ZyXEL Communications COMET 336, User Manual

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56 Voice Operation
Code Sent to DTE
Meaning
<DLE>s
Silence. Sent in Voice Receive Mode after the silence detection timer (#VSP) expires
and if valid voice has not been detected (#VSS). In general, <DLE>s is sent if no sound
was detected at all. This differs slightly from Quiet (<DLE>q) in that it can be used by
the DTE in its discrimination algorithms as a means of determining if anything at all is
coming from the remote station. If the DTE ignores the <DLE>s code, the modem
automatically resets its timer and sends the code again if the #VSP time period again
expires. This allows the DTE time to react to what may be a false detection of silence.
<DLE>t
Handset Off-Hook. Sent one time when the local handset transition from on-hook to off-
hook is detected in any of the three voice submodes.
<DLE>u
Underrun. Sent in Voice Transmit Mode when the voice transmit buffer becomes empty
without receiving a <DLE><ETX> or <DLE><CAN> command first. The modem
remains in transmit mode, but issues the <DLE>u to indicate that silence is being
generated. When the DTE resumes sending bytes, the modem allows a small number of
bytes to build up in the buffer before re-enabling the transmitter
to avoid repeated underruns. However, with the underrun condition, the modem does not
wait for the XOFF threshold (or timer) to be met before resuming, as it does on an
initial transmit or resume operation because the remote listener may be unaware of the
underrun, and keeping the silence short may serve to mask the underrun altogether.
<DLE>T
Timing Mark. Sent in Voice Receive Mode, and placed in the data stream at 1 second
intervals, when enabled by #VTM = 10.
<DLE><ETX>
End of Stream. <DLE><ETX> is sent to denote the end of a voice data stream, similar
to fax Class 1 and 2. This occurs in Voice Receive Mode only after the DTE issues the
key abort.
7.2.5 Shielded <DLE> Commands from the DTE Most commands issued for voice are
implemented as extensions to the AT command set, and are accepted only if the modem
is in a valid command mode, such as Online Voice Command Mode. However, there
are some operations which are available to the DTE without necessitating a switch to
Online Voice Command Mode. The most obvious of these is the <DLE><ETX> which
the DTE issues during Voice Transmit Mode to terminate an output message. Table 7-3
lists shielded <DLE> commands recognized by the modem.