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Echo, Echo Cancellation and Gateway settings

I'm having issues with slight echo on PSTN calls through our 6608 blade. The echo isn't severe, slight enough that it's been this way for a year, but I think I should be able to eliminate it. When I look at active calls through the CLI on my 6000, I see that echo cancelation is disabled. How do you enable it? This 6000 is non-IOS. Otherwise, I was looking at adjusting three settings on the gateway config in call manager:

TX-Level CSU - set at 0dB

Audio Signal Adjustment into IP Network - NoDbPadding

Audio Signal Adjustment from IP Network - NoDbPadding

Is this the right place to look? My interpretation is that TX-Level CSU is the signal power sent to the pstn, the base level so to speak, and that the other two are the your minor adjustments for incoming and outgoing signal. So if I hear a slight echo of my speech on my end(not using speakerphone), how would I adjust?

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Re: Echo, Echo Cancellation and Gateway settings

The echo cancellers on the 6608 cannot be disabled. Under some loads it appears to be disabled, but the issue is cosmetic only. See bug ID CSCea32399:

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCea32399

For best echo cancellation performance on the 6608 platform, it is highly recommended that you run CallManager 3.3(3) with the latest service release applied, which is service release 3 as of this writing. Service release (I believe) 2 and above ship with new 6608 loads which implement the more advanced, better-performing G.168 echo canceller code currently in use on IOS gateways as opposed to the older and less capable G.165 code. Echoes are typically recognized and eliminated faster, and you can configure maximum tail lengths of up to 64ms (32ms being the max for G.165). Maximum cancellable ERL (echo return loss) is also configurable.

There is documentation on CCO that recommends playing with DB padding in and out of the IP network. That's a crude and not very effective means of trying to get echo to go away. Those documents pre-date the implementation of G.168 ECANs on the 6608, and if you upgrade, you shouldn't have to mess with these settings.

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