Packet switching
Data in the header is used by networking hardware to direct the packet to its destination, where the payload is extracted and used by an operating system, application software, or higher layer protocols.
The new concept found little resonance among network implementers until the independent work of Welsh computer scientist Donald Davies at the National Physical Laboratory in 1965.
[7] The concept of switching small blocks of data was first explored independently by Paul Baran at the RAND Corporation during the early 1960s in the US and Donald Davies at the National Physical Laboratory (NPL) in the UK in 1965.
[1][2][3][11] In the late 1950s, the US Air Force established a wide area network for the Semi-Automatic Ground Environment (SAGE) radar defense system.
Recognizing vulnerabilities in this network, the Air Force sought a system that might survive a nuclear attack to enable a response, thus diminishing the attractiveness of the first strike advantage by enemies (see Mutual assured destruction).
[19][20] In June that year, he gave a paper "Time Sharing in Large Fast Computers" at the UNESCO Information Processing Conference in Paris where he passed the concept on to J. C. R.
[31] Roger Scantlebury, a member of Davies' team, presented their work (and referenced that of Baran) at the October 1967 Symposium on Operating Systems Principles (SOSP).
To deal with packet permutations (due to dynamically updated route preferences) and datagram losses (unavoidable when fast sources send to a slow destinations), he assumed that "all users of the network will provide themselves with some kind of error control",[28] thus inventing what came to be known as the end-to-end principle.
[38][61][62][63] A contemporary of Roberts' from MIT, Leonard Kleinrock had researched the application of queueing theory in the field of message switching for his doctoral dissertation in 1961–62 and published it as a book in 1964.
[64] Davies, in his 1966 paper on packet switching,[26] applied Kleinorck's techniques to show that "there is an ample margin between the estimated performance of the [packet-switched] system and the stated requirement" in terms of a satisfactory response time for a human user.
[67] Roberts and Taylor recognized the issue of response time was important, but did not apply Kleinrock's methods to assess this and based their design on a store-and-forward system that was not intended for real-time computing.
[93] In May 1974, Vint Cerf and Bob Kahn described the Transmission Control Program, an internetworking protocol for sharing resources using packet-switching among the nodes.
In the mid-late 1970s and early 1980s, national and international public data networks emerged using X.25 which was developed with participation from France, the UK, Japan, USA and Canada.
[123] The dispute over priority became a public issue after Donald Davies posthumously published a paper in 2001 in which he denied that Kleinrock's work was related to packet switching.
[75][76] This earlier dispute is exemplified by BBN's Will Crowther, who in a 1990 oral history described Paul Baran's packet switching design (which he called hot-potato routing), as "crazy" and non-sensical, despite the ARPA team having advocated for it.
[127] Former IPTO director Bob Taylor also joined the debate, stating that "authors who have interviewed dozens of Arpanet pioneers know very well that the Kleinrock-Roberts claims are not believed".
[131] Primary sources and historians recognize Baran and Davies for independently inventing the concept of digital packet switching used in modern computer networking including the ARPANET and the Internet.
[1][2][38][132][133] Kleinrock has received many awards for his ground-breaking applied mathematical research on packet switching, carried out in the 1970s, which was an extension of his pioneering work in the early 1960s on the optimization of message delays in communication networks.
Packet switching is associated with connectionless networking because, in these systems, no connection agreement needs to be established between communicating parties prior to exchanging data.
AppleTalk included features that allowed local area networks to be established ad hoc without the requirement for a centralized router or server.
[158][159][160][161] The contract for its implementation was awarded to an Anglo French consortium led by the UK systems house Logica and Sesa and managed by Andrew Karney.
[180][181] The proposal was not taken up nationally but the following year, he designed a local network using "interface computers", today known as routers, to serve the needs of NPL and prove the feasibility of packet switching.
The entire suite provided routing and packet delivery, as well as higher level functions such as a reliable byte stream, along with numerous applications.
A number of computer facilities serving the Science Research Council (SRC) community in the United Kingdom developed beginning in the early 1970s.
In the early 1980s a standardisation and interconnection effort started, hosted on an expansion of the SERCnet research network and based on the Coloured Book protocols, later evolving into JANET.
DATAPAC was developed by Bell-Northern Research which was a joint venture of Bell Canada (a common carrier) and Northern Telecom (a telecommunications equipment supplier).
[221][222][223] Nine member states of the European Economic Community contracted with Logica and the French company SESA to set up a joint venture in 1975 to undertake the Euronet development, using X.25 protocols to form virtual circuits.
[235] Tymnet utilized virtual call packet switched technology including X.25, SNA/SDLC, BSC and ASCII interfaces to connect host computers (servers) at thousands of large companies, educational institutions, and government agencies.
Its purpose was to extend networking benefits for computer science departments at academic and research institutions that could not be directly connected to ARPANET due to funding or authorization limitations.
Initially created to link researchers to the nation's NSF-funded supercomputing centers, through further public funding and private industry partnerships it developed into a major part of the Internet backbone.
