[pjsip] bug in write_port()?? - conference.c

Anshuman S. Rawat arawat at 3clogic.com
Fri Feb 22 07:31:10 EST 2008


HI Nanang,

Thanks for the input. We have actually disabled VAD (wasn't working too well 
for us) so are streaming silence packets too. That's we see this behaviour. 
Anyway, we did a small 'fix' for fixing the issue and works well now.

Not sure if this has been put as a 'bug' by Benny?

Regards,
Anshuman

----- Original Message ----- 
From: Nanang Izzuddin
To: pjsip list
Sent: Thursday, February 21, 2008 2:23 AM
Subject: Re: [pjsip] bug in write_port()?? - conference.c


Hi Anshuman,

I tried revision 1805 on my PC at clock rate 16kHz codec PCMU
(note: conference.c last modified was on rev 1715, so we should have same 
conference code).
On silence, packets are sent every about 1 second.
When not silence, the intervals are 4ms, 27ms, 28ms, 4ms, 27ms, 28ms, ... 
(repeated with small +/-)
however this should be acceptable and normalizable by common jitter buffer.

However I experienced a bit shock that it happened as you mentioned.
But then I realized that I put wrong wireshark setting on time display 
format.
After I set time display format to 'since previous displayed packet' and put 
display filter (one direction only),
the result is as I mentioned above.

nanang



On 20/02/2008, Anshuman S. Rawat <arawat at 3clogic.com> wrote:
Hi Benny,

>From our wireshark/ethereal reports we were seeing RTP packets being sent 
out consistently at 10ms intervals instead of 20ms which is what ptime is 
(with G729 & G711 codecs - did not try any other codec). As it turned out 
that RTP packets were sent at 10ms intervals when silence was detected and 
20ms when audio is detected.

The issue was traced to the write_port() in conference.c. Seems like 
resampling is not done for silence/null frames and sent directly over the 
wire resulting in a RTP packet every 10ms. Though this did not cause any 
noticeable voice quality issue but it will definitely cause serious impact 
on the receiver's JB. Note - clock rate for conf bridge is 16000.

This looks like a bug to us. We are at revision 1738 so not sure if this has 
been fixed in a later revision. Or is it intended to do exactly as reported 
above? If yes, why?

Thanks,
Anshuman


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