[Asterisk-Users] FAX, IAX and *....Maybe I'm dreaming...:-)

Steve Underwood steveu at coppice.org
Sun Dec 14 17:24:04 MST 2003

ProvoCityPower wrote:

> The question asked here, "why on earth you want to push fax data over 
> a VoIP link at
> all. Fax compression isn't very efficient." may speak volumes about 
> the future role of VOIP. My plans are to role out a VOIP connection to 
> thousands of Customers. Many have legacy fax equipment. Am I to assume 
> that they will toss out their fax equipment and join the PC based 
> faxing crowd? I don't think I can control this. If I am going to offer 
> an aternative to the legacy wire providers then I have to offer a 
> comparable service. One that for example allows a customer to use a 
> legacy fax machine in the same way.
> If this thought sidetracks the intent of this thread, you have my 
> apologies, but I do think that legacy fax functionality is essential.

Legacy FAX will be very important for years. The last people to abandon 
it are the most senior managers. Therefore, apart from anything else, 
their buyin to a change to VoIP depends on keeping their olde worlde FAX 
facilities alive. However, I think this has nothing to do with the 
original poster's intent.

Sending FAXes over IP as audio is dumb. Its troublesome, error prone, 
and consumes too much bandwidth. The right way is to use a FAX modem to 
translate between audio and the digital data stream of the image itself. 
Then the compact image data can be conveyed reliably. If the far end is 
not using IP, another modem can be used to return the FAX to its 
analogue form for delivery. If you wish to interwork traditional 
analogue FAX machines, with newer IP capable FAX machines you *have* to 
do this. This is what the H323 protocols do. T.38 is the relevant FAX 
over IP protocol. I don't know if there is a similar SIP standard, but 
there should be. FAX to e-mail and e-mail to FAX is the other inportant 
way to blend the old with the new.


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