[Asterisk-Dev] echo, delay and dropped packets in channel driver

[Ben Kramer]

heya,

Im the maintainer of the VoiceTronix channel driver (chan_vpb.c), and am
trying to track down an issue involving the issue in the subject.
A customer reported a 160ms delayed echo, which I can reproduce, when
bridging via ast_bridge. This is when a vpb channel is bridge to any
other channel via ast_bridge, including SIP and VPB, a native vpb/vpb
bridge doesn't have this problem.
I have been trying to track down where the delay is being introduced.
Here are a few things I have noticed:
1) the average time between receiving frames to write out to the board
is 19ms, often dropping to 18 or 17ms. It is rarely 20ms or more, even
though the we are being sent 20ms frames.
2) I enabled logging in ast_generic_bridge to see the servicing of the
channels, and I often see one channel or the other being serviced twice
in a row.

A decided to try and record the echo being heard, so added a Monitor()
command to the demo extens. What I see in the record files is no echo,
but I often see 20/40/60/80 ms gaps of silence in both the in and out
files.

Can anybody give me any ideas, comments, or pointers where to go from
here ?

Cheers,

Ben.