[Asterisk-Dev] has somebody ever tested faxdetection ?

[Thomas Häger]

Hi all,

lately we had a little bug with misdn echo cancel. If a fax was detected 
we got a kernel freeze.
This was caused by NULL pointer access inside of our echocanceler code. 
In this context we wanted to test this issue by calling a fax machine to 
effect the kernel freeze. But nothing happend. So we debugged a little 
bit, and we saw that the tone of 2100 Hz was never detected ... 
respectively the amount of 3 cyles were never reached.

In debugging we saw several values for "det->tone_cycle_duration", but 
no value was between   (425*8) 3400 and (475*8) 3800.
This must happens more than twice, so that ec will be disabled.
Has someone an idea what exactly is the meaning of these values 
(3400-3800) ?
You can find the function in "zaptel/ecdis.h".

We have tested it as follows:

SIP --> Asterisk --> chan_msidn (TE) ---> PSTN / ISDN(PtP) ---> 
faxmachine other side.
How customers reported us, they got a kernel freeze in this case. But we 
didn't get a kernel freeze, because the 2100Hz was never detected, and 
EC was enabled all the time.
We tested also fax detection with playing back a reference audio file of 
2100 Hz (5 sec.), but nothing happened.

Has someone enough experiences with fax detection and can give us a hint 
why the fax detection didn't work for our configuration ?


Thanks,

Thomas5
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