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

Nanang Izzuddin nanang.izzuddin at gmail.com
Wed Feb 20 15:53:26 EST 2008

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
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.


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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