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:
“How difficult the task to quench the fire and the pride of private ambition, and to sacrifice ourselves and all our hopes and expectations to the public weal! How few have souls capable of so noble an undertaking! How often are the laurels worn by those who have had no share in earning them! But there is a future recompense of reward, to which the upright man looks, and which he will most assuredly obtain, provided he perseveres unto the end.”
—Abigail Adams (1744–1818)
“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)
“Mental health data from the 1950’s on middle-aged women showed them to be a particularly distressed group, vulnerable to depression and feelings of uselessness. This isn’t surprising. If society tells you that your main role is to be attractive to men and you are getting crow’s feet, and to be a mother to children and yours are leaving home, no wonder you are distressed.”
—Grace Baruch (20th century)
“Of what use, however, is a general certainty that an insect will not walk with his head hindmost, when what you need to know is the play of inward stimulus that sends him hither and thither in a network of possible paths?”
—George Eliot [Mary Ann (or Marian)