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Designing and Expanding the Network 2 - 31
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Figure 2-12. Fiber Network With 3 Concentrators
In Figure 2-12, the fiber equivalent distance between transceivers attached
to Concentrators C and D is:
3 * 190 m + 1000 m + 1000 m + 500 m + 1000 m = 4070 m
Because this is less than 4200 meters, the configuration is legal.
In Figure 2-12, if the main link from Concentrator A to Concentrator C
faults, the signal path (enabled through redundancy) includes Concentrator
B. By adding Concentrator B, the fiber equivalent distance has become too
great and the network cannot work because the path between
Concentrators C and D is C-B-A-D:
4 * 190 + 1000 m + 2000 m + 500 m + 500 m + 1000 m = 5760 m
Because the sum is greater than 4200 meters, this configuration is not
legal. When designing a redundant network, be sure to consider the
backup route distance.