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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 emulation, 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 communica-
       tion software  that  uses  modem  commands:  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-capa-
       ble 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 follow-
       ing 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 CON-
       NECT message is sent to the application and the protocol described below is started  imme-
       diately.

       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 respectively.

       On outgoing voice calls, the emulator responds with VCON upon connection 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 considered 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  protocol
       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, indicating 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 3.1pre4			    1999/09/06				    isdn_audio(4)
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