In the newer software versions, the IRAD is not assigned to answer a line, so you have to give it a line assignment if you want it to answer remotely. The IRAD is designed to work with Nortel NRU software (Nortel Remote Utilities) that can be downloaded from Nortel if you have access.
On site, I use an external IRAD tied to a station with direct connect to do backups and programming.
NCSS NCTS NCTE