[asterisk-dev] Problems with massively (continously) growing skew

[Michael Maier]

Hello!

I'm facing a massive problem during sending or receiving of fax (spandsp, pjsip,
asterisk 16.9 bundled pjsip). Affected are always the packages sent by asterisk.
The packages received are pretty perfect.

Tracetool is pcapsipdump.

Problem can't be seen that massive during "normal" (non) fax calls (maybe just a
little bit).


What can be seen?

Inbound fax:
- Fax passthrough (alaw)
- Fax received by asterisk
- no Jitterbuffer
- after about 1 minute of duration (> 6100 packages):
  skew rises from +-0 to -30 (from one package to the
  other) and all following packages afterwards have -19.9
  ms (one package seems to be just dropped without any
  sequence error (sequence counter is ok))
- Another 4000 packages later one more dropped package
  (without sequence error) from -19.9 to -52 and
  afterwards all following packages -39.9 ms (sampling
  rate: 20 ms) -> exactly the same as before but from -19
  to - 40 ms.
- Duration: ~ 2 minutes
- always reproducible


Outbound fax
- Fax passthrough (alaw)
- sent via iaxmodem through asterisk (iaxmodem connected
  to asterisk via iax). No jitterbuffer!
- skew is rising continuously (+362 ms after 363 s
  duration -> every second +1 ms)
- always reproducible


Does anybody has any idea?


Thanks
Michael