[Asterisk-Users] FAX difference IAXModem / Hylafax and spandsp app_rxfax

[Lee Howard]

James Armstrong wrote:

> I was wondering if anyone would know why receiving a fax via an 
> extension -> IAXModem -> Hylafax would work, but fax -> rxfax 
> (spandsp) does not. When I try to use the app_rxfax the fax machine 
> reports a comm error. If I use the IAXModem client connected to 
> Hylafax it works.


HylaFAX supports ECM in Class 1, and so undoubtedly the fax session with 
rxfax was quite different from the fax session with HylaFAX.  So it's 
not a perfect apples-to-apples comparison, but I would generally 
consider HylaFAX to be more mature than rxfax/txfax.

The fact that the fax works with iaxmodem but not with rxfax means that 
the error is not with spandsp (the library), but rather with the rxfax 
application.

> I don't mind the Hylafax method, but I want to be able to route the 
> fax/pdf to a mail address based on the extension/DID called. As it is 
> right now, Hylafax does not know which DID was called and only sends 
> notifications to a general mailbox. 


Then you're missing something.  HylaFAX does (or at least could) know 
the extension that was dialed.  You should be using HylaFAX 4.2.2 or 
4.2.3, and your modem config file should have these lines in it:

  ModemResetCmds:  AT+VCID=1
  CallIDPattern:  "NDID="

That will parse the modem output for "NDID=" responses and put them into 
the CallID array which is passed to faxrcvd and FaxDispatch.  So if 
you're using the default modem config file provided with IAXmodem then 
you'd refer to $CALLID4.  See 'man callid' for a more detailed explanation.

Lee.