Nortel Networks 311 Signaling, Analog line call operation

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 downcall 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 TelephoneNetwork (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