AT&T DEFINITY 7200 series - Manual (Page 50)

1-30 MULTIPLEXED COMMUNICATION
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T1
T1
T1 DIGITAL
PBX
DMI
HOST
CEM HOST
CDM
CSU
DACS
#5ESS
PRIVATE
T1
FACILITIES
#4ESS
T1
T1
CHANNEL
BANK
CSU
ANALOG PBX
T1
T1
HOST
DIGITAL
PBX
CSU
CEM CDM CSU
CSU
T1
T1
T1
T1
T1
Legend: CDM = channel division multiplexer
CEM = channel expansion multiplexer
CSU = customer service unit
DACS = digital access and cross-connect system
Figure 1-9. T1 Trunk Multiplexing
directly access the OCU port on the D4 channel bank by first passing the signal through a digital service
unit (DSU) that is set to communicate at 2.4, 4.8, 9.6, or 56 kbps. The signal passes from the terminal,
through the DSU, to the OCU data-port card on the D4 channel bank. The T1 channel that the OCU data-
port card creates is devoid of signaling so it can pass the digital data untouched. At the central office, the
channel is selected from T1 input for special handling and is directed to DDS where it is forwarded to its
destination. The destination terminal or host must also be equipped with a DSU.