ZyXEL Communications GS1920-48HPv2, Руководство пользователя

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Chapter 24 Multicast
GS1920v2 Series User’s Guide
204
Fig ure 144
MVR Network Example
Type s o f MVR Po rts
In MVR, a source port is a port on the Switch that can send and receive multicast traffic in a multicast
VLAN while a receiver port can only receive multicast traffic. Once configured, the Switch maintains a
forwarding table that matches the multicast stream to the associated multicast group.
MVR Mo de s
You can set your Switch to operate in either dynamic or compatible mode.
In dynamic mode, the Switch sends IGMP leave and join reports to the other multicast devices (such as
multicast routers or servers) in the multicast VLAN. This allows the multicast devices to update the
multicast forwarding table to forward or not forward multicast traffic to the receiver ports.
In compatible mode, the Switch does not send any IGMP reports. In this case, you must manually
configure the forwarding settings on the multicast devices in the multicast VLAN.
Ho w MVR Wo rks
The following figure shows a multicast television example where a subscriber device (such as a
computer) in VLAN 1 receives multicast traffic from the streaming media server,
S
, via the Switch.
Multiple subscriber devices can connect through a port configured as the receiver on the Switch.
When the subscriber selects a television channel, computer
A
sends an IGMP report to the Switch to join
the appropriate multicast group. If the IGMP report matches one of the configured MVR multicast group
addresses on the Switch, an entry is created in the forwarding table on the Switch. This maps the
subscriber VLAN to the list of forwarding destinations for the specified multicast traffic.
When the subscriber changes the channel or turns off the computer, an IGMP leave message is sent to
the Switch
to leave the multicast group. The Switch sends a query to VLAN 1 on the receiver port (in this
case, an uplink port on the Switch). If there is another subscriber device connected to this port in the
same subscriber VLAN, the receiving port will still be on the list of forwarding destination for the multicast
traffic. Otherwise, the Switch removes the receiver port from the forwarding table.