AT&T MERLIN LEGEND Release 3.1 System Manager's Manual page 86

Control Unit
800 NI-BRI Module
For Release 4.0 and later systems, this module supplies eight line/trunk jacks for
connecting central office facilities that use the standard National ISDN 1
(Integrated Services Digital Network 1) protocol and the BRI (Basic Rate
Interface) access arrangement (this combination is abbreviated NI-1 BRI ).
These digital facilities are available from COs in many areas.
Each facility actually includes three "virtual" lines: two B-channels for carrying
voice and data and one D-channel for handling signaling and maintenance.
NOTE:
The 800 NI-BRI module is not available in Behind Switch mode.
Summary
Figure 3–3 shows each module; Table 3–1 lists the number of available jacks for
each module and presents a brief description of the equipment you can
connect to it.
NOTE:
Modules labeled "GS/LS" can accept ground-start trunks, loop-start trunks, or a
combination of both types of trunks.
3–12
System Components