Triple-Play Service Deployment

Chapter 7: Troubleshooting Video Service in the Field
The focus of QoS is upon metrics that can be instrumented and
provide direct insight into variables in network performance.
Consider the elapsed time from when the new channel is selected
on the remote to when the new program first appears on the
display. In this example, total elapsed time would be difficult to
instrument and it would not provide direct measurement of
network variables. The time to fill up the video buffers and decode
the new channel program is a delay or time component fixed by the
network design: STB decode buffer size, Group of Picture (GoP)
settings in the video flow, and delivery bite rates for the program.
Thus, a more revealing metric is one that measures the time from
sending the message to obtain the new channel to receipt of the
first video packet of the new channel. This metric measures the
network performance directly, the variable parameter of Internet
Group Management Protocol (IGMP) latency.
IGMP is the signaling protocol used to access broadcast video
services that use a multicast network design to efficiently manage
network bandwidth. IGMP enables each STB to obtain only the
programming that the viewer is interested in watching, conserving
bandwidth in the access network. In this implementation, a join
message is sent from the STB to the network.The join message asks
the network to send the requested program/channel to the STB by
joining a multicast group carrying the desired broadcast channel.
IGMP latency is the period between the time the join message is
sent and the time the first video packet is received by the STB.Thus,
IGMP latency is a measure of both service provisioning and the
network’s response performance.
Figure 7.3 shows an example of an IGMP message flow when a
broadcast program, Channel 2, is requested and then a channel
change to another program, Channel 3, is requested.
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