Nortel BCM ISDN2e (Basic rate interface) media bay module

The basic rate interface media bay module (BRIM) connects a maximum of four BRI ISDN loops to the BCM system. The BRIM only recognizes the T-interface used in European networks. To use the BRIM with the U-interface, typical in North American networks, you require an external NT1 box to convert the U-interface to a T-interface.
Each BRI ISDN loop you connect adds two telephone lines to the BCM system. Therefore, each BRIM adds a maximum of eight lines to the BCM system through the four RJ-48C jacks on the faceplate. The LEDs beside each RJ-48C jack are on when the ISDN line is active

Nortel BCM ISDN2e Media Bay User Guide / Manual

Nortel BRIM faceplate