[Asterisk-Users] iaxtel and jitterbuffer

Kris Boutilier
2004-08-29T15:16:15Z

Is timestamp information calculated purely from the relative timestamps of
each frame of the current incoming stream or is there some degree of RTC
synchronization expected between the two endpoints?

Similarly, are jitter calculations made seperately for each discrete channel
(ie. the IAX level) or are they based on an aggregate of all channels
between each pair of two endpoints (ie. the TCP/IP level)?

k.

-----Original Message-----
From: steve@daviesfam.org [mailto:steve@daviesfam.org]
Sent: August 29, 2004 12:53 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] iaxtel and jitterbuffer


{clip}

The jitter buffer makes all its decisions about dejittering based on the
timestamps of incoming frames.  There a fundamental expectation that the
sending side is correctly stamping each frame - 20msec, 40msec etc etc.

The problem is that the sending side doesn't always do that.  Sometimes
for one reason or another the stamps "jump".  The receiver has no way
of
telling that the sender mangled the timestamps, and assumes that the
packets with the new stamps have been delayed, or arrived early, or
whatever.  Either way, the jitter buffer does its thing and unknowingly
makes things worse.

Unfortunately, this is why you can still be better off without it - but
the problem really needs to be fixed by fixing the timestamp generation on
the sender.

Steve