Hardware Reference
In-Depth Information
Figure 17.6. Coaxial cable.
Twisted-Pair Cable
Twisted-pair cable is just what its name implies: insulated wires within a protective casing with a
specified number of twists per foot. Twisting the wires reduces the effect of electromagnetic
interference (EMI, which can be generated by nearby cables, electric motors, and fluorescent
lighting) on the signals being transmitted. Shielded twisted pair (STP) refers to the amount of
insulation around the cluster of wires and therefore its immunity to noise. You are probably familiar
with unshielded twisted pair (UTP) cable; it is often used for telephone wiring.
Figure 17.7
shows
UTP cable;
Figure 17.8
illustrates STP cable.
Figure 17.7. A UTP cable.
Figure 17.8. An STP cable.
Shielded Versus Unshielded Twisted Pair
When cabling was being developed for use with computers, it was first thought that shielding
the cable from external interference was the best way to reduce interference and provide for
greater transmission speeds. However, it was discovered that twisting the pairs of wires is a