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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<TITLE>isdn_audio - audio extension of ttyI ISDN character devices</TITLE>
<!--#include virtual="/ssi/js.shtml" -->
<!--#include virtual="/ssi/buttondefs.shtml" -->
</HEAD>
<BODY BGCOLOR="#FFFFFF">
<TABLE WIDTH="100%">
<TR>
<TD ALIGN=LEFT WIDTH="90"><!--#include virtual="/ssi/b_home.shtml" --></TD>
<TD ALIGN=RIGHT WIDTH="90"><!--#include virtual="/ssi/b_index.shtml" --></TD>
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<PRE>
isdn_audio - audio extension of ttyI ISDN character devices
</PRE>
<H2>DESCRIPTION</H2><PRE>
This document describes the audio related extensions of
the modem emulation, provided by <EM>/dev/ttyIx</EM>.
The ISDN tty devices are equipped with a modem emulation
implementing a set of traditional and some special AT com­
mands. This provides easy use together with almost all
communication software that uses modem commands: <STRONG>mini­</STRONG>
<STRONG>com</STRONG>(1), <STRONG>seyon</STRONG>(1), <STRONG>XCept</STRONG>(1), <STRONG>uucico</STRONG>(8), <STRONG>mgetty</STRONG>(8), <STRONG>dip</STRONG>(8),
<STRONG>pppd</STRONG>(8) and more. When enabled during kernel configura­
tion, the emulator is capable of a reduced set of commands
to support audio. To use audio features, an 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 ISDN tty devices is always 64000
bps.
</PRE>
<H2>AUDIO RELATED AT COMMAND SET</H2><PRE>
This description does <STRONG>not</STRONG> include the standard AT command
set. For a description of the standard AT command set,
provided by the Linux ISDN subsystem, see <STRONG>ttyI</STRONG>(4). All
commands starting with <STRONG>AT+</STRONG> except <STRONG>AT+FCLASS</STRONG> are enabled
only, if audio mode is active. The following <STRONG>audio</STRONG>
<STRONG>related</STRONG> <STRONG>AT</STRONG> <STRONG>commands</STRONG> are supported by ISDN tty devices:
<STRONG>AT+FCLASS=0</STRONG>
Disable audio mode (default). This command sets
register <EM>18</EM> to <EM>4</EM>.
<STRONG>AT+FCLASS=8</STRONG>
Enable audio mode (default). This command sets reg­
ister <EM>18</EM> to <EM>5</EM>.
<STRONG>AT+FCLASS=?</STRONG>
Show possible modes.
<STRONG>AT+FCLASS?</STRONG>
Show current mode.
<STRONG>AT+VNH=</STRONG><EM>x</EM>
No function, provided for compatibility only.
<STRONG>AT+VNH=?</STRONG>
Always showing "1".
<STRONG>AT+VNH?</STRONG>
Always showing "1".
<STRONG>AT+VLS=</STRONG><EM>x</EM>
Select line <EM>x</EM>, where <EM>x</EM> is one of the following:
0 = No device.
2 = Phone line.
<STRONG>AT+VLS=?</STRONG>
Always showing "0,2".
<STRONG>AT+VLS?</STRONG>
Show current line.
<STRONG>AT+VRX</STRONG> Start audio recording. See below for more informa­
tion.
<STRONG>AT+VSD=</STRONG><EM>x</EM><STRONG>,</STRONG><EM>y</EM>
No function, provided for compatibility only. Pos­
sible parameters:
<EM>x</EM> = 0 ... 31
<EM>y</EM> = 0 ... 255
<STRONG>AT+VSD=?</STRONG>
Show possible parameters.
<STRONG>AT+VSD?</STRONG>
Show current parameters.
<STRONG>AT+VSM=</STRONG><EM>x</EM>
Select audio data format to <EM>x</EM>, where <EM>x</EM> is:
2 = ADPCM-2
3 = ADPCM-3
4 = ADPCM-4
5 = aLAW
6 = uLAW
<STRONG>AT+VSM=?</STRONG>
Show possible audio data formats.
<STRONG>AT+VSM?</STRONG>
Show current audio data format.
