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$Id: README.audio,v 1.1.1.1 2001-09-10 07:44:10 simons Exp $
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ISDN subsystem for Linux.
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Description of audio mode.
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When enabled during kernel configuration, the tty emulator of the ISDN
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subsystem is capable of a reduced set of commands to support audio.
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This document describes the commands supported and the format of
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audio data.
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Commands for enabling/disabling audio mode:
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AT+FCLASS=8 Enable audio mode.
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This affects the following registers:
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S18: Bits 0 and 2 are set.
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S16: Set to 48 and any further change to
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larger values is blocked.
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AT+FCLASS=0 Disable audio mode.
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Register 18 is set to 4.
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AT+FCLASS=? Show possible modes.
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AT+FCLASS? Report current mode (0 or 8).
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Commands supported in audio mode:
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All audio mode commands have the one of the following form:
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AT+Vxx? Show current setting.
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AT+Vxx=? Show possible settings.
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AT+Vxx=v Set simple parameter.
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AT+Vxx=v,v ... Set complex parameter.
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where xx is a two-character code and v are alphanumerical parameters.
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The following commands are supported:
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AT+VNH=x Auto hangup setting. NO EFFECT, supported
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for compatibility only.
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AT+VNH? Always reporting "1"
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AT+VNH=? Always reporting "1"
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AT+VIP Reset all audio parameters.
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AT+VLS=x Line select. x is one of the following:
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2 = Phone line.
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AT+VLS=? Always reporting "0,2"
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AT+VLS? Show current line.
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AT+VRX Start recording. Emulator responds with
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CONNECT and starts sending audio data to
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the application. See below for data format
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AT+VSD=x,y Set silence-detection parameters.
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Possible parameters:
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x = 0 ... 31 sensitivity threshold level.
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(default 0 , deactivated)
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y = 0 ... 255 range of interval in units
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of 0.1 second. (default 70)
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AT+VSD=? Report possible parameters.
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AT+VSD? Show current parameters.
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AT+VSM=x Select audio data format.
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Possible parameters:
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2 = ADPCM-2
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3 = ADPCM-3
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4 = ADPCM-4
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5 = aLAW
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6 = uLAW
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AT+VSM=? Show possible audio formats.
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AT+VTX Start audio playback. Emulator responds
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with CONNECT and starts sending audio data
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received from the application via phone line.
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General behavior and description of data formats/protocol.
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when a connection is made:
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On incoming calls, if the application responds to a RING
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with ATA, depending on the calling service, the emulator
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responds with either CONNECT (data call) or VCON (voice call).
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On outgoing voice calls, the emulator responds with VCON
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upon connection setup.
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Audio recording.
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When receiving audio data, a kind of bisync protocol is used.
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Upon AT+VRX command, the emulator responds with CONNECT, and
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starts sending audio data to the application. There are several
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escape sequences defined, all using DLE (0x10) as Escape char:
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End of audio data. (i.e. caused by a
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hangup of the remote side) Emulator stops
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recording, responding with VCON.
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Abort recording, (send by appl.) Emulator
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stops recording, sends DLE,ETX.
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Escape sequence for DLE in data stream.
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0 Touchtone "0" received.
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...
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9 Touchtone "9" received.
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# Touchtone "#" received.
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* Touchtone "*" received.
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A Touchtone "A" received.
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B Touchtone "B" received.
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C Touchtone "C" received.
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D Touchtone "D" received.
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q quiet. Silence detected after non-silence.
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s silence. Silence detected from the
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start of recording.
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Currently unsupported DLE sequences:
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c FAX calling tone received.
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b busy tone received.
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Audio playback.
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When sending audio data, upon AT+VTX command, emulator responds with
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CONNECT, and starts transferring data from application to the phone line.
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The same DLE sequences apply to this mode.
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Full-Duplex-Audio:
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When _both_ commands for recording and playback are given in _one_
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AT-command-line (i.e.: "AT+VTX+VRX"), full-duplex-mode is selected.
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In this mode, the only way to stop recording is sending
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and the only way to stop playback is to send .
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