Nortel Networks 311

Operation 603

Ordinarily,an incoming call on a reverse-wired trunk without reverse-wiring

compensation presents ringing on the tip lead rather than on the ring lead.

Since the software expects to see a ground on the tip lead, it interprets

the end of the ﬁrst ringing signal as a switchhook ﬂash. But since the

interval between ringing signals exceeds the switchhook ﬂash time of 512

milliseconds, the software assumes a far-end disconnect. This causes the

call to be presented to a console loop key and then immediately removed.

The reverse-wiring compensation feature operates as follows. If an

apparent disconnect takes place immediately after the ﬁrst ringing signal,

the software time stamps the event and temporarily remove the call from

the console loop key.

If another such ringing/disconnect event occurs during the No Ringing

Detector (NRD) time, the trunk is considered "possibly reverse-wired"

and a threshold counter starts. Calls on trunks identiﬁed as possibly

reverse-wiredare presented to the attendant during the initial r ing, removed,

and then continuously presented after the second ring. If a call on a

possibly reverse-wiredtr unk is abandoned beforethe attendant answers, it

is disconnected after the NRD timer expires.

A trunk identiﬁed as possibly reverse-wired is switchedby the software

to loop start processing after the second ring. This switching takes place

on a call-by-call basis. So if a previously correctly wired trunk becomes

reverse-wired, the nextincoming call is marked as possibly reverse-wired

and the threshold count begins.

If the threshold count exceeds its limit, an error message is printed and the

trunk is registered as "positively reverse wired." Once identiﬁed as positively

reversewired, the call is presented continuously from the ﬁrst ring. When a

reverse-wiredtrunk becomescorrectly wired, the ﬁrstsubsequent call clears

the threshold counter and normal ground start processing is implemented.

Note 1: The far-end can reverse battery and ground upon receipt of

attendant answer.

Note 2: The near-end provides a high-impedance (>150k ohms)

disconnect signal of at least 50 ms before reconnecting the ground

detector.

The Meridian 1 software includes a feature for detecting reverse wiring

(connection of near-end tip and ring leads to far-end ring and tip leads,

respectively) on ground start trunks with far-end answer supervision.

Ordinarily,an incoming call on a reverse-wired trunk without reverse-wiring

compensation presents ringing on the tip lead rather than on the ring

lead. Since software expects to see a ground on the tip lead, it interprets

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311 01.04 Standard

Release 5.0 23 May 2008