AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 105

Hardware Components
Adapters
Adapters connect adjuncts to
both voice and data signals.
System Adapters
Three adapters connect directly to the control unit: the channel service unit
(CSU), the Loop-Start Trunk Adapter, and the Universal Paging Access Module
(UPAM).
Channel Service Unit
The CSU is the interface between the 100D module and the DS1 facility
provided by the telephone company. This facility contains 24 channels on one
4-pair wire that connects to the back of the CSU. The CSU then connects to the
modular jack on the 100D module.
There is an Extended Super Frame (ESF) T1 CSU and a 551 T1 L1 CSU. The
ESF T1 CSU is recommended for this system because it allows the unit to be
maintained without interrupting service and provides diagnostic and testing
capabilities, and it is the only CSU that provides bipolar 8 zero code substitution
(B8ZS) line coding. The lower-cost 551 T1 L1 CSU performs most of the
functions of the ESF T1 CSU but does not provide the B8ZS line coding required
for 64-kbps data and for maintenance features. The 551 T1 L1 CSU does not
provide diagnostic and testing capabilities; also, it is not recommended for
Video Conferencing applications.
Figures 2-11 and 2-12 detail the CSU connections.
system and stations. They provide access for
the
Adapters and Adjuncts 2-31