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Management Information Systems

Notes
Figure 6.10: Coaxial Cable

For LANs, coaxial cable offers several advantages. It can be run with fewer boosts from repeaters
for longer distances between network nodes than either STP or UTP cable. Repeaters regenerate
the signals in a network so that they can cover greater distances. Coaxial cable is less expensive
than fiber-optic cable, and the technology is well known; it has been used for many years for all
types of data communication.
When working with cable, you need to consider its size. As the thickness, or diameter, of the
cable increases, so does the difficulty in working with it. Many times cable must be pulled
through existing conduits and troughs that are limited in size. Coaxial cable comes in a variety
of sizes. The largest diameter (1 centimeter [cm]) was specified for use as Ethernet backbone
cable because historically it had greater transmission length and noise-rejection characteristics.
This type of coaxial cable is frequently referred to as Thicknet. As its nickname suggests, Thicknet
cable can be too rigid to install easily in some situations because of its thickness. The general
rule is that the more difficult the network medium is to install, the more expensive it is to install.
Coaxial cable is more expensive to install than twisted-pair cable. Thicknet cable is almost never
used except for special-purpose installations.
A connection device known as a vampire tap was used to connect network devices to Thicknet.
The vampire tap then was connected to the computers via a more flexible cable called the
attachment unit interface (AUI). Although this 15-pin cable was still thick and tricky to terminate,
it was much easier to work with than Thicknet.
In the past, coaxial cable with an outside diameter of only 0.35 cm (sometimes referred to as
Thinnet) was used in Ethernet networks. Thinnet was especially useful for cable installations
that required the cable to make many twists and turns. Because it was easier to install, it was also
cheaper to install. Thus, it was sometimes referred to as Cheapernet. However, because the
outer copper or metallic braid in coaxial cable comprises half the electrical circuit, special care
had to be taken to ensure that it was properly grounded. Grounding was done by ensuring that
a solid electrical connection existed at both ends of the cable. Frequently, however, installers
failed to properly ground the cable. As a result, poor shield connection was one of the biggest
sources of connection problems in the installation of coaxial cable. Connection problems resulted
in electrical noise, which interfered with signal transmittal on the networking medium. For this
reason, despite its small diameter, Thinnet no longer is commonly used in Ethernet networks.
The most common connectors used with Thinnet are BNC, short for British Naval Connector or
Bayonet Neill Concelman, connectors (see Figure 6.11). The basic BNC connector is a male type
mounted at each end of a cable. This connector has a center pin connected to the center cable
conductor and a metal tube connected to the outer cable shield. A rotating ring outside the tube
locks the cable to any female connector. BNC T-connectors are female devices for connecting

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