A LAN is usually a network of Ethernet links connecting together, for example, the computers, servers and printers of an enterprise and is normally considered to be contained within a single site. LANs can be extended to, for example, a computer terminal in a remote location or they can be joined together to form a wider area network. VLANs take this a stage further and comprise a common Ethernet switched network in which the links can be partitioned to provide capacity for several individual LANs. In this way, the LANs share a common infrastructure and benefit from the economies of scale. In 21CN VLANs allow us to partition the capacity of the links according to the needs of the different types of service, for example, voice and video.