AT&T MERLIN LEGEND Communications System PBX System Planning Manual page 71

Trunks
DS1 Facility (1OOD Module)
3-16 Trunk Options
Use these instructions only if the system has a 100D module. Because of
the complexity of DS1 facility planning, consult with your AT&T
representative or authorized dealer as you work through these instructions.
A Digital Signal 1 (DS1) facility is a transmission system that transports digital
signals in the DS1 format. The 100D module is the interface that allows the
connection of DS1 facilities to the system. Through this module, voice and data
calls can be placed on or received by a DS1 facility.
Note: The small processor module supports one 100D module; the large
processor module supports up to three 100D modules.
Twenty-four Digital Signal O (DSO) channels, each operating at 64 kbps, plus
framing bits, are multiplexed, forming a DS1 signal of 1.544 Mbps. Each DSO
channel within the DS1 signal corresponds to a logical endpoint. Even though
there is only one physical jack, the 100D module supports up to 24 logical
endpoints ( IDs) or ports (one for each channel).
In DS1 format, calls to other digital communications systems (digital PBXs) or
central offices remain digital, and signals do not need to be converted to analog
for acceptance by the connecting trunk.
To connect the 100D module to a DS1 facility, a channel service unit (CSU) is
normally used to regulate the transmission into and out of the 100D module so
that the module matches the transmission of the outside facility. The CSU is a
hardware component needed when two endpoints are located in different
buildings or when the distance between the two endpoints makes line repeaters
necessary. Repeaters re-amplify incoming signals so that signal strength is not
lost over long distances.
To ensure that both ends of the DS1 facility "speak the-same language," the
following options are set during programming:
Type of Service
Frame Format
Line Code
Line Compensation
Clock Synchronization
Signaling Mode
The appropriate setting for each option is determined by the transmission facility
to which the module is connected. Each option is discussed below.