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Catalyst 2984G, 2948G-GE-TX, and 2980G Switch Hardware Installation Guide
78-6286-05
Appendix C Differential Mode Delay
modes. This is in contrast to an unconditioned launch, which, in the worst case,
might concentrate all of its light in the center of the fiber-optic cable, exciting
only two or more modes equally.
A significant variation in the amount of DMD is produced from one MMF cable
to the next. No reasonable test can be performed to survey an installed cable plant
to assess the effect of DMD. Therefore, you must use a mode-conditioning patch
cord for all interfaces using MMF when the link span exceeds 984 feet (300
meters). For link spans less than this, you can omit the patch cord (there is no
problem using it on short links).