In all the Nortel systems I've done over the years, they have a pair on the output block for auxillary ringing. If a set or a line is programmed for 'aux ring = Yes' then the system makes the contacts close and open like a switch. Its basically a contact closure used to operate an external device.

In the 1100, I could use an analog port for line voltage ringing, but what about a device that is looking for contact closures?

Thanks.
Jim