EXTender 1100A Switch and Remote Module System Administrator’s
Guide
75
Echo Problems
Understanding and Correcting Echo Problems
The Switch Module and Remote Module employ the industry standard G.165 echo
canceller with some proprietary improvements to help eliminate or reduce echo. However,
it is not possible to cancel all instances of echo 100% of the time. It should be noted that
echo perceived by extended PBX users will not be perceived by the party on the other
end of the call.
Remote Module Impact on Echo
Because the Remote Modules deal exclusively with digital audio on the line side of a PBX,
they cannot cause any echo. However, if you experience any echo from your connection
to the PSTN (Public Switched Telephony Network), the Remote Module application could
make it noticeable because of increased delay in the audio path. For example, if echo
occurs on a line after only a few milliseconds, your ear cannot detect the echo. However,
if the echo occurs after 100, 50, or even 20 milliseconds, your ear will likely detect the
problem. The G.165 echo canceller can cancel echo only up to certain limitations.
If you experience echo on all external calls, you probably have a problem with your PSTN
analog lines connected to your PBX. Analog lines that are out of specification can
generate a great deal of echo when interfacing with your PBX. Non-extended PBX
telephones may not perceive the echo, due to the fact that echo without delay does not
sound
like echo.
If you have a noticeable echo problem, you should look into the following:
Cause:
The most common causes of consistent echo on all external calls are analog trunk
lines that are out of specification, or a problem with the termination within the PBX.
Most commonly there is an impedance mismatch between the analog line and your
PBX. Also, the db level of the analog circuit may be too high. Analog circuits that are
“hot” are a common cause of echo. Again, that echo may not be perceived on non-
extended telephones, but that is only because there is no delay.
Possible solution:
If you have analog lines, you should consult your local telephone company and ask
for the exact specifications of that line. They may need to go onsite to measure the
characteristics of your analog circuits. If you only experience echo occasionally on
external calls, your system is probably fine. The echo probably only occurs when
calling to or receiving calls from a party that is using:
à
analog lines
à
a cell telephone
à
analog trunks on their telephone system. In this case there is little you can
do. The echo canceller included with the Remote Modules will usually
cancel this echo after a second or two, but occasionally the echo goes
beyond its capabilities. However, it should be noted that the party on the
other end of the call will not experience this echo. If you experience a slight
echo on all external calls, but it goes away after a second or two, that is
normal with analog trunk lines. If you have analog trunks on your PBX, the
echo canceller frequently takes a second or two to detect levels of what is
echo and what is voice, and then it starts to cancel the echo. The only way
to eliminate that situation is to replace your analog trunks with digital trunk
lines.
Document Number: M-1100A-MUC
Version: Rev AG
© Copyright 2008 Citel plc All Rights Reserved
