[asterisk-dev] Channel Driver's Write callback called with 140ms intervals

critch critch at basesys.com
Mon Nov 26 10:21:08 CST 2007

On Mon, 2007-11-26 at 10:35 -0200, Paulo Garcia wrote:
> Hi,
> I'm doing some performance tests in our channel driver and I realized
> that in calls between our channel and a SIP phone, the write callback
> is called almost the time in 20ms intervals, which is correct.
> However, sometimes the callback is called with longer intervals
> between each call: 60ms, 80ms and reaching 140ms.
> First I thought that as a SIP call, due to network conditions, the
> frame can be buffered somewhere and then when the write callback is
> called after, e.g., 60ms, I would have a frame 3 times greater then
> the regular one (480 samples rather than 160) but the frame size is
> always of 160 samples.

Many reasons exist for this. 

SIP is UDP based. If you lose a packet, you will not get it later. 

Some phones have silence suppression, such that they don't fill the
bandwidth with the sound of silence. For those, asterisk would receive
notice of the silence, but no audio. I do not know the current state of
dealing with silence.

critch <critch at basesys.com>

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