The UE also provides Request Type as "MA PDU Request" and the same PDU Session ID in the UL NAS Transport message. If there is no N3/N9 tunnel for this access, the N3/N9 tunnel for this access is established.
- If the UE wants to re-activate user-plane resources on one access of the MA PDU Session, e.g. based on access network performance measurement and/or ATSSS rules, then the UE shall initiate the UE Triggered Service Request procedure over this access.
- If the network wants to re-activate the user-plane resources over 3GPP access or non-3GPP access of the MA PDU Session, the network shall initiate the Network Triggered Service Request procedure, as specified in clause 4.22.7 of TS 23.502 [3].
- If the UE wants to move the non-3GPP user-plane resources of the MA PDU Session from a source non-3GPP access (e.g. source N3IWF or TNGF) to a target non-3GPP access (e.g. target N3IWF or TNGF), the UE initiates a Mobility Registration Update via the target non-3GPP access as described in TS 23.502 [3], clause 4.22.9.5. This procedure may also be used to move the non-3GPP user-plane resources of single access PDU Session(s).
NOTE 8: The UE can request activation of single access PDU Session(s) over the target non-3GPP access while performing Mobility Registration Update procedure according to the existing procedure.
- The SMF may add, remove or update one or more individual ATSSS rules of the UE by sending new or updated ATSSS rules with the corresponding Rule IDs to the UE.
A MA PDU Session may be established either:
a) when it is explicitly requested by an ATSSS-capable UE; or
b) when an ATSSS-capable UE requests a single-access PDU Session but the network decides to establish a MA PDU Session instead. This is an optional scenario specified in clause 4.22.3 of TS 23.502 [3], which may occur when the UE requests a single-access PDU Session but no policy (e.g. no URSP rule) and no local restrictions in the UE mandate a single access for the PDU Session.
A MA PDU Session may be established during a PDU Session modification procedure when the UE moves from EPS to 5GS, as specified in clause 4.22.6.3 of TS 23.502 [3].
The AMF indicates as part of the Registration procedure whether ATSSS is supported or not. When ATSSS is not supported, the UE shall not
- request establishment of a MA PDU Session (as described in clause 4.22.2 of TS 23.502 [3]); or
- request addition of User Plane resources for an existing MA PDU Session (as described in clause 4.22.7 of TS 23.502 [3]); or
- request establishment of a PDU Session with "MA PDU Network-Upgrade Allowed" indication (as described in clause 4.22.3 of TS 23.502 [3]); or
- request PDU Session Modification with Request Type of "MA PDU request" or with "MA PDU Network-Upgrade Allowed" indication after moving from EPC to 5GC (as described in clause 4.22.6.3 of TS 23.502 [3]).
The AMF indicates as part of the Registration procedure whether it supports non-3GPP access path switching. When the AMF does not indicate support of non-3GPP access path switching, the UE shall not perform the Mobility Registration Update procedure for non-3GPP access path switching, i.e. to switch traffic from a source non-3GPP access to a target non-3GPP access. The SMF indicates as part of the PDU Session Establishment procedure whether it supports non-3GPP access path switching. If the UE has one or more PDU sessions and at least one serving SMF for the PDU Sessions supports non-3GPP access path switching, the UE may include ("Non-3GPP path switching while using old AN resources") indication when the UE performs the Mobility Registration Update procedure for non-3GPP access path switching. If the UE is registered to different PLMNs over 3GPP and non-3GPP accesses, the UE shall use the capability received over non-3GPP access to determine whether to perform the Mobility Registration Update procedure for non-3GPP path switching and whether to include ("Non-3GPP access path switching while using old AN resources") indication.
NOTE 9: If the AMF receives ("Non-3GPP path switching while using old AN resources") indication from Mobility Registration Update procedure and the serving SMF(s) for PDU Session(s) is not supporting non-3GPP access path switching, the non-3GPP access path switching can still be performed with the AMF triggering for each PDU Session the release of the old user plane resources before new user plane resources are established.
An ATSSS-capable UE may decide to request a MA PDU Session based on the provisioned URSP rules. In particular, the UE should request a MA PDU Session when the UE applies a URSP rule, which triggers the UE to establish a new PDU Session and the Access Type Preference component of the URSP rule indicates "Multi-Access" (see TS 23.503 [45]). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.3 Policy for ATSSS Control | If dynamic PCC is to be used for the MA PDU Session, the PCF may take ATSSS policy decisions and create PCC rules that contain MA PDU Session Control information, (as specified in TS 23.503 [45]), which determines how the uplink and the downlink traffic of the MA PDU Session should be distributed across the 3GPP and non-3GPP accesses. If dynamic PCC is not deployed, local policy in SMF is used.
The SMF receives the PCC rules with MA PDU Session Control information and maps these rules into (a) ATSSS rules, which are sent to the UE and (b) N4 rules, which are sent to the UPF. The ATSSS rules are provided as a prioritized list of rules (see clause 5.32.8), which are applied by the UE to enforce the ATSSS policy in the uplink direction and the N4 Rules are applied by the UPF to enforce the ATSSS policy in the downlink direction.
The ATSSS rules are sent to UE with a NAS message when the MA PDU Session is created or updated by the SMF, e.g. after receiving updated/new PCC rules from the PCF. Similarly, the N4 rules are sent to UPF when the MA PDU Session is created or updated by the SMF.
The details of the policy control related to ATSSS are specified in TS 23.503 [45]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.4 QoS Support | The 5G QoS model for the Single-Access PDU Session is also applied to the MA PDU Session, i.e. the QoS Flow is the finest granularity of QoS differentiation in the MA PDU Session. One difference compared to the Single-Access PDU Session is that in a MA PDU Session there can be separate user-plane tunnels between the AN and the PSA, each one associated with a different access. However, the QoS Flow is not associated with specific access, i.e. it is access agnostic, so the same QoS is supported when the traffic is distributed over 3GPP and non-3GPP accesses. The SMF shall provide the same QFI in 3GPP and non-3GPP accesses so that the same QoS is supported in both accesses.
A QoS Flow of the MA PDU Session may be either Non-GBR or GBR depending on its QoS profile.
For a Non-GBR QoS Flow, the SMF provides a QoS profile to both 5G-ANs during MA PDU Session Establishment or MA PDU Session Modification procedure:
- During MA PDU Session Establishment procedure, the QoS profile to both ANs if the UE is registered over both accesses.
- During MA PDU Session Modification procedure, the QoS profile is provided to the 5G-AN(s) over which the user plane resources are activated.
For a GBR QoS Flow, the SMF shall provide a QoS profile to 5G-AN(s) as follows:
- If the PCC rule allows a GBR QoS Flow in a single access, the SMF provides the QoS profile for the GBR QoS Flow to the access network allowed by the PCC rule.
- If the PCC rule allows a GBR QoS Flow in both accesses and the Steering Mode is different from Redundant, the SMF decides to which access network to provide the QoS profile for the GBR QoS Flow based on its local policy (e.g. the access where the traffic is ongoing according to the Multi Access Routing rule).
- If the PCC rule allows a GBR QoS Flow in both accesses and the Steering Mode is Redundant, the SMF provides the QoS profile for the GBR QoS Flow to both access networks. Whenever the SMF recognizes that resources are not allocated in one access network, the SMF shall notify the PCF about the resource allocation failure and indicate the respective Access Type. Whenever the SMF recognizes that resources are not allocated in both access networks, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
NOTE 1: The SMF knows about the allocation of resources in an access network from the interaction with the access network during GBR QoS Flow establishment/modification as well as during the release of resources by the access network.
For a GBR QoS Flow, traffic splitting is not supported. If the UPF determines that it cannot send GBR traffic over the current ongoing access e.g. based on the N4 rules and access availability and unavailability report from the UE as described in clause 5.32.5.3, the UPF shall send an Access Availability report to the SMF.
Based on the Access Availability report and if the Steering Mode is different from Redundant, the SMF decides whether to move GBR QoS Flows to the other access when one access is not available:
- if the PCC rule allows the GBR QoS Flows only on this access, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
- if the corresponding PCC rule allows the GBR QoS Flow on both accesses and the other access is not available, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
- if the PCC rule allows the GBR QoS Flow on both accesses and the other access is available, the SMF shall try to move the GBR QoS Flow to the other access. The SMF may trigger a PDU session modification procedure to provide the QoS profile to the other access and release the resources for the GBR QoS Flow in the current access.
- if Notification Control parameter is not included in the PCC rule for the GBR QoS Flow and the other access does not accept the QoS profile, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
- if the Notification Control parameter is included in the PCC rule, the SMF shall notify the PCF that GFBR can no longer be guaranteed. After the other access accepts the QoS profile, the SMF shall notify the PCF that GFBR can again be guaranteed. If the other access does not accept the QoS profile, the SMF shall delete the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
NOTE 2: The ATSSS rule for GBR QoS Flow only allows the UE to steer traffic over a single access so that the network knows in which access the UE sends GBR traffic. If the network wants to move GBR QoS Flow to the other access, the network needs to update ATSSS rule of the UE.
Based on the Access Availability report and if the Steering Mode is Redundant, the SMF behaves as follows:
- if both accesses are not available, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
NOTE 3: The UPF can detect that both accesses are not available based on implementation specific means.
- when one of the accesses becomes unavailable while the other access is still available, the SMF shall neither release the resources for the GBR QoS Flow nor notify the PCF that GFBR can no longer be guaranteed (if the Notification Control parameter is included in the PCC rule).
NOTE 4: The access network will typically release the resources for a GBR QoS Flow if there is no traffic transferred for a certain amount of time and this will then trigger the SMF notification to PCF described above.
When the MA PDU Session is established or when the MA PDU Session is modified, the SMF may provide QoS rule(s) to the UE via one access, which are applied by the UE as specified in clause 5.7.1.4. The QoS rule(s) provided by SMF via one access are commonly used for both 3GPP access and non-3GPP access, so the QoS classification is independent of ATSSS rules.
The derived QoS rule generated by Reflective QoS is applied independently of the access on which the RQI was received. When any of the MPTCP functionality, MPQUIC-UDP functionality or the MPQUIC-IP functionality is used in the UE, the UE shall use the IP address/prefix of the MA PDU Session and the final destination address to generate the derived QoS rule.
When any of the MPTCP functionality, MPQUIC-UDP functionality or MPQUIC-IP functionality is enabled for the MA PDU Session:
- any QoS rules or PDRs that apply to the MA PDU Session IP address/prefix and port also apply (a) to the MPTCP "link-specific multipath" IP addresses/prefixes and ports used by the UE to establish MPTCP subflows over 3GPP and non-3GPP accesses and (b) to the "MPQUIC link-specific multipath" IP addresses/prefixes and ports used by the UE to transmit UDP/IP flows over 3GPP and non-3GPP accesses; and
- any QoS rules or PDRs that apply to the IP address/prefix and port of the final destination server in DN also apply (a) to the IP address and port of the MPTCP proxy for corresponding MPTCP subflows that are terminated at the proxy; and (b) to the IP address and port of the MPQUIC proxy for corresponding UDP/IP flows that are terminated at the proxy.
When the MPQUIC-E functionality is enabled for the MA PDU Session:
- any QoS rules or PDRs that apply to the source MAC address for the MA PDU Session of Ethernet type also apply to the "MPQUIC link-specific multipath" IP addresses/prefixes and ports used by the UE to transmit Ethernet flows over 3GPP and non-3GPP accesses.
- any QoS rules or PDRs that apply to the destination MAC address of the server in DN for the MA PDU Session of Ethernet type also apply to the IP address and port of the MPQUIC proxy for corresponding Ethernet flows that are terminated at the proxy.
NOTE 5: How these associations are made when the MPTCP functionality, MPQUIC-UDP functionality, MPQUIC-IP functionality or MPQUIC-E functionality is enabled for the MA PDU session is left up to the UE and UPF implementations. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5 Access Network Performance Measurements | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.1 General principles | When an MA PDU Session is established, the network may provide the UE with Measurement Assistance Information. This information assists the UE in determining which measurements shall be performed over both accesses, as well as whether measurement reports need to be sent to the network.
Measurement Assistance Information shall include the addressing information of a Performance Measurement Function (PMF) in the UPF, the UE can send PMF protocol messages to:
- For a PDU Session of IP type, Measurement Assistance Information contains one IP address for the PMF, one UDP port associated with 3GPP access and another UDP port associated with non-3GPP access. PMF messages sent by UE to one of these UDP ports, shall be transmitted to UPF via the QoS Flow associated with the default QoS rule.
- For a PDU Session of Ethernet type, Measurement Assistance Information contains one MAC address associated with 3GPP access and another MAC address associated with non-3GPP access. PMF messages sent by UE to one of these MAC addresses, shall be transmitted to UPF via the QoS Flow associated with the default QoS rule.
NOTE 1: To protect the PMF in the UPF (e.g. to block DDOS to the PMF), the IP addresses of the PMF are only accessible from the UE IP address via the N3/N9 interface.
NOTE 2: After the MA PDU Session is released, the same UE IP address/prefix is not allocated to another UE for MA PDU Session in a short time.
If the SMF determines that access performance measurements per QoS Flow shall be applied for the MA PDU Session, then the Measurement Assistance Information shall also include a list of QoS Flows on which access performance measurements may be performed. For each QoS Flow in this list, the following information is included:
- The QFI of the associated QoS Flow.
- For a PDU Session of IP type, one UDP port associated with 3GPP access and another UDP port associated with non-3GPP access. PMF messages sent by UE to one of these UDP ports, shall be transmitted to UPF via the associated QoS Flow.
- For a PDU Session of Ethernet type, one MAC address associated with 3GPP access and another MAC address associated with non-3GPP access. PMF messages sent by UE to one of these MAC addresses, shall be transmitted to UPF via the associated QoS Flow.
The QoS rules and the N4 rules provided by SMF to UE and to UPF respectively shall include information (e.g. packet filters containing the UDP port or the MAC address associated with a QoS Flow), which enables the UE and UPF to route a PMF message to a specific QoS Flow.
The UE and the UPF may need to perform access performance measurements in order to estimate the Round-Trip Time (RTT) and/or the Packet Loss Rate (PLR) that an SDF is expected to experience when transmitted on a certain access type. Based on these measurements and the provisioned ATSSS rules in the UE and MAR rules in the UPF, the UE and the UPF decide how to distribute the traffic of an SDF across the two accesses.
If the UE and the UPF decide to initiate access performance measurements to estimate the RTT and/or the PLR for an SDF, the access performance measurements shall be performed either
(a) using the QoS Flow associated with the default QoS rule; or
(b) using the target QoS Flow, which is the QoS Flow that the SDF traffic is transmitted on.
When the access performance measurements are using the target QoS Flow, it is termed that "access performance measurements per QoS Flow" are applied for the MA PDU Session.
The UE shall indicate in its ATSSS capabilities that it supports access performance measurements per QoS Flow. Based on this UE capability and other information (such as local policy), the SMF determines whether access performance measurements per QoS Flow shall be applied for the MA PDU Session or not. If the SMF determines that access performance measurements per QoS Flow shall be applied for the MA PDU Session, then:
- The SMF determines a list of QoS Flows over which access performance measurements may be performed and provides this list to the UE (within the Measurement Assistance Information) and to the UPF.
- The UE and the UPF may initiate access performance measurements on one or more of the QoS Flows included in this list. The UE and the UPF shall be able to receive and respond to PMF messages sent on any QoS Flow included in this list.
- The SMF may update the list of QoS Flows over which access performance measurements may be performed during the lifetime of a MA PDU Session, e.g. when a new PCC rule that could benefit from PMF access performance measurements is bound to a QoS Flow.
NOTE 3: The SMF can e.g. add a QoS Flow into the list when at least one PCC Rule is bound to that QoS Flow that is using one of the Steering Modes where performance measurements via PMF are applicable, such as Lowest Delay Steering Mode or a Steering Mode where threshold values have been provided.
The UE shall perform access performance measurements per QoS Flow only when this is explicitly indicated in the Measurement Assistance Information, i.e. only when the UE receives the list of QoS Flows over which access performance measurements may be performed. Otherwise, the UE shall perform access performance measurements based on the QoS Flow associated with the default QoS rule. The UPF shall perform access performance measurements per QoS Flow only when this is explicitly indicated by SMF, i.e. only when the UPF receives the list of QoS Flows over which access performance measurements may be performed. Otherwise, the UPF shall perform access performance measurements based on the QoS Flow associated with the default QoS rule. In this case the UPF learns what QoS Flow to use as described in TS 29.244 [65].
The UE and the UPF may decide not to initiate access performance measurements using PMF over a certain target QoS Flow, when they already have access performance measurements for another target QoS Flow which they determine can be reused.
NOTE 4: How the UE and UPF determine that the performance measurements using a certain target QoS Flow apply to another target QoS Flow is based on implementation, e.g. AN resource to QoS Flow mapping in the UE or getting similar access measurements results with other QoS Flow.
When access performance measurements for an SDF are performed based on the target QoS Flow, the UE needs to be able to determine the QoS Flow a downlink packet arrives on. In order to enable this, the SMF shall include downlink Packet Filter information in the QoS rule provided to UE matching this SDF, unless Reflective QoS is used for the SDF.
NOTE 5: For example, if a QoS Flow requires to activate Reflective QoS, the SMF does not need to provide downlink QoS Flow information for the QoS Flow to minimize usage of packet filters. When a data packet is received over a QoS Flow, the UE can decide whether to check the downlink QoS Flow information based on the existence of SDAP header for the QoS Flow.
The addressing information of the PMF in the UPF is retrieved by the SMF from the UPF during N4 session establishment. If the UPF receives from the SMF, during N4 session establishment or modification procedure, a list of QoS Flows over which access performance measurements may be performed, the UPF allocates different UDP ports per QoS Flow per access for IP PDU sessions, or allocates different MAC addresses per QoS Flow per access for Ethernet PDU sessions. For IP PDU sessions, the UPF sends the PMF IP addressing information and the UDP ports with the QFI of the associated QoS Flow to the SMF. For Ethernet PDU sessions, the UPF sends the MAC addresses with the QFI of the associated QoS Flow to the SMF.
The following PMF protocol messages can be exchanged between the UE and the UPF:
- Messages to allow for Round Trip Time (RTT) measurements, i.e. when the "Smallest Delay" steering mode is used or when either "Priority-based", "Load-Balancing" or "Redundant" steering mode is used with RTT threshold value being applied;
- Messages to allow for Packet Loss Rate (PLR) measurements, i.e. when steering mode is used either "Priority-based", "Load-Balancing" or "Redundant" steering mode is used with PLR threshold value being applied;
- Messages for reporting Access availability/unavailability by the UE to the UPF.
- Messages for sending UE-assistance data to UPF. Such messages may be sent from the UE to UPF only when the UE receives the UE-assistance indicator in an ATSSS rule, as specified in clause 5.32.8. Further details are provided in clause 5.32.5.5.
- Messages for sending Suspend Traffic Duplication and Resume Traffic Duplication from UPF to UE to suspend or resume traffic duplication as defined in clause 5.32.5.6.
Since steering modes can be different in up-link and down-link, the UE needs to be able to handle PMF protocol messages for RTT and PLR measurements received from UPF even if it is not using one of the steering modes associated with the RTT and PLR measurements (and vice versa).
The PMF protocol is specified in TS 24.193 [109].
The PMF protocol messages used for access availability/unavailability reports shall be sent on the QoS Flow associated with the default QoS rule. The PMF protocol messages used for access performance measurements shall be sent either on the QoS Flow associated with the default QoS rule, or on the target QoS Flow, as specified above.
The QoS Flow associated with the default QoS rule for MA PDU Session is Non-GBR QoS Flow.
The UE shall not apply the ATSSS rules and the UPF shall not apply the MAR rules for the PMF protocol messages.
When the UE requests a MA PDU session and indicates it is capable to support one or more of the steering functionalities below:
- the "MPTCP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode" (as specified in clause 5.32.6.1);
- the "MPQUIC-UDP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode" (as specified in clause 5.32.6.1);
- the "MPQUIC-IP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode";
- the "MPQUIC-E functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode";
the network may send Measurement Assistance Information for the UE to send Access availability/unavailability reports to the UPF. In this case, the UE and UPF shall not perform RTT and PLR measurements using PMF as the UE and UPF can use measurements available at the MPTCP layer and/or at the MPQUIC layer.
5.32.5.1a Address of PMF messages
As described in clause 5.32.5.2, 5.32.5.2a and 5.32.5.3, a UE and UPF may exchange PMF messages to measure access performance and report access availability/unavailability. When the UE and UPF exchanges PMF message, source and destination address of the PMF messages shall be assigned as follows:
1. In the case of a MA PDU Session of IP type:
- If access performance measurements are performed only over the QoS Flow associated with the default QoS rule, the PMF in the UE sends PMF messages to the PMF in the UPF over UDP/IP. The destination IP address is the IP address contained in the Measurement Assistance Information and the destination UDP port is one of the two UDP ports contained in the Measurement Assistance Information. One UDP port is used for sending PMF messages to UPF over 3GPP access and the other UDP port is used for sending PMF messages to UPF over non-3GPP access. The source IP address is the IP address assigned to UE for the MA PDU Session and the source UDP port is a UDP port that is dynamically allocated by the UE for PMF communication. This source UDP port in the UE remains the same for the entire lifetime of the MA PDU Session.
If access performance measurements per QoS Flow is performed, the Measurement Assistance Information contains UDP ports, one for each QoS Flow and access combination. When the UE sends PMF message over a QoS Flow of an access, the UE shall set the destination UDP port as the UDP port for the QoS Flow and the access in Measurement Assistance information.
- If access performance measurements are performed only over the QoS Flow associated with the default QoS rule, the PMF in the UPF sends PMF messages to the PMF in the UE over UDP/IP. The source IP address is the same IP address as the one provided in the Measurement Assistance Information and the source UDP port is one of the two UDP ports as provided in the Measurement Assistance Information. One UDP port is used for sending PMF messages to UE over 3GPP access and the other UDP port is used for sending PMF messages to UE over the non-3GPP access. The destination IPv4 address is the IPv4 address assigned to UE for the MA PDU Session (if any) and the destination IPv6 address is an IPv6 address selected by the UE from the IPv6 prefix assigned for the MA PDU Session (if any). The destination UDP port is the dynamically allocated UDP port in the UE, which is contained in all PMF messages received from the UE.
If access performance measurements per QoS Flow is performed, when the UPF sends PMF message over a QoS Flow of an access, the UPF shall set the source UDP port with the UDP port for the QoS Flow and the access as the one for the QoS Flow and the access provided in Measurement Assistance information.
- If the UE receives Measurement Assistance Information, the UE shall inform the network via the user plane about the UE's dynamically allocated UDP port and the IPv6 address if IPv6 is used for PMF messages, so that it is possible for the UPF to know the UE's IPv6 address (if applicable) and dynamically allocated UDP port as soon as the MA PDU Session has been established.
NOTE 1: Regardless of whether access performance measurements per QoS Flow is applied or not, the UE only allocates a single UDP port for PMF messages.
2. In the case of a MA PDU Session of Ethernet type:
- The PMF in the UE sends PMF messages to the PMF in the UPF over Ethernet. The Ethertype is the Ethertype contained in the Measurement Assistance Information. If access performance measurements are performed only over the QoS Flow associated with the default QoS rule, the destination MAC address is one of the two MAC addresses contained in the Measurement Assistance Information. One MAC address is used for sending PMF messages to UPF over 3GPP access and the other MAC address is used for sending PMF messages to UPF over non-3GPP access. The source MAC address is a MAC address of the UE, which remains the same for the entire lifetime of the MA PDU Session.
If access performance measurements per QoS Flow is performed, Measurement Assistance Information contains MAC addresses for each QoS Flow and each access. When the UE sends PMF message over a QoS Flow of an access, the UE shall set the destination MAC address as the MAC address for the QoS Flow and the access in Measurement Assistance information.
- The PMF in the UPF sends PMF messages to the PMF in the UE over Ethernet. The Ethertype is the same Ethertype as the one provided in the Measurement Assistance Information. If access performance measurements are performed only over the QoS Flow associated with the default QoS rule, the source MAC address is one of the two MAC addresses as provided in the Measurement Assistance Information. One MAC address is used for sending PMF messages to UE over 3GPP access and the other MAC address is used for sending PMF messages to UE over non-3GPP access. The destination MAC address is the MAC address of the UE, which is contained in all PMF messages received from the UE.
If access performance measurements per QoS Flow is performed, when the UPF sends PMF message over a QoS Flow of an access, the UPF shall set the source MAC address with the MAC address for the QoS Flow and the access as the one for the QoS Flow and the access provided in Measurement Assistance information.
- If the UE receives Measurement Assistance Information, the UE shall inform the network via the user plane about the UE's MAC address so that it is possible for the UPF to know the UE's MAC address as soon as the MA PDU Session has been established.
NOTE 2: Regardless of whether access performance measurements per QoS Flow is applied or not, the UE only use a single MAC address. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.2 Round Trip Time Measurements | RTT measurements can be conducted by the UE and UPF independently. There is no measurement reporting from one side to the other. RTT measurements are defined to support the "Smallest Delay", "Priority-based", "Load Balancing" or "Redundant" steering mode (i.e. when RTT threshold value is applied).
The estimation of the RTT by the UE and by the UPF is based on the following mechanism:
1. The PMF in the UE sends over the user plane PMF-Echo Request messages to the PMF in the UPF and the PMF in the UPF responds to each one with a PMF-Echo Response message. Similarly, the PMF in the UPF sends over the user plane PMF-Echo Request messages to the PMF in the UE and the PMF in the UE responds to each one with a PMF-Echo Response message.
2. When the UP connection of the MA PDU session is deactivated on an access, no PMF-Echo Request messages are sent on this access. The PMF in the UPF shall not send PMF-Echo Request on this access if the UP connection is not available or after it receives notification from the (H-)SMF to stop sending the PMF-Echo Request on this access.
3. The UE and the UPF derive an estimation of the average RTT over an access type and QoS Flow by averaging the RTT measurements obtained over this access type and QoS Flow.
5.32.5.2a Packet Loss Rate Measurements
The UE and the UPF may decide to estimate the Packet Loss Rate (PLR) for an SDF over both accesses. For example, the UE may take this decision when an ATSSS rule in the UE requires the traffic of an SDF to be steered in accordance with a PLR-based threshold condition (e.g. PLR < 2%).
The UE and the UPF calculate the PLR for an SDF by exchanging PMF-PLR Report messages, as specified below. A PMF-PLR Report message is sent over 3GPP access or over non-3GPP access, using either the QoS Flow associated with the default QoS rule or a "target" QoS Flow, as specified in clause 5.32.5.1.
