Nortel NT1R20 Description page 52

Page 28 of 290 Description
553-3001-105 Standard 5.00 June 1999
SL-1 Network loop signaling
messages to and receive messages from the peripheral equipment cards. A
typical message to the PE card directs the card to enable the front panel fault
LED, enable ringing onto a particular line, or light the message waiting lamp
for a particular line. A typical message from the PE card tells the system
processor that a line has gone off hook.
Messages are sent and received during timeslot zero. An enable signal TS0
(timeslot zero enable) is generated during each timeslot zero. When the
network card has a message for a particular peripheral card, it asserts the card
enable signal for that card along with the TS0 signal. This continues on
successive TS0s until a complete message has been sent.
The network card regularly polls the PE cards during TS0 to see if any of
them has a message to be sent. When a PE card has a message waiting, it
responds to the poll by sending a series of ones during the next five successive
timeslot zeros. The network card responds by sending a "message send
enable" message (all 1s). The PE card replies by sending 1, 1, 1, 0, and then
the message in successive timeslot zeros.
SL-1 Network loop signaling is used to send