Packet switching

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Packet switching, in computer networking and telecommunications, is the now-dominant communications paradigm in which packets (units of information carriage) are routed between nodes over data links shared with other traffic. This contrasts with the other principal paradigm, circuit switching, which sets up a dedicated connection between the two nodes for their exclusive use for the duration of the communication. Packet switching is used to optimize the use of the bandwidth available in a network, to minimize the transmission latency (i.e. the time it takes for data to pass across the network), and to increase robustness of communication.


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[edit] Packet routing

Packets are routed to their destination as determined by a routing algorithm. The routing algorithm can create paths based on various metrics and desirable qualities of the routing path. For example, low latency may be of paramount concern and everything else is secondary, or a minimum hop count.

It's also entirely possible to have to weigh the various metrics against each other. For example, reducing the hop count could increase the latency to an unacceptable limit and some kind of balance would need to be found. For multi-parameter optimization, some form of optimization may be needed.

Once a route is determined for a packet it is entirely possible that the route may change for the next packet, thus leading to a case where packets from the same source headed to the same destination could be routed differently.

Packet switching influenced the development of the Actor model of concurrent computation in which messages sent to the same address may be delivered in an order different from the order in which they were sent.

[edit] Packet switching in the networks

The most well-known use of the packet switching is the internet. The internet uses the internet protocol suite over a variety of data link layer protocols. For example, Ethernet and Frame relay are very common. Newer mobile phone technologies (e.g., GPRS, I-mode) also use packet switching.

X.25 is a notable use of packet switching in that, despite being based on packet switching methods, it provided 'Virtual Circuits' to the user. In 1978, X.25 was used to provide the first international and commercial packet switching network, the International Packet Switched Service (IPSS).

Packet switching is also called connectionless networking because no connections are established.

Asynchronous Transfer Mode (ATM) is a hybrid technology, which uses cell relay instead of packet switching.

Fast packet switching is a packet switching technique that increases the throughput by eliminating overhead.

[edit] History of packet switching

The concept of packet switching had two independent beginnings, with Paul Baran and Donald Davies (Abbate, 2000). Leonard Kleinrock conducted early research and published a book in the related field of digital message switching (without the packets) in 1961, and also later played a leading role in building and management of the world's first packet switched network, the ARPANET.

Baran developed the concept of packet switching during his research for the US Air Force into survivable communications networks, first published as RAND Paper P-2626 in 1962[1], and then including and expanding somewhat within a series of eleven papers titled On Distributed Communications in 1964 [2]. Baran's P-2626 paper described a general architecture for a large-scale, distributed, survivable communications network. The paper focuses on three key ideas: first, use of a decentralized network with multiple paths between any two points; and second, dividing complete user messages into what he called message blocks (later called packets); then third, delivery of these messages by store and forward switching.

Baran's study made its way to Robert Taylor (computer scientist) and J.C.R. Licklider at the Information Processing Technology Office, both wide-area network evangelists, and it helped influence Lawrence Roberts to adopt the technology when Taylor put him in charge of development of the ARPANET.

Baran's packet switching work was similar to the research performed independently by Donald Davies at the National Physical Laboratory, UK. In 1965, Davies developed the concept of packet switched networks and proposed development of a UK wide network. He gave a talk on the proposal in 1966, after which a person from the Ministry of Defense told him about Baran's work. Davies met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, bringing the two groups together.

Interestingly, Davies had chosen some of the same parameters for his original network design as Baran, such as a packet size of 1024 bits. Roberts and the ARPANET team took the name "packet switching" itself from Davies work.

In 1970, Davies helped build a packet switched network called the Mark I to serve the NPL in the UK. It was replaced with the Mark II in 1973, and remained in operation until 1986, influencing other research in the UK and Europe. [3]

[edit] See also

[edit] References

  • Leonard Kleinrock, Information Flow in Large Communication Nets, (MIT, Cambridge, May 31, 1961) Proposal for a Ph.D. Thesis
  • Leonard Kleinrock. Information Flow in Large Communication Nets (RLE Quarterly Progress Report, July 1961)
  • Leonard Kleinrock. Communication Nets: Stochastic Message Flow and Delay (Mcgraw-Hill, New York, 1964)
  • Paul Baran et al., On Distributed Communications, Volumes I-XI (RAND Corporation Research Documents, August, 1964)
  • Paul Baran, On Distributed Communications Networks (IEEE Transactions on Communications Systems, March 1964)
  • D. W. Davies, K. A. Bartlett, R. A. Scantlebury, and P. T. Wilkinson, A digital communications network for computers giving rapid response at remote terminals (ACM Symposium on Operating Systems Principles. October 1967)
  • R. A. Scantlebury, P. T. Wilkinson, and K. A. Bartlett, The design of a message switching Centre for a digital communication network (IFIP 1968)
  • Larry Roberts and Tom Merrill, Toward a Cooperative Network of Time-Shared Computers (Fall AFIPS Conference. October 1966)
  • Lawrence Roberts, The Evolution of Packet Switching (Proceedings of the IEEE, November, 1978)
  • Packet Switching History and Design, site reviewed by Baran, Roberts, and Kleinrock
  • Abbate, J [2000], Inventing the Internet MIT Press ISBN 0-262-51115-0

[edit] Further reading

  • Katie Hafner, Where Wizards Stay Up Late (Simon and Schuster, 1996) pp 52-67

[edit] External links

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

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