5 Functions of M1 interface for MBMS

36.4403GPPEvolved Universal Terrestrial Radio Access Network (E-UTRAN)General aspects and principles for interfaces supporting Multimedia Broadcast Multicast Service (MBMS) within E-UTRANRelease 17TS

5.1 General

“M1” Interface: MBMS GW – eNB

The M1 interface is the user plane interface of MBMS between MBMS GW and eNB. IP multicast is used to deliver the downlink packets over the M1 interface and there is no uplink data over M1 radio network layer. SYNC protocol (TS 25.446 [7]) is used over the M1 interface to keep the content synchronization for MBMS service data transmission.

5.2 Multicast group management function

IP multicast is used to deliver the packets over the M1 interface. The M1 interface has the function to manage the IP multicast groups. The MBMS GW maintains the IP multicast groups. The MBMS GW allocates the IP multicast group address when the session arrives, and may release it at session stop. At the eNB side, the eNB joins the IP multicast group to receive the MBMS User Plane data at session start, leaves the IP multicast group when the session stops, may leave the IP multicast group when the session suspends and may rejoin the IP multicast group when the session resumes.

5.3 Content synchronization function

The packets delivered over M1 interface will be synchronously transmitted by eNBs. To support the inter-eNB content synchronization, SYNC protocol layer is defined between BM-SC to eNB, which is used to carry additional information that enable eNBs to identify the timing for radio frame transmission and detect packet loss. Every packet in M1 contains the SYNC protocol information which is encapsulated at BM-SC.