There are four major types of cable in use in networks today: Coaxial (coax), unshielded twisted pair (UTP), shielded twisted pair (STP) and fiber optic.

Coaxial Cable (Coax)

Coax can be a good solution for small networks. Because it is generally wired in a bus topology, it requires less cable than other solutions and doesn't require a hub. It's generally easy to install the connections. Coax also offers relatively high immunity to interference from noise sources, so it is often used in manufacturing environments.

There are some disadvantages to coax, though. The same bus topology which makes it less expensive makes it more difficult to isolate problems. These days its LAN use is pretty much confined to 10BASE2 Ethernet. The new high-speed networks are not supporting coax, so this cabling may be a dead end.

Coax used for Ethernet networks is 50 Ohms. Coax for cable TV (CATV) is 75 Ohms. Using the wrong cable for your network will cause network problems.

Unshielded Twisted Pair (UTP)

UTP can support telephone, 4 & 16 Mbps Token Ring, Ethernet, 100 Mbps Ethernet, Copper FDDI (CDDI), 155 Mbps ATM, and, well you get the picture. UTP cable is rated by the EIA/TIA standards into categories.

• Category 3 is rated to 10 MHz, suitable for Ethernet (10 Mb/s)
• Category 4 is rated to 20 MHz, suitable for Token Ring (16 Mb/s).
• Category 5 is rated to 100 MHz, suitable for Fast Ethernet (100 Mb/s) and ATM (155 Mb/s).

These days the best value on pricing is Category 3 and Category 5. Category 3 is the low price choice for today's cable plant, and there are plans to support 100 Mbps over Category 3 cable by using all 4 pair (100BASE-T4, for example). The price gap between Category 4 and Category 5 is so small that most people are going right to Category 5.

You may hear of Level 5 cable. UL rates cable from level 1 to 5; Levels 3-5 correspond to Categories 3-5. UL Levels 1 and 2 are voice grade cable; EIA/TIA has not designated any cable as Level 1 or 2.

UTP cable is generally wired in a star topology, with the troubleshooting advantages associated with stars. Although most of the topologies listed above require only 2 pair (4 wires), the specific 2 pair used varies by network type. Telephone requires only 1 pair for a single line phone. If you install 4 pair cabling, it will support any possible combination without requiring you to determinate (put new connectors) on each connection if you change network types.

Shielded Twisted Pair (STP)

STP has come to mean two entirely different types of cable. The original STP cabling was proposed by IBM and was used for Token Ring networks. It sported a Universal Data Connector (UDC) which was large and neither male nor female (the connectors could always plug into each other). The cable was bulky, and had a shield around each pair, plus a shield around all of the pairs. It was rated to 16 MHz. IBM called this Type 1 cable.

Type 1 STP cable really doesn't have much of a future except in IBM, Token-Ring shops due to its low speed, bulkiness, connector size, and one-network support.

Recently, a new version of STP cable has been introduced and promoted by companies like ITT Datacomm. Instead of shielding around each pair, it has only one shield around the entire cable. This type of STP cabling uses an RJ-45 connector with some metal on it so that the system can be grounded. Its not bulky, and it's easy to work with and terminate.

The jury is still out on whether or not this shielding is needed, but proponents say it will become critical as 155 Mbps signals are transmitted for ATM usage. I've seen in EMI tests that STP cable radiates less signal than UTP cable. Overall, though, the new STP has all the advantages of UTP, and perhaps better signal carrying capability. While I chose UTP for my installation, STP bears close watching.

Fiber optic

Fiber optic cable offers up the possibility of near infinite bandwidth and perfect immunity to noise. The trade-off is simply cost and difficulty of installation. It costs significantly more to purchase fiber optic cable, connectors, patch panels, jumper cables, tools, and network interface cards (NICs). You don't have to worry about where to ground the cable, either.

Since this is a Home Area Network, I'm going to put off discussing fiber until some future date. Please feel free to send me email on this topic, since I have some experience with installation and troubleshooting.