Nortel Networks Circuit Card 311 - Manual (Page 619)

Operation 619
Figure 173
DID trunk, loop DR call states - incoming call from CO
An incoming call from the CO places a low resistance loop across the tip and
ring leads. Dial pulses or DTMF signals are then presented from the CO.
When the call is presented and the terminating party answers, the Universal
Trunk Card reverses battery and ground on the tip and ring leads to the CO.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
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