Download Frontline LAN Troubleshooting Guide

Frontline LAN troubleshooting guide
would arrive at the far end later in time than the light that
traveled straight down the core. This caused a sharply transmitted
pulse to arrive as a rounded bump. Firing pulses at high data rates
resulted in the rounded bumps blurring together and becoming
impossible for the receiver to distinguish one from the next. This
is called modal dispersion.
The next generation of cable was called graded index, which uses
a different composition of glass as you progress outward from the
core, which causes the light rays to bend back toward the center.
Instead of bouncing off the cladding, light in this type of fiber
tends to flow more like a sinusoidal wave, often without quite
touching the cladding. This type of fiber reduces the modal
dispersion, permitting the transmitted signals to be recovered at
greater distances than older step-index fiber.
Laser optimized multimode is manufactured with glass having a
much more consistent refractive index. This permits the VCSEL
lasers used with Gigabit Ethernet to excite fewer modes during
transmission, which in turn results in less modal dispersion. The
transmitted signal arrives more sharply defined at the far end,
which permits higher signaling rates to be transmitted. The early
laser optimized fiber that was first introduced in the mid 1990s
is not capable of supporting 10 Gigabit. More recent formulations
of glass and better manufacturing processes that result in a
more tightly controlled refractive index began appearing as early
as 1999, and are rated for 10 Gigabit. At the same time, since
the glass core is wider, more modes may exist; the popularity of
62.5µm multimode is waning in favor of the narrower 50µm
multimode fiber. Since there are fewer modes found in the 50µm
cable, the signal may be reliably recovered at greater distances and
at higher data rates.
Fluke Networks
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