I am having an issue where users report some echo on the IP phones every now and then that lasts the whole call. The echo they hear is their voice back on the IP Phone. The outside party does not hear echo.
The voice port config is echo-cancel erl worst-case 0, no comfort noise
Because the problem is intermittent, it might be useful to try to determine some kind of a pattern (is that a contradiction?) before making any changes. For example, testing may help answer whether:
1. Echo is heard on every N'th call, or perhaps on every call that uses channel 'Y' of a particular PRI.
2. Echo is heard on calls to or from a particular area code.
3. Echo is heard on calls that use a particular set of DSP resources on the gateway
Other things to look for as well include whether the version of IOS or DSP code is the recommended version. If you have the output of 'show version', and 'show diag' these may be helpful. For example, there's a known defect whose symptoms are similar to what you describe, and this is documented in CSCsd54344 - DSP: Persistent echo heard on c5510 DSPs with 4.4.13 DSPware or higher.
If a defective code or DSP has been ruled out, then use the relevant commands such as echo cancel, input gain, or output attenuation as outlined in the good document below to reduce the echo.
IntroductionCUCM Routing RulesDial String implementation PolicyCUCM Routing LogicSIP URI Call Routing Analysis+++ Case Study: 1 ++++++ Case Study: 2 +++Conclusion
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