The calculation of the PLR by the UE and by the UPF is based on the following mechanism. It is assumed that the PLR should be calculated for a target QoS Flow, however, the same mechanism applies when the PLR should be calculated for the QoS Flow associated with the default QoS rule.
- The UE requests from UPF to start counting the number of received UL packets by sending a PMF-PLR Count Request message over the target QoS Flow. The UPF starts counting of the received UL packets over the target QoS Flow and over the access network which the PMF-PLR Count Request message was received from. The UE starts counting the transmitted UL packets over the target QoS Flow and access network when it sends a PMF-PLR Count Request message to UPF.
- The UE stops the counting and requests from UPF to report the number of counted UL packets by sending a PMF-PLR Report Request message over the target QoS Flow. The UPF stops the counting and sends a PMF-PLR Report Response message over the QoS Flow including the number of UL packets counted since it received the last PMF-PLR Count Request message.
NOTE 1: A PMF-PLR Report Request message can also indicate to UPF to start counting packets if the UE wants to measure the Packet Loss Rate again.
- The UE calculates the UL packet loss ratio based on the local counting result of the number of transmitted UL packets and reported number of received UL packets in the UPF.
- The UPF applies the same procedure for calculating the DL PLR, i.e. it sends to UE a PMF-PLR Count Request message on a target QoS Flow to request from UE to start counting the number of DL packets received on this target QoS Flow. As defined in clause 5.32.5.1, the UE determines which DL packets are received on the target QoS Flow by checking the QFI included in the header of DL packets (e.g. in the SDAP header). If no QFI is included in the header of a DL packet, the UE determines the QFI for this DL packet by applying the Packet Filters for downlink in the QoS Rules received from SMF.
- When the UP connection of the MA PDU session is deactivated on an access, no PMF-PLR messages are sent on this access. The PMF in the UPF shall not send PMF-PLR message on this access if the UP connection is not available or after it receives notification from the (H-)SMF to stop sending the PMF-PLR message on this access.
- The UE and the UPF derive an estimation of the average PLR per QoS Flow over an access type by averaging the PLR measurements obtained over this access.
NOTE 2: The details of the packet loss measurements, including error cases and mechanisms for improving the measurement accuracy, are considered in the Stage 3 specifications. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.3 Access Availability/Unavailability Report | If required by the network in the Measurement Assistance Information, the UE shall provide access availability/unavailability reports to the network. How the UE detects the unavailability and the availability of an access is based on implementation. The CM state of a UE is not a factor when determining whether the 3GPP access is available. When the UE detects the unavailability/availability of an access, it shall:
- build a PMF-Access Report containing the access type and an indication of availability/unavailability of this access;
- send the PMF-Access Report to the UPF via the user plane.
The UPF shall acknowledge the PMF-Access Report received from the UE. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.4 Protocol stack for user plane measurements and measurement reports | Figure 5.32.5.4-1: UE/UPF measurements related protocol stack for 3GPP access and for an MA PDU Session with type IP
In the case of an MA PDU Session with type Ethernet, the protocol stack over 3GPP access is that same as the one in the above figure, but the PMF protocol operates on top of Ethernet, instead of UDP/IP.
Figure 5.32.5.4-2: UE/UPF measurements related protocol stack for Untrusted non-3GPP access and for an MA PDU Session with type IP
In the case of an MA PDU Session with type Ethernet, the protocol stack over Untrusted non-3GPP access is the same as the one in the above figure, but the PMF protocol operates on top of Ethernet, instead of UDP/IP.
Figure 5.32.5.4-3: UE/UPF measurements related protocol stack for Trusted non-3GPP access and for an MA PDU Session with type IP
In the case of an MA PDU Session with type Ethernet, the protocol stack over Trusted non-3GPP access is the same as the one in the above figure, but the PMF protocol operates on top of Ethernet, instead of UDP/IP. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.5 UE Assistance Operation | When UE-assistance operation is authorized by the PCF in the PCC Rule, the SMF provides an indication for UE-assistance in the ATSSS Rule to the UE, as described in clause 5.32.8 and in the MAR to the UPF, as described in clause 5.8.5.8.
If the UE receives the UE-assistance indicator in an ATSSS rule (as specified in clause 5.32.8) and the UE decides to apply a different UL traffic distribution for an SDF than the default UL traffic distribution indicated in the Steering Mode component of the ATSSS rule (e.g. because the UE is running out of battery), then the following applies:
- The UE may apply any split percentages for the UL traffic distribution of an SDF, based on implementation specific criteria.
- The UE may send a PMF-UAD (UE Assistance Data) message to UPF that contains the split percentages that may be used by UPF for all DL traffic that the UE-assistance operation applies. The UPF acknowledges the reception of the PMF-UAD message by sending a PMF-UAD complete message to the UE.
NOTE: If the UE has multiple ATSSS rules that allow UE-assistance operation and the UE decides to use different UL split percentages for their respective SDFs, then the split percentages included in the PMF-UAD message are selected by the UE based on implementation specific criteria.
- The UPF may apply the information in a received PMF-UAD message to align the DL traffic distribution for traffic that is allowed to use UE-assistance operation, i.e. traffic where the MAR contains a Steering Mode Indicator set to UE-assistance operation.
- If the UE decides to terminate the UE assistance operation, the UE may send a PMF-UAT (UE Assistance Termination) message to the UPF indicating that the UE assistance operation is terminated and the UE performs the UL traffic distribution according to the split percentages in the ATSSS rule received from the network. If the UPF receives the PMF-UAT message, the UPF acknowledges the reception by sending a PMF-UAT complete message and performs DL traffic distribution by applying the split percentages included in the MAR. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.5.6 Suspend and Resume Traffic Duplication | As part of the Redundant Steering Mode, a UPF can decide to suspend traffic duplication for a UE by sending PMF- Suspend Duplication Request message to the UE. How the UPF determines to suspend traffic duplication is implementation specific.
NOTE 1: The Suspension of traffic duplication can be caused by e.g. the locally detected UPF congestion. In that way the UPF can stop receiving duplicated traffic via 3GPP and non-3GPP access network simultaneously.
The UPF may indicate in the PMF-Suspend Duplication Request message the type of traffic (i.e. GBR or non-GBR) for which traffic duplication is being suspended. The PMF-Suspend Duplication Request message is sent over the user plane of any available access network of the MA PDU Session. Once the UE receives the PMF-Suspend Duplication Request message from the UPF, the UE shall stop duplicating the type of traffic for which traffic duplication is suspended.
If the UPF does not provide the type of traffic (GBR or non-GBR) in the PMF-Suspend Duplication Request message, traffic duplication is suspended for all traffic for which traffic duplication is being performed. Once UPF suspended traffic duplication and if no Primary Access is configured, both the UE and the UPF decide, based on their own implementation, which access network to use for sending UL and DL traffic. If the Primary Access is configured, both the UE and the UPF use the Primary Access for sending UL and DL traffic.
The UPF may decide to resume traffic duplication for a UE by sending the PMF-Resume Duplication Request message. How the UPF determines to resume traffic duplication is implementation specific.
NOTE 2: Traffic duplication can be resumed e.g. when the UPF has detected that local congestion has diminished.
Once the UE receives the PMF-Resume Duplication Request message from the UPF, the UE may restart to duplicate the type of traffic for which traffic duplication is resumed based on the provided Redundant steering mode policies and UE implementation. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6 Support of Steering Functionalities | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.1 General | The functionality in an ATSSS-capable UE that can steer, switch and split the MA PDU Session traffic across 3GPP access and non-3GPP access, is called a "steering functionality". An ATSSS-capable UE may support one or more of the following types of steering functionalities:
- Steering functionalities based on multi-path protocols:
- Steering functionality that applies the MPTCP protocol (IETF RFC 8684 [81]) and is called "MPTCP functionality" (see clause 5.32.6.2.1). This steering functionality can be applied to steer, switch and split the TCP traffic flows identified in the ATSSS/N4 rules. The MPTCP functionality in the UE may communicate with an associated MPTCP Proxy functionality in the UPF, by using the MPTCP protocol over the 3GPP and/or the non-3GPP user plane.
- Steering functionalities based on MPQUIC that apply the QUIC protocol (IETF RFC 9000 [166], IETF RFC 9001 [167], IETF RFC 9002 [168]) and its multipath extensions (draft-ietf-quic-multipath [174]). The MPQUIC functionality in the UE may communicate with an associated MPQUIC Proxy functionality in the UPF, by using the QUIC protocol and its multipath extensions over the 3GPP and/or the non-3GPP user plane. The following MPQUIC steering functionalities are supported:
- "MPQUIC-UDP" steering functionality that can be applied to steer, switch and split UDP traffic flows identified in the ATSSS/N4 rules.
- "MPQUIC-IP" steering functionality that can be applied to steer, switch and split IP traffic identified in the ATSSS/N4 rules.
- "MPQUIC-E" steering functionality that can be applied to steer, switch and split Ethernet traffic identified in the ATSSS/N4 rules.
- Steering functionalities based on data switching:
- A steering functionality called "ATSSS Low-Layer functionality", or ATSSS-LL functionality (see clause 5.32.6.3.1): This steering functionality can be applied to steer, switch and split all types of traffic, including TCP traffic, UDP traffic, Ethernet traffic, etc.
NOTE: Filters used in ATSSS rules related with a MA PDU Session of type Ethernet can refer to IP level parameters such as IP addresses and TCP/UDP ports.
The UE indicates to the network its supported steering functionalities and steering modes by including in the UE ATSSS Capability one or more of the following capabilities:
1) ATSSS-LL functionality with any steering mode.
In this case, the UE indicates that it is capable to steer, switch and split all traffic of the MA PDU Session by using the ATSSS-LL functionality with any steering mode allowed for ATSSS-LL, as specified in clause 5.32.8.
2) MPTCP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode. The MPTCP functionality shall be used only when the type of the MA PDU Session is IPv4, IPv6, or IPv4v6.
In this case, the UE indicates that:
a) it is capable to steer, switch and split the TCP traffic of the MA PDU Session by using the MPTCP functionality with any steering mode, as specified in clause 5.32.8; and
b) it is capable to steer and switch all other traffic (i.e. the non-MPTCP traffic) of the MA PDU Session by using the ATSSS-LL functionality with the Active-Standby steering mode, as specified in clause 5.32.8.
3) MPQUIC-UDP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode. The MPQUIC-UDP functionality shall be used only when the type of the MA PDU Session is IPv4, IPv6, or IPv4v6.
In this case, the UE indicates that:
a) it is capable to steer, switch and split the UDP traffic of the MA PDU Session by using the MPQUIC-UDP functionality with any steering mode, as specified in clause 5.32.8; and
b) it is capable to steer and switch all other traffic (i.e. the non-MPQUIC traffic) of the MA PDU Session by using the ATSSS-LL functionality with the Active-Standby steering mode, as specified in clause 5.32.8.
4) MPQUIC-IP functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode. The MPQUIC-IP functionality shall be used only when the type of the MA PDU Session is IPv4, IPv6, or IPv4v6.
In this case, the UE indicates that:
a) it is capable to steer, switch and split all traffic of the MA PDU Session, by using the MPQUIC-IP functionality with any steering mode, as specified in clause 5.32.8. and
b) it is capable to steer and switch all traffic of the MA PDU Session by using the ATSSS-LL functionality with the Active-Standby steering mode, as specified in clause 5.32.8.
5) MPQUIC-E functionality with any steering mode and ATSSS-LL functionality with only Active-Standby steering mode. MPQUIC-E functionality shall be used only when the type of the MA PDU Session is Ethernet.
In this case, the UE indicates that:
a) it is capable to steer, switch and split all traffic of the MA PDU Session of type Ethernet, by using the MPQUIC-E functionality with any steering mode, as specified in clause 5.32.8. and
b) it is capable to steer and switch all traffic of the MA PDU Session by using the ATSSS-LL functionality with the Active-Standby steering mode, as specified in clause 5.32.8.
6) MPQUIC-IP functionality with any steering mode without any ATSSS-LL functionality. The MPQUIC-IP functionality shall be used only when the type of the MA PDU Session is IPv4, IPv6, or IPv4v6. This capability shall be provided when the UE supports only MPQUIC-IP functionality.
In this case, the UE indicates that it is capable to steer, switch and split all traffic of the MA PDU Session by using the MPQUIC-IP functionality with any steering mode, as specified in clause 5.32.8.
The above steering functionalities are schematically illustrated in the Figure 5.32.6.1-1, which shows an example model for an ATSSS-capable UE supporting the MPTCP functionality, the MPQUIC functionality(ies) and the ATSSS-LL functionality. The MPTCP flows and the MPQUIC flows in this figure represent the traffic of the applications for which MPTCP protocol can be applied and for which MPQUIC protocol can be applied respectively. The five different IP addresses illustrated in the UE are further described in clause 5.32.6.2.1 and in clause 5.32.6.2.2. When the MPTCP functionality and the MPQUIC functionality(ies) are both applied, the addresses (IP@1, IP@2) used for MPTCP functionality may be the same as the addresses (IP@4, IP@5) used for MPQUIC functionality(ies).
Figure 5.32.6.1-1: Steering functionalities in an example UE model
Within the same IP type MA PDU Session, it is possible to simultaneously steer different packet flows by different steering functionalities. For the same packet flow, only one steering functionality shall be used. For the same Ethernet type MA PDU Session, either ATSSS-LL steering functionality or MPQUIC-E steering functionality is enabled.
All steering functionalities in the UE shall take ATSSS decisions (i.e. decide how to steer, switch and split the traffic) by using the same set of ATSSS rules. Similarly, all ATSSS decisions in the UPF shall be taken by applying the same set of N4 rules, which support ATSSS. The ATSSS rules and the N4 rules supporting ATSSS are provisioned in the UE and in the UPF respectively, when the MA PDU Session is established.
If the UE supports multiple steering functionalities, it shall use the provisioned ATSSS rules (see TS 23.503 [45]) to decide which steering functionality to apply for a specific packet flow. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.2 Steering Functionalities based on multi-path protocols | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.2.1 MPTCP Functionality | As mentioned in clause 5.32.6.1, the MPTCP functionality in the UE applies the MPTCP protocol (IETF RFC 8684 [81]) and the provisioned ATSSS rules for performing access traffic steering, switching and splitting. The MPTCP functionality in the UE may communicate with the MPTCP Proxy functionality in the UPF using the user plane of the 3GPP access, or the non-3GPP access, or both.
The MPTCP functionality may be enabled in the UE when the UE provides an "MPTCP capability" during PDU Session Establishment procedure.
The network shall not enable the MPTCP functionality when the type of the MA PDU Session is Ethernet.
If the UE indicates it is capable of supporting the MPTCP functionality, as described in clause 5.32.2 and the network agrees to enable the MPTCP functionality for the MA PDU Session then:
i) An associated MPTCP Proxy functionality is enabled in the UPF for the MA PDU Session by MPTCP functionality indication received in the Multi-Access Rules (MAR).
ii) The network allocates to UE one IP address/prefix for the MA PDU Session and two additional IP addresses/prefixes, called "MPTCP link-specific multipath" addresses/prefixes; one associated with 3GPP access and another associated with the non-3GPP access. In the UE, these two IP addresses/prefixes are used only by the MPTCP functionality. Each "MPTCP link-specific multipath" address/prefix assigned to UE may not be routable via N6. The MPTCP functionality in the UE and the MPTCP Proxy functionality in the UPF shall use the "MPTCP link-specific multipath" addresses/prefixes for subflows over non-3GPP access and over 3GPP access and MPTCP Proxy functionality shall use the IP address/prefix of the MA PDU session for the communication with the final destination. In Figure 5.32.6.1-1, the IP@3 corresponds to the IP address of the MA PDU Session and the IP@1 and IP@2 correspond to the "MPTCP link-specific multipath" IP addresses. The following UE IP address management applies:
- The MA PDU IP address/prefix shall be provided to the UE via mechanisms defined in clause 5.8.2.2.
- The "MPTCP link-specific multipath" IP addresses/prefixes shall be allocated by the UPF and shall be provided to the UE via SM NAS signalling.
NOTE 1: After the MA PDU Session is released, the same UE IP addresses/prefixes are not allocated to another UE for MA PDU Session in a short time.
NOTE 2: The act of the UPF performing translation on traffic associated with the "MPTCP link-specific multipath" addresses to/from the MA PDU session IP address can lead to TCP port collision and exhaustion. The port collision can potentially occur because the UE also uses the MA PDU session IP address for non-MPTCP traffic and this causes the port namespace of such address to be owned simultaneously by the UE and UPF. In addition, the port exhaustion can potentially occur when the UE creates a large number of flows, because multiple IP addresses used by the UE are mapped to a single MA PDU session IP address on the UPF. The UPF needs to consider these problems based on the UPF implementation and avoid them by, for example, using additional N6-routable IP addresses for traffic associated to the link-specific multipath addresses/prefixes. How this is done is left to the implementation.
iii) The network shall send MPTCP proxy information to UE, i.e. the IP address, a port number and the type of the MPTCP proxy. The following type of MPTCP proxy shall be supported in this release:
- Type 1: Transport Converter, as defined in IETF RFC 8803 [82].
The MPTCP proxy information is retrieved by the SMF from the UPF during N4 session establishment.
The UE shall support the client extensions specified in IETF RFC 8803 [82].
iv) The network may indicate to UE the list of applications for which the MPTCP functionality should be applied. This is achieved by using the Steering Functionality component of an ATSSS rule (see clause 5.32.8).
NOTE 3: To protect the MPTCP proxy function (e.g. to block DDOS to the MPTCP proxy function), the IP addresses of the MPTCP Proxy Function are only accessible from the two "MPTCP link-specific multipath" IP addresses of the UE via the N3/N9 interface.
v) When the UE indicates it is capable of supporting the MPTCP functionality with any steering mode and the ATSSS-LL functionality with only the Active-Standby steering mode (as specified in clause 5.32.6.1) and these functionalities are enabled for the MA PDU Session, then the UE shall route via the MA PDU Session the TCP traffic of applications for which the MPTCP functionality should be applied (i.e. the MPTCP traffic), as defined in bullet iv. The UE may route all other traffic (i.e. the non-MPTCP traffic) via the MA PDU Session, but this type of traffic shall be routed on one of 3GPP access or non-3GPP access, based on the received ATSSS rule for non-MPTCP traffic (see clause 5.32.2). The UPF shall route all other traffic (i.e. non-MPTCP traffic) based on the N4 rules provided by the SMF. This may include N4 rules for ATSSS-LL, using any steering mode as instructed by the N4 rules. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.2.2 MPQUIC Functionalities | MPQUIC functionalities are supported as follows:
- The MPQUIC functionalities enable steering, switching and splitting of data traffic between the UE and UPF, in accordance with the ATSSS policy created by the network.
- The operation of the MPQUIC-UDP functionality is based on IETF RFC 9298 [170] "proxying UDP in HTTP", which specifies how UDP traffic can be transferred between a client (UE) and a proxy (UPF) using the IETF RFC 9114 [171] HTTP/3 protocol.
The MPQUIC-UDP functionality may be enabled for an MA PDU Session with type IPv4, IPv6 or IPv4v6, when both the UE and the network support this functionality. The MPQUIC-UDP functionality shall not be enabled when the type of the MA PDU Session is Ethernet.
- The operation of the MPQUIC-IP functionality is based on RFC 9484 [214] "Proxying IP in HTTP", which specifies how IP traffic can be transferred between a client (UE) and a proxy (UPF) using the IETF RFC 9114 [171] HTTP/3 protocol.
The MPQUIC-IP functionality may be enabled for a MA PDU Session with type IPv4, IPv6 or IPv4v6, when both the UE and the network support this functionality. The MPQUIC-IP functionality shall not be enabled when the type of the MA PDU Session is Ethernet.
- The operation of the MPQUIC-E functionality is based on IETF draft-ietf-masque-connect-ethernet [215] "Proxying Ethernet in HTTP", which specifies how Ethernet traffic can be transferred between a client (UE) and a proxy (UPF) using the IETF RFC 9114 [171] HTTP/3 protocol.
The MPQUIC-E functionality may be enabled when the type of the MA PDU Session is Ethernet. In case MPQUIC-E functionality is enabled for an Ethernet type PDU Session, the SMF indicates PDU Session type as IP in the N2 information to NG-RAN, as described in TS 23.502 [3].
The HTTP/3 protocol operates on top of the QUIC protocol (IETF RFC 9000 [166], IETF RFC 9001 [167] , IETF RFC 9002 [168]), which supports simultaneous communication over multiple paths, as defined in draft-ietf-quic-multipath [174].
The MPQUIC functionality(ies) in the UE communicates with the associated MPQUIC Proxy functionality(ies) in the UPF (see Figure 4.2.10-1) using the user plane of the 3GPP access, or the non-3GPP access, or both.
The MPQUIC-UDP, MPQUIC-IP and MPQUIC-E functionality(ies) are composed of three components:
1) QoS flow selection & Steering mode selection: This component in the UE initiates the establishment of one or more multipath QUIC connections, after the establishment of the MA PDU Session and, for each uplink UDP flow for MPQUIC-UDP functionality), IP flow (for MPQUIC-IP functionality) and Ethernet flow (for MPQUIC-E functionality), it selects a QoS flow (based on the QoS rules), a steering mode and a transport mode (based on the ATSSS rules). This component in the UPF selects, for each downlink traffic flow of respective type, a QoS flow (based on the N4 rules), a steering mode and a transport mode (based on the N4 rules). The supported transport modes are defined below.
In the UE, this component is only used in the uplink direction, while, in the UPF, this component is only used in the downlink direction.
2) HTTP/3 layer: Supports the HTTP/3 protocol defined in RFC 9114 [171] and the extensions defined in:
- IETF RFC 9298 [170] for supporting UDP proxying over HTTP;
- IETF RFC 9484 [214] for supporting IP proxying over HTTP;
- IETF draft-ietf-masque-connect-ethernet: [215] for supporting Ethernet proxying over HTTP;
- IETF RFC 9297 [172] for supporting HTTP datagrams; and
- IETF RFC 9220 [173] for supporting Extended CONNECT.
The HTTP/3 layer selects a multipath QUIC connection to be used for each traffic flow and allocates a new QUIC stream on this connection that is associated with the traffic flow. It also configures this QUIC stream to apply a specific steering mode.
In the UE, the HTTP/3 layer implements an HTTP/3 client, while, in the UPF, it implements an HTTP/3 proxy.
3) QUIC layer: Supports the QUIC protocol as defined in the applicable IETF specifications (IETF RFC 9000 [166], IETF RFC 9001 [167], IETF RFC 9002 [168]) and the extensions defined in:
- IETF RFC 9221 [169] for supporting unreliable datagram transport with QUIC; and
- draft-ietf-quic-multipath [174] for supporting QUIC connections using multiple paths simultaneously.
When any one of the MPQUIC functionalities is applied, the protocol stack of the user plane is depicted in figure below.
Figure 5.32.6.2.2-1: UP protocol stack when an MPQUIC functionality is applied
If the UE indicates that it is capable of supporting any one of the MPQUIC-UDP, MPQUIC-IP or MPQUIC-E functionalities, as described in clause 5.32.2 and the network agrees to enable the corresponding MPQUIC Proxy functionality(ies) for the MA PDU Session then:
i) An associated MPQUIC Proxy functionality is enabled in the UPF for the MA PDU Session.
ii) The network allocates two IP addresses/prefixes, called "MPQUIC link-specific multipath" addresses/prefixes; one associated with 3GPP access and another associated with the non-3GPP access (in the case of IP based PDU Session Types, the MPQUIC link-specific multipath addresses/prefixes are allocated in addition to the UE IP address/prefix for the MA PDU Session). In the UE, these two link-specific multipath IP addresses/prefixes are used only by the associated MPQUIC functionality. Each "MPQUIC link-specific multipath" address/prefix assigned to UE may not be routable via N6. The MPQUIC functionality in the UE and the associated MPQUIC Proxy functionality in the UPF shall use the "MPQUIC link-specific multipath" addresses/prefixes for transmitting traffic flows over non-3GPP access and over 3GPP access. In the case of IP based PDU session type, the MPQUIC Proxy functionality shall use the IP address/prefix of the MA PDU session for the communication with the final destination. In Figure 5.32.6.1-1, the IP@3 corresponds to the IP address of the MA PDU Session and the IP@4 and IP@5 correspond to the "MPQUIC link-specific multipath" addresses. In the case of Ethernet based PDU session type, the MAC addresses in the Ethernet frame received from UE, as described in clause 5.6.10.2, shall be used by the MPQUIC Proxy functionality for the communication with the final destination. The following UE IP address management applies:
- The MA PDU IP address/prefix shall be provided to the UE via mechanisms defined in clause 5.8.2.2.
- The "MPQUIC link-specific multipath" IP addresses/prefixes shall be allocated by the UPF and shall be provided to the UE via SM NAS signalling.
NOTE 1: After the MA PDU Session is released, the same UE IP addresses/prefixes are not allocated to another UE for MA PDU Session in a short time.
NOTE 2: When both MPQUIC-UDP and MPQUIC-IP functionalities are enabled for a single MA PDU Session, the network allocates a common single pair of "MPQUIC link-specific multipath" addresses/prefixes to be used for both MPQUIC-UDP and MPQUIC-IP functionalities.
iii) The network shall send MPQUIC proxy information to UE, i.e. one IP address of UPF, one UDP port number and the proxy type (e.g. "connect-udp"). This information is used by the UE for establishing multipath QUIC connections with the UPF, which implements the MPQUIC Proxy functionality.
When both MPQUIC-UDP and MPQUIC-IP functionalities are enabled for a single MA PDU Session, if the MPQUIC proxy information is common for MPQUIC-UDP and MPQUIC-IP, the network sends a single MPQUIC proxy information (i.e. one IP address of MPQUIC proxy and one UDP port number) to the UE, to be used for both MPQUIC-UDP and MPQUIC-IP functionalities.
iv) After the MA PDU Session is established, the UE determines the number of multipath QUIC connections to be established with the UPF. The UE determines to establish at least as many multipath QUIC connections as the number of QoS flows of the MA PDU Session, i.e. one multipath QUIC connection per QoS flow. Each multipath QUIC connection carries the traffic mapped to a single QoS flow.
Security aspects are defined in TS 33.501 [29].
