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

[Dan]

Hi,

----- Original Message ----- 
From: "Alastair Maw" <asterisk at almaw.com>
To: <asterisk-users at lists.digium.com>
Sent: Friday, December 12, 2003 4:58 PM
Subject: Re: [Asterisk-Users] FAX, IAX and *....Maybe I'm dreaming...:-)


> On 12/12/03 13:56, Dan wrote:
> > This is because the fax is transmitted using the audio stream.
> > It is not related to the signaling protocol (SIP/IAX etc.) but to the
audio
> > codec used.
>
> Fax uses FSK modulation to transmit the data. If you compress this in a
> lossy way (GSM, MP3, whatever) then the integrity of the data is
> affected (more or less seriously depending on the codec used). Fax
> machines are generally quite picky, so compressing faxes is unlikely to
> work.
>
> I'm wondering why on earth you want to push fax data over a VoIP link at
> all. Fax compression isn't very efficient.

Who wants that???
By fax data I mean the data contained in a fax (basically a picture file),
not the fax data audio stream.
It can be converted (GIF or JPG) then sent reliable over a slow IP link.
Just a special codec at both ends, able to pass the data to the fax app or a
fax machine connected to a TDM400/ AT or whatever.

> It would be much less
> bandwidth intensive to decode the fax and send it over as proper data
> rather than audio, compressed using gzip/gif/png/something else.

This is exactly what would be great to have it.

BR,
Dan