A.14 Notification of PLMN Change
29.2143GPPPolicy and charging control over Rx reference pointRelease 17TS
When the P-CSCF receives an initial REGISTER SIP message from an attached UE, the P-CSCF may subscribe to notifications of PLMN ID changes corresponding to the PLMN where the UE is located using the procedure specified in clause 4.4.6.9.
When the P-CSCF receives the AA-Answer or RA-Request from the PCRF, the P-CSCF stores the PLMN identifier received within 3GPP-SGSN-MCC-MNC AVP and behaves as defined in 3GPP TS 24.229 [17].
The P-CSCF shall cancel the subscription to notification for changes of the PLMN used by the UE when the user is de-registered from the IM CN subsystem.