For the downlink traffic to which the MPQUIC functionality is to be applied, the QoS rules provided to UE include downlink QoS information and the UE applies the downlink QoS information to establish multipath QUIC connections for the QoS flows used for the downlink traffic only.
v) During a QUIC connection establishment, the UE and UPF negotiate QUIC transport parameters and indicate (a) support of QUIC Datagram frames and (b) support of multipath. They indicate support of QUIC Datagram frames by providing the "max_datagram_frame_size" transport parameter with a non-zero value (see RFC 9221 [169]) and they indicate support of multipath by providing the "enable_multipath" transport parameter (see draft-ietf-quic-multipath [174]).
In addition, during a QUIC connection establishment the QoS flow associated with this connection is determined. The UE sends all traffic of a QUIC connection over the QoS flow associated with this QUIC connection. This enables the UPF to determine the QoS flow associated with a QUIC connection and to select a QUIC connection for sending the downlink traffic of a QoS flow.
vi) After a QUIC connection establishment, the HTTP/3 client in the UE and the HTTP/3 proxy in the UPF negotiate HTTP settings and indicate support of HTTP Datagrams (see RFC 9297 [172]) and support of Extended CONNECT (see RFC 9220 [173]). To use MPQUIC-UDP for a UDP traffic flow, the UE then sends a HTTP/3 CONNECT request (see RFC 9298 [170]) to the HTTP/3 proxy in the UPF. To use MPQUIC-IP for an IP traffic flow, the UE then sends a HTTP/3 CONNECT-IP request (see IETF RFC 9484 [214]) to the HTTP/3 proxy in the UPF. To use MPQUIC-E for an Ethernet traffic flow, the UE then sends a HTTP/3 CONNECT-Ethernet request (see IETF draft-ietf-masque-connect-ethernet [215]) to the HTTP/3 proxy in the UPF.
vii) The network may indicate to UE the list of applications for which the MPQUIC-UDP, MPQUIC-IP or MPQUIC-E functionality should be applied. This is achieved by using the Steering Functionality component of an ATSSS rule (see clause 5.32.8).
5.32.6.2.2.1 Supported Transport Modes
The MPQUIC-UDP, MPQUIC-IP and MPQUIC-E functionalities support the following transport modes for transmitting a traffic flow between UE and UPF. The PCF selects which of these transport modes shall be applied for a traffic flow (SDF). The selected transport mode is provided to UE and UPF within the ATSSS rules and N4/MAR rules respectively.
- Datagram mode 2: This transport mode encapsulates UDP packets, IP packets and Ethernet frames, as applicable, within QUIC Datagram frames and provides unreliable transport with no sequence numbering and no packet reordering / deduplication. The transport mode is defined in RFC 9298 [170] for MPQUIC-UDP functionality, in IETF RFC 9484 [214] for MPQUIC-IP functionality and in draft-ietf-masque-connect-ethernet [215] for MPQUIC-E functionality.
- Datagram mode 1: This transport mode is an extension of the mode defined in IETF RFC 9298 [170], IETF RFC 9484 [214] and draft-ietf-masque-connect-ethernet [215]. It encapsulates packets within QUIC Datagram frames and provides unreliable transport but with sequence numbering and with packet reordering / deduplication. It can be applied for any traffic flow. The details of the datagram mode 1 are defined in TS 24.193 [109].
- Stream mode: This transport mode is readily supported by the QUIC protocol. It encapsulates packets within QUIC Stream frames and provides reliable transport with sequence numbering and with packet reordering / deduplication. It can be applied for traffic flows where it is known that the application does not perform retransmissions.
NOTE 1: The Stream mode provides strict reliability and in-order delivery with re-transmissions and therefore can lead to melt down phenomena when reliable traffic (e.g. QUIC) is carried, or counteracts application decisions when UDP is selected to avoid reliability and/or in-order delivery. Therefore, it can be avoided for applications which perform their own reliability mechanisms.
NOTE 2: When a steering mode is supported by ATSSS-LL for a traffic flow (e.g. Active-Standby), one of the MPQUIC-UDP, MPQUIC-IP or MPQUIC-E steering functionalities can be selected if additional features, which are not supported by the ATSSS-LL steering functionality and PMF, are required for the traffic steering/switching/splitting of the traffic flow. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.3 Steering Functionalities based on data switching | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.6.3.1 ATSSS-LL Functionality | The ATSSS-LL functionality in the UE does not apply a specific protocol. It is a data switching function, which decides how to steer, switch and split the uplink traffic across 3GPP and non-3GPP accesses, based on the provisioned ATSSS rules and local conditions (e.g. signal loss conditions). The ATSSS-LL functionality in the UE may be applied to steer, switch and split all types of traffic, including TCP traffic, UDP traffic, Ethernet traffic, etc. The ATSSS-LL functionality does not support the Redundant Steering Mode.
The ATSSS-LL functionality may be enabled in the UE when the UE provides an "ATSSS-LL capability" during the PDU Session Establishment procedure.
The ATSSS-LL functionality or MPQUIC-E functionality is required in the UE for MA PDU Session of type Ethernet.
In addition:
- When the UE neither supports the MPTCP functionality, nor the MPQUIC-UDP functionality, nor the MPQUIC-IP functionality, the ATSSS-LL functionality is mandatory in the UE for an MA PDU Session of type IP.
The network shall also support the ATSSS-LL functionality as defined for the UE. The ATSSS-LL functionality in the UPF is enabled for a MA PDU Session by ATSSS-LL functionality indication received in the Multi-Access Rules (MAR). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.7 Interworking with EPS | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.7.1 General | Multi-access connectivity using ATSSS established via EPC only is not supported.
Interworking for MA PDU Session, if allowed by the network, is based on the interworking functionality specified in clause 5.17.2, with the differences and clarifications described in the following clauses.
A PDN Connection in EPS may be modified into a MA PDU Session when transferred to 5GS if the UE and the SMF+PGW-C support the ATSSS feature. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.7.2 Interworking with N26 Interface | Interworking with N26 interface is based on clause 5.17.2.2, with the following differences and clarifications:
- When the UE is registered to the same PLMN over 3GPP and non-3GPP accesses and the UE request a new MA PDU Session via non-3GPP access, the AMF also includes the indication of interworking with N26 to SMF.
- The SMF does not request EBI allocation when MA PDU Session is established only over non-3GPP access. If MA PDU Session is released over 3GPP access, the allocated EBI(s) for the MA PDU Session is revoked by the SMF as described in clause 4.11.1.4.3 of TS 23.502 [3].
- The SMF does not request EBI allocation for GBR QoS Flow if the GBR QoS Flow is only allowed over non-3GPP access.
- If the UE and the network support MA PDU Sessions with 3GPP access connected to EPC, the MA PDU Session may be simultaneously associated with user-plane resources on 3GPP access network connected to EPC and with non-3GPP access network connected to 5GC. This case is further described in clause 5.32.1 and in clause 4.22.2.3 of TS 23.502 [3].
- If the UE or the network does not support MA PDU Session with 3GPP access connected to EPC, the MA PDU Session is handled as follows:
- When UE moves from 5GS to EPS, for both idle mode and connected mode mobility, if the MA PDU Session is moved to EPS as a PDN connection, the SMF triggers PDU Session Release procedure to release the MA PDU Session over Non-3GPP access in 5GS. UE and SMF remove ATSSS related contexts e.g. ATSSS rules, Measurement Assistance Information.
- When UE moves from 5GS to EPS, for both idle mode and connected mode mobility, if the MA PDU Session is not moved to EPS as a PDN connection, the 3GPP access of this MA PDU session becomes unavailable and the AMF notifies the SMF. In turn, the SMF may decide to move the traffic to Non-3GPP access of the MA PDU session, if it is available. When UE moves back from EPS to 5GS, after the UE is registered over the 3GPP, the UE may add user-plane resources over the 3GPP access to the MA PDU session by triggering PDU Session Establishment procedure as specified in clause 5.32.2.
- After UE moves from EPS to 5GS, for both idle mode and connected mode mobility, if the UE requires MA PDU session, or if no policy in the UE (e.g. no URSP rule) and no local restrictions mandate a single access for the PDU Session, UE triggers the PDU Session Modification procedure as described in clause 4.22.6.3 of TS 23.502 [3] to provide the ATSSS Capability to SMF+PGW-C. The SMF+PGW-C may determine whether to modify this PDU Session to a MA PDU Session in 5GS, e.g. based on SMF+PGW-C and UE's ATSSS Capability, subscription data and local policy. If dynamic PCC is to be used for the MA PDU Session, the PCF decides whether the MA PDU session is allowed or not based on operator policy and subscription data. If the MA PDU Session is allowed, the SMF provides ATSSS rule(s) and Measurement Assistance Information to the UE. If the UE receives ATSSS rules and is not registered to non-3GPP access, the UE establishes the second user-plane over non-3GPP access after the UE is registered to non-3GPP access. If UE was registered to non-3GPP access in 5GS, the UP resources over non-3GPP access are also established by the SMF using the PDU Session Modification procedure.
- If the MA PDU Session is established using one 3GPP access path via 5GC and one non-3GPP access path via ePDG/EPC and the UE moves from NG-RAN/5GC to E-UTRAN/EPC, the SMF+PGW-C may keep the MA PDU Session if MA PDU Sessions with 3GPP access and non-3GPP access user plane resources both connected to EPC is allowed based on operator policy.
- If the MA PDU Session is established using one 3GPP access path via 5GC and one non-3GPP access path via ePDG/EPC and the UE moves from NG-RAN/5GC to E-UTRAN/EPC, the SMF+PGW-C may release the user plane resources either over 3GPP access or non-3GPP access if MA PDU Sessions with 3GPP access and non-3GPP access user plane resources both connected to EPC is not allowed based on operator policy. In this case, while the UE is connected to EPC via both 3GPP access and non-3GPP access, the UE shall not trigger PDN Connection establishment to add an additional EPC access leg to the MA PDU Session. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.7.3 Interworking without N26 Interface | Interworking without N26 interface is based on clause 5.17.2.3, with the following differences and clarifications:
- After UE moves from 5GS to EPS, UE may send a PDN Connectivity Request with "handover" indication to transfer the MA PDU Session to EPS. Then, if the UE or the network does not support MA PDU Session with 3GPP access connected to EPC, the SMF+PGW-C triggers to release MA PDU in 5GS. If UE does not transfer the MA PDU Session to EPS, UE keeps the MA PDU Session in 5GS and UE may report to UPF that 3GPP access is unavailable, all MA PDU Session traffic is transported over N3GPP access. Later, if UE returns to 5GS, UE may report the 3GPP access availability to UPF. If the UE and the network support MA PDU Session with 3GPP access connected to EPC, the UE includes a "handover" indication and a "MA PDU Request" indication as well as the PDU Session ID in the PCO and the SMF+PGW-C keeps the user-plane resources over non-3GPP access in 5GC as described in clause 4.22.6.2.5 of TS 23.502 [3].
- After UE moves from EPS to 5GS, UE may trigger PDU Session Establishment procedure to transfer the PDN Connection to 5GS. During the PDU Session Establishment procedure, if the PDN Connection was not used as the 3GPP access leg of the MA PDU Session, the UE may request to establish a MA PDU Session by including "MA PDU Request" or, if no policy in the UE (e.g. no URSP rule) and no local restrictions mandate a single access for the PDU Session, the UE may include the "MA PDU Network-Upgrade Allowed" indication. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.32.8 ATSSS Rules | As specified in clause 5.32.3, after the establishment of a MA PDU Session, the UE receives a prioritized list of ATSSS rules from the SMF. The structure of an ATSSS rule is specified in Table 5.32.8-1.
Table 5.32.8-1: Structure of ATSSS Rule
Information name
Description
Category
SMF permitted to modify in a PDU context
Scope
Rule identifier
Unique identifier to identify the ATSSS Rule
Mandatory
No
PDU context
Rule Precedence
Determines the order in which the ATSSS rule is evaluated in the UE.
Mandatory
(NOTE 1)
Yes
PDU context
Traffic Descriptor
This part defines the Traffic descriptor components for the ATSSS rule.
Mandatory
(NOTE 2)
Application descriptors
One or more application identities that identify the application(s) generating the traffic (NOTE 3).
Optional
Yes
PDU context
IP descriptors
(NOTE 4)
One or more 5-tuples that identify the destination of IP traffic.
Optional
Yes
PDU context
Non-IP descriptors
(NOTE 4)
One or more descriptors that identify the destination of non-IP traffic, i.e. of Ethernet traffic.
Optional
Yes
PDU context
Access Selection Descriptor
This part defines the Access Selection Descriptor components for the ATSSS rule.
Mandatory
Steering Mode
Identifies the steering mode that should be applied for the matching traffic and associated parameters.
Mandatory
(NOTE 8)
Yes
PDU context
Steering Mode Indicator
Indicates either autonomous load-balance operation or UE-assistance operation if steering mode is set to "Load Balancing".
Optional
(NOTE 6)
Yes
PDU context
Threshold Values
(NOTE 9)
A Maximum RTT and/or a Maximum Packet Loss Rate.
Optional
(NOTE 6)
Yes
PDU context
Steering Functionality
Identifies whether the MPTCP functionality, the MPQUIC-UDP functionality, the MPQUIC-IP functionality, the MPQUIC-E functionality or the ATSSS-LL functionality should be applied for the matching traffic.
Optional
(NOTE 5)
(NOTE 8)
Yes
PDU context
Transport Mode
Identifies the transport mode (see clause 5.32.6.2.2.1) that should be used for the matching traffic, when the Steering Functionality is the MPQUIC-UDP functionality, MPQUIC-IP functionality or MPQUIC-E functionality.
Optional
(NOTE 7)
Yes
PDU context
NOTE 1: Each ATSSS rule has a different precedence value from the other ATSSS rules.
NOTE 2: At least one of the Traffic Descriptor components is present.
NOTE 3: An application identity consists of an OSId and an OSAppId.
NOTE 4: An ATSSS rule cannot contain both IP descriptors and Non-IP descriptors.
NOTE 5: If the UE supports only one Steering Functionality, this component is omitted.
NOTE 6: The Steering Mode Indicator and the Threshold Values shall not be provided together.
NOTE 7: The Transport Mode shall be included when the Steering Functionality is the MPQUIC-UDP functionality, MPQUIC-IP functionality or MPQUIC-E functionality. In all other cases, the Transport Mode shall not be included.
NOTE 8: The Steering functionality "ATSSS-LL functionality" shall not be provided together with Steering Mode "Redundant".
NOTE 9: If the Steering Mode is "Redundant", either a Maximum RTT or a Maximum Packet Loss Rate may be provided, but not both.
The UE evaluates the ATSSS rules in priority order.
Each ATSSS rule contains a Traffic Descriptor (containing one or more components described in Table 5.32.8-1) that determines when the rule is applicable. An ATSSS rule is determined to be applicable when every component in the Traffic Descriptor matches the considered service data flow (SDF).
Depending on the type of the MA PDU Session, the Traffic Descriptor may contain the following components (the details of the Traffic Descriptor generation are described in clause 5.32.3):
- For IPv4, or IPv6, or IPv4v6 type: Application descriptors and/or IP descriptors.
- For Ethernet type: Application descriptors and/or Non-IP descriptors.
One ATSSS rule with a "match all" Traffic Descriptor may be provided, which matches all SDFs. When provided, it shall have the least Rule Precedence value, so it shall be the last one evaluated by the UE.
NOTE 1: The format of the "match all" Traffic descriptor of an ATSSS rule is defined in stage-3.
Each ATSSS rule contains an Access Selection Descriptor that contains the following components:
- A Steering Mode, which determines how the traffic of the matching SDF should be distributed across 3GPP and non-3GPP accesses. The following Steering Modes are supported:
- Active-Standby: It is used to steer a SDF on one access (the Active access), when this access is available and to switch the SDF to the available other access (the Standby access), when Active access becomes unavailable. When the Active access becomes available again, the SDF is switched back to this access. If the Standby access is not defined, then the SDF is only allowed on the Active access and cannot be transferred on another access.
- Smallest Delay: It is used to steer a SDF to the access that is determined to have the smallest Round-Trip Time (RTT). As defined in clause 5.32.5, measurements may be obtained by the UE and UPF to determine the RTT over 3GPP access and over non-3GPP access. In addition, if one access becomes unavailable, all SDF traffic is switched to the other available access. It can only be used for the Non-GBR SDF.
- Load-Balancing: It is used to split a SDF across both accesses if both accesses are available. It contains the percentage of the SDF traffic that should be sent over 3GPP access and over non-3GPP access. Load-Balancing is only applicable to Non-GBR SDF. In addition, if one access becomes unavailable, all SDF traffic is switched to the other available access, as if the percentage of the SDF traffic transported via the available access was 100%.
- Priority-based: It is used to steer all the traffic of an SDF to the high priority access, until this access is determined to be congested. In this case, the traffic of the SDF is sent also to the low priority access, i.e. the SDF traffic is split over the two accesses. In addition, when the high priority access becomes unavailable, all SDF traffic is switched to the low priority access. How UE and UPF determine when a congestion occurs on an access is implementation dependent. It can only be used for the Non-GBR SDF.
- Redundant (without Threshold Values): It is used to duplicate traffic of an SDF on both accesses if both accesses are available. A Primary Access (either 3GPP access or Non-3GPP access) may be provided to the UE in the ATSSS rules and to the UPF in the N4 rules. If a Primary Access is provided, UE and UPF shall send all data packets of the SDF on the Primary Access and may duplicate data packets of the SDF on the other access. How many and which data packets are duplicated by UE and UPF on the other access is based on implementation. If the Primary Access is not provided to UE and UPF, the UE and UPF shall send all data packets of the SDF on both accesses. It can be used for GBR and Non-GBR SDF.
- A Steering Mode Indicator, which indicates that the UE may change the default steering parameters provided in the Steering Mode component and may adjust the traffic steering based on its own decisions. Only one of the following Steering Mode Indicators may be provided:
- Autonomous load-balance indicator: This indicator may be provided only when the Steering Mode is Load-Balancing. When provided, the UE may ignore the percentages in the Steering Mode component (i.e. the default percentages provided by the network) and may autonomously determine its own percentages for traffic splitting, in a way that maximizes the aggregated bandwidth in the uplink direction. The UE is expected to determine its own percentages for traffic splitting by performing measurements across the two accesses. The UPF may apply a similar behaviour when the autonomous load-balance indicator is included in an N4 rule.
- UE-assistance indicator: This indicator may be provided only when the Steering Mode is Load-Balancing. When provided by the network, it indicates that (a) the UE may decide how to distribute the UL traffic of the matching SDF based on the UE's internal state (e.g. when the UE is in the special internal state, e.g. lower battery level) and that (b) the UE may inform the UPF how it decided to distribute the UL traffic of the matching SDF. In the normal cases, although with this indicator provided, the UE shall distribute the UL traffic as indicated by the network.
NOTE 2: Typically, the UE-assistance indicator can be provided for SDFs for which the network has no strong steering requirements. For example, when the network has no strong steering requirements for the default traffic of an MA PDU Session, the network can indicate (i) that this traffic must be steered with Load-Balancing steering mode using 50% - 50% split percentages and (ii) that the UE is allowed to use other split percentages, such as 0% - 100%, if this is needed by the UE to optimize its operation (e.g. to minimize its battery consumption).
- Threshold Values: One or more threshold values may be provided when the Steering Mode is Priority-based or when the Steering Mode is Load-Balancing with fixed split percentages (i.e. without the Autonomous load-balance indicator or UE assistance indicator). One threshold value may be provided when the Steering Mode is Redundant. A threshold value may be either a value for RTT or a value for Packet Loss Rate. The threshold values are applicable to both accesses and are applied by the UE and UPF as follows:
- Load-Balancing Steering Mode with fixed split percentages (i.e. without the Autonomous load-balance indicator or UE assistance indicator): When at least one measured parameter (i.e. RTT or Packet Loss Rate) on one access exceeds the provided threshold value, the UE and UPF may stop sending traffic on this access, or may continue sending traffic on this access but should reduce the traffic on this access by an implementation specific amount and shall send the amount of reduced traffic on the other access. When all measured parameters (i.e. RTT and Packet Loss Rate) for both accesses do not exceed the provided threshold values, the UE and UPF shall apply the fixed split percentages.
- Priority-based Steering Mode: When one or more threshold values are provided for the Priority-based Steering Mode, these threshold values should be considered by UE and UPF to determine when an access becomes congested. For example, when a measured parameter (i.e. RTT or Packet Loss Rate) on one access exceeds the provided threshold value, the UE and UPF may consider this access as congested and send the traffic also to the low priority access.
- Redundant Steering Mode: When the measured Packet Loss Rate exceeds the provided threshold value on both accesses, the UE and UPF shall duplicate the traffic of the SDF on both accesses. When the measured RTT exceeds the provided threshold value on both accesses, the UE and UPF may duplicate the traffic of the SDF on both accesses based on implementation. When the measured parameter (i.e. either RTT or Packet Loss Rate) exceeds the provided threshold value on one access only, the UE and UPF shall send the traffic of the SDF only over the other access. When the measured parameter (i.e. either RTT or Packet Loss Rate) does not exceed the provided threshold value on any access, the UE and UPF shall send the traffic of the SDF only over the Primary Access. The Primary Access (either 3GPP access or Non-3GPP access) may be provided to the UE in the ATSSS rules and to the UPF in the N4 rules. If the Primary Access is not provided to the UE and UPF, UE and UPF shall select a Primary Access based on their own implementation (e.g. using the lowest RTT access or the lowest Packet Loss Rate access). If measurement results on an access are not available for a parameter, it is considered that the measured parameter for this access has not exceeded the provided threshold value. If a threshold value is provided when the Steering Mode is Redundant, the Steering Mode can only be used for Non-GBR SDF.
- A Steering Functionality, which identifies whether the MPTCP functionality, or the MPQUIC-UDP functionality, or the MPQUIC-IP functionality, or the MPQUIC-E functionality, or the ATSSS-LL functionality should be used to steer the traffic of the matching SDF. This is used when the UE supports multiple functionalities for ATSSS, as specified in clause 5.32.6 ("Support of Steering Functions").
- A Transport Mode, which identifies the transport mode that should be applied by the MPQUIC-UDP functionality, MPQUIC-IP functionality or MPQUIC-E functionality for the matching traffic. The transport modes supported by the MPQUIC-UDP functionality, MPQUIC-IP functionality and MPQUIC-E functionality are defined in clause 5.32.6.2.2.1.
NOTE 3: There is no need to update the ATSSS rules when one access becomes unavailable or available.
As an example, the following ATSSS rules could be provided to UE:
a) "Traffic Descriptor: UDP, DestAddr 1.2.3.4", "Steering Mode: Active-Standby, Active=3GPP, Standby=non-3GPP":
- This rule means "steer UDP traffic with destination IP address 1.2.3.4 to the active access (3GPP), if available. If the active access is not available, use the standby access (non-3GPP)".
b) "Traffic Descriptor: TCP, DestPort 8080", "Steering Mode: Smallest Delay":
- This rule means "steer TCP traffic with destination port 8080 to the access with the smallest delay". The UE needs to measure the RTT over both accesses, in order to determine which access has the smallest delay.
c) "Traffic Descriptor: TCP traffic of Application-1", "Steering Mode: Load-Balancing, 3GPP=20%, non-3GPP=80%", "Steering Functionality: MPTCP":
- This rule means "send 20% of the TCP traffic of Application-1 to 3GPP access and 80% to non-3GPP access by using the MPTCP functionality".
d) "Traffic Descriptor: TCP traffic of Application-1", "Steering Mode: Load-Balancing, 3GPP=20%, non-3GPP=80%, "Threshold Value for Packet Loss Rate: 1%", "Steering Functionality: MPTCP":
- This rule means "send 20% of the TCP traffic of Application-1 to 3GPP access and 80% to non-3GPP access as long as the Packet Loss Rate does not exceed 1% on both accesses, by using the MPTCP functionality. If the measured Packet Loss Rate of an access exceeds 1%, then the TCP traffic of Application-1 may be reduced on this access and sent via the other access".
e) "Traffic Descriptor: UDP traffic of Application-1", "Steering Mode: Load-Balancing, 3GPP=30%, non-3GPP=70%", "Steering Functionality: MPQUIC-UDP", "Transport Mode: Datagram mode 1":
- This rule means "send 30% of the UDP traffic of Application-1 to 3GPP access and 70% to non-3GPP access by using the MPQUIC-UDP steering functionality with the Datagram mode 1".
f) "Traffic Descriptor: com.example.app0, TCP", "Steering Mode: Redundant", "Steering Functionality: MPTCP":
- This rule means "traffic duplication is applied by the MPTCP steering functionality to the TCP traffic of application com.example.app0 and 100% of the traffic is duplicated over both accesses".
g) "Traffic Descriptor: com.example.app1, TCP", "Steering Mode: Redundant, Primary Access=3GPP, Threshold Value for Packet Loss Rate: 0.1%", "Steering Functionality: MPTCP":
- This rule means "traffic duplication is applied to the TCP traffic of application com.example.app1. If the measured PLR exceeds 0.1% on both accesses, all matched traffic is duplicated on both accesses. If the measured PLR exceeds 0.1% on one access only (either 3GPP or non-3GPP access), all matched traffic is sent over the other access only. If the measured PLR does not exceed 0.1% on any access, all matched traffic is sent over 3GPP access only as this is the Primary Access".
h) "Traffic Descriptor: com.example.app2, TCP", "Steering Mode: Redundant, Threshold Value for Packet Loss Rate: 0.1%", "Steering Functionality: MPTCP".
- This rule means "traffic duplication is applied to the TCP traffic of application com.example.app2. If the measured PLR exceeds 0.1% on both accesses, all matched traffic is duplicated and transmitted on both accesses. If the measured PLR exceeds 0.1% on one access only (either 3GPP or non-3GPP access), all matched traffic is sent over the other access only. If the measured PLR does not exceed 0.1% on any access, the UE or UPF selects the access based on their own implementation, e.g. the access with lower Packet Loss Rate to transmit all matched traffic".
i) "Traffic Descriptor: com.example.app3, IP", "Steering Mode: Load-Balancing, 3GPP=40%, non-3GPP=60%", "Steering Functionality: MPQUIC-IP", "Transport Mode: Datagram mode 1":
- This rule means "send 40% of the IP traffic of application com.example.app3 to 3GPP access and 60% to non-3GPP access by using the MPQUIC-IP functionality with the Datagram mode 1". |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33 Support for Ultra Reliable Low Latency Communication | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.1 General | The following features described in 5.33 may be used to enhance 5GS to support Ultra Reliable Low Latency Communication (URLLC):
- Redundant transmission for high reliability communication.
In this Release, URLLC applies to 3GPP access only.
When a PDU Session is to serve URLLC QoS Flow, the UE and SMF should establish the PDU Session as always-on PDU Session as described in clause 5.6.13.
