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.TH isdn_audio 4 "1999/09/06" "ISDN 4 Linux 3.27" "Special files"
.SH NAME
isdn_audio \- audio extension of ttyI ISDN character devices
.SH DESCRIPTION
This document describes the audio related extensions of the modem
emulation, provided by
.IR /dev/ttyIx .

The
.SM ISDN
tty devices are equipped with a modem emulation implementing a set of
traditional and some special AT commands. This provides easy use
together with almost all communication software that uses modem
commands:
.BR minicom (1),
.BR seyon (1),
.BR XCept (1),
.BR uucico (8),
.BR mgetty (8),
.BR dip (8),
.BR pppd (8)
and more. When enabled during kernel configuration, the emulator
is capable of a reduced set of commands to support audio. To use
audio features, an
.SM ISDN
card with a audio-capable low-level driver is needed. Currently
the only audio-capable drivers are the teles and HiSax driver.

The port speed of the
.SM ISDN
tty devices is always 64000 bps.

.SH AUDIO RELATED AT COMMAND SET
This description does
.B not
include the standard AT command set. For a description of the standard
AT command set, provided by the Linux
.SM ISDN
subsystem, see
.BR ttyI (4).
All commands starting with
.B AT+
except
.B AT+FCLASS
are enabled only, if audio mode is active.
The following 
.B audio related AT commands
are supported by
.SM ISDN
tty devices:
.TP
.B AT+FCLASS=0
Disable audio mode (default). This command sets register
.IR 18 " to " 4 .
.TP
.B AT+FCLASS=8
Enable audio mode. This command sets register
.IR 18 " to " 5 .
.TP
.B AT+FCLASS=?
Show possible modes.
.TP
.B AT+FCLASS?
Show current mode.
.TP
.BI AT+VNH= x
No function, provided for compatibility only.
.TP
.B AT+VNH=?
Always showing "1".
.TP
.B AT+VNH?
Always showing "1".
.TP
.B AT+VIP
Reset all audio parameters.
.TP
.BI AT+VLS= x
Select line
.IR x ", where " x
is one of the following:
.RS
0 = No device.
.br
2 = Phone line.
.RE
.TP
.B AT+VLS=?
Always showing "0,2".
.TP
.B AT+VLS?
Show current line.
.TP
.B AT+VRX
Start audio recording. See below for more information.
.TP
.BI AT+VSD= x , y
Set silence-detection parameters. 
.RS
Possible parameters:
.br
.IR x " = 0 ... 31  sensitivity threshold level."
.br
(default 0 , deactivated)
.br
.IR y " = 0 ... 255 range of interval in units of 0.1 second. (default 70)"
.RE
.TP
.B AT+VSD=?
Show possible parameters.
.TP
.B AT+VSD?
Show current parameters.
.TP
.BI AT+VSM= x
Select audio data format to
.IR x ", where " x " is:"
.RS
2 = ADPCM-2
.br
3 = ADPCM-3
.br
4 = ADPCM-4
.br
5 = aLAW
.br
6 = uLAW
.RE
.TP
.B AT+VSM=?
Show possible audio data formats.
.TP
.B AT+VSM?
Show current audio data format.
.TP
.B AT+VTX
Start audio playback. See below for more information.
.SH GENERAL BEHAVIOUR
On incoming calls, if the application responds to a
.BR RING " by sending " ATA ,
depending on the calling service, the emulator responds with either
.BR CONNECT " (data call) or " VCON " (voice call)."

When starting audio playback or recording, the emulator responds
with
.BR CONNECT .
After that, the data transfer  protocol described below is used.
It is possible to initiate full duplex data transfer by issuing
.B AT+VRX+VTX
in a
.B single
command. In this case,
.B no
CONNECT message is sent to the application and the protocol described
below is started immediately.

When stopping audio playback or recording, the message returned by
the emulator depends on how the data transfer is stopped. If the
data transfer is stopped by a remote hangup,
.B NO CARRIER
is sent to the application, while stopping data transfer with one
of the DLE sequences,
.B VCON
is sent. In any case, the message is preceded by the appropriate
DLE sequence for end of audio data and/or abort respectively.

On outgoing voice calls, the emulator responds with
.B VCON
upon connection setup.
.SH AUDIO DATA FORMAT
When recording or playing back audio data, a kind of modified bisync
protocol is used. When recording audio data, the modem emulator is
considered to be the
.BR sender ,
while the application is the
.BR receiver .
When playing back, this relationship is reversed: The modem emulator acts
as
.BR receiver ,
while the application is the
.BR sender .
With the bisync protocol the character
.B DLE
(0x10) has a special meaning and is used like an escape character.
It is always followed by a second character which has the following
meanings defined:
.TP
.BR ETX " (0x03)"
End of audio data. This code has to be sent by the
.BR sender ,
indicating end of audio data.
.TP
.BR DC4 " (0x14)"
Abort sending. This code has to be sent by the
.BR receiver ,
when it wishes to abort receiving data. The
.B sender
has to reply by stop sending data and finally indicating end of audio data.
.TP
.BR DLE " (0x10)"
a single byte with value 0x10 in the data stream.
.TP
.B 0
Touch-tone "0" received. Valid only in direction from emulator to application.
.TP
.B 1
Touch-tone "1" received. Valid only in direction from emulator to application.
.TP
.B 2
Touch-tone "2" received. Valid only in direction from emulator to application.
.TP
.B 3
Touch-tone "3" received. Valid only in direction from emulator to application.
.TP
.B 4
Touch-tone "4" received. Valid only in direction from emulator to application.
.TP
.B 5
Touch-tone "5" received. Valid only in direction from emulator to application.
.TP
.B 6
Touch-tone "6" received. Valid only in direction from emulator to application.
.TP
.B 7
Touch-tone "7" received. Valid only in direction from emulator to application.
.TP
.B 8
Touch-tone "8" received. Valid only in direction from emulator to application.
.TP
.B 9
Touch-tone "9" received. Valid only in direction from emulator to application.
.TP
.B #
Touch-tone "#" received. Valid only in direction from emulator to application.
.TP
.B *
Touch-tone "*" received. Valid only in direction from emulator to application.
.TP
.B A
Touch-tone "A" received. Valid only in direction from emulator to application.
.TP
.B B
Touch-tone "B" received. Valid only in direction from emulator to application.
.TP
.B C
Touch-tone "C" received. Valid only in direction from emulator to application.
.TP
.B D
Touch-tone "D" received. Valid only in direction from emulator to application.
.SH AUTHOR
Fritz Elfert <fritz@isdn4linux.de>
.SH SEE ALSO
.BR ttyI (4).