Nortel Networks 553-3001-211 manual Message waiting, Analog line supervision

Overview Page 43 of 894

Message waiting

Line cards that are equipped with the message waiting feature receive notification that a message is waiting across the Card LAN link (IPE cards). On cards that drive a message waiting light, the light is turned on by connecting the ring side of the telephone line to the –150 V dc power supply. When the line card senses that the telephone has gone off-hook, it removes the –150 V dc voltage until the telephone goes back on-hook. Line cards that use an interrupted dial tone to indicate message waiting do nothing until the receiver is picked up. The line card then interrupts the dial tone at a regular interval to indicate that a message is waiting.

In both cases, the message waiting indication will continue until the user checks his or her messages. At that time, the system will cancel the message waiting indication by sending another message across the Card LAN link or 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

•hook flash disconnect supervision

Battery reversal answer and disconnect supervision

Battery reversal 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 8 on page 45. 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 system sends a message that

Circuit Card Description and Installation