The coded representation of the physical or logical location of a source or destination resource, such as a register, a memory partition, an application, or a node or station. An address may be contained in an address field associated with a data unit, such as a block, cell, frame, or packet, in order that switches, routers, and other devices can forward the data unit to the destination device across a network. Alternatively, an address might be used to set up a path between originating and destination devices, such as voice telephone sets, to connect a call. A PSTN telephone number, for example, is a logical address associated with a physical port on a physical central office (CO) switch connected to a physical copper circuit terminating in a physical device such as a PBX, key system, or telephone set at a fixed physical location. A cellular telephone number is a logical address associated with a physical station that typically is mobile, perhaps across networks. An Internet Protocol (IP) address is a logical address associated with a data terminal or other physical network element that may be either fixed in location or mobile, perhaps across networks. See also E.164, IP address, logical, and physical.