Section: 17 Usage of Diameter on Gmb interface
Content: Signalling between GGSN and BM-SC is exchanged at Gmb reference point. BM-SC functions for different MBMS bearer services may be provided by different physical network elements. To allow this distribution of BM-SC functions, the Gmb protocol must support the use of proxies to correctly route the different signalling interactions in a manner which is transparent to the GGSN. The GGSN uses the Gmb interface - to request authorisation/deactivation of a user for a multicast MBMS service, - to register/de-register the GGSN for receiving a multicast MBMS service. - to receive indication of session start, session update and session stop messages, which shall cause the GGSN, SGSN and RAN to set up/tear down the appropriate resources for the service. For further details, see 3GPP TS 23.246[ Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description ]  [65]. - to receive indication if IP multicast distribution to UTRAN should be used for the MBMS user plane data. The support of Gmb within the GGSN is optional, and needed for MBMS. The Gmb application is defined as an IETF vendor specific Diameter application, where the vendor is 3GPP. The vendor identifier assigned by IANA to 3GPP (http://www.iana.org/assignments/enterprise-numbers) is 10415. The Gmb application identifier value assigned by IANA is 16777223. The Gmb application identifier value shall be included in the Auth-Application-Id AVP. The BM-SC and the GGSN shall advertise the support of the Gmb application by including the value of the application identifier in the Auth-Application-Id AVP and the value of the 3GPP (10415) in the Vendor-Id AVP of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands as specified in IETF RFC 6733 [111], i.e. as part of the Vendor-Specific-Application-Id AVP. The Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands are specified in the Diameter Base Protocol.