User guide

Telephony and Multimedia Services
1/1551-HSC 901 35/3 Uen C 2005-12-02
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8.6 Multicast Handling
The EDA system supports IP multicasting, which is especially suitable for
multimedia services in order to avoid overloading the network for example if
more end-users receive video over IP simultaneously.
Multicasting actually means that a network node sends a packet addressed
to a special group address. Nodes that are interested in this group register
to receive packets addressed to the group. IP multicasting is a method to
utilize the available bandwidth in an effective way. Instead of broadcasting
all packets only one multicast packet is transmitted. The switches and
routers will transmit the packet to the members of the multicast group only.
When using IGMP snooping the switch listens to IGMP messages to build a
mapping table and associate forwarding filters. It dynamically configures
the switch ports to forward IP multicast traffic only to those ports associated
with multicast hosts.
In this way the IP multicast technology:
− reduces the total traffic load in the network by eliminating
unnecessary traffic.
− only requested broadcasts is transmitted downstream
− only one downstream to several listeners
In the EDA network multicasting groups can be established, so that video
transmissions are sent only to the members of the multicast group. The
IGMP protocol handles packet inspection to ensure that the packet is
transmitted to the multicast group members only. This is also called IGMP
snooping. This is illustrated in Figure 54 on page 80,.