Nortel Circuit Card 311 Reference page 605

Trunks identified as possibly reverse wired are switched by 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 next incoming 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." When identified as positively
reverse wired, the call is presented continuously from the first ring. When a
reverse-wired trunk becomes correctly wired, the first subsequent call clears
the threshold counter and normal ground start processing is implemented.
The CS 1000 software includes a feature for detecting reverse wiring
(connection of the near-end tip and ring leads to the far-end ring and tip
leads) 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 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-wired are presented to the attendant during the initial ring,
removed, and then continuously presented after the second ring. If a call on
a possibly reverse-wired trunk is abandoned before the attendant answers,
it is disconnected after the NRD timer expires.
A trunk identified as possibly reverse-wired is switched by 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 next incoming call is marked as possibly reverse-wired
and the threshold count begins.
Copyright © 2003-2008, Nortel Networks
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Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Operation 605