Nortel Circuit Card, Installation Manual, Page: 46 / 908

Page 46 of 906 Overview
553-3001-211 Standard 3.00 August 2005
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 48 . 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.