[Asterisk-Users] TE405P and echo

[Kris Boutilier]

> -----Original Message-----
> From: McQuiggan, Mark xt46480 [mailto:Mark_McQuiggan at adp.com]
> Sent: Wednesday, March 23, 2005 12:28 PM
> To: asterisk-users at lists.digium.com
> Subject: [Asterisk-Users] TE405P and echo
> 
>Peter Svensson wrote:
>
>>On Tue, 22 Mar 2005, McQuiggan, Mark  xt46480 wrote:
>>
>>  
>>
>>>I am using a SIP softphone (X-lite, SIPPS or Firefly) connected to an
>>>Asterisk v 1.0.3 PBX.  The PBX is also connected via a ISDN-PRI crossover
>>>cable to a Avaya Definity Generic 3 PBX via a TE405P card. All outside of
>>>the office calls go through the Definity.  Here's the issue:
>>> 
>>>Calls to internal SIP extensions, Definity extensions, other offices within
>>>our private network (through the Definity), and cell phones are great.  When
>>>I call outside of the office to POTS lines (like my home), there is a most
>>>noticeable echo of my voice.  The party on the line hears no echo.  Any
>>>efforts on the configuring the SIP softphones, and within zapata.conf, have
>>>been for naught.
>>> 
> {clip}
> 
> I have noticed that any of the zapata.conf echo cancel parameters seem to have no effect on an ISDN-PRI line, using pri_net signalling (I used the voip-info.org wiki for the configuration).  If this is true, and I am not making some dumb mistake, is there another signalling mode that I can use on a Definity that will take advantage of echo-cancel?
> 

The echo cancellation code does not have any relationship to PRI-ness of at T1. So long as the channel is a B channel and the echo cancellation is correctly specified in zapata.conf then the code _will_ be active on the channel. This is the exact formatting I have used to specify bearer channels 1-23 of the PRI to my PBX (not a Definity):

 ; Norstar #1 (Wharf Road)
 context=in-t1nstar
 group=1
 callerid=asreceived
 usecallerid=yes
 hidecallerid=no
 usecallingpres=yes
 rxgain=0
 txgain=0
 echocancel=yes
 echotraining=yes ;100
 echocancelwhenbridged=no
 switchtype=dms100
 pridialplan=local
 signalling=pri_net
 channel => 1-23

Then I can fire up the asterisk console and issue a 'zap show channel 10' and, when on hook (or its off hook and the echo can has been disabled by the relevant in band disable-tones) I see:

 ...
 Echo Cancellation: 128 taps unless TDM bridged, currently OFF
 ...

If the channel is offhook I see:

 ... 
 Echo Cancellation: 128 taps unless TDM bridged, currently ON
 ...

If I were to specify a different number of taps for the echo can (ie. echocancel=256) then I would see the different number of taps in the  'zap show...' accordingly.

If all of this agrees with your system then it follows that the code is indeed enabled and being called but the algorithm is failing for some reason. For that you would need to work on determining if the signal levels on the T1 are correct for the echo canceller implementation and adjust the relevant constants in zaptel/mec2_const.h if it's not. 

See http://bugs.digium.com/bug_view_page.php?bug_id=0002820 for a starting point. Also search the asterisk-users archives for a recent thread titled 'Tweaking AGGRESSIVE_SUPPRESSOR'

Hope that helps.

Kris Boutilier
Information Services Coordinator
Sunshine Coast Regional District