[Asterisk-Users] Echo in CAPI channels

[Derek Conniffe]

I've been wondering about this too.  I've now got two telephone systems 
side by side - my old system is an analogue PBX connected to ZyXel 
routers (Prestige 100s) which give me POTS lines from the ISDN NT1 boxes 
and its only since I've started with Asterisk that I've come across echo 
(I have echo problems with X100P cards and analogue lines too). 

When I first started using Asterisk I used I4L, a ELSA pci ISDN card and 
chan_modem but I had really strong echo problems so on the advice of a 
guy I know who introduced me to Asterisk I moved to an AVM and 
chan_capi.  Another funny thing is that guy I just mentioned uses ISDN 
and chan_capi too and he's never experienced any echo problems at all - 
I wonder if its something to do with my configuration being different to 
his in some way?

Derek

Robert Rozman wrote:

>Hi,
>
>who does this echo canceling if you use ordinary ISDN phone (you hear no
>echo) ?
>
>Regards,
>
>robert.
>
>----- Original Message ----- 
>From: <steve at daviesfam.org>
>To: "Asterisk Users Mailing List - Non-Commercial Discussion"
><asterisk-users at lists.digium.com>
>Sent: Friday, October 29, 2004 1:12 PM
>Subject: Re: [Asterisk-Users] Echo in CAPI channels
>
>
>  
>
>>On Fri, 29 Oct 2004, Derek Conniffe wrote:
>>
>>    
>>
>>>I also get echo also but whats interesting is that I only get an echo if
>>>the person at the far end (via. the telephone company) is using an
>>>analogue phone line.  If they are on ISDN or a cell phone there is no
>>>      
>>>
>echo.
>  
>
>>>I'm only using basic ISDN (not primary rate) connections with chan_capi
>>>and AVM Fritz PCI cards.  I'd love to hear how to fix this.
>>>
>>>Derek
>>>      
>>>
>>Hi Derek,
>>
>>Your practical experience exactly matches the theory.
>>
>>"Electrical echo" can be introduced when digital or 4-wire connections are
>>converted to two wire.
>>
>>ISDN and cell-phone is all digital.
>>
>>As for fixing it with chan_capi - not so easy.  The latest chan_capi
>>(0.3.5) has only a very basic echo cancellation - configured using
>>"echosquelch" or "echocancel" in capi.conf.  You could try adjusting
>>those and see if it helps.
>>
>>Steve
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>
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-- 


Derek Conniffe
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