ZyXEL Communications GS3700 Series, Handbook

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Designing an IPTV Network
4.1 Introduction for IGMP
Before we begin designing an IPTV Network, there are 3 important
concepts of Zyxel’s IGMP (Internet Group Management Protocol) and
IGMP Snooping that administrators should be aware of.
4.1.1 What are General Queries and Group Specific Queries?
General Query : The querier will send query messages to the multicast
clients to learn which multicast groups still have active members within
the network.
Group Specific Query : When the client leaves a multicast group and
sends a leave group message, the querier will send this query message
to learn if a particular group has any other active members on a
downlink port.
4.1.2 What are IGMP Snooping Querier Modes?
There are 3 Querier Modes: Auto, Fixed and Edge.
Fixed : To have the Switch always use the port as an IGMP query port.
Select this when you connect an IGMP multicast server to the port.
Edge : Prevents the switch from using the port as an IGMP query port.
The Switch will not keep any record of an IGMP router being connected
to this port. The switch does not forward IGMP join or leave packets to
this port.
Auto : The port behaves as a Fixed port if the port receives any IGMP
queries. The port behaves as an Edge port if the port receives no IGMP
queries within a period of time.