[Iaxclient-devel] Latency and decoding of GSM streams under IAX2/iaxClient

[Steven S. <ss...@so...>]

I have been playing with IAX Phone and the library in an attempt to
determine what is the cause of the fairly large delay that seems to take
place when using IAX phone.

From what I can tell, the process of encoding the PC's linear PCM stream
into GSM packets is fairly fast.  The process of decoding GSM frames into a
linear PCM stream is fairly slow.  This is anecdotal, but is seems fairly
consistent from PC to PC.

The delay for audio data coming FROM my IAX Phone and going TO my
Grandstream BT101 (and through my Asterisk where it is trans-coded from GSM
to G.711) is minimal - perhaps 100-200ms.  The delay for sound FROM the
Grandstream to IAX Phone through Asterisk (which again trans-codes the g.711
to GSM) is MUCH larger -- perhaps as much as 750-1000ms.

I suppose the additional delay could be the fault of the Asterisk in the
middle, but somehow I seriously doubt it.  Does anybody out there have any
guess as to the culprit?  In testing the same scenarios with Firefly, I
found that the latency is noticeably less.  Does this indicate PA, or
perhaps the version of the GSM code, or is it the set of ring buffers in the
audio interface?

Any suggestions would be helpful!

Thanks

Steve

Steven Sokol
Owner/Manager
Sokol & Associates, LLC

Phone:  816.822.1807
IaxTel: 700.613.9004
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