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5.4.4.2.1 UE-originating case
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When the S-CSCF receives the request containing the access-network-charging-info parameter in the P-Charging-Vector, the S-CSCF shall store the access-network-charging-info parameter from the P-Charging-Vector header field. The S-CSCF shall retain access-network-charging-info parameter in the P-Charging-Vector header field when the request is forwarded to an AS. However, the S-CSCF shall not include the access-network-charging-info parameter in the P-Charging-Vector header field when the request is forwarded outside the home network of the S-CSCF.
When the S-CSCF receives any request or response (excluding CANCEL requests and responses) related to a UE-originated dialog or standalone transaction, the S-CSCF shall insert previously saved values into the P-Charging-Vector header field before forwarding the message within the S-CSCF home network, including towards AS.
When the S-CSCF receives any request or response (excluding ACK requests and CANCEL requests and responses) related to a UE-originated dialog or standalone transaction, the S-CSCF may insert previously saved values into the P-Charging-Function-Addresses header field before forwarding the message within the S-CSCF home network, including towards AS.
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5.4.4.2.2 UE-terminating case
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When the S-CSCF receives 180 (Ringing) or 200 (OK) (to INVITE) responses containing the access-network-charging-info parameter in the P-Charging-Vector, the S-CSCF shall store the access-network-charging-info parameter from the P-Charging-Vector header field. The S-CSCF shall retain the access-network-charging-info parameter in the P-Charging-Vector header field when the response is forwarded to an AS. However, the S-CSCF shall not include the access-network-charging-info parameter in the P-Charging-Vector header field when the response is forwarded outside the home network of the S-CSCF.
When the S-CSCF receives any request or response (excluding CANCEL requests and responses) related to a UE-terminated dialog or standalone transaction, the S-CSCF shall insert previously saved values into the P-Charging-Vector header field before forwarding the message within the S-CSCF home network, including towards AS.
When the S-CSCF receives any request or response (excluding ACK requests and CANCEL requests and responses) related to a UE-terminated dialog or standalone transaction, the S-CSCF may insert previously saved values into the P-Charging-Function-Addresses header field before forwarding the message within the S-CSCF home network, including towards AS.
When the S-CSCF receives an error response (to INVITE) for an existing early dialog, and if the S-CSCF does not forward the response immediately (if the S-CSCF forked the INVITE request it may wait for additional final responses), the S-CSCF does not have knowledge of having received an 199 (Early Dialog Terminated) provisional response on the same early dialog, and the associated INVITE request included the "199" option-tag in the Supported header field, and the INVITE request did not include the "100rel" option tag in the Require header field, the S-CSCF shall trigger and send an unreliable 199 (Early Dialog Terminated) provisional response, using the same "tag" To header field parameter value as the error response, as specified in RFC 6228 [142].
When the S-CSCF has forked an initial INVITE request, and it has received:
- a 2xx response associated with one of the early dialogs, the S-CSCF shall in each CANCEL request it generates as specified in RFC 3261 [26] insert a Reason header field with a "SIP" protocol header field parameter value, a "200" cause header field parameter value, and a "Call completed elsewhere" text header field parameter value, as specified in RFC 3326 [34A]; or
- a 6xx response associated with one of the early dialogs, the S-CSCF shall, in each CANCEL request it generates as specified in RFC 3261 [26] insert a Reason header field with "SIP" protocol header field parameter value, a cause header field parameter value representing the response code (e.g. "603") in the received response, and a text header field parameter with a value associated with the response code (e.g. a "Declined" value in the case of a "603" response code), as specified in RFC 3326 [34A].
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5.4.5 Call release
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5.4.5.1 S-CSCF-initiated session release
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5.4.5.1.1 Cancellation of a session currently being established
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Upon receipt of a network internal indication to release a session which is currently being established, the S-CSCF shall:
1) cancel the related dialogs by sending the CANCEL request according to the procedures described in RFC 3261 [26]; and
2) send an appropriate response to the sender of the original INVITE request.
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5.4.5.1.2 Release of an existing session
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Upon receipt of a network internal indication to release an existing multimedia session, the S-CSCF shall:
1) if the S-CSCF serves the calling user of the session, generate a BYE request destined for the called user based on the information saved for the related dialog, including:
- a Request-URI, set to the stored Contact header field provided by the called user;
- a To header field, set to the To header field value as received in the 200 (OK) response for the initial INVITE request;
- a From header field, set to the From header field value as received in the initial INVITE request;
- a Call-ID header field, set to the Call-Id header field value as received in the initial INVITE request;
- a CSeq header field, set to the CSeq value that was stored for the direction from the calling to the called user, incremented by one;
- a Route header field, set to the routeing information towards the called user as stored for the dialog;
- a Reason header field that contains proper SIP response code;
- further header fields, based on local policy;
- treat the BYE request as if received directly from the calling user, i.e. the S-CSCF shall send the BYE request to the internal service control and based on the outcome further on towards the called user; and
2) if the S-CSCF serves the calling user of the session, generate an additional BYE request destined for the calling user based on the information saved for the related dialog, including:
- a Request-URI, set to a contact address obtained from the stored Contact header field if provided by the calling user. If the stored Contact header field contained either a public or a temporary GRUU, the S-CSCF shall set the Request-URI either to:
a) the contact address bound to the respective GRUU, if the stored Contact header field did not include an "ob" SIP URI parameter; or
b) the contact address that the UE used to send the initial INVITE request, if the stored Contact header field included an "ob" SIP URI parameter;
NOTE 1: Since the same public GRUU can be bound to multiple contact addresses of the UE that were registered as specified in RFC 5626 [92], the S-CSCF selects the contact address that the UE used to send the initial INVITE request.
- a To header field, set to the From header field value as received in the initial INVITE request;
- a From header field, set to the To header field value as received in the 200 (OK) response for the initial INVITE request;
- a Call-ID header field, set to the Call-Id header field value as received in the initial INVITE request;
- a CSeq header field, set to the CSeq value that was stored for the direction from the called to the calling user, incremented by one – if no CSeq value was stored for that session the S-CSCF shall generate and apply a random number within the valid range for CSeqs;
- a Route header field, set to the routeing information towards the calling user as stored for the dialog;
- a Reason header field that contains proper SIP response code;
- further header fields, based on local policy;
- send the BYE request directly to the calling user.
3) if the S-CSCF serves the called user of the session, generate a BYE request destined for the called user based on the information saved for the related dialog, including:
- a Request-URI, set to a contact address that the S-CSCF uses to send the in-dialog requests towards the called UE as defined in RFC 5626 [92] and RFC 5627 [93];
- a To header, set to the To header value as received in the 200 (OK) response for the initial INVITE request;
- a From header, set to the From header value as received in the initial INVITE request;
- a Call-ID header, set to the Call-Id header value as received in the initial INVITE request;
- a CSeq header, set to the CSeq value that was stored for the direction from the calling to the called user, incremented by one;
- a Route header, set to the routeing information towards the called user as stored for the dialog;
- a Reason header that contains proper SIP response code;
- further headers, based on local policy;
- send the BYE request directly to the called user; and
4) if the S-CSCF serves the called user of the session, generate an additional BYE request destined for the calling user based on the information saved for the related dialog, including:
- a Request-URI, set to the stored Contact header field provided by the calling user;
- a To header, set to the From header field value as received in the initial INVITE request;
- a From header, set to the To header field value as received in the 200 (OK) response for the initial INVITE request;
- a Call-ID header, set to the Call-Id header field value as received in the initial INVITE request;
- a CSeq header, set to the CSeq value that was stored for the direction from the called to the calling user, incremented by one – if no CSeq value was stored for that session the BYE shall generate and apply a random number within the valid range for CSeqs;
- a Route header field, set to the routeing information towards the calling user as stored for the dialog;
- a Reason header field that contains proper SIP response code;
- further headers, based on local policy;
- treat the BYE request as if received directly from the called user, i.e. the S-CSCF shall send the BYE request to the internal service control and based on the outcome further on towards the calling user.
Upon receipt of the 2xx responses for both BYE requests, the S-CSCF shall release all information related to the dialog and the related multimedia session.
5.4.5.1.2A Release of the existing dialogs due to registration expiration
When:
1) the registration lifetime of the only public user identity currently registered with its associated set of implicitly registered public user identities (i.e. no other is registered) and bound either to the contact address of the UE or to the registration flow and the associated contact address (if the multiple registration mechanism is used) expires;
2) there are still active multimedia sessions that includes either this user's contact address or the registration flow and the associated contact address (if the multiple registration mechanism is used);
3) the session was initiated by or terminated towards the user using the public user identity currently registered or with one of the implicitly registered public used identities bound either to the contact address of the UE or to the registration flow and the associated contact address (if the multiple registration mechanism is used);
then the S-CSCF shall:
- release each of these multimedia sessions by applying the steps listed in the subclause 5.4.5.1.2. The S-CSCF shall only release dialogs associated with the multi media sessions originated or terminated towards the registered user's contact address or the registration flow and the associated contact address (if the multiple registration mechanism is used).
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5.4.5.1.3 Abnormal cases
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Upon receipt of a request on a dialog for which the S-CSCF initiated session release, the S-CSCF shall terminate the received request and answer it with a 481 (Call/Transaction Does Not Exist) response.
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5.4.5.2 Session release initiated by any other entity
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Upon receipt of a 2xx response for a BYE request matching an existing dialog, the S-CSCF shall delete all the stored information related to the dialog.
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5.4.5.3 Session expiration
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If the S-CSCF requested the session to be refreshed periodically, and the S-CSCF got the indication that the session will be refreshed, when the session timer expires, the S-CSCF shall delete all the stored information related to the dialog.
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5.4.6 Call-related requests
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5.4.6.1 ReINVITE
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5.4.6.1.1 Determination of served user
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Void.
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5.4.6.1.2 UE-originating case
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For a reINVITE request or UPDATE request from the UE within the same dialog, the S-CSCF shall store the updated access-network-charging-info parameter from P-Charging-Vector header field in the received SIP request. The S-CSCF shall retain the access-network-charging-info parameter in the P-Charging-Vector header field when the request is forwarded to an AS. However, the S-CSCF shall not include the access-network-charging-info parameter in the P-Charging-Vector header field when the request is forwarded outside the home network of the S-CSCF.
For a reINVITE request from the UE, if the request is to be forwarded to an AS that is located within the trust domain, the S-CSCF shall retain the access-network-charging-info parameter from the P-Charging-Vector header field; otherwise, the S-CSCF shall remove the access-network-charging-info parameter from the P-Charging-Vector header field.
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5.4.6.1.3 UE-terminating case
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For a reINVITE request or UPDATE request destined towards the UE within the same dialog, when the S-CSCF receives the 200 (OK) response (to the INVITE request or UPDATE request), the S-CSCF shall store the updated access-network-charging-info parameter from the P-Charging-Vector header field. The S-CSCF shall retain the access-network-charging-info parameter in the P-Charging-Vector header field when the response is forwarded to the AS. However, the S-CSCF shall not include the access-network-charging-info parameter in the P-Charging-Vector header field when the 200 (OK) response is forwarded outside the home network of the S-CSCF.
For any SIP response to an INVITE request, if the response is to be forwarded to an AS that is located within the trust domain, the S-CSCF shall retain the access-network-charging-info parameter from the P-Charging-Vector header field; otherwise, the S-CSCF shall remove the access-network-charging-info parameter from the P-Charging-Vector header field.
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5.4.7 Void
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5.4.7A GRUU management
5.4.7A.1 Overview of GRUU operation
The S-CSCF provides a service of assigning and translating GRUUs for use by registered UEs, unless "Loose-Route Indication" indicating the HSS requires the loose-route mechanism as described in 3GPP TS 29.228 [14] has been provisioned in the service profile of the registered public user identity. This is conducted as specified in RFC 5627 [93] and RFC 5628 [94]. Two kinds of GRUUs are assigned: public GRUUs and temporary GRUUs.
NOTE: If the UE performs the functions of an external attached network (e.g an enterprise network) the UE could have self allocated its own GRUUs. In this version of the specification only UE self allocated public GRUUs are supported. Routeing to a specific UE self-allocated public GRUUs requires that "Loose-Route Indication" indicating the HSS requires the loose-route mechanism as described in 3GPP TS 29.228 [14] is provisioned in the service profile of the served public user identity. Use of UE self-allocated temporary GRUUs is not supported in this version of the specification and requests addressed to UE self allocated temporary GRUUs will fail to be routed to the UE.
Each assigned GRUU represents an association between a public user identity and an instance ID provided by a registering UE. It is used to address a particular UE that possesses the instance ID and registers with the public user identity. The GRUU also denotes a contact address registered with a public user identity when the contact address has a "+sip.instance" header field parameter containing the GRUU instance ID.
The S-CSCF issues GRUUs as part of the registration process, and also reports GRUUs as part of notifications for subscriptions to the "reg" event package. The S-CSCF always issues GRUUs in pairs – a public GRUU and a temporary GRUU. In case of implicit registration the S-CSCF assigns a unique public GRUU and a unique temporary GRUU for each public user identity.
The S-CSCF may also support the procedures for allocating public GRUUs and supporting the generation of temporary GRUUs by the functionality within the UE that performs the role of registrar as specified in RFC 6140 [191] as well as the procedures to route requests containing such GRUUs.
5.4.7A.2 Representation of public GRUUs
Each public GRUU shall conform to all requirements specified in RFC 5627 [93].
If the Contact URI in the Contact header field does not contain a "bnc" URI parameter, then the S-CSCF constructs a public GRUU by adding a "gr" SIP URI parameter to the canonical for m of the SIP URI which contains a public user identity.
