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

[Paulo Garcia]

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.

In my test, we receive a SIP call and the dialplan starts another call
to a digital channel. After the call is answered in the other side
wait a while and then hangup. During this time, I saw that the
interval between the last write callback call and the current one can
be longer than 20ms.

I'm using a powerful machine and my asterisk process during the test
uses less than 15% CPU. I'm also verifying my channel driver code to
check if there is something that can cause this delay but I didn't
find anything so far.

It doesn't happens so often but I'm concerned this is happening.

Any thoughts to help me find out where to looking at?

Thanks in advance!

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Paulo Garcia