[asterisk-dev] Problems with massively (continously) growing skew
m1278468 at mailbox.org
Sun Apr 5 13:18:18 CDT 2020
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:
> 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 
The red line represents the outbound packets/s. The green line are the incoming
Example 2 
The green line represents the outbound packets/s. The red line are the incoming
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