Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams (sequences of packets) over a shared network. When traversing network adapters, switches, routers and other network nodes, packets are buffered and queued, resulting in variable delay and throughput depending on the traffic load in the network.

Packet switching contrasts with another principal networking paradigm, circuit switching, a method which sets up a limited number of dedicated connections of constant bit rate and constant delay between nodes for exclusive use during the communication session. In case of traffic fees (as opposed to flat rate), for example in cellular communication services, circuit switching is characterized by a fee per time unit of connection time, even when no data is transferred, while packet switching is characterized by a fee per unit of information.

Two major packet switching modes exist; (1) connectionless packet switching, also known as datagram switching, and (2) connection-oriented packet switching, also known as virtual circuit switching. In the first case each packet includes complete addressing or routing information. The packets are routed individually, sometimes resulting in different paths and out-of-order delivery. In the second case a connection is defined and preallocated in each involved node during a connection phase before any packet is transferred. The packets include a connection identifier rather than address information, and are delivered in order. See below.

Packet mode communication may be utilized with or without intermediate forwarding nodes (packet switches or routers). In all packet mode communication, network resources are managed by statistical multiplexing or dynamic bandwidth allocation in which a communication channel is effectively divided into an arbitrary number of logical variable-bit-rate channels or data streams. Statistical multiplexing, packet switching and other store-and-forward buffering introduces varying latency and throughput in the transmission. Each logical stream consists of a sequence of packets, which normally are forwarded by the multiplexers and intermediate network nodes asynchronously using first-in, first-out buffering. Alternatively, the packets may be forwarded according to some scheduling discipline for fair queuing, traffic shaping or for differentiated or guaranteed quality of service, such as weighted fair queuing or leaky bucket. In case of a shared physical medium, the packets may be delivered according to some packet-mode multiple access scheme.

History[link]

The concept of switching small blocks of data was first explored by Paul Baran in the early 1960s. Independently, Donald Davies at the National Physical Laboratory (NPL) in the UK had developed the same ideas a few years later (Abbate, 2000).

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.

Baran developed the concept of message block 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^[1] then published as RAND Paper P-2626 in 1962 and then including and expanding somewhat within a series of eleven papers titled On Distributed Communications in 1964. 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 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 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 Defence (MoD) told him about Baran's work. A member of Davies' team 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. In 1966 Davies proposed that a network should be built at the laboratory to serve the needs of NPL and prove the feasibility of packet switching. The NPL Data Communications Network entered service in 1970. Roberts and the ARPANET team took the name "packet switching" itself from Davies's work.

The first computer network and packet switching network deployed for computer resource sharing was the Octopus Network at the Lawrence Livermore National Laboratory that began connecting four Control Data 6600 computers to several shared storage devices (including an IBM 2321 Data Cell^[2] in 1968 and an IBM Photostore^[3] in 1970) and to several hundred Teletype Model 33 ASR terminals for time sharing use starting in 1968.^[4]

In 1973 Vint Cerf and Bob Kahn wrote the specifications for Transmission Control Protocol (TCP), an internetworking protocol for sharing resources using packet-switching among the nodes.

Connectionless and connection-oriented packet switching[link]

The service actually provided to the user by networks using packet switching nodes can be either connectionless (based on datagram messages), or virtual circuit switching (also known as connection oriented). Some connectionless protocols are Ethernet, IP, and UDP; connection oriented packet-switching protocols include X.25, Frame relay, Multiprotocol Label Switching (MPLS), and TCP.

In connection-oriented networks, each packet is labeled with a connection ID rather than an address. Address information is only transferred to each node during a connection set-up phase, when the route to the destination is discovered and an entry is added to the switching table in each network node through which the connection passes. The signalling protocols used allow the application to specify its requirements and the network to specify what capacity etc. is available, and acceptable values for service parameters to be negotiated. Routing a packet is very simple, as it just requires the node to look up the ID in the table. The packet header can be small, as it only needs to contain the ID and any information (such as length, timestamp, or sequence number) which is different for different packets.

