Nortel NT1R20 Description page 61

In both cases, the message waiting indication will continue until the user
checks his or her messages. At that time, the Meridian 1 system will cancel
the message waiting indication by sending another message across the Card
LAN link or SL-1 network loop.
Analog line supervision
Analog line supervision features are used to extend the answer supervision
and disconnect supervision signals when the line card is connected to an
intelligent terminal device (Key system or intelligent pay phone). Two types
of analog line supervision are provided, battery reversal answer and
disconnect supervision, and hook flash disconnect supervision.
Note: Analog Line Supervision features are only supported on
Meridian 1 processors that are running Release 21 software (or greater).
Battery reversal answer and disconnect supervision
answer and disconnect supervision is only used for calls that originate from
the terminal device. It provides both far-end answer supervision and far-end
disconnect supervision signals to the terminal device. In an intelligent pay
phone application, these signals provide the information necessary to
accurately compute toll charges.
In the idle state, and during dialing and ringing at the far end, the line card
provides a ground signal on the tip lead and battery on the ring lead (see
Figure 14). When the far-end answers, these polarities are reversed. The
reversed battery connection is maintained as long as the call is established.
When the far-end disconnects, the Meridian 1 system sends a message that
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
only used for incoming calls that terminate at the terminal device (typically a
Key system), see Figure 15. The disconnect signal is indicated by the removal
of the ground connection to the tip lead for a specific period of time. The
period of time is programmable using LD10, and ranges from a minimum of
10 milliseconds to a maximum of 2.55 seconds. See the X11 input/output
guide (553-3001-400) for more information.
Description
Battery reversal
Hook flash disconnect supervision is
Line cards Description
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