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T1 CrossConnect Installation & Operation Manual
2 – Theory of Operation
Version 2
There are cases, however, where a counter-rotating ring is not as efficient as a unidirectional ring.
One such example involves a network with a large number of overlapping circuits (Figure 2-13). The
traffic patterns in this network require 12 bi-directional circuits from site A to site C, and 12 more
circuits from site C to site D. In a counter-rotating ring, the maximum number of circuits in any
segment of the ring is limited to 12. In this example, the T1 link from site A to site B is filled to this 12
circuit capacity, as is the T1 link from site C to site D. However, the circuits all overlap between sites B
and C, requiring double the available capacity. For this application, the counter-rotating ring can only
provide 12 of the required circuits, and the unidirectional ring is clearly more efficient. Another
example where the unidirectional ring is more efficient than the counter-rotating ring is in point-to-
multipoint distribution. If, for example, the network applications require each circuit to pass through
every node for multi-point monitoring, the counter-rotating ring provides a maximum of 12 circuits,
while the unidirectional ring can provide up to 24.
Figure 2-13. Counter-rotating Ring Configuration with Less than 24 Circuits
To make the decision on which ring configuration best suits your communications requirements, first
evaluate performance of the counter-rotating ring. In many cases, this ring type yields more than 24
circuits, making it the clear choice. If the counter-rotating ring cannot support 24 circuits in the
2-14
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