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

[Tilghman Lesher]

On Friday 12 December 2003 07:25, Dan wrote:
> Hi,
>
> It would be great if the IAX protocol will be able to tranfer fax
> data (even converted in another format) between Asterisk boxes,
> using low bandwidth codecs like GSM.
> I know that this is possible only with the G.711 now (passing faxes
> using the audio stream), but.... maybe in the future...some native
> support will permit this.

You're not going to get that working because GSM is a lossy codec.
It is able to get extreme savings in size, because it optimizes out
parts of the sound that most humans don't hear.  However, that same
bandwidth that humans don't hear is exactly the bandwidth that the fax
application uses to transmit valuable portions of the image.

Therefore, the GSM codec is never going to be appropriate for sending
faxes.  Besides, if you need low bitrates for your IP connection,
you're likely to experience delays in the fax negotiation -- which
will probably result in a failed fax attempt.  If you want to be able
to send faxes in this way, then negotiate the fax at one end, and
email the resulting TIFF to the other end.

-Tilghman