<STRONG>AT+VTX</STRONG> Start audio playback. See below for more informa­
tion.
</PRE>
<H2>GENERAL BEHAVIOUR</H2><PRE>
On incoming calls, if the application responds to a <STRONG>RING</STRONG>
by sending <STRONG>ATA</STRONG>, depending on the calling service, the emu­
lator responds with either <STRONG>CONNECT</STRONG> (data call) or <STRONG>VCON</STRONG>
(voice call).
When starting audio playback or recording, the emulator
responds with <STRONG>CONNECT</STRONG>. After that, the data transfer
in a <STRONG>single</STRONG> command. In this case, <STRONG>no</STRONG> 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, <STRONG>NO</STRONG> <STRONG>CARRIER</STRONG> is sent to the application, while stop­
ping data transfer with one of the DLE sequences, <STRONG>VCON</STRONG> is
sent. In any case, the message is preceeded by the appro­
priate DLE sequence for end of audio data and/or abort
respectively.
On outgoing voice calls, the emulator responds with <STRONG>VCON</STRONG>
upon connection setup.
</PRE>
<H2>AUDIO DATA FORMAT</H2><PRE>
When recording or playing back audio data, a kind of modi­
fied bisync protocol is used. When recording audio data,
the modem emulator is considered to be the <STRONG>sender</STRONG>, while
the application is the <STRONG>receiver</STRONG>. When playing back, this
relationship is reversed: The modem emulator acts as
<STRONG>receiver</STRONG>, while the application is the <STRONG>sender</STRONG>. With the
bisync protocol the character <STRONG>DLE</STRONG> (0x10) has a special
meaning and is used like an escape character. It is
always followed by a second character which has the fol­
lowing meanings defined:
<STRONG>ETX</STRONG> (0x03)
End of audio data. This code has to be sent by the
<STRONG>sender</STRONG>, indicating end of audio data.
<STRONG>DC4</STRONG> (0x14)
Abort sending. This code has to be sent by the
<STRONG>receiver</STRONG>, when it wishes to abort receiving data.
The <STRONG>sender</STRONG> has to reply by stop sending data and
finally indicating end of audio data.
<STRONG>DLE</STRONG> (0x10)
a single byte with value 0x10 in the data stream.
<STRONG>0</STRONG> Touch-tone "0" received. Valid only in direction
from emulator to application.
<STRONG>1</STRONG> Touch-tone "1" received. Valid only in direction
from emulator to application.
<STRONG>2</STRONG> Touch-tone "2" received. Valid only in direction
from emulator to application.
<STRONG>3</STRONG> Touch-tone "3" received. Valid only in direction
from emulator to application.
from emulator to application.
<STRONG>5</STRONG> Touch-tone "5" received. Valid only in direction
from emulator to application.
<STRONG>6</STRONG> Touch-tone "6" received. Valid only in direction
from emulator to application.
<STRONG>7</STRONG> Touch-tone "7" received. Valid only in direction
from emulator to application.
<STRONG>8</STRONG> Touch-tone "8" received. Valid only in direction
from emulator to application.
<STRONG>9</STRONG> Touch-tone "9" received. Valid only in direction
from emulator to application.
<STRONG>#</STRONG> Touch-tone "#" received. Valid only in direction
from emulator to application.
<STRONG>*</STRONG> Touch-tone "*" received. Valid only in direction
from emulator to application.
<STRONG>A</STRONG> Touch-tone "A" received. Valid only in direction
from emulator to application.
<STRONG>B</STRONG> Touch-tone "B" received. Valid only in direction
from emulator to application.
<STRONG>C</STRONG> Touch-tone "C" received. Valid only in direction
from emulator to application.
<STRONG>D</STRONG> Touch-tone "D" received. Valid only in direction
from emulator to application.
</PRE>
<H2>AUTHOR</H2><PRE>
Fritz Elfert &lt;fritz@wuemaus.franken.de&gt;
</PRE>
<H2>SEE ALSO</H2><PRE>
<A HREF="ttyI.shtml">ttyI</A>(4).
</PRE>
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