The MBMS architecture is based on the following principles:
- MBMS architecture shall enable the efficient usage of radio-network and core-network resources, with the main focus on the radio interface efficiency. Specifically, multiple users should be able to share common resources when receiving identical traffic.
- The MBMS architecture shall support common features for MBMS multicast and broadcast modes, e.g. both modes shall preferably use the same low-layer bearer for data transport over the radio interface.
- The MBMS architecture does not describe the means by which the BM-SC obtains the service data. The data source may be external or internal to the PLMN e.g content servers in the fixed IP network, any UE attached to the PLMNMBMS shall support both IP multicast and IP unicast sources.
- MBMS architecture should re-use, to the extent possible, existing 3GPP network components and protocol elements thus minimizing necessary changes to existing infrastructure and providing a solution based on well-known concepts.
- MBMS shall be a point-to-multipoint bearer service for IP packets in the PS domain.
- MBMS shall be interoperable with IETF IP Multicast.
- MBMS shall support IETF IP Multicast addressing.
- It shall be possible for UEs to receive MBMS when the terminal is attached.
- It shall be possible for UEs to receive MBMS data in parallel to other services and signalling (e.g. paging, voice call).
- MBMS shall support different quality of service levels. The mechanisms for this are for further study, one example is repetitions to all users.
- MBMS service areas shall be defined per individual service with a per cell granularity.
- MBMS is not supported in the CS domain.
- When the UE is already receiving data of an MBMS service, it shall be possible for the UE to be notified about a forthcoming and potentially about an ongoing data transfer from other MBMS services.
- Charging data shall be provided per subscriber for MBMS multicast mode .
- The MBMS bearer service concept should contain the decision making process for selection of point-to-point or point-to-multipoint configurations.
- The architecture should be able to provide home MBMS multicast services to users when roaming outside their home network as subject to interoperator agreements.
- MBMS should be designed to minimise power consumption within the mobile station.
- Applications shall be tolerant to packet loss and duplication caused by e.g. UE mobility or transmission loss.
- The backwards compatibility of the MBMS service to the R99 IP multicast delivery mechanism shall be considered. Interworking possibilities between MBMS capable network elements and non-MBMS capable network elements (e.g. interworking with R99 IP Multicast service GGSNs) shall be described.
- The MBMS standard should avoid placing excessive signalling load requirements on the network. In particular, the MBMS standard should permit operators to configure their networks so that when a UE, which is not actually receiving a media stream, changes between GSM and UMTS cells in the same Routeing Area, there is no significant signalling traffic load on the network.
MBMS Architecture is as shown above. The dotted lines means functions / reference points that are optional. Gp applies only when SGSN and GGSN are in different PLMN.
SGSN: In the MBMS architecture the SGSN performs user individual service control functions and the SGSN concentrates all individual users of the same MBMS service into a single MBMS service. The SGSN maintains a single connection with the source of the MBMS data.
GGSN: The GGSN terminates the MBMS GTP tunnels from the SGSN and links these tunnels via IP multicast with the MBMS data source.
BM-SC: The BM-SC is an MBMS data source. MBMS data may be scheduled in the BM-SC, e.g. for transmission to the user every hour. It offers interfaces over that content provider can request data delivery to users. The BM-SC may authorise and charge content provider.
MBMS Data Sources: The architecture allows for other MBMS broadcast/multicast data sources. Internal data sources may directly provide their data. Data delivery by external sources is controlled by Border Gateways (BG) which may allow for example data from single addresses and ports to pass into the PLMN for delivery by an MBMS service.
Optional Network Elements:
- The SGSN may use CAMEL to handle pre-paid services, e.g. credit checking for on-line charging.
- The Cell Broadcast Centre (CBC) may be used to announce MBMS services to the users. How this is accomplished is FFS.
- The BM-SC might use OSA-SCS to interact with third parties.