V.21 Modem for ISDN4BSD.

INTRODUCTION:

The modem is implemented in software and is rather simple minded.

It works with my Telebit TB2500 and Zyxel 2864I modems.

There are plenty of knobs and handles which can be adjusted and I have
no real idea what to set them to for best all-round performance.

The carrier detect timer may be a bit short tempered, and this is
probably why the dialing modem needs to be told to talk V.21 up
front.  If this code were mode tolerant of loss of carrier auto
negotiation might work.

When you get carrier ("CONNECT 300"), you must press a key before the
login banner gets printed.  See the comments in "input_byte" why this
is.

THE KERNEL PART:

Implementes a crude "send these tones" facility, but it is enough to
take most of the real-time worries out of doing FSK modulation in
software.  If suitably extended, the code could also be used to
send DTMF tones and other similar signals.

INSTALLATION:

The program is started from /etc/isdn/isdnd.rc:

entry
        name                    = I4BTEL
        usrdevicename           = tel
        usrdeviceunit           = 0
        isdncontroller          = 0
        isdnchannel             = -1
        local-phone-incoming    = 2934812934
        remote-phone-incoming   = *
        dialin-reaction         = answer
        answerprog              = v21modem
        b1protocol              = raw
        idletime-incoming       = 5


Poul-Henning (phk@freebsd.org)
19991212

$FreeBSD: src/share/examples/isdn/v21/README,v 1.1.2.1 2001/08/10 14:59:48 obrien Exp $
$DragonFly: src/share/examples/isdn/v21/README,v 1.2 2003/06/17 04:36:57 dillon Exp $