If the Contact URI in the Contact header field contains a "bnc" URI parameter and if the S-CSCF supports RFC 6140 [191], then the S-CSCF constructs a public GRUU by adding both "bnc" and "gr" SIP URI parameters to the canonical form of the SIP URI from the To header field of the REGISTER request
The "gr" SIP URI parameter serves as an indicator that the URI is in fact a GRUU and if the "+sip.instance" header field parameter from the Contact address contains an IMEI URN or a MEID URN then it carries a value that encodes the IMEI based instance ID that is defined in 3GPP TS 23.003 [3] or the MEID based instance ID which is defined in RFC 8464 [187] otherwise it carries the value received in the "+sip.instance" header field parameter.
By default, the value of the "gr" SIP URI parameter is a copy of the value of the "+sip.instance" header field parameter from a Contact address registered with the S-CSCF, with escaping of special characters as specified in RFC3261 [26].
The public GRUU that is returned in the "pub-gruu" parameter in the 200 (OK) response to the REGISTER request is constructed using the canonical form of the SIP URI of the public user identity from the To header field of the REGISTER request provided that public user identity is not barred. If the public user identity from the To header field of the REGISTER request is barred then the public GRUU that is returned in the "pub-gruu" parameter in the 200 (OK) response to the REGISTER request is constructed using the canonical form of the SIP URI of the default public user identity.
NOTE 1: The default public user identity is always provisioned as a SIP URI.
If the "+sip.instance" header field parameter from the Contact address contains an IMEI URN, as specified in RFC 7254 [153] or an MEID URN, as specified in RFC 8464 [187], then the value of the "gr" SIP URI parameter is generated by the S-CSCF using the name-based UUID algorithm defined in RFC 4122 [154]. The following applies to the algorithm:
1) the "name space ID" shall be a UUID generated for use across the administrative domain and shall use the algorithm for creating a UUID from truly random numbers specified in RFC 4122 [154];
NOTE 2: If the generated UUID is changed, then newly created GRUUs will not match those that were created with the previous UUID. Therefore, the UUID needs to remain the same in order to create consistent GRUUs. This means that the namespace UUID needs to be the same for all S-CSCFs within the domain for which the public GRUU is hosted (it cannot be generated at run time by the S-CSCF as that would produce different values).
2) SHA-1 shall be used as the hash algorithm; and
3) the "name" is made up of a concatenation of the ASCII representation (see RFC 20 [212]) of:
a) if IMEI, the TAC and SNR portions of the IMEI; or
b) if MEID, the Manufacturer Code and the Serial Number portions of the MEID;
from the "+sip.instance" header field parameter.
Only the IMEI shall be use for generating an instance ID for a multi-mode UE that supports both 3GPP and 3GPP2 defined radio access networks, and the S-CSCF shall follow the procedures for an IMEI as described above.
The S-CSCF shall store the "gr" parameter used in a public GRUU and the associated value received in a "+sip.instance" header field parameter.
The public GRUU for a particular association of public user identity and instance ID is persistent. The same public GRUU will be returned each time a registration is performed with a particular pair of public user identity and instance ID.
5.4.7A.3 Representation of temporary GRUUs
NOTE 1: For UEs performing the functions of an external attached network that support RFC 6140 [191] the S-CSCF does not allocate temporary GRUUs but assists the functionality within the UE that performs the role of registrar in allocating it's own temporary GRUUs by providing to the UE the "temp-gruu-cookie" header field parameter that uniquely identifies the registration. The functionality within the UE that performs the role of registrar then is able to allocate its own temporary GRUUs as per RFC 6140 [191] procedures.
Each temporary GRUU shall conform to all requirements specified in RFC 5627 [93].
Because of the limited lifetime of an temporary GRUU, only the S-CSCF that created a temporary GRUU is required to understand how to translate that GRUU to the corresponsing public user identity and instance ID.
The temporary GRUU that is returned in the "temp-gruu" parameter in the 200 (OK) response to the REGISTER request is mapped to the public user identity from the To header field of the REGISTER request provided that public user identity is not barred. If the public user identity from the To header field of the REGISTER request is barred then the temporary GRUU that is returned in the "temp-gruu" parameter in the 200 (OK) response to the REGISTER request is mapped to the default public user identity.
NOTE 2: The default public user identity is always provisioned as a SIP URI.
The specific representation of a temporary GRUU may be decided by each S-CSCF implementation. Temporary GRUUs must route to the assigning S-CSCF without requiring each assigned GRUU to be stored in the HSS.
The S-CSCF may choose a representation of temporary GRUUs that requires no extra state to be retained, such as that specified in RFC 5627 [93]. Alternatively, the S-CSCF may choose a stateful representation. This is an implementation choice.
NOTE 3: One possible implementation is for the S-CSCF to have a statically configured wildcard PSI that routes to it, with each temporary GRUU being encoded so that it matches the wildcard.
5.4.7A.4 GRUU recognition and validity
The S-CSCF shall recognize those GRUUs it has assigned, verify their validity, and extract the associated public user identity or stored identity of the UE that represents the functionality within the UE that performs the role of registrar and instance ID. This is true for both public GRUUs and temporary GRUUs.
NOTE 1: The S-CSCF only validates and extracts the associated public user identity and instance ID for GRUUs that it assigned.
GRUUs are distinguished from other URIs by the presence of a "gr" SIP URI parameter. Public GRUUs are distinguished from temporary GRUUs by the presence of a value for the "gr" SIP URI parameter.
The instance ID is obtained from a public GRUU by using the "gr" parameter to retrieve the stored associated instance ID. The public user identity or stored identity of the UE that represents the functionality within the UE that performs the role of registrar is extracted from a public GRUU by removing the "gr" SIP URI parameter.
The S-CSCF can recognize a public GRUU as valid if the "gr" parameter contains a value that was stored in the S-CSCF during generation of the public GRUU, and the derived public user identity compares equal, according to the comparison rules of RFC3261 [26], to a public user identity active within the S-CSCF or a stored identity of the UE that represents the functionality within the UE that performs the role of registrar from which a public GRUU was created. When validating public GRUUs the S-CSCF shall ignore the presence of any "sg" SIP URI parameter when determining if a public GRUU is one allocated by the S-CSCF.
NOTE 2: The UE that supports RFC 6140 [191] and performs the functions of an external attached network, adds a unique "sg" SIP URI parameter value to the public GRUU supplied by the S-CSCF when generating public GRUUs for its registering UAs.
The public user identity and instance ID are derived from a temporary GRUU via implementation specific means consistent with the way temporary GRUUs are constructed. The S-CSCF shall determine the validity of a temporary GRUU in conformance with RFC 5627 [93], and if the GRUU was allocated using RFC 6140 [191] procedures then in conformance with RFC 6140 [191] or using implementation specific means.
The S-CSCF regards a UE self-allocated public GRUU as valid if "Loose-Route Indication" indicating the HSS requires the loose-route mechanism as described in 3GPP TS 29.228 [14] is provisioned in the service profile of the served public user identity.
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5.4.8 Emergency service
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5.4.8.1 General
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The S-CSCF shall handle the emergency registration as per the needs of the normal registration.
NOTE 1: Emergency specific procedures for the Cx interface are specified in annex G in 3GPP TS 29.228 [14].
NOTE 2: When receiving an emergency service request then the S-CSCF handles the emergency service request as per the procedures in subclause 5.4.3.2. The Route header field indicating the URI associated with the E-CSCF is included by a P-CSCF or an AS.
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5.4.8.2 Initial emergency registration or user-initiated emergency reregistration
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When the S-CSCF receives a REGISTER request; and the Contact header field includes a "sos" SIP URI parameter that indicates that this is an emergency registration, the S-CSCF shall perform the actions as specified in subclause 5.4.1.1 with the following additions:
1) when handling unprotected REGISTER request or protected REGISTER request, the S-CSCF:
a) shall deregister only contacts that were registered as part of emergency registration; and
b) shall not deregister contacts that were registered as part of non-emergency registration;
NOTE 1: other conditions triggering contact deregistration are described in subclause 5.4.1.
2) for the protected REGISTER request, when the S-CSCF receives a REGISTER request with the "integrity-protected" header field parameter in the Authorization header field set to "yes", "tls-yes" or "ip-assoc-yes", i.e. for the protected REGISTER request, and the Contact header field includes a "sos" SIP URI parameter that indicates that this is an emergency registration, the S-CSCF shall identify the user by the public user identity as received in the To header field and the private user identity as received in the Authorization header field of the REGISTER request;
3) if operator policy does not require that emergency service requests are forwarded to the S-CSCF, the S-CSCF shall not include a Service-Route header field in the 200 (OK) response to the REGISTER request;
4) the S-CSCF shall not include a temporary GRUU in the 200 (OK) response to the REGISTER request;
5) the S-CSCF shall in the Contact header field of the 200 (OK) response to the REGISTER request include only the URI that was successfully emergency registered and in this URI include the "sos" SIP URI parameter;
NOTE 2 Only including the emergency registered contact in the 200 (OK) response to the REGISTER request deviates from bullet 8 in section 10.3 of RFC 3261 [26].
NOTE 3: In the case where the S-CSCF returns a GRUU in the Contact header field of the 200 (OK) response to the REGISTER request, the "sos" SIP URI parameter is appended to the URI and not included as a Contact header field parameter. The public GRUU that is returned in the 200 (OK) response includes the "sos" SIP URI parameter as a parameter of the URI included in the "pub-gruu" Contact header field parameter.
6) store the Path header field and the contact information including all header field parameters contained in the Contact header field;
NOTE 4: The Path header field and contact information used for the emergency dialogs destined for the UE and obtained during the emergency registration can be different than the Path header field used for the non-emergency communication and obtained during the non-emergency registration.
NOTE 5: The S-CSCF will not perform the network-initiated deregistration procedure for an emergency registration, but will let it expire. A new emergency registration will overwrite any previous emergency registration.
7) the S-CSCF shall not send any third-party REGISTER requests to any AS;
8) void
9) determine the duration of the registration by checking the value of the registration expiration interval value in the received REGISTER request and based on local policy; and
NOTE 6: The value of the emergency registration time is subject to national regulation and can be subject to roaming agreements.
10) for any bindings created by the emergency registration, mark those bindings as created by an emergency registration.
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5.4.8.3 User-initiated emergency deregistration
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When S-CSCF receives a REGISTER request with the registration expiration interval value containing zero and the Contact header field contains a contact address that has been registered for emergency service (i.e. the "sos" SIP URI parameter that indicates that this is an emergency registration is included in the Contact header field), the S-CSCF shall reject the REGISTER request by sending a 501 (Not Implemented) response.
NOTE: The UE cannot deregister its emergency public user identity.
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5.4.8.4 Network-initiated emergency deregistration
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The S-CSCF shall not perform a network-initiated emergency deregistration.
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5.4.8.5 Network-initiated emergency re-authentication
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If a given public user identity and the associated contact address have been registered via emergency registration, the S-CSCF shall not re-authenticate this public user identity.
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5.4.8.6 Subscription to the event providing registration state
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If a S-CSCF receives a SUBSCRIBE request addressed to S-CSCF containing the Event header field with the reg event package with the Contact header field that contains a contact address that has been registered for emergency service, the S-CSCF shall reject the SUBSCRIBE request for the reg-event package by sending a 489 (Bad Event) response.
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5.4.8.7 Notification of the registration state
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When the user performs an emergency registration or when the emergency registration expires, the S-CSCF shall not send a NOTIFY request to the subscribers to the reg event package of the respective user.
The contact address that has been registered for emergency service shall not be included in the NOTIFY requests sent to the subscribers to the reg event package of the user.
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5.5 Procedures at the MGCF
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5.5.1 General
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The MGCF, although acting as a UA, does not initiate any registration of its associated addresses. These are assumed to be known by peer-to-peer arrangements within the IM CN subsystem. Therefore table A.4/1 and dependencies on that major capability shall not apply.
The use of the Path and Service-Route header fields shall not be supported by the MGCF.
For all SIP transactions identified:
- if priority is supported, as containing an authorised Resource-Priority header field, or, if such an option is supported, relating to a dialog which previously contained an authorised Resource-Priority header field;
the MGCF shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the MGCF shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value.
NOTE: The special treatment can include filtering, higher priority processing, routeing, call gapping. The exact meaning of priority is not defined further in this document, but is left to national regulation and network configuration.
When the MGCF sends any request or response related to a dialog, the MGCF may insert previously saved values into P-Charging-Vector and P-Charging-Function-Addresses header fields before sending the message.
The MGCF shall use a GRUU referring to itself (as specified in RFC 5627 [93]) when inserting a contact address in a dialog establishing or target refreshing SIP message. This specification does not define how GRUUs are created by the MGCF; they can be provisioned by the operator or obtained by any other mechanism. A GRUU used by the MGCF when establishing a dialog shall remain valid for the lifetime of the dialog. The GRUU used by the MGCF shall not reveal calling party related information.
The MGCF shall handle requests addressed to its currently valid GRUUs when received outside of the dialog in which the GRUU was provided.
EXAMPLE: Upon receipt of an INVITE request addressed to a GRUU assigned to a dialog it has active, and containing a Replaces header field referencing that dialog, the MGCF will be able to establish the new call replacing the old one.
