[cisco-voip] Echo Cancellation and 7911 Phone Loads

[Wes Sisk]

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
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> cisco-voip mailing list
>>> cisco-voip at puck.nether.net
>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://puck.nether.net/pipermail/cisco-voip/attachments/20100901/7e0ebad6/attachment.html>