[Asterisk-bsd] MeetMe drift

[Michael Iedema]

Hello David,

Yes, I'm digging up this issue, yet again. :)

>    I should probably also point out that while this may help your problem,
> it won't completely solve it because it is only one piece of the puzzle.
> The timer inaccuracy results in extra conference latency over time, but
> the other problem is that delays in scheduling the Asterisk process can
> cause big and sudden jumps in latency that this new ztdummy.c won't fix.
>    The real problem is that Asterisk allows voice packets to back up in
> its input queue, and that has an unbounded queue depth.
>    Attached is a patch to Asterisk's channel.c that limits the queue
> depth of voice frames to a maximum of just 2 frames (40ms) on the channel
> input queue. Under certain circumstances, this may result in an occasional
> dropped voice frame, but that is better in my opinion than adding extra
> latency to the call.

Some reports of audio quality problems coming in from the AskoziaPBX
community seem to incriminate this patch. When this occurs on IAX
channels, enabling / increasing the jitterbuffer seems to help which
leads me to a dropped frame issue.

This makes sense as these systems are usually low-power embedded or
SBC systems. Removing this patch from my build process should take
care of the problem but I really like the idea of such a patch
providing tangible feedback when the system's limits have been
exceeded instead of merely increasing delay infinitely.

My question, do you have a recommended higher value for this queue
limit? I was thinking of setting it to 5 frames. This would be roughly
100ms which, in a round-trip situation would lead to a maximum of
200ms of delay being contributed to the call. This is, as I understand
it, the theoretical limit in delay that a call can have before its
participants are unable to coordinate their conversation.

Thoughts?

Once again, thanks for contributing and providing insight into these issues!

Regards,
-Michael