Nortel Networks 311 Loop Start Mode

Line cards 37

•Incoming calls

•Outgoing calls

•Calls disconnected by the CO

•Calls disconnected by the telephone

Loop Start Mode

In Loop Start mode, the A and B bits meaning is:

•Transmitfrom LTI:A bit = 0 (tip ground on); B bit = Ringing (0=on, 1=off)

•Receive to LTI:A bit = Loop (0=open, 1=closed); B bit = 1 (no ring

ground)

When a T1 channel is idle, the Lineside T1 card simulates a ground on the

tip lead and –48Vdc on the ring lead to the terminal equipment by setting its

transmit A bit to 0 and transmit B bit to 1. Accordingly, an on-hook channel

on the terminal equipment simulates an open loop toward the Lineside T1

card, causing the Lineside T1 card’s receive bits to be set to A = 0 and

receive B = 1.

Incoming calls Incoming calls to terminal equipment attached to the

Lineside T1 card can originate either from stations that are local (served

by the PBX), or remote (served through the PSTN). Toprovide the ringing

signal to a telephone the Lineside T1 card simulates an additional 90V on

the ring lead to the terminal equipment by alternating the transmit B bit

between 0 and 1 (0 during ring on, 1 during ring off). When an incoming

call is answered by the terminal equipment going off-hook, the terminal

equipment simulates tripping the ringing and shutting off ringing, causing

the Lineside T1 card’s receive A bit to be changed from 0 to 1.

Outgoing calls During outgoing calls from the terminal equipment,

a channel is seized when the station goes off-hook. This simulates a

low-resistance loop across the tip and ring leads toward the Lineside T1

card, causing the lineside T1’s receive A bit to be changed from 0 to 1. This

bit change prepares the Lineside T1 to receive digits. Outward address

signaling is then applied from the terminal equipment in the form of DTMF

tones or loop (interrupting) dial pulses that are signaled by the receive A

bit pulsing between 1 and 0.

Call disconnect from far end PSTN, private network or local

Station When a call is in process, the central ofﬁce may disconnect the

call from the CS 1000E, CS 1000M, and Meridian 1. If the Lineside T1

port has been conﬁgured with the supervised analog line (SAL) feature,

the Lineside T1 card responds to the distant end disconnect message by

momentarily changing its transmit A bit to 1 and then returning it to 0. The

duration of time that the transmit A bit remains at 1 before returning to 0

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311 01.04 Standard

Release 5.0 23May 2008