Nortel Networks Circuit Card User Manual

 Overview

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.

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 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 on 

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 on 

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.