PSTN bad Quality


I have some customer who complains about the quality of the calls on the FXO.

  • Static Sound
  • Echo Sound

We try everything…PSNT detection…fxo tunning…same result.

When i try with Sip trunk line…no probleme , the quality is good.

The probleme is that some client is under contract with other phone compagny ( very expensive to broke the contract ) or no internet bandwidth.

I read in other forum, that the FXO Gateway like * GXW4104 * can solve the problem ( the hardware is more solide than the UCM ).

What do you think ?



Have you tried the same PSTN line on an analog phone if it feels good or if you have the same problem?
Have you done the various possible tests on UCM?


If there is static, then the source of the static needs to be determined. Static is in the analog realm meaning that it is not possible to generate static digitally. As Damiano suggested, you need to get an analog phone and test the lines over some period of time by making and taking numerous calls over the analog phone lines while using the analog phone. While your at it, you should also listen for echo.

If the complaint is that the client is hearing their own echo, then in the UCM you can try and lower the TX gain:

The echo in this case is caused by too much energy being input to the analog line and the excess is reflected back (echo). Adjusting the gain downward may help to eliminate or minimize, but the risk is that the far end may complain of the sound being too low.

I am assuming that you have read the manual and run the various tests for the analog lines in both the analog trunk settings as well as the interface settings.