isdn4linux and fax

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Hi,

Sven Liessem wrote:
> > > So now I'm wondering where the problem is. Is there really no way
> > > to have fax on internal isdn cards ???
> > 
> > No. Unless you have really fast CPU, starve the rest of the system,
> > and invest *LOTS* of time in programming the stuff.
> 
> Well that's the point that is VERY strange, at least for me. I understand
> these arguments when we're talking about class 1 support because the
> software must do everyting. 

Uh, no. It's a *LOT* more dirty work than "mere" class 1 support. You
have *tones* on the line (digitized tones, to be precise). Now you have to
analyze those waveforms, to find out what BITS are meant by these tones
(V.21, V.17, whatever).

If you have a card that has no DSP (which is the normal case for cheap
ISDN cards), you have to do all this on the host CPU. In real-time.

> Fax class 2 seems to boil down (sorry if
> this is VERY simplistic) to a couple of AT commands followed by a data
> flow including some special sequences (end of line, page and so on).

This is true. But then you have to do someone to do the A/D-D/A handling...

> As the DSP does the protocol handling, if the card reacts like an analog
> class 2 modem when you use it through ttyIxx, which seems to be the case for
> the USR which claims to be a Courier, what else do you have to program ?
> All just should work fine with a standard mgetty and sendfax.

The USR I-Modem works fine, but it's actually a "normal" modem (you don't
access it via ttyIxx either, it has a standard ttyS* serial port).

For things like TELES or Fritz! boards, there is no DSP on the card, and
thus, no class 1/class 2/whatever support.

gert

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