B.12 Notification Access Type Change

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

When the P-CSCF receives an initial SIP REGISTER message or a SIP INVITE message from an attached UE, the P-CSCF may request from the PCF the information about the access type the UE is attached to using the procedure specified in clauses 4.2.2.2, 4.2.3.2 and 4.2.6.2.

NOTE 1: This procedure is not applicable for IMS registrations for Emergency sessions.

NOTE 2: The P-CSCF can request information about the access type as part of the SIP session setup when it is only interested in the related information when the IMS session is ongoing.

If the P-CSCF requests information about the access type, the P-CSCF shall also subscribe within the same Npcf_PolicyAuthorization service operation to notifications for changes of the access type used by the UE. The P-CSCF shall include an entry of the "AfEventSubscription" data type in the "events" attribute with the "event" attribute set to the value "ACCESS_TYPE_CHANGE".

When the P-CSCF receives from the PCF the access type:

– in the subscription request response within the HTTP response; or

– in the notification of access type change in an HTTP POST request from the PCF,

the P-CSCF shall store the access type information received within the "accessType" attribute and the RAT type information received within "ratType" attribute and use the received information as per P-CSCF procedures in 3GPP TS 24.229 [32].

The P-CSCF may receive subsequent notifications for changes of the access type from the PCF according to clause 4.2.5.2. When the P-CSCF receives a notification of the change of the access type used by the UE, the P-CSCF shall store the new access type information and RAT type information and use the received information as per P-CSCF procedures in 3GPP TS 24.229 [32].

NOTE 3: The subscription to receive information about the access type will be cancelled when the corresponding Individual Application Session Context resource is removed by the P-CSCF (i.e. when the UE is de‑REGISTERED or the related SIP call is released).