A public switched data network (PSDN) is a publicly available packet-switched network, distinct from the PSTN.
Originally this term referred only to Packet Switch Stream (PSS), an X.25-based packet-switched network, mostly used to provide leased-line connections between local area networks and the Internet using permanent virtual circuits (PVCs). Today, the term may refer not only to Frame Relay and Asynchronous Transfer Mode (ATM), both providing PVCs, but also to Internet Protocol (IP), GPRS, and other packet-switching techniques.
Whilst there are several technologies that are superficially similar to the PSDN, such as Integrated Services Digital Network (ISDN) and the Digital Subscriber Line (DSL) technologies, they are not examples of it. ISDN utilizes the PSTN circuit-switched network, and DSL uses point-to-point circuit switching communications overlaid on the PSTN local loop (copper wires), usually utilized for access to a packet-switched broadband IP network.
Short for packet-switched data network, a data communications network that is based on the principles of packet switching, as opposed to circuit switching that is used in public telephone networks. Packet-switched networks do not establish physical communication channels between communicating devices like circuit-switched networks do. Instead, signals are formed into fixed-length packets that are affixed with a source and destination address and packet ordering details. The packets then rely on network routers to read the address data and route the packets through the network to their destinations. When the packets arrive at the receiving device, the packet ordering data is used to reassemble the original signal. One advantage of packet-switched networks is that packets from different sources going to different destinations can share common data pathways.
Famous quotes containing the words public, switched, data and/or network:
“He believes without reservation that Kentucky is the garden spot of the world, and is ready to dispute with anyone who questions his claim. In his enthusiasm for his State he compares with the Methodist preacher whom Timothy Flint heard tell a congregation that “Heaven is a Kentucky of a place.””
—For the State of Kentucky, U.S. public relief program (1935-1943)
“When I am on a stage, I am the focus of thousands of eyes and it gives me strength. I feel that something, some energy, is flowing from the audience into me. I actually feel stronger because of these waves. Now when the play’s done, the eyes taken away, I feel just as if a circuit’s been broken. The power is switched off. I feel all gone and empty inside of me—like a balloon that’s been pricked and the air’s let out.”
—Lynn Fontanne (1887–1983)
“To write it, it took three months; to conceive it three minutes; to collect the data in it—all my life.”
—F. Scott Fitzgerald (1896–1940)
“A culture may be conceived as a network of beliefs and purposes in which any string in the net pulls and is pulled by the others, thus perpetually changing the configuration of the whole. If the cultural element called morals takes on a new shape, we must ask what other strings have pulled it out of line. It cannot be one solitary string, nor even the strings nearby, for the network is three-dimensional at least.”
—Jacques Barzun (b. 1907)