[Asterisk-Users] Re: Incoming echo cancel

[Kris Boutilier]

The fact that your SIP people are hearing their own voice, but the inbound caller is not is the correct behaviour for your 'echoless' digital termination. If you were to tap the channel in the T1 leaving your premises you would find that the echo is coming in from beyond your interfaces. Similarly if you called another party that was also on all-digital facilities (ie. call back into one of your own DIDs) then you should find there is no echo experienced by either party.

The fact that the second port does not echo at all simply suggests that carrier has a different arrangement of equipment. If they're a dedicated long-distance carrier they probably have echo cancellation active on all of their trunks all the time to compensate for the 'long distance' echos that would become audiable to ordinary callers.

An interesting trick is to set up a T1 DID to answer with the echo() application. Try calling in to it from a regular land line - then try calling into it from a cellphone. In most cases cellphone calls pass through fairly heavy-duty cancellation and you'll find the artificially generated echo dissapears. 

> -----Original Message-----
> From: Jon Bebeau [mailto:jbebeau at 1nettw.net]
> Sent: Friday, March 11, 2005 1:32 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Re: Incoming echo cancel
> 
> 
> I'm having echo too - ISDN-PRI using a Sangoma card to the PSTN.  My SIP 
> outgoing calls have an echo about 80% of the time, but only on a local T1. 
> It only an echo to the SIP caller; the called party never hears the echo.  I 
> have a second T1-PRI (port 2 of the same card) to a long distance carrier 
> with no echo problem, ever.  Played around with all the echo stuff, you 
> identified below.  Seems there is much ambiguity on the guidance as much of 
> the echo suggestions apply only to analog lines.  It's unclear how there can 
> be an echo on a T1-PRI (digital) anyway.
> 
> Jon
> 
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