In connectionless networks, each packet is labeled with a destination address, source address, and port numbers; it may also be labeled with the sequence number of the packet. This precludes the need for a dedicated path to help the packet find its way to its destination, but means that much more information is needed in the packet header, which is therefore larger, and this information needs to be looked up in power-hungry content-addressable memory. Each packet is dispatched and may go via different routes; potentially, the system has to do as much work for every packet as the connection-oriented system has to do in connection set-up, but with less information as to the application's requirements. At the destination, the original message/data is reassembled in the correct order, based on the packet sequence number. Thus a virtual connection, also known as a virtual circuit or byte stream is provided to the end-user by a transport layer protocol, although intermediate network nodes only provides a connectionless network layer service.

Packet switching in networks[link]

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 (the time it takes for data to pass across the network), and to increase robustness of communication.

The best-known use of packet switching is the Internet and most local area networks. The Internet is implemented by the Internet Protocol Suite using a variety of Link Layer technologies. For example, Ethernet and Frame Relay are 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. These virtual circuits carry variable-length packets. In 1978, X.25 provided the first international and commercial packet switching network, the International Packet Switched Service (IPSS). Asynchronous Transfer Mode (ATM) also is a virtual circuit technology, which uses fixed-length cell relay connection oriented packet switching.

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. 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".^[5] Modern routers, however, do not require these technologies to be able to forward variable-length packets at multigigabit speeds across the network.

X.25 vs. Frame Relay packet switching[link]

Both X.25 and Frame Relay provide connection-oriented packet switching, also known as virtual circuit switching. A major difference between X.25 and Frame Relay packet switching is that X.25 is a reliable protocol, based on node-to-node automatic repeat request, while Frame Relay is a non-reliable protocol, maximum packet length is 1000 bytes. Any retransmissions must be carried out by higher layer protocols. The X.25 protocol is a network layer protocol, and is part of the X.25 protocol suite, also known as the OSI protocol suite. It was widely used in switching networks during the 1980s and early 1990s, for example as an alternative to circuit mode terminal switching, and for automated teller machines. Frame relay is a further development of X.25. The simplicity of Frame Relay made it considerably faster and more cost effective than X.25 packet switching. Frame relay is a data link layer protocol, and does not provide logical addresses and routing. It is only used for "semi-permanent" connections, while X.25 connections also can be established for each communication session. Frame Relay was used to interconnect LANs or LAN segments, mainly in the 1990s by large companies that had a requirement to handle heavy telecommunications traffic across wide area networks.^[6]:250 Despite the benefits of frame relay packet switching, many international companies are staying with the X.25 standard. In the United States, X.25 packet switching was used heavily in government and financial networks that use mainframe applications. Many companies did not intend to cross over to Frame Relay packet switching because it is more cost effective to use X.25 on slower networks. In certain parts of the world, particularly in Asia-Pacific and South America regions, X.25 was the only technology available.^[7]

See also[link]

• Message switching
• Circuit switching
• Store and forward delay
• Time-Driven Switching - a bufferless approach to packet switching
• Public switched data network
• Packet switched network
• Optical burst switching

References[link]

Bibliography[link]

• 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. 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[link]

• 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
• Arthur Norberg, Judy E. O'Neill, Transforming Computer Technology: Information Processing for the Pentagon, 1962-1982 (Johns Hopkins University, 1996)

External links[link]

• Oral history interview with Paul Baran. Charles Babbage Institute University of Minnesota, Minneapolis. Baran describes his working environment at RAND, as well as his initial interest in survivable communications, and the evolution, writing and distribution of his eleven-volume work, "On Distributed Communications." Baran discusses his interaction with the group at ARPA who were responsible for the later development of the ARPANET.
• 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 is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

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Leonard Kleinrock
Leonard Kleinrock and the first Interface Message Processor
Born	(1934-06-13) June 13, 1934 (age 78) New York City
Residence	Los Angeles
Nationality	United States
Fields	Engineering Computer science
Institutions	UCLA
Alma mater	City College of New York, MIT
Doctoral advisor	Edward Arthurs[1]
Doctoral students	Chris Ferguson
Known for	Internet development
Notable awards	National Medal of Science[2]

