User`s manual
AT Command Reference Manual
7-2 1048
In this mode, and when the sampling rate is 7.2 kHz, the modem detects and reports DTMF, dial tone, and busy tone
cadence as enabled by the #VTD command. Additionally, the modem detects and reports inactivity (periods of silence) as
enabled by the #VSS command. The modem can exit the Voice Receive Mode only via a DTE Key Abort, or via Disconnect
Inactivity timer (S30) expiration.
7.1.3 Voice Transmit Mode
Voice Transmit Mode is entered when the DTE issues the #VTX command in order to transmit voice data. In this mode,
when the sampling rate is 7.2 kHz, the modem continues to detect and report DTMF and calling tones if enabled by the
#VTD command. This mode is typically used when playing back greeting messages or previously received/recorded
messages.
In this mode:
1. If the Voice Sub-configuration is in operation, voice decompression is provided by the ADPCM codec, and the
decompressed ADPCM voice data is then reconstituted into analog voice by the DAC at the original compression
quantization sample-per-bits rate.
2. If the Audio Sub-configuration is in operation, PCM decoding is provided by the linear PCM decoder, and the decoded
audio data is then reconstituted into analog voice by the DAC at the original 1 sample/8 bits rate.
7.2 VOICE/AUDIO CAPABILITIES
7.2.1 Call Establishment - Originate
Directed Originate (Dial as a specific modem type)
For most call originations, it is known ahead of time what type of call is being attempted, and it is acceptable to disconnect if
the remote side of the connection does not cooperate. In this case, the modem can be configured ahead of time with the
existing +FCLASS (and +FAE=0 or +FAA=0) or the #CLS command to be a data, fax, or voice/audio modem. For Data and
Fax Modes, the modem subsequently either succeeds with the desired type of connection, or eventually hangs up. For the
Voice/Audio Mode, the DTE has the option of hanging up if there are indications that the remote station has not answered in
voice, thus implementing a directed originate for voice. The following are the three connection type choices:
Voice/Audio
The modem dials and reports call progress to the DTE, which reduces to reporting “NO DIALTONE", "BUSY”, or "NO
ANSWER".
The modem allows the DTE to program a time period, which if elapsed after any ringback is detected, forces the modem to
assume the remote has gone off-hook. A secondary time period (safety valve) can define a maximum elapsed time after
dialing for receiving no ringback before the modem assumes that the remote has gone off-hook. This safety valve is devised
in case the remote picks up the telephone before any ringback is generated, and no other tones are detected. In this mode,
the modem is attempting to make a voice connection only and therefore, while waiting for ringback to disappear, it is also
feasible to disconnect upon detection something which is definitely not voice from the remote, such as any answer tone. The
modem provides detection of “ringback went away or never came”.
Fax
The modem dials and reports call progress to the DTE as in all modes. A Fax Class 1 or Fax Class 2 handshake is pursued
according to the current configuration.
Data
The modem dials and reports call progress to the DTE as in all modes. A data handshake is pursued according to the
current configuration.
Adaptive Originate (Dial with Voice/Data/Fax Discrimination)
The DTE may wish to originate a call which adapts to the remote answerer. For instance, the user may wish to send a voice
message if a human picks up the telephone, but a facsimile if a fax machine answers. The modem can facilitate this type of
adaptive originate by extending what it does for the directed originate modes. After determining that the remote station has
picked up the line, the modem goes back to Online Voice Command Mode, thus terminating the “connecting state.” Once in
this mode, the modem reports what it receives from the answerer via specific result codes to the DTE. The DTE can then
have the option of pursuing a data, fax, or voice/audio connection.