Triple-Play Service Deployment

Chapter 6: Troubleshooting Video in the Headend
far apart to synchronize. Incorrect descriptor tags for secondary
audio when the set top box tries to switch could also be
problematic. The error-causing scenarios are infinite. Turning up a
series of equipment with known good content and validating
reliable operation is a basic task; however, it is quite complex to go
live with real-time content from outside sources, and ramp up to a
high volume of services where real-time rate-shaping and
bandwidth management is being performed.
MPEG Transport Test and Visibility
TR 101-290 is an excellent tool, ideal for monitoring and validation.
But it lacks the functionality to support in-depth troubleshooting.
The use of error counters, as illustrated in Figure 6.5, helps extend
its usefulness as a troubleshooting tool as it provides visibility into
historical performance. For those sporadic, short-lived errors in the
MPEG transport that have a drastic effect on a decoder, it can be
very helpful to see the historical TR 101-290 performance. In this
instance, however, TR 101-290 provides only an idea of where to
look. For instance, TR 101-290 alarms in the PCR fields suggest
looking more closely at PCR performance. But, those problems
could be caused by a number of events directly and indirectly
connected to the PCR itself. The PCR values may have been
entered or modified incorrectly either at the encoder or at some
remux later in the broadcast chain; there may be excessive
network jitter; or packet loss may have disrupted the PCR spacing
in the stream.
Troubleshooting the MPEG stream with active analysis is required
to identify the source of these problems. The same is true for
structural items, including PID presence and identification in the
PAT and PMT tables.TR 101-290 will tell us if a PID referenced in the
PAT/PMT is not present in the stream, but without visibility into the
stream itself, it is impossible to know if that element is truly
missing or whether it is there and stamped with a different PID
number.
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