Nortel Circuit Card 311 Reference page 648

648 NT8D14 Universal Trunk card
Figure 197
Two-way, loop DR, tie trunk call states - outgoing call through far-end PBX to CO
Outgoing automatic, incoming dial operation
Incoming calls
When the NT8D14 Universal Trunk card is seized by the far-end on an
incoming call, a low-resistance loop is placed across the tip and ring leads.
Addressing is then sent by the far-end in the form of battery-ground or
loop pulses, or DTMF tones. The trunk is released at the far-end when
the loop is opened. When the near-end detects an open loop, it returns to
a normal state.
Copyright © 2003-2008, Nortel Networks
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Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008