Nortel Networks 553-3001-211 manual Ground start operation, Reverse-wiring compensation

Page 566 of 894 NT8D14 Universal Trunk card

Ground start operation

Ground start operation is configured in software and implemented through software download messages. In the idle state, the tip conductor from the CO is open and a high-resistance negative battery is present on the ring lead.

Incoming calls

In an incoming call, after ground is detected on the tip, the universal trunk card scans for a ringing detection signal before presenting the call to an attendant and tripping the ringing. When the attendant answers, a low resistance is placed across the tip and ring conductors, which trips CO ringing and establishes a speech path. See Figure 116 on page 567 and Figure 117 on page 568.

Reverse-wiring compensation

The CS 1000 Release 4.0 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.

553-3001-211 Standard 2.00 September 2004