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Echo and Static on Calls

I have a customer with the UC320 and 5 SPA508 phoes in the Key System setup and 3 Analog Phones lines to the PSTN.

I have made three trips to the customer's site to work on reports of Echo, Static, and One Way audio on external calls.   I have yet to experience any of these symptoms on any test calls I have made.    I have checked each analog phone line with my butt set, and have not heard any echo or static.   I have run the Impedance Matching on each line and made the suggested changes.   Still no issues.   An hour after I leave, I get a call saying they are still having issues.

The software version is 2.13 on the UC320.   The only thing that I have heard on test calls is a low level white noise present in the handset.   This noise is not heard on the phone lines when using my butt set, or by the receiving party on PSTN calls.  This occurs on more that one phone.

The audio levels have been lowered on the phones to about half-way the audio scale.   The impedance changes did make the volume levels appear louder on the phones, hence the volume level adjustments.

Any ideas on this issue?   There is no SIP trunking used.  Just the 3 analog lines to the PSTN.

Cisco Employee

Echo and Static on Calls


There are a number of FXO related fixes in the 2.1.4(3) release which is available for LD (limited deployment) usage.

Please review the steps below and the below link provides the installation PMF and a seperate link to the Release Notes:

  1. Customer      system is upgraded to firmware release 2.1.4(3) or higher.       Installation PMF and release notes can be found here:

  1. Configuration      is Applied
  2. Run      impedance matching on each of the FXO ports
  3. Retest      for customer complaint
  4. If      the problem still persists, feedback should be submitted against the case      number and the case escalated to L2 for the FXO tiger team to work the      issue.
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