NOTE 1: How the UE knows whether a PDU Session is to serve a URLLC QoS Flow when triggering PDU Session establishment is up to UE implementation.
NOTE 2: No additional functionality is specified for URLLC in order to support Home Routed roaming scenario in this Release. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.2 Redundant transmission for high reliability communication | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.2.1 Dual Connectivity based end to end Redundant User Plane Paths | In order to support highly reliable URLLC services, a UE may set up two redundant PDU Sessions over the 5G network, such that the 5GS sets up the user plane paths of the two redundant PDU Sessions to be disjoint. The user's subscription indicates if user is allowed to have redundant PDU Sessions and this indication is provided to SMF from UDM.
NOTE 1: It is out of scope of 3GPP how to make use of the duplicate paths for redundant traffic delivery end-to-end. It is possible to rely on upper layer protocols, such as the IEEE 802.1 TSN (Time Sensitive Networking) FRER (Frame Replication and Elimination for Reliability) [83], to manage the replication and elimination of redundant packets/frames over the duplicate paths which can span both the 3GPP segments and possibly fixed network segments as well.
NOTE 2: The following redundant network deployment aspects are within the responsibility of the operator and are not subject to 3GPP standardization:
- RAN supports dual connectivity and there is sufficient RAN coverage for dual connectivity in the target area.
- UEs support dual connectivity.
- The core network UPF deployment is aligned with RAN deployment and supports redundant user plane paths.
- The underlying transport topology is aligned with the RAN and UPF deployment and supports redundant user plane paths.
- The physical network topology and geographical distribution of functions also supports the redundant user plane paths to the extent deemed necessary by the operator.
- The operation of the redundant user plane paths is made sufficiently independent, to the extent deemed necessary by the operator, e.g. independent power supplies.
Figure 5.33.2.1-1 illustrates an example user plane resource configuration of dual PDU Sessions when redundancy is applied. One PDU Session spans from the UE via Master RAN node to UPF1 acting as the PDU Session Anchor and the other PDU Session spans from the UE via Secondary RAN node to UPF2 acting as the PDU Session Anchor. As described in TS 37.340 [31], NG-RAN may realize redundant user plane resources for the two PDU Sessions with two NG-RAN nodes (i.e. Master RAN node and Secondary RAN node as shown in Figure 5.33.2.1-1) or a single NG-RAN node. In both cases, there is a single N1 interface towards AMF.
Based on these two PDU Sessions, two independent user plane paths are set up. UPF1 and UPF2 connect to the same Data Network (DN), even though the traffic via UPF1 and UPF2 may be routed via different user plane nodes within the DN.
In order to establish two redundant PDU Sessions and associate the duplicated traffic coming from the same application to these PDU Sessions, URSP as specified in TS 23.503 [45] may be used, or alternatively the UE may perform this task independently from URSP.
When URSP is used to establish two redundant PDU Sessions, duplicated traffic from the application, associated to the redundant PDU Sessions, is differentiated by two distinct traffic descriptors, each in a distinct URSP rule. These traffic descriptors need to have different DNNs, IP descriptors or non-IP descriptors (e.g. MAC address, VLAN ID), so that the two redundant PDU Sessions are matched to the Route Selection Descriptors of distinct URSP rules. These Route Selection Descriptors of distinct URSP rules may include corresponding RSNs and PDU Session Pair IDs. The Route Selection Descriptors share same PDU Session Pair ID, if included, to denote the two traffic are redundant with each other. How does UE determines the PDU Session Pair ID and/or RSN from the matched URSP rules is described in clause 6.6.2 of TS 23.503 [45].
When the UE performs the establishment of two redundant PDU Sessions and the duplication of traffic independently from URSP, the UE may establish two redundant PDU Sessions even when the application does not duplicate the traffic and the application does not provide two distinct traffic descriptors. In this case the UE may set the RSN and PDU Session Pair ID in the PDU Session Establishment Request message based on UE implementation.
NOTE 3: As an example, the UE may use the implementation of FRER (Frame Replication and Elimination for Reliability), IEEE Std 802.1CB-2017 [83], in the UE's operating system.
If the operator decides to allow UE to use its own mechanisms to determine PDU Session Pair ID and RSN (where such UE capability is known based on local PCF configuration based on e.g. deployment, terminal implementation or policies per group of UE(s)), then the PCF shall not include PDU Session Pair ID and RSN in URSP rule.
The redundant user plane set up applies to both IP and Ethernet PDU Sessions.
Figure 5.33.2.1-1: Example scenario for end to end redundant User Plane paths using Dual Connectivity
Support of redundant PDU Sessions include:
- UE initiates two redundant PDU Sessions and may provide PDU Session Pair ID (optional) and the RSN (optional). Different combinations of RSN, DNN and S-NSSAI are used for each PDU Session within a given pair of redundant PDU Sessions. Different combinations of PDU Session Pair ID, DNN and S-NSSAI are used between the different pairs of redundant PDU Session.
- The UE may include a PDU Session Pair ID and/or RSN in each of the PDU Session establishment Request when it establishes redundant PDU Sessions. UE determines the PDU Session Pair ID and/or RSN based on UE local mechanism or the matched URSP rules.
- The SMF determines whether the PDU Session is to be handled redundantly. The determination is based on the presence of the PDU Session Pair ID and/or RSN in the PDU Session Establishment Request or the determination is based on an indication that redundant PDU Session is required provided by PCF for the PDU Session, if dynamic PCC applies for the PDU Session or the combination of the S-NSSAI, DNN, user subscription and local policy configuration in the SMF if dynamic PCC is not used for the PDU Session. If the PDU session is to be handled redundantly and the PDU Session Pair ID was not included in the PDU Session Establishment request, the SMF uses S-NSSAI, DNN and local configuration to determine the PDU Session Pair ID. If the PDU session is to be handled redundantly and RSN was not included in the PDU Session Establishment request, the SMF uses S-NSSAI, DNN to determine the RSN value. The RSN differentiates the PDU Sessions that are handled redundantly and indicates redundant user plane requirements for the PDU Sessions in NG-RAN.
- The SMF shall provide the RSN and PDU Session Pair ID to the NG-RAN for a redundant PDU Session.
- Operator configuration of UPF selection ensures the appropriate UPF selection for disjoint paths.
- At establishment of the PDU Sessions or at transitions to CM-CONNECTED state, the RSN parameter indicates to NG-RAN that redundant user plane resources shall be provided for the given PDU Sessions by means of dual connectivity. The PDU Session Pair ID identifies the two redundant PDU Sessions that belong together. The value of the RSN parameter and the PDU Session Pair ID indicates redundant user plane requirements for the PDU Sessions. This request for redundant handling is made by indicating the RSN to the NG-RAN node on a per PDU Session granularity. PDU Sessions associated with different RSN values shall be realized by different, redundant UP resources. Based on the RSN, the PDU Session Pair ID and RAN configuration, the NG-RAN sets up dual connectivity as defined in TS 37.340 [31] so that the sessions have end to end redundant paths. When there are multiple PDU Sessions with the RSN parameter set, of different values of RSN and the same PDU Session Pair ID, this indicates to NG-RAN that CN is requesting dual connectivity to be set up and the user plane shall be handled as indicated by the RSN parameter, the PDU Session Pair ID and the associated RAN configuration. If the RSN value and PDU Session Pair ID are provided to the NG-RAN, NG-RAN shall consider the RSN value and PDU Session Pair ID when it associates the PDU Sessions with NG-RAN UP.
NOTE 4: The decision to set up dual connectivity remains in NG-RAN as defined today. NG-RAN takes into account the additional request for the dual connectivity setup provided by the CN.
- Using NG-RAN local configuration, NG-RAN determines whether the request to establish RAN resources for a PDU Session is fulfilled or not considering user plane requirements indicated by the RSN parameter and the PDU Session Pair ID by means of dual connectivity. If the request to establish RAN resources for PDU Session can be fulfilled by the RAN, the PDU Session is established even if the user plane requirements indicated by RSN cannot be satisfied. The decision for each PDU Session is taken independently (i.e. rejection of a PDU Session request shall not release the previously established PDU Session). The RAN shall determine whether to notify the SMF if the RAN resources indicated by the RSN parameter and the PDU Session Pair ID can no longer be maintained and SMF can use that to determine if the PDU Session should be released.
- In the case of Ethernet PDU Sessions, the SMF has the possibility to change the UPF (acting as the PSA) and select a new UPF based on the identity of the Secondary RAN node for the second PDU Session if the Secondary RAN node is modified (or added/released), using the Ethernet PDU Session Anchor Relocation procedure described in clause 4.3.5.8 of TS 23.502 [3].
- The SMF's charging record may reflect the RSN information.
- The RSN parameter and the PDU Session Pair ID, if available, is transferred from Source NG-RAN to Target NG-RAN in the case of handover. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.2.2 Support of redundant transmission on N3/N9 interfaces | If the reliability of NG-RAN node, UPF and CP NFs are high enough to fulfil the reliability requirement of URLLC services served by these NFs, but the reliability of single N3 tunnel is considered not high enough, e.g. due to the deployment environment of backhaul network, the redundant transmission may be deployed between PSA UPF and NG-RAN via two independent N3 tunnels, which are associated with a single PDU Session, over different transport layer path to enhance the reliability. SMF may make use of Redundant Transmission Experience analytics provided by NWDAF, as described in clause 6.13 of TS 23.288 [86], to determine whether redundant transmission for the PDU session of the URLLC shall be performed or (if activated) shall be stopped.
To ensure the two N3 tunnels are transferred via disjointed transport layer paths, the SMF or PSA UPF should provide different routing information in the tunnel information (e.g. different IP addresses or different Network Instances) and these routing information should be mapped to disjoint transport layer paths according to network deployment configuration. The SMF indicates NG-RAN and PSA UPF that one of the two CN/AN Tunnel Info is used as the redundancy tunnel of the PDU Session accordingly. The redundant transmission using the two N3/N9 tunnels are performed at QoS Flow granularity and are sharing the same QoS Flow ID.
During or after a URLLC QoS Flow establishment, if the SMF decided that redundant transmission shall be performed based on authorized 5QI, NG-RAN node capability, operator configuration and/or Redundant Transmission Experience analytics, the SMF informs the PSA UPF and NG-RAN to perform redundant transmission via N4 interface and N2 information accordingly. In this case, NG-RAN should also provide different routing information in the tunnel information (e.g. different IP addresses) and these routing information should be mapped to disjoint transport layer paths according to network deployment configuration.
NOTE 1: The NG-RAN node capability to support the redundant transmission on N3/N9 can be configured in the SMF per network slice or per SMF service area.
If duplication transmission is performed on N3/N9 interface, for each downlink packet of the QoS Flow the PSA UPF received from DN, the PSA UPF replicates the packet and assigns the same GTP-U sequence number to them for the redundant transmission. The NG-RAN eliminates the duplicated packets based on the GTP-U sequence number and then forwards the PDU to the UE.
For each uplink packet of the QoS Flow the NG-RAN received from UE, the NG-RAN replicates the packet and assigns the same GTP-U sequence number to them for redundant transmission. These packets are transmitted to the PSA UPF via two N3 Tunnels separately. The PSA UPF eliminates the duplicated packet based on the GTP-U sequence number accordingly.
NOTE 2: How to realize the sequence number for support of GTP-U duplication over N3/N9 is up to stage 3.
NOTE 3: For redundant transmission on N3/N9 interfaces, reordering is not required on the receiver side.
The PSA UPF and NG-RAN may transmit packets via one or both of the tunnels per QoS Flow based on SMF instruction.
NOTE 4: The AMF selects an SMF supporting redundant transmission based on the requested S-NSSAI and/or DNN.
During UE mobility, when the UE moves from NG-RAN supporting redundant transmission to NG-RAN not supporting redundant transmission, the SMF may release the QoS Flow which are subject to redundant transmission.
Figure 5.33.2.2-1 illustrates the case that the redundant transmission is performed only on N3 interface. These packets are transmitted to the NG-RAN via two N3 Tunnels separately. The RAN node and PSA UPF shall support the packet replication and elimination function as described above.
Figure 5.33.2.2-1: Redundant transmission with two N3 tunnels between the PSA UPF and a single NG-RAN node
Two Intermediate UPFs (I-UPFs) between the PSA UPF and the NG-RAN may be used to support the redundant transmission based on two N3 and N9 tunnels between a single NG-RAN node and the PSA UPF. The NG-RAN node and PSA UPF shall support the packet replication and elimination function as described above.
Figure 5.33.2.2-2: Two N3 and N9 tunnels between NG-RAN and PSA UPF for redundant transmission
In figure 5.33.2.2-2, there are two N3 and N9 tunnels between NG-RAN and PSA UPF for the URLLC QoS Flow(s) of the same PDU Session for redundant transmission established during or after a URLLC QoS Flow establishment. In the case of downlink traffic, the PSA UPF duplicates the downlink packet of the QoS Flow from the DN and assigns the same GTP-U sequence number to them. These duplicated packets are transmitted to I-UPF1 and I-UPF2 via N9 Tunnel 1 and N9 Tunnel 2 separately. Each I-UPF forwards the packet with the same GTP-U sequence number which receives from the PSA UPF to NG-RAN via N3 Tunnel 1 and N3 Tunnel 2 respectively. The NG-RAN eliminates the duplicated packet based on the GTP-U sequence number. In the case of uplink traffic, the NG-RAN duplicates the packet of the QoS Flow from the UE and assigns the same GTP-U sequence number to them. These duplicated packets are transmitted to I-UPF1 and I-UPF2 via N3 Tunnel 1 and N3 Tunnel 2 separately. Each I-UPF forwards the packet with the same GTP-U sequence number which receives from the NG-RAN to PSA UPF via N9 Tunnel 1 and N9 Tunnel 2 respectively. The PSA UPF eliminates the duplicated packets based on the GTP-U sequence number.
The I-UPFs inserted on one leg of the redundant paths shall not behave in an UL CL or Branching Point role. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.2.3 Support for redundant transmission at transport layer | Redundant transmission can be supported within the 5G System without making any assumption on support for protocols such as IEEE FRER in the application layer (DN only) at the same time it can be supported without requiring redundant GTP-U tunnel over N3. The backhaul provides two disjoint transport paths between UPF and NG-RAN. The redundancy functionality within NG-RAN and UPF make use of the independent paths at transport layer. Support of redundant transmission at transport layer requires no 3GPP protocol impact.
Following are the required steps:
- UE establishes the PDU session for URLLC services. Based on DNN, S-NSSAI, knowledge of supporting redundant transmission at transport layer and other factors as described in clause 6.3.3, SMF selects a UPF that supports redundant transmission at transport layer for the PDU session. One N3 GTP-U tunnel is established between UPF and NG-RAN.
The knowledge of supporting redundant transmission at transport layer can be configured in the SMF, or be configured in UPF and then obtained by the SMF via N4 capability negotiation during N4 Association setup procedure.
- For DL data transmission, UPF sends the DL packets on N3 GTP-U tunnel. Redundant functionality in the UPF duplicates the DL data on the transport layer. Redundant functionality in the NG-RAN eliminates the received duplicated DL data and sends to NG-RAN.
- For UL data transmission, NG-RAN sends the received UL packets on N3 GTP-U tunnel, the Redundant functionality in the NG-RAN performs the redundant handling on the backhaul transport layer. The Redundant functionality in the UPF eliminates the received duplicated UL data and sends to UPF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.3 QoS Monitoring for packet delay | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.3.1 General | QoS Monitoring for packet delay can be applied based on 3rd party application request or PCF policy control or both, e.g. to assist URLLC services. The packet delay between UE and PSA UPF is a combination of the RAN part of UL/DL packet delay as defined in TS 38.314 [120] and UL/DL packet delay between NG-RAN and PSA UPF. The NG-RAN is required to provide the QoS monitoring results on the RAN part of UL/DL packet delay measurement. The measurement of the UL/DL packet delay between NG-RAN and PSA UPF can be performed on different levels of granularities, i.e. per QoS Flow per UE level, or per GTP-U path level, subject to the operators' configuration.
The PCF generates the authorized QoS Monitoring policy for a service data flow based on the QoS Monitoring request received from the AF (as described in clause 6.1.3.21 of TS 23.503 [45]). The PCF includes the authorized QoS Monitoring policy in the PCC rule and provides it to the SMF.
When SMF receives the authorized QoS Monitoring policy for packet delay in a PCC rule from the PCF (as described in clause 6.1.3.21 of TS 23.503 [45]), SMF configures the UPF(s) and NG-RAN to perform delay measurements according to the method selected: per QoS Flow per UE QoS measurement (as described in clause 5.33.3.2) or per GTP-U Path measurement (as described in clause 5.33.3.3). The SMF configure the UPF to report the QoS monitoring results for the QoS Flow as described in clause 5.8.2.18 with parameters determined by the SMF based on the authorized QoS Monitoring policy received from the PCF and/or local configuration.
The UPF reporting behaviour for QoS Monitoring for packet delay of a QoS Flow is the same when per QoS Flow per UE level measurement (described further in clause 5.33.3.2) or when per GTP-U path level measurement (described further in clause 5.33.3.3) is used. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.3.2 Per QoS Flow per UE QoS Measurement | SMF may activate the end to end UL/DL packet delay measurement between UE and PSA UPF for a QoS Flow during the PDU Session Establishment or Modification procedure.
The SMF sends a QoS Monitoring request to the PSA UPF via N4 and NG-RAN via N2 signalling to request the QoS monitoring between PSA UPF and NG-RAN. The QoS Monitoring request may contain monitoring parameters determined by SMF based on the authorized QoS Monitoring policy received from the PCF and/or local configuration.
The NG-RAN initiates the RAN part of UL/DL packet delay measurement based on the QoS Monitoring request from SMF. NG-RAN reports the RAN part of UL/DL packet delay result to the PSA UPF in the UL data packet or dummy UL packet.
If the NG-RAN and PSA UPF are time synchronised, the one way packet delay monitoring between NG-RAN and PSA UPF is supported.
If the NG-RAN and PSA UPF are not time synchronised, it is assumed that the UL packet delay and the DL packet delay between NG-RAN and PSA UPF are the same.
For both time synchronised and not time synchronised between NG-RAN and PSA UPF, the PSA UPF creates and sends the monitoring packets to the RAN in a measurement frequency, decided by the PSA UPF, taking the Reporting frequency for QoS Monitoring received from the SMF into account:
- The PSA UPF encapsulates in the GTP-U header with QFI, QoS Monitoring Packet (QMP) indicator (which indicates the packet is used for UL/DL packet delay measurement) and the local time T1 when the PSA UPF sends out the DL monitoring packets.
- The NG-RAN records the local time T1 received in the GTP-U header and the local time T2 at the reception of the DL monitoring packets.
- When receiving an UL packet from UE for that QFI or when the NG-RAN sends a dummy UL packet as monitoring response (in case there is no UL service packet for UL packet delay monitoring), the NG-RAN encapsulates QMP indicator, the RAN part of UL/DL packet delay result, the time T1 received in the GTP-U header, the local time T2 at the reception of the DL monitoring packet and the local time T3 when NG-RAN sends out this monitoring response packet to the UPF via N3 interface, in the GTP-U header of the monitoring response packet.
NOTE 1: When the NG-RAN sends the dummy UL packet as monitoring response to PSA UPF depends on NG-RAN's implementation.
- The PSA UPF records the local time T4 when receiving the monitoring response packets and calculates the round trip (if not time synchronized) or UL/DL packet delay (if time synchronized) between NG-RAN and anchor PSA UPF based on the time information contained in the GTP-U header of the received monitoring response packet. If the NG-RAN and PSA UPF are not time synchronised, the PSA UPF calculates the UL/DL packet delay between the NG-RAN and the PSA UPF based on the (T2-T1+T4-T3)/2. If the NG-RAN and PSA UPF are time synchronised, the PSA UPF calculates the UL packet delay and DL packet delay between the NG-RAN and the PSA UPF based on (T4-T3) and (T2-T1), respectively. The PSA UPF calculates the UL/DL packet delay between UE and PSA UPF based on the received RAN part of UL/DL packet delay result and the calculated UL/DL packet delay between RAN and PSA UPF.
NOTE 2: If the NG-RAN and PSA UPF are not time synchronised, it can cause inaccurate result of UL/DL packet delay.
- The PSA UPF reports the QoS Monitoring results as described in clause 5.8.2.18.
If the redundant transmission on N3/N9 interfaces is activated, the UPF and NG-RAN performs QoS monitoring for both UP paths. The UPF reports the packet delays of the two UP paths independently to the SMF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.33.3.3 GTP-U Path Measurement | The SMF can request to activate QoS monitoring for the GTP-U path(s) between all UPF(s) and the (R)AN based on locally configured policies. Alternatively, when a QoS monitoring policy is received in a PCC rule and the QoS monitoring is not yet active for the DSCP corresponding to the 5QI in the PCC rule, the SMF activates QoS Monitoring for all UPFs currently in use for this PDU Session and the (R)AN. In this case, the SMF performs the QoS Flow Binding without taking the QoS Monitoring Policy within the PCC rule into account. The SMF sends the QoS monitoring policy to each involved UPF and the (R)AN via N4 interface and via N2 interface respectively.
NOTE 1: The PCC rule containing a QoS monitoring policy is just a trigger for the SMF to instruct the UPFs to initiate the GTP-U based QoS Monitoring.
A GTP-U sender performs an estimation of RTT to a GTP-U receiver on a GTP-U path by sending Echo messages and measuring time that elapses between the transmission of Request message and the reception of Response message. A GTP-U sender computes an accumulated packet delay by adding RTT/2, the processing time and, if available, an accumulated packet delay from an upstream GTP-U sender (i.e. an immediately preceding GTP-U sender in user plane path) thus the measured accumulated packet delay represents an estimated elapsed time since a user plane packet entered 3GPP domain.
It is expected that a GTP-U sender determines RTT periodically in order to detect changes in transport delays. QoS monitoring is performed by a GTP-U end-point (UP function) that receives, stores and executes the QoS monitoring policy as described below for a QoS Flow. QoS monitoring is performed by comparing a measured accumulated packet delay with the stored parameters. If the GTP-U end-point (the PSA UPF, in the case of accumulated packet delay reporting) determines that the packet delay exceeds the value of a stored parameter, then the node triggers QoS monitoring alert signalling to the relevant SMF or to the OA&M function as further described in TS 29.244 [65].
NOTE 2: Echo Request message and Echo Response message are sent outside GTP-U tunnels (the messages are using TEID set to 0). If underlying transport is using QoS differentiation (e.g. IP DiffServ) then it is up to the implementation to ensure that the Echo messages are classified correctly and receive similar treatment by the underlaying transport as GTP-U GTP-PDUs carrying QoS Flows (user data).
When QoS Monitoring is used to measure the packet delay for a QoS Flow, the following applies:
- Packet delay measurement is performed by using GTP-U Echo Request/Response as defined in the TS 28.552 [108], in the corresponding user plane transport path(s), independent of the corresponding PDU Session and the 5QI for a given QoS Flow.
- RAN measures and provides the RAN part of UL/DL packet delay towards UPF (in the GTP-U header of the respective QoS Flow via N3).
- The UPF calculates the UL/DL packet delay by combining the received measurements of RAN part with the measurements of N3/N9 interface (N9 is applicable when I-UPF exists).
- The UPF reports the QoS Monitoring results as described in clause 5.8.2.18.
QoS Monitoring can also be used to measure the packet delay for transport paths to influence the mapping of QoS Flows to appropriate network instances, DSCP values as follows:
- SMF activates QoS monitoring for the GTP-U path(s) between all UPF(s) and all (R)AN nodes based on locally configured policies.
- UPF does measurement of network hop delay per transport resources that it will use towards a peer network node identified by an IP destination address (the hop between these two nodes) and port. The network hop measured delay is computed by sending an Echo Request over such transport resource (Ti) and measuring RTT/2 when Echo Response is received.
- UPF maps {network instance, DSCP} into Transport Resource and measures delay per IP destination address and port. Thus, for each IP destination address, the measured delay per (network instance, DSCP) entry is determined.
- The UPF performing the QoS monitoring can provide the corresponding {Network instance, DSCP} along with the measured accumulated packet delay for the corresponding transport path to the SMF. The UPF reports the measurement results to the SMF based on some specific conditions e.g. first time, periodic, event triggered, when thresholds for reporting towards SMF (via N4) are reached.
- Based on this, SMF can determine QoS Flow mapping to the appropriate {Network instance, DSCP} considering {5QI, QoS characteristics, ARP} for the given QoS Flow. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34 Support of deployments topologies with specific SMF Service Areas | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.1 General | When the UE is outside of the SMF Service Area, or current SMF cannot serve the target DNAI for the traffic routing for local access to the DN or when the UE is within the SMF service area as well as Local Offloading Management service area and Local Offloading Management (see clause 6.10 of TS 23.548 [130] and clause 5.34.11) is allowed, an I-SMF is inserted between the SMF and the AMF. The I-SMF has a N11 interface with the AMF and a N16a interface with the SMF and is responsible of controlling the UPF(s) that the SMF cannot directly control. The exchange of the SM context and forwarding of tunnel information if needed are done between two SMFs directly without involvement of AMF.
Depending on scenario, a PDU Session in non-roaming case or local breakout is either served by a single SMF or served by an SMF and an I-SMF. When a PDU Session is served by both an SMF and an I-SMF, the SMF is the NF instance that has the interfaces towards the PCF and CHF.
In this Release of the specification, deployments topologies with specific SMF Service Areas apply only for 3GPP access.
The SMF shall release or reject the PDU Session if the DNN of the PDU Session corresponds to a LADN and the I-SMF is inserted to the PDU Session.
NOTE 1: This implies that operators need to plan the LADN deployment in such a way that the LADN Service area needs to be within the SMF Service Area, but not across SMFs' Service Areas.
NOTE 2: This is to cover the case where the UE is not in or moves out of SMF Service Area and an I-SMF is inserted to the PDU Session e.g. during PDU Session Establishment, Service Request. If the PDU Session is maintained with I-SMF, the SMF is not be able to enforce the LADN Service control, e.g. SMF is not notified in the case of Service Request.
Independent of whether deployments topologies with specific SMF Service Areas apply, the SMF may trigger the PDU Session re-establishment to the same DN, if the PDU Session is associated with the SSC mode 2 or SSC mode 3.
NOTE 3: SSC mode 2 or SSC mode 3 can be used to optimize SMF location for a PDU Session and/or, depending on deployment, ensure that the UE is always within the service area of the SMF controlling the PDU Session. In this case (when PDU Session continuity over the PLMN is not required) procedures described in this clause are not needed.
