[Asterisk-Dev] IAX2 Receiver Reports

[steve at daviesfam.org]

On Tue, 28 Dec 2004, Steve Kann wrote:

> This shouldn't matter. The PING/PONG will still give an accurate RTT 
> estimate, and the jitterbuffer delay that's returned will be the 
> _maximum_ delay. I think it turns out, in practice, that the maximum 
> delay is usually just about what happens to most packets, because most 
> packets are sent in a consistent time, while a few packets are late 
> (because of buffering spikes, etc). Regardless, we're trying to give an 
> upper bound to the delay, and while 1/2rtt + "delay" would be a better 
> upper bound, rtt+delay is more conservative, because it takes into 
> account differing delay lengths.


This is where I always had trouble when trying to report measurements from 
the jitter buffer - just because the jitter buffer is a particular size, 
doesn't in my opinion tell you too much about how long a frame will be 
delayed.  If its true that we are just looking at delay "spikes" then you 
are right.  But I tended to see that the delay jumps higher for seconds or 
tens of seconds, sometimes followed by lost packets and a return to lower 
delay (symptom of congestion and a router running out of buffer).  
Timestamp discontinuities made things more complicated.

Still - the thing is to try it and see how things go.

Steve