Nortel business policy switch 2000, User Manual

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Chapter 2 Network configuration 129
Using the Business Policy Switch 2000 Version 2.0
Multicast stream from exiting any other port that does not connect to another host
member, thus conserving bandwidth. The following section describes how
Business Policy Switches provide the same benefit as IP Multicast routers, but in
the local area.
IGMP is used by IP Multicast routers to learn about the existence of host group
members on their directly attached subnets (see RFC 2236). The IP Multicast
routers get this information by broadcasting IGMP queries and listening for IP
hosts reporting their host group memberships. This process is used to set up a
client/server relationship between an IP Multicast source that provides the data
streams and the clients that want to receive the data.
Figure 35 shows how IGMP is used to set up the path between the client and
server. As shown in this example, the IGMP host provides an IP Multicast stream
to designated routers that forward the IP Multicast stream on their local network
only if there is a recipient.
The client/server path is set up as follows:
1 The designated router sends out a host membership query to the subnet and
receives host membership reports from end stations on the subnet.
2 The designated routers then set up a path between the IP Multicast stream
source and the end stations.
3 Periodically, the router continues to query end stations on whether or not to
continue participation.
4 As long as any client continues to participate, all clients, including
nonparticipating end stations on that subnet, receive the IP Multicast stream.
IP Multicast can be optimized in a LAN by using IP Multicast filtering switches,
such as the Business Policy Switch.
As shown in Figure 35 , a non-IP Multicast filtering switch causes IP Multicast
traffic to be sent to all segments on the local subnet.
Note:
Although the nonparticipating end stations can filter the IP
Multicast traffic, the IP Multicast traffic still exists on the subnet and
consumes bandwidth.