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Media
An important part of designing and installing an Ethernet is
selecting the appropriate Ethernet medium. There are four
major types of media in use today: Thickwire for 10BASE5
networks, thin coax for 10BASE2 networks, unshielded twisted
pair (UTP) for 10BASE-T networks and fiber optic for
10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL)
networks.
This wide variety of media reflects the evolution of
Ethernet and also points to the technology's flexibility.
Thickwire was one of the first cabling systems used in
Ethernet but was expensive and difficult to use. This
evolved to thin coax, which is easier to work with and less
expensive.
The
most popular wiring schemes are 10BASE-T and 100BASE-TX,
which use unshielded twisted pair (UTP) cable. This is
similar to telephone cable and comes in a variety of grades,
with each higher grade offering better performance.
Level 5 cable is the highest, most expensive grade, offering
support for transmission rates of up to 100 Mbps. Level 4
and level 3 cable are less expensive, but cannot support the
same data throughput speeds; level 4 cable can support
speeds of up to 20 Mbps; level 3 up to 16 Mbps.
The 100BASE-T4 standard allows for support of 100 Mbps
Ethernet over level 3 cable, but at the expense of adding
another pair of wires (4 pair instead of the 2 pair used for
10BASE-T); for most users, this is an awkward scheme and
therefore 100BASE-T4 has seen little popularity. Level 2 and
level 1 cables are not used in the design of 10BASE-T
networks.
For
specialized applications, fiber-optic, or 10BASE-FL,
Ethernet segments are popular. Fiber-optic cable is more
expensive, but it is invaluable for situations where
electronic emissions and environmental hazards are a
concern.
Fiber-optic cable is often used in interbuilding
applications to insulate networking equipment from
electrical damage caused by lightning. Because it does not
conduct electricity, fiber-optic cable can also be useful in
areas where large amounts of electromagnetic interference
are present, such as on a factory floor.
The Ethernet standard allows for fiber-optic cable segments
up to 2 kilometers long, making fiber optic Ethernet perfect
for connecting nodes and buildings that are otherwise not
reachable with copper media.
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