Broadcasting In UMTS

[mansoor2]

<table><tbody><tr><td><i>Broadcast and Multicast before Release 6</i>
To date, the following services (defined in R99 and R4) are available:
<ol><li>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
</li><li>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.
</li></ol>

<br><i>General Description of MBMS [2]</i>
3GPP has defined two modes of operation of MBMS
<ul><li>the broadcast mode
</li><li>the multicast mode
</li></ul>

<i>MBMS broadcast mode</i>
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.
<br>
<center>
<img src="http://www.3g4g.co.uk/Tutorial/ZG/Mbms/broadcast.gif">
</center>
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.
<i>MBMS multicast mode</i>
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. <br>
<center>
<img src="http://www.3g4g.co.uk/Tutorial/ZG/Mbms/multicast.gif">
</center>

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.
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