Networks that connect machines situated over geographical distances larger than the 1 km covered by ethernet are known as wide area networks. Some wide area networks are regional networks which connect systems within a city, state, or region. There are also several national and international networks.
Membership in a regional or national network is usually extended to entire local networks. In other words, the nodes in a wide area network tend to be local networks themselves, as opposed to single machines. Connection to a regional or national network is through a gateway in the local network that links the local network to other networks in the regional network.
Wide area networks started up as a way of linking together sites with common interests. For example, the Energy Sciences Network (ESNET) connects university, academic, and industrial research labs funded by the US Department of Energy. NSFNET, sponsored by the National Science Foundation, is a hierarchical network with a very high bandwidth ``backbone'' connecting several regional NSF networks. Each of these networks is administered separately. If a department or research group wishes to join a regional or national network, it applies to the administrator for membership. Once connected, it pays dues to cover operational costs and follows guidelines set by the network administration.
Figure 4: ESNET Sites in the US.