The MGCF may support retrieval of NP data, subject to local policy. The interface used at the MGCF to retrieve the NP data is out of scope of this specification. Retrieval of NP data is relevant only if the Request-URI contains an international public telecommunications number. For requests from the IM CN subsystem network, if the Request-URI contains a tel-URI with an "npdi" tel-URI parameter, as defined in RFC 4694 [112], NP data has been obtained previously and NP data retrieval is not needed, but still may still be performed if required by local policy. If NP data is retrieved by the MGCF, and the request is routed to the IM CN subsystem, the MGCF shall add the tel-URI NP parameters to the Request-URI as defined in RFC 4694 [112]: an "npdi" tel-URI parameter is added to indicate that NP data retrieval has been performed, and if the number is ported, an "rn" tel-URI parameter is added to identify the ported-to routeing number.
The MGCF NP procedures also apply when the request contains a Request-URI in the form of a SIP URI user=phone, where the "npdi" and "rn" tel-URI parameters are contained in the userinfo part of the SIP URI.
The MGCF supports as a network option the inclusion of the XML MIME schema for PSTN. In cases where the XML MIME for PSTN is included the Content-Type header field is set to "application/vnd.etsi.pstn+xml" and the Content-Disposition to "signal" with the "handling" parameter set to "optional".
The MGCF shall log all SIP requests and responses that contain a "logme" header field parameter in the SIP Session-ID header field if required by local policy.
When sending a failure response to any received request, depending on operator policy, the MGCF may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "mgcf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17.
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5.5.2 Subscription and notification
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Void.
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5.5.3 Call initiation
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5.5.3.1 Initial INVITE
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5.5.3.1.1 Calls originated from circuit-switched networks
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When the MGCF receives an indication of an incoming call from a circuit-switched network, the MGCF shall:
1) generate an INVITE request:
- set the Request-URI to the "tel" format using an E.164 address or to the "sip" format using an E164 address in the user portion and set user=phone in accordance with 3GPP TS 29.163 [11B];
NOTE 1: Details how to set the host portion are out of scope of the document. However, when a SIP URI is used the host portion needs to be part of the domain name space owned by the I-CSCF
- include the "100rel" option tag in the Supported header field (as defined in RFC 3262 [27]);
- include the "precondition" option tag in the Supported header field (as defined in RFC 3312 [30] as updated by RFC 4032 [64]) if the MGCF supports the SIP preconditions mechanism;
- not indicate the requirement for the precondition mechanism by using the Require header field;
- create a new, globally unique value for the "icid-value" header field parameter and insert it into the P-Charging-Vector header field;
- insert a type 2 "orig-ioi" header field parameter into the P-Charging-Vector header field. The MGCF shall set the type 2 "orig-ioi" header field parameter to a value that identifies the sending network in which the MGCF resides and the type 2 "term-ioi" header field parameter shall not be included;
- based on local policy, add an "fe-addr" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier; and
- if services that require knowledge of the adjacent network are provided within the network, based on operator policy, insert a Via "received-realm" header field parameter, as defined in RFC 8055 [208];
When the MGCF receives a 1xx or 2xx response to an initial request for a dialog, the MGCF shall store the value of the received "term-ioi" header field parameter received in the P-Charging-Vector header field, if present.
NOTE 2: Any received "term-ioi" header field parameter will be a type 2 IOI. The type 2 IOI identifies the sending network of the response message.
Upon receiving a 199 (Early Dialog Terminated) provisional response to an established early dialog the MGCF shall release resources specifically related to that early dialog.
Based upon local policy, the MGCF may support preferred circuit carrier access (RFC 4694 [112]). If such routeing is applicable for the call, the MGCF shall perform the interworking of the carrier identification code from the circuit switched signalling protocol as described in 3GPP TS 29.163 [11B].
If resource priority in accordance with RFC 4412 [116] is required for a dialog, then the MGCF shall include the Resource-Priority header field in all requests associated with that dialog.
If overlap signalling using the multiple-INVITE method is supported as a network option, several INVITE requests with the same Call ID and the same From header field (including "tag" header field parameter) that relate to the same call can be sent by the MGCF. The MGCF shall route those INVITE requests to the same next hop.
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5.5.3.1.2 Calls terminating in circuit-switched networks
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When the MGCF receives an initial INVITE request with Supported header field indicating "100rel", the MGCF shall:
1) based on local policy, store the "fe-identifier" header field parameter of the P-Charging-Vector header field, if present;
2) store the value of the "orig-ioi" header field parameter received in the P-Charging-Vector header field, if present;
NOTE 1: Any received "orig-ioi" header field parameter will be a type 2 IOI. The type 2 IOI identifies the sending network of the request message.
3) send a 100 (Trying) response;
4) after a matching codec is found or no codec is required at the MGW, send 183 "Session Progress" response:
- set the Require header field to the value of "100rel";
- store the values received in the P-Charging-Function-Addresses header field;
- store the value of the "icid-value" header field parameter received in the P-Charging-Vector header field; and
- insert a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the initial INVITE request, a type 2 "term-ioi" header field parameter and the "icid-value" header field parameter. The MGCF shall set the type 2 "term-ioi" header field parameter to a value that identifies the network in which the MGCF resides, the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the previously received value of "icid-value" header field parameter in the request. Based on local policy, the MGCF shall include the stored "fe-identifier" header field parameter in the P-Charging-Vector header field.
If a codec is required and the MGCF does not find an available matching codec at the MGW for the received initial INVITE request, the MGCF shall:
- send 503 (Service Unavailable) response if the type of codec was acceptable but none were available and the MGCF is unable to handle further requests received from the same upstream entity on the transport address where the INVITE request was received (i.e. MGCF is overloaded by SIP requests);
- send 500 (Server Internal Error) response if the type of codec was acceptable but none were available and the MGCF is able to handle further requests received from the same upstream entity on the transport address where the INVITE request was received (i.e. MGCF is not overloaded by SIP requests); or
- send 488 (Not Acceptable Here) response if the type of codec was not supported, and may include SDP in the message body to indicate the codecs supported by the MGCF/MGW.
Based upon local policy, the MGCF may support preferred ciruit carrier access (RFC 4694 [112]), if such routeing is applicable for the call.
NOTE 2: Interworking of the "cic" tel-URI parameter, if present in a tel-URI or in the userinfo part of a SIP URI with user=phone Request-URI, to the circuit switched signalling protocol is described in 3GPP TS 29.163 [11B].
The MGCF may support resource priority in accordance with RFC 4412 [116] if required for a dialog. The MGCF shall use compatible namespace and priority levels to the capabilities supported in the CS network.
Based on local policy, the MGCF shall include the stored "fe-identifier" header field parameter in the P-Charging-Vector header field, add its own address or identifier as "fe-addr" element of the "fe-identifier" header field parameter of the P-Charging-Vector header field and send the P-Charging-Vector header field in the related final response.
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5.5.3.2 Subsequent requests
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5.5.3.2.1 Calls originating in circuit-switched networks
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When the MGCF generate a subsequent request in accordance with 3GPP TS 29.163 [11B], the MGCF shall:
a) add a P-Charging-Vector header field with the "icid-value" header field parameter set to the value populated in the initial request for the dialog and a type 2 "orig-ioi" header field parameter. The MGCF shall set the type 2 "orig-ioi" header field parameter to a value that identifies the sending network in which the MGCF resides and shall not set the type 2 "term-ioi" header field parameter.
When the MGCF receives a 1xx or 2xx response to a subsequent request for a dialog, the MGCF shall store the value of the received "term-ioi" header field parameter in the P-Charging-Vector header field, if present.
When the MGCF receives 183 (Session Progress) response to an INVITE request, the MGCF shall:
- store the values received in the P-Charging-Function-Addresses header field.
The MGCF shall send an UPDATE request when the following conditions are fulfilled:
- conditions as specified in 3GPP TS 29.163 [11B]; and
- the MGCF receives 200 (OK) response to a PRACK request
NOTE: When the MGCF is confirming the successful resource reservation using an UPDATE request (or a PRACK request) and the MGCF receives a 180 (Ringing) response or a 200 (OK) response to the initial INVITE request before receiving a 200 (OK) response to the UPDATE request (or a 200 (OK) response to the PRACK request), the MGCF does not treat this as an error case and does not release the session.
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5.5.3.2.2 Calls terminating in circuit-switched networks
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When the MGCF receives a subsequent request, the MGCF shall:
1) store the value of the "orig-ioi" header field parameter received in the P-Charging-Vector header field, if present.
NOTE: Any received "orig-ioi" header field parameter will be a type 2 IOI. The type 2 IOI identifies the sending network of the request message.
When the MGCF generate a response to a subsequent request in accordance with 3GPP TS 29.163 [11B], the MGCF shall, insert a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the subsequent request, a type 2 "term-ioi" header field parameter and the "icid-value" header field parameter. The MGCF shall set:
1) the type 2 "term-ioi" header field parameter to a value that identifies the network in which the MGCF resides;
2) the "orig-ioi" header field parameter set to the previously received value of "orig-ioi" header field parameter in the subsequent request; and
3) the "icid-value" header field parameter set to the previously received value of "icid-value" header field parameter in the subsequent request.
When the MGCF receives an indication of a ringing for the called party of outgoing call to a circuit-switched network, the MGCF shall:
- send 180 (Ringing) response to the UE.
When the MGCF receives an indication of answer for the called party of outgoing call to a circuit-switched network, the MGCF shall:
- send 200 (OK) response to the UE. The 200 (OK) response shall include an P-Asserted-Identity header field if corresponding information is received from the circuit-switched network.
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5.5.4 Call release
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5.5.4.1 Call release initiated by a circuit-switched network
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When the MGCF receives an indication of call release from a circuit-switched network, the MGCF shall:
- send a BYE request to the UE.
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5.5.4.2 IM CN subsystem initiated call release
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NOTE: The release of a call towards the circuit-switched network additionally requires signalling procedures other than SIP in the MGCF that are outside the scope of this document.
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5.5.4.3 MGW-initiated call release
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When the MGCF receives an indication from the MGW that the bearer was lost, the MGCF shall:
- send a BYE request towards the UE; and
- may include Error-Info header field with a pointer to additional information indicating that bearer was lost.
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5.5.5 Call-related requests
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5.5.5.1 Session modification
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5.5.5.1.0 General
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This subclause applies after the 2xx response to the initial INVITE request has been sent or received.
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5.5.5.1.1 Session modifications originating from circuit-switched networks
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If the precondition mechanism was used during the session establishment, as described in subclause 5.5.3.1.1 or 5.5.3.1.2, the MGCF shall indicate support of the precondition mechanism during a session modification. If the precondition mechanism was not used during the session establishment, the MGCF shall not indicate support of the precondition mechanism during a session modification.
In order to indicate support of the precondition mechanism during a session modification, upon generating a reINVITE request, an UPDATE request with an SDP body, or a PRACK request with an SDP body, the MGCF shall:
a) indicate the support for the precondition mechanism using the Supported header field;
b) not indicate the requirement for the precondition mechanism using the Require header field; and
c) if a reINVITE request is being generated, indicate the support for reliable provisional responses using the Supported header field,
and follow the SDP procedures in clause 6 for the precondition mechanism.
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5.5.5.1.2 Session modifications terminating in circuit-switched networks
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When the MGCF receives a reINVITE request for hold/resume operation, the MGCF shall:
- send a 100 (Trying) response;
- after performing interaction with MGW to hold/resume the media flow, send a 200 (OK) response.
Upon receiving a reINVITE request, an UPDATE request, or a PRACK request that indicates support for the precondition mechanism by using the Supported header field or requires use of the precondition mechanism by using the Require header field, the MGCF shall:
a) if the precondition mechanism was used during the session establishment, as described in subclause 5.5.3.1.1 or 5.5.3.1.2, use the precondition mechanism for the session modification; and
b) if the precondition mechanism was not used during the session establishment, and
1) if use of the precondition mechanism is required using the Require header field, reject the request by sending a 420 (Bad Extension) response; and
2) if the support of the precondition mechanism is indicated using the Supported header field, not use the precondition mechanism for the session modification.
If the precondition mechanism is used for the session modification, the MGCF shall indicate support for the preconditions mechanism, using the Require header field, in responses that include an SDP body, to the session modification request.
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5.5.6 Further initial requests
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When the MGCF responds to an OPTIONS request with a 200 (OK) response, the MGCF may include a message body with an indication of the DTMF capabilities and supported codecs of the MGCF/MGW.
NOTE: The detailed interface for requesting MGCF/MGW capabilities is not specified in this version of the document. Other solutions can be used in the interim.
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5.6 Procedures at the BGCF
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5.6.1 General
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The use of the Path and Service-Route header fields shall not be supported by the BGCF.
For all SIP transactions identified:
- if priority is supported, as containing an authorised Resource-Priority header field, or, if such an option is supported, relating to a dialog which previously contained an authorised Resource-Priority header field;
the BGCF shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the MGCF shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value.
NOTE: The special treatment can include filtering, higher priority processing, routeing, call gapping. The exact meaning of priority is not defined further in this document, but is left to national regulation and network configuration.
When the BGCF receives any request or response related to a dialog or standalone transaction, the BGCF may insert previously saved values into a P-Charging-Vector header field before forwarding the message.
When the BGCF receives any request or response (excluding ACK requests and CANCEL requests and responses) related to a dialog or standalone transaction, the BGCF may insert previously saved values into a P-Charging-Function-Addresses header field before forwarding the message.
With the exception of 305 (Use Proxy) responses, the BGCF may recurse on a 3xx response only when the domain part of the URI contained in the 3xx response is in the same domain as the BGCF. For the same cases, if the URI is an IP address, the BGCF shall only recurse if the IP address is known locally to be a address that represents the same domain as the BGCF.
The BGCF shall log all SIP requests and responses that contain a "logme" header field parameter in the SIP Session-ID header field if required by local policy.
