[cisco-voip] Echo Cancellation and 7911 Phone Loads

Wed Sep 1 17:24:26 EDT 2010

…and you can remove the "customer" part completely to get the public  
version of the link (if available) to give to people without a CCO  
account.

…
Don't look at me, my iPod maid that spilling mistake.

On 2010-09-01, at 4:45 PM, Wes Sisk <wsisk at cisco.com> wrote:

> Hi Jeff,
>
> Apologies for the 'partner' links. Most of the time you can replace  
> 'partner' with 'customer' and get the content.
>
> /Wes
>
> Jeff Ruttman wrote:
>>
>> Thanks again, Wes.
>>
>> I see you mentioned SLIPS, and I had seen that as a possible cause,  
>> but there are zero, so I had ruled that out.  Should have had that  
>> in my little list, though.
>>
>> I've certainly got more to go on now, and I can see this last doc  
>> you referenced.  (I'm not a Partner, so I was "forbidden" some of  
>> the other docs you linked me to.)  Crappy part is the echo is  
>> intermittent--of course--so all I can really do is make a change  
>> then wait and see.  I've sent a number of calls out that circuit to  
>> test myself, and I've not heard any echo.
>>
>> jeff
>>
>> From: Wes Sisk [mailto:wsisk at cisco.com]
>> Sent: Wednesday, September 01, 2010 9:54 AM
>> To: Jeff Ruttman
>> Cc: Cisco VOIP
>> Subject: Re: [cisco-voip] Echo Cancellation and 7911 Phone Loads
>>
>> Hi Jeff,
>>
>> Inline, ws.
>>
>> Jeff Ruttman wrote:
>>>
>>> Thanks Wes.
>>>
>>> Well I've expanded echo cancellation on the gateway.  (PRI with  
>>> MGCP, CCM6.1)  So your first paragraph is saying that most likely  
>>> echo is generated too "far away" (too much delay) from my GW to  
>>> cancel the tail end echo coming into our system--even with my  
>>> expanded echo cancellation in place.  So only the telco might have  
>>> a chance of cancelling that echo "closer to" the echo source.
>> ws: echo is generated too far from the ipphone, like at the the  
>> other endpoint. If you call me and hear your own voice then most  
>> likely the echo is being generated in my phone.  Your gateway is  
>> closest to me so will have the best chance of canceling the echo as  
>> the original signal and echo signal are closest in time in your  
>> network at the gateway.  But, in the end, it really is a problem  
>> with my customer premise equipment (CPE). I should be canceling the  
>> echo.  The best place to fix it is in my network.  Next best is in  
>> the carrier, next is in your CPE.
>>>
>>> As I understand it, I might also change phone loads (hence my  
>>> question about 7911s).  And I might try some gain/attenuation  
>>> settings on the GW as well--or so I've read.
>> ws: Yes, there is tuning on the gateway to get the most out of the  
>> available ecans. If the echo is coming back within the cancellation  
>> coverage then you just need to get levels and ERL in line so the  
>> ecans can do their jobs.
>>>
>>> So in a VOIP system that has echo, I can:
>>>
>>> 1. Bug the telco
>>> 2. Expand echo cancellation on the GW
>>> 3. Attenuation/gain statements on GW
>> There are several parameters on gateways for possible tuning. These  
>> include:
>> ecan coverage
>> NLP - non linear processor
>> ERL - echo return loss - primarily affected by Input Gain and  
>> Output Attenuation
>> Noise - any noise introduced on the circuit causes the echo signal  
>> to not match the original signal. This prevents echo from being  
>> detected and canceled.  Examples of noise include any slips or  
>> errors on T1's and electrical cables (60Hz, fluorescent lights  
>> especially) located too close to analog (FXS/FXO) connections.  I  
>> believe the parameters are covered pretty well here:
>> http://www.cisco.com/en/US/customer/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtml
>>> 4. Change phone load
>>>
>>> At least so far that's all I've found I can tinker with.  Is that  
>>> about it?
>>>
>>> Anyone use attenuation or gain statements on their GWs?  I know  
>>> the statements, but I don't know what their function really is,  
>>> whether I would use one or the other or both, or what I would set  
>>> them to.
>> ws: see the article above.  Use IG and OA to get ERL that works for  
>> ECAN.
>>>
>>> Thanks
>>> jeff
>>>
>>>
>>>
>>> From: Wes Sisk [mailto:wsisk at cisco.com]
>>> Sent: Tuesday, August 31, 2010 2:00 PM
>>> To: Jeff Ruttman
>>> Cc: Cisco VOIP
>>> Subject: Re: [cisco-voip] Echo Cancellation and 7911 Phone Loads
>>>
>>> Talker echo is usually caused by echo at far end tail circuit.   
>>> With VOIP that delay is going to be too long for the talker's  
>>> phone to cancel.  It will have to canceled closer to the source of  
>>> the echo.
>>>
>>> Otherwise, AFAIK, all cisco phones (except soft) have local ecan  
>>> to prevent speaker audio from going back into mic.
>>>
>>>
>>> http://www.voiptroubleshooter.com/problems/echo.html
>>> http://www.cisco.com/en/US/partner/docs/ios/solutions_docs/voip_solutions/EA_ISD.html
>>> http://www.cisco.com/en/US/partner/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtml
>>>
>>> /Wes
>>>
>>> Jeff Ruttman wrote:
>>>>
>>>> Greetings,
>>>>
>>>> Can someone confirm or deny my memory?  I recall reading that  
>>>> phone loads for 7911 phones don't really contain echo  
>>>> cancellation programming.  In looking now, I can't find much info  
>>>> on echo cancellation in relation to different phone models/loads  
>>>> in general and nothing on 7911s.
>>>>
>>>> We have an office mostly full of 7911s recently complaining of  
>>>> talker echo.  There are loads out on cisco.com newer than the  
>>>> ones we're using, and while it's not hard to change phone loads,  
>>>> it would be pointless to do it if the phone loads don't contain  
>>>> echo cancellation.
>>>>
>>>> Any insight?
>>>>
>>>> Thanks
>>>> jeff
>>>>
>>>> _______________________________________________
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>>>> cisco-voip at puck.nether.net
>>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>>
>>>
>>
>
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