MBMS is a point-to-multipoint service in which data is transmitted from a single source entity to multiple recipients. Transmitting the same data to multiple recipients allows network resources to be shared. The MBMS bearer service offers two modes:

• Broadcast Mode;
• Multicast Mode.

Broadcast Mode is supported for EPS and GPRS, and Multicast Mode is supported for GPRS. MBMS for EPS supports E-UTRAN and UTRAN. MBMS for GPRS supports UTRAN and GERAN. MBMS architecture enables the efficient usage of radio-network and core-network resources, with an emphasis on radio interface efficiency. MBMS is realised by the addition of a number of new capabilities to existing functional entities of the 3GPP architecture and by addition of a number of new functional entities. The existing PS Domain functional entities (GGSN, SGSN, MME, E-UTRAN, UTRAN, GERAN and UE) are enhanced to provide the MBMS Bearer Service. In the EPS a functional entity MBMS GW exists at the edge between the CN and the BM-SC. In the bearer plane, this service provides delivery of IP Multicast datagrams from the Gi and SGi-mb reference points to UEs with a specified Quality of Service. In the control plane, this service provides mechanisms for:

• managing the MBMS bearer service activation status of UEs (in the case of multicast mode);
• outsourcing authorisation decisions to the MBMS User Service (i.e. to the BM-SC) (in the case of multicast mode);
• providing control of session initiation/modification/termination by the MBMS User Service and managing bearer resources for the distribution of MBMS data (in the case or multicast and broadcast modes).

A particular instance of the MBMS Bearer Service is identified by an IP Multicast Address and an APN Network Identifier. A TMGI also can be used to identify one MBMS Bearer Service inside one PLMN. For GPRS the boundary of the MBMS Bearer Service is the Gmb and Gi reference points as shown in Figure 1a below. The former provides access to the control plane functions and the latter the bearer plane. For EPS the boundary is the SGmb and the SGi-mb as shown in Figure 1b below. A functional entity, the Broadcast Multicast Service Centre (BM-SC) provides a set of functions for MBMS User Services. BM-SC functions for different MBMS User Services may be supported from the same or different physical network elements.