Leonard Kleinrock (born June 13, 1934) is an American engineer and computer scientist. A computer science professor at UCLA's Henry Samueli School of Engineering and Applied Science, he made several important contributions to the field of computer networking, in particular to the theoretical side of computer networking. He also played an important role in the development of the ARPANET, the precursor to the Internet, at UCLA.^[3]

His most well-known and significant work is his early work on queueing theory, which has applications in many fields, among them as a key mathematical background to packet switching, the basic technology behind the Internet. His initial contribution to this field was his doctoral thesis at the Massachusetts Institute of Technology in 1962, published in book form in 1964; he later published several of the standard works on the subject. He described this work as:

"Basically, what I did for my PhD research in 1961–1962 was to establish a mathematical theory of packet networks..."

His theoretical work on hierarchical routing, done in the late 1970s with his then-student Farouk Kamoun, is now critical to the operation of today's worldwide Internet.

Education and career[link]

Kleinrock was born in New York City on June 13, 1934 to a Jewish family,^[4] and graduated from the noted Bronx High School of Science in 1951. He received a Bachelor of Electrical Engineering degree in 1957 from the City College of New York, and a master's degree and a doctorate (Ph.D.) in electrical engineering and computer science from the Massachusetts Institute of Technology in 1959 and 1963 respectively. He then joined the faculty at the University of California at Los Angeles (UCLA), where he remains to the present day; during 1991–1995 he served as the Chairman of the Computer Science Department there.^[5]

ARPANET and the Internet[link]

The first message on the ARPANET was sent by UCLA student programmer Charley Kline, at 10:30 p.m, on October 29, 1969 from Boelter Hall 3420, the school's main building.^[6] Supervised by Kleinrock, Kline transmitted from the university's SDS Sigma 7 host computer to the Stanford Research Institute's SDS 940 host computer. The message text was the word "login"; the "l" and the "o" letters were transmitted, but the system then crashed. Hence, the literal first message over the ARPANET was "lo". About an hour later, having recovered from the crash, the SDS Sigma 7 computer effected a full "login". The first permanent ARPANET link was established on November 21, 1969, between the IMP at UCLA and the IMP at the Stanford Research Institute. By December 5, 1969, the entire four-node network was established.^[7]

In 1988, Kleinrock was the chairman of a group that presented the report Toward a National Research Network to the U.S. Congress.^[8] This report was highly influential and was used to develop the High Performance Computing Act of 1991,^[9] that was influential in the development of the Internet as it is known today.^[10] Funding from the bill was used in the development of the 1993 web browser Mosaic, at the National Center for Supercomputing Applications (NCSA).^[11]

Room 3420 at Boelter Hall was restored to its condition of 1969 and converted into The Kleinrock Internet Heritage Site and Archive. It opened to the public with a grand opening attended by internet pioneers October 29, 2011.^[6][12]

Awards[link]

He has received numerous professional awards. Kleinrock was selected to receive the prestigious National Medal of Science, the nation's highest scientific honor, from President George W Bush in the White House on September 29, 2008. "The 2007 National Medal of Science to Leonard Kleinrock for his fundamental contributions to the mathematical theory of modern data networks, and for the functional specification of packet switching, which is the foundation of Internet technology. His mentoring of generations of students has led to the commercialization of technologies that have transformed the world."^[2] In 2010 he shared the Dan David Prize.^[13] In 2012, Kleinrock was inducted into the Internet Hall of Fame by the Internet Society.^[14]

See also[link]

• ARPANET
• Computer Science
• UCLA Engineering School
• Internet pioneers
• Nerds 2.0.1 - 1998 documentary in which Kleinrock gives a lengthy interview
• Plan 55-A, a message switching system analyzed in Kleinrock's thesis.

