Peripherals and Networking - Strata Study Guide - page 97

Cables
The most common type of cabling used for Ethernet networks is an unshielded twisted
pair (UTP) cable with an RJ-45 connector at each end. RJ stands for Registered Jack.
Telephone systems also use RJ connectors, so you're probably familiar with that connector
type already. An RJ-45 connector is slightly wider than a normal telephone plug (an
RJ-11 or RJ-14), though, so it doesn't fi t in telephone outlets. Figure 3-12 shows an RJ-45
connector.

FIGURE 3.12 Ethernet cable with RJ-45 connector

UTP cable carries data on pairs of wires. The types of UTP cables used for Ethernet
have four pairs (eight wires total). The pairs of wires are twisted in order to minimize any
magnetic interference that may be generated as the electrical signals pass through the wires.
Each pair shares a color scheme. For example, the fi rst pair is orange and orange-and-
white. The other colors are green, blue, and brown, each pair with one solid wire and one
striped with white.
The cables are considered unshielded because they don't have any special built-in
protection from magnetic interference that may come from outside of the cable. Shielded
twisted pair cables (STP) are also available for Ethernet use, but they're much more
expensive and so are used only in situations where magnetic interference is a problem.