Networking: A Beginner's Guide
Many older networks (those built prior to circa 1992) still have coaxial cable installed.
Most of this coaxial cable is the thin variety, which is RG-58, and is used with Thin
Ethernet. A few may also use the thicker RG-8 cable for Thick Ethernet, but this is rare.
Thin Ethernet cabling is wired in a bus arrangement, where each network segment
starts with a terminator that connects to the end of the cable, runs to each node in turn,
and ends with another terminator on the other end. The terminators contain special
50-ohm resistors, and the network cable will not work unless both are installed.
All the connectors in a Thin Ethernet system are BNC connectors, a quick-release
bayonet-style connector, both reliable and easy to use. BNC connectors come in a
variety of different styles to enable you to make just about any network connection you
need along the bus. T-connectors have two female BNC connectors on each side of the
crossbar of the T and a male BNC connector at the end of the shaft of the T. The two
female connectors are used for the RG-58 cable coming into and out of a node, while the
male connector attaches to a female BNC connector on the node's Ethernet card. Barrel
connectors have two female connectors that are used to connect two Thin Ethernet wires
together. Barrel connectors are also available in different shapes, including an elbow bend
and a U-shaped bend, but usually the simple straight barrel connector is used. Figure 4-2,
earlier in the chapter, shows the various parts of a Thin Ethernet BNC cable system.
Coaxial cable has a central conductor, which can be either a solid, single copper wire
or a stranded set of wires. A white plastic material surrounds the central conductor,
which is surrounded by a metal foil and then a braided wire shield. The shield is finally
wrapped in a plastic cable sheath.
Cable types must not be mixed in any coaxial network. If the network uses, say,
RG-58A/U, then that is what you must always use--not any other coaxial cable. Not mixing
RG-58A/U and RG-58/U is also a good idea because they have ever-so-slightly different signaling
characteristics. (A/U cable uses a stranded center conductor, while /U--sometimes called C/U--
uses a solid center conductor.)
Twisted-Pair Performance Designations
Level or Category
Not performance rated
100 Mbps to 1 Gbps