Content for  TS 24.229  Word version:  18.4.0

Upon receipt of an initial request or a stand-alone transaction, the S-CSCF shall:

• perform the procedures for the UE-originating case as described in subclause 5.4.3.2 if the request makes use of the information for UE-originating calls, which was added to the Service-Route header field entry of the S-CSCF during registration (see subclause 5.4.1.2.2F), e.g. the message is received at a certain port or the topmost Route header field contains a specific user part or parameter; or,
• perform the procedures for the UE-originating case as described in subclause 5.4.3.2 if the topmost Route header field of the request contains the "orig" parameter. The S-CSCF shall remove the "orig" parameter from the topmost Route header field; or,
• perform the procedures for the UE-terminating case as described in subclause 5.4.3.3 if this information is not used by the request.

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 of 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 from the UE an initial request for a dialog, which contains a GRUU and an "ob" SIP URI parameter in the Contact header field, and multiple contact addresses have been registered for the specific GRUU, then for all subsequent in-dialog requests sent toward the UE's, the S-CSCF shall populate the Request-URI with the registered contact address from which the UE sent the initial request for the dialog. When performing SIP digest without TLS, when the S-CSCF receives from the served user an initial request for a dialog or a request for a standalone transaction, the S-CSCF may perform the steps in subclause 5.4.3.6 to challenge the request based on local policy. When performing GPRS-IMS-Bundled authentication, when the S-CSCF receives from the served user an initial request for a dialog or a request for a standalone transaction, the S-CSCF shall check whether a "received" header field parameter exists in the Via header field provided by the UE. If a "received" header field parameter exists, S-CSCF shall compare the (prefix of the) IP address received in the "received" header field parameter against the UE's IP address (or prefix) stored during registration. If no "received" header field parameter exists in the Via header field provided by the UE, then S-CSCF shall compare the (prefix of the) IP address received in the "sent-by" parameter against the IP address (or prefix) stored during registration. If the stored IP address (or prefix) and the (prefix of the) IP address in the "received" Via header field parameter provided by the UE do not match, the S-CSCF shall reject the request with a 403 (Forbidden) response. In case the stored IP address (or prefix) and the (prefix of the) IP address in the "received" Via header field parameter provided by the UE do match, the S-CSCF shall proceed as described in the remainder of this subclause. If the S-CSCF supports HSS based P-CSCF restoration, and receives a request from a P-CSCF that the S-CSCF considers is not reachable, the S-CSCF shall consider this P-CSCF as being reachable. If the S-CSCF supports PCRF based P-CSCF restoration, and receives a request from a P-CSCF that the S-CSCF considers is in a not reachable, the S-CSCF shall consider this P-CSCF as being reachable. When the S-CSCF receives from the served user or from a PSI 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 (see step 3) 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: When the S-CSCF receives, an initial request for a dialog or a request for a standalone transaction, from an AS acting on behalf of an unregistered user, the S-CSCF shall: When the S-CSCF receives a request initiated by the served user for which the S-CSCF does not have the user profile or does not trust the data that it has (e.g. due to restart), the S-CSCF shall attempt to retrieve the user profile from the HSS. If the S-CSCF receives a Diameter result code of DIAMETER_UNABLE_TO_COMPLY as defined in TS 29.228, the S-CSCF supports S-CSCF restoration procedures, and the Request-URI of the request does not match an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031, then the S-CSCF shall:

1. reject the request by returning a 504 (Server Time-out) response to the UE;
2. assume that the UE supports version 1 of the XML Schema for the 3GPP IM CN subsystem XML body if support for the 3GPP IM CN subsystem XML body as described in subclause 7.6 in the Accept header field is not indicated; and
3. include in the 504 (Server Time-out) response:
   • a Content-Type header field with the value set to associated MIME type of the 3GPP IM CN subsystem XML body as described in subclause 7.6.1;
   • a P-Asserted-Identity header field set to the value of the SIP URI of the S-CSCF included in the Service-Route header field (see subclause 5.4.1.2.2F) during the registration of the user whose UE sent the request causing this response; and
   • a 3GPP IM CN subsystem XML body:
     1. an <ims-3gpp> element with the "version" attribute set to "1" and with an <alternative-service> child element, set to the parameters of the alternative service;
        1. a <type> child element, set to "restoration" (see table 7.6.2) to indicate that S-CSCF restoration procedures are supported;
        2. a <reason> child element, set to an operator configurable reason; and
        3. an <action> child element, set to "initial-registration" (see table 7.6.3).

Depending on operator configuration (see subclause 5.4.1.8), when the S-CSCF receives a request with a Request-URI that does not match an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031, the request initiated by the served user for which the S-CSCF has modified but not synchronized the service profile for the served user and the S-CSCF supports S-CSCF restoration procedures, then the S-CSCF shall reject the request as described in items I), II) and III). 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 5; 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 served 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 served 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 containing a Relayed-Charge header field, and the next hop is not an AS, the S-CSCF shall remove the Relayed-Charge header field from the forwarded response. When the S-CSCF receives any response to the above request, the S-CSCF may: When the S-CSCF receives any response to the above request, the S-CSCF shall: When the S-CSCF receives any response to the above request containing a "term-ioi" header field parameter in the P-Charging-Vector header field, the S-CSCF shall: When the S-CSCF receives any 1xx or 2xx response to the initial request for a dialog, if the response corresponds to an INVITE request, the S-CSCF shall save the Contact and Record-Route header field values in the response in order to be able to release the session if needed. When the S-CSCF receives any 1xx or 2xx response to an initial request for a dialog or a request for a standalone transaction, if the response is forwarded within the S-CSCF home network and not to an AS, the S-CSCF shall insert a P-Charging-Function-Addresses header field populated with values received from the HSS. When the S-CSCF, upon sending an initial INVITE request that includes an IP address in the SDP offer (in "c=" parameter), receives an error response indicating that the IP address type is not supported, (e.g., the S-CSCF receives the 488 (Not Acceptable Here) with 301 Warning header field indicating "incompatible network address format"), the S-CSCF shall either:

• fork the initial INVITE request to the IBCF; or
• process the error response and forward it using the Via header field.

When the S-CSCF receives from the 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 an INVITE dialog, the S-CSCF shall replace the saved Contact header field values in the response such that the S-CSCF is able to release the session if needed. If the S-CSCF inserted in the initial request for the dialog the header field parameters into the Feature-Caps header field then the S-CSCF 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. When the S-CSCF receives from the served user a subsequent request other than 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: With the exception of 305 (Use Proxy) responses, the S-CSCF shall not recurse on 3xx responses.