[asterisk-users] reduce dialtone volume on zap channel.

[Don Pobanz]

Tom Rymes wrote: 

>Dan,
>
>If I have followed this thread correctly, your problem 
>is that, when you pick up a local analog phone connected 
>to asterisk through a zap channel, asterisk generates 
>a dialtone, and everything works fine, except that the 
>echo is intolerable. Then, you install an echo canceller, 
>and then asterisk cannot reliably register your DTMF  
>digits when you pick up the phone and dial. In other 
>words, your problem shows up when you install the echo 
>cancellers.

Yes you understand correctly. 

>Do you have the echo cans installed between your local 
>extension and the zap channel? I assume so, because 
>otherwise they should have no effect on your DTMF. 

Yes 
analog phone (Aastra PT390)
  |
channel bank (Adtran TA750)
  |
T1 echo can (Orion Telecom) 
  |
Asterisk 1.2.13 (Dell poweredge 1750)

>Maybe I'm missing something, but I was always of  
>the impression that echo cancellers are installed 
>between asterisk and the PSTN, not between the local 
>handset and asterisk. 

I also have a T1 echo canceller between asterisk and 
the pstn. That will help with the echo for SIP phones. 

>That way, the echo canceller is 
>only in the media stream when you place a call  
>out to the PSTN. I assume that you don't have echo 
>problems calling from one local analog extension to 
>another. 

I do have echo extension to extension! That is the 
issue I am trying to eliminate. 

>If you do, however, I would suggest that 
>maybe your problem is bigger than just a DTMF issue.

This may be bigger than DTMF. However, since this is 
in service, I need to keep it running. 

I have worked with Digium and with Orion to try and 
resolve this. Digium has ssh into the system on 4 
different occasions. Orion assures me that they have 
thousands of these same echo cancellers in service but 
have never seen the issues I am having. 

Some of the things I have done are. 
 1 - moved TE410P cards to their own interrupts
 2 - modified levels in Asterisk, echo cancellers and 
channel bank. (I have a few pages of test results.) 
I have set levels to Digium recommended levels and to 
Orion recommended levels. I have also tried a whole 
bunch of other levels. By changing levels, I can get 
better results (8% errors instead of 20 or 25%). However, 
an error rate above 2% is unacceptable.  
 3 - turned off vpm support in TE412P card
 4 - turned off frame buffer 
 5 - moved to another server (Dell 1650 poweredge) with 
different TE410P cards. 
 6 - loaded different versions of zaptel and of 
asterisk (all in the 1.2.x version)
 7 - swapped Digium cards with a spare 

Once asterisk recognizes a pressed digit, all of the rest 
of the digits are recognized. The only different for the 
first digit is the presence of dialtone. That was why 
I was trying to reduce the dialtone volume. 

Maybe this is not the correct solution. But hey, I need to 
try something! The TE412P card with echo cancellers enabled 
did not offer satisfactory results. (too much echo). 

Don Pobanz
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