Question: What is the purpose of including the Gmb application identifier value in the Auth-Application-Id AVP?
Option 1: To indicate support for IP multicast distribution to UTRAN.
Option 2: To request authorisation/deactivation of a user for a multicast MBMS service.
Option 3: To register/de-register the GGSN for receiving a multicast MBMS service.
Option 4: To advertise the support of the Gmb application by the BM-SC and the GGSN.
Explanation: The correct answer is Option 4 because including the Gmb application identifier value in the Auth-Application-Id AVP allows the BM-SC and the GGSN to advertise their support for the Gmb application, which is necessary for MBMS. This is specified in IETF RFC 6733 as part of the Vendor-Specific-Application-Id AVP.