Introduction
Point to multipoint services exist today which allow data from a single source entity to be transmitted to multiple endpoints. These services are expected to be used extensively over wireless networks, hence there is a need for a capability in the PLMN to efficiently support them. The Multimedia Broadcast/Multicast Service (MBMS) will provide this capability for such broadcast/multicast services provided by the home environment and other VASPs.
MBMS is an IP datacast (IPDC) service that can be offered via exsiting UMTS and GSM networks. It would be possible for the user to interact with this service via an uplink channel. This feature causes this service to be more complicated as it is not as straightforward as a Unicast service like conventional digital telivision.
MBMS is a UMTS release 6 feature and according to [1] it is already very popular with operators and equipment manafacturers. It is expected that Networks would be supporting MBMS by Q4, 2007 while UE's will be supporting MBMS by Q2, 2008. As per [1], 30% of UE's will be supporting MBMS by 2010. Release 6 was finalised in June 2005.
It is important to note that MBMS is not just a technology to preserve capacity or reduce costs - by providing an efficient means to reliably distribute multimedia content over 3G networks but also an opportunity for 3G network operators to deliver new and innovative revenue-generating services to their subscribers.
Difference between Broadcast and Multicast
| BROADCAST | MULTICAST |
|---|---|
| Broadcast service is a unidirectional point-to-multipoint service in which data is transmitted from single source to multiple UE's in the associated broadcast area | Muticast service is a unidirectional point-to-multipoint service in which data is transmitted from single source to Multicast group in associated Multicast area. |
| These are push type services. The end user does not have to subscribe to be part of broadcast group | The end user has to be part of Multicast group to receive them. |
| No interaction possible | Interaction possible. In this case multicast users have a return channel for the interaction procedure. |
| They are free | They could be free or paid type. |
Broadcast and Multicast before Release 6
To date, the following services (defined in R99 and R4) are available:
- A cell broadcast service (CBS) [15, 16] allowing for low bit-rate data to be transmitted to all subscribers in a set of given cells over a shared broadcast channel. This service offers a message-based service
- An IP-Multicast service [13, 14] allowing for mobile subscribers to receive multicast traffic. This service does not allow for multiple subscribers to share radio or core network resources and as such does not offer any advantages as far as resource utilization within the PLMN and over the radio access network.
General Description of MBMS [2]
3GPP has defined two modes of operation of MBMS
- the broadcast mode
- the multicast mode
MBMS broadcast mode
The broadcast mode is a unidirectional point-to-multipoint transmission of multimedia data (e.g. text, audio, picture, video) from a single source entity to all users in a broadcast service area. The broadcast mode is intended to efficiently use radio/network resources e.g. data is transmitted over a common radio channel. Data is transmitted in the broadcast service area as defined by the network (Home environment). MBMS data transmission should adapt to different RAN capabilities or different radio resource availability, e.g. by reducing the bitrate of the MBMS data.
Figure above gives an example of how a network can be configured to broadcast a variety of high bit rate services to users within the associated broadcast service area. A broadcast service received by the UE, involves one or more successive broadcast sessions. A broadcast service might, for example, consist of a single on-going session (e.g. a media stream) or may involve several intermittent sessions over an extended period of time (e.g. messages).
The difference between the CBS of R99 and Broadcast of R6 is that CBS is used for low bit rate services (messaging) while the broadcast mode enables the broadcast of multimedia services (Audio, Video etc).
An example of a service using the broadcast mode could be advertising or a welcome message to the network. As not all users attached to the network may wish to receive these messages then the user shall be able to enable/disable the reception of these broadcast service on his UE. The broadcast mode differs from the multicast mode in that there is no specific requirement to activate or subscribe to the MBMS in broadcast mode.
The broadcast mode should allow terminals to minimise their power consumption. It is expected that charging data for the end user will not be generated for this mode. The reception of the traffic in the broadcast mode is not guaranteed. The receiver may be able to recognize data loss.
MBMS multicast mode
The multicast mode allows the unidirectional point-to-multipoint transmission of multimedia data (e.g. text, audio, picture, video) from a single source point to a multicast group in a multicast service area. The multicast mode is intended to efficiently use radio/network resources e.g. data is transmitted over a common radio channel. Data is transmitted in the multicast service area as defined by the network (Home environment). In the multicast mode there is the possibility for the network to selectively transmit to cells within the multicast service area which contain members of a multicast group. MBMS data transmission should adapt to different RAN capabilities or different radio resource availability, e.g. by reducing the bitrate of the MBMS data.
A multicast service received by the UE, involves one or more successive multicast sessions. A multicast service might, for example, consist of a single on-going session (e.g. a multimedia stream) or may involve several intermittent multicast sessions over an extended period of time (e.g. messages). An example of a service using the multicast mode could be a football results service for which a subscription is required.
Unlike the broadcast mode, the multicast mode generally requires a subscription to the multicast subscription group and then the user joining the corresponding multicast group. The subscription and group joining may be made by the PLMN operator, the user or a third party on their behalf (e.g. company). Unlike the broadcast mode, it is expected that charging data for the end user will be generated for this mode.
Reception of multicast services cannot be guaranteed over the access network. For many applications and services guaranteed data reception may be carried out by higher layer services or applications which make use of MBMS. Multicast mode should allow terminals to minimise their power consumption.
The multicast mode defined in this specification should not be confused with IP Multicast (discussed above). There are similarities between these two services and such similarities may be exploited in 3GPP networks given that 3GPP multicast mode has been defined with consideration to maximizing efficiency on the radio interface and of network resources.
Multicast mode shall be inter-operable with IETF IP Multicast. This could allow the best use of IP service platforms to help maximize the availability of applications and content so that current and future services can be delivered in a more resource efficient manner. Figure above shows a general high level overview of multicast mode network.