Line cards 37• Incoming calls• Outgoing calls• Calls disconnected by the CO• Calls disconnected by the telephoneLoop Start ModeIn Loop Start mode, the A and B bits meaning is:• Transmit from 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 ringground)When a T1 channel is idle, the Lineside T1 card simulates a ground on thetip lead and –48Vdc on the ring lead to the terminal equipment by setting itstransmit A bit to 0 and transmit B bit to 1. Accordingly, an on-hook channelon the terminal equipment simulates an open loop toward the Lineside T1card, causing the Lineside T1 card’s receive bits to be set to A = 0 andreceive B = 1.Incoming calls Incoming calls to terminal equipment attached to theLineside T1 card can originate either from stations that are local (servedby the PBX), or remote (served through the PSTN). To provide the ringingsignal to a telephone the Lineside T1 card simulates an additional 90V onthe ring lead to the terminal equipment by alternating the transmit B bitbetween 0 and 1 (0 during ring on, 1 during ring off). When an incomingcall is answered by the terminal equipment going off-hook, the terminalequipment simulates tripping the ringing and shutting off ringing, causingthe 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 alow-resistance loop across the tip and ring leads toward the Lineside T1card, causing the lineside T1’s receive A bit to be changed from 0 to 1. Thisbit change prepares the Lineside T1 to receive digits. Outward addresssignaling is then applied from the terminal equipment in the form of DTMFtones or loop (interrupting) dial pulses that are signaled by the receive Abit pulsing between 1 and 0.Call disconnect from far end PSTN, private network or localStation When a call is in process, the central office may disconnect thecall from the CS 1000E, CS 1000M, and Meridian 1. If the Lineside T1port has been configured with the supervised analog line (SAL) feature,the Lineside T1 card responds to the distant end disconnect message bymomentarily changing its transmit A bit to 1 and then returning it to 0. Theduration of time that the transmit A bit remains at 1 before returning to 0Nortel Communication Server 1000Circuit Card ReferenceNN43001-311 01.04 StandardRelease 5.0 23 May 2008Copyright © 2003-2008, Nortel Networks.
