telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

, message switching involves messages routed in their entirety, one hop at a time. It evolved from

circuit switching Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full ...

and was the precursor of

packet switching In telecommunications, packet switching is a method of grouping data into '' packets'' that are transmitted over a digital network. Packets are made of a header and a payload. Data in the header is used by networking hardware to direct the p ...

History

Western Union The Western Union Company is an American multinational financial services company, headquartered in Denver, Colorado. Founded in 1851 as the New York and Mississippi Valley Printing Telegraph Company in Rochester, New York, the company cha ...

operated a message switching system, Plan 55-A, for processing

telegrams Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...

in the 1950s.

Leonard Kleinrock Leonard Kleinrock (born June 13, 1934) is an American computer scientist and a long-tenured professor at UCLA's Henry Samueli School of Engineering and Applied Science. In the early 1960s, Kleinrock pioneered the application of queueing theor ...

wrote a doctoral thesis at the

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of th ...

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 The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

was Wesley Clark's April 1967 proposal for using Interface Message Processors to create a message switching network.

Packet switching In telecommunications, packet switching is a method of grouping data into '' packets'' that are transmitted over a digital network. Packets are made of a header and a payload. Data in the header is used by networking hardware to direct the p ...

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 Donald Watts Davies, (7 June 1924 – 28 May 2000) was a Welsh computer scientist who was employed at the UK National Physical Laboratory (NPL). In 1965 he conceived of packet switching, which is today the dominant basis for data communic ...

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 A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are m ...

. 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 Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in ...

' network. Email is a common application for message switching. A delay in delivering email is allowed real-time data transfer between two computers.

Examples

Hop-by-hop

Telex The telex network is a station-to-station switched network of teleprinters similar to a telephone network, using telegraph-grade connecting circuits for two-way text-based messages. Telex was a major method of sending written messages electroni ...

forwarding and

UUCP UUCP is an acronym of Unix-to-Unix Copy. The term generally refers to a suite of computer programs and protocols allowing remote execution of commands and transfer of files, email and netnews between computers. A command named is one of the pr ...

are examples of message switching systems. When this form of switching is used, no physical path is established in advance between sender and receiver. Instead, when the sender has a block of data to be sent, it is stored in the first switching office (i.e. router) then forwarded later one hop at a time. Each block is received in its entity form, inspected for errors and then forwarded or re-transmitted. A form of store-and-forward network. Data is transmitted into the network and stored in a switch. The network transfers the data from switch to switch when it is convenient to do so, as such the data is not transferred in real-time. Blocking can not occur, however, long delays can happen. The source and destination terminal need not be compatible, since conversions are done by the message switching networks. A message switch is "transactional". It can store data or change its format and bit rate, then convert the data back to their original form or an entirely different form at the receive end. Message switching multiplexes data from different sources onto a common facility. A message switch is one of the switching technologies.

Store and forward delays

Since message switching stores each message at intermediate nodes in its entirety before forwarding, messages experience an end to end delay which is dependent on the message length, and the number of intermediate nodes. Each additional intermediate node introduces a delay which is at minimum the value of the minimum transmission delay into or out of the node. Note that nodes could have different transmission delays for incoming messages and outgoing messages due to different technology used on the links. The transmission delays are in addition to any propagation delays which will be experienced along the message path. In a message-switching centre an incoming message is not lost when the required outgoing route is busy. It is stored in a queue with any other messages for the same route and retransmitted when the required circuit becomes free. Message switching is thus an example of a delay system or a queuing system. Message switching is still used for telegraph traffic and a modified form of it, known as packet switching, is used extensively for data communications.

Advantages

The advantages to message switching are: * Data channels are shared among communication devices, improving the use of bandwidth. * Messages can be stored temporarily at message switches, when network congestion becomes a problem. * Priorities may be used to manage network traffic. * Broadcast addressing uses bandwidth more efficiently because messages are delivered to multiple destinations.

References

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History

Examples

Store and forward delays

Advantages

See also

References

Further reading