SPA3102 PSTN Echo

Question

Hi there,
I have several SPA3102s in my enviroment that I am using to connect legacy PSTN lines to the VoIP network. Calls come in on the PSTN lines and are routed to our Asterisk server by the gateways. The Asterisk server connects the calls to the correct IP phone extensions. When calls come in this way (or go out using the same line) the inside party hears an echo of themselves. During an individual call, quality fluctuates but the echo is present during every call. Calls between IP extensions have no echo. Calls connected to the PSTN network through a different gateway from the same IP extension have no echo.
So far I have upgraded all gateways to the current firmware and followed the troubleshooting steps outlined here; http://www.cisco.com/en/US/products/ps10024/products_qanda_item09186a0080a359cc.shtml
with no luck. Turning off the built in echo reducing features makes the calls consistent, with bad echo constant throughout all PSTN calls but none of the other steps reduce the echo as much as the built in features. I have searched the forums and not found anyone else have this problem with just the PSTN port. Does anyone have any ideas?

Answer 1

Hey guys, have you tried the following to reduce echo on the SPA3102.
Q. 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 tweaking.
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 point.
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 medium.
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  hearing.
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.