[Asterisk-Users] Re: PRI echo issues: solvable?

[alan]

> Subject: RE: [Asterisk-Users] PRI echo issues: solvable?

"Kris Boutilier" <Kris.Boutilier at scrd.bc.ca> wrote:

> > On Tuesday 11 October 2005 11:49, alan wrote:
> > > After solving the other "low hanging fruit" audio issues in our Asterisk
> > > PBX, we are left with occasional cases of severe echo which we have not
> > > found a solution for yet.
> >
> {clip}
> >
> > > Most calls have minimal, acceptable echo levels. But occasionally, we
> > > get a call where the echo is delayed by a substantial amount (sometimes
> > > around 250ms), and sounds as loud as the remote party.
> >
> > Yup.
> >
>

I finally got time to spend on looking into this again.

> If you were to use ztmonitor on the channel to record the transmit and
> receive sides to separate wav files, drive an impulse down the channel
> (ie. a sharp, loud click) and then load the files into a tool where
> they could be viewed side by side you'd see the actual echo endpath
> (tail) length.

How does one use ztmonitor to record into separate files for transmit
and receive? My ztmonitor man page doesn't describe how to do this, it
only allows one -f File specification.

When I monitored a sample conversation with ztmonitor, it recorded both
channels in one file. Then I set up a call from the number which gives
us "big echo". Although I heard echo when I was on the call, the
recorded version of the call did not record the echo.

There are two possibilities here:
1. it wasn't recording the incoming call leg.
2. the echo is entirely internal to our system

I couldn't see how #1 could be the case when the immediately previous
ztmonitor recorded both call legs. On the other hand, I told the remote
party to just put the phone down so I have no evidence that any sound
they made was missing.

But I can't see how #2 is the case either, since it only affects certain
phone numbers, and it affects them consistently whenever it happens.

I have a feeling I just did something wrong, so I'll go back and try
again. I'll also try a greater echocancel= value and see if it
helps.

Thanks,

Alan Ferrency
pair Networks, Inc.
alan at pair.com