Design Reference

join a TV channel and IGMP leaves to exit the channel. After a viewer changes channels, an
IGMPv2 leave for the old channel (multicast group) is issued, and a membership report for the new
channel is sent. If viewers change channels continuously, the number of joins and leaves can
become large, particularly if many viewers attach to the switch.
VSP 4000 supports more than a thousand joins and leaves per second, which is well adapted to TV
applications.
Important:
For IGMPv3, Avaya recommends that you ensure a join rate of 1000 per second or less. This
ensures the timely processing of join requests.
If you use the IGMP proxy functionality at the receiver edge, you reduce the number of IGMP
reports received by VSP 4000. This provides better overall performance and scalability.
Fast Leave
IGMP Fast Leave supports two modes of operation: single-user mode and multiple-user mode.
In single-user mode, if more than one member of a group is on the port and one of the group
members leaves the group, everyone stops receiving traffic for this group. A group-specific query is
not sent before the effective leave takes place.
Multiple-user mode allows several users on the same port or VLAN. If one user leaves the group
and other receivers exist for the same stream, the stream continues. The switch tracks the number
of receivers that join a given group. For multiple-user mode to operate properly, do not suppress
reports. This ensures that the switch properly tracks the correct number of receivers on an interface.
The Fast Leave feature is particularly useful in IGMP-based TV distribution where only one receiver
of a TV channel connects to a port. If a viewer changes channels quickly, you create considerable
bandwidth savings if you use Fast Leave.
You can implement Fast Leave on a VLAN and port combination; a port that belongs to two different
VLANs can have Fast Leave enabled on one VLAN (but not on the other). Thus, with the Fast Leave
feature enabled, you can connect several devices on different VLANs to the same port. This
strategy does not affect traffic after one device leaves a group to which another device subscribes.
For example, you can use this feature when two TVs connect to a port through two set-top boxes,
even if you use the single-user mode.
To use Fast Leave, you must first enable explicit host tracking. IGMP uses explicit host tracking to
track all source and group members. Explicit host tracking is disabled by default. For configuration
information, see Configuring IP Multicast Routing Protocols on Avaya Virtual Services Platform 4000
Series , NN46251–504.
Last member query interval tuning
If an IGMPv2 host leaves a group, it notifies the router by using a leave message. Because of the
IGMPv2 report suppression mechanism, the router cannot access information of other hosts that
require the stream. Thus, the router broadcasts a group-specific query message with a maximum
response time equal to the last member query interval (LMQI).
Because this timer affects the latency between the time that the last member leaves and the time
the stream actually stops, you must properly tune this parameter. This timer can especially affect TV
delivery or other large-scale, high-bandwidth multimedia applications. For instance, if you assign a
value that is too low, this can lead to a storm of membership reports if a large number of hosts are
subscribed. Similarly, assigning a value that is too high can cause unwanted high-bandwidth stream
IP multicast network design
112 Network Design Reference for Avaya VSP 4000 Series December 2014
Comments? [e-mail]