Technical information

Troubleshooting and Repair
73
Loop Start Line/Trunk
The Loop Start Line/Trunk serves the standard domestic applications
and small businesses that have key systems and PBX applications.
Figure 13: Loop Start Line/Trunk
Table 6: Loop Start Line/Trunk Summary
Signal
Loop Start Line PBX
Outgoing
Loop Start Line PBX
Incoming
Seize
Tip-Ring leads activated
(shorted); Loop Current
flows in line
90Vac is applied to
Ring lead in 2 sec on,
4 sec off cadence
Seize
Acknowledgment
Loop Current and/or dial
tone generated
-
Digits
Loop Current toggled
(Rotary) or DTMF
-
(Sheet 1 of 2)