Nortel Networks Circuit Card - Manual (Page 534)

Page 534 of 906 NT8D02 and NTDK16 Digital Line cards
553-3001-211 Standard 3.00 August 2005
lines carry multiplexed PCM voice, data, and signaling information as TCM
loops.
The purpose of each digital line interface circuit is to de-multiplex data from
the DS-30X Tx channel into eight integrated voice and data bitstreams. The
circuits then transmit those bitstreams as Bi-Polar Return to Zero, Alternate
Mark Inversion (BPRZ-AMI) data to the eight TCM loops. They also perform
the opposite action: they receive eight BPRZ-AMI bitstreams from the TCM
loops and multiplex them onto the DS-30X Rx channel. The two digital line
interface circuits perform the multiplexing and de-multiplexing functions for
the 16 digital telephone lines.
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 Server and return incoming call status information to the Call Server
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.