In this Release, how TSC (as defined in clauses 5.27 and 5.28) is supported for PDU Sessions involving an I-SMF is not specified.
In this Release, Redundant User Plane Paths as defined in clause 5.33.2.2 is not supported for PDU Sessions involving an I-SMF.
Redundant PDU sessions support as defined in clause 5.33.2.1 is supported for PDU Sessions involving an I-SMF, when different S-NSSAIs are used for the redundant PDU sessions.
Redundant User Plane Paths as defined in clause 5.33.2.3 is supported for PDU Sessions involving an I-SMF only if this PDU session is established for a S-NSSAI referring to network instances requiring redundant transmission at transport layer.
QoS monitoring (as defined in clause 5.33.3) is supported as long as SMF and not I-SMF initiates the QoS monitoring function.
Dynamic CN PDB provisioning (as defined in clause 5.7.3.4) is supported for PDU Sessions involving an I-SMF.
In this Release, no dedicated functionality is specified for I-SMF and N16a in order to support NPN. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.2 Architecture | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.2.1 SBA architecture | In non-roaming case the SBA architecture described in Figure 4.2.3-1 shall apply. In local breakout scenarios the SBA architecture described in Figure 4.2.4-1 shall apply. In Home Routed scenarios the SBA architecture described in Figure 4.2.4-3 shall apply. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.2.2 Non-roaming architecture | Figure 5.34.2.2-1 depicts the non-roaming architecture with an I-SMF insertion to the PDU Session without UL-CL/BP, using reference point representation.
NOTE 1: N16a is the interface between SMF and I-SMF.
NOTE 2: N38 is the interface between I-SMFs.
Figure 5.34.2.2-1: Non-roaming architecture with I-SMF insertion to the PDU Session in reference point representation, with no UL-CL/BP
Figure 5.34.2.2-2 depicts the non-roaming architecture for an I-SMF insertion to the PDU Session with UL-CL/BP, using reference point representation.
Figure 5.34.2.2-2: Non-roaming architecture with I-SMF insertion to the PDU Session in reference point representation, with UL-CL/BP
For Local Offloading Management scenario in TS 23.548 [130], the architecture in Figure 5.34.2.2-2 applies with an additional reference point N88a for interface between I-SMF and EASDF, which is not shown for simplicity. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.2.3 Roaming architecture | Figure 5.34.2.3-1 depicts 5G System roaming architecture in the case of local break out scenario where the SMF controlling the UPF connecting to NG-(R)AN is separated from the SMF controlling PDU Session anchor, using the reference point representation.
Figure 5.34.2.3-1: Roaming 5G System architecture with SMF/I-SMF - local breakout scenario in reference point representation
For the case of home routed scenario, Figure 4.2.4-6 applies. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.3 I-SMF selection, V-SMF reselection | The AMF is responsible of detecting when to add or to remove an I-SMF or a V-SMF for a PDU Session. For this purpose, the AMF gets from NRF information about the Service Area, supported DNAI(s) of SMF(s) and SMF(s) supporting Local Offloading Management. Local Offloading Management described in clause 5.34.11 and in clause 6.10 of TS 23.548 [130].
During mobility events such as Hand-Over or AMF change, if the service area of the SMF does not include the new UE location, then the AMF selects and inserts an I-SMF which can serve the UE location and the S-NSSAI. If I-SMF is inserted for Local Offloading Management for a case when the UE is within or outside the anchor SMF service area and within Local Offloading Management service area, the AMF selects and inserts an I-SMF which can serve the UE location, the S-NSSAI and support Local Offloading Management. Conversely if the AMF detects that an I-SMF is no more needed (as the service area of the SMF includes the new UE location and if the I-SMF was not inserted for Local Offloading Management or the UE is outside the Local Offloading Management service area) it removes the I-SMF and interfaces directly with the SMF of the PDU Session. If the AMF detects that the SMF cannot serve the UE location (e.g. due to mobility), then the AMF selects a new I-SMF serving the UE location. If the existing I-SMF (or V-SMF) cannot serve the UE location (e.g. due to mobility) and the service area of the SMF does not include the new UE location (or the PDU Session is Home Routed), then the AMF initiates an I-SMF (or V-SMF) change. A V-SMF change may take place either at intra-PLMN or inter-PLMN mobility.
According to the PCC rules related with AF influence traffic mechanism regarding DNAI(s), the SMF determines the target DNAI which is applicable to the current UE location and which can be based on the common DNAI (if applicable) as described in TS 23.548 [130]. If current (I-)SMF cannot serve the target DNAI or if the SMF can serve the target DNAI and existing I-SMF is not needed, the SMF may send the target DNAI information to the AMF for triggering I-SMF (re)selection or removal, e.g. the AMF performs I-SMF (re)selection or removal based on the target DNAI and supported DNAI(s) of (I-)SMF. If the SMF determines that target DNAI currently served by I-SMF should not be used for the PDU Session hence the existing I-SMF is not needed (e.g. due to the updated PCC rules removes DNAI(s) that was provided in the previous PCC rules), the SMF sends the target DNAI information without including target DNAI to AMF, which may trigger the I-SMF removal.
At PDU Session Establishment in non-roaming and roaming with LBO scenarios, if the AMF or SCP cannot select an SMF with a Service Area supporting the current UE location for the selected (DNN, S-NSSAI) and required SMF capabilities, the AMF selects an SMF for the selected (DNN, S-NSSAI) and required capabilities and in addition selects an I-SMF serving the UE location and the S-NSSAI.
Compared to the SMF selection function defined in clause 6.3.2, the following parameters are not applicable for I-SMF/V-SMF selection:
- Data Network Name (DNN).
- Subscription information from UDM.
NOTE 1: All SMF(s) and I-SMF are assumed to be able to control the UPF mapping between EPC bearers and 5GC QoS Flows.
If HR-SBO roaming is allowed for a PDU Session, the DNN is also considered for V-SMF selection.
If delegated SMF discovery is used at PDU Session establishment:
1. The AMF sends Nsmf_PDUSession_CreateSMContext Request to SCP and includes the parameters as defined in clause 6.3.2 (e.g. the DNN, required SMF capabilities, UE location) as discovery and selection parameters. If the SCP successfully selects an SMF matching all discovery and selection parameters, the SCP forwards the Nsmf_PDUSessionCreateSMContext Request to the selected SMF.
2. If the SCP cannot select an SMF matching all discovery and selection parameters, the SCP returns a dedicated error to AMF. In this case the I-SMF also need be discovered.
3. Upon reception of the error from the SCP that an SMF matching all discovery and selection parameters cannot be found, the AMF performs the discovery and selection of the SMF from NRF (thus not providing the UE location as a discovery parameter). The AMF may indicate the maximum number of SMF instances to be returned from NRF, i.e. SMF selection at NRF.
4. The AMF sends Nsmf_PDUSession_CreateSMContext Request to SCP, which includes the endpoint (e.g. URI) of the selected SMF and the discovery and selection parameters as defined in clause 6.3.2 except the DNN and the required SMF capabilities, i.e. parameter for I-SMF selection. The SCP performs discovery and selection of the I-SMF and forwards the Nsmf_PDUSession_CreateSMContext Request to the selected I-SMF.
5. The I-SMF sends the Nsmf_PDUSession_Create Request towards the SMF via the SCP; the I-SMF uses the received endpoint (e.g. URI) of the selected SMF to construct the target destination to be addressed. The SCP forwards the Nsmf_PDUSession_Create Request to the SMF.
6. The SMF answers to the I-SMF that answers to the AMF; in this answer the AMF receives the I-SMF ID.
7. Upon reception of a response from I-SMF, based on the received I-SMF ID, the AMF may obtain the SMF Service Area of the I-SMF from NRF. The AMF uses the SMF Service Area of the I-SMF to determine the need for I-SMF relocation upon subsequent UE mobility.
If delegated I-SMF discovery is used once the PDU Session establishment has been established, the procedure starts at step 4 above and is further detailed in the messages flows in clause 23 of TS 23.502 [3].
If delegated V-SMF discovery is used for V-SMF reselection, clause 6.3.2 applies, but there is no need for discovery and selection of the H-SMF. This is further detailed in the messages flows in clause 23 of TS 23.502 [3]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.4 Usage of an UL Classifier for a PDU Session controlled by I-SMF | This clause applies only in the case of non-roaming or LBO roaming as control of UL CL/BP in VPLMN is not supported in HR case.
When I-SMF is involved for a PDU Session, it is possible that the UL CL controlled by I-SMF is inserted into the data path of the PDU Session. The usage of an ULCL controlled by I-SMF in the data path of a PDU Session is depicted in Figure 5.34.4-1.
Figure 5.34.4-1: User plane Architecture for the Uplink Classifier controlled by I-SMF
The I-SMF determines whether UL CL will be inserted based on information received from SMF and the I-SMF selects the UPFs acting as UL CL and/or PDU Session Anchor providing local access to the Data Network. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.5 Usage of IPv6 multi-homing for a PDU Session controlled by I-SMF | This clause applies only in the case of non-roaming or LBO roaming as control of UL CL/BP in VPLMN is not supported in HR case.
When I-SMF is involved for a PDU Session, it is possible that the BP controlled by I-SMF is inserted into the data path of the PDU Session. The usage of a BP controlled by I-SMF in the data path of a PDU Session is depicted in Figure 5.34.5-1.
Figure 5.34.5-1: Multi-homed PDU Session: Branching Point controlled by I-SMF
The I-SMF determines whether BP will be inserted based on information received from SMF and the I-SMF selects the UPFs acting as BP and/or PDU Session Anchor providing local access to the Data Network. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.6 Interaction between I-SMF and SMF for the support of traffic offload by UPF controlled by the I-SMF | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.6.1 General | This clause applies only in the case of non-roaming or LBO roaming as control of UL CL/Branching Point in VPLMN is not supported in HR case. It applies for the architectures described in clauses 5.34.4 and 5.34.5
If the local offloading management is applied for the PDU session, see clause 6.10 of TS 23.548 [130] and clause 5.34.11.
When the I-SMF is inserted into a PDU Session, e.g. during PDU Session establishment or due to UE mobility, the I-SMF may provide the DNAI list it supports to the SMF. Based on the DNAI list information received from I-SMF, the SMF may provide the DNAI(s) of interest for this PDU Session for local traffic steering and Local Offloading Management Policy received from PCF that indicates IP range(s) and/or FQDN(s) allowed to be routed to the local part of a DN to the I-SMF e.g. immediately or when a new or updated or removed PCC rule(s) is/are received. The DNAI(s) of interest is derived from PCC rules. The Local Offloading Management Policy received from PCF is sent via SMF to the I-SMF.
The I-SMF is responsible for the insertion, modification and removal of UPF(s) to ensure local traffic steering. The SMF does not need to have access to local configuration or NRF output related with UPF(s) controlled by I-SMF. Based on the DNAI(s) of interest for this PDU Session for local traffic steering and UE location the I-SMF determines which DNAI(s) are to be selected, selects UPF(s) acting as UL CL/BP and/or PDU Session Anchor based on selected DNAI and insert these UPF(s) into the data path of the PDU Session. If the Indication of considering N6 delay is received the I-SMF triggers N6 delay measurement by considering the N6 delay measurement assistance information as part of EAS Deployment Information as described in clause 6.2.3.4 of TS 23.548 [130].
When a UL CL/BP has been inserted, changed or removed, the I-SMF indicates to the SMF that traffic offload have been inserted, updated or removed for a DNAI, providing also the IPv6 prefix that has been allocated if a new IPv6 prefix has been allocated for the PDU Session.
From now on the SMF and I-SMF interactions entail:
- Notifying the SMF with the new Prefix (multi-Homing case): the SMF is responsible of issuing Router Advertisement message. The SMF constructs a link-local address as the source IP address. The Router Advertisement message includes the IPv6 multi-homed routing rules provided to the UE to select the source IPv6 prefix among the prefixes related with the PDU Session according to RFC 4191 [8]. The SMF sends the Router Advertisement message to the UE via the PSA UPF controlled by the SMF.
- N4 interactions related with traffic offloading. The SMF provide N4 information to the I-SMF for how the traffic shall be detected, enforced, monitored in UPF(s) controlled by the I-SMF: the SMF issues requests to the I-SMF containing N4 information to be used for creating / updating /removing PDR, FAR, QER, URR, etc. The N4 information for local traffic offload provided by the SMF to the I-SMF are described in clause 5.34.6.2.
- Receiving N4 notifications related with traffic usage reporting: the I-SMF forwards to the SMF N4 information corresponding to UPF notifications related with traffic usage reporting; the SMF aggregates and constructs usage reports towards PCF/CHF.
NOTE: How the SMF decides what traffic steering and enforcement actions are enforced in UPF(s) controlled by I-SMF is left for implementation.
The I-SMF is responsible of the N4 interface towards the local UPF(s) including:
- the usage of AN Tunnel Info received from the 5G AN via the AMF in order to build PDR and FAR;
- requesting the allocation of the CN Tunnel Info between local UPFs (if needed);
- to control UPF actions when the UP of the PDU Session becomes INACTIVE.
- provide Trace Requirements on the N4 interface towards the UPF(s) it is controlling, using Trace Requirements received from AMF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.6.2 N4 information sent from SMF to I-SMF for local traffic offload | The SMF generates N4 information for local traffic offload based on the available DNAI(s) indicated by the I-SMF, PCC rules associated with these DNAI(s) and charging requirement. This N4 information is sent from the SMF to the I-SMF after UL CL/Branching Point insertion/update/removal and the I-SMF uses this N4 information to derive rules installed in the UPFs controlled by the I-SMF.
The N4 information for local traffic offload corresponds to rules and parameters defined in clause 5.8.5, i.e. PDR, FAR, URR and QER. It contains identifiers allowing the SMF to later modify or delete these rules.
N4 information for local traffic offload is generated by the SMF without knowledge of how many local UPF(s) are actually used by the I-SMF. The SMF indicates whether a rule within N4 information is enforced in UL CL/ Branching Point or local PSA. If the rule is applied to the local PSA, the N4 information includes the associated DNAI. The I-SMF generates suitable rules for the UPF(s) based on the N4 information received from SMF.
NOTE: The SMF is not aware of whether there is a single PSA or multiple PSA controlled by I-SMF.
The following parameters are managed by the I-SMF:
- The 5G AN Tunnel Info.
- CN tunnel info between local UPFs.
- Network instance (if needed).
The N4 information exchanged between I-SMF and SMF are not associated with a N4 Session ID but are associated with an N16a association allowing the SMF to modify or delete the N4 information at a later stage.
The I-SMF generates an N4 Session ID and for each rule a Rule ID (unless the ones received from the SMF can be used) and maintains a mapping between the locally generated identifiers and the ones received from the SMF. The I-SMF replaces those IDs in the PDR(s), QER(s), URR(s) and FAR(s) received from the SMF. When the I-SMF receives the N4 information, the Network instance (if needed) included in the rules sent to the UPF is generated by I-SMF. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.7 Event Management | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.7.1 UE's Mobility Event Management | When an I-SMF is involved in a PDU Session, the SMF and I-SMF independently subscribe to "UE mobility event notification" service provided by AMF. The AMF treats the SMF's and I-SMF's subscription separately and notifies the event directly to the SMF or I-SMF. If the SMF does not know the serving AMF address, the SMF gets the serving AMF address from the UDM as described in clause 5.2.3.2.4, TS 23.502 [3] and subscribes directly with the serving AMF.
In the case of AMF change (e.g. Inter NG-RAN node N2 based handover), the target AMF receives mobility event subscription information from the source AMF and updates the mobility event subscription information with the SMF and I-SMF independently (i.e. target AMF allocates the Subscription Correlation ID for each event and notifies the respective SMFs and I-SMF as described in clause 5.3.4.4).
In the case of I-SMF change or I-SMF insertion (e.g. at Inter NG-RAN node N2 based handover), the subscription of mobility event (from AMF) is not transferred from the old I-SMF or SMF to the new I-SMF, the new I-SMF triggers a new subscription event if the new I-SMF wants to receive the corresponding mobility event. In the case of I-SMF removal, the subscription of mobility event at the AMF is not transferred from the old I-SMF to the SMF, the SMF triggers a new subscription event if the SMF wants to receive the corresponding mobility event.
The subscription from the old SMF entity (old I-SMF, SMF) is removed via an explicitly request from this old SMF entity. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.7.2 SMF event exposure service | Consumers of SMF events do not need to be aware of the insertion / removal / change of an I-SMF as they always subscribe to the SMF of the PDU Session.
Except for the events documented in the present clause, the I-SMF does not need to support the events defined in clause 5.2.8.3.1 of TS 23.502 [3].
For Events "First downlink packet per source of the downlink IP traffic (buffered / discarded / transmitted)" and UPF event exposure for User DataUsage Measures and User DataUsage Trends, when an I-SMF is involved in the PDU Session, the SMF subscribes / unsubscribes onto I-SMF for the PDU Session ID on behalf of the event consumer (e.g. at I-SMF insertion or when a consumer subscribes or un subscribes while an I-SMF serves the PDU Session) and the I-SMF or I-UPF directly notifies the event consumer. At I-SMF change, the related SMF event subscriptions are not transferred from source I-SMF to the target I-SMF. The SMF may trigger new subscription event to the target I-SMF if the SMF wants to receive the corresponding SMF or UPF event or to continue the UPF event subscription for the final consumer. At I-SMF change or removal the corresponding subscription is removed in the source I-SMF when it removes the context associated with the PDU Session Id. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.7.3 AMF implicit subscription about events related with the PDU Session | When creating an association with a SMF or I-SMF for a PDU Session, the AMF implicitly subscribes to SMF / I-SMF about events related with the PDU Session (the AMF provides the relevant notification information to the SMF or the I-SMF respectively). This implicit subscription is implicitly released when the corresponding association with the SMF / I-SMF is removed (e.g. as no more needed due to a I-SMF insertion / change / removal). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.8 Support for Cellular IoT | This clause defines the specific impacts of deployments topologies with specific SMF Service Areas on how 5GS supports Cellular IoT as defined in clause 5.31.
For a PDU Session supporting Control Plane CIoT 5GS Optimisation as defined in clause 5.31.4:
- For a PDU Session towards a DNN/S-NSSAI for which the SMF Selection Subscription data includes an Invoke NEF Indication (i.e. for a PDU Session which will be anchored in NEF), the AMF never inserts an I-SMF.
When an I-SMF is inserted to serve a PDU Session, the I-SMF supports the features that, as specified in clause 5.31, apply to the V-SMF in the case of Home Routed.
NOTE: This can require the SMF to subscribe onto I-SMF about RAT type change for a PDU Session as described in clause 4.23 of TS 23.502 [3]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.9 Support of the Deployment Topologies with specific SMF Service Areas feature within and between PLMN(s) | When Deployments Topologies with specific SMF Service Areas need to be used in a PLMN for a S-NSSAI, all AMF serving this S-NSSAI are configured to support Deployments Topologies with specific SMF Service Areas.
NOTE 1: The specifications do not support AMF selection related with Deployment Topologies with specific SMF Service Areas.
For HR roaming, the AMF discovers at PDU Session establishment whether a H-SMF supports V-SMF change based on feature support indication received from the NRF, possibly via the SCP. When the V-PLMN requires Deployments Topologies with specific SMF Service Areas but no H-SMF can be selected that supports V-SMF change, a H-SMF not supporting V-SMF change may be selected by the VPLMN. In that case and if a V-SMF serving the full VPLMN is available, AMF should prefer to select such V-SMF.
In this release of the specifications, when an AMF detects the need to change the V-SMF while the H-SMF does not support V-SMF change, the AMF shall not trigger V-SMF change but shall trigger the release of the PDU Session.
NOTE 2: The AMF can determine whether the H-SMF supports V-SMF change based on NRF look up. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.10 Support for 5G LAN-type service | This clause defines how 5GS supports 5G LAN-type service as defined in clause 5.29 in the case of deployments topologies with specific SMF Service Areas.
The UE may be connected with the PSA via an I-UPF which is controlled by the I-SMF. In this case, traffic switching (e.g. UPF local traffic switching) is controlled by the SMF as described in clause 5.29.4 without any specific knowledge or involvement of the I-SMF to support the 5G LAN-type service. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.34.11 Support for Local Offloading Management | When the Local Offloading Management is allowed based on SMF selection subscription data and the UE is within the local offloading management service area, an I-SMF supporting the Local Offloading Management is inserted between the SMF and the AMF, even if the UE is within the SMF service area. The local offloading management service area may be locally configured in AMF per S-NSSAI and DNN, or generated in the AMF based on the received I-SMF profile received from the NRF.
NOTE: The I-SMF profile includes the local offloading management service area supported for the I-SMF.
When an I-SMF is inserted to support Local Offloading Management to manage edge computing information locally, EAS deployment information management, EASDF selection, configuration and DNS message handling are performed by I-SMF as described in TS 23.548 [130].
The local offloading policy indicates IP range(s) and/or FQDN(s) allowed to be routed to the local part of a DN as specified in clause 6.4 of TS 23.503 [45].
The detailed procedures on I-SMF insertion during and after PDU session establishment and on EAS discovery are described in clause 6.10 of TS 23.548 [130]. The UL CL and UPF(s) may be inserted, changed, or removed by the I-SMF for the traffic offloaded for Local Offloading Management. For more detail handling (e.g. the interaction between I-SMF and SMF), refer to clause 6.10 of TS 23.548 [130]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35 Support for Integrated access and backhaul (IAB) | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.1 IAB architecture and functional entities | Integrated access and backhaul (IAB) enables wireless in-band and out-of-band relaying of NR Uu access traffic via NR Uu backhaul links. In this Release of the specification, NR satellite access is not applicable. The serving PLMN may provide the mobility restriction for NR satellite access as specified in clause 5.3.4.1
The Uu backhaul links can exist between the IAB-node and:
- a gNB referred to as IAB-donor; or
- another IAB-node.
The part of the IAB node that supports the Uu interface towards the IAB-donor or another parent IAB-node (and thus manages the backhaul connectivity with either PLMN or SNPN it is registered with) is referred to as an IAB-UE.
In this Release of the specification, the IAB-UE function does not apply to the NR RedCap UE.
At high level, IAB has the following characteristics:
- IAB uses the CU/DU architecture defined in TS 38.401 [42] and the IAB operation via F1 (between IAB-donor and IAB-node) is invisible to the 5GC;
- IAB performs relaying at layer-2 and therefore does not require a local UPF;
- IAB supports multi-hop backhauling;
- IAB supports dynamic topology update, i.e. the IAB-node can change the parent node, e.g. another IAB-node, or the IAB-donor, during operation, for example in response to backhaul link failure or blockage.
Figure 5.35.1-1 shows the IAB reference architecture with two backhaul hops, when connected to 5GC.
Figure 5.35.1-1: IAB architecture for 5GS
The gNB-DU in the IAB-node is responsible for providing NR Uu access to UEs and child IAB-nodes. The corresponding gNB-CU function resides on the IAB-donor gNB, which controls IAB-node gNB-DU via the F1 interface. IAB-node appears as a normal gNB to UEs and other IAB-nodes and allows them to connect to the 5GC.
The IAB-UE function behaves as a UE and reuses UE procedures to connect to:
- the gNB-DU on a parent IAB-node or IAB-donor for access and backhauling;
- the gNB-CU on the IAB-donor via RRC for control of the access and backhaul link;
- 5GC, e.g. AMF, via NAS;
- OAM system via a PDU session or PDN connection (based on implementation).
NOTE: The 5GC, e.g. SMF, may detect that a PDU session for the IAB-UE is for the OAM system access, e.g. by checking the DNN and/or configuration. It is up to the operator configuration to choose whether to use 1 or multiple QoS Flows for OAM traffic and the appropriate QoS parameters, e.g. using 5QI=6 for software downloading and 5QI=80 with signalled higher priority or a pre-configured 5QI for alarm or control traffic.
The IAB-UE can connect to 5GC over NR (SA mode) or connect to EPC (EN-DC mode). The UE served by the IAB-node can operate in the same or different modes than the IAB-node as defined in TS 38.401 [42]. The operation mode with both UE and IAB-node connected to EPC is covered in TS 23.401 [26]. Operation modes with UE and IAB-node connected to different core networks are described in clause 5.35.6. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.2 5G System enhancements to support IAB | In IAB operation, the IAB-UE interacts with the 5GC using procedures defined for UE. The IAB-node gNB-DU only interacts with the IAB-donor-CU and follows the CU/DU design defined in TS 38.401 [42].
For the IAB-UE operation, the existing UE authentication methods as defined in TS 33.501 [29] applies. Both USIM based methods and EAP based methods are allowed and NAI based SUPIs can be used.
The following aspects are enhanced to support the IAB operation in the Registration procedure as defined in clause 4.2.2.2 of TS 23.502 [3]:
- The IAB-node provides an IAB-indication to the IAB-donor-CU when the RRC connection is established as defined in TS 38.331 [28]. When the IAB-indication is received, the IAB-donor-CU selects an AMF that supports IAB and includes the IAB-indication in the N2 INITIAL UE MESSAGE as defined in TS 38.413 [34] so that the AMF can perform IAB authorization;
- the UE Subscription data as defined in clause 5.2.3 of TS 23.502 [3] is enhanced to include the authorization information for the IAB operation;
- Authorization procedure during the UE Registration procedure is enhanced to perform verification of IAB subscription information;
- If the IAB operation is not authorized and IAB-UE is not allowed to be registered, the AMF rejects the IAB-UE's registration or de-register the IAB-UE. The AMF initiates UE Context setup/modification procedure by providing IAB authorized indication with the value set to "not authorized" to the NG-RAN, if the IAB-UE is still allowed to be registered;
- If the IAB operation is authorized, UE Context setup/modification procedure is enhanced to provide IAB authorized indication with the value set to "authorized" to NG-RAN.
After registered to the 5G system, the IAB-node remains in CM-CONNECTED state if the IAB operation is authorized. In the case of radio link failure, the IAB-UE uses existing UE procedure to restore the connection with the network. The IAB-UE uses Deregistration Procedure as defined in clause 4.2.2.3 of TS 23.502 [3] to disconnect from the network. In the case of controlled IAB-node release as specified in clause 8.9.10 of TS 38.401 [42] (including the case when authorization state of the IAB-node is changed from authorized to non-authorized), after UE Context Modification message to NG-RAN with authorization indication as not authorized and after a certain period (e.g. based on the expiration of a timer configured on the AMF), the AMF may trigger the IAB-UE Deregistration. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.3 Data handling and QoS support with IAB | Control plane and user plane protocol stacks for IAB operation are defined in TS 38.300 [27].
