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Modaldispersion,whichisthespreadingofthesignalovertimecausedbythedifferent
propagation modes in the fiber.
For multimode transmission, modal dispersion, rather than chromatic dispersion or
attenuation, usually limits the maximum bit rate and link length. For single-mode
transmission,modaldispersionisnotafactor.However,athigherbitratesandoverlonger
distances, chromatic dispersion limits the maximum link length.
An efficient optical data link must have enough light to exceed the minimum power that
the receiver requires to operate within its specifications. In addition, the total dispersion
mustbewithinthelimitsspecifiedforthetypeoflinkinTelcordiaTechnologiesdocument
GR-253-CORE (Section 4.3) and International Telecommunications Union (ITU)
document G.957.
When chromatic dispersion is at the maximum allowed, its effect can be considered as
a power penalty in the power budget. The optical power budget must allow for the sum
of component attenuation, power penalties (including those from dispersion), and a
safety margin for unexpected losses.
Related Topics • Calculating the EX8200 Switch Fiber-Optic Cable Power Budget on page 120
• Calculating the EX8200 Switch Fiber-Optic Cable Power Margin on page 121
• Optical Interface Support in EX8200 Switches on page 60
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Chapter6:CableRequirements