Calling Line Identifier
MX602 - PRELIMINARY INFORMATION
14
5.2.2 Overview
A successful CIDCW transaction as described by Bellcore SR-TSV-002476, consists of a sequence of actions between
the CPE (Customer Premises Equipment - e.g. a telephone) and the Central Office as indicated in Figure 14.
Signals originating
from far end CPE
and Central Office
far voice
CAS
FSK data
far voice
Signals originating
at near end CPE
near voice
ACK
D
near voice
F
A
B
C
E
A. Normal conversation with both near and far voice present.
B. Central Office mutes far end voice, emits CAS and becomes silent
C. CPE recognizes CIDCW initiation and mutes near end voice and keypad
D. CPE emits DTMF ACK to Central Office to signal its readiness to receive Caller ID data stream
E. Central Office recognizes ACK and emits FSK Data stream of Caller ID data which is received and decoded by CPE
F. CIDCW transaction is complete. CPE unmutes near end voice and Central Office unmutes far end voice returning to
normal conversation with both near and far voice present.
Figure 14, CIDCW Transaction From Near End CPE Perspective
From the near end CPE’s perspective, the initiation of a CIDCW transaction is characterized by two events occurring in
sequence: (1) a CAS dual tone is received, and (2) a subsequent quiet period passes as far end speech continues to be
muted. These two events can be detected by the MX602’s Dual Tone Alert detector and FSK level detector, respectively.
Caller ID and CIDCW end products typically use a microcontroller to manage the transfer and display of Caller ID data.
The same microcontroller is easily used to observe and control the MX602 CIDCW transaction initiation detection process.
It measures an MX602 DET output pulse duration, mutes near end voice, subsequently watches for DET output activity,
and controls whether the MX602 is in Dual Tone Alert or FSK Receive modes as shown in Figure 15.
Signals originating
at far end CPE
far voice
CAS
FSK data
far voice
and Central Office
Signals originating
at near end CPE
near voice
1
ACK
near voice
Time (T2) for mute to take effect
Detection Algorithm
State (see following text)
2
3
4
5
1
MX602 mode
Tone Alert Detect
FSK Receive
Tone Alert Detect
MX602 DET output
Initiate mute of near end voice when
DET output has been high for time T1
No DET high activity during 50ms ‘quiet’ period
window confirms CIDCW transaction initialization
The width of a valid DET pulse is
minimum T3 and maximum 65ms
See text for details of times T1, T2 & T3
Figure 15, CIDCW Transaction Initiation with MX602 Operation
Different strategies may be used for CIDCW transaction initiation detection. The simplest strategy detects only the CAS
dual tone. More complex strategies may detect both the CAS dual tone as well as the following far end voice quiet period
© 1998 MX•COM Inc.
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