Triple-Play Service Deployment

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Solving Voice Quality Problems
Chapter 8: Troubleshooting VoIP
Even when phones are working, the quality may be unacceptable.
The problem may be either conversation quality or voice quality.
Conversation quality is impacted by dropped or incomplete calls,
voice clipping and silence suppression.Voice quality is impacted by
pops, clicks, garbled words, and echo. Poor quality is usually caused
by problems with the CPE, TDM, or network packet performance.
When attempting to resolve quality issues, it is important to
distinguish between controllable factors and non-controllable
factors. For instance, field technicians have limited control over
CPE performance, but they do have control of network
performance and its impact on CPE performance.
If a customer indicates that voice quality is bad, excessive echo is
present, and there are garbling and clicking sounds on the line,
the first step the technician must take is to verify the customer’s
complaint by evaluating quality from the end user’s perspective.
The test set is used in IP phone emulation mode to place test
calls. Based on whether or not same problem is observed on the
test set, the CPE can be ruled out or established as the cause of
the problem.
To establish subjective voice quality, the technician must listen to
a live test call for imperfections and monitor and correlate
network metrics to call imperfections. The handheld test set
enables the technician to test the line from multiple locations to
isolate the source of the trouble. In the enterprise, calls can be
placed from the next router down all the way through to the
ingress router to diagnose whether the problem is on the LAN or
on the WAN link. On the residential side, calls can be placed
outside the home where the copper pair terminates onto the
home wiring system or home networking system or the back of
the customer modem in order to further segment the problem.