When sending a failure response to any received request, depending on operator policy, the BGCF may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "bgcf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17.
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5.6.2 Common BGCF procedures
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When determining where to route the received request, the originating BGCF may use the information obtained from other protocols or any other available databases.
The BGCF may support retrieval of NP data as part of the procedures to determine where to route the request. Retrieval of NP data by the BGCF is subject to local policy. Retrieval of NP data is relevant only if the Request-URI contains an international public telecommunications number. The interface used at the BGCF to retrieve the NP data is out of scope of this specification. If the Request-URI contains a tel-URI with an "npdi" tel-URI parameter, as defined in RFC 4694 [112], NP data has been obtained previously and NP data retrieval is only performed if required by local policy. If NP data is retrieved by the BGCF, the BGCF shall add the tel-URI NP parameters to the Request-URI as defined in RFC 4694 [112]: an "npdi" tel-URI parameter is added to indicate that NP data retrieval has been performed, and if the number is ported, an "rn" tel-URI parameter is added to identify the ported-to routeing number. The "rn" tel-URI parameter may be used by the BGCF for routeing the request.
The BGCF NP procedures also apply when the request contains a Request-URI in the form of a SIP URI user=phone, where the "npdi" and "rn" tel-URI parameters are contained in the userinfo part of the SIP URI.
When the BGCF receives a request, the BGCF shall forward the request:
- to an MGCF within its own network; or
- to another network containing a BGCF, or I-CSCF; or
- where the request is for another network, to an IBCF in its own network, if local policy requires IBCF capabilities towards another network; or
- where the Ici interface is used to interconnect two networks and the destination network is beyond such interface, to an IBCF in its own network.
When forwarding the request to the next hop, the BGCF may leave the received Request-URI unmodified.
If the request is not routed to a BGCF or to an entity that implements the additional routeing functionality, the BGCF shall remove the P-Served-User header field prior to forwarding the request.
When the BGCF receives a request and the Request-URI contains a tel URI in local number format or a SIP URI with the user part not starting with a + and the "user" SIP URI parameter equals "phone", the BGCF shall not forward the request to an entity in another network (e.g. BGCF, I-CSCF) unless the local policy (e.g. routeing of service numbers) requires forwarding the request outside the network. If local policy does not allow forwarding the request outside the network and additional routeing capabilities as defined in annex I are locally available, the BGCF shall attempt translation of the local number. If the translation fails, the BGCF shall send an appropriate SIP response to the originator. If local policy does not allow forwarding the request outside the network and additional routeing capabilities as defined in annex I are not locally available, the BGCF shall either:
- forward the request to any appropriate entity in its own network where additional routeing functionality are available; or
- send an appropriate SIP response to the originator.
The BGCF need not Record-Route the INVITE and the SUBSCRIBE requests. While the next entity may be a MGCF acting as a UA, the BGCF shall not apply the procedures of RFC 3323 [33] relating to privacy. The BGCF shall store the values received in the P-Charging-Function-Addresses header field. The BGCF shall store the value of the "icid-value" header field parameter received in the P-Charging-Vector header field and retain the "icid-value" header field parameter in the P-Charging-Vector header field.
NOTE 1: The means by which the decision is made to forward to an MGCF or to another network is outside the scope of the present document, but can be by means of a lookup to an external database, or can be by data held internally to the BGCF.
If the BGCF supports carrier routeing, then the BGCF shall support the following procedures, based on local policy:
a) if the BGCF is configured to populate an operator configured preassigned carrier into a tel-URI contained in the Request-URI, and a preassigned carrier is required for this call, then the BGCF shall include the "cic" tel-URI parameter in the Request-URI identifying the preassigned carrier (as described in RFC 4694 [112]); or
b) if the BGCF is configured to populate the freephone carrier ID, and a freephone carrier is required for this call, then the BGCF shall include the "cic" tel-URI parameter in the Request-URI identifying the freephone carrier (as described in RFC 4694 [112]).
The BGCF carrier routeing procedures also apply when the Request-URI is in the form of a SIP URI user=phone, where the "cic" tel-URI parameter is contained in the userinfo part of the SIP URI.
The BGCF shall not add the "cic" tel-URI parameter in the Request-URI if the parameter already exists in the tel-URI.
NOTE 2: Local policy should be able to control the interaction and precedence between routeing on "cic" parameter versus routeing based on "rn" parameter.
NOTE 3: The means to configure the BGCF with the pre-assigned carrier is outside the scope of this document.
If
a) the BGCF supports indicating the traffic leg as specified in RFC 7549 [225];
b) an "iotl" SIP URI parameter is not already included in the Request-URI; and
NOTE 4: If an "iotl" SIP URI parameter is included it contains the value "visitedA-homeB" inserted by the TRF in the roaming architecture for voice over IMS with local breakout scenario.
c) required by local policy;
the BGCF shall before forwarding the request:
a) if the Request-URI contains a SIP URI, append the "iotl" SIP URI parameter set to "homeA-homeB" to the Request-URI; and
b) if the Request-URI contains a tel URI that can be converted to a SIP URI by the BGCF:
- convert the tel URI in the Request-URI to the form of a SIP URI with user=phone; and
- append an "iotl" SIP URI parameter with a value set to "homeA-homeB" in the Request-URI.
NOTE 5: If the "iotl" SIP URI parameter can not be included by the above procedure, the upstream nodes have to determine the II-NNI traversal scenario by analysing the content of the SIP request (implementation dependent) or using the default II-NNI traversal scenario type.
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5.6.3 Specific procedures for INVITE requests and responses
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When the BGCF receives an INVITE request that contains a Feature-Caps header field with the "+g.3gpp.home-visited" header field parameter, the BGCF shall decide based on local policy whether to perform loopback routeing for this request. The BGCF shall:
a) if loopback routeing is not to be performed for this request remove any "+g.3gpp.trf" or "+g.3gpp.home-visited" header field parameter from the Feature-Caps header field of the outgoing request;
b) if loopback routeing is applied for this request:
i) remove all entries in the Route header field;
ii) if a "+g.3gpp.trf" header field parameter with a parameter value containing a valid URI, is included in the Feature-Caps header field of the request, insert the URI in a Route header field;
iii) if a "+g.3gpp.trf" header field parameter, with a parameter value containing a valid URI is not included in the Feature-Caps header field of the request, insert a locally configured TRF address, associated with the visited network for this call (as identified in the "+g.3gpp.home-visited" header field parameter), in the Route header field;
iv) remove any "+g.3gpp.home-visited" header field parameter from the Feature-Caps header field of the outgoing request;
v) if included in the incoming request, remove the "+g.3gpp.trf" header field parameter from the Feature-Caps header field from the outgoing request;
vi) insert the "+g.3gpp.loopback" header field parameter, as specified in subclause 7.9A.4 in the Feature-Caps header field of the request, in accordance with RFC 6809 [190]. If providing the identifier of the home network is supported by the BGCF and the visited network, the BGCF may based on operator agreement insert the "+g.3gpp.loopback" header field parameter set to the identifier of the home network;
vii) remove the "orig-ioi" header field parameter received in the P-Charging-Vector header field, if present. The BGCF shall insert a type 1 "orig-ioi" header field parameter into the P-Charging-Vector header field and shall set the type 1 "orig-ioi" header field parameter to a value that identifies the home network of the served user (i.e. the network in which the BGCF resides). The BGCF shall not include the "term-ioi" header field parameter; and
viii) if the BGCF supports indicating the traffic leg associated with a URI as specified in RFC 7549 [225] and if an "iotl" SIP URI parameter is not included in the TRF URI in the Route header field, the BGCF if required by local policy, append an "iotl" URI parameter with a value set to "homeA-visitedA" to the URI in the Route header field; and
c) if the final decision on loopback routeing is deferred to a subsequent entity in the home network, a further BGCF, then, retain in the request a Feature-Caps header field with the "+g.3gpp.home-visited" header field parameter with the parameter value set to the identifier of the visited network. The BGCF is expected to know by means of network configuration that such a subsequent entity exists;
If the BGCF inserts its own Record-Route header field, the BGCF may require the periodic refreshment of the session to avoid hung states in the BGCF. If the BGCF requires the session to be refreshed, the BGCF shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE: Requesting the session to be refreshed requires support by at least one of the UEs. This functionality cannot automatically be granted, i.e. at least one of the involved UEs needs to support it.
If overlap signalling using the multiple-INVITE method is supported as a network option, several INVITE requests with the same Call ID and the same From header field (including "tag" header field parameter) can be received outside of an existing dialog. Such INVITE requests relate to the same call and the BGCF shall route such INVITE request received during a certain period of time to the same next hop.
If the BGCF inserted in the initial request for the dialog the header field parameters into the Feature-Caps header field then the BGCF shall include the header field parameters with the same parameter values into the Feature-Caps header field in any target refresh request for the dialog, and in each 1xx or 2xx response to target refresh request sent in the same direction.
Based on local policy, the BGCF shall add an "fe-addr" element of the "fe-identifier" header field parameter of the P-Charging-Vector header field with its own address or identifier to an initial request.
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5.6.4 Specific procedures for subsequent requests and responses
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When the BGCF receives a subsequent request whose initial request applied loopback routeing, the BGCF shall:
a) remove the "orig-ioi" header field parameter received in the P-Charging-Vector header field, if present. The BGCF shall insert a type 1 "orig-ioi" header field parameter into the P-Charging-Vector header field and shall set the type 1 "orig-ioi" header field parameter to a value that identifies the home network of the served user (i.e. the network in which the BGCF resides). The BGCF shall not include the "term-ioi" header field parameter.
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5.7 Procedures at the Application Server (AS)
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5.7.1 Common Application Server (AS) procedures
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5.7.1.0 General
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When sending a failure response to any received request, depending on operator policy, the AS may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "as" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17. An AS when sending a failure response will add in the URN the "role" header field parameter set to the corresponding AS role listed in subclause 7.2.17.
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5.7.1.1 Notification about registration status
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The AS may support the REGISTER method in order to discover the registration status of the user. If a REGISTER request arrives and the AS supports the REGISTER method, the AS shall store the registration expiration interval value from the request and generate a 200 (OK) response or an appropriate failure response. For the success case, the 200 (OK) response shall contain a registration expiration interval value equal to the value received in the REGISTER request. The AS shall store the values received in P-Charging-Function-Addresses header field. Also, the AS shall store the values of the "icid-value" header field parameter and "orig-ioi" header field parameter if present in the P-Charging-Vector header field from the REGISTER request.
NOTE 1: The user can have one or more contacts registered after a 3rd party REGISTER request with an Expires header field set to a value "0" has been received. If an AS needs more detailed knowledge of the user registration status, the AS can subscribe to the reg event package.
If a Contact header field is included in the REGISTER request including a "+g.3gpp.registration-token" header field parameter as defined in subclause 7.9.7, the AS supporting this feature shall store the value of the "+g.3gpp.registration-token" header field parameter.
NOTE 2: The S-CSCF can set this token to the same value as used in the "id" parameter identifying the contact in the "reg" event package, allowing the AS to retrieve the value from the "reg" event package. The AS can know by configuration or other means if the S-CSCF uses this value.
The AS shall insert a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the REGISTER request, a type 3 "term-ioi" header field parameter in the response to REGISTER and the "icid-value" header field parameter. The AS shall set the type 3 "term-ioi" header field parameter to a value that identifies the service provider from which the response is sent, the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the previously received value of "icid-value" header field parameter in the request.
Upon receipt of a third-party REGISTER request, with the Content-Type header field or with a MIME body part's Content-Type header field set according to subclause 7.6 (i.e. "application/3gpp-ims+xml"), independent of the value or presence of the Content-Disposition header field or a MIME body part's Content-Type header field, independent of the value or presence of Content-Disposition parameters or MIME body part's Content-Disposition parameters, then the following treatment is applied:
- if the third-party REGISTER request includes an IM CN subsystem XML body with an <ims-3gpp> element, including a version attribute, with the <service-info> child element or a MIME body part containing an <ims-3gpp> element with a <service-info> XML child element as described in subclause 7.6, then the AS may retrieve the service information within the <service-info> XML child element of the <ims-3gpp> element.
Upon receipt of a third-party REGISTER request, with the Content-Type header field or with a body part's Content-Type header field set to "message/sip" and including a "message/sip" MIME body of the incoming REGISTER request, or the 200 (OK) response to the incoming REGISTER request then the AS may retrieve information from the "message/sip" MIME body or body part.
Upon receipt of a third-party REGISTER request, the AS may subscribe to the reg event package for the public user identity registered at the user's registrar (S-CSCF) as described in RFC 3680 [43] and RFC 6665 [28].
On sending a SUBSCRIBE request, the AS shall populate the header fields as follows:
a) a Request-URI set to the resource to which the AS wants to be subscribed to, i.e. to a SIP URI that contains the public user identity of the user that was received in the To header field of the third-party REGISTER request;
b) a From header field set to the AS's SIP URI;
c) a To header field, set to a SIP URI that contains the public user identity of the user that was received in the To header field of the third-party REGISTER request;
d) an Event header field set to the "reg" event package;
e) a P-Asserted-Identity header field set to the SIP URI of the AS; and
NOTE 3: The S-CSCF expects the SIP URI used in the P-Asserted-Identity header field to correspond to the SIP URI, which identified this AS in the initial filter criteria of the user to whose registration state the AS subscribes to.
f) a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17] and a type 3 "orig-ioi" header field parameter. The type 3 "orig-ioi" header field parameter identifies the service provider from which the request is sent. The AS shall not include the type 3 "term-ioi" header field parameter.
