Nortel Networks 553-3001-211 manual Analog line call operation, Incoming calls, Outgoing calls

Page 40 of 894 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.

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 on page 41.

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 on page 42. 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.

553-3001-211 Standard 2.00 September 2004