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LTE (3G till Rel 6 - MBMS) - 14

MBMS [Under LTE > 3G till Rel 6]
» MBMS stage 1 - 22.146, Rel 6 «
» MBMS architecture - 23.246, Rel 6 «
» MBMS in RAN - 25.346, Rel 6 «

In this article, we will look at an important feature, MBMS, added in Rel 6 for both GSM and UMTS. MBMS stand for Multimedia Broadcast and Multicast Service.

Service indicate that an end-to-end support is needed in RAN and CN.

Multimedia indicate support for (user data containing) multiple media formats (like audio, video, text, picture etc.).

Broadcast indicate that the service is of broadcast type i.e. of point-to-multipoint type and available to all users.

Multicast indicate that the service is of multicast type i.e. of point-to-multipoint type and available to set of users (belonging to certain group).

As a whole, MBMS provide end-to-end support (from content provider till terminals) for Multimedia (packet switched) data transfer in Broadcast and Multicast modes.

Broadcast data is available to all users whereas multicast data is meant for set of users.

In both broadcast and multicast, the transmission is going to be common (mostly) and one-way i.e. there is no return path (feedback loop). If feedback loop is provided, it has to be provided one per user and this would spoil the main purpose.

The idea behind broadcast/multicast transmission is to save resources by using (small amount of) common point-to-multipoint resources rather than individual (number of) point-to-point resources. MBMS goes a step further: in multicast mode, depending on number of users, network can choose an approach - either point-to-point (unicast) or point-to-multipoint transmissions - that would result in optimum use of resources on a cell by cell basis. In multicast mode,
- user need to specifically make a request to network to join (and leave) the particular service
- network can initiate recounting procedure
This way, network remain aware of number of users tuned to particular multicast service and can maintain resource optimisation.

It is apparent that MBMS service is suitable for specific types of data like streaming data. Some popular applications of MBMS could be: 1) live transmission of major events like soccer games, award ceremonies, 2) repeated or time scheduled transmission of music, movies, advertisements, network welcome messages, highlights of games, news, weather etc.

Each MBMS service consists of number of sessions; each session has start, stop with data transfer/idle periods in between as shown in an example below. Each MBMS service has phases: Subscription (multicast only) - Service announcement - Joining (multicast only) - Session start - MBMS notification - Data transfer - Session stop - Leaving (multicast only).



In next article, we will have a look at changes needed for implementing MBMS support in UTRAN.

References: 3G Evolution: HSPA and LTE by Dahlman, Parkvall, Sköld, and Beming, release 6 document at 3GPP.

Copyright © Samir Amberkar 2010-11§

3G till Rel 6 - Updated L2 stack « LTE Index » 3G till Rel 6 - MBMS cont.