Subscriber Initiates Outgoing Call; Subscriber Receives Incoming Call; Circuit Interactions For An Idle Condition (Ground Start); Circuit Conditions When A Subscriber Initiates An Outgoing Call (Ground Start) - ADC FRC-754 4B Technical Practice

Circuit Operation
Table 6.
Operation

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
Subscriber
requests
dialtone
CO returns
dialtone
Subscriber
Dials

Subscriber Receives Incoming Call

The following occurs for an incoming call (see
• FLC-704 detects a ringing signal from the CO, along with Tip-ground
• FLC-704 signal the FRC-754 to connect Tip-ground and ringing to the PBX
• PBX goes off-hook and the FRC-754, through the FLC-704 closes the loop between Tip and Ring, the CO
disconnects ringing and establishes an audio path
6

Circuit Interactions for an Idle Condition (Ground Start)

CO Switch FLC-704 COCU FRC-754 RTCU Subscriber
⇐
Ring - no ground
On-hook
CO Switch FLC-704 COCU FRC-754 RTCU Subscriber
⇒
Tip - No ground
No ringing
⇐
Ring - ground
On-hook
⇒
Tip - ground
Dialtone
⇐
Ring - no ground
Off-hook
DP or DTMF
Table 8
January 6, 2003
⇐
Ring - no
ground
On-hook
Table 7
⇒
Tip - No ground
No ringing
⇐
Ring - ground
On-hook
⇒
Tip - ground
Dialtone
⇐
Ring - no
ground
Off-hook
DP or DTMF
for circuit interactions):
SCP-FRC754-042-03H
for circuit interactions):
FRC-754 List 4B