Designing and Expanding the Network 2 -31
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Figure 2-12. Fiber Network With 3 Co ncentrators
In Figure 2-12, the fiber equivalent distance between transceivers a ttached
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 throug h redundancy) includes Concentrator
B. By adding Concentrator B, the fiber equivalent distance has become too
great and the network cannot work because the pa th be tween
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 42 00 meters, this configuration is not
legal. When designing a redundant network, be sure to consider the
backup route distance.