QoS management for IAB can remain transparent to the 5GC. If NG-RAN cannot meet a QoS requirement for a QoS Flow to IAB-related resource constraints, the NG-RAN can reject the request using procedures defined in TS 23.502 [3].
The IAB-UE function can establish a PDU session or PDN connection, e.g. for OAM purpose (protocol stack not shown here). In that case, the IAB-UE obtains an IP address/prefix from the core network using normal UE procedures. The IAB-UE's IP address is different from that of the IAB-node's gNB DU IP address.
NOTE: For OAM traffic, based on their specific requirements, operators can select QoS characteristics and reference them by pre-configured 5QI(s) or using signalled QoS characteristics within the operator's network. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.4 Mobility support with IAB | For UEs, all existing NR intra-RAT mobility and dual-connectivity procedures are supported when the UE is served by an IAB-node except for the cases of NR satellite access. For a UE served by an IAB-node when the serving IAB-node changes its IAB-donor-CU due to mobility, the mobility support is specified in clause 5.35A.1 and clause 5.35A.3. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.5 Charging support with IAB | IAB-donor has all the information regarding the UE and the IAB-node and corresponding mapping of the bearers. The PDU sessions for the UE and IAB-node are separate from IAB-node onwards to the core network. Therefore, the existing charging mechanism as defined in clause 5.12 can be used to support IAB. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.35.6 IAB operation involving EPC | When the IAB-donor gNB has connection to both EPC and 5GC, based on PLMN configuration, there are two possible operation modes:
- the IAB-node connects to a 5GC via the IAB-donor gNB, while the UEs served by the IAB-node connect to EPC with Dual Connectivity as defined in TS 37.340 [31]. In this operation mode, the IAB-donor gNB has connection to an eNB and the 5GC is restricted for IAB-node access only; and
- the IAB-node connects to an EPC via the IAB-donor gNB with Dual Connectivity as defined in TS 37.340 [31], while the UEs served by the IAB-node connect to the 5GC. In this operation mode, the EPC is restricted for IAB-node access only.
To support the above operation modes, the IAB-UE shall be configured to select only a specific PLMN (as defined in TS 23.122 [17]) and whether it needs to connect to 5GC or EPC.
NOTE: For a particular PLMN, it is expected that only one of the modes would be deployed in a known region.
5.35A Support for Mobile Base Station Relay (MBSR)
5.35A.1 General
The MBSR uses the IAB architecture as defined in clause 5.35 and operates as an IAB node (with an IAB-UE and gNB-DU) with mobility when integrated with the serving PLMN. The architecture described in clause 5.35 applies unless specific handling is specified in clause 5.35A. Additionally, the following limitations apply to the MBSR:
- the MBSR has a single hop to the IAB-donor node;
- NR Uu is used for the radio link between a MBSR and served UEs and between MBSR and IAB-donor node.
Regulatory requirements (e.g. emergency services, priority services) are supported when UEs access 5GS via a MBSR. LCS framework as defined in TS 23.273 [87] is used for providing the location service to the served UEs, with additional enhancements described in clause 5.35A.5.
Roaming of the MBSR is supported, i.e. a MBSR can be integrated with a VPLMN's IAB-donor gNB node. The corresponding enhancements to support MBSR roaming are described in clause 5.35A.4.
CAG mechanism as defined in clause 5.30 can be used for the control of UE's access to the MBSR. Optional enhancements to the CAG mechanism for MBSR use are described in clause 5.35A.7.
For a MBSR node to operate as a MBSR, it provides a mobile IAB-indication to the IAB-donor-CU when the RRC connection is established as defined in TS 38.331 [28]. When the mobile IAB-indication is received, the IAB-donor-CU selects an AMF that supports mobile IAB-node and includes the mobile IAB-indication in the N2 INITIAL UE MESSAGE as defined in TS 38.413 [34] so that the AMF can perform MBSR authorization as described in clause 5.35A.4. If the MBSR node is not authorized, e.g. due to the MBSR authorization indication from AMF, it also provides the mobile IAB-indication when establishing new RRC connection so that the AMF supporting mobile IAB-node will be selected by the IAB-donor-CU, to ensure that the operation related to MBSR authorization status change for a registered MBSR node can be performed as described in clause 5.35A.4. If the MBSR receives MBSR authorized indication from AMF, it provides the information about the authorization result to its IAB-DU component based on non-standardized interface as described in clause 5.35A.4.
As defined in TS 38.331 [28], when a MBSR includes the mobile IAB-indication when establishing the RRC connection, it shall not include the IAB-indication as described in clause 5.35.2.
After the IAB-UE performs registration procedure in 5GS, further mobility procedure can be performed to change the IAB-donor-DU, the IAB-donor-CU as specified in TS 38.401 [42]. The mobility support of UEs served by the MBSR is specified in clause 5.35A.3
5.35A.2 Configuration of the MBSR
In order for an MBSR to operate as a mobile IAB node, it receives configuration from the OAM system of the serving PLMN as specified in TS 38.401 [42]. The MBSR (IAB-UE) establishes a secure and trusted connection to the OAM server only if it is authorized to operate as MBSR in the serving PLMN as defined in TS 38.401 [42].
In addition, the MBSR(IAB-UE) is assumed to be configured with preferred PLMN lists and forbidden PLMNs by the HPLMN to perform PLMN selection as specified in TS 23.122 [17].
When a PDU session is used for the MBSR to access the OAM server, the MBSR (IAB-UE) establishes a dedicated PDU session for the OAM traffic. The serving PLMN provides an Allowed NSSAI and establishes the PDU session for the OAM server access, considering the S-NSSAI and DNN requested by MBSR and/or the default values in subscription data. The MBSR can be (pre-)configured with UE policy or provisioned using existing UE Policy mechanism as defined in TS 23.503 [45] including the OAM access PDU session parameters for the authorized PLMNs.
5.35A.3 Mobility support of UEs served by MBSR
5.35A.3.1 UE mobility between a fixed cell and MBSR cell
For UEs in RRC_IDLE and RRC_INACTIVE state when a MBSR goes out-of-service, procedure for cell (re‑)selection as specified in TS 38.304 [50] for RRC_IDLE and RRC_INACTIVE is used between MBSR cell and other cells.
If the MBSR goes out-of-service (due to e.g. MBSR moves to an area where the MBSR is not allowed to provide the relay service), the NG-RAN triggers the handover procedures to the neighbouring cells for UEs in RRC_CONNECTED state served by the MBSR. Any change of authorization state of the MBSR is also handled according to clause 5.35A.4.
The IAB-donor-CU triggers handover procedure when it is possible for the UEs accessing emergency service and being served by the MBSR, if MBSR is about to become unavailable to provide the services.
5.35A.3.2 UE mobility between MBSR cells
Similar to the behaviours described in clause 5.35A.3.1, UEs and NG-RAN use existing procedures as specified in clause 8.23 of TS 38.401 [42], TS 23.502 [3], or TS 38.304 [50] to handle the mobility between MBSR cells.
5.35A.3.3 UE mobility when moving together with a MBSR cell
For a UE served by a MBSR cell, it may observe change of TAC and/or cell IDs, even if it is still connected to the same MBSR. This can trigger mobility registrations, as defined in TS 23.502 [3], if the new TAC is not in the TAI list in the RA.
5.35A.3.4 MBSR mobility
The mobility of MBSR between different IAB-donor gNBs is described in clause 8.23 of TS 38.401 [42].
If a MBSR operates without PDU sessions,
- For N2 Handover, the NG-RAN triggers the N2 handover procedure for a dummy PDU session and includes the related dummy PDU session information in the Handover Required message, as specified in TS 38.413 [34] towards the AMF of the MBSR (IAB-UE). The AMF checks the UE context it stores for the MBSR (IAB-UE) and since it includes no PDU sessions, the AMF shall not forward the PDU Session information it receives in the Handover Required message to any SMF. The AMF shall then perform the handover procedures as specified in clause 4.9.1.3 of TS 23.502 [3] without involving any SMF and it includes in the Handover Request message towards the target NG-RAN the PDU session information received in the Handover Required message with an indication to cause the target NG-RAN to ignore the received PDU session information (No PDU Session Indication IE defined in TS 38.413 [34]). If the AMF is reallocated during the handover, the target AMF checks whether the UE context for the MBSR (IAB-UE) it receives from the source AMF includes any PDU sessions related information and if none is detected, it continues the handover without involving any SMF and it includes in the Handover Request message towards the target NG-RAN with an indication to cause the target NG-RAN to ignore the received PDU session information (No PDU Session Indication IE defined in TS 38.413 [34]).
- For Xn Handover: the NG-RAN triggers the Xn handover procedure for a dummy PDU session and includes the related dummy PDU session information in the Path Switch Request message, as specified in TS 38.413 [34]. The AMF checks the UE context it stores for the MBSR (IAB-UE) and since it includes no PDU sessions, the AMF shall then perform the handover procedures as specified in clause 4.9.1.2 of TS 23.502 [3] without involving any SMF and it includes in the Path Switch Acknowledge towards the target NG-RAN dummy PDU session information. The NG-RAN ignores the received PDU session information from the AMF as it has no PDU sessions in the RAN UE context.
5.35A.4 MBSR authorization
For a MBSR, the subscription information stored in the HPLMN indicates whether it is authorized to operate as MBSR and the corresponding location and time information as specified in TS 23.502 [3].
NOTE 1: For non-roaming MBSRs, the operator local policy can be taken into consideration for MBSR authorization, e.g. based on the network status, or a limit on the number of MBSRs operating in a certain area.
When the MBSR (IAB-UE) performs initial registration with the serving PLMN, it indicates the request to operate as a MBSR as described in clause 5.35A.1. The AMF authorizes the MBSR based on the subscription information and provides MBSR authorized indication to the MBSR node over NAS and NG-RAN over NGAP as described in the registration procedure in TS 23.502 [3]. The MBSR establishes the connection to OAM system using the configuration information for MBSR operation upon the reception of MBSR authorization indication (authorized). The MBSR provides the information about the authorization result (authorized) to its IAB gNB-DU component. When the AMF formulates the registration area for an authorized MBSR, the TAs included in the registration area are authorized for MBSR operation homogenously, taking any MBSR Operation allowed information in subscription data and operator local policy into account.
NOTE 2: The MBSR support can be deployed in certain Network Slices based on operator configuration and Network slicing functionalities (e.g. the function specified in clause 5.15.18) can be applied when suitable.
When MBSR roaming is supported, a roaming agreement between VPLMN and HPLMN regarding MBSR operation is in place. The AMF can make use of the subscription data for authorization of the MBSR in the V-PLMN.
MBSR (IAB gNB-DU) can use IAB-node integration procedure or inter-IAB-donor gNB mobility procedure to integrate into the serving PLMN to provide service.
NOTE 3: How the MBSR obtains the configuration information for MBSR operation is described in clause 5.35A.2.
If the MBSR operation is not authorized (e.g. due to location or time limitation, or due to lack of authorization altogether to operate as MBSR), the AMF of the MBSR (IAB-UE) can indicate to the MBSR (IAB-UE) that it is not allowed to act as an MBSR, i.e. the MBSR authorization indication (not authorized), as part of registration procedure. The AMF may provide the indication in a Registration Accept (if the PLMN allows the MBSR IAB-UE to be registered in the PLMN). In this case, the AMF includes the MBSR authorization indication (not authorized) to IAB-donor-gNB. The MBSR provides the information about the authorization result (not authorized) to its IAB-DU component. The AMF may reject the Registration (if the PLMN does not allow the MBSR IAB-UE to be registered in the PLMN).
When the MBSR authorization state changes for a registered MBSR node (either authorized, or not authorized), the AMF of the MBSR (IAB-UE) updates the MBSR (IAB-UE) and the NG-RAN accordingly. Based on the operator configuration, the AMF may use either Deregistration (with re-registration required indication) or the UE Configuration Update procedure to inform the MBSR regarding the updated authorization status:
- The Deregistration with re-registration required indication procedure is used, when the AMF of the MBSR (IAB-UE) intends to keep the MBSR (IAB-UE) registered. The AMF of the MBSR (IAB-UE) provides the new authorization indication to MBSR (IAB-UE) as described above, when the MBSR performs initial Registration procedure after the deregistration.
- The Deregistration procedure without re-registration required indication is used if the PLMN does not allow the MBSR (IAB-UE) to remain registered in the PLMN.
- When UE Configuration Update procedure is used, the AMF provides the new authorization indication to the MBSR (IAB-UE) in the UE Configuration Update Command. The MBSR provides the information about the new authorization status to its IAB-DU component.
The AMF of the MBSR (IAB-UE) informs the NG-RAN (i.e. the IAB-donor gNB) of the new authorization status using UE Context Modification, Initial Context Setup procedure or the DOWNLINK NAS TRANSPORT message, with the following principles:
- If the authorization state changes from authorized to not authorized and AMF uses the UE Configuration Updated procedure to update the MBSR, the AMF updates the NG-RAN with the new authorization indication (not authorized) by including this information in the DOWNLINK NAS TRANSPORT message. The NG-RAN completes handover of the UEs served by the MBSR before releasing the F1 connection to the MBSR IAB-DU.
- If the authorization state changes from authorized to not authorized and the AMF uses the Deregistration procedure to update the MBSR, the AMF sends the UE Context Modification message to NG-RAN with the authorization indication as not authorized. Then, if the AMF receives a NGAP UE CONTEXT RELEASE REQUEST message from the NG-RAN with a cause code indicating the NG-RAN node has completed the operation for a non-authorized MBSR, including e.g. the handover of the UEs the MBSR was serving as defined in TS 38.413 [34], or after a certain period (e.g. based on the expiration of a timer configured on the AMF) the AMF executes the deregistration procedure with MBSR and releases the NAS signalling connection.
If the Network-initiated Deregistration procedure is triggered for MBSR (IAB-UE) that is registered with authorization to act as MBSR, the AMF sends the UE Context Modification message to the NG-RAN (i.e. the IAB-donor gNB) and updates the NG-RAN with the authorization indication as not authorized. Then, if the AMF receives a NGAP UE CONTEXT RELEASE REQUEST message from the NG-RAN with a cause code indicating that the NG-RAN node has completed the operation for a non-authorized MBSR, including e.g. the handover of the UEs the MBSR was serving as defined in TS 38.413 [34], or after a certain period (e.g. based on the expiration of a timer configured on the AMF) the AMF executes the deregistration procedure with MBSR and releases the NAS signalling connection.
NOTE 4: The AMF delays the MBSR de-registration to allow the IAB-donor gNB to move all connected UEs via MBSR to other cells as specified in clause 8.9.10 of TS 38.401 [42].
If a PDU session is used to provide OAM access for MBSR when it is not authorized but remains registered, the AMF of the MBSR (IAB-UE) may notify the SMF serving the PDU session for O&M access to trigger the release of the PDU Session.
NOTE 5: The mechanism applies to both roaming and non-roaming MBSR operations.
5.35A.5 Location Service Support of UEs served by MBSR
When a UE accesses 5GS via a MBSR, it can use the location service as defined in TS 23.273 [87]. However, in order to provide accurate estimation of the UE location, LMF needs to take the location of the MBSR into account. Enhancements to the LCS framework for MBSR support is described in clause 5.9 of TS 23.273 [87].
5.35A.6 Providing cell ID/TAC of MBSR for services
The TAC and cell ID broadcasted by the MBSR cell(s) are configured and reconfigured e.g. upon mobility as specified in TS 38.401 [42].
After the MBSR is authorized as defined in 5.35A.4, when a UE is served by a cell of this MBSR, the IAB-donor-CU may provide 'Additional ULI' in addition to User Location Information, in N2 messages. The 'Additional ULI' is the ULI of the IAB-UE. The AMF may consider the 'Additional ULI' when it determines UE location and manages the UE location related functions (e.g. Mobility Restrictions).
When the AMF provides user location information to other NFs (e.g. LMF as specified in clause 5.9 of TS 23.273 [87]) for a UE connected via MBSR, the AMF may also send the Additional ULI received via N2 messages.
5.35A.7 Control of UE access to MBSR
CAG Identifier is used to control the access of UE via MBSR (i.e. mobile IAB-node) and existing CAG mechanism defined in clause 5.30.3 can be used for managing UE's access to MBSR, with the following additional considerations:
- When the MBSR is allowed to operate as an IAB node for a PLMN, the MBSR is configured, either during the communication with the serving PLMN OAM or (pre-)configuration mechanism, with a CAG identifier which is unique within the scope of this PLMN. If the MBSR is (pre-)configured with the PLMN list in which the MBSR is allowed to operate as MBSR, the corresponding CAG Identifier per PLMN is also configured in the MBSR.
NOTE 1: The CAG for MBSR is supported as part of the PNI-NPN concept described in clause 5.30.3.
- NG-RAN and 5GC support the UE access control based on the CAG identifier associated with the MBSR cell and the allowed CAG identifiers for the UE that supports CAG functionality.
- For the UE that does not support CAG functionality, NG-RAN and 5GC are allowed to use not only CAG mechanism but also the other existing mechanism e.g. forbidden Tracking Area, to manage its access to MBSR.
- Time validity information may be provided together with the CAG Identifier(s) for the MBSR(s) that the UE can access. The Allowed CAG list will be provided to UE and AMF for enforcement, to make sure that UE not accessing the MBSR cell outside of the time duration. For example, if the time when a certain CAG is allowed for a UE is up, the CAG for the UE is revoked from the network.
NOTE 2: Control of the MBSR access to the serving network is based on normal mobility restriction management based on subscription data form MBSR (i.e. IAB-UE). |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.36 RIM Information Transfer | The purpose of RIM Information Transfer is to enable the transfer of RIM information between two RAN nodes via 5GC. The RIM Information Transfer is specified in TS 38.413 [34].
When the source AMF receives RIM information from source NG-RAN towards target NG-RAN, the source AMF forwards the RIM information to the target AMF, as described in TS 38.413 [34] and TS 29.518 [71]. The AMF does not interpret the transferred RIM information. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37 Support for high data rate low latency services, eXtended Reality (XR) and interactive media services | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.1 General | This clause provides an overview of 5GS functionalities for support of XR services (AR/VR applications) and interactive media services that require high data rate and low latency communication, e.g. cloud gaming and tactile/multi-modal communication services according to service requirements documented in TS 22.261 [2]. The standardized 5QI characteristics for such interactive services are provided in Table 5.7.4-1 and TSCAI is used to describe the related traffic characteristics as defined in clause 5.27.2. Further enhancements for these interactive media services are as follows:
- The 5GS may support QoS policy control for multi-modal traffic, see clause 5.37.2.
- The 5GS may support network information exposure which can be based on ECN markings for L4S, see clause 5.37.3 or 5GS exposure API, see clause 5.37.4.
- The 5GS may support PDU Set based handling including PDU Set identification and marking, see clause 5.37.5.
- The 5GS may ensure that the UL and DL packets together meet the requested round trip delay and also update the delay for UL and DL considering QoS monitoring results, see clause 5.37.6.
- The 5GS may perform per-flow Packet Delay Variation (PDV) monitoring and policy control according to AF provided requirements, see clause 5.37.7.
- The 5GC may provide traffic assistance information to the NG-RAN to enable Connected mode DRX power saving, see clause 5.37.8.
- The 5GS may consider dynamically changed traffic characteristics for better resource management, see clause 5.37.10.
- The 5GS may support traffic identification for multiplexed media flows in the same transport layer connection, see clause 5.37.11.
- The 5GC may perform PDU Set Importance based transport level packet marking, see clause 5.8.2.7.
- The 5GC may provide the Multi-modal Service ID to NG-RAN, see clause 5.37.2.
NOTE: Home-routed roaming deployments cannot always support the low latency communication requirements of XR services or interactive media services. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.2 Policy control enhancements to support multi-modal services | A multi-modal service is a communication service that consists of several data flows that relate to each other and that are subject to application coordination. The data flows can transfer different types of data (for example audio, video, positioning, haptic data) and may come from different sources(e.g. a single UE, a single device or multiple devices connected to the single UE, or multiple UEs).
For the single UE case, it is expected that those data flows are closely related and require strong application coordination for the proper execution of the multi-modal application and therefore, all those data flows are transmitted in a single PDU session.
The Nnef_AFsessionWithQoS service allows the AF to provide, at the same time, for each data flow that belongs to the multi-modal service, a Multi-modal Service ID, the service requirements and the QoS monitoring requirements:
- The Multi-modal Service ID is an explicit indication that data flows are related to a multi-modal service. The PCF may use this information to derive the correct PCC rules and to apply appropriate QoS policies for the data flows that are part of a specific multi-modal application.
- The AF may provide QoS monitoring requirements for data flows associated to a multi-modal service to the PCF . The PCF generates the authorized QoS Monitoring policy for each data flow.
NOTE 1: In order to start the QoS monitoring for the data flows associated to a multi-modal service within a certain period of time, the PCF needs to receive the QoS monitoring requirements for those data flows from AF within a single request or, in case of multiple requests, within a short period of time.
If the AF provides a Multi-modal Service ID for data flows to 5GS, then the PCF may include it, based on operator configuration, in PCC rules, and the SMF forwards it to NG-RAN in N2 SM information when establishing and/or updating the corresponding QoS Flows.
NOTE 2: Based on an SLA between the network operator and an application service provider, the Multi-modal Service ID can uniquely identify a specific multi-modal communication service instance. The related 5GS behaviour is not further specified in this specification and is assumed to be determined by the operator configuration related to the SLA.
In addition to the features that are provided for the case that the data flows are associated with a single UE, the following features are provided for the case where the data flows are associated with more than one UE:
- The same DNN/S-NSSAI combination for the multi-modal service should be selected by each of the involved UEs. The URSP Rule evaluation framework is used to ensure that the same DNN/S-NSSAI is selected.
- The AF should use the same Multi-modal Service ID in the interactions with the PCF(s) for all the involved UEs that relate to a multi-modal service. The PCF may take this information into account (e.g. to apply a specific QoS policy) when processing each AF request independently. The data flows contribute to the service experience, but are still valid stand-alone, as they are transmitted over separate PDU Sessions to/from the involved UEs.
- If multiple PCFs are involved, the PCFs take policy decisions according to the input provided by the AF. There is no support for policy coordination among the multiple PCFs in this Release of the specification. Policy decisions are taken by each PCF separately on a per PDU Session basis. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.3 Support of ECN marking for L4S to expose the congestion information | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.3.1 General | L4S (Low Latency, Low Loss and Scalable Throughput) is described in IETF RFC 9330 [159], IETF RFC 9331 [160] and IETF RFC 9332 [161]. It exposes congestion information by marking ECN bits in the IP header of the user IP packets between the UE and the application server to trigger application layer rate adaptation.
In 5G System, ECN marking for L4S may be supported. ECN marking for L4S is enabled on a per QoS Flow basis in the uplink and/or downlink direction and may be used for GBR and non-GBR QoS Flows. In the case of 3GPP access, ECN marking for the L4S in the IP header is supported in either the NG-RAN (see clause 5.37.3.2 and TS 38.300 [27]), or in the PSA UPF (see clause 5.37.3.3). In the case of untrusted/trusted non-3GPP access, ECN marking for L4S in the IP header is supported in the N3IWF/TNGF (see clause 5.37.3.4, clause 6.2.9 and clause 6.2.9A).
NOTE 1: Based on operator's network configuration and policies, SMF decides whether NG-RAN or PSA UPF based ECN marking for L4S is used.
In the case of ECN marking for L4S by PSA UPF, the NG-RAN is instructed to perform congestion information monitoring and report to the PSA UPF the congestion information (i.e. a percentage of packets that UPF uses for ECN marking for L4S) of the QoS Flow on UL and/or DL directions via GTP-U header extension to PSA UPF and accordingly, the PSA UPF may mark the UL and/or DL direction packets of the QoS Flow.
NOTE 2: As for any QoS Flow, QoS rules in the UE and PDRs in the PSA UPF control which packets are bound to the L4S enabled QoS flow. The Packet Filter Set in the QoS rule or PDR can use packet filter(s) in clause 5.7.6.2 (e.g. match packets with ECT(1) or CE (See RFC 9331 [160]) together with IP 5 tuple) to steer traffic to an L4S enabled QoS Flow.
NOTE 3: A QoS Flow may be enabled with ECN marking for L4S requirement e.g. statically when a PDU session is established based on configuration in SMF or PCF, or dynamically based on detection of the L4S traffic (e.g. match packets with ECT(1) or CE (See RFC 9331 [160]) together with IP 5 tuple) in the IP header whereby SMF or PCF triggers a setup of a QoS Flow enabled for L4S, or by requests by an AF.
NOTE 4: To support this functionality, the UE needs to support L4S feedback as described in IETF RFC 9330 [159], which is not in the scope of 3GPP.
When serving PSA UPF or NG-RAN is changed e.g. due to inter-NG-RAN handover or PSA UPF relocation, target NG-RAN and target PSA UPF, if supported, should continue to perform ECN marking for L4S for the QoS Flow. However, if not available (i.e. ECN marking for L4S is not supported in both, target NG-RAN and target PSA UPF), AF should be notified that ECN marking for L4S can no longer be performed if ECN marking for L4S had been enabled for the QoS Flow based on AF request. When ECN marking for L4S is supported again either in target NG-RAN or in target PSA UPF, AF should be notified that ECN marking for L4S can be performed again if ECN marking for L4S had been enabled for the QoS Flow based on AF request. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.3.2 Support of ECN marking for L4S in NG-RAN | ECN marking for L4S may be supported in NG-RAN as specified in TS 38.300 [27].
To enable ECN marking for L4S in NG-RAN, dedicated QoS Flow(s) are used for carrying L4S enabled IP traffic. The SMF may be instructed, based on either dynamic or predefined PCC rule, to provide an indication for ECN marking for L4S to NG-RAN for a corresponding QoS Flow(s) in UL and/or DL directions. In the absence of such PCC rule, the use of ECN marking for L4S in NG-RAN on a QoS Flow is controlled by a coordinated configuration in NG-RAN and 5GC.
NOTE: In home-routed roaming scenarios, a coordinated configuration in NG-RAN and 5GC would require an appropriate SLA between the HPLMN and the VPLMN.
The criteria based on which NG-RAN decides to mark ECN bits for L4S is NG-RAN implementation specific.
