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EDA 1200 Services

Figure 25 IP Multicasting using IGMP Snooping for Video Services

The way that a node subscribes and leaves a multicast group depends on the

IGMP version used. For version 2 and 3 the following messages apply:

• Join: The node sends a report (join) message to the multicast group

address.

• Leave: The node sends a leave message to the multicast group address.

IGMP snooping is the layer 2 function that optimizes IP Multicasting in a layer 2

network. A switch uses IGMP snooping to learn where to send multicast data

streams, and possibly also when to stop, even if the router has not stopped yet.

IGMP snooping may be combined with suppression (for example, forwarding

only one response to a query even though three responses were received from

the same port), in order to reduce signalling traffic.

The implementation of the multicast and IGMP functions depends on the node

they are implemented in. Please refer to:

• EDA 1200 Node User Guides for general EDA implementation

• EDA 1200 DSL Line Features description for IP DSLAM implementation

• EDA 1200 Fiber and Cat5 Line Features description for EFN324

implementation

3.3.1 Source Specific Multicast

With IGMPv3 (RFC 3376) a new mode has been introduced Source Specific

Multicast (SSM). The previous mode has been named Any Source Multicast

(ASM). The difference between SSM and ASM is that in SSM the client (for

example Set Top Box) specifies both the group address and the source (IP

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APC IP DSLAM Guide de l'utilisateur Page 39