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:
“I ask whether the mere eating of human flesh so very far exceeds in barbarity that custom which only a few years since was practised in enlightened England:Ma convicted traitor, perhaps a man found guilty of honesty, patriotism, and suchlike heinous crimes, had his head lopped off with a huge axe, his bowels dragged out and thrown into a fire; while his body, carved into four quarters, was with his head exposed upon pikes, and permitted to rot and fester among the public haunts of men!”
—Herman Melville (1819–1891)
“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)
“Parents need all the help they can get. The strongest as well as the most fragile family requires a vital network of social supports.”
—Bernice Weissbourd (20th century)