Twisted-pair cable

The most popular type of cable today is twisted-pair cable, or UTP. (The U stands for unshielded, but no one says unshielded twisted pair. Just twisted pair will do.) UTP cable is even cheaper than thin coaxial cable, and best of all, many modern buildings are already wired with twisted-pair cable because this type of wiring is often used with modern phone systems. Figure below shows a twisted-pair cable.

When you use UTP cable to construct an Ethernet network, you connect the computers in a star arrangement. In the center of the star is a device called a hub. Depending on the model, Ethernet hubs enable you to connect from 4 to 24 computers using twisted-pair cable.

An advantage of UTP's star arrangement is that if one cable goes bad, only the computer attached to that cable is affected; the rest of the network continues to chug along. With coaxial cable, a bad cable affects the entire network, and not just the computer to which the bad cable is connected.

Here are a few other details that you should know about twisted-pair cabling:

• UTP cable consists of pairs of thin wire twisted around each other; several such pairs are gathered up inside an outer insulating jacket. Ethernet uses two pairs of wires, or four wires altogether. The number of pairs in a UTP cable varies, but it is often more than two.
• UTP cable comes in various grades called Categories. Don't use anything less than Category 5 cable for your network. Although cheaper, it may not be able to support faster networks.
  Although higher Category cables are more expensive than lower Category cables, the real cost of installing Ethernet cabling is the labor required to actually pull the cables through the walls. As a result, I recommend that you always spend the extra money to buy Category 5 cable.
• If you want to sound like you know what you're talking about, say "Cat 5" instead of "Category 5."
• Although Category 5 cable is fine for 100Mbps networks, the newer 1000Mbps networks require an even better cable. Category 5e cable (the e stands for enhanced), and Category 6 cable will support 1000Mbps networks.
• UTP cable connectors look like modular phone connectors but are a bit larger. UTP connectors are officially called RJ-45 connectors.
• Like thinnet cable, UTP cable is also sold in prefabricated lengths. However, RJ-45 connectors are much easier to attach to bulk UTP cable than BNC cables are to attach to bulk coaxial cable. As a result, I suggest that you buy bulk cable and connectors unless your network consists of just two or three computers. A basic crimp tool to attach the RJ-45 connectors costs about $50.
• The maximum allowable cable length between the hub and the computer is 100 meters (about 328 feet).