Product Overview
363-704-104-01, Revision 01
6
June 22, 1998
FLC-704 List 4
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
for circuit interactions).
Subscriber Initiates Outgoing Call.
The following occurs when a PBX requests service for an outgoing call
(see
for circuit interactions):
•
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 6.
Circuit Interactions for an Idle Condition (Ground Start)
Operation
CO Switch
FLC-704 List 4 COCU
FRL-754 List 4 RTCU
Subscriber
Circuit Idle
Tip - no ground
No ringing
⇒
Tip - no ground
No ringing
⇒
⇐
Ring - no ground
On-hook
⇐
Ring - no ground
On-hook
Table 7.
Circuit Conditions When a Subscriber Initiates an Outgoing Call (Ground Start)
Operation
CO Switch
FLC-704 List 4 COCU
FRL-754 List 4 RTCU
Subscriber
CO Idle
Tip - No ground
No ringing
⇒
Tip - No ground
No ringing
⇒
Subscriber requests
dialtone
⇐
Ring - ground
On-hook
⇐
Ring - ground
On-hook
CO returns dialtone
Tip - ground
Dialtone
⇒
Tip - ground
Dialtone
⇒
Subscriber Dials
⇐
Ring - no ground
Off-hook
DP or DTMF
⇐
Ring - no ground
Off-hook
DP or DTMF
