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Circuit Operation
C
O
IRCUIT
PERATION
The following paragraphs define the FRC-754 circuit operation when using loop start for subscriber lines or
ground start for PBX lines. Each FRC-754 circuit has an associated LED that indicates when the line is off-hook,
idle, ringing, or under test (see
Loop Start Operation
The following section summarizes the loop start sequences for on-hook (idle), subscriber inititated outgoing calls,
subscriber received incoming calls, and busy conditions.
On-hook (Idle) Condition
Loop start idle condition is a Ring-lead negative and Tip-lead positive from the CO with the same condition out
of the RT toward the subscriber (see
Table 2. Circuit Interactions for an Idle Condition (Loop Start)
Operation
Circuit Idle
Subscriber Initiated Outgoing Call
The following occurs when the calling line goes off-hook (see
•
loop current flows and is detected by the FRC-754 CU
•
FLC-704 receives an off-hook signal from the RT
•
FLC-704 generates an off-hook condition to the CO switch
•
CO sends dial tone
•
FRC-754 passes a dial pulse or Dual Tone Multi Frequency (DTMF) signal through the FLC-704 from the
subscriber and forwards these to the CO
Table 3. Circuit Interactions When a Subscriber Initiates an Outgoing Call (Loop Start)
Operation
CO Idle
Subscriber
goes off-hook
CO returns
dialtone
Subscriber
Dials
4
Table 1 on page
2).
Table 2
for circuit interactions).
FLC-704
CO Switch
COCU
⇒
No ringing
⇐
On-hook
FLC-704
CO Switch
COCU
⇒
No ringing
⇐
Off-hook
⇒
Dialtone
⇐
DP or DTMF
January 6, 2003
FRC-754 RTCU Subscriber
⇒
No ringing
⇐
On-hook
Table 2 on page 4
for circuit interactions):
FRC-754 RTCU Subscriber
⇒
No ringing
⇐
Off-hook
⇒
Dialtone
⇐
DP or DTMF
SCP-FRC754-042-03H
FRC-754 List 4B
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