The cable topology describes the way that stations on the network are connected together. Each topology has its own advantages and disadvantages. Structured Wiring Systems use the star topology. There are three major cable topologies: Daisy Chain, Bus, and Star. Computer networks generally use one topology, though ARCnet can mix bus and star. Office telephones (one extension per phone) use a star configuration, while home telephones (all on one extension) are often daisy chained.

Daisy Chain

In a daisy chain, each station is plugged into the device upstream and downstream from itself. Phonenet and Etherwave are two cabling systems that daisy chain devices together.

Advantages: These are very easy to put together. They require a minimum of cable because you only need enough cable to chain the stations together. It's easy to add more devices anywhere in the chain. You don't have to worry about having enough network jacks present.

Disadvantages: A component failure (particularly with Etherwave) or cable failure in midstream will down the entire network. Also, if you want to add a device in the middle of the chain, the network will be down while you add the device. The cabling for these networks is generally out in the open, and more vulnerable to accidental disconnections and breaks.

Bus Topology

In a bus topology, all stations are attached to the same cable. The most popular networks using a bus topology are 10BASE2 and 10BASE5 Ethernet. Arcnet can also run on a bus topology.

Advantages: A bus requires less cable because you only need enough to chain the stations together. There is no central point of failure on a bus because there's no hub.

Disadvantages: However, a bus can be even more vulnerable to failure than a star because any problem impacts the entire network. A bus can make troubleshooting difficult for this very same reason -- how do you isolate a problem?

Star Topology

In a star topology, each station has a cable leading back to a central hub. The most popular networks using a star topology are 10BASE-T Ethernet and Token Ring.

Advantages: A star can simplify troubleshooting because stations can be disconnected from the hub one at a time until the problem is isolated. (Actually, you can do this with a bus, but you'd be running all over the building.) The hub may have extra features like LEDs that indicate activity and errors on each port, making it even easier to isolate problems. With the introduction of switches, you can dramatically increase network performance by replacing the hub with a switch.

Disadvantages: It requires more cable to wire a star. A hub failure can knock out the entire network. Stars can be more expensive because of the cost of the hub.