Content for  TS 24.229  Word version:  18.4.0

For all SIP transactions identified:

• if priority is supported, as containing an authorised Resource-Priority header field or a temporarily 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 S-CSCF shall give priority over other transactions or dialogs. This allows special treatment for such transactions or dialogs. If priority is supported, the S-CSCF shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value. When the S-CSCF receives, destined for a registered served user, an initial request for a dialog or a request for a standalone transaction, and the request is received either from a functional entity within the same trust domain or contains a valid original dialog identifier or the dialog identifier (From, To and Call-ID header fields) relates to an existing request processed by the S-CSCF, then prior to forwarding the request, the S-CSCF shall: If the S-CSCF receives any response to the above request, the S-CSCF shall:

1. If the response contains a "logme" header field parameter in the SIP Session-ID header field then log the response based on local policy.

If the S-CSCF supports HSS based P-CSCF restoration and

1. receives a 404 (Not Found) response;
2. fails to receive any SIP response from a P-CSCF serving a non-roaming user within a configurable time; or
3. receives a 408 (Request Timeout) response or a 504 (Server Time-out) response:
   • including a Restoration-Info header field defined in subclause 7.2.11 set to "noresponse"; and
   • the "+g.3gpp.ics" Contact header field parameter with a value set to "server" was not included in the REGISTER request when the UE registered;

the S-CSCF shall:

• send a 480 (Temporarily Unavailable) response;
• initiate the HSS based P-CSCF restoration procedure towards the served user as specified in TS 23.380; and
• if b) or c) above applied consider the P-CSCF as not reachable.

If the S-CSCF supports PCRF based P-CSCF restoration and receives a 404 (Not Found) response, the S-CSCF shall consider the P-CSCF to be in a non-working state and shall initiate the PCRF based P-CSCF restoration procedure towards the served user as specified in TS 23.380. If the S-CSCF:

1. fails to receive a SIP response within a configurable time; or
2. receives a 408 (Request Timeout) response or a 5xx response from the AS without previously receiving a 1xx response to the original SIP request, and without previously receiving a SIP request from the AS that contained the same original dialog identifier as the original request;

the S-CSCF shall:

• if the default handling defined in the filter criteria indicates the value "SESSION_CONTINUED" as specified in TS 29.228 or no default handling is indicated, execute the procedure from step 4; and
• if the default handling defined in the filter criteria indicates the value "SESSION_TERMINATED" as specified in TS 29.228, either forward the received response or, if the request is an initial INVITE request, send a 408 (Request Timeout) response or a 5xx response towards the originating UE as appropriate (without verifying the matching of filter criteria of lower priority and without proceeding for further steps).

If the S-CSCF receives any final response from the AS, the S-CSCF shall forward the response towards the originating UE (without verifying the matching of filter criteria of lower priority and without proceeding for further steps). When the S-CSCF receives any response to the above request and forwards it to an AS, the S-CSCF shall remove any "orig-ioi", "term-ioi" and "transit-ioi" header field parameter if received in a P-Charging-Vector header field, insert a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the request, a type 3 "term-ioi" header field parameter, and based on operator option insert a Relayed-Charge header field in the response. The S-CSCF shall set the type 3 "term-ioi" header field parameter to a value that identifies the sending network of the response, the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter and include in the Relayed-Charge header field the received "transit-ioi" header field parameter from the P-Charging-Vector header field. When the S-CSCF receives, destined for an unregistered served user or a statically pre-configured PSI, an initial request for a dialog or a request for a standalone transaction, the S-CSCF shall:

1. Void.
2. execute the procedures described in 1, 2, 3, 3C, 3D, 4, 5, 6, 7, 11, 13, 13B, 13C and 14 in the above paragraph (when the S-CSCF receives, destined for the registered served user, an initial request for a dialog or a request for a standalone transaction).
3. In case that no more AS needs to be contacted, then S-CSCF shall return an appropriate unsuccessful SIP response. This response may be a 480 (Temporarily unavailable) and terminate these procedures.

Prior to performing S-CSCF Registration/Deregistration procedure with the HSS, the S-CSCF decides which HSS to query, possibly as a result of a query to the Subscription Locator Functional (SLF) entity as specified in TS 29.228 or use the value as received in the P-User-Database header field in the initial request for a dialog or a request for a standalone transaction as defined in RFC 4457. The HSS address received in the response to SLF query can be used to address the HSS of the public user identity with further queries. If the HSS indicates to the S-CSCF that there is already another S-CSCF assigned for the user, the S-CSCF shall return a 305 (Use Proxy) response containing the SIP URI of the assigned S-CSCF received from the HSS in the Contact header field. When the S-CSCF receives any response to the above request containing a Relayed-Charge header field, and the next hop is not an AS, the S-CSCF shall remove the Relayed-Charge header field. When the S-CSCF receives any 1xx or 2xx response to the initial request for a dialog (whether the user is registered or not), the S-CSCF shall:

