Voice Playback
To begin playback of a message recorded via handset or microphone, or
of a message recorded during a voice call, the DTE must configure the modem
for Voice Mode (#CLS-8) and select the proper relay setup (#VLS) to instruct
the modem whether to use the handset or speaker. The modem responds to the
#VLS command by issuing a relay activate command to select the input device.
The hardware must provide a means of selecting a handset and/or microphone
instead of the telephone line, as this input device. When a device other
than the telephone line is selected, the modem immediately enters Online
Voice Command Mode (indicated by VCON). DTMF detection is thus enabled as
soon as the DTE selects the device, such as a handset, although the user
still needs to physically pick up the telephone before he can issue DTMF
tones. Once selected, however, the user can indeed pick up the telephone
and "press buttons." Even if the DTE has not entered Voice Receive
or Transmit Modes (#VTX or #VRX), these DTMF tones are delivered via shielded
codes, identically when a physical telephone connection exists but the DTE
has not yet commanded receive nor transmit.
When the DTE decides to play the message, it issues the #VTX command, and
the modem immediately switches to Voice Transmit Mode. Since the speaker
of handset is already switched in, the modem immediately issues the CONNECT
message indicating that the modem is in Voice Transmit Mode and is expecting
voice data from the DTE.
A subsequent <DLE><ETX>has to be issued to switch back to Online
Voice Command Mode.
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