Hardware Reference
In-Depth Information
where interference can be a problem, you need to route the cable away from the interfer-
ence, use an external shield, or substitute STP for UTP near interference sources.
Four standard types of UTP cabling exist and are still used to varying degrees:
•
Category 3 cable
—The original type of UTP cable used for Ethernet networks was
also the same as that used for business telephone wiring. This is known as Category
3, or voice-grade UTP cable, and it is measured according to a scale that quantifies
the cable's data-transmission capabilities. The cable itself is 24 AWG (American Wire
Gauge, a standard for measuring the diameter of a wire) and copper-tinned with solid
conductors, with100-105ohmcharacteristic impedance andaminimum oftwotwists
per foot. Category 3 cable is largely obsolete because it is only adequate for networks
running at up to 16Mbps, so it cannot be used with Fast or Gigabit Ethernet.
•
Category 5 cable
—The faster network types require greater performance levels. Fast
Ethernet (100BASE-TX) uses the same two-wire pairs as 10BASE-T, but Fast Ether-
net needs a greater resistance to signal crosstalk and attenuation. Therefore, the use of
Category 5 UTP cabling is essential with 100BASE-TX Fast Ethernet. Although the
100BASE-T4 version of Fast Ethernet can use all four-wire pairs of Category 3 cable,
this flavor of Fast Ethernet is not widely supported and has practically vanished from
the marketplace. If you try to run Fast Ethernet 100BASE-TX over Category 3 cable,
youwillhaveaslowandunreliablenetwork.Category5cableiscommonlycalledCat
5 and is also referred to as Class D cable.
ManycablevendorsalsosellanenhancedformofCategory5cablecalledCategory5e
(specified by Addendum 5 of the ANSI/TIA/EIA-568-A cabling standard). Category
5e cable can be used in place of Category 5 cable and is especially well suited for use
in Fast Ethernet networks that might be upgraded to Gigabit Ethernet in the future.
Category 5e cabling must pass several tests not required for Category 5 cabling. Even
though you can use both Category 5 and Category 5e cabling on a Gigabit Ethernet
(1000BASE-TX) network, Category 5e cabling provides better transmission rates and
a greater margin of safety for reliable data transmission.
•
Category 6 cable
—Category 6 cabling (also called Cat 6 or Class E) can be used in
place of Cat 5 or 5e cabling and uses the same 8P8C (RJ-45) connectors as Cat 5 and
5e. Cat 6 cable handles a frequency range of 1MHz-250MHz, compared to Cat 5 and
5e's 1MHz-100MHz frequency range. Cat 6 is suitable for Gigabit Ethernet at stand-
ard distances of up to 100 meters (328 ft.), and can even be used for 10 Gigabit Ether-
net at reduced distances of up to 55 meters (180 ft.).
•
Category 6a cable
—Category6acabling(alsocalledCat6aorClassEA)canbeused
in place of Cat 6, 5 or 5e cabling and uses the same 8P8C (RJ-45) connectors. Cat 6a
