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

[Michael Maier]

Hello!

Meanwhile, I tested several different versions of spandsp - but always the same
problem. I tested another platform (for iaxmodem) - same behavior, too.

All tests are done with Asterisk 16.9.0 / pjsip.


At first, let's concentrate on the inbound faxes. It's asterisk, which receives
the fax on its own (no other tool involved).


On 04.04.20 at 15:33 Michael Maier wrote:
> 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

I found another way to demonstrate the problem: using Wiresharks I/O Graph in
statistics (packets/second). Here you can see very well the problem: there are
missing packets - but without any sequence error - they are just not created.
Testcase here is a pretty short fax. The exactly same behavior can be found with
longer faxes, too.

You can find find two screenshots (2 examples) here:

Example 1 [1]
The red line represents the outbound packets/s. The green line are the incoming
packet/s.

Example 2 [2]
The green line represents the outbound packets/s. The red line are the incoming
packet/s.


Thanks
Kind regards
Michael


[1] https://www.bilder-upload.eu/bild-898820-1586108183.png.html

[2] https://www.bilder-upload.eu/bild-eaf123-1586109449.png.html