Upon receipt of a dialog establishing NOTIFY request, as specified in RFC 6665 [28], associated with the SUBSCRIBE request, the AS shall:
1) store the information for the so established dialog;
2) store the expiration time as indicated in the "expires" header field parameter of the Subscription-State header field, if present, of the NOTIFY request. Otherwise the expiration time is retrieved from the Expires header field of the 2xx response to SUBSCRIBE request; and
3) follow the procedures specified in RFC 6665 [28].
Upon receipt of any response, the AS shall store the value of the "term-ioi" header field parameter received in the P-Charging-Vector header field if present.
NOTE 4: Any received term-ioi parameter will be a type 3 term-ioi. The type 3 term-ioi identifies the network operator from which the response was sent.
NOTE 5: Upon receipt of a NOTIFY request with all <registration> element(s) having their state attribute set to "terminated" (i.e. all public user identities are deregistered) and the Subscription-State header field set to "terminated", the AS considers the subscription to the reg event package terminated, i.e. as if the AS had sent a SUBSCRIBE request with an Expires header field containing a value of zero.
Upon receipt of a NOTIFY request for the dialog associated with the subscription to the reg event package, the AS shall:
- store the information for the established dialog;
- store the expiration time as indicated in the "expires" header field parameter of the Subscription-State header field, if present, of the NOTIFY request. Otherwise the expiration time is retrieved from the Expires header field of the 2xx response to SUBSCRIBE request;
- store the value of the "orig-ioi" header field parameters if present in the P-Charging-Vector header field. The AS shall insert a P-Charging-Vector header field in the response to the NOTIFY request containing the "orig-ioi" header field parameter, if received in the NOTIFY request, a type 3 "term-ioi" header field and the "icid-value" header field parameter;
- set the type 3 "term-ioi" header field parameter to a value that identifies the service provider from which the response is sent, the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the previously received value of "icid-value" header field parameter in the request; and
- follow the procedures specified in RFC 6665 [28].
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5.7.1.2 Extracting charging correlation information
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When an AS receives an initial request for a dialog or a request for a standalone transaction, the AS shall store the values received in the P-Charging-Vector header field, e.g. "orig-ioi" header field parameter, if present, and "icid-value" header field parameter, and retain the P-Charging-Vector header field in the message. The AS shall store the values received in the P-Charging-Function-Addresses header field and retain the P-Charging-Function-Addresses header field in the message.
When an AS sends any request or response related to a dialog or standalone transaction, the AS shall insert previously saved values into the P-Charging-Vector header field and may insert previously saved values into the P-Charging-Function-Addresses header field before sending the message.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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5.7.1.3 Access-Network-Info and Visited-Network-ID
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The AS may receive information about the served user core network in REGISTER requests from S-CSCF. This information can be obtained either from the P-Access-Network-Info header field and P-Visited-Network-ID header field in the REGISTER request or can be obtained from those header fields in the body of the REGISTER request.
The AS may also receive information about the served user access network in other requests (excluding CANCEL requests and responses). This information can be obtained from the P-Access-Network-Info header field.
The AS can use the P-Access-Network-Info and P-Visited-Network-ID header fields to provide an appropriate service to the user.
5.7.1.3A Determination of the served user
5.7.1.3A.1 General
The determination of the served user is different per session:
- for an originating session, the procedure is described in subclause 5.7.1.3A.2; and
- for a terminating session the procedure is described in subclause 5.7.1.3A.3.
If the AS supports the P-Served-User header field as defined in RFC 5502 [133] and RFC 8498 [239] and the P-Served-User header field is included in the received request, the AS can determine the session case related to the request, as specified in 3GPP TS 29.228 [14], from the P-Served-User header field parameters if available.
5.7.1.3A.2 AS serving an originating user
If an AS receives a request on behalf of an originating user:
- and the AS supports the P-Served-User header field as defined in RFC 5502 [133], the AS shall determine the served user by taking the identity contained in the P-Served-User header field if available;
- otherwise, if the AS supports the History-Info header field as defined in RFC 7044 [66] the AS shall determine the served user from the content of the History-Info header field if available; and
- otherwise, the AS shall determine the served user by taking the identity contained in P-Asserted-Identity header field.
5.7.1.3A.3 AS serving a terminating user
If an AS receives a request on behalf of a terminating user:
- and the AS supports the P-Served-User header field as defined in RFC 5502 [133], the AS shall determine the served user by taking the identity contained in the P-Served-User header field if available;
- otherwise, if the AS supports the History-Info header field as defined in RFC 7044 [66] the AS shall determine the served user from the content of the History-Info header field if available; and
- otherwise, the AS shall determine the served user from the content of the Request-URI.
5.7.1.3B Determination of the used registration
A prerequisite for the procedure in this subclause is that a REGISTER request has been received including a Contact header field with a "+g.3gpp.registration-token" header field parameter and that the AS supports using this token to identify the registration.
When receiving an initial request for a dialog or a request for a standalone transaction, or a response to such request the AS shall if a "+g.3gpp.registration-token" header field parameter as defined in subclause 7.9A.8 is included in a Feature-Caps header field use this value to identify the registration used for this initial request for a dialog or this request for a standalone transaction or a response to such request by comparing it to the value of the "+g.3gpp.registration-token" Contact header field parameter stored when the user registered.
NOTE: The Include Register Request or Include Register Response indication in the initial Filter Criteria can be used to provide the incoming REGISTER request or 200 (OK) response to the incoming REGISTER request containing the instance ID to the AS. The AS can use the mechanism in this subclause to determine the instance ID for subsequent requests and responses.
If the AS routes the originating request to another entity than the S-CSCF, the AS shall remove the "+g.3gpp.registration-token" header field parameter from the Feature-Caps header field before forwarding the request.
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5.7.1.4 User identity verification at the AS
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The procedures at the AS to accomplish user identity verification are described with the help of figure 5-1. Procedures for user identity verification using the Identity header field are specified in subclause 5.7.1.25.
NOTE: Different means can be used to represent or transport the credentials. Such mechanisms are subject to operator policy and can e.g. include the P-Asserted-Identity header field, the Authorization header field or other mechanisms not specified by 3GPP TS 24.229.
When the AS receives a SIP initial or standalone request, excluding REGISTER request, that does not contain credentials, the AS shall:
a) if a Privacy header field is present in the initial or standalone request and the Privacy header field value is set to "id" or "user", then the user and the request are considered as anonymous, and no further actions are required. The AS shall consider the request as authenticated;
b) if there is no Privacy header field present in the initial or standalone request, or if the Privacy header field contains a value other than "id" or "user", then the AS shall check for the presence of a P-Asserted-Identity header field in the initial or standalone request. Two cases exist:
i) the initial or standalone request contains a P-Asserted-Identity header field. This is typically the case when the user is located inside a trusted domain as defined by subclause 4.4. In this case, the AS is aware of the identity of the user and no extra actions are needed. The AS shall consider the request as authenticated; and
ii) the initial or standalone request does not contain a P-Asserted-Identity header field. This is typically the case when the user is located outside a trusted domain as defined by subclause 4.4. In this case, the AS does not have a verified identity of the user. The AS shall check the From header field of the initial or standalone request. If the From header field value in the initial or standalone request is set to "Anonymous" as specified in RFC 3261 [26], then the user and the request are considered as anonymous and no further actions are required. If the From header field value does not indicate anonymity, then the AS shall challenge the user by issuing a 401 (Unauthorized) response including a challenge as per procedures described in RFC 3261 [26].
When the AS receives a SIP initial or standalone request that contains credentials but it does not contain a P-Asserted-Identity header field the AS shall check the correctness of the credentials as follows:
a) If the credentials are correct, then the AS shall consider the identity of the user verified, and the AS shall consider the request as authenticated;
b) If the credentials are not correct, the AS may either rechallenge the user by issuing a 401 (Unauthorized) response including a challenge as per procedures described in RFC 3261 [26] (up to a predetermined maximum number of times predefined in the AS configuration data), or consider the user as anonymous. If the user is considered anonymous, the AS shall consider the request as authenticated.
Figure 5-1: User identity verification flow at the AS
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5.7.1.5 Request authorization
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Once the AS have tried to verify the identity of the user, the AS either has a verified identity of the user or it considers the user as anonymous.
If the user is considered anonymous, the AS shall check whether the authorization policy defined for this request allows anonymous requests. If anonymous requests are allowed, then the AS can proceed with the requested functionality, otherwise, the AS shall not proceed with the requested functionality.
If the user is identified by an identity, the AS shall apply the authorization policy related to the requested functionality to detect whether the particular user is allowed to request the functionality. The authorization policy may require a verified identity of a user.
If the request is authorized then the AS shall continue with the procedures as defined for that request.
If the request is not authorized, the AS shall either:
- reject the request according to the procedures defined for that request e.g., by issuing a 403 (Forbidden) response; or
- send a 2xx final response if the authorization policy requires to deny the requested functionality, whilst appearing to the user as if the request has been granted.
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5.7.1.6 Event notification throttling
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If the AS has a local configuration information limiting the rate at which notification generation is allowed, then the AS shall take that information into account. Such local configuration information could be e.g. the shortest time period between issuing consecutive NOTIFY requests.
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5.7.1.7 Local numbering
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5.7.1.7.1 Interpretation of the numbers in a non-international format
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If home operator's local policy defines a prefix string(s) to enable subscribers to differentiate dialling a geo-local number and/or a home-local number and if the phone number in a non-international format in the Request-URI includes such a prefix, the AS shall interpret the received number in a non-international format as a geo-local number or as a home-local number according to the prefix.
If the phone number in a non-international format in the Request-URI includes a "phone-context" tel URI parameter, the AS shall:
1) if the "phone-context" tel URI parameter contains access technology information or the home network domain name prefixed by the "geo-local." string, interpret it as a geo-local number;
2) if the "phone-context" tel URI parameter contains the home network domain name, interpret it as a home-local number; or
3) if the "phone-context" tel URI parameter contains any other value, apply general procedures for translation.
NOTE 1: If business communication services are provided to the calling user, and the "phone-context" tel URI parameter contains a value associated with a private numbers, it is expected that any needed translation of the number information is handled by the corresponding business communication AS.
If the phone number in a non-international format in the Request-URI includes both operator defined prefix and a "phone-context" tel URI parameter and those information are contradictory, the AS shall ignore either the prefix or the "phone-context" tel URI parameter according to operator policy.
If the phone number in a non-international format in the Request-URI does not include either a "phone-context" tel URI parameter or an operator defined prefix, the AS shall interpret the phone number in a non-international format either as a geo-local number or as a home-local number according to operator policy.
NOTE 2: Operator must ensure that service setting dialling strings do not reach local numbering AS by setting appropriately the precedences of the initial filter criteria.
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5.7.1.7.2 Translation of the numbers in a non-international format
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When an AS receives a request having a geo-local number in a non-international format in the Request-URI, the AS shall use the "phone-context" tel URI parameter to determine the visited access network, if the "phone-context" tel URI parameter in the Request-URI is available. If the "phone-context" tel URI parameter in the Request-URI is not available, the AS may determine the visited access network based on the available P-Access-Network-Info header fields containing the access-type field, if it is available in the received request, or by means outside the scope of this document.
If the visited access network is determined:
1) if the home network supports the roaming architecture for voice over IMS with local breakout, and an incoming INVITE request contains a Feature-Caps header field with the "+g.3gpp.home-visited" header field parameter, the AS may choose to not attempt translation of some geo-local numbers and defer the translation to the visited network after loopback has been performed; or
2) the AS shall attempt to determine whether the geo-local number:
a) corresponds to a home local service number that can be used by a roaming user;
b) is used to access a service in the visited network; or
c) is used to access the local addressing plan of the visited network
- and translate the received geo-local number to a globally routeable SIP URI or an international tel URI:
NOTE 1: During the translation the AS can contact an entity in the visited access network for getting the needed information. The protocol and procedures for this is outside the scope of this specification.
NOTE 2: The AS can translate the tel URI to a SIP URI by including the 'telephone-subscriber' part of the received tel URI to the user part of the SIP URI and setting the domain name of the SIP URI to indicate the domain name of the network of the phone number based on the received "phone-context" tel URI parameter.
NOTE 3: In addition to the service numbers corresponding to a service in the visited network the home network can also support service numbers corresponding to services in the home network as geo-local service numbers.
When an AS receives a request having a home-local number in a non-international format in the Request-URI, the AS shall determine whether the home-local number is used to access a service or the local addressing plan and translate the received home-local number to a globally routeable SIP URI or an international tel URI:
When an AS receives a request having any other number in a non-international format in the Request-URI, the AS shall attempt to determine whether it is used to access a service in the third network or the local addressing plan of the third network and translate the received number in a non-international format to a globally routeable SIP URI or an international tel URI:
NOTE 4: The AS can translate the tel URI to a SIP URI by including the 'telephone-subscriber' part of the received tel URI to the user part of the SIP URI and setting the domain name of the SIP URI to indicate the domain name of the network of the phone number based on the received "phone-context" tel URI parameter;
NOTE 5: If business communication services are provided to the calling user, and the "phone-context" tel URI parameter contains a value associated with a private numbers, it is expected that any needed translation of the number information is handled by the corresponding business communication AS.
If the translation at the AS fails, the AS shall either send an appropriate SIP response or leave the Request-URI unmodified and route the request based on the topmost Route header field, based on local policy.
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5.7.1.8 GRUU assignment and usage
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It is possible for an AS to use a GRUU referring to itself when inserting a contact address in a dialog establishing or target refreshing SIP message.
This specification does not define how GRUUs are created by the AS; they can be provisioned by the operator or obtained by any other mechanism. The GRUU shall remain valid for the time period in which features addressed to it remain meaningful.
