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System Description
The operator can select Alarm reporting to occur on a wide variety of conditions. Consult Appendix
C, Alarm Definitions for the complete listing of alarm conditions and their definitions.
The DSU facilitates fault isolation in a digital network by providing comprehensive loopback and
testing capabilities that include Local Test, Remote Loop, Data Loop, and Self Test. The operator
can use the loopbacks and tests to isolate system faults to a particular DTE, data set, or line.
Application
The SC 553 DSU is intended principally for space efficient, high density central site installations.
It is fully compatible with remote GDC NMS 553 DSUs.
Note
Power failure at the master site can result in loss of management communication with the remote. If that
occurs, you must perform Remote Wakeup to correct the condition.
Fault Tolerant Switching Application
Figure 1-1
presents an example of the DSU's redundant T1 features being employed for a Fault
Tolerant Switching application. This application depends on both the DSUs' installation environ-
ment and their configuration. It requires that the DSUs be configured for ESF line coding; and it
works only for data communications, not voice. When SC553 DSUs are used for this application
the Diagnostic Communication Channel that supports management of the remote DSUs must be
embedded in the ESF Facilities Data Link (FDL).
The DSUs must be installed in a ring arrangement as shown in the figure. The illustration shows a
ring of 4 DSUs that supports 2 fractional T1 links, designated primary and backup. The selection of
which T1 is to be primary and which is to be secondary is arbitrary. The selection does affect how
the DSUs are configured.
The Channel Redundancy configuration option controls operation of the redundant T1 feature and
automatic fault recovery. Enabling the option causes the DSU to respond to signal loss at its
configured T1 interface (Channel Routing Option) by redirecting channel data to its other T1 in-
terface. The DSU generates a Redundancy alarm when signal loss causes it to redirect channel data.
The following table shows Channel Routing and DS0 assignment information for the fractional T1
links in the illustrated ring arrangement.
DSU
1
2
3
4
The DTEs at the ends of each fractional T1 link need to be at approximately equal distances from
their ends of the T1 line.
1-4
Transmit Timing
Fallback Timing
Option
Option
Receive
Cascade
(Network)
Receive
Cascade
(Network)
Cascade
Receive(Network)
Receive
Cascade
(Network)
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Application
Channel Routing
Option
Network
First group of DS0s,
starting at 1
Network
Cascade
Second group of DS0s,
continuing sequentially
Cascade
from the FT1A group
DS0s
076R155-000
Issue 7
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