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Coral IPx Office Installation Manual Shared Service Cards
9-49
Dial T
on
e Detector (DTD)
9
9.7
Dial Tone Detector (DTD)
0
The U-RMI Office and U-MR Office cards provide 16 (max: 32*) port DTD (Dial Tone
Detector) circuits for enhanced dialing, such as busy outside number auto-redial.
(max: *)
The max. number is dependent on the number of URC resource
points.
The DTD circuits are used to detect and identify standard call progress tones such as
dial tone, busy tone, reorder (fast busy) tone and ringback tone. The DTD is required
to support system features such as Automatic Called Number Redial (ACNR, also
called Scanner).
The DTD may also be utilized to force a station user to wait for a dial tone before
dialing to the central office. This increases the effectiveness of the toll restriction by
prohibiting users from dialing an unrestricted code before the central office is ready,
and then making a toll call when the dial tone is heard.
Each tone detection circuit of the DTD consists of a sophisticated audio noise level
detector. This circuit monitors audio signals and determines a constant or ambient
level, and then determines the presence of noise above ambient.
During operation, the system passes digitized voice signals from a port to be
monitored, through the Pulse Code Modulation (PCM) switching matrix to one of the
noise level detection circuits of the DTD. The presence of a call progress tone is
typically characterized by a sustained, non-fluctuating noise level.
The DTD then multiplies the periods that the tone is present and the periods of silence.
The durations of tone and silence are assembled to form a cadence (or rhythm pattern)
that is compared with an internal list of call progress tones and their associated
cadence. By matching the cadence of the monitored tone with the one contained in the
list, the DTD identifies the tone and reports the tone type via the peripheral bus to the
system processor.
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1 General Description