ZyXEL Communications 4728F User Manual

Chapter 24 Multicast

XGS-4526/4528F/4728F User’s Guide

Once configured, the Switch maintains a forwarding table that matches the 
multicast stream to the associated multicast group.

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. 

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. 

Figure 103   MVR Multicast Television Example