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System Description
D
DTE 1
SC553
DSU
C
X
C
SC553
DTE 3
DSU
D
Fault Tolerant Switching Application:
The application requires the DSUs to be connected in a ring topology. In the example shown there are two
fractional T1 data links: FT1A - Site 1 to Site 2, and FT1B - Site 3 to Site 4.
Normal operation:
T1A carries all channel data and the FDL management channel between 1 and 2; 3 is cascaded to
1; 4 is cascaded to 2. T1B carries no channel data; it does carry the FDL management channel
between 3 and 4.
T1A Loss:
DSUs reconfigure automatically to route all channel data over T1B; 1 cascades to 3; 2 cascades to
4; FDL management channel between 1 and 2 is lost.
Failure Between FT1A & FT1B (X or Y):
DSUs 3 and 4 reconfigure automatically to route FT1B channel data over T1B; FT1A channel data
continues to operate over T1A.
Consult accompanying text for further information on the Fault Tolerant Switching application.
Figure 1-1
076R155-000
Issue 7
N
T1A
N
T1B
Fault Tolerant Switching
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Fault Tolerant Switching Application
DTE 2
D
SC553
N
DSU
C
FT1A
Y
DTE 4
C
SC553
N
DSU
D
FT1B
Key:
D = DTE Port
C = Cascade Port
N = Network Interface
1-5
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