Public switched data network
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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.
[edit] See also
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