[Asterisk-biz] PRI and echo cancelation ...

[David Mandelstam]

In any line carrying AC there is always some electrical reflection at the
terminations unless the line termination is electrically perfect. The human
ear is so sensitive that reflections at the terminations of analog telephone
lines are almost always large enough to cause perceived echo.

However, all long distance (greater than 600km) calls are routinely echo
cancelled by the network, as are all cell phone calls. ISDN calls, being all
digital have no electrical echo, nor do other digital calls such as VoIP
connections. It is really only the local analog circuits that are a problem.

David Mandelstam

> -----Original Message-----
> From: asterisk-biz-bounces at lists.digium.com 
> [mailto:asterisk-biz-bounces at lists.digium.com] On Behalf Of 
> Michael Blood
> Sent: Sunday, August 21, 2005 11:53 AM
> To: 'Commercial and Business-Oriented Asterisk Discussion'
> Subject: RE: [Asterisk-biz] PRI and echo cancelation ...
> 
> That is interesting,  do you know how they are able to 
> convert the digital signal to analog (pri to pots) without an echo?  
> I have never had a problem on any lines where the telco does 
> conversion.
> 
> Michael Blood 
> 
> -----Original Message-----
> From: asterisk-biz-bounces at lists.digium.com
> [mailto:asterisk-biz-bounces at lists.digium.com] On Behalf Of 
> Eric Wieling aka ManxPower
> Sent: Sunday, August 21, 2005 8:20 AM
> To: stotaro; Commercial and Business-Oriented Asterisk Discussion
> Subject: Re: [Asterisk-biz] PRI and echo cancelation ...
> 
> 
> > From: "Michael Blood" <Michael at Matraex.com>
> 
> > Agreed,  this should be on the Users List.
> > My experience has been that PRIs have much less trouble.
> > The echo typcially comes from the analog to digital conversion. I 
> > personally believe the reason for this is that the Analog 
> to Digital 
> > conversion that happens at the telco is done with much 
> higher quality 
> > equipment with much higher quality echo cancellation than if it is 
> > done on your asterisk box.
> 
> As far as I can tell most local telcos don't do echocan on 
> for local calls.
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