asterisk users - Mar 2007 - TDM-400, Polycom SIP phones, and echo problems

Hi:

I am working on a new system with a TDM-400P card with three FXO modules
and one FXS module.

The system has been in place for a week. Users are complaining of echo
problems. I have noticed this echo myself. It varies in severity. It is
sometimes bad enough to make it difficult to converse, but the users
find it generally unacceptable. They miss their old phones, which just
worked. As you can imagine, this is not the way to get them excited
about this technology.

I have used the 1.4 branch version of fxotune to tune the card. These
are the echo statistics I get on the affected channels.
> asterisk1 asterisk # fxotune -d -b 1 -w 1004
> Dumping module /dev/zap/1
> echo ratio = 0.0077 (85.5 / 11145.0)
> Done!
> asterisk1 asterisk # fxotune -d -b 3 -w 1004
> Dumping module /dev/zap/3
> echo ratio = 0.0296 (330.2 / 11145.0)
> Done!
According to the wiki, both those echo ratios should be more than
sufficient to let the echo canceller handle the echo. Residual echo is
present, however. It doesn't interfere with conversation, but I could
see how it would be irritating, especially if you never had it before.
The call experience should get better, rather than worse -- especially
if we're using Polycom IP 650s.

Questions:

- What settings might I tweak to eliminate this remaining echo?
- Is there a hardware or software echo canceller that will do a more
thorough job of it?
- How is the HPEC in dealing with this echo?

Hi Stephen,

I'm sure someone here can help with the echo, but I just wanted to say I
can highly recommend the Sangoma a200d boards with Octasic hardware echo
cans.  I spent a couple months trying to deal with echo using a TDM400p
and even a Vegastream SIP gateway with hardware echo can.  The quality
of the Octasic echo can on the Sangoma kit is amazing- literally 5
minutes after installing my a200d my echo was gone.  Once it has
converged (which happens very quickly), its just like a "normal"
phone.
With the Vega most of the echo was gone due to the echo can, but we saw
echo in "double-talk" situations.  

 

It was more expensive, but definitely worth it.  

 

I would definitely also look into the new HPEC or Sangoma Softecho,
which I just saw on the wiki (voip-info.org).  Might be a good option,
though I haven't tried either (there was a discussion on this list about
the HPEC canceller just a few days ago)

Pete

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On Mar 12, 2007, at 7:12 PM, Stephen Bosch wrote:
> Hi:
>
> I am working on a new system with a TDM-400P card with three FXO 
> modules
> and one FXS module.
>
> The system has been in place for a week. Users are complaining of echo
> problems. I have noticed this echo myself. It varies in severity. It is
> sometimes bad enough to make it difficult to converse, but the users
> find it generally unacceptable. They miss their old phones, which just
> worked. As you can imagine, this is not the way to get them excited
> about this technology.
>
> I have used the 1.4 branch version of fxotune to tune the card. These
> are the echo statistics I get on the affected channels.
>
>> asterisk1 asterisk # fxotune -d -b 1 -w 1004
>> Dumping module /dev/zap/1
>> echo ratio = 0.0077 (85.5 / 11145.0)
>> Done!
>> asterisk1 asterisk # fxotune -d -b 3 -w 1004
>> Dumping module /dev/zap/3
>> echo ratio = 0.0296 (330.2 / 11145.0)
>> Done!
>
> According to the wiki, both those echo ratios should be more than
> sufficient to let the echo canceller handle the echo. Residual echo is
> present, however. It doesn't interfere with conversation, but I could
> see how it would be irritating, especially if you never had it before.
> The call experience should get better, rather than worse -- especially
> if we're using Polycom IP 650s.
>
> Questions:
>
> - What settings might I tweak to eliminate this remaining echo?
> - Is there a hardware or software echo canceller that will do a more
> thorough job of it?
> - How is the HPEC in dealing with this echo?
It's as good (if not better) than using Octasic hardware echo 
cancellation.  I would definitely download it and install it.  And IIRC 
it comes free with the purchase of your TDM card from Digium.

Matthew Fredrickson