[asterisk-dev] media watchdog for res_fax

[Steve Underwood]

On 01/03/2011 10:03 PM, Kevin P. Fleming wrote:
> On 01/03/2011 07:02 AM, Kristijan Vrban wrote:
>> In https://issues.asterisk.org/view.php?id=18557 i noticed that
>> app_fax has a watchdog to
>> identify a media (T.30) timeout. But res_fax not. The question: Should
>> res_fax also have this
>> watchdog, would a patch be merged ?
>>
>>  From app_fax.c
>>
>> /* Watchdog. I have seen situations when remote fax disconnects
>> (because of poor line
>>     quality) while SpanDSP continues staying in T30_STATE_IV_CTC 
>> state forever.
>>     To avoid this, we terminate when we see that T30 state does not
>> change for 5 minutes.
>>     We also terminate application when more than 30 minutes passed 
>> regardless of
>>     state changes. This is just a precaution measure - no fax should
>> take that long */
>>
>> #define WATCHDOG_TOTAL_TIMEOUT    30 * 60
>> #define WATCHDOG_STATE_TIMEOUT    5 * 60
>
> I would expect the T.30 stack in the res_fax_* module to handle such 
> loss of media... but it doesn't sound like it would be a bad idea for 
> res_fax to do this as well.
>
All timing in the spandsp FAX engine is derived from the media. If the 
media stops, so does the timing. In at least some versions of app_fax we 
picked up a lack of media (something like a one second timeout), and 
went into a separately timed mode. I guess the res_fax module isn't 
doing that.

Steve