[Asterisk-Dev] has somebody ever tested faxdetection ?

[Thomas Häger]

Hi Steve,

ah! I understand. Is it so that faxmachines aren't configurde for 
sending ec-disable tone ?
Is this a special setting at the faxmachine, or will it be sent 
everytime normally ?


Greetings,

Thomas.

Steve Underwood schrieb:

> Thomas Häger wrote:
>
>> 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".
>
>
> The detector you are looking at does not detect continuous 2100Hz 
> tone. It detects a 2100Hz tone with phase reversals every 450ms. This 
> is the echo canceller disable tone specified in G.164/G.165. It is not 
> the FAX answer tone. The numbers you quote allow a suitable tolerance 
> for the 450ms.
>
>> 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 ?
>
>
> The FAX answer tone is detected in *, not in the driver.
>
> Regards,
> Steve
>
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