This article is one in a series to assist in the setup,
troubleshooting, and maintenance of Cisco Small Business products (formerly
Linksys Business Series).
Technical Tips Conventions for more information on document
How can I reduce the PSTN echo on SPA3102?
A. Experiencing echoes in the PSTN line is a common problem. This is
because the SPA3102 passes calls from the PSTN to LINE1 by converting it to
VoIP internally then converts it back to analog. This process does not produce
any echo, however, it can add about 30ms of latency to the call which later
produces the echo.
Reducing the Echo on the PSTN Line
Make sure you are running the latest firmware. Everything should be
set to factory defaults, or at least undo all the previous
Disable all the echo cancellation functions of your SPA3102. These
settings can be found on line 1 and PSTN line tabs of your SPA3102.
Echo Canc Enable = No
Echo Canc Adaptive Enable = No
Echo Supp Enable = No
Remove devices connected to your phone line except the SPA3000.
This includes all the extension cables and splitters. These can
cause impedance problems which lead to echoes.
Set the FXO port Impedance on the PSTN tab to 220+820||120nF, and
set FXS Port Impedance to 220+820||115nF as a starting
Look for Network Jitter Level on the PSTN Line tab
and set it to low. Then, look for Jitter Buffer
Adjustment and set it to disable.
This reduces the delay across your SPA3000.
Note: If you are using a poor quality VoIP service, go to the Line 1
tab and look for Network Jitter Level. Set it to
low and set the Jitter Buffer Adjustment from
up to down. However, if you are using a poor
quality PSTN, set the Network Jitter Level to
Go to the PSTN Line under Audio Configuration. Look for
Preferred Codec and set it to your preferred settings, then
lock it in by setting the Use Pref Codec Only to
yes. Adjust these settings if you are accessing your PSTN line
via VoIP from a remote network. Then, go to Line 1 and set Preferred
Codec with the same settings you set with PSTN Line. Under
Preferred Codec Only set it to no.
These settings reduce your latency and can make the echo less
obvious or easier to catch with the echo canceller.
Power cycle the SPA3000 by powering down the device.
This sometimes fixes the problem especially after changing the
physical phone wiring.
Make some test calls and observe if you can hear an echo. If yes,
the problem might be that you are sending too much power down the line and it
gets reflected back somewhere as an echo. Even if you have good wiring but you
are too close to the mouthpiece, you will still hear an echo. To resolve this,
you need to increase the level of Gain by going to PSTN and
look for SPA To PSTN Gain, then slowly adjust the level until
you can clearly hear the person on the other line.
Note: If you enable Echo Supp Enable, you will negate
these parameters. The echo suppression is just an automatic gain control. It is
recommended to keep it disabled.
Make a test call to someone with a phone that works via the SPA's
PSTN line, or call in to the PSTN line. If the remote party is hearing an echo,
your phone might be loud and is experiencing feedback in the microphone. Lower
the PSTN to SPA Gain until you are comfortable hearing the person on the other
line. If the remote user can still hear an echo, try using a different phone
plugged into the SPA. If this solves the problem, your phone might not be
working properly, or there is an impedance mismatch between your phone and the
SPA. Try changing the FXS Port Impedance to 600 on the
Regional tab and change the FXO port
impedance to 600 or global. If this
does not help, change it back. The impedance will only affect what the remote
party hears and will not help remove the echo you are
After lowering the echo to a tolerable level, go back to the
PSTN tab and enable Echo Can Enable by
selecting Yes, OK. Check if the echo has improved. If the echo
is tolerable at this level, leave the adaptive echo canceller off. You should
have the echo level down to a level that can be filtered by the echo canceller.
If you are using a sip device to talk through your PSTN line, you should
probably do all the echo cancellation at that device and leave it switched off
in the SPA.