Message switching

In telecommunications, message switching involves messages routed in their entirety, one hop at a time. It evolved from circuit switching and was the precursor of packet switching. An example of message switching is email in which the message is sent through different intermediate servers to reach the mail server for storing. Unlike packet switching, the message is not divided into smaller units and sent independently over the network. Western Union operated a message switching system, Plan 55-A, for processing telegrams in the 1950s. Leonard Kleinrock wrote a doctoral thesis at the Massachusetts Institute of Technology in 1962 that analyzed queueing delays in this system. Message switching was built by Collins Radio Company, Newport Beach, California, during the period 1959–1963 for sale to large airlines, banks and railroads. The original design for the ARPANET was Wesley Clark's April 1967 proposal for using Interface Message Processors to create a message switching network. Packet switching was incorporated into the design by Larry Roberts after the first ACM Symposium on Operating Systems Principles in October 1967 based on the work of both Donald Davies and Paul Baran who had been working on the idea of packet switching independently of each other . Message switching systems are nowadays mostly implemented over packet-switched or circuit-switched data networks. Each message is treated as a separate entity. Each message contains addressing information, and at each switch this information is read and the transfer path to the next switch is decided. Depending on network conditions, a conversation of several messages may not be transferred over the same path. Each message is stored (usually on hard drive due to RAM limitations) before being transmitted to the next switch. Because of this it is also known as a 'store and forward' network. Email is a common application for message switching. A delay in delivering email is allowed real-time data transfer between two computers.