SMC Networks 6924MT, Management Manual

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IGMP Multicast Filtering
Multicasting is used to support real-time applications such as video
conferencing or streaming audio. A multicast server does not have to
establish a separate connection with each client. It merely broadcasts its
service to the network, and any hosts which want to receive the multicast
register with their local multicast switch/router. Although this approach
reduces the network overhead required by a multicast server, the broadcast
traffic must be carefully pruned at every multicast switch/router it passes
through to ensure that traffic is only passed on the hosts which subscribed
to this service.
This switch uses IGMP (Internet Group Management Protocol) to query
for any attached hosts who want to receive a specific multicast service. The
switch looks up the IP Multicast Group used for this service and adds any
port which received a similar request to that group. It then propagates the
service request on to any neighboring multicast switch/router to ensure
that it will continue to receive the multicast service. (For more
information, see “IGMP Protocol” on page 4-7.)