3Com 7700 Configuration Manual page 125

Figure 5 Multicast Packet Transmission with IGMP Snooping
Multicast router
Layer 2
Ethernet switch
Video stream
Multicast
Nonmulticast
group
group
member
member
Implement IGMP Snooping
This section introduces related switch concepts of IGMP Snooping:
Router Port: The port directly connected to the multicast router.
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Multicast member port: The port connected to the multicast member. The
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multicast member refers to a host joined a multicast group.
MAC multicast group: The multicast group is identified with MAC multicast
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address and maintained by the Switch 7700.
Router port aging time: Time set on the router port aging timer. If the switch
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has not received any IGMP general query message before the timer times out,
it considers the port no longer a router port.
Multicast group member port aging time: When a port joins an IP multicast
■
group, the aging timer of the port begins timing. The multicast group member
port aging time is set using this timer. If the switch has not received any IGMP
report message before the timer times out, it transmits IGMP specific query
message to the port.
Maximum response time: When the switch transmits IGMP specific query
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message to the multicast member port, the Switch 7700 starts a response
timer, which times before the response to the query. If the switch has not
received any IGMP report message before the timer times out, it will remove
the port from the multicast member ports
The Switch 7700 runs IGMP Snooping to listen to the IGMP messages and map
the host and its ports to the corresponding multicast group address. To implement
IGMP Snooping, Switch 7700 processes different IGMP messages in the way
illustrated in the figure below:
Internet/Intranet
Video stream
Video
Video stream
stream
Nonmulticast
group
member
IGMP Snooping 117
Video stream
VOD server