Packet switching is a communications method in which packets (discrete blocks of data) are routed between nodes over data links shared with other traffic. In Information technology, a packet is a formatted unit of Data carried by a Packet mode Computer network. Routing is the process of selecting paths in a network along which to send network traffic A node ( Latin nodus, ‘knot’ is a critical element of any Computer network. In each network node, packets are queued or buffered, resulting in variable delay. This contrasts with the other principal paradigm, circuit switching, which sets up a limited number of constant bit rate and constant delay connections between nodes for their exclusive use for the duration of the communication. In Telecommunications a circuit switching network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals

Packet mode or packet-oriented communication may be utilized with or without a packet switch, in the latter case directly between two hosts. In Computer networking, a network host, Internet host or host is a Computer connected to the Internet. Examples of that are point-to-point data links, digital video and audio broadcasting or a shared physical medium, such as a bus network, ring network, or hub network.

Packet mode communication is a statistical multiplexing technique, also known as a dynamic bandwidth allocation method, where a physical communication channel is effectively divided into an arbitrary number of logical variable bit-rate channels or data streams. Statistical multiplexing is a type of communication link sharing very similar to Dynamic bandwidth allocation (DBA Dynamic Bandwidth Allocation (DBA is a technique by which traffic bandwidth in a shared telecommunications medium can be allocated on demand and fairly between different users of Each logical stream consists of a sequence of packets, which normally are forwarded by a network node asynchronously in a first-come first-serve fashion. FIFO is an Acronym for First In First Out, an abstraction in ways of organizing and manipulation of data relative to time and prioritization Alternatively, the packets may be forwarded according to some scheduling discipline for fair queuing or differentiated and/or guaranteed Quality of service. Fair queuing is a Scheduling algorithm used in computer and Telecommunications networks to allow multiple packet flows to fairly share the link In case of a shared physical media, the packets may be delivered according to some packet-mode multiple access scheme. In Telecommunications and Computer networks, a channel access method or multiple access method allows several terminals connected to the same

The service actually provided to the user by networks using packet switching internally to the network can be datagrams (connectionless messages), and/or virtual circuit switching (also known as connection oriented). In a packet-switched network connectionless mode transmission is a transmission in which each packet is prepended with a header containing a destination In Telecommunications and Computer networks, a virtual circuit ( VC) synonymous to virtual connection and Virtual channel, is a In Telecommunications connection-oriented describes a means of transmitting data in which the devices at the end points use a preliminary protocol to establish an End-to-end Some connectionless protocols are Ethernet, IP, and UDP; connection oriented protocols include X.25, Frame relay, Asynchronous Transfer Mode (ATM), Multiprotocol Label Switching (MPLS), and TCP. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol User Datagram Protocol ( UDP) is one of the core protocols of the Internet Protocol Suite. X25 is an ITU-T standard Network layer protocol for packet switched Wide area network (WAN communication In the context of Computer networking, frame relay consists of an efficient Data transmission technique used to send digital information In electronic digital data transmission systems the Network protocol Asynchronous Transfer Mode (ATM encodes data traffic into small fixed-sized cells MPLS redirects here For other uses see Mpls In Computer networking and Telecommunications, Multi Protocol Label Switching The Transmission Control Protocol (TCP is one of the core protocols of the Internet Protocol Suite.

