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T1 CrossConnect Installation & Operation Manual
2 – Theory of Operation
Version 2
Figure 2-11. Single T1 Ring in Counter-rotating Configuration
Protection switching always requires unused capacity around the ring. In a single T1 counter-rotating
ring, provides this unused capacity by leaving half of the T1 time slots empty in both directions around
the ring. When a failure occurs, the CrossConnect Systems connected to the failed T1 line switch to
alternate maps as they did in the unidirectional ring. However, instead of re-routing an entire T1, only
the active time slots (half of the total) are re-routed. Usually the lower-numbered time slots (1 to 12)
are used for normal operation. During a failure, time slots 1 to 12 are mapped to unused time slots 13
to 24 in the opposite direction. Figure 2-12 shows the counter-rotating ring after a T1 failure between
sites C and D. Notice that the traffic between sites A and B is undisturbed, still using time slot 1 in
both directions between the two sites. The traffic between sites C and D, however, has been re-
directed around the ring away from the failure, using previously unused time slot 13.
2-12
GatesAir
Intraplex Products
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