Communication networks that are regional, nationwide, or worldwide in geographic area, with a minimum distance typical of that between major metropolitan areas. Smaller networks include metropolitan and local-area networks. A communication network provides common transmission, multiplexing, and switching functions that enable users to transport data between many sources and many destinations. Under ideal circumstances, the data that arrive at the destination are identical to the data that were sent. The rate of arrival of bits at any point in the network is said to be the data rate at that point and is typically measured in bits per second. These bits may come from one source or from a multiplicity of sources. The capacity of a network to transmit at a cerain data rate is known as its bandwidth.