Using Mvr In A Multicast Television Application - Cisco 2950 - Catalyst Switch Configuration Manual

Chapter 21 Configuring IGMP Snooping and MVR
Understanding Multicast VLAN Registration

Using MVR in a Multicast Television Application

In a multicast television application, a PC or a television with a set-top box can receive the multicast
stream. Multiple set-top boxes or PCs can be connected to one subscriber port, which is a switch port
configured as an MVR receiver port. Figure 21-3 is an example configuration. DHCP assigns an IP
address to the set-top box or the PC. When a subscriber selects a channel, the set-top box or PC sends
an IGMP report to Switch A to join the appropriate multicast. If the IGMP report matches one of the
configured multicast MAC addresses, the switch CPU modifies the hardware address table to include this
receiver port and VLAN as a forwarding destination of the specified multicast stream when it is received
from the multicast VLAN. Uplink ports that send and receive multicast data to and from the multicast
VLAN are called MVR source ports.
When a subscriber changes channels or turns off the television, the set-top box sends an IGMP leave
message for the multicast stream. The switch CPU sends an IGMP group-specific query through the
receiver port VLAN. If there is another set-top box in the VLAN still subscribing to this group, that
set-top box must respond within the maximum response time. If the CPU does not receive a response, it
eliminates the receiver port as a forwarding destination for this group.
If the Immediate-Leave feature is enabled on a receiver port, the port leaves a multicast group more
quickly. Without Immediate Leave, when the switch receives an IGMP leave message from a subscriber
on a receiver port, it sends out an IGMP query on that port and waits for IGMP group membership
reports. If no reports are received in a configured time period, the receiver port is removed from multicast
group membership. With Immediate Leave, an IGMP query is not sent from the receiver port on which
the IGMP leave was received. As soon as the leave message is received, the receiver port is removed
from multicast group membership, which speeds up leave latency. Enable the Immediate Leave feature
only on receiver ports to which a single receiver device is connected.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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