Figure 1-9. T1 Trunk Multiplexing - AT&T DEFINITY 2500 series Network Manual

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MULTIPLEXED COMMUNICATION
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HOST
T1
DIGITAL
T1
PBX
T1
CSU
T1
PRIVATE
T1
FACILITIES
CSU
T1
CHANNEL
BANK
ANALOG PBX
Legend: CDM = channel division multiplexer
CEM = channel expansion multiplexer
CSU = customer service unit
DACS = digital access and cross-connect system
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.
T1
CEM
CSU
DACS
T1
#5ESS

Figure 1-9. T1 Trunk Multiplexing

T1
CDM CSU
T1
#4ESS
T1
CSU
T1
CDM
CEM
DIGITAL
PBX
HOST
DMI
T1
HOST