Nortel Networks 553-3001-211 manual Digital line call operation, Lineside T1 call operation

Page 44 of 894 Overview

causes the line card to revert the battery and ground signals to the normal state to signal that the call is complete.

Hook Flash disconnect supervision

Hook flash disconnect supervision is only used for incoming calls that terminate at the terminal device (typically a Key system). See Figure 9 on page 46. The disconnect signal is indicated by the removal of the ground connection to the tip lead for a specific length of time. The length of time is programmed in LD10, and ranges from a minimum of 10 milliseconds to a maximum of 2.55 seconds. See Software Input/Output: Administration (553-3001-311) for more information.

Digital line call operation

Digital line call operation is controlled entirely by use of messages between the digital telephone and the system. These messages are carried across the TCM loop interface. There is no call connection sequence similar to the one used for analog telephone line operation.

Lineside T1 call operation

The lineside T1 card’s call operation is performed differently depending on whether the T1 link is configured to process calls in loop start mode or ground start mode. Configuration is performed through dip switch settings on the lineside T1 card.

The lineside T1 card performs calls processing separately on each of its 24 channels. Signaling is performed using the “A/B robbed bit” signaling standard for T1 communication.

A/B robbed bit signaling simulates standard analog signaling by sending a meaningful combination of ones and zeros across the line that correlates to the electrical impulses that standard analog signaling sends. For example, to represent that an analog line interface unit is idle, the analog line card provides a ground on the tip lead and –48Vdc on the ring lead. The lineside T1 card accomplishes the same result by sending its A bit as 0 (translated as ground on the tip lead) and its B bit as 1 (translated as –48V dc on the ring lead). However, measuring the voltage of the ring lead on the T1 line would not return –48V dc, since actual electrical impulses are not being sent.

553-3001-211 Standard 2.00 September 2004