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New Member

Echo in Call Manager Express

Hi All,

I have a problem with echo in a CME installation. The users are at times experiencing echo while on calls. They are hearing their own voice delayed slightly in their own hand set. The say that it is often with a call that has been transferred to them.

The environment is very simple. There are only 12 phones and they are not sharing the network, at this stage, with data. The connectivity to the PSTN is via BRI.

The router is a 2811 with a 16 port POE switch card.

Attached is the relevant parts of the config. Any help would be greatly appreciated.

Regards,

Scott

4 REPLIES

Re: Echo in Call Manager Express

Scott,

Echo is usually due to two things.

Long echo - Tail circuit is outside the range of the IOS echo cancellation unit thus the router cannot account for the echo. Default for the IOS for awhile was 8ms. New echo cancellation standards are applied in 12.3 and higher that allow you to up the echo cancellation range upwards to 64ms. On the latest codes this is now the default setting. You need to show voice-port to verify this is set to 64ms.

Loud echo - This happens when the output attenuation or the input gain on your gateway is set too loud. Typically this is determined by checking a suspect call with Show call active voice. From there you can measure what your output volume is when it leaves the gateway and the return call volume before and after echo cancellation. I have attached the document that shows how to troubleshoot that issue. Essentially you tweak the volume settings (output attenuation and input gain commands) on the gateway until the echo is accounted for.

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtml#echoenhance

Of course the long echo is easier to troubleshoot as the IOS does everything for you. All you need to do is make sure the cancellation range is set high enough. It does say in the documents not to set it higher than need be but the new ITU standard cancellators now are recommended to be set at the highest number available.

Here is also a more concise document on echo in general on VOIP networks.

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml#wp1041385

Please rate the posts

Thanks

Fred

New Member

Re: Echo in Call Manager Express

Hey Scott,

Does'nt look like you have any echo coverage on the POTS side. You may want to remedy this by;

!

!

voice-port 0/0/0

echo-cancel enable

echo-cancel coverage 32

shut

no shut

!

voice-port 0/0/1

echo-cancel enable

echo-cancel coverage 32

shut

no shut

!

end

Furthermore, echo cancelation has been known to "not" work in several 12.3/12.4 Mainline and T-Train releases.

You may wish to refer to this documentation for more info;

direct link= http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml#wp1041691

Regards,

Steve.

New Member

Re: Echo in Call Manager Express

Hi Steve,

Thanks for that.

I forgot to mention that the original config did include the echo-cancel coverage 32 in it, but we removed it for a trial.

How do I find out if the version I am running is not working with this command?

It is c2800nm-spservicesk9-mz.124-4.XC.bin

Thanks,

Scott

New Member

Re: Echo in Call Manager Express

Scott,

I have had a quick look and there is an interesting bug which doesnt relate to a fix, but rather 12.3T code and the echo canceller. Soft speech does not allow the echo canceller to detect a sufficient anomally whereas a simple digit press on the keypad allows the echo cancellation to take place.

The fact the you are running XC code makes me suspect you may be encoutering this problem.

In any case you can read the bug yourself @

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCsb68986&cco_product=IOS&fset=Voice&swver=12.4&keyw=echo&target=4&train=XC

Try the keypad or speaker volume to see if the echo canceller is any better at spotting the problem.

Regards,

Steve.

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