[asterisk-users] SIP to IAX2 with delayed echo

Steve Totaro stotaro at totarotechnologies.com
Thu Nov 20 17:58:43 CST 2008

On Thu, Nov 20, 2008 at 6:27 PM, Dave Platt <dplatt at radagast.org> wrote:
>> Coming from outside the network, setting up for a couple rounds of
>> NATting isn't going to work well.  They are not seeing it between
>> phones.  Others, using the polycom phones have reported echo between two
>> SIP on a 4ms ping trip.
> Could this be due to a purely acoustic echo within the Polycom handsets?
> I encountered a nasty echo / hollow sound when using a cheap USB
> "telephone" to connect to my Asterisk system (via KPhoneSI).  The
> echoing was due to acoustic feedback - the handset body acted as a
> very nice channel for sound waves from the back side of the
> speaker down to the microphone cartridge.
> I opened up the handset, added some damping materials (panel-
> vibration-damping and soft-foam sheeting, left over from a
> car stereo speaker installation I did), closed it back up,
> and the echoing was gone.
> You might not notice in some calls, if the Polycom phones have
> silence-detection turned on for those calls and if the amount
> of feedback falls below the phones' silence threshold.  If
> the phone silence-detection algorithm were turned off on
> other calls, the echo would then be audible.

Troubleshooting is simple.  Register X-Lite and see if the problem
goes away.  If so it is IAX2, a moving target that sometimes works OK
but more often does not.

If the X-Lite softphone does not show echo, then it has something to
do with the Polycoms,  If you still have echo, then drop IAX2, if that
doesn't do it, then mess with the polycoms.

When will Asterisk get VAD?

Steve Totaro
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