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30 Overview
Each TCM loop interface circuit can service loops up to 3500 ft. in length
when using 24 gauge wire. The circuit allows for a maximum ac signal loss
of 15.5 dB at 256 KHz and a maximum DC loop resistance of 210 ohms.
Signaling
The digital line interface units also contain signaling and control circuits
that establish, monitor, and take down call connections. These circuits
work with the system controller to operate the digital line interface circuits
during calls. The circuits receive outgoing call signaling messages from the
controller and return incoming call status information to the controller over
the DS-30X network loop.
Analog line call operation
The applications, features, and signalling arrangements for each line
interface unit are configured in software and implemented on the card
through software download messages. When an analog line interface unit is
idle, it provides a voltage near ground on the tip lead and a voltage near
–48 V dc on the ring lead to the near-end station. (The near-end station is
the telephone or device that is connected to the analog line card by the tip
and ring leads.) An on-hook telephone presents a high impedance toward
the line interface unit on the card.
Incoming calls
Incoming calls to a telephone that is connected to an analog line card can
originate either from stations that are local (served by the PBX), or remote
(served through the Public Switched Telephone Network (PSTN)). The
alerting signal to a telephone is 20 Hz (nominal) ringing. When an incoming
call is answered by the near-end station going off-hook, a low-resistance dc
loop is placed across the tip and ring leads (towards the analog line card)
and ringing is tripped. See Figure 6 "Call connection sequence - near-end
station receiving call" (page 31).
Outgoing calls
For outgoing calls from the near-end station, a line interface unit is seized
when the station goes off-hook, placing a low-resistance loop across the tip
and ring leads towards the analog line card. See Figure 7 "Call connection
sequence - near-end originating call" (page 32). When the card detects
the low-resistance loop, it prepares to receive digits. When the system is
ready to receive digits, it returns dial tone. Outward address signaling is
then applied from the near-end station in the form of loop (interrupting)
dial pulses or DTMF tones.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Copyright © 2003-2008, Nortel Networks
.