[cisco-voip] Echo Cancellation and 7911 Phone Loads

[Mike King]

Don't forget another source of Echo (and this ties into Wes's CPE comment)

Check to see if they have headsets.  All of my Echo complaints always
involve mis-configured Headsets.

Mike

On Wed, Sep 1, 2010 at 11:33 AM, Jeff Ruttman <ruttmanj at carewisc.org> 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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