Figure 27-3 Keystone Modular (left) or 110 Connect Modular (right)
Extending Ethernet Beyond the 90 Meter Limit with Fiber
Optic Cable
Fiber optic cables have conductors made of glass, rather than metal. A typical fiber
cable is composed of a glass core that carries the light signals. The core is encased in
cladding that keeps the light contained in the core.
No electrical impulses are carried over a fiber optic cable as in a metal cable. Instead,
the electrical impulses are converted to pulses of light that indicate whether a bit is 1
or a 0.
Signals on metal cables and the light in a fiber optic cable travel at approximately the
same speed, but light meets less resistance as it travels along the cable. Therefore,
light signals go further with less attenuation. Fiber optic links on simple LANs can run
without a repeater to distances of more than 3.5 kilometers.
Fiber based cabling systems are more reliable than metallic cabling systems because
they are immune to electrical noise generated by support equipment in the building.
Despite shielding, grounding, and bypassing, metallic cables can behave like
antennas, making them susceptible to RF noise. The greater the length of the cable,
the greater the possibility it will be subject to interference from nearby electrical
equipment.
In addition, metallic cables are subject to an effect that produces voltage potentials
between the cable and electrical ground. This can occur in large buildings or campus
environments where equipment is powered from multiple AC power panels that are not
operating at the same AC ground potential.
At the very least, the voltage potential can skew the data signals on the cable, causing
transient disruptions and or occasional losses of data. If the voltages are great
Chapter 27
Extending Ethernet Beyond the 90 Meter Limit with Fiber Optic Cable
27-3
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