[cisco-voip] Echo Cancellation and 7911 Phone Loads

Thu Sep 2 10:18:37 EDT 2010

Cool.  Didn't know that.  Thanks all!

jeff

________________________________

From: Lelio Fulgenzi [mailto:lelio at uoguelph.ca] 
Sent: Wednesday, September 01, 2010 4:24 PM
To: Wes Sisk
Cc: Jeff Ruttman; Cisco VOIP
Subject: Re: [cisco-voip] Echo Cancellation and 7911 Phone Loads

...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>
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>
http://www.cisco.com/en/US/customer/tech/tk652/tk698/technologies_tech_n
ote09186a0080149a1f.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>
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.voiptroubleshooter.com/problems/echo.html

<http://www.cisco.com/en/US/partner/docs/ios/solutions_docs/voip_solutio
ns/EA_ISD.html>
http://www.cisco.com/en/US/partner/docs/ios/solutions_docs/voip_solution
s/EA_ISD.html

<http://www.cisco.com/en/US/partner/tech/tk652/tk698/technologies_tech_n
ote09186a0080149a1f.shtml>
http://www.cisco.com/en/US/partner/tech/tk652/tk698/technologies_tech_no
te09186a0080149a1f.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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