I.1A General

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

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 additional routeing functionality shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the priority treatment of transactions or dialogs shall be adjusted according to the most recently received authorized Resource-Priority header field or backwards indication value.

NOTE 1: 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.

NOTE 2: These SIP transactions are exempt from network management controls.

If logging is in progress for this dialog, check whether a trigger for stopping logging of SIP signalling has occurred, as described in RFC 8497 [140] and configured in the trace management object defined in 3GPP TS 24.323 [8K]. If a stop trigger event has occurred then stop logging of signalling, else determine, by checking its debug configuration, whether to log the response.

With the exception of 305 (Use Proxy) responses, the additional routeing functionality shall not recurse on 3xx responses.

If the additional routeing functionality inserts its own Record-Route header field, then the additional routeing functionality may require the periodic refreshment of the session to avoid hung states. If the network element requires the session to be refreshed, the additional routeing functionality shall apply the procedures described in RFC 4028 [58] clause 8.

NOTE 3: 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.

Based on local policy the additional routeing function shall add in requests and in responses in the P-Charging-Vector header field a "transit-ioi" header field parameter with an entry which identifies the operator network which the request or response is transitting or with a void entry.

Based on local policy the additional routeing function shall delete or void in requests and in responses in the P-Charging-Vector header field any received "transit-ioi" header field parameter value.