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T1 CrossConnect Installation & Operation Manual
2 – Theory of Operation
Version 2
counter-clockwise direction. This unused path provides the extra capacity which is utilized in the case
of a T1 failure.
Figure 2-9. Unidirectional Ring Configuration
Figure 2-10 shows this same ring after a failure has occurred in the T1 line between sites C and D. The
CrossConnect Systems at sites C and D have each detected the T1 failure and switched to alternate
maps. The CrossConnect System at site C redirects the traffic normally sent toward site D back around
the ring in the opposite direction toward site B, using the normally empty inner (counter-clockwise)
path. The CrossConnect System at site D no longer expects to see incoming traffic from site C, and
looks instead for the same traffic to appear coming from site A on the inner path. The CrossConnect
Systems at sites A and B have not detected any failure and continue in normal operation. (Notice that
in normal mode, all the DCS systems must connect the unused inner path straight-through.) The
condition in Figure 2-10 is a stable configuration in which all circuits have been automatically
redirected away from the failed T1 line.
2-10
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