LANs are great for the small areas they encompass, but other mechanisms must be used for wide area networks, such as the Internet. Imagine trying to detect collisions if the whole world were on one single Ethernet!

WANs, wide area networks, use a variety of network topologies, which are ways of arranging the connecting wires between the hosts of the network. If there are only two hosts, then a single wire between them is the only imaginable topology. When there are three, suddenly different possibilities begin to develop.