Core Issue
These are a few of the possible causes for the echo:
- A level mismatch with the local Telco
- A bad IP phone load
Note: Echo takes a number of forms. Who hears the echo and what device is at the other end are important characteristics. A talker hearing his own voice echoed is known as talker echo and is uncommon. A listener hearing the speakers voice echoed is the usual case. The echo can be minimally delayed with some loss, being perceived as Tunnel voice or more seriously delayed with little loss, being perceived as a second discrete signal or echo.
Resolution
To resolve this issue, choose from one of these options:
- If the IP user hears the echo, it suggests that the audio power originating from the IP network is too high.
The result is a signal reflection in hybrid equipment in the Public Switched Telephone Network (PSTN) or PBX. It is perceived by the IP phone user as an echo due to the processing delay in the packet network. In this case, use a positive output attenuation value. This reduces the level of the signal on the output from the gateway.
It is also possible to reduce the level of the echo signal. Use a negative gain on input to the gateway from the PSTN.
For information on configuring gateways in this case, refer to IP phone user hears an echo of his voice on a call to a PSTN phone. This case also includes further references for configuration and background information.
- If the PSTN user hears the echo, there are a number of possibilities:
- There could be an issue with the IP phone acoustic coupler. If only IP phones are involved across an end-to-end digital network, then this is the likely problem. Ensure that you are running the latest appropriate IP phone load. For latest phone load versions, refer to Ip phone software download
- The audio power from the PSTN could be too high and a reflection occur due to the hybrid on an analog router voice port. This kind of problem will not occur on digital voice ports.
The echo signal returned from a gateway hybrid should be performed at the speed of light. Therefore, it should actually not be perceived as an echo by the PSTN user unless some other delay has been inserted into the PSTN, such as a toll bypass network. Another scenario where echo might be perceived is between IP phones across the PSTN.
Increasing the attenuation output from the gateway to the PSTN may resolve the problem if an additional PSTN delay is expected. Otherwise, it is unlikely to resolve the issue.
- Acoustic feedback could be in the IP phone hand piece. This feedback would include the loud speaker feeding a signal back into the hand piece microphone. In this case, reduce the signal input to the gateway from the PSTN through a negative input gain command.
For more information on resolving echo problems, refer to these documents:
Voice Gateways
IOS gateways
