History
In the 1980's, many companies shared resources over a single network. This was generally accomplished using the company's existing Private Branch Exchange (PBX). The PBX is a company's private telephone network used to connect users within the company. Due to the inherent reliability of the Plain Old Telephone Service (POTS) and the cost effectiveness of the PBX, the PBX was the (early) logical choice to use as the platform for integration of voice and date service.
The Internet Protocol (IP), part of the TCP/IP suite (developed by the U.S. Department of Defense to link dissimilar computers across many kinds of data networks) seemed to have the necessary qualities to become the successor of the Public Switched Telephone Network (PSTN). IP works in a packet-switching method: the data is sliced and bundled into packets (pieces of information). These packets are transmitted from the source end-point to the destination end-point by moving from router to router until they reach their destination. No circuit is closed between the two end points as in the circuit-switched PSTN. IP as a connectionless mode is very efficient because no bandwidth is spent when there is nothing to transmit. When transmission is needed, IP enables using all the free bandwidth.
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