In the case of inter NG-RAN UE mobility, if the ECN marking for L4S has been enabled on source NG-RAN, but the target NG-RAN does not support ECN marking for L4S, then the SMF may, if supported, enable ECN marking for L4S in PSA UPF as defined in clause 5.37.3.3. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.3.3 Support of ECN marking for L4S in PSA UPF | To enable ECN marking for L4S by a PSA UPF, a QoS Flow level ECN marking for L4S indicator may be sent by SMF to PSA UPF over N4. SMF also indicates to NG-RAN to report the congestion information (i.e. a percentage of packets that UPF uses for ECN marking for L4S) of the QoS Flow on UL and/or DL directions via GTP-U header extension to PSA UPF and accordingly, the PSA UPF may mark the UL and/or DL direction packets of the QoS Flow. If there is no UL packet when report for DL and/or UL needs to be provided, NG-RAN may generate an UL Dummy GTP-U Packet for such a reporting.
The SMF may be instructed, based on either dynamic or predefined PCC rule, to provide an indication for ECN marking for L4S to PSA UPF for a corresponding QoS Flow(s) in UL and/or DL directions.
Upon successful activation of congestion information reporting for UL and/or DL directions, PSA UPF uses information sent by NG-RAN in GTP-U header extension (see TS 38.415 [116] and TS 38.300 [27]) to perform ECN bits marking for L4S for the corresponding direction.
NOTE: How the congestion information is converted to ECN markings is UPF implementation specific.
The criteria based on which NG-RAN decides to provide the congestion information is up to NG-RAN implementation.
In the case of PSA UPF relocation, if the ECN marking for L4S has been enabled on source PSA UPF, SMF should select a target PSA UPF supporting ECN marking for L4S. If the target PSA UPF does not support ECN marking for L4S, then SMF may, if supported, switch to ECN marking for L4S in target NG-RAN by following clause 5.37.3.2. In such case, the target NG-RAN stops sending congestion information to the target PSA UPF.
In the case of inter NG-RAN UE mobility, if the congestion information reporting has been enabled on source NG-RAN while the target NG-RAN does not support congestion information reporting, then the SMF shall inform PSA UPF to stop ECN marking for L4S. If ECN marking for L4S is supported by the target NG-RAN, the SMF may instruct the target NG-RAN to perform ECN marking for L4S in NG-RAN by following clause 5.37.3.2. For a given QoS Flow, if the target NG-RAN supports congestion information reporting, the target NG-RAN shall report congestion information to UPF once it is available. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.3.4 Support of ECN marking for L4S in N3IWF and TNGF | ECN marking for L4S may be supported in N3IWF and TNGF, as specified in clauses 6.2.9 and 6.2.9A, respectively.
To enable ECN marking for L4S in N3IWF and TNGF, dedicated QoS Flow(s) and non-3GPP access resources (i.e. IPsec Child SAs) are used for carrying L4S enabled IP traffic. The SMF may be instructed, based on either dynamic or predefined PCC rule, to provide an indication for ECN marking for L4S to N3IWF and TNGF for a L4S enabled QoS Flow(s) in UL and/or DL directions. In the absence of such PCC rule, the use of ECN marking for L4S in N3IWF and TNGF, on a QoS Flow is controlled by a coordinated configuration in N3IWF,TNGF and 5GC.
For DL, intermediate non-3GPP access nodes (i.e. N3IWF and TNGF) map the L4S-enabled QoS Flows to L4S enabled non-3GPP access resources.
NOTE: Any non-3GPP access node (i.e. N3IWF and TNGF) supporting L4S and acting as an IP-in-IP tunnel endpoint between the XR application client and server is assumed to implement encapsulation and decapsulation as specified in IETF RFC 6040 [198] and IETF RFC 9599 [199].
The criteria based on which N3IWF and TNGF decide to mark ECN bits for L4S is implementation specific.
ECN marking for L4S in W-AGF and 5G-RG is specified in clause 4.17.2 of TS 23.316 [84]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.4 Network Exposure of 5GS information | 5GS and XR/media services cooperate to provide a better user experience using External Network Exposure.
Based on the AF request, the 5GS can expose the following information based on the QoS Monitoring as defined in clause 5.33.3 and/or clause 5.45:
- The UL and/or DL congestion information monitoring (see clause 5.45.3).
Based on the PCC rule from PCF, the SMF requests the NG-RAN to report congestion information (i.e. a percentage of congestion level for exposure) via GTP-U header to PSA UPF. This NG-RAN reported congestion information is sent to the PSA UPF in a common information element to support congestion information exposure and to support ECN marking for L4S in PSA UPF as described in clause 5.37.3.3. In the case of congestion information exposure, the PSA UPF interprets the RAN reported information as the percentage of congestion level for exposure and exposes the corresponding UL and/or DL congestion information via Nupf_EventExposure service or via SMF/PCF/NEF as described in clause 5.8.2.18. It can be applied to a Non-GBR or GBR QoS Flow. In the case of ECN marking for L4S in PSA UPF, the PSA UPF interprets the RAN reported information as percentage of packets that UPF uses for ECN marking for L4S as described in clause 5.37.3.3.
- The UL and/or DL Data rate information (see clause 5.45.4).
Based on the PCC rule from PCF, the SMF requests the PSA UPF to measure and report the information. They may be exposed to the AF directly by PSA UPF via Nupf_EventExposure service or via SMF/PCF/NEF as described in clause 5.8.2.18.
- The round trip delay for two service data flows considering the UL direction of a service data flow and the DL direction of another service data flow in the same PDU Session.
It is determined based on the QoS Monitoring for packet delay of individual QoS Flows as described in clause 5.33.3. The PCF derives the separate QoS monitoring policies for each direction packet delay (see clause 5.33.3) based on AF request and local policy. The PCF provides the two QoS Monitoring policies in the PCC rules for the service data flows. The PSA UPF reports the delay information per QoS Flow to the SMF. The SMF reports to PCF. The PCF derives round trip delay information based on the two direction's packet delay result for the service data flows and exposes the information to the AF directly or via NEF.
- The round trip delay for one service data flow.
If the service data flow is mapped to two QoS Flows (i.e. the UL traffic and DL traffic of the service data flow are separated into two QoS flows respectively) in the same PDU Session, similarly to the round trip delay for two service data flows over two QoS flows, the PCF triggers QoS Monitoring for each direction packet delay of individual QoS flows respectively and derives round trip delay based on the two direction QoS flows' packet delay monitored result.
NOTE: How PCF calculates the requested round trip delay for multiple QoS Flows from delays of individual QoS Flows is not specified in this specification.
- The UL and/or DL available bitrate for a GBR QoS Flow (see clause 5.45.6).
For a GBR QoS Flow, based on the PCC rule from PCF, the SMF requests the NG-RAN to report the UL and/or DL available bitrate. The NG-RAN reports the UL and/or DL available bitrate information to the PSA UPF via the GTP-U header of UL packets.
The SMF further requests the PSA UPF to expose the available bitrate to the AF directly or via local NEF, as described in clause 5.8.2.18.
The AF may provide the Alternative QoS parameter set requirements and Averaging Window to the NEF/PCF for the GBR QoS Flow as specified in clause 4.15.6.6 of TS 23.502 [3].
Upon AF request, 5GS may expose the UL and DL data rate limitation information for a non-GBR service data flow or a PDU Session to the AF. The data rate limitation information is defined as the maximum data rate that can be achieved for the service data flow or the PDU Session:
- For a new or ongoing data sessions bound to an AF session, the PCF provides the uplink and downlink maximum bit rate authorized for the service data flow as data rate limitation information, by means of the AF session with QoS procedure as defined in clause 4.15.6.6 and clause 4.15.6.6a of TS 23.502 [3].
- When the AF subscribes to event notifications for a PDU Session, the PCF provides the authorized Session-AMBR as data rate limitation information by means of the Npcf_EventExposure service as defined in clause 5.2.5.7 of TS 23.502 [3]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.5 PDU Set based Handling | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.5.1 General | A PDU Set is comprised of one or more PDUs carrying an application layer payload such as a video frame or video slice. The PDU Set based QoS handling by the 5G-AN is determined by PDU Set QoS Parameters in the QoS profile of the QoS Flow (specified in clause 5.7.7) and PDU Set Information provided by the PSA UPF via N3/N9 interface as described in clause 5.37.5.2. The PDU Set based Handling can be applied for GBR and non-GBR QoS Flows. The AF should provide PDU Set related assistance information for dynamic PCC control. One or more of the following PDU Set related assistance information may be provided to the NEF/PCF using the AF session with required QoS procedures in clauses 4.15.6.6 and 4.15.6.6a of TS 23.502 [3].
- PDU Set QoS Parameters as described in clause 5.7.7
- Protocol Description: Indicates the transport protocol used by the service data flow (e.g. RTP, SRTP) and information, e.g. the following:
- RTP [185] or SRTP [186];
- RTP or SRTP with RTP Header Extensions, including:
- RTP Header Extensions for PDU Set Marking as defined in TS 26.522 [179];
- Other RTP Header Extensions as defined RFC 8285 [189], RFC 9143 [207];
- RTP or SRTP without RTP Header Extensions, but together with RTP Payload Format (e.g. H.264 [187] or H.265 [188]);
- RTP or SRTP with RTP Header Extensions for PDU Set Marking as defined in TS 26.522 [179] and together with RTP Payload Format (e.g. H.264 [187] or H.265 [188]);
- RTP or SRTP with other RTP Header Extensions following RFC 8285 [189] and together with RTP Payload Format (e.g. H.264 [187] or H.265 [188]).
NOTE 1: With the Protocol Description options combining SRTP together with RTP Payload Format the UPF can still obtain some of the PDU Set information from the RTP Header (refer to Annex A of TS 26.522 [179]).
- Media over QUIC (MoQ) Transport, IETF draft-ietf-moq-transport [201] (as further described in clause 5.37.9.2).
When RTP Header Extensions for PDU Set Marking (as defined in TS 26.522 [179] or other RTP header extensions as defined in RFC 8285 [189] is included, the differentiation between different RTP Header Extension Types should be supported.
When RTP Payload Format is included, the differentiation between different RTP Payload Formats should be supported.
NOTE 2: Multiplexing of different transport protocols and different media traffic for differentiated PDU Set based handling is not supported in the current Release.
The Protocol Description can be UL only, DL only or UL and DL. The Protocol Description for UL and DL traffic may be different.
For end-to-end encrypted traffic, PDU Set Information is received as media related information from the Application Server, see clause 5.37.9.
NOTE 3: Identification of PDU Set information for end-to-end encrypted traffic is supported in the DL direction only.
AF provided PDU Set QoS Parameters and UL and/or DL Protocol Description may be used in determining the PCC Rule by the PCF as defined in clause 6.1.3.27.4 of TS 23.503 [45] and the DL Protocol Description may be used for identifying the PDU Set Information and PDU Set Information marking by the PSA UPF.
When the SMF receives the PCC rule, the SMF performs binding of the PCC rule to one QoS Flow as described in clause 6.1.3.2.4 of TS 23.503 [45]. At least one of the following shall be included in the PCC rule to enable PDU Set based QoS handling: 1) a PSIHI and/or 2) both PSDB and PSER. Based on the PCC rule, the SMF adds the PDU Set QoS Parameters to the QoS Profile of the QoS Flow as described in clause 6.2.2.4 of TS 23.503 [45]. Alternatively, the SMF may be configured to support PDU Set based Handling without receiving PCC rules from a PCF.
If no DL PDU Set QoS parameters are included in the PCC rule, but a DL Protocol Description is included in the PCC rule received by the SMF and the PSA UPF supports PDU Set Handling (i.e. supports to perform PDU Set Information marking), the SMF may, based on the local operator policy, send to the NG-RAN, a DL PDU Set Information Marking Support Indication indicating that the DL PDU Set Information marking is supported.
For the downlink direction, the PSA UPF identifies PDUs that belong to PDU Sets and marks them accordingly as described in clause 5.37.5.2. If the PSA UPF receives a PDU that does not belong to a PDU Set based on Protocol Description for PDU Set identification, then the PSA UPF still maps it to a PDU Set and determines the PDU Set Information as described in clause 5.37.5.2.
NOTE 4: If the PSA UPF receives a PDU that does not belong to a PDU Set, then it is assumed that the UPF determines the PDU Set Importance value based on pre-configuration.
For the uplink direction, the UE may identify PDU Sets and how this is done is left up to UE implementation. The SMF may send the UL Protocol Description associated with the QoS rule to UE.
NOTE 5: Using the Protocol Description or not is left to UE implementation. The use of Protocol Description does not impact QoS Flow Mapping in the UE.
In this Release, the PDU Set based handling is supported in 5GS for a UE registered in 3GPP access for single access PDU Session with IP PDU Session Type, for a UE registered in untrusted or trusted non-3GPP accesses for single access PDU Session with IP PDU Session Type, and for a 5G-RG registered in W-5GAN for single access PDU Session with IP PDU Session Type. The support of PDU Set based handling in 5G-RG is specified in TS 23.316 [84]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.5.2 PDU Set Information and Identification | To support PDU Set based QoS handling, the PSA UPF identifies PDUs that belong to a PDU Set and determines the below PDU Set Information and sends it to the 5G-AN in the GTP-U header. The PDU Set Information is used by the 5G-AN for PDU Set based QoS handling as described above.
The PDU Set Information comprises:
- PDU Set Sequence Number.
- Indication of End PDU of the PDU Set.
- PDU Sequence Number within a PDU Set.
- PDU Set Size in bytes.
- PDU Set Importance, which identifies the relative importance of a PDU Set compared to other PDU Sets within a QoS Flow.
The 5G-AN may use the Priority Level (see clause 5.7.3.3) across QoS Flows and PDU Set Importance within a QoS Flow for PDU Set level packet discarding in presence of congestion.
NOTE 1: In addition to considering the PDU Set Importance within a QoS Flow, 5G-AN could also consider the relative PDU Set Importance across QoS Flows of the same Priority Level when determining which PDU Set needs to be discarded, which is up to implementation and configuration of operator.
NOTE 2: The PDU Set Information can be different for different PDU Sets within a QoS Flow.
If the 5G-AN has provided a PDU Set based handling support Indication indicating that PDU Set handling is supported and a DL Protocol Description together with 1) a PSIHI and/or 2) PSDB and PSER is included in the PCC rule, the SMF instructs PSA UPF to perform PDU Set marking and may provide the PSA UPF the DL Protocol Description used by the service data flow. The DL Protocol Description may be received in the PCC rule, based on information provided by the AF or by PCF local policies as described in clause 5.37.5.1.
If the DL PDU Set Information Marking Support Indication has been sent to the 5G-AN (as described in clause 5.37.5.1) and the 5G-AN has provided a PDU Set based handling support Indication indicating that PDU Set handling is supported, the SMF instructs PSA UPF to perform PDU Set marking and provides the PSA UPF the DL Protocol Description used by the service data flow.
PSA UPF can identify the PDU Set Information using the DL Protocol Description and the received transport protocol headers and payload or using implementation specific means. The details of the RTP/SRTP headers, header extensions and/or payloads used to identify PDU Set Information are defined in TS 26.522 [179].
For end-to-end encrypted traffic, PDU Set Information is received as media related information from the Application Server, see clause 5.37.9.
For each DL PDU received on N6 for which PDU Set based QoS handling is indicated from the SMF, the PSA UPF applies the rules for PDU Set identification and provides the available PDU Set Information to the 5G-AN in the GTP-U header.
NOTE 3: The PSA UPF is expected to assign a unique PDU Set Sequence Number in the GTP-U header to each PDU Set of the QoS Flow. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.5.3 Non-homogenous support of PDU set based handling in NG-RAN | The SMF, by sending PDU Set QoS parameters (as described in clause 5.7.7.1) or a DL PDU Set Information Marking Support Indication (as described in clause 5.37.5.1) to the NG-RAN, requests the NG-RAN to activate PDU Set handling for a given QoS Flow and the NG-RAN provides the SMF with a PDU Set Based Handling Support Indication if the PDU Set based handling is supported. Based on this indication, SMF may activate the PDU Set identification and marking in the PSA UPF as described in clause 5.37.5.2.
During mobility procedures that result in the change of NG-RAN, the target NG-RAN provides to the SMF a PDU Set Based Handling Support Indication if it supports PDU Set based handling, as specified in TS 38.413 [34]. Based on the target NG-RAN indication, the SMF may, upon completion of the mobility procedure, initiate the PDU Session modification procedure to provide PDU Set QoS parameters or the DL PDU Set Information Marking Support Indication to NG-RAN and may configure the PSA UPF to activate the PDU Set identification and marking. If the PDU Set Based Handling Support Indication is not received from the target NG-RAN and PDU Set identification and marking is active in the PSA UPF, the SMF may deactivate it.
In the case where the PSA UPF identifies and marks PDUs with PDU Set information in GTP-U header, it shall start doing so from a complete PDU Set.
NOTE: Based on the PDU Set Based Handling Support Indication from the target NG-RAN, the SMF can update the QoS profile and, if applicable, Alternative QoS Profiles as defined in clauses 5.7.1.2 and 5.7.1.2a to include the PDU Set QoS parameters respectively. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.6 UL/DL policy control based on round-trip latency requirement | For XR and other interactive media services that require very low Round-Trip (RT) latency, Uplink-Downlink policy control may be supported to meet the RT latency requirement. RT latency requirement is the upper bound for the sum of UL delay and DL delay of a single data flow or two different data flows between UE and N6 termination point at the UPF. PCF may support Uplink-Downlink policy control based on RT latency requirement based on an RT latency indication from AF (as defined in clause 6.1.3.27.2 of TS 23.503 [45]) during the AF session with the required QoS procedure as defined in clause 4.15.6.6 of TS 23.502 [3].
The AF can provide an RT latency indication with a single direction delay requirement between the UE and the PSA UPF expressed as the QoS Reference parameter or individual QoS parameters (as defined in clause 6.1.3.22 of TS 23.503 [45]). The RT latency indication indicates the need to meet the RT latency requirement for data flow, i.e. doubling of the single direction delay requirement between the UE and the PSA UPF expressed by the QoS Reference parameter or individual QoS parameter.
PCF determines the data flow's UL PDB and DL PDB based on the RT latency requirement. The UL PDB and DL PDB can be unequal, but their sum shall not exceed the RT latency requirement. The PCF shall generate two PCC rules, one for UL QoS flow for UL traffic of the data flow and one for DL QoS flow for DL traffic of the data flow, respectively. PCF shall assign the 5QIs for each of these two PCC rules according to the derived UL PDB and DL PDB.
To support UL and DL delay tracking, the QoS monitoring for UL packet delay and the DL packet delay (as defined in clause 6.1.3.21 of TS 23.503 [45]) shall be triggered respectively to request tracking the UL packet delay of the QoS flow used in UL and DL packet delay of the QoS flow used in DL independently. Based on the QoS monitoring results, the PCF may readjust the UL PDB and/or DL PDB under the consideration of the RT latency requirement to better fit the new situation.
The Uplink-Downlink policy control based on round-trip latency requirement for two unidirectional service data flows is described in clause 6.1.3.27.2 of TS 23.503 [45].
NOTE: How the PCF derives the round-trip latency and takes policy decisions is up to the implementation. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.7 5GS Packet Delay Variation monitoring and reporting | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.7.1 General | The 5GS Packet Delay Variation is the variation of packet delay measured between UE and PSA UPF. The AF may send the requirement for Packet Delay Variation monitoring to 5GS together with the requirement for packet delay measurement, as described in clause 6.1.3.26 of TS 23.503 [45].
Upon AF request for Packet Delay Variation monitoring together with packet delay monitoring, the PCF triggers the QoS monitoring procedure and obtains the UL, DL or RT QoS Monitoring result from the SMF. After receiving the QoS Monitoring result, the PCF derives the 5GS Packet Delay Variation based on the QoS Monitoring result and then reports to the AF/NEF both packet delay measurements and Packet Delay Variation.
The details of the QoS Monitoring and QoS Monitoring for packet delay are described in clauses 5.45 and 5.33.3.
NOTE: The derivation of 5GS Packet Delay Variation by PCF, based on QoS Monitoring, is implementation dependent. The Packet Delay Variation calculation method needs to be the same within the PLMN, based on operator policy.
QoS Monitoring is used to obtain measurement of QoS parameters of individual QoS Flows. PCF determines the measurements required based on input from AF and enables the measurements by generating an authorized QoS Monitoring Policy for the PCC Rule as specified in clause 6.1.3.21 of TS 23.503 [45]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.8 UE power saving management | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.8.1 General | The following traffic assistance information may be provided by the CN to NG-RAN in order to configure UE power saving management scheme for connected mode DRX:
- UL and/or DL Periodicity;
- N6 Jitter Information associated with the DL Periodicity;
- Indication of End of Data Burst.
The UL and/or DL Periodicity and N6 Jitter Information associated with the DL Periodicity are provided by the CN to NG RAN via TSCAI. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.8.2 Periodicity and N6 Jitter Information associated with Periodicity | In the procedures for setting up or updating an AF session with QoS, the 5G System may be provided with UL/DL Periodicity information for NG-RAN to configure UE power management for connected mode DRX. The UL/DL Periodicity information is provided by the AF to the PCF via NEF or directly to the PCF when the AF is trusted.
NOTE 1: AF can provide the updated periodicity and 5G system can provide the updated UL/DL periodicity to NG-RAN.
If UL/DL Periodicity information is available at the PCF, the PCF sends the Periodicity information received from the AF/NEF to the SMF. In accordance with the operator's local policies, the PCF may include an indication for SMF to request the UPF to perform N6 Traffic Parameter(s) measurement (i.e. N6 Jitter Information associated with the DL Periodicity and if not provided by the AF, UL/DL periodicity) within the PCC Rules.
Upon reception of a PCC rule with Periodicity information, the SMF determines the TSCAI and forwards it to the NG-RAN. If the PCC rule indicates to perform N6 Traffic Parameter measurements, the SMF shall request the UPF to monitor and periodically or event-triggered report the N6 Traffic Parameters (i.e. the N6 Jitter Information associated with the DL Periodicity and, if not provided by the AF, UL/DL periodicity) using the N4 Session Modification procedure, see clause 5.8.5.11. If the measurement of N6 Jitter Information associated with the DL Periodicity is required and the DL Periodicity is available at the SMF, the SMF also sends the DL Periodicity to the UPF. The UPF reports the measured N6 Traffic Parameters to SMF via N4 interface.
NOTE 2: How the UPF derives the N6 jitter and periodicity (i.e. when periodicity is not provided by the AF) is implementation dependent.
At reception of measured N6 Traffic Parameter(s) from the UPF in the N4 Session Level Report, the SMF includes the N6 Jitter Information associated with the DL Periodicity together with the DL periodicity and the UL periodicity if not provided by the AF in the TSCAI and forwards it to the NG-RAN in an NGAP message, see clause 5.27.2.
NOTE 3: In order to prevent frequent updates from the UPF, the UPF sends the N6 Jitter Measurement Report periodically or only when the N6 jitter is larger than a threshold.
The N6 Jitter Information associated with the DL Periodicity indicates the range of the positive or negative deviation of the arrival time of first arrived packet of a Data Burst compared to the ideal Data Burst start time which is determined based on the DL periodicity. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.8.3 End of Data Burst Indication | An indication of End of Data Burst may be provided to the NG-RAN by the PSA UPF, e.g. to configure UE power management schemes like connected mode DRX.
Based on the End of Data Burst Marking Indication in a PCC rule and/or on local operator policies, SMF should request the PSA UPF to detect the last PDU of the data burst and mark the End of Data burst in the GTP-U header of the last PDU in downlink. The SMF may provide the PSA UPF the End of Data Burst Marking Indication and Protocol Description used by the service data flow. The Protocol Description may be received in the PCC rule, based on information provided by the AF or by PCF local policies as described in clause 5.37.5.1.
According to the request and information from the SMF, the UPF identifies the last PDU of a Data burst in the DL traffic using the DL Protocol Description and the received transport protocol headers as defined in TS 26.522 [179] or using implementation specific means and provides an End of Data Burst indication to the NG-RAN in GTP-U header of the last PDU of the Data burst.
For end-to-end encrypted traffic, the End of Data Burst Indication is received as media related information from the Application Server, see clause 5.37.9.
NOTE: There can be some packets from the Data Burst received by NG-RAN after the PDU with End of Data Burst Indication if packets are received out of sequence. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.9 Support of transferring media related information over N6 | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.9.1 General | This clause describes the procedure to support transferring of media related information (i.e. information related to the media being transmitted, either explicitly provided by the AS or inferred from protocol headers or payload, e.g. PDU Set Information, Data Burst Size, etc.) over N6. Such support is necessary is when the end-to-end connection for XR and media traffic between the UE and Application Server is fully encrypted thus UPF not being able to identify, for example, PDU set information.
On-path N6 signalling methods are used to transfer media related information over N6 where media related information is sent together with the encrypted payload allowing media related information to be received synchronously with the media packet. The following on-path N6 signalling methods are supported:
- Using Media over QUIC (MoQ), as defined in IETF draft-ietf-moq-transport [201], whose usage is further defined in clause 5.37.9.2.
- Use of connect-UDP for Using Proxying-UDP-in-HTTP, as defined in IETF RFC 9298 [170] and QUIC-Aware Proxy, draft-ietf-masque-quic-proxy [200], whose usage is further defined in clause 5.37.9.3
- Using UDP-Options, as defined in IETF draft-ietf-tsvwg-udp-options [202], whose usage is further defined in clause 5.37.9.4.
When Media over QUIC is used the UPF identifies PDU Set Information and End of Data Burst Indication from media related information specified in [201].
When Proxying-UDP-in-HTTP RFC 9298 [170] or QUIC-Aware Proxy [200] or UDP-Options, IETF draft-ietf-tsvwg-udp-options [202], is used, the following media related information are supported:
- PDU Set Information (as described in clause 5.37.5.2).
- End of Data Burst Indication (as described in clause 5.37.8.3).
- Expedited Transfer Indication (as described in clause 5.37.10).
- Data Burst Size (as described in clause 5.37.10).
- Time to Next Burst (as described in clause 5.37.10).
The mechanisms defined in clause 5.37.9 address only UE to XRM server (AS) communication and do not address UE-UE XRM communications. The mechanisms defined in clause 5.37.9 support only downlink media related information delivery to the UPF.
The media related information is encrypted and integrity protected between the UPF and the AS, as defined in TS 33.501 [29]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.9.2 Usage of Media Over QUIC in order to Handle end-to-end encrypted XR and media flows | When a PSA UPF that supports MoQ relay functionality has been selected, encrypted Metadata associated with traffic can be transported between the UPF and the AS via Media over QUIC (MoQ), IETF draft-ietf-moq-transport [201].
A PSA UPF supporting the MoQ relay functionality can be selected by SMF with the consideration of the DNN and S-NSSAI provided by UE.
NOTE 1: The application client in the UE uses MoQ Transport protocol and establishes a MoQ connection using the address of MoQ Relay between the application client and MoQ relay in UPF as defined in MoQ, IETF draft-ietf-moq-transport [201].
