Category 5 Cables
Category 5 cable, commonly known as Cat 5, is an unshielded twisted
pair type cable designed for high signal integrity. The actual standard defines
specific electrical properties of the wire, but it is most commonly known as
being rated for its Ethernet capability of 100 Mbit/s.
Its specific standard designation is EIA/TIA-568.
Cat 5 cable
typically has three twists per inch of each twisted pair of 24 gauge copper
wires within the cable. Another important characteristic is that the wires are
insulated with a plastic (FEP) that has low dispersion, that is, the dielectric
constant of the plastic does not depend greatly on frequency. Special attention
also has to be paid to minimizing impedance mismatches at connection points.
It is often used
in structured cabling for computer networks such as fast Ethernet, although it
is often used to carry many other signals such as basic voice services, token
ring, and ATM (at up to 155 Mbits/s, over short
distances).
The other well
known flavor of this type of cable is the 10 Mbit/s
Category 3 cable. Less well known is the 20 Mbit/s Cat 4. Cat 4 offered only a small advance in speed over
Cat3, and was generally ignored in favour of Cat 5.
Cat 1 and Cat 2 are 1 Mbit/s systems for voice and
low-speed data.
Patch leads created
from Cat 5 are often terminated with RJ-45 electrical connectors. Normal Cat 5
cables are wired "straight through" and connect a computer to a hub.
In other words, pin 1 is connected to pin 1, pin 2 to pin 2, etc. The RJ-45 pinout for a Cat 5 cable can either be TIA-568A or
TIA-568B. TIA-568A is used by some phone systems and Token Ring. Most
everything else, such as the Ethernet standards 10BASE-T and 100BASE-TX, use
TIA-568B.
In Ethernet,
"crossover" Cat-5 cables are used to connect two hubs together, in
which pairs two and three are reversed. Crossover cables can also be used to
connect two PC's NICs directly (with no intervening
hub).
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