John:
Thanks for the description, it is very good.
Here is the scenario in which this customer is experiencing echo.
Polycom ---> Asterisk ---> Internet ---> Polycom
also
Polycom ---> Asterisk ---> IX Private Line (delay 10ms) ---> Polycom
also
Polycom ---> Asterisk ----> SIP Trunk to carrier ---> Carrier's CLASS 5 --->
PSTN
This particular customer is seeing echo in all three scenarios. Hence the
reason I'm looking into the AEC and AES features of the Polycom.
Bill
----- Original Message -----
From: "John Lange" <[EMAIL PROTECTED]>
To: <[email protected]>
Cc: <[EMAIL PROTECTED]>
Sent: Friday, July 13, 2007 4:38 PM
Subject: Re: [on-asterisk] Polycom Echo Problems
Echo *always* comes from the far end point.
The amount a given person perceives the echo is determined by how loud
and how delayed the echo is. Volume and delay are influenced by a number
of factors along the call path.
Echo is a very complex issue but I'll try and give a brief explanation.
In the situation where you have a Polycom phone connected to an Asterisk
server which is in turn connected to the PSTN talking to a residential
wireline customer, e.g.:
Polycom <--> Asterisk <--> PRI <--> Wireline Handset
If the Polycom customer hears echo it's coming from the wireline handset
(and/or the hybrid but I'm trying to keep this example simple). Most
consumer handsets just don't care about generating echo because its
never been a problem. So echo is normal on all local wireline calls but
you don't perceive (hear) echo because the echo is not delayed.
Now when you throw Asterisk in the mix the act of encoding and decoding
the voice adds delay. This added delay causes you to perceive echo even
though the volume of the echo is roughly the same.
Technically, to solve echo you fix the endpoint that's causing the echo.
But since you can't replace every wireline phone ever made and the telco
certainly isn't going to help you that isn't a practical solution.
The best you can do is put an echo canceler as close as you can to the
endpoint and in this case it's on the Asterisk box. Unfortunately
Asterisk's standard built in echo cancelers are crap. They don't even
come close to reaching the level of the ITU G.164 standard for echo
cancel.
That is why you buy cards with add-on hardware echo cancelers that meet
the G.164 standard (Sangoma, Digium).
Recently you can also buy add-on software echo cancellation from both
Sangoma & Digium which meet the G.164 standard but beware it exacts a
heavy toll on your CPU. But depending on call volume and hardware it
might work just fine for you.
All of this is a long winded way of saying; you can tune your phone
settings until your blue in the face but you won't get rid of the echo.
Sorry.
So to prove my theory conduct the following tests:
Polycom <--> Polycom (no echo)
Polycom <--> Cell phone (no echo) (cell phones do extensive echo cancel)
Polycom <--> Longdistance (no echo) (telcos do echo cancel on LD)
Polycom <--> wireline residential (echo!!)
That is why your customer reports intermittent echo problems.
Hope the above helps you out.
John
On Fri, 2007-07-13 at 12:51 -0400, Bill Sandiford wrote:
Intermittently, both have the echo. They have other other sets in the
office not experiencing the echo problem. Their PSTN connection has been
properly tuned for echo (via Milliwatt, etc).
I'm just looking for a good config for AEC and AES on the Polys (and
perhaps
gains). By default they are turned off in the stock sip.cfg
----- Original Message -----
From: "Jim Van Meggelen" <[EMAIL PROTECTED]>
To: "'Bill Sandiford'" <[EMAIL PROTECTED]>; <[email protected]>
Sent: Friday, July 13, 2007 12:30 PM
Subject: RE: [on-asterisk] Polycom Echo Problems
> Couple of things that need to be known:
>
> Who has the echo? Your users? or the people who are calling them?
> How does the system connect to the outside world? (PSTN)
>
> Jim
>
>
>
>> -----Original Message-----
>> From: Bill Sandiford [mailto:[EMAIL PROTECTED]
>> Sent: July 13, 2007 12:23 PM
>> To: [email protected]
>> Subject: [on-asterisk] Polycom Echo Problems
>>
>> Hi All:
>>
>> I'm having a problem with a customer that has a bunch of
>> Polcom 501 and 601 sets. They are complaining about echo.
>>
>> Does anyone have some suggestions for some good settings for
>> AEC and AES in sip.cfg for the Polys? Any other suggested
>> settings or changes to the stock sip.cfg?
>>
>> Thanks,
>> Bill Sandiford
>> Telnet Communications
>> 905-674-2000 x100
>> [EMAIL PROTECTED]
>>
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