[Asterisk-Users] IAX Jitter Buffer

[George Pajari]

We have a customer who is connected to our PSTN gateway using IAX and
noticing that even when the traffic from their site is modest their outbound
audio has short dropouts. Inbound audio is fine. (They have ADSL so it is
expected that outbound audio would be the first to experience problems.)

We have several questions to pose to the collective wisdom of this list.

Q1: Are there any statistics collected/available or diagnostics tools to
tell us how much of this can be attributed to packet loss and how much to
packet jitter and to measure quantitatively how bad this is?

The use of the jitterbuffer in iax.conf seems to have problems. Extensive
searching turns up comments such as:

1. "jitterbuffer, unfortunately, is buggy and don't work as expected."
    [asterisk-users/2003-July/016029.html.]

2. " This supports my thinking that there is some sort of broken logic in
the IAX jitter buffer" - HRH Mark Spencer
    [http://www.marko.net/asterisk/archives/0302/0077.html]

When we enabled jitterbuffer the sound quality seemed to improve but we
noticed some problems:

(a) sometime we would get only one-way audio;
(b) other times we would experience no audio in one direction for between 1
and 4 seconds and then things would seem to work fine;
(c) some times users reported a "clipped" and almost "half duplex" sound
quality as the flow of the conversation shifted back and forth.

We also noticed some wingnut values for Lag and Jitter such as:
Lag: -65476ms
Jitter: 12897799ms

PSTN gateway is "CVS-04/20/04-01:11:29 "
Client machine is "CVS-HEAD-06/02/04-07:56:41"

Searching the Asterisk bug lists shows some significant fixes (1696, 1643).

Q2: Is jitterbuf working well enough to try again?

Q3: Any other suggestions for improving voice quality with IAX links?


Thanks.

g.