ZyXEL Communications COMET 336 User Manual page 57

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.
50 Voice Operation