Information Technology Reference
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cedures. The use of modular connectors and twisted-pair wire for LANs was made
popular by the availability of inexpensive, existing components that were originally
intended for telephone system use. Unfortunately, users soon learned that the cable
needed to have specific characteristics, such as minimum twists per foot, to work
properly. The cable needed to meet certain performance levels that varied with the
application. A cable vendor's rating system, supplemented by Underwriters
Laboratories testing, eventually was incorporated into the TIA-568 cabling system.
The rating system divides wire and components into numbered categories that are
associated with increasing levels of performance needed for LAN operation.
Seven numbered categories of TIA-568-C cabling are now specified, as shown
in Table 3.1, although low-performance Categories 1 and 2 are specifically excluded
from consideration in the standard. Two of the remaining categories, Category 3
and Category 4, are officially dropped for new installations, although both may
continue to be used for the appropriate purposes in existing locations. Category 3
can support 10 and 16 MHz networks, such as traditional Ethernet and Token-
Ring, and rarely-seen Category 4 supports up to 20 MHz.
Category 5 has been dropped for new installations, and replaced by Category
5e, which is now the “entry level” for UTP cabling. Category 5e supports 100 MHz
(100 to 1000 Mbps) networks, as well as the lower speeds.
Cabling devices are often rated by the industry both in bandwidth (in MHz or
GHz) and in throughput or data rate (in Mbps or Gbps). Regardless of which num-
ber you see, the bandwidth of a component is the limiting parameter. This is because
data encoding techniques often obscure the actual cable signaling-rate, which is
bandwidth limited. For example, the older 10 and 16 Mbps Ethernet and Token-Ring
networks require matching cable bandwidths of 10 and 16 MHz because their sig-
naling structure actually operates at those bandwidths. But 100 Mbps network tech-
TABLE 3.1
UTP Wiring Performance Categories
Wire
Nominal
Performance
Gauge
Impedance
Transmission
Typical Uses
Category 1
18-26
Not specified
Audio, DC
Speaker wire, door bells :-)
Category 2
22-26
Not specified
Up to 1.5 MHz
Analog telephone
Category 3
22-24
100 ohms ± 10%
Up to 16 MHz
10BaseT, 4/16 Token-Ring
Category 4
22-24
100 ohms ± 10%
Up to 20 MHz
10BaseT, 4/16 Token-Ring
Category 5/5e 22-24
100 ohms ± 10%
Up to 100 MHz 100BaseTX, ATM, 1000BaseT (4)
Category 6
22-24
100 ohms ± 10%
Up to 200 MHz 1000BaseTX
Category AC6
22-24
100 ohms ± 10%
Up to 500 MHz
10BaseT
Category 7
22
100 ohms ± 10%
Up to 1200 MHz 10GBaseT, multimedia
