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isdn_audio(4)			 Special files			 isdn_audio(4)

NAME
       isdn_audio - audio extension of ttyI ISDN character devices

DESCRIPTION
       This  document describes the audio related extensions of the modem emu‐
       lation, provided by /dev/ttyIx.

       The 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  com‐
       mands:  minicom(1),  seyon(1),  XCept(1), uucico(8), mgetty(8), dip(8),
       pppd(8) and more. When enabled during kernel configuration, the	emula‐
       tor  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.

AUDIO RELATED AT COMMAND SET
       This description does not include the standard AT command  set.	For  a
       description  of the standard AT command set, provided by the Linux ISDN
       subsystem,  see	ttyI(4).   All	commands  starting  with  AT+	except
       AT+FCLASS  are  enabled	only,  if audio mode is active.	 The following
       audio related AT commands are supported by ISDN tty devices:

       AT+FCLASS=0
	      Disable audio mode (default). This command sets register	18  to
	      4.

       AT+FCLASS=8
	      Enable audio mode. This command sets register 18 to 5.

       AT+FCLASS=?
	      Show possible modes.

       AT+FCLASS?
	      Show current mode.

       AT+VNH=x
	      No function, provided for compatibility only.

       AT+VNH=?
	      Always showing "1".

       AT+VNH?
	      Always showing "1".

       AT+VIP Reset all audio parameters.

       AT+VLS=x
	      Select line x, where x is one of the following:
	      0 = No device.
	      2 = Phone line.

       AT+VLS=?
	      Always showing "0,2".

       AT+VLS?
	      Show current line.

       AT+VRX Start audio recording. See below for more information.

       AT+VSD=x,y
	      Set silence-detection parameters.
	      Possible parameters:
	      x = 0 ... 31  sensitivity threshold level.
	      (default 0 , deactivated)
	      y = 0 ... 255 range of interval in units of 0.1 second. (default
	      70)

       AT+VSD=?
	      Show possible parameters.

       AT+VSD?
	      Show current parameters.

       AT+VSM=x
	      Select audio data format to x, where x is:
	      2 = ADPCM-2
	      3 = ADPCM-3
	      4 = ADPCM-4
	      5 = aLAW
	      6 = uLAW

       AT+VSM=?
	      Show possible audio data formats.

       AT+VSM?
	      Show current audio data format.

       AT+VTX Start audio playback. See below for more information.

GENERAL BEHAVIOUR
       On incoming calls, if the application responds to  a  RING  by  sending
       ATA,  depending	on  the	 calling  service,  the emulator responds with
       either CONNECT (data call) or VCON (voice call).

       When starting audio playback or recording, the emulator	responds  with
       CONNECT.	  After	 that,	the data transfer  protocol described below is
       used.  It is possible to initiate full duplex data transfer by  issuing
       AT+VRX+VTX  in  a  single  command. In this case, 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, NO CARRIER is sent to the
       application,  while  stopping  data  transfer  with  one	 of  the   DLE
       sequences,  VCON	 is sent. In any case, the message is preceeded by the
       appropriate DLE sequence for end of audio  data	and/or	abort  respec‐
       tively.

       On  outgoing  voice calls, the emulator responds with VCON upon connec‐
       tion setup.

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 con‐
       sidered to be the sender, while the application is the receiver.	  When
       playing back, this relationship is reversed: The modem emulator acts as
       receiver, while the application is the sender.  With the bisync	proto‐
       col  the character 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:

       ETX (0x03)
	      End of audio data. This code has to be sent by the sender, indi‐
	      cating end of audio data.

       DC4 (0x14)
	      Abort sending. This code has to be sent by the receiver, when it
	      wishes  to abort receiving data. The sender has to reply by stop
	      sending data and finally indicating end of audio data.

       DLE (0x10)
	      a single byte with value 0x10 in the data stream.

       0      Touch-tone "0" received. Valid only in direction	from  emulator
	      to application.

       1      Touch-tone  "1"  received. Valid only in direction from emulator
	      to application.

       2      Touch-tone "2" received. Valid only in direction	from  emulator
	      to application.

       3      Touch-tone  "3"  received. Valid only in direction from emulator
	      to application.

       4      Touch-tone "4" received. Valid only in direction	from  emulator
	      to application.

       5      Touch-tone  "5"  received. Valid only in direction from emulator
	      to application.

       6      Touch-tone "6" received. Valid only in direction	from  emulator
	      to application.

       7      Touch-tone  "7"  received. Valid only in direction from emulator
	      to application.

       8      Touch-tone "8" received. Valid only in direction	from  emulator
	      to application.

       9      Touch-tone  "9"  received. Valid only in direction from emulator
	      to application.

       #      Touch-tone "#" received. Valid only in direction	from  emulator
	      to application.

       *      Touch-tone  "*"  received. Valid only in direction from emulator
	      to application.

       A      Touch-tone "A" received. Valid only in direction	from  emulator
	      to application.

       B      Touch-tone  "B"  received. Valid only in direction from emulator
	      to application.

       C      Touch-tone "C" received. Valid only in direction	from  emulator
	      to application.

       D      Touch-tone  "D"  received. Valid only in direction from emulator
	      to application.

AUTHOR
       Fritz Elfert <fritz@isdn4linux.de>

SEE ALSO
       ttyI(4).

ISDN 4 Linux 3.12		  1999/09/06			 isdn_audio(4)
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