APC IP DSLAM User's Guide download pdf (Page 38)

EDA 1200 System Overview

In Multicasting, a data stream is sent to a multicast group address in the

reserved range between 224.0.0.0 to 239.255.255.255. Routers distribute the

multicast streams using multicast routing protocols. Hosts (usually a Set Top

Box or a PC) can subscribe to the specific multicast group using the Internet

Group Multicast Protocol (IGMP). Routers and switches in the network will then

ensure that the subscribing hosts will receive the data stream.

Figure 24 IP Multicasting in the Network

A multicast router (or another designated multicast querier) sends queries

in order to find out whether there are interested nodes for multicast groups,

and whether the already subscribing nodes are still interested in receiving.

Interested nodes will then reply to the query. The query mechanism ensures

that the data stream will not be sent indefinitely, if a subscriber has just turned

off the set top box, thus not issuing a leave message.

IGMP is a protocol used by IP hosts and multicast routers to manage multicast

group membership. The IGMP messages depend on the IGMP version.

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APC IP DSLAM User's Guide Page 38