5.9 Routing of mid-session signalling

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

During the signalling exchanges that occur to establish an IM Session, the following elements must ensure future signalling messages related to this session are routed through them:

– P‑CSCF serving the originating UE, in order to generate the CDR record in the roaming case, and to force release of the resources used for the session.

– S‑CSCF serving the originating UE, in order to invoke any service logic required at session setup completion, and to generate the CDR record at session termination.

– S‑CSCF serving the terminating UE, in order to invoke any service logic required at session setup completion, and to generate the CDR record at session termination.

– P‑CSCF serving the terminating UE, in order to generate the CDR record in the roaming case, and to force release of the resources used for the session.

Other CSCFs (e.g. I‑CSCFs) may optionally request this as well, for example if they perform some function needed in handling mid-session changes or session clearing operations.

All signalling message from the UE related to IMS sessions shall be sent to the P‑CSCF.