The Routing Area Update procedure transfers the MBMS UE Context status between UE and SGSN. This MBMS UE Context status identifies MBMS UE contexts, which are lost or deactivated only on one side. All MBMS UE Contexts, which are active on one side only shall be deactivated locally. If the UE wishes to re-activate the related MBMS bearer service, it shall join the MBMS bearer service again. See clause 8.2 "MBMS Multicast Service Activation"
The UE sends Routeing Area Update Request to the SGSN. It includes the MBMS UE Context status, which indicates the UE's active MBMS UE Contexts.
The SGSN sends Routeing Area Update Accept to the UE. It includes the MBMS UE Context status, which indicates the UE's MBMS UE Contexts that are stored in the SGSN.
An SGSN that supports MBMS shall indicate MBMS feature support to the UE during Routing Area Update procedure in the Routing Area Update Accept message and during GPRS attach procedure in the Attach Accept message. The UE then knows it can use already activated MBMS bearers, or activate new MBMS bearers according to clause 8.2 "MBMS Multicast Service Activation"
An SGSN that does not support MBMS will not indicate MBMS feature support to the UE. This indicates to the UE that MBMS bearers are no longer supported, which may allow the UE to use point-to-point bearers for MBMS data transfer. In this case, the UE shall deactivate all active MBMS UE Contexts locally.