The SMF may get the address of MoQ Relay from the UPF during N4 session management procedure as defined in the clause 4.4.1 of TS 23.502 [3] or the SMF may get MoQ relay address related to the PSA UPF from the NRF as described in clause 5.2.7.3.2 of TS 23.502 [3]. In the former case, the SMF indicates the PSA UPF to provide MoQ relay address in N4 Session Establishment/Modification Request and the PSA UPF returns MoQ relay address in N4 Session Establishment/Modification Response.
NOTE 2: The application client can obtain the MoQ relay address via application layer-based schemes.
In the case the EASDF based DNS procedure as described in clause 6.2.3.2.2 of TS 23.548 [130] is used, after SMF has received FQDN in DNS message report from EASDF, SMF determines the FQDN is for MoQ and gets the address of MoQ relay and then SMF provides DNS message handling rule with the address of MoQ relay to instruct EASDF to return the address of MoQ Relay in PSA UPF by setting the Forwarding Action as Respond directly to the DNS request according to TS 23.548 [130]. In this case a local PSA UPF supporting MoQ Relay maybe selected by SMF.
NOTE 3: It is assumed an application client can send a DNS query to resolve FQDN.
NOTE 4: The FQDN can be the FQDN for MoQ traffic and preconfigured in SMF or it can be the FQDN of the MoQ Relay and preconfigured in SMF and application client. It is assumed there is SLA between operator and application service provider for using MoQ relay functionality provided by operator.
NOTE 5: In some other case, the application client can also obtain the MoQ relay address from the MoQ application server via the query during the MoQ session establishment between the application client and the MoQ application server as in MoQ, IETF draft-ietf-moq-transport [201], which is out of the scope of 3GPP. The MoQ application server can get the MoQ relay address via local configuration.
NOTE 6: Different MoQ application servers can correspond to different MoQ relays that are deployed on the same PSA UPF.
The AF provided Protocol Description indicating Media over QUIC Transport, IETF draft-ietf-moq-transport [201] can be used in determining the PCC Rule by the PCF as defined in clause 6.1.3.27.4 of TS 23.503 [45]. Based on the PCC rule, the SMF instructs the PSA UPF to perform PDU Set Information identification. Upon receiving the MoQ SUBSCRIBE message from UE application client, the MoQ relay can establish n upstream MoQ subscription to the MoQ application server if there is no existing subscription yet.
For the downlink service data flow using MoQ Transport, the PSA UPF can identify the PDU Set Information from the MoQ Metadata as defined in clause 7 of MoQ, IETF draft-ietf-moq-transport [201] that is extracted by the MoQ relay and provide the available PDU Set Information to the RAN in the GTP-U header.
NOTE 7: The mappings between the MoQ Metadata and the PDU Set Information can be based on local configuration, or operator-determined implementations. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.9.3 Use of connect-UDP | When the traffic is UDP and encrypted end-to-end, the UPF may be configured by the SMF establish a connection to an HTTP/3 AS proxy using connect-UDP according to IETF RFC 9298 [170], acting as an HTTP/3 client configured to use a UDP proxy. The AS then provides media related information within HTTP datagrams. The media related information in the HTTP datagrams is protected by the security of the QUIC connection established between the UPF and the AS proxy. The mechanism for exchanging HTTP Datagrams and the associated format is defined in IETF RFC 9298 [170] and IETF RFC 9297 [172].
The AF may provide via the NEF an indication of support of connect-UDP protocol to deliver media related information for encrypted traffic together with the corresponding UDP proxy address and the corresponding QoS requirements. This is done using the AF session with QoS procedure (as defined in clause 4.15.6.6 of TS 23.502 [3]), Then:
- The PCF generates PCC rules including On-path N6 signalling information for Connect-UDP as defined in TS 23.503 [45].
- The SMF provides N4 rules to the UPF including the corresponding On-path N6 connection information.
- In the uplink direction, PDR rules are used to detect the UDP traffic flow subject to usage of connect-UDP and the associated FAR rules include the request to establish a connection to the AS proxy address using the connect-UDP protocol.
- In the downlink direction, PDR rules are used to detect the UDP traffic flows and QER rules are used to associate them with proper QoS related marking (e.g. including PDU set marking as defined in clause 5.37.5),
The connection is established by the UPF, at the latest at reception of an UL UDP packet matching an N4 rule with On-path N6 connection information, if not already established. UPF may use the same or different QUIC connections for different UEs depending on implementation. In order to reuse the connection, UPF sends CONNECT requests for different UEs over a single QUIC connection to the AS proxy, opening different QUIC streams to handle the traffic for the UEs.
If the traffic is carried over QUIC, UPF and AS proxy may agree on using the Forwarded Mode in IETF draft-ietf-masque-quic-proxy [200], which allows for forwarding of packets without requiring full re-encapsulation and re-encryption. In that case, the AS proxy provides the media related information within datagrams, together with the forwarded QUIC packets.
By default, UPF and AS proxy use Tunnelling Mode in IETF draft-ietf-masque-quic-proxy [200] to exchange XRM traffic. When Tunnelling Mode is used the AS provides media related information in HTTP Datagrams.
NOTE 1: During the QUIC connection establishment between the UE and the AS proxy, the UPF can learn the end-to-end QUIC Connection IDs that are used in the end-to-end flows from UE to AS and those used in the flows from AS to UE. Based on the learnt Connection ID(s), the UPF can negotiate with AS proxy according to IETF draft-ietf-masque-quic-proxy [200] to get Virtual Connection IDs (VCID(s)) corresponding to the end-to-end Connection IDs. These virtual CIDs can then be used by UPF and AS to support the Forwarded Mode.
When Forwarded Mode is active and possible for UL direction, the UPF sends UL QUIC packet towards the AS proxy using the Virtual Connection IDs negotiated via QUIC aware proxying with HTTP, IETF draft-ietf-masque-quic-proxy [200]; such UL traffic contains only the UDP payload received from the UE.
When Forwarded Mode is active and possible for DL direction, media related information is included by the AS into the forwarded UDP payload packets via a packet transform defined by 3GPP. The UPF uses a 3GPP defined packet transform (see TS 29.561 [132]) to retrieve the media related information and the content of the original end-to-end QUIC packet.
During the negotiation between UPF and AS proxy to activate the Forwarded Mode, the UPF and the AS proxy agree on the 3GPP packet transform to apply in the DL direction.
NOTE 2: The connect-UDP client in the UPF can only extract the full CIDs from e2e QUIC long-header packets to use these values in REGISTER_CLIENT_CID and REGISTER_TARGET_CID capsules defined in IETF draft-ietf-masque-quic-proxy [200]. Prior to forwarding QUIC packets with short header, the connect-UDP client (UL) and the proxy (DL) check whether the destination CID is identical to an already registered CIDs, if not, the packets are sent in tunnelled-mode.
NOTE 3: The format of HTTP Datagrams and the format of Forwarded Mode Datagrams carrying media related information are defined in TS 29.561 [132]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.9.4 Usage of UDP Option transferring media related information over N6 | The mechanism described in this clause uses connect-udp in tunnel mode for On-path N6 signalling to establish a UDP tunnel between the UPF as HTTP/3 client and the AS as HTTP/3 proxy according to clause 5.37.9.2 to securely transfer media related information. This clause defines the differences with the mechanisms defined in clause 5.37.9.2 when media related information is carried over UDP Option.
The media related information is encoded into UDP-Option as defined in IETF draft-ietf-tsvwg-udp-options [202] and transferred through the UDP tunnel over N6, in which the inner UDP datagram contains end-to-end encrypted XRM media packet between AS proxy and UE and the outer UDP datagram between AS proxy and UPF contains UDP-Option carrying media related information (see Annex W).
NOTE: The format of the media related information carried by the specific UDP-Option and exchanged between the UPF and the AS proxy is defined in TS 29.561 [132]).
Editor's note: The details for documenting and assigning a UDP option kind value for carrying media related information in IETF are pending collaboration with IETF.
The usage of UDP-Option transferring media related information over N6 is supported as defined in clause 5.37.9.2 with following differences:
- When the AF provides On-path N6 signalling information for connect-udp, it may also provide an indication of UDP-Option in Protocol Description for transferring media related information. This is to instruct the PSA UPF that the media related information is carried in UDP-Option in UDP datagram over N6.
- The inner UDP datagrams contain the unmodified payload for both UL and DL traffic and the media related information is included in the UDP option of the DL outer UDP datagram.
- The UPF supports the HTTP/3 Client functionality for negotiation of security keys used for encrypting media related information carried in the UDP-Option. The UPF shall remove the UDP-Option carrying media related information before forwarding the XRM media packets over right PDU Session towards the (R)AN and the UE.
Editor's note: Security keys for UDP-Option can be negotiated using connect-udp upgrade token in tunnelled mode between the UPF and AS proxy. The details are up to SA WG3. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.10 Supporting dynamically changing traffic characteristics via the User Plane | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.10.1 DL Data Burst Size marking | The Data Burst Size may be provided to the NG-RAN in the downlink GTP-U header by the UPF in order to assist radio resource management. As described in clause 6.1.3.27.5 of TS 23.503 [45] the PCF may include a Data Burst Size Marking Indication within a PCC Rule to request the UPF to identify and mark the Data Burst Size of the data burst for the corresponding QoS Flow. The PCF also includes the DL Protocol Description received from AF.
Based on the Data Burst Size Marking Indication in a PCC Rule, the SMF instructs the UPF to identify and mark the Data Burst Size of the data burst in downlink for the corresponding PDR. The SMF may provide the UPF the Protocol Description received in the PCC Rule.
According to the Data Burst Size Marking Indication and DL Protocol Description from the SMF, the UPF identifies in the first DL packets of the data burst the Data Burst Size carried in an N6 RTP Header Extension/ transport protocol header as defined in TS 26.522 [179]. The UPF sends the identified Data Burst size to NG-RAN in the downlink GTP-U header of the first PDUs of the data burst. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.10.2 Time to Next Burst marking | The time to next data burst, which is the interval between the transmission of the last PDU in the current data burst and the first PDU of the next data burst, may be provided to the NG-RAN by the UPF to assist NG-RAN's behaviour in downlink. As described in clause 6.1.3.27.5 of TS 23.503 [45] the PCF may include a Time to Next Burst Marking Indication within a PCC Rule to request the UPF to identify and mark the time to next data burst for the corresponding QoS Flow. The PCF also includes the DL Protocol Description received from AF.
Based on the Time to Next Burst indication in a PCC Rule, the SMF instructs the UPF to identify and mark the time interval to next data burst in downlink. The SMF may provide the UPF the Protocol Description used by the service data flow received in the PCC Rule.
According to the Time to Next Burst indication and DL Protocol Description from the SMF, the UPF identifies the time interval to next data burst carried in an N6 RTP Header Extension/transport protocol header as defined in TS 26.522 [179] and sends the identified time interval to next data burst to NG-RAN in a downlink GTP-U header.
Time to next data burst marking is only used when the deployment is such that the time to next data burst is sufficiently accurate i.e. the jitter (e.g. the N6 jitter) is sufficiently limited without impact to the accuracy of the time to next data burst. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.10.3 Expedited Data Transfer with reflective QoS | Expedited Data Transfer with reflective QoS can be requested by AF to expedite the data transfer of larger payload for IP flow(s) of XR application. Expedited Data Transfer can be used for non-GBR SDF only.
To enable Expedited Data Transfer, the AF provides two media flows that contains the same SDF filter associated with different QoS requirements, one media flow is associated with Expedited Transfer Indication set to TRUE and the other one set to FALSE.
Expedited Data Transfer requires the PSA UPF to detect the "Expedited Transfer Indication" (contained in N6 metadata or in RTP Header Extension) in the downlink service data flow. To enable expedited transfer for encrypted traffic where the "Expedited Transfer Indication" is contained in N6 metadata, the AF provides information to enable transferring media related information over N6 (in clause 5.37.9). To enable expedited transfer for non-encrypted traffic where the "Expedited Transfer Indication" is contained in the RTP Header Extension, the AF may provide related protocol description information.
If the UE supports Reflective QoS, the PCF generates a PCC rule for each media flow with Expedited Transfer Indication based on the AF request. For the SDF with Expedited Transfer Indication set to TRUE, the Reflective QoS control is enabled in the PCC rule. And for the SDF with Expedited Transfer Indication set to FALSE, it is up to operator configuration to enable the Reflective QoS control or not in the PCC rule. Further details are described in clause 6.1.3.27 of TS 23.503 [45].
The SMF receives these two PCC rules and generates two PDRs including the Expedited Transfer Indication in the PDI. Expedited Transfer Indication is set to TRUE in the one PDR and to FALSE in the other. If UPF receives the PDRs with the Expedited Transfer Indication, it shall also detect "Expedited Transfer Indication" in the downlink packets (as described in clause 5.37.9 for encrypted traffic, or in RTP Header Extension/transport protocol header as defined in TS 26.522 [179]) to process the DL packets based on one of these two PDRs. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.37.11 Traffic identification and differentiated QoS for multiplexed media flows | XR and interactive media services can send data traffic of different media components with different QoS requirements. Several media flows could be multiplexed on the same end-to-end transport layer connection. In order to uniquely identify each media flow, the IP Packet Filter can further include multiplexed media specific (S)RTP Multiplexed Media Identification Information to differentiate the media flow among multiple media flows that share the same transport layer related elements in the packet filter (see clause 5.7.6.2).
The AF may provide individual QoS requirements for each individual RTP media flow within the multiplexed data flows and for the (S)RTCP that controls the (S)RTP transmission, by including the (S)RTP Multiplexed Media Identification Information associated with the individual QoS requirements within the flow description in the "AF session with the required QoS" procedure specified in clauses 4.15.6.6 and 4.15.6.6a of TS 23.502 [3]. The policy control related to multiplexed media flows identification is specified in clause 6.1.3.22 of TS 23.503 [45].
If a UE indicates support of (S)RTP Multiplexed Media Identification Information in the IP packet filter, it shall indicate this to the SMF at PDU Session establishment and the SMF provides this UE capability information to the PCF. The PCF considers such UE capability information when providing the PCC rules to the SMF.
If (S)RTP Multiplexed Media Identification Information is received in the PCC rule, the SMF provides (S)RTP Multiplexed Media Identification Information to the UPF in the corresponding PDR(s) and also to the UE in the QoS Rule if the UE has indicated that it supports (S)RTP Multiplexed Media Identification Information in IP packet filter. If the UE has not indicated so, the SMF shall not provide the (S)RTP Multiplexed Media Identification information in the QoS Rule to the UE. Reflective QoS shall not be applied to SDFs which are identified with (S)RTP Multiplexed Media Identification Information defined in clause 5.7.6.2. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38 Support for Multi-USIM UE | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.1 General | A network and a Multi-USIM UE may support one or more of the following features for Multi-USIM UE operation:
- Connection Release as described in clause 5.38.2;
- Paging Cause Indication for Voice Service, as described in clause 5.38.3;
- Reject Paging Request, as described in clause 5.38.4;
- Paging Restriction, as described in clause 5.38.5;
- Paging Timing Collision Control, as described in clause 5.38.6.
In the Registration procedure (as specified in clause 4.2.2.2.2), when a Multi-USIM UE has more than one USIM active, supports and intends to use one or more Multi-USIM specific features, it indicates to the AMF the corresponding Multi-USIM feature(s) are supported (except for the Paging Timing Collision Control feature). Based on the received indication of the supported Multi-USIM features from the UE, the AMF shall indicate to the UE the support of the Multi-USIM features based on the Multi-USIM features supported by network and any preference policy by the network, if available. When a UE returns to having only one USIM active from a Multi-USIM UE that previously indicated to the network it supported Multi-USIM feature(s), the UE shall indicate all the Multi-USIM features are not supported to the network for that USIM. The AMF shall only indicate the support of Paging Restriction feature together with the support of either Connection Release feature or Reject Paging Request feature.
The Multi-USIM UE includes the support of individual features for Connection Release, Paging Cause Indication for Voice Service, Reject Paging Request and Paging Restriction as specified in clause 5.4.4a.
NOTE: The Paging Timing Collision Control feature being based on the Mobility Registration Update and it doesn't require capability exchange between the UE and network.
The network shall not indicate support for any Multi-USIM feature to the UE as part of the Emergency Registration procedure.
A Multi-USIM UE shall use a separate PEI for each USIM when it registers with the network. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.2 Connection Release | A Multi-USIM UE may request the network to release the UE from RRC_CONNECTED state in 3GPP access for a USIM due to activity on another USIM in 3GPP access, if both UE and network indicate the Connection Release feature is supported to each other.
In the case of NAS connection release procedure, the UE indicates that it requests to be released from RRC_CONNECTED state, by initiating either a Service Request procedure over 3GPP access or a Registration procedure over 3GPP access (if case the UE needs to perform Registration Update at the same time with this network, including the case where the Registration Request is sent due to mobility outside the Registration Area, i.e. before detecting whether the network supports the feature in the new Tracking Area, provided that the network has already indicated support for Connection Release feature in the current stored Registration Area), by including a Release Request Indication. If supported by the UE and network, the UE may also provide, only together with the Release Request Indication, Paging Restriction Information, as specified in clause 5.38.5, which requests the network to restrict paging. If the UE is performing an Emergency Registration then it shall not include a Release Request Indication.
For NR/5G access, an AS method for the UE to request the network to release the UE from RRC_CONNECTED state is specified in TS 38.300 [27]. This mechanism does not allow the UE to indicate Paging Restrictions.
NOTE 1: When both the access stratum and NAS based approaches for requesting the connection release are supported by the UE and the network, it depends on the UE implementation which of the two to use (for example: based on the preferred end state (RRC_INACTIVE or RRC_IDLE) and whether Paging Restriction Information is to be provided).
NOTE 2: When there is no PLMN-wide support for the Connection Release feature, it can occur that upon Mobility Registration Update with Release Request indication the UE is not released by the network. The UE behaviour, when it detects that the network does not support the feature in a new RA, is outside the scope of this specification. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.3 Paging Cause Indication for Voice Service | A Multi-USIM UE and the network may support Paging Cause Indication for Voice Service feature.
The network that supports Paging Cause Indication for Voice Service feature shall provide a Voice Service Indication for IMS voice service in the Paging message, only if the UE indicates the Paging Cause Indication for Voice Service feature is supported to the network. The network determines the IMS voice service based on the Paging Policy Indicator as specified in clause 5.4.3.2.
Upon reception of the Voice Service Indication in NGAP Paging Message from AMF, the NG-RAN supporting Paging Cause Indication for Voice Service should include the Voice Service Indication in the Uu Paging message to the UE.
When the UE context in the AMF indicates Paging Cause Indication for Voice Service feature is supported, in order to require NG RAN to deliver the Voice Service Indication in RAN paging for the UE in RRC_INACTIVE state, the AMF provides an indication indicating the Paging Cause Indication for Voice Service feature is supported to the NG-RAN. Upon reception of the indication, the NG-RAN that supports the feature stores a Paging Cause Indication for Voice Service indication in its the UE context. For a UE in RRC_INACTIVE, the NG-RAN should provide the Voice Service Indication in the RAN Paging message only when there is Paging Cause Indication for Voice Service indication in the UE context and detects the downlink data which triggers the RAN Paging message is related to voice service based on the Paging Policy Indicator, in the header of the received downlink data, as specified in clause 5.4.3.2.
UE that supports the Paging Cause Indication for Voice Service feature is capable of differentiation between Paging from a network that does not support the Paging Cause Indication for Voice Service feature and Paging without the Voice Service Indication. How the UE distinguishes the Paging from a RAN that does not support the Paging Cause Indication for Voice Service feature and Paging without the Voice Service Indication is defined in TS 38.331 [28]. The UE determines whether the Paging Cause Indication for Voice Service feature is supported in the current Registration Area by 5GC based on the MUSIM capability exchange with the AMF, see clause 5.38.1. The UE determines that the Paging Cause Indication for Voice Service feature is supported if it is supported by both the RAN, as indicated in the received Uu Paging message and by 5GC, as indicated in the MUSIM capability exchange with the AMF.
The UE uses the Paging Cause Indication for Voice Service as described in TS 24.501 [47] and TS 38.331 [28]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.4 Reject Paging Request | A Multi-USIM UE may set up a connection to respond to a page with a Reject Paging Indication to the network indicating that the UE does not accept the paging and requests to return to CM-IDLE state after sending this response, if both UE and network indicate the Reject Paging Request feature is supported to each other.
Upon being paged by the network, the Multi-USIM UE in CM-IDLE state attempts to send a Service Request message to the paging network including the Reject Paging Indication as the response to the paging, unless it is unable to do so, e.g. due to UE implementation constraints. In addition to the Reject Paging Indication, the UE may include Paging Restriction Information as specified in clause 5.38.5 in the Service Request message, if supported by UE and network.
NOTE: A Multi-USIM UE in RRC_INACTIVE state can decide to not initiate the RRC connection resumption procedure, e.g. when it decides not to respond to the paging message due to UE implementation constraints as specified in TS 24.501 [47] and TS 38.331 [28]. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.5 Paging Restriction | A Multi-USIM UE and the network may support Paging Restriction. A Multi-USIM UE, if the AMF indicates that the network supports Paging Restriction feature, may indicate Paging Restriction Information in the Service Request or Registration Request message (including the case where the Registration Request is sent due to mobility outside the Registration Area, i.e. before detecting whether the network supports the feature in the new Tracking Area, provided that the network has already indicated support for Paging Restriction feature in the current stored Registration Area) as specified in clauses 5.38.2 and 5.38.4.
Based on operator policy the AMF may accept or reject the Paging Restriction Information requested by the UE. If the AMF accepts the Paging Restriction Information from the UE, the AMF stores the Paging Restriction Information from the UE in the UE context. If the AMF rejects the Paging Restriction Information, the AMF removes any stored Paging Restriction Information from the UE context and discards the UEs requested Paging Restriction Information. The AMF informs the UE about the acceptance/rejection of the requested Paging Restriction Information in the Registration Accept or Service Accept message.
If the UE does not provide any Paging Restriction Information in the Service Request over 3GPP access or the Registration Request over 3GPP access, the AMF removes any stored Paging Restriction Information from the UE context.
The Paging Restriction Information may indicate any of the following:
a) all paging is restricted; or
b) all paging is restricted, except paging for voice service (IMS voice); or
c) all paging is restricted, except for certain PDU Session(s); or
d) all paging is restricted, except paging for voice service (IMS voice) and certain PDU session(s).
NOTE 1: The UE expects not to be paged for any purpose in case a). The UE expects to be paged only for voice service in case b). The UE expects to be paged only for certain PDU Session(s) in case c). The UE expects to be paged for voice service and certain PDU session(s) in case d). The AMF can page the UE for mobile terminated signalling based on local policy considering the stored Paging Restriction Information, except for case a). In this case, to comply with the UE provided Paging Restriction Information, the AMF can trigger AN release procedure as soon as possible after the mobile terminated signalling procedure is executed.
NOTE 2: In the case of roaming, the Paging Restrictions for voice service implied by bullet b) and d) depends on the existence of an agreement with the HPLMN to support voice service via IMS. Hence the support of Paging Restrictions in bullets b) and d) takes the IMS voice service agreement into consideration.
NOTE 3: When there is no PLMN-wide support for the Paging Restriction feature, it can occur that upon Mobility Registration Update with Paging Restriction Information the UE detects the network does not support the feature. If so, the UE assumes that no Paging Restriction Information is applied. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.38.6 Paging Timing Collision Control | To avoid possible paging occasion collision and to enhance the likelihood that paging is received successfully for different USIMs, a Multi-USIM UE may need a new 5G-GUTI to modify the timing of the Paging Occasions (POs) for a USIM when the USIM's registration is not emergency registration. When a Multi-USIM UE needs a 5G-GUTI assignment, it performs a Mobility Registration Update without any specific indication (i.e. it is using a normal Registration procedure). This triggers the AMF to allocate a new 5G-GUTI and provide it to the Multi-USIM UE in the Registration Accept message.
NOTE: It is recommended to avoid excessive signalling load from UE due to this procedure. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.39 Remote provisioning of credentials for NSSAA or secondary authentication/authorization | |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.39.1 General | The UE's subscribed network (i.e. HPLMN, or subscribed SNPN) may provide functionalities to provision or update the credentials used for NSSAA or credentials used for secondary authentication/authorization to the UE. The provisioning procedure is supported via User Plane.
For User Plane Remote Provisioning, the UE establishes a PDU Session that is used for remote provisioning, e.g. by using DNN(s)/S-NSSAI(s) which can access the PVS. The AMF selects an SMF used for remote provisioning using the SMF discovery and selection functionality as described in clause 6.3.2. If the SMF is configured with the PVS address(es) and/or PVS FQDN(s), the SMF shall send the PVS address(es) and/or PVS FQDN(s) per DNN/S-NSSAI to the UE via PCO during PDU Session Establishment procedure, based on the UE's subscribed DNN(s)/S-NSSAI(s) and the UE's request of PVS information from the network. Alternatively, the UE may be configured with an address of a PVS or the PVS may subscribe for UE Reachability Notification and may use the Application Triggering procedure as specified in TS 23.502 [3] to trigger the UE to initiate the setup of a connection for remote provisioning. |
fbecc7f0dcf9784c6066646052ab0c0e | 23.501 | 5.39.2 Configuration for the UE | In order to enable UP Remote Provisioning of credentials for NSSAA or secondary authentication/authorization, UE Configuration Data for UP Remote Provisioning are either pre-configured on the UE or provided by the network to the UE. UE Configuration Data for UP Remote Provisioning provided by the network take precedence over corresponding configuration data stored in the UE.
UE Configuration Data for UP Remote Provisioning consist of PVS IP address(es) and/or PVS FQDN(s). The PVS IP address or PVS FQDN may be associated with dedicated DNN(s) and/or S-NSSAI(s).
If the UE does not have any PVS IP address or PVS FQDN after the establishment of a PDU Session used for UP remote provisioning, the UE may construct an FQDN for PVS discovery as defined in TS 23.003 [19].
The UE Configuration Data for UP Remote Provisioning may be stored in the ME.
The UE Configuration Data for UP Remote Provisioning (i.e. PVS IP address(es) or PVS FQDN(s)) associated with dedicated DNN(s) and/or S-NSSAI(s) may be locally configured in the SMF. The UE Configuration Data for UP Remote Provisioning, if available, shall be provided to the UE during the establishment of any PDU Session used for UP Remote Provisioning as part of Protocol Configuration Options (PCO) in the PDU Session Establishment Response, if the UE has requested the PVS information via PCO in the PDU Session Establishment Request. |
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