ZyXEL Communications COMET 336, User Manual

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Voice Operation 55
dial tone continues to be detected and the DTE does not react. This allows the DTE the
flexibility of ignoring what could be a false dial tone detection.
<DLE>e
European Data Modem Calling Tone. Sent when the V.25 1300 Hz Calling Tone (Data
Modem) is detected in a voice submode. The modem assumes that the calling tone is
valid, and sends this code only after 4 seconds of proper cadence has been detected. If
the DTE does not react to the <DLE>e and calling tone continues, the code is sent again
as often as once every 4 seconds.
<DLE>f
Bell Answer Tone. Sent when Bell 2225 Hz Answer Tone (Data) is detected. If the
DTE fails to react to the code and the modem continues to detect Answer tone, the code
is repeated as often as every 1/2 second.
<DLE>h
Hung Up Handset. Sent immediately when the modem detects that the local handset has
hung-up (i.e., has transitioned from off-hook to on-hook) while in any of the three voice
submodes.
<DLE>o
Overrun. Sent in Voice Receive Mode if the voice receive data buffer overflows, in
which case, the latest data is lost in favor of retaining the oldest data in the buffer. (The
DTE may not have been reading data from the modem lately.) The modem inserts the
<DLE>o at the end of the buffer, thus marking the location where data was lost by the
DTE. The modem does not append <DLE>o codes to the buffer contiguously. If more
than one data byte is lost before the DTE begins reading again, there is only on <DLE>o
code in the data stream. However, if the DTE resumes reading, and then once again
allows the buffer to overflow, a new <DLE>o is appended to the data by the modem.
Thus, the <DLE>o does not indicate how many bytes of contiguous data has been lost,
but may report multiple gaps of lost data in the data stream.
<DLE>q
Quiet. Sent in Voice Receive Mode following any remaining data in the receive voice
buffer when the silence detection timer (#VSP) expires and there has been voice data
passed to the DTE. Note that with #VSS=0, the Quiet message never occurs. In general,
<DLE>q is sent if first there was sound, and now there is no sound, and means that
somebody has stopped talking, and according to the criteria selected in the #VSP and
#VSS settings, is probably not going to start again. If the DTE ignores the <DLE>q
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
silence detection.
Table 7-2. Shielded Codes Sent to the DTE (Contd)