[asterisk-users] FAX reliability

[Lee Howard]

Steve Underwood wrote:
> Hi Lee,
>
> Lee Howard wrote:
>> Hi Steve,
>>
>> Steve Underwood wrote:
>>> In chan_dahdi.c there is now code that extends the buffering inside 
>>> dadhi when a FAX is detected, and puts the buffering back to normal 
>>> at the end. This isn't really a cure - its more of a bandaid. 
>>> However, I expect it has the desired effect if they have put it into 
>>> the trunk code.
>>>
>>> You need to enable this feature in chan_dahdi.conf.
>>>   
>>
>>> Very interestingly, many people who have problems sending from 
>>> app_txfax or app_fax have no problem sending from iaxmodem + 
>>> HylaFAX. It seems Asterisk can feed a zaptel/dahdi channel much more 
>>> reliably when passing a signal through, than when generating on in 
>>> an app.
>>
>> So are the chan_dahdi.c developments mentioned of any practical value 
>> to iaxmodem users?
> That's a good question, and I have no idea about the answer. Some 
> people who have had problems sending from app_txfax say iaxmodem + 
> HylaFAX works OK on the same machine. This seems strange, as you might 
> expect a problem in scheduling I/O would affect passthrough as well as 
> applications. What I don't know is whether they just have a lot less 
> trouble with iaxmodem, or they have no trouble at all.
>
> Do you get reports from people who say receive is stable, but transmit 
> is not?

There have been a few reports of that situation, but all of them that I 
recall had to do with people who were trying to use VoIP for fax 
(HylaFAX and iaxmodem tend to be much more tolerant of the audio 
cut-outs caused by jitter than are other receivers).

Otherwise, no, I don't have any of those situations that I can point out.

I suppose that I'd need to make some recordings to say for certain 
whether audio cut-outs were occurring.  However, what would really be 
nice would be to see some comments come from whatever developer at 
Digium made those chan_dahdi.c modifications.

Thanks,

Lee.