Internet Group Membership Authentication Protocol - Avaya 8800 Planning And Engineering

Multicast network design
number of hosts are subscribed. Similarly, assigning a value that is too high can cause
unwanted high-bandwidth stream propagation across the network if users change channels
rapidly. Leave latency is also dependent on the robustness value, so a value of two equates
to a leave latency of twice the LMQI.
Determine the proper LMQI setting for your particular network through testing. If a very large
number of users are connected to a port, assigning a value of three may lead to a storm of
report messages when a group-specific query is sent. Conversely, if streams frequently start
and stop in short intervals, as in a TV delivery network, assigning a value of ten may lead to
frequent congestion in the core network.
Another performance-affecting factor that you need to be aware of is the error rate of the
physical medium. It also affects the proper choice of LMQI values. For links that have high
packet loss, you may find it necessary to adjust the robustness variable to a higher value to
compensate for the possible loss of IGMP queries and reports.
In such cases, leave latency is adversely impacted as numerous group-specific queries are
unanswered before the stream is pruned. The number of unanswered queries is equal to the
robustness variable (default two). The assignment of a lower LMQI may counterbalance this
effect. However, if you set it too low it may actually exacerbate the problem by inducing storms
of reports on the network. Keep in mind that LMQI values of three and ten, with a robustness
value of two, translate to leave latencies of six tenths of a second and two seconds,
respectively.
When you choose a LMQI, consider all of these factors to determine the best setting for the
given application and network. Test that value to ensure that it provides the best performance.
Important:
In networks that have only one user connected to each port, Avaya recommends that you
use the Fast Leave feature instead of LMQI, since no wait is required before the stream
stops. Similarly, the robustness variable does not impact the Fast Leave feature, which is
an additional benefit for links with high loss.

Internet Group Membership Authentication Protocol

Internet Group Membership Authentication Protocol (IGAP) is a multicast authentication and
accounting protocol. With IGAP authentication and accounting features, service providers and
enterprises can manage and control multicast groups on their networks.
IGAP is an IETF Internet draft that extends the functionality of the Internet Group Management
Protocol (IGMPv2) and uses a standard authentication server with IGAP extensions.
212 Planning and Engineering — Network Design November 2010