Multiplex techniques
Circuit mode (constant bandwidth)
TDM · FDM · WDM Polarization multiplexing Spatial multiplexing (MIMO)
Statistical multiplexing (variable bandwidth)
Packet mode · Dynamic TDM FHSS · DSSS · OFDMA
Related topics
Channel access methods Media Access Control (MAC)
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It is also entirely possible to have to weigh the various metrics against each other. For multiplexing in electronics and signal processing see Multiplexer. In Telecommunications a circuit switching network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals Time-Division Multiplexing ( TDM) is a type of Digital or (rarely analog Multiplexing in which two or more signals or bit streams are transferred Frequency-division multiplexing ( FDM) is a form of signal Multiplexing where multiple Baseband signals are Modulated on different frequency In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations Spatial multiplexing is a transmission technique in MIMO Wireless communication to transmit independent and separately encoded data signals so called streams Statistical multiplexing is a type of communication link sharing very similar to Dynamic bandwidth allocation (DBA Packet switching is a network communications method that splits data traffic (digital representations of text sound or video data into chunks called packets, that are then This article is about the medium access technology The name "TDMA" is also commonly used in the United States to refer to D-AMPS, which is a mobile telephone Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using In Telecommunications direct-sequence spread spectrum ( DSSS) is a Modulation technique Orthogonal Frequency-Division Multiple Access ( OFDMA) is a multi-user version of the popular Orthogonal frequency-division multiplexing (OFDM digital modulation scheme In Telecommunications and Computer networks, a channel access method or multiple access method allows several terminals connected to the same The Media Access Control (MAC Data communication protocol sub-layer also known as the Medium Access Control is a sublayer of the Data Link Layer specified in the 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. In Mathematics, the term optimization, or mathematical programming, refers to the study of problems in which one seeks to minimize or maximize a real function

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. In Computer science, the Actor model is a mathematical model of Concurrent computation that treats "actors" as the universal primitives of concurrent

Contents 1 Packet switching in networks 2 History of packet switching 3 See also 4 References 5 Further reading 6 External links

Packet switching in networks

Main article: Packet switched network

Packet switching is used to optimize the use of the channel capacity available in digital telecommunication networks such as computer networks, to minimize the transmission latency (i. A Packet Switched Network, or PSN refers to the packet switched networks that existed before the Internet In Electrical engineering, Computer science and Information theory, channel capacity is the tightest upper bound on the amount of Information Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable e. the time it takes for data to pass across the network), and to increase robustness of communication. Robustness is the quality of being able to withstand stresses pressures or changes in procedure or circumstance

The most well-known use of packet switching is the Internet and local area networks. The Internet is a global system of interconnected Computer networks The Internet uses the Internet protocol suite over a variety of data link layer protocols. The Internet Protocol Suite (commonly TCP/IP) is the set of Communications protocols used for the Internet and other similar networks The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the For example, Ethernet and frame relay are very common. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs In the context of Computer networking, frame relay consists of an efficient Data transmission technique used to send digital information Newer mobile phone technologies (e. g. , GPRS, I-mode) also use packet switching. General Packet Radio Service (GPRS is a Packet oriented Mobile Data Service available to users of Global System for Mobile Communications (GSM and NTT DoCoMo 's i-mode is a Wireless internet service popular in Japan.

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. X25 is an ITU-T standard Network layer protocol for packet switched Wide area network (WAN communication In Telecommunications and Computer networks, a virtual circuit ( VC) synonymous to virtual connection and Virtual channel, is a These virtual circuits carry variable-length packets. In 1978, X.25 was used to provide the first international and commercial packet switching network, the International Packet Switched Service (IPSS). Year 1978 ( MCMLXXVIII) was a Common year starting on Sunday (link displays the 1978 Gregorian calendar) X25 is an ITU-T standard Network layer protocol for packet switched Wide area network (WAN communication The International Packet Switched Service (IPSS was created in 1978 by a collaboration between the United Kingdom's General Post Office, Western Union International Asynchronous Transfer Mode (ATM) also is a virtual circuit technology, which uses fixed-length cell relay connection oriented packet switching. In electronic digital data transmission systems the Network protocol Asynchronous Transfer Mode (ATM encodes data traffic into small fixed-sized cells In Telecommunications cell relay refers to a method of statistically multiplexing fixed-length packets, i

Datagram packet switching is also called connectionless networking because no connections are established. Technologies such as Multiprotocol Label Switching (MPLS) and the Resource Reservation Protocol (RSVP) create virtual circuits on top of datagram networks. MPLS redirects here For other uses see Mpls In Computer networking and Telecommunications, Multi Protocol Label Switching The Resource ReSerVation Protocol ( RSVP) described in RFC 2205 is a Transport layer protocol designed to reserve resources across a network Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications.

MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells" ^[1]. Modern routers, however, do not require these technologies to be able to forward variable-length packets at multigigabit speeds across the network. A router ('rautər in the USA 'rutər in the UK and Ireland, or either pronunciation in Australia and Canada is a Computer whose software and hardware are usually

History of packet switching

The concept of packet switching was first explored by Paul Baran in the early 1960s, and then independently a few years later by Donald Davies (Abbate, 2000). Paul Baran (born April 29, 1926) was one of the three inventors of Packet-switched networks along with Donald Davies and Leonard Kleinrock Donald Watts Davies, CBE FRS ( June 7, 1924 &ndash May 28, 2000) was a Welsh Computer scientist

Leonard Kleinrock conducted early research in queueing theory which would be important in packet switching, and published a book in the related field of digital message switching (without the packets) in 1961; he also later played a leading role in building and management of the world's first packet switched network, the ARPANET. Leonard Kleinrock PhD (born June 13, 1934 in New York) is a Computer scientist, and a professor of computer science at UCLA Queueing theory is the mathematical study of waiting lines (or queues ' In Telecommunications, message switching was the precursor of Packet switching, where messages were routed in their entirety one hop at a time The ARPANET ( Advanced Research Projects Agency Network) developed by ARPA of the United States Department of Defense, was the world's first operational

Baran developed the concept of packet switching during his research at the RAND Corporation for the US Air Force into survivable communications networks, first presented to the Air Force in the summer of 1961 as briefing B-265 ^[2] then 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]. The RAND Corporation ( R esearch AN d D evelopment is a Nonprofit global policy Think tank first formed to offer research and analysis 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. __FORCETOC__ Decentralization or Decentralisation (see Spelling differences) is the process of dispersing Decision-making governance closer to the people 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

Baran's study made its way to Robert Taylor 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. Robert W Taylor (born 1932 was director of ARPA 's Information Processing Techniques Office (1965-69 founder and later manager of Xerox PARC 's Computer Joseph Carl Robnett Licklider ( March 11, 1915  &ndash June 26, 1990) known simply as J Lawrence Roberts may refer to Lawrence Roberts (scientist, one of the 4 "fathers" of the Internet Lawrence Roberts (basketball The ARPANET ( Advanced Research Projects Agency Network) developed by ARPA of the United States Department of Defense, was the world's first operational

Baran's packet switching work was similar to the research performed independently by Donald Davies at the National Physical Laboratory, UK. Donald Watts Davies, CBE FRS ( June 7, 1924 &ndash May 28, 2000) was a Welsh Computer scientist The National Physical Laboratory (NPL is the national Measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington 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. The Association for Computing Machinery, or ACM, was founded in 1947 as the world's first scientific and educational Computing society

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's work.

See also

• Store and forward delay
• Circuit switching
• Message switching
• Public switched data network
• Packet switched network
• Optical burst switching
• Statistical multiplexing
• ALOHAnet

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: I Introduction to Distributed Communications Network (RAND Memorandum RM-3420-PR. August 1964)
• Paul Baran, On Distributed Communications Networks, (IEEE Transactions on Communications Systems, March 1964)
• D. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization 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)

Further reading

• Katie Hafner, Where Wizards Stay Up Late (Simon and Schuster, 1996) pp 52-67
• Janet Abbate, Inventing the Internet (MIT Press, 2000) ISBN 0-262-51115-0

External links

• Packet Switching History and Design, site reviewed by Baran, Roberts, and Kleinrock
• Paul Baran and the Origins of the Internet
• A Brief History of the Internet

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing ( FOLDOC) is an online searchable encyclopedic Dictionary of Computing subjects The GNU Free Documentation License ( GNU FDL or simply GFDL) is a Copyleft License for free documentation designed by the Free Software

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