The AS shall handle requests addressed to its currently valid GRUUs when received outside of the dialog in which the GRUU was provided.
EXAMPLE: Upon receipt of an INVITE request addressed to a GRUU assigned to a dialog it has active, and containing a Replaces header field referencing that dialog, the AS will be able to establish the new call replacing the old one, if that is appropriate for the features being provided by the AS.
When an AS is acting as a routeing B2BUA (as defined in subclause 5.7.5) it may provide a contact address that is not a GRUU when the contact address in the incoming message that is being replaced is not a GRUU.
When an AS is acting as a routeing B2BUA forwards a SIP request it shall transparently forward a received Contact header field when the Contact header field contains a GRUU. When transparently forwarding a received Contact header field of a dialog-forming request, the AS shall include its own URI in a Record-Route header field in order to ensure that it is included on the route of subsequent requests.
When an AS acts as UA or Initiating B2BUA it shall use a GRUU as the contact address if the AS acts as a notifier per RFC 6665 [28] and RFC 7647 [231], otherwise the AS may provide a contact address that is not a GRUU in cases where it can ascertain that valid requests that could result from the use of that contact and follow the usage rules of RFC 5627 [93] will reach the element. In all other cases the AS shall use a GRUU.
An AS acting as a UA or an initiating B2BUA on behalf of a public user identity can provide a GRUU in the contact address referring to itself as described above. When the AS provides a GRUU on behalf of a user, subsequent dialog-initiating requests sent to that GRUU will be routed directly to the AS, thus bypassing terminating services assigned to the user. If the AS wishes to have terminating services applied for the user, the AS may generate a new terminating request addressed to a public GRUU associated with the public user identity of the user.
NOTE 1: If the AS wishes to have terminating services applied when the public user identity on whose behalf the AS is acting is unregistered, then the options available to the AS depend on whether or not the subscriber has ever previously registered with the IM CN subsystem. In the case where the public user identity had previously registered with the IM CN subsystem, then the AS can use the most recently allocated public GRUU if available. In the case where the user has never registered with the IM CN subsystem, then the AS can use the public user identity itself.
NOTE 2: Once terminating services have been applied, it is assumed that the terminating S-CSCF will route the request back to this AS via the initial filter criteria. In order for this to work, the initial filter criteria of the target user need to be configured so that the AS is invoked at the appropriate time relative to other terminating ASs (say, after the required terminating services have been applied). The mechanism to ensure that the AS is invoked by the initial filter criteria at the appropriate time is outside the scope of this specification (e.g. the user's filter criteria could be statically configured to invoke the AS at the correct time, or the AS could use the Dynamic Service Activation Information mechanism to activate the appropriate filter criteria).
When an AS acts as a UA or an initiating B2BUA, and is originating or terminating a request on behalf of a public user identity, and privacy is required, the AS shall ensure that any GRUU provided in the contact address in the request does not reveal the public user identity of the user.
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5.7.1.9 Use of ICSI and IARI values
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Based on service logic, an AS can validate an ICSI value received in an Accept-Contact header field or received in a P-Asserted-Service header field and reject the request if necessary.
A trusted AS may insert a P-Asserted-Service header field in a request for a new dialog or standalone transaction. An untrusted AS may insert a P-Preferred-Service header field in a request for a new dialog or standalone transaction. If the request is related to an IMS communication service that requires the use of an ICSI then the AS:
- shall include the ICSI value (coded as specified in subclause 7.2A.8.2), for the IMS communication service that is related to the request in either a P-Asserted-Service header field or a P-Preferred-Service header field depending whether the AS is trusted or not according to RFC 6050 [121].
When an AS that is acting as a UA or initiating B2BUA or routeing B2BUA sends an initial request for a dialog or a request for a standalone transaction, the AS may include an Accept-Contact header field containing:
- an ICSI value (coded as specified in subclause 7.2A.8.2) in a g.3gpp.icsi-ref media feature tag as defined in subclause 7.9.2 and RFC 3841 [56B]; and
- one or more IARI values (coded as specified in subclause 7.2A.9.2) that are related to the request in a g.3gpp.iari-ref media feature tag as defined in subclause 7.9.3 and RFC 3841 [56B];
if the ICSI or IARIs for the IMS communication service and IMS application are known.
The AS may:
- include the received ICSI and IARI values;
- replace or remove received ICSI and IARI values; or
- include new ICSI and IARI values.
When the AS acting as a UA or initiating B2BUA or routeing B2BUA sends a SIP request or a SIP response related to an IMS communication service, the AS may include in the Contact header field:
- in a g.3gpp.icsi-ref media feature tag as defined in subclause 7.9.2 one or more ICSI values (coded as specified in subclause 7.2A.8.2); and
- one or more IARI values (coded as specified in subclause 7.2A.9.2) in a g.3gpp.iari-ref media feature tag, for the IMS applications, that are related to the request as defined in subclause 7.9.2 and RFC 3840 [62];
if the ICSI or IARIs for the IMS communication service and IMS application are known. The AS may:
- include the received ICSI and IARI values;
- replace or remove received ICSI values; or
- include new ICSI and IARI values.
When sending a 18x or 2xx response to a request on behalf of an originating user, then the AS may insert a Feature-Caps header field with the "+g.3gpp.icsi-ref" header field parameter into the response, as specified in RFC 6809 [190]. The parameter value is set according to subclause 7.9A.2.
NOTE 3: The AS can insert the Feature-Caps header field e.g. based on operator policy, IMS communication service specification or depending whether other AS already inserted the Feature-Caps header field with the "+g.3gpp.icsi-ref" header field parameter in the response.
When sending a request on behalf of a terminating user, then the AS may insert a Feature-Caps header field with the "+g.3gpp.icsi-ref" header field parameter. The parameter value is set according to subclause 7.9A.2.
NOTE 4: The AS can insert the Feature-Caps header field e.g. based on operator policy, IMS communication service specification or depending whether other AS already inserted the Feature-Caps header field with the "+g.3gpp.icsi-ref" header field parameter in the request.
If the AS inserted the header field parameters in the Feature-Caps header field in the request or in 18x or 2xx response to request then the AS shall include the header field parameters with the same parameter values into the Feature-Caps header field in any target refresh request, and in each 1xx or 2xx response to target refresh request sent in the same direction.
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5.7.1.10 Carrier selection
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An AS may play a role in support of carrier selection as defined in RFC 4694 [112].
NOTE 1: In general, ASs do not need to support carrier selection, Rather a specific AS or a few ASs in a network will be used for carrier selection,
When an AS that supports carrier selection receives an initial request with a Request-URI in the form of a tel-URI that contains a "cic" tel-URI parameter inserted by the UE and if configured per operator policy, the AS may validate the value of the "cic" parameter. If an AS that supports carrier selection determines the "cic" parameter received in the initial request to be valid, as configured per operator policy, the AS shall process the request accordingly. If an AS supports carrier selecton and determines the "cic" parameter received in the initial request to be invalid, then the AS shall remove the "cic" parameter and process the request as if no "cic" had been received from the UE.
When an AS that support carrier selection receives an initial request with a Request-URI in the form of a tel-URI, the AS may, based on operator policy, insert an appropriate value for the "cic" tel-URI parameter as defined in RFC 4694 [112].
NOTE 2: For example, the AS that supports preferred carrier could insert a "cic" tel-URI parameter that identifies the originating user's preassigned carrier, or the carrier assigned to a called freephone number.
When an AS that support carrier selection receives an initial request with a Request-URI in the form of a SIP URI user=dialstring (see RFC 4967 [103]), the AS may translate the SIP URI to a valid tel-URI or a valid SIP URI user=phone comprising a userinfo part containing the tel-URI and a domain matching the domain of the original SIP URI user=dialstring. If the received SIP URI user=dialstring is successfully converted, then the AS shall replace the Request-URI with the newly created tel-URI or SIP URI user=phone. The AS shall then process the request as if it had arrived from the UE containing this tel-URI or SIP URI user=phone in the Request-URI.
NOTE 3: This specification does not make any assumptions regarding how these procedures are mapped to ASs; whether all procedures are supported by a single AS or spread across multiple ASs. However, this specification does assume that the responsibility for ensuring that the UE complies with the carrier selection procedures defined in RFC 4694 [112] will be performed by a single AS (e.g. validate "cic"), and the filter criteria will be configured so that this AS is invoked before other ASs that have carrier selection responsibilities.
The AS carrier selection procedures also apply when the request contains a Request-URI in the form of a SIP URI user=phone, where the "cic" tel-URI parameter is contained in the userinfo part of the SIP URI.
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5.7.1.11 Tracing
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An AS can retrieve tracing configuration information from the HSS via the Sh reference point. The AS tracing configuration can use the parameters specified in 3GPP TS 24.323 [8K] but need not structure them as a management object.
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5.7.1.12 Delivery of original destination identity
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If the service the AS provides needs to deliver the original destination identity to the UE, the AS shall insert a new hi-entry to the last hi-entry of History-Info header field including "mp" header field parameter as specified in RFC 7044 [66].
NOTE: If the "mp" header field parameter is present in the hi-entries within the History-Info header field, the information of the original destination number or URI, e.g. the service number for freephone, will be found in the hi-entry whose index-val matches the value of the first hi-entry with "mp" header field parameter.
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5.7.1.13 CPC and OLI
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The AS may populate the "cpc" and "oli" URI parameters in each initial request for a dialog or a request for a standalone transaction in the tel URI or SIP URI representation of telephone numbers in the P-Asserted-Identity header field based on their origin source.
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5.7.1.14 Emergency transactions
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Identification of emergency transactions for termination in the public network by an AS are outside the scope of this document, and are dependent on many application specific considerations.
Where an AS decides to generate an emergency request on behalf of its served user, the AS shall meet the following conditions:
1) the UE is in the same network as the S-CSCF (i.e. that the UE is not roaming).
NOTE 1: How the above is determined is outside the scope of this document and will depend on the application supported. Possible mechanisms could be: 1) that the AS only receives requests that are from non-roaming UEs; 2) analysis of the P-Access-Network-Info header field in a received request from the UE.
The AS generate the request with the following contents:
1) include in the Request-URI an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031 [69]. An additional sub-service type can be added if information on the type of emergency service is known;
2) a Route header field with the topmost Route header field set to the URI associated with an E-CSCF;
3) if the AS is part of the trust domain of the network, a P-Asserted-Identity header field containing the identity of the UE served by the AS;
4) if the AS is not part of the trust domain of the network, a P-Preferred-Identity header field containing the identity of the UE served by the AS;
5) if a GRUU is available for the UE served by the AS, provide the GRUU as part of a Contact header field;
NOTE 2: If the AS is not already aware of the GRUU of the UE due to previously receiving it in a Contact header, and the UE is registered, the GRUU can be obtained using either the subscription to the reg events package or using the third-party registration procedure with the REGISTER request including a "message/sip" MIME body of the 200 (OK) response for the REGISTER request as described in subclause 5.7.1.1.
6) if a location is available at the AS in any form, include a Geolocation header field with that location;
7) a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17];
8) if the AS supports calling number verification using signature verification and attestation information as specified in subclause 3.1 and if required by operator policy, the AS shall perform attestation of the user identity by inserting:
- a "verstat" tel URI parameter, specified in subclause 7.2A.20, to the tel URI or SIP URI with a user=phone parameter in the From header field or the P-Asserted-Identity header field;
- an Attestation-Info header field, specified in subclause 7.2.18; and
an Origination-Id header field, specified in subclause 7.2.19, set to a UUID identifying the AS which is configured based on local policy and requirements from national regulation; and
9) if the AS supports priority verification using assertion of priority information as specified in subclause 3.1 and if required by operator policy, the AS shall add a Resource-Priority header field containing a namespace of "esnet" as defined in RFC 7135 [197].
If the AS does not receive any response to the INVITE request (including its retransmissions); or receives a 3xx response or 480 (Temporarily Unavailable) response to an INVITE request, the AS shall select a new E-CSCF and forward the INVITE request.
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5.7.1.15 Protecting against attacks using 3xx responses
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The AS upon receiving a 3xx response to a request from the served UE that contains a Contact header field may remove the Contact header field or modify the response code from 3xx to an appropriate non 2xx response code (e.g. 5xx response code) based on operator policy before sending the response towards the UE.
NOTE: Automatically recursing on untrusted 3xx responses opens up the UE to being redirected to premium rate URIs without the user's consent. An AS that protects against attacks using 3xx responses needs to ensure that it doesn't break services that depend on 3xx responses being passed to the UE. Subclause 5.1.2A.1.1 specifies how a UE protects itself against attacks using 3xx responses. For some services an AS could automatically recurse on a 3xx response.
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5.7.1.16 Support of Roaming Architecture for Voice over IMS with Local Breakout
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5.7.1.16.1 Preservation of parameters
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An AS in a network supporting the roaming architecture for voice over IMS with local breakout shall not change the value of the "icid-value" header field parameter in the P-Charging-Vector header field received in the INVITE request when the AS sends any request or response related to an INVITE transaction.
NOTE: An AS that determines that loopback is not a viable option can change or remove any of the above parameters if required by the application logic performed by the AS.
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5.7.1.16.2 Preference for loopback routeing not to occur
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When the AS is accessed by a network supporting roaming architecture for voice over IMS with local breakout, and the incoming INVITE request contains a Feature-Caps header field with the "+g.3gpp.home-visited" header field parameter, the AS can indicate to the S-CSCF its preference for loopback routeing not to occur by removing the "+g.3gpp.home-visited" header field parameter from the Feature-Caps header field from any outgoing INVITE request back to the S-CSCF. Reasons for such an indication might include the need to terminate media streams at an MRF in the home network.
