Re: [hylafax-users] faxing over sip

[Aidan Van Dyk <aidan@xxxxxxxx>]

* A J Stiles <hylafax_resp@xxxxxxxxxxxxxxx> [071123 07:59]:

> Is there a protocol where you take the raw zeros and ones that would have been 
> sent to the fax machine's modem, bundle them up into packets, send the 
> resultant packets over a packet-switched network and recreate the image "at 
> leisure"  (i.e., not relying on the carrier frequency or bit rate for timing; 
> if necessary, we can buffer it and play it back at a fixed rate)  from the 
> reassembled packets at the far end?  Because it seems to me that this would 
> be the best way to get fax working properly with packet-switching.  If SIP 
> can handle other types of packet beside audio, so much the better.

That's basically T.38, without the "at leisure".  

But because "T.30" is a "negotiation" protocol, where both sides need to
talk to eachother, the "at leasure" *needs* to be pretty much
real-time...

T.38 is the IP equivalent of analog, where basically, instead
of "modulating" the T.30 protocol into an analog sound, it's
encapsulated into ip packets, as described earlier.  Of course, it's not
just a straight "dump" of the protocol into a reliable channel (like
TCP) because they tried to make it able to do everything, including
being a  "transparent" middle between to analog T.30 speakers, etc as
well...

If you can really afford "at leasure" (where you can't really know if
the receiver got your fax), it *is* being done already.  It's T.37
(store and forward), which is basically a specialized case of receiving
a fax at one point, and then emailing it somewhere specific.  Sounds
kind of like what HylaFAX has been able to do since forever ;-)

a.

-- 
Aidan Van Dyk                                             aidan@xxxxxxxx
Senior Software Developer                          +1 215 825-8700 x8103
iFAX Solutions, Inc.                                http://www.ifax.com/

Attachment: signature.asc
Description: Digital signature