Nortel Circuit Card 311 Reference page 515

The digital line interface circuits also contain signaling and control circuits
that establish, supervise, and take down call connections. These circuits
work with the on-card microcontroller to operate the digital line interface
circuits during calls. The circuits receive outgoing call signaling messages
from the Call Processor and return incoming call status information to the
Call Processor over the DS-30X network loop.
TCM loop interface circuit
Each digital telephone line terminates on the NT8D02 Digital Line card
at a TCM loop interface circuit. The circuit provides transformer coupling
and foreign voltage protection between the TCM loop and the digital line
interface circuit. It also provides battery voltage for the digital telephone.
To prevent undesirable side effects from occurring when the TCM loop
interface cannot provide the proper signals on the digital phone line, the
card microcontroller can remove the ±15 V dc power supply from the
TCM loop interfaces. This happens when either the microcontroller gets a
command from the NT8D01 controller card to shut down the channel, or
the digital line card detects a loss of the 1 KHz frame synchronization
signal. The ±15 V dc power supply signal is removed from all 16 TCM loop
interface units at the same time.
Each TCM loop interface circuit can service loops up to 3500 ft. in length
when using 24-gauge wire. They support a maximum ac signal loss of 15.5
dB at 256 KHz and a maximum dc loop resistance of 210 ohms.
Each digital telephone line terminates on the digital line card at a TCM
loop interface circuit. The circuit provides transformer coupling and foreign
voltage protection between the TCM loop and the digital line interface
circuit. It also provides battery voltage for the digital telephone.
To prevent undesirable side effects from occurring when the TCM loop
interface cannot provide the proper signals on the digital phone line, the
card microcontroller can remove the ±15 V dc power supply from the
TCM loop interfaces. This happens when either the microcontroller gets a
command from the NT8D01 controller card to shut down the channel or the
digital line card detects a loss of the 1 KHz frame synchronization signal.
The ±15 V dc power supply signal is removed from all 16 TCM loop interface
units at the same time.
Each TCM loop interface circuit can service loops up to 3500 ft. in length
when using 24-gauge wire. They allow for a maximum AC signal loss of
15.5 dB at 256 KHz and a maximum DC loop resistance of 210 ohms.
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
Functional description 515