1. if the response corresponds to an INVITE request, save the Contact and Record-Route header field values in the response such that the S-CSCF is able to release the session if needed;
2. if the response is not forwarded to an AS (i.e. the response is related to a request that was matched to the first executed initial filter criteria):
   1. remove the received "transit-ioi" header field parameter if present and insert a type 2 "term-ioi" header field parameter in the P-Charging-Vector header field of the outgoing response. The type 2 "term-ioi" header field is set to a value that identifies the sending network of the response and the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter. Values of "orig-ioi" and "term-ioi" header field parameters in the received response are removed; and
   2. if the S-CSCF supports using a token to identify the registration, remove the "+g.3gpp.registration-token" Feature-Caps header field parameter, defined in subclause 7.9A.8, if received in the response;
3. in case the served user is not considered a privileged sender then:
   1. if the P-Asserted-Identity header field contains only a SIP URI and in the case where the S-CSCF has knowledge that the SIP URI contained in the received P-Asserted-Identity header field is an alias SIP URI for a tel URI, the S-CSCF shall add a second P-Asserted-Identity header field containing this tel URI, including the display name associated with the tel URI, if available; and
   2. if the P-Asserted-Identity header field contains only a tel URI, the S-CSCF shall add a second P-Asserted-Identity header field containing a SIP URI. The added SIP URI shall contain in the user part a "+" followed by the international public telecommunication number contained in tel URI, and user's home network domain name in the hostport part. The added SIP URI shall contain the same value in the display name as contained in the tel URI. The S-CSCF shall also add a "user" SIP URI parameter equals "phone" to the SIP URI;
4. in case the response is sent towards the originating user, the S-CSCF may retain the P-Access-Network-Info header field based on local policy rules and the destination user (Request-URI);
5. save an indication that GRUU routeing is to be performed for subsequent requests sent within this same dialog if:
   1. there is a record-route position saved as part of the initial dialog request state; and
   2. the contact address in the response is a valid GRUU assigned by the S-CSCF as specified in subclause 5.4.7A.4 or a temporary GRUU self assigned by the UE based on the "temp-gruu-cookie" header field parameter provided to the UE;
6. if the S-CSCF supports using a token to identify the registration and if a registration exists, add a "+g.3gpp.registration-token" Feature-Caps header field parameter, as defined in subclause 7.9A.8, set to the same value as included in the "+g.3gpp.registration-token" Contact header field parameter of the third party REGISTER request sent to the AS when the UE registered; and
7. if the response is forwarded within the S-CSCF home network and not to an AS, insert a P-Charging-Function-Addresses header field populated with values received from the HSS.

When the S-CSCF receives a response to a request for a standalone transaction (whether the user is registered or not), then:

1. in case the served user is not considered a privileged sender then:
   1. if the P-Asserted-Identity header field contains only a SIP URI and in the case where the S-CSCF has knowledge that the SIP URI contained in the received P-Asserted-Identity header field is an alias SIP URI for a tel URI, the S-CSCF shall add a second P-Asserted-Identity header field containing this tel URI, including the display name associated with the tel URI, if available; and
   2. if the P-Asserted-Identity header field contains only a tel URI, the S-CSCF shall add a second P-Asserted-Identity header field containing a SIP URI. The added SIP URI shall contain in the user part a "+" followed by the international public telecommunication number contained in tel URI, and user's home network domain name in the hostport part. The added SIP URI shall contain the same value in the display name as contained in the tel URI. The S-CSCF shall also add a "user" SIP URI parameter equals "phone" to the SIP URI; and
2. in case the response is forwarded to an AS that is located within the trust domain, the S-CSCF shall retain the access-network-charging-info parameter in the P-Charging-Vector header field; otherwise, the S-CSCF shall remove the access-network-charging-info parameter in the P-Charging-Vector header field.

When the S-CSCF receives the 200 (OK) response for a standalone transaction request, the S-CSCF shall: When the S-CSCF receives, destined for a served user, a target refresh request for a dialog, prior to forwarding the request, the S-CSCF shall: When the S-CSCF receives any response to the above request, the S-CSCF shall: When the S-CSCF receives any 1xx or 2xx response to the target refresh request for a dialog (whether the user is registered or not), the S-CSCF shall: When the S-CSCF receives, destined for the served user, a subsequent request other than target refresh request for a dialog, prior to forwarding the request, the S-CSCF shall: When the S-CSCF receives any response to the above request, the S-CSCF shall: When the S-CSCF receives a response to a a subsequent request other than target refresh request for a dialog, in case the response is 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. With the exception of 305 (Use Proxy) responses, the S-CSCF shall not recurse on 3xx responses.

The original dialog identifier is an implementation specific token that the S-CSCF encodes into the own S-CSCF URI in a Route header field, prior to forwarding the request to an AS. This is possible because the S-CSCF is the only entity that creates and consumes the value. The token may identify the original dialog of the request, so in case an AS acting as a B2BUA changes the dialog, the S-CSCF is able to identify the original dialog when the request returns to the S-CSCF. In a case of a standalone transaction, the token indicates that the request has been sent to the S-CSCF from an AS in response to a previously sent request. The token can be encoded in different ways, such as e.g., a character string in the user-part of the S-CSCF URI, a parameter in the S-CSCF URI or port number in the S-CSCF URI. The S-CSCF shall ensure that the value chosen is unique so that the S-CSCF may recognize the value when received in a subsequent message of one or more dialogs and make the proper association between related dialogs that pass through an AS. An original dialog identifier is sent to each AS invoked due to iFC evaluation such that the S-CSCF can associate requests as part of the same sequence that trigger iFC evaluation in priority order (and not rely on SIP dialog information that may change due to B2BUA AS).