Public Switched Telephone Network
Public Land Mobile Networks need to connect to the Public Switched Telephone Network (PSTN) in order to route calls.
The PSTN is the world's collection of interconnected voice-oriented public telephone networks, in much the same way that the Internet is the concentration of the world's public IP-based packet-switched networks. It is both commercially- and government-owned. This aggregation of circuit-switching telephone networks has evolved greatly from the days of Alexander Graham Bell, and in the late 20th century became almost entirely digital in nature — except for the final link from the central (local) telephone office to the user (the local loop). It also extends into mobile as well as fixed telephones.
The PSTN also furnishes much of the Internet's long-distance infrastructure and, for the majority of users, the access network as well. Because Internet Service Providers (ISPs) pay the long-distance carriers for access to their infrastructure, and share the circuits among many users through packet switching, the end Internet user avoids having to pay usage tolls to anyone other than their ISP.
Many observers believe that the long-term future of the PSTN is to be just one application of the Internet — however, the Internet has some way to go before this transition can be made. For example, the Quality of Service (QoS) guarantee is one aspect that needs to be improved for Voice over IP (VOIP) technology.
The PSTN is largely governed by technical standards created by the ITU-T, and uses E.163/E.164 addresses (usually called telephone numbers) for addressing. A number of large private telephone networks are not connected to the PSTN, and are used for military purposes (such as the Defense Switched Network). There are also private networks run by large companies which are linked to the PSTN, but only through controlled gateways such as private branch exchanges.
Read more about this topic: Public Land Mobile Network
Famous quotes containing the words public, switched, telephone and/or network:
“During the Civil War the area became a refuge for service- dodging Texans, and gangs of bushwhackers, as they were called, hid in its fastnesses. Conscript details of the Confederate Army hunted the fugitives and occasional skirmishes resulted.”
—Administration in the State of Texa, 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)
“It’s a hard feeling when everyone’s in a hurry to talk to somebody else, but not to talk to you. Sometimes you get a feeling of need to talk to somebody. Somebody who wants to listen to you other than “Why didn’t you get me the right number?””
—Heather Lamb, U.S. telephone operator. As quoted in Working, book 2, by Studs Terkel (1973)
“How have I been able to live so long outside Nature without identifying myself with it? Everything lives, moves, everything corresponds; the magnetic rays, emanating either from myself or from others, cross the limitless chain of created things unimpeded; it is a transparent network that covers the world, and its slender threads communicate themselves by degrees to the planets and stars. Captive now upon earth, I commune with the chorus of the stars who share in my joys and sorrows.”
—Gérard De Nerval (1808–1855)