NOTE: If the original dialog identifier sent by the S-CSCF is not preserved by the AS in the outgoing requests, then loopback routeing will not occur.
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5.7.1.17 Delivery of network provided location information
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If the AS supports delivery of network provided location information, and the AS performs the retrieval of cell id and/or UE time zone via Sh interface, the AS shall insert the P-Access-Network-Info header field with the cell id, local-time-zone parameter and/or the "daylight-saving-time" parameter, including a "network-provided" parameter in the incoming request or response. Additionally, if required by local operator policy and the AS is able to deduce a Geographical Identifier from the Cell Global Identity (CGI) or form the Service Area Identifier (SAI), the AS shall include an operator-specific-GI header field parameter. The P-Access-Network-Info header field shall only be inserted if there is not already a network provided information.
When the AS receives, in a SIP request or response, a P-Access-Network-Info header field which does not contain the operator-specific-GI header field parameter, contains a Cell Global Identity (CGI) or a Service Area Identifier (SAI) information and contains the "network provided" header field parameter, if required by local operator policy and if the AS is able to deduce a Geographical Identifier from the contained Cell Global Identity (CGI) or form the contained Service Area Identifier (SAI), the AS shall instert an operator-specific-GI header field parameter in that received network provided P-Access-Network-Info header field.
The AS can obtain a Geographical Identifier from the CLF by using the e2 interface (see ETSI ES 283 035 [98]).
NOTE: ETSI ES 283 035 [98] Release 3 enables querying a CLF using the User-Data-Request command in which the Global-Access-Id AVP contains the 3GPP-User-Location-Info AVP with a CGI or a SAI value to get a corresponding Geographical Identifier. If multiple CLFs are deployed, the AS can dertermine which CLF to query based on the CGI or the SAI values or can use a DIAMETER proxy if deployed.
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5.7.1.18 Delivery of MRB address information
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A visited MRB address can be received during session establishment. If an AS receives the URI of an MRB in a "+g.3gpp.mrb" header field parameter included in a Feature-Caps header field of an INVITE request, it shall store this URI. If the AS requests allocation of MRF resources from an MRB in its own network, either in in-line or query mode, the AS shall forward the visited network MRB URI in the request.
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5.7.1.19 Overload control
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5.7.1.19.1 Outgoing subscriptions to load-control event
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Based on operator policy, the AS may subscribe to the load-control event package with one ore more target SIP entities. The list of target SIP entities is provisioned.
Subscription to the load-control event package is triggered by internal events (e.g. the physical device hosting the SIP entity is power-cycled) or through a management interface.
The AS shall perform subscriptions to the load-control event package to a target entity in accordance with RFC 6665 [28] and with RFC 7200 [201]. When subscribing to the load-control event, the AS shall:
1) Send a SUBSCRIBE request in accordance with RFC 6665 [28] and with RFC 7200 [201] to the target entity, with the following elements:
- an Expires header field set to a network specific value;
2) If the target entity is located in a different network and local policy requires the application of IBCF capabilities, forward the request to an IBCF acting as an exit point.
The AS shall automatically refresh ongoing subscriptions to the load-control event package either 600 seconds before the expiration time if the initial subscription was for greater than 1200 seconds, or when half of the time has expired if the initial subscription was for 1200 seconds or less.
The AS can terminate a subscription according to RFC 6665 [28].
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5.7.1.19.2 Incoming subscriptions to load-control event
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If subscriptions to load-control event package is supported, the AS shall handle incoming subscriptions to the load-control event package in accordance with RFC 6665 [28] and with RFC 7200 [201]. When the AS receives a SUBCRIBE request for the load-control event from an unauthorised or unexpected source, the AS shall generate a "403 forbidden" response to the SUBSCRIBE request.
If the AS receives a SUBSCRIBE request from an authorised source the AS shall:
2) Generate a "200 OK" response to the SUBSCRIBE request with the following settings:
- an Expires header field, set to either the same or a decreased value as the Expires header field in SUBSCRIBE request; and
- the Contact header field set to an identifier uniquely associated to the SUBSCRIBE request that may help correlating refreshes.
3) In case of an initial subscription, determine the list of load filters applicable to the subscriber, create an XML document to represent this information and send it as an attachement to a NOTIFY request towards the subscriber. If no applicable load filters are identified when the subscription request is received, an empty document is attached to the NOTIFY request.
Subsequent NOTIFY requests with updated or new filters may then be sent as the actual load of the target entity evolves.
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5.7.1.20 Procedures in the AS for resource sharing
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5.7.1.20.1 General
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An AS supporting resource sharing shall use the "+g.3gpp.registration-token" header field parameter in the Contact header field of the incoming third-party REGISTER request and the "+g.3gpp.registration-token" header field parameter in the Feature-Caps header field in the initial INVITE request or provisional responses to the initial INVITE to identify the UE.
The AS supporting resource sharing shall only include the Resource-Share header field in requests and responses destined to the served user and in all other cases remove the header field.
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5.7.1.20.2 UE-originating case
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If the AS supporting resource sharing receives a response or request destined to the served user containing a Resource-Share header field, the AS shall remove that header field from the outgoing response or request.
Upon receiving an SDP answer in a provisional response or a 200 (OK) response to an initial INVITE request from a UE served by a P-CSCF supporting resource sharing, the AS supporting resource sharing shall determine whether resource sharing can be applied.
NOTE 1: An AS can learn that a P-CSCF supports resource sharing from the Resource-Share header field with the value "supported" in the initial REGISTER request that is contained in the "message/sip" MIME body of the third-party REGISTER request received when the UE registered.
NOTE 2: The conditions for resource sharing are outside the scope of the present document.
If the AS:
1) determines that at least one media stream in the initial SDP answer is subject to resource sharing, the AS shall in the outgoing response include a Resource-Share header field as described in subclause 7.2.13.4 with the following clarifications:
a) the AS shall set the "origin" header field parameter to "session-initiator"; and
b) if
- a session exists that can share resources with the dialog created by the initial INVITE request involving the same UE, the AS shall include a new sharing key set to the value of the sharing key in the other session and use this sharing key to identify the resource sharing rule for this media stream in this session; and
- no session exists that can share resources with the dialog created by the initial INVITE request, the AS shall include a new sharing key unique among all UEs registered by the user and use this sharing key to identify the resource sharing rule for this media stream in this session; and
2) determines that resource sharing can never be applied for any of the media streams in the SDP answer, the AS shall include a Resource-Share header field set to the value "no-media-sharing" in the outgoing response.
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5.7.1.20.3 UE-terminating case
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5.7.1.20.3.1 Determine resource sharing using the initial SDP offer
Upon receiving an initial INVITE request containing an initial SDP offer destined for the served user, the AS supporting resource sharing shall if at least one registered UE is served by a P-CSCF supporting resource sharingdetermine if resource sharing can be applied.
NOTE 1: An AS can learn that a P-CSCF supports resource sharing from the Resource-Share header field with the value "supported" in the initial REGISTER request that is contained in the "message/sip" MIME body of the third-party REGISTER request received when the UE registered.
NOTE 2: The condition for resource sharing is outside the scope of the present document.
If the AS:
1) determines that at least one media stream in the initial SDP answer is subject to resource sharing, the AS shall in the outgoing request include a Resource-Share header field as described in subclause 7.2.13.4 with the following clarifications:
a) the AS shall set the "origin" header field parameter to "session-receiver";
b) the AS shall include a new sharing key part that is determined as follows:
A) if the AS is aware of only one registered contact:
I) if a session exists where media in the existing session can be shared with media in the new SDP offer, the sharing key in the INVITE request shall be set to the value of the sharing key used in the existing session and the AS shall use this sharing key to identify the resource sharing rules for each media stream in the session; or
II) if no session exists where media in the existing session can be shared with media in the new SDP offer, the AS shall create a new sharing key that is unique among all sessions that exist on the UE. This new sharing key shall be included in the INVITE request and is used to identify the resource sharing rules for each media stream in this session; and
B) if the AS is aware of more than one registered contacts:
I) if the AS is using an Accept-Contact header field, Reject-Contact header field, and/or a GRUU in the request URI to target a specific registered UE and a session exists on the target UE where media in the existing session can be shared with media in the new SDP offer, the sharing key in the INVITE request shall be set to the value of the sharing key used in the existing session and the AS shall use this sharing key to identify the resource sharing rules for each media stream in the session; or
II) if no session exists on the target UE (or on the set of UEs when more than one UE is registered and the S-CSCF can fork the INVITE request to more than one UE) where media in the existing session can be shared with media in the new SDP offer, the AS shall create a new sharing key that is unique among all sessions that exist for all UEs registered for the server user. This new sharing key shall be included in the INVITE request and is used to identify the resource sharing rules for each media stream in this session; and
c) if the AS is aware of more than one registered contact and the AS is not using an Accept-Contact header field, Reject-Contact header field, and/or a GRUU in the request URI to target a specific registered UE (so that the S-CSCF is allowed to fork the INVITE request to one or more UEs) and sessions exist with any registered UE where media in an existing session can be shared with media in the new SDP offer, the existing-sharing-key-list part in the INVITE shall be set to the value of the sharing keys used in the existing sessions; and
2) determines that resource sharing can not be applied, the AS shall include a Resource-Share header field set to the value "no-media-sharing" in the outgoing request.
5.7.1.20.3.2 Determine resource sharing using the initial SDP answer
Upon receiving a PRACK request or an ACK request destined to a UE served by a P-CSCF supporting resource sharing that contains an initial SDP answer, the AS supporting resource sharing shall determine if resource sharing can be applied.
NOTE 1: An AS can learn that a P-CSCF supports resource sharing from the Resource-Share header field with the value "supported" in the initial REGISTER request when that is contained in the "message/sip" MIME body of the third-party REGISTER request received the UE registered.
NOTE 2: The condition for resource sharing is outside the scope of this technical specification.
If the AS:
1) determines that at least one media stream in the initial SDP answer is subject to resource sharing, the AS shall in the outgoing request include a Resource-Share header field as described in subclause 7.2.13.4 with the following clarifications:
a) the "origin" header field parameter shall be set to "session-receiver"; and
b) if
- a session exists that can share resources involving the same UE, the AS shall include a new sharing key set to the value of the sharing key in the other session and use this sharing key to identify the resource sharing rule for this media stream in this dialog; and
- no session exists that can share resources, the AS shall include a new sharing key unique among all UEs registered by the user and use this sharing key to identify the resource sharing rule for this media stream in this dialog; and
2) determines that resource sharing can never be applied for any of the media streams in the SDP answer, the AS shall include a Resource-Share header field with the value "no-media-sharing" as described in subclause 7.2.13.4 in the outgoing response.
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5.7.1.20.4 Updating the resource sharing options
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If the AS during the duration of the call determines that the resource sharing options needs to be changed (e.g. if media streams are added by the UE), then the AS shall include a Resource-Share header field with the updated resource sharing options as specified in subclause 7.2.13, in the outgoing request or response causing the reason for change.
NOTE: If more than one dialog exists and the update is sent before the session invitation is accepted by the terminating user, the resource sharing options are determined per individual dialog.
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5.7.1.20.5 Abnormal cases
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If the AS receives a request or response from a served user containing a Resource-Share field with the value "no-media-sharing", the AS shall no longer apply resource sharing with sessions involving the UE sending the request or response.
If the AS receives a request or response from a served user containg an SDP offer conflicting with an earlier decision to share resources, the AS shall include in the response carrying the SDP answer towards the served user a Resource-Share header field with the value "no-media-sharing" along with the "origin" header field parameter set to "session-initiator" or "session-receiver" as appropriate and no longer apply resource sharing with sessions involving the UE sending the request or response.
NOTE: A typical example when this can happen is the communication waiting use case. If the UE sends a 200 (OK) response to the INVITE request without putting the first call on hold, the UE's behaviour is then regarded as unpredictable and resource sharing cannot be used towards that UE.
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5.7.1.21 Dynamic Service Interaction
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If an AS supports dynamic service interaction, the AS should insert the Service-Interact-Info header field into the SIP messages before those messages are sent out. The Service-Interact-Info field is filled with the service identities of the services which have been executed. Additionally, the AS may insert into the Service-Interact-Info header field with the identities of the services which may have confliction with the executed services according to local policy.
NOTE: No service identifiers are defined in this release of the present document.
If the AS supports dynamic service interaction, it should take the information contained in any received Service-Interact-Info header field into account when executing service logic.
If the AS does not recognize the service identities contained in the Service-Interact-Info header field, they should be ignored.
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5.7.1.22 Service access number translation
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When the AS is accessed by a service access number (e.g. toll free, premium service) and performes a translation of this number into a routeable number, the AS shall include in the outgoing request:
1) the Request-URI set to the targeted SIP URI containing the "cause" SIP URI parameter, defined in RFC 4458 [68], set to the value "380" defined in RFC 8119 [230]; and
2) the History-Info header field constructed according to RFC 7044 [66] in which the hi-targeted-to-uri of the last hi-entry is set to the new Request-URI with the "cause" SIP URI parameter, defined in RFC 4458 [68], set to the value "380" defined in RFC 8119 [230].
A service access number does not constrain the number format. A local service number as defined in TS 23.228 [7] and described in subclause 5.7.1.7 can be a service access number.
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5.7.1.23 Procedures in the AS for priority sharing
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.23.1 General
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An AS supporting priority sharing and if according to local policy shall apply priority sharing as specified in the following subclauses.
NOTE: The MCPTT server is the only AS in the present document defined to use priority sharing (see 3GPP TS 24.379 [8ZE]).
