Mitel SX-200 EL Technician's Handbook page 82

Technician's Handbook
Table 6: Loop Start Line/Trunk Summary (Continued)
Signal
Receipt of Digits
Answer Supervision Some COs can reverse
Disconnect
Supervision
Test/Verify (Loop Start)
Verify far-end (CO) circuits by using a standard telephone set in place
of the Loop Start trunk circuit.
Verify near-end (PBX Loop Start) circuits by connecting to a local PBX
ONS circuit.
Check for appropriate voltages on Tip-Ring in each call state.
During off-hook condition, 18 mA DC minimum should be drawn from
the CO (typical 25-40 mA).
Some Key/PBX systems may be polarity sensitive; reverse Tip-Ring to
verify.
72
Loop Start Line PBX
Outgoing
Audible Tones - Busy,
Reorder, Ringback dependent
upon digits dialed and called
party condition
current flow
Near- end termination:
PBX/Telephone can break
Loop Current
Loop Start Line PBX
Incoming
-
Tip-Ring leads activated
(shorted); Loop Current
flows in line
Near- end termination:
PBX/Telephone can
break Loop Current
(Sheet 2 of 2)