AT&T MERLIN LEGEND Release 3.1 System Manager's Manual page 79

Control Unit
Line/Trunk and Extension Modules
Line/trunk and extension modules have jacks for connecting telephone
company lines/trunks and extension wires to the control unit. The system
supports 17 types of line/trunk and extension modules. For maximum flexibility,
some modules support only lines/trunks, some only extensions, and some a
combination of the two.
Each module has a label that contains its name. As noted in Chapter 2, "About
the System," the names of the modules identify their capacities and capabilities.
The first digit indicates the number of line/trunk jacks a module supports, while
the last two digits describe the number of extension jacks it supports. Following
the number may be letters that indicate the type of trunk or trunks it supports; for
example, LS for loop-start and GS for ground-start . A line/trunk module name
with no letter following it supports loop-start trunks. The following are examples
of module names:
The 408 GS/LS MLX module provides four trunk jacks supporting ground-
start and/or loop-start trunks and eight MLX extension jacks.
The 016 module (Release 4.0 and later only) provides 16 extension jacks
that, in this case, supply tip/ring (T/R) connections for single-line
telephones, modems, voice messaging systems that serve the system as
a whole, and other components.
This section provides a table that describes the equipment you can connect to
each module, then includes some specific information about the modules that
connect extensions and the modules that connect lines/trunks, and a final
summary.
System Components
3–5