An AS supporting priority sharing shall only include a Priority-Share header field in requests and responses destined to the served user and in all other cases remove the header field.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.23.2 Session originating procedures
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If the Feature-Caps header field with the g.3gpp.priority-share feature-capability indicator was included in the "message/sip" MIME body in the third-party REGISTER request and when the AS determines that priority sharing can be applied, the AS supporting priority sharing shall:
1) include the Priority-Share header field with the value "allowed" defined in subclause 7.2.16 in a 18x and 2xx response to the initial INVITE request; or
2) include the Priority-Share header field with the value "allowed" defined in subclause 7.2.16 in a subsequent request or a response to subsequent requests destined to the served user.
If priority sharing can not be applied any longer, the AS shall include the Priority-Share header field, defined in subclause 7.2.16, with the value "not-allowed" in a request or response destined to the served user.
NOTE: The AS can enable or disable priority sharing by including the Priority-Share header field with the value "allowed" or "not-allowed" as specified above until the session is released.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.23.3 Session terminating procedures
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If the incoming REGISTER request contained in the "message/sip" MIME body of a third-party REGISTER request the g.3gpp.priority-share feature-capability indicator in a Feature-Caps header field and when the AS determines that priority sharing can be applied, the AS supporting priority sharing shall:
1). include the Priority-Share header field with the value "allowed" defined in subclause 7.2.16 in the initial INVITE request destined to the served user; or
2) include Priority-Share header field with the value "allowed" defined subclause 7.2.16 in a subsequent request or responses to a subsequent request destined to the served user.
If priority sharing can not be applied any longer, the AS shall include the Priority-Share header field, defined in subclause 7.2.16, with the value "not-allowed" in a request or response destined to the served user.
NOTE: The AS can enable or disable priority sharing by including the Priority-Share header field with the value "allowed" or "not-allowed" as specified above until the session is released.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.24 Handling re-INVITE request collisions
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An AS shall handle re-INVITE request collisions as specified in RFC 3261 [26] with the clarification in this subclause.
When the AS receives a SIP 491 (Request Pending) response to a re-INVITE request initiated by the AS and sent towards the remote user, the AS shall:
1) if the AS is serving the user at the originating side of the call, act as the the owner of the Call-ID of the dialog ID and should select a randomly choosen time to be between 2.1 and 4 seconds in units of 10 ms; and
2) if the AS is serving the user at the terminating side of the call, act as not being the owner of the Call-ID of the dialog ID and should select a randomly choosen time to be between 0 and 2 seconds in units of 10 ms.
When the AS receives a SIP 491 (Request Pending) response to a re-INVITE request initiated by the AS and sent towards the served user, the AS shall:
1) if the AS is serving the user at the originating side of the call, act as not being the owner of the Call-ID of the dialog ID and should select a randomly choosen time to be between 0 and 2 seconds in units of 10 ms; and
2) if the AS is serving the user at the terminating side of the call, act as the owner of the Call-ID of the dialog ID and should select a randomly choosen time to be between 2.1 and 4 seconds in units of 10 ms.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.25 Assertion verification using the Identity header field
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.25.1 General
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RFC 8224 [252] describes a mechanism where an authentication service after verifying the calling number identity inserts a signature over selected header fields. A verification service can then use this signature to trust the correctness of the identity.
RFC 8946 [265] describes a mechanism where an authentication service after verifying the diverting number identity inserts a signature over selected header fields. A verification service can then use this signature to trust the correctness of the diverting identity.
RFC 8443 [279] describes a mechanism where an authentication service after verifying the Resource-Priority header field inserts a signature over the Resource-Priority header field. A verification service can then use this signature to trust the correctness of the Resource-Priority header field.
RFC 9027 [278] extends a mechanism defined in RFC 8443 [279] to enable authentication of the header field value "psap-callback" of the Priority header field and inserts a signature over the Resource-Priority header field and the header field value "psap-callback" provided in the Priority header field. A verification service can then use this signature to trust the correctness of the Resource-Priority header field and header field value "psap-callback" of the Priority header field.
draft-ietf-stir-passport-rcd [302] describes a mechanism where an authentication service after verifying the Call-Info header field containing RCD info inserts a signature over that Call-Info header field. A verification service can then use this signature to trust the correctness of the Call-Info header field containing RCD info.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.25.2 Originating procedures
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An originating AS supporting the calling number verification using signature verification and attestation information, as defined in subclause 3.1:
1) may based on local policy insert an Identity header field as specified in RFC 8224 [252] for all initial INVITE requests and MESSAGE requests and shall for this purpose use the identity in the P-Asserted-Identity header field or the From header field; or
NOTE 1: This option is kept from the original release-14 functionality. If the AS knows the IBCF supports invoking an AS for providing an Identity header field the below actions are more efficient.
2) may based on local policy perform attestation of the identity of the served user by:
a) inserting a "verstat" tel URI parameter, specified in subclause 7.2A.20; in the From header field or the P-Asserted-Identity header field if not already present;
b) insert an Origination-Id header field as specified in subclause 7.2.19 and an Attestation-Info header field specified in subclause 7.2.18, if not already present; and
c) if the RCD verification using assertion of RCD info functionality is implemented within the Calling number verification using signature verification and attestation information feature, as specified in subclause 3.1, inserting a "rcd-np" header field parameter, in the Call-Info header field if not already present.
Editor's note: [WI: NG_RTC_Ph2, CR#6714] Definition of the "rcd-np" Call-Info header field parameter is FFS.
If the AS performs originating services on behalf of a diverting user, the AS may assert the identity of the diverting user by inserting a "verstat" tel URI parameter, specified in subclause 7.2A.20, in the History-Info hi-entry representing the diverting user.
If the AS supports priority verification using assertion of priority information as specified in subclause 3.1 and if allowed by local operator policy, the AS may insert an Identity header field as described in RFC 8443 [279] and RFC 9027 [278], and shall for this purpose use the resource priority of the Resource-Priority header field in the received initial INVITE or re-INVITE request.
NOTE 2: For sessions terminating in another domain, only one of the following entities needs to be configured to provide an Identity header field for the resource priority: the IBCF or the AS. Which functional entity inserts the Identity header field is subject to network configuration and local policy.
NOTE 3: How the AS asserts the authenticity of the Resource-Priority header field value is out of scope of the present document.
If the AS supports RCD verification using assertion of RCD info as standalone feature, as specified in subclause 3.1, required by the local policy and the Call-Info header field with RCD info is included in the initial INVITE request or MESSAGE request, the AS may:
- based on local policy, perform attestation of the RCD info of the served user by adding the "rcd-np" header field parameter in the Call-Info header field; or
- insert the Identity header field as described in draft-ietf-stir-passport-rcd [302];
in the forwarded initial INVITE request or MESSAGE request.
NOTE 4: For sessions terminating in another domain, only one of the following entities needs to be configured to provide an Identity header field for the RCD info: the IBCF or the AS. Which functional entity inserts the Identity header field is subject to network configuration and local policy.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.25.3 Terminating procedures
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Upon receiving an initial INVITE request or a MESSAGE request containing one or more Identity header fields, an AS supporting the calling number verification using signature verification and attestation information, as defined in subclause 3.1, shall if the network indicated support for the calling number verification during registration:
- if no "verstat" tel URI parameter is present for the identity to be verified in the From or P-Asserted-Identity header field, and no "rcd-np" parameter is present in the Call-Info header field (if the RCD verification using assertion of RCD info functionality is implemented within the Calling number verification using signature verification and attestation information feature, as specified in subclause 3.1), perform user identity verification of the originating user identity using the Identity header field containing a PASSporT SHAKEN JSON Web Token, specified in RFC 8588 [261] and with rcd PASSporT claims specified in draft-ietf-stir-passport-rcd [302], and based on local policy all Identity header fields containing a PASSporT div JSON Web Token, specified in RFC 8946 [265], in the received request. Based on the outcome of the verification insert a "verstat" tel URI parameter, specified in subclause 7.2A.20, with a value representing the outcome of the verification in the tel URI or SIP URI with the user=phone parameter of each P-Asserted-Identity header field or From header field where the URI contains the calling number that was tested for verification and based on local policy in all verified identities in the History-Info header field, and insert the "rcd-np" parameter in the Call-Info header field containing the RCD info.
If no Identity header field is present in the received INVITE or MESSAGE request, but an Origination-Id header field along with an Attestation-Info header field set either to "B" or "C" is present, the AS shall set the verstat tel URI parameter to the value "No-TN-Validation".
If the AS supports priority verification using assertion of priority information as specified in subclause 3.1 and if allowed by local operator policy, the AS may verify that the Priority and Resource-Priority header field values are authorized. To do so, the AS:
• verifies the Identity header fields containing a PASSporT rph JSON Web Token as specified in RFC 8443 [279] and RFC 9027 [278] if included in the initial INVITE or re-INVITE request; and
• verifies that the Priority and Resource-Priority header field values are authorized by valid "rph" PASSporT claims.
The AS shall populate the Priority-Verstat header field associated with the Resource-Priority header field and include the Priority-Verstat header field in the forwarded SIP request.
If the AS supports RCD verification using assertion of RCD info as standalone feature, as specified in subclause 3.1, and required by the local policy, the AS shall verify that RCD information or RCD URL included in the Call-Info header field are authorized. To do so, the AS:
- verifies the Identity header field containing a PASSporT rcd JSON Web Token as specified in draft-ietf-stir-passport-rcd [302] if included in the initial INVITE request; and
- verifies that the Call-Info header field RCD values are authorized by valid "rcd" PASSporT claim.
Based on the outcome of the verification, the AS may insert the "rcd-np" parameter in the Call-Info header field containing the RCD info the in the forwarded initial INVITE request or MESSAGE request.
The AS may report any verification failure of an Identity header field to the appropriate upstream signing service by populating for each reported Identity header field verification error a Reason header field in the next provisional or final response to the INVITE or MESSAGE request, where the Reason header field "protocol" value is set to "STIR", as specified in RFC 9410 [294] and RFC 9366 [296], and the "cause" header field parameter contains the 4xx response code of the failing PASSporT, as defined in RFC 8224 [252]. Additionally, the AS may include the "ppi" header field parameter containing the failing PASSporT.
NOTE 1: For sessions originating in another domain, only one of the following entities needs to be configured to verify the Identity header field for the resource priority: the IBCF or the AS. Which functional entity inserts the Identity header field verification is subject to network configuration and local policy.
NOTE 2: Multiple Reason header fields with the protocol value set to "STIR" are not supported in the present document.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.25.4 Procedures over the Ms reference point
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If the AS receives a verificationRequest as specified in annex V, the AS verifies the request and when verified generates a verificationResponse, as specified in annex V, including a "verstat" claim for the verified identity.
If the AS receives a signingRequest, specified in annex V, the AS sends the signed information in a signingResponse as specified in annex V.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.26 Procedures in the AS for 3GPP PS data off
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An AS that supports 3GPP PS data off can receive in the message/SIP MIME body in a third party REGISTER request the REGISTER request sent by the UE. If this REGISTER request contains a "+g.3gpp.ps-data-off" Contact header field parameter the AS can determine that the UE supports 3GPP PS data off, and the value of the parameter indicates the 3GPP PS data off status. When the AS receives an initial request for a dialog or a standalone transaction destined to the served user, if:
- the latest "+g.3gpp.ps-data-off" Contact header field parameter, specified in subclauce 7.9.8, that was received in a third party REGISTER request, as specified above, was set to "active" in the UE; and
- the service the AS supports is not configured as a 3GPP PS data off exempt service to be used in the HPLMN,the EHPLMN or the subscribed SNPN, or the service the AS support is not configured as a 3GPP PS data off exempt service to be used in the VPLMN or the non-subscribed SNPN;
the AS shall not send the request to the UE via GPRS IP-CAN, EPS IP-CAN or 5GS IP-CAN.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.27 AS support for access update procedures
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.27.1 General
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The AS can indicate that it supports in-call access update procedures by sending a feature-capability indicator including a public service identity indicating to where to send the updates.
When the AS receives a MESSAGE request with a P-Charging-Vector header field containing an "icid-value" header field parameter matching the "icid-value" header field parameter of an existing dialog, the AS can use the location information in the received MESSAGE request to update the location information for the dialog identified by the Call-Id.
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.27.2 Originating procedures
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If the AS supports in-call access update procedures and the AS is interested in receiving updates of changes of IP-CAN or PLMN the AS shall include in responses to an initial INVITE request a g.3gpp.in-call-access-update feature-capability indicator with a value set to a public service identity resolving to the AS.
When the AS receives a Handover-Info header field defined in subclause 7.2.22 with the header field value set to "handover-completed", then the AS shall send an INVITE or UPDATE request towards the originating UE including an SDP offer with the previous SDP, including the same SDP version parameter, and include the Handover-Info header field with the "Role" header field value set to a value "session-initiator".
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.27.3 Terminating procedures
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If the AS supports access update procedures and the AS is interested in receiving updates of changes of IP-CAN or PLMN the AS shall include in the INVITE request a g.3gpp.in-call-access-update feature-capability indicator with a value set to a public service identity resolving to the AS.
When the AS receives a Handover-Info header field defined in subclause 7.2.22 with the header field value set to "handover-completed", then the AS shall send an INVITE or UPDATE request towards the terminating UE including an SDP offer with the previous SDP, including the same SDP version parameter, and include the Handover-Info header field with the "Role" header field value set to a value "session-receiver".
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d3a3ac3f64ab68e4fcef5ea9a665f70a
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24.229
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5.7.1.28 Rich Call Data
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