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363-753-142-01, Revision 01
Circuit Operation
The following paragraphs define the FRC-753 circuit operation when using loop start for subscriber lines or
ground start for PBX lines. Each FRC-753 circuit has an associated LED that indicates when the line is off-hook,
idle, ringing, or under test. See
Loop Start Idle. Loop start idle condition is a Ring lead negative and Tip lead positive from the COT shelf with
the same conditions out of the RT toward the subscriber. The following occurs when the calling line goes
off-hook:
•
loop current flows and is detected by the FRC-753
•
FLC-703 receives an off-hook signal from the RT
•
FLC-703 generates an off-hook signal to the CO to begin current flow
•
CO sends dial tone
•
FRC-753 recognizes dial pulses or Dual Tone Multi Frequency (DTMF) signalling, from the subscriber and
forwards these as loop current breaks, or DTMF signalling, to the CO
The following occurs for an incoming call:
•
FLC-703 detects a ringing signal from the CO
•
FLC-703 signals the FRC-753 which then connects ringing to the subscriber
•
subscriber line goes off-hook and the FRC-753, by means of the FLC-703, signals the CO to disconnect
ringing and establish an audio path
Ground Start Idle. Ground start idle condition is a Tip lead open and Ring lead negative into the COT and Tip
lead open and Ring lead negative at the RT. The following occurs when a PBX requests service for an outgoing
call by grounding the Ring lead at the RT:
•
FRC-753 signals the FLC-703
•
FLC-703 operates a Ring ground relay that requests dial tone from the CO (this makes the circuit busy, or
seizes it, for outgoing calls to prevent others from using it, for example, prevents glare where different users
can seize a line at the same time)
•
CO sends dial tone and grounds the Tip to signal the PBX to begin dialing
•
FLC-703 detects Tip ground, closes the loop between Tip and Ring, and signals the FRC-753 to send Tip
ground to the PBX
•
PBX removes the original Ring ground condition and completes the loop (Tip and Ring)
The following occurs for an incoming call:
•
FLC-703 detects a ringing signal from the CO, along with Tip ground
•
FLC-703 signals the FRC-753 which then connects Tip ground and ringing to the PBX
•
PBX goes off-hook and the FRC-753, by means of the FLC-703, signals the CO to disconnect ringing and
establish an audio path
Caller ID. When caller ID (a CLASS feature) is activated, the CO generates a signal to the subscriber between
the first and second bursts of the ringing signal only (for example, PG-Flex supports on-hook transmission).
Forward-Disconnect Function. The forward-disconnect function releases a called line that was left on hold
or an answering set that requires a loop open to be able to turn off.
FRC-753 List 4B
Table 1 on page
4.
July 23, 1999
Overview
3
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