Works[link]

• Kleinrock, Leonard (July 1961). "Information Flow in Large Communication Nets". Ph.D. Thesis Proposal (Massachusetts Institute of Technology). http://www.lk.cs.ucla.edu/LK/Bib/REPORT/PhD/proposal.html. 
• Kleinrock, Leonard (July 1961). "Information Flow in Large Communication Nets". RLE Quarterly Progress Report ([Massachusetts Institute of Technology]]). http://www.lk.cs.ucla.edu/LK/Bib/REPORT/RLEreport-1961.html. 
• Kleinrock, Leonard (April 1962). "Information Flow in Large Communication Nets". RLE Quarterly Progress Report (Massachusetts Institute of Technology). http://www.lk.cs.ucla.edu/LK/Bib/REPORT/RLEreport-1962.html. 
• Kleinrock, Leonard (December 1962). "Message Delay in Communication Nets with Storage" (PDF). (PhD thesis) (Cambridge, MA: Massachusetts Institute of Technology). http://dspace.mit.edu/bitstream/handle/1721.1/11562/33840535.pdf. 
• Kleinrock, Leonard (1964). Communication Nets: Stochastic Message Flow and Design. McGraw-Hill. pp. 220. ISBN 978-0486611051. 
• Kleinrock, Leonard (2 January 1975). Queueing Systems: Volume I – Theory. New York: Wiley Interscience. pp. 417. ISBN 978-0471491101. 
• Kleinrock, Leonard (22 April 1976). Queueing Systems: Volume II – Computer Applications. New York: Wiley Interscience. pp. 576. ISBN 978-0471491118. 
• Kleinrock, Leonard; Kamoun, Farok (January 1977). "Hierarchical Routing for Large Networks, Performance Evaluation and Optimization". Computer Networks 1 (3): 155–174. 
• Kleinrock, Leonard; Gail, Richard (12 April 1996). Queueing Systems: Problems and Solutions. Wiley-Interscience. pp. 240. ISBN 978-0471555681. 

References[link]

External links[link]

• "Leonard Kleinrock's Home Page". UCLA. http://www.lk.cs.ucla.edu/. Retrieved 11 February 2004. 
• "KIHC: The Kleinrock Internet History Center at UCLA". UCLA. http://internethistory.ucla.edu/. Retrieved 11 November 2004. 
• "Bibliography". UCLA. http://www.lk.cs.ucla.edu/publications.html. Retrieved 24 May 2012. 
• "Network history links". http://www.lk.cs.ucla.edu/internet_history.html. Retrieved 11 November 2004. ^{[dead link]}
• "Oral history interview with Leonard Kleinrock". University of Minnesota, Minneapolis: Charles Babbage Institute. 3 April 1990. http://purl.umn.edu/107411. Retrieved 15 May 2008.  Kleinrock discusses his work on the ARPANET.

Kleinrock discusses his dissertation work in queuing theory, and his move to the University of California at Los Angeles (UCLA). As one of the main contractors for the ARPANET, Kleinrock describes his involvement in discussions before the official DARPA request was issued, the people involved in the ARPANET work at UCLA, the installation of the first node of the network, the Network Measurement Center, and his relationships with Lawrence Roberts and the IPT Office, Bolt, Beranek and Newman, and the Network Analysis Corporation.

• "Oral history interview with Howard Frank". University of Minnesota, Minneapolis: Charles Babbage Institute. http://purl.umn.edu/107294. Retrieved 1 July 2008.  Frank describes his work on the ARPANET, including his interaction with Roberts and the IPT Office.
• Video: Interview with Leonard Kleinrock. ACM. http://portal.acm.org/citation.cfm?doid=1008213.1008229. Retrieved 7 May 2006. 
• Video: Leonard Kleinrock on the first Internet connection. http://www.newsroom.ucla.edu/portal/ucla/electronicplay.aspx?fid=28176&id=E0C5478. Retrieved 25 August 2008. 
• Video: Leonard Kleinrock displays Internet's first router. http://www.newsroom.ucla.edu/portal/ucla/electronicplay.aspx?fid=28175&id=E0C5478. Retrieved 25 August 2008. 
• Video: Leonard Kleinrock on packet-switching, early Internet. http://www.newsroom.ucla.edu/portal/ucla/electronicplay.aspx?fid=28174&id=E0C5478. Retrieved 25 August 2008.