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Circuit Operation
Table 5.
Operation
Circuit busy
Ground Start Operation
The following section summarizes the ground start sequences for on-hook (idle), subscriber inititated outgoing
calls, subscriber received incoming calls, and busy conditions.
Idle Condition
Ground start idle condition is a Tip-lead open and Ring-lead negative from the CO and Tip lead open and
Ring-lead negative at the RT (see
Table 6.
Operation
Circuit Idle
Subscriber Initiates Outgoing Call
The following occurs when a PBX requests service for an outgoing call (see
•
PBX grounds Ring lead at the RT
•
FRC-754 signals the FLC-704
•
FLC-704 operates a Ring-ground relay that requests dial tone from the CO (this makes the circuit busy, or
seizes it, for outgoing calls, and blocks any incoming calls prior to the PBX dialing (that is, it prevents glare
where incoming and outgoing calls may occur simultaneously on the same line). Glare occurs when both ends
of a telephone line or trunk are seized at the same time.
•
CO sends dial tone and grounds the Tip to signal the PBX to begin dialing
•
FLC-704 detects Tip-ground, closes the loop between Tip and Ring, and signals the FRC-754 to send Tip
ground to the PBX
•
PBX removes the original Ring-ground condition and completes the loop (Tip and Ring)
Table 7.
Circuit Conditions When a Subscriber Initiates an Outgoing Call (Ground Start)
Operation
CO Idle
6
Circuit Interactions for a Busy Condition (Loop Start)
FLC-704
CO Switch
COCU
⇒
No ringing
⇐
Off-hook
Table 6
for circuit interactions).
Circuit Interactions for an Idle Condition (Ground Start)
CO Switch
FLC-704 COCU
⇒
Tip - no
ground
No ringing
⇐
Ring - no ground
On-hook
CO Switch
FLC-704 COCU
⇒
Tip - No
ground
No ringing
January 6, 2003
FRC-754
Subscriber
RTCU
⇒
No ringing
⇐
Off-hook
FRC-754
Subscriber
RTCU
⇒
Tip - no ground
No ringing
⇐
Ring - no ground
On-hook
Table 7
for circuit interactions):
FRC-754
Subscriber
RTCU
⇒
Tip - No ground
No ringing
SCP-FRC754-042-03H
FLC-704 List 4B
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