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Home , Frank Heart, History of the Internet, Ivan Sutherland, Jon Postel, MCI Communications, Ray Tomlinson

Barry M. Leiner, Vinton G. Cerf, David D. Clark, Robert E. Kahn, , Daniel C. Lynch, , Lawrence G. Roberts, Stephen S. Wolff

The Past and Future History of the the of future technology

HE INTERNET HAS REVOLUTIONIZED THE AND COMMUNICA- tions world like nothing before. The telegraph, , , and T computer have all set the stage for the Internet’s unprecedented inte- gration of capabilities. The Internet is at once a worldwide capability, a mechanism for information dissemination, and a medium for collaboration and interaction between individuals and their with- out regard for geographic location.

The Internet also represents one of the most suc- many aspects—technological, organizational, and cessful examples of sustained investment and commit- community. And its influence reaches not only to the ment to research and development in information technical fields of computer communications but infrastructure. Beginning with early research in packet throughout society as we move toward increasing use switching, the government, industry, and academia of online tools to accomplish electronic commerce, have been partners in evolving and deploying this information acquisition, and community operations.2 exciting new technology. Today, terms like “[email protected]” and “http://www.acm.org” trip Origins lightly off the tongue of random people on the street.1 The first recorded description of the social interactions The Internet today is a widespread information that could be enabled through networking was a series infrastructure, the initial prototype of what is often of memos written August 1962 by J.C.R. Licklider of called the National (or Global or Galactic) Information MIT, discussing his “Galactic Network” concept [6]. Infrastructure. Its history is complex and involves Licklider envisioned a globally interconnected set of

1 Perhaps this is an exaggeration due to the lead author’s residence in Silicon Valley. 2For a more detailed version of this article, see http://www.isoc.org/internet-history.

102 February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM computers through which everyone could quickly stration of this new network technology. Also in 1972, access data and programs from any site. In spirit, the electronic mail, the initial “hot” application, was intro- concept was much like the Internet today. While at duced. In March, of BBN wrote the DARPA,3 he convinced the people who would be his basic message send-and-read , motivated successors there—Ivan Sutherland, Bob Taylor, and by ARPANET developers’ need for an easy coordina- MIT researcher Lawrence G. Roberts—of the impor- tion mechanism. From there, email took off as the most tance of this networking concept. popular network application and as a harbinger of the Leonard Kleinrock of MIT published the first paper kind of people-to-people communication activity we on theory in July 1961 [5]. Klein- see on the World-Wide Web today. rock convinced Roberts of the theoretical feasibility of communications using packets rather than circuits—a Initial Internetting Concepts major step toward computer networking. The other The original ARPANET grew into the Internet based key step was to make the computers talk to each other. on the idea that there would be multiple independent Exploring this idea in 1965 while working with networks of rather arbitrary design. Beginning with Thomas Merrill, Roberts connected the TX-2 com- the ARPANET as the pioneering packet-switching puter in Massachusetts to the Q-32 in California network, it soon grew to include packet satellite net- through a low-speed dial-up telephone line [8], creat- works, ground-based packet radio networks, and other ing the first-ever (though small) wide-area computer networks. Today’s Internet embodies a key underlying network. The result of this experiment: confirmation technical idea: open-architecture networking. In this that time-sharing computers could work well approach, the choice of any individual network tech- together, running programs and retrieving data as nec- nology is not dictated by a particular network archi- essary on remote machines, but that the circuit- tecture but can be selected freely by a provider and switched telephone system was totally inadequate for made to interwork with the other networks through a the job. Thus confirmed was Kleinrock’s conviction of meta-level “ architecture.” Each net- the need for packet switching. work can be designed to fit a specific environment and In late 1966, Roberts went to DARPA to develop user requirements. the concept and quickly put The idea of open-architecture networking—intro- together a plan for the ARPANET, publishing it in duced by Kahn in late 1972 shortly after arriving at 1967 [7]. Bolt, Beranek and Newman Corp. (BBN), DARPA—was guided by four critical ground rules: under ’s leadership, developed the ARPANET switches (called IMPs), with Robert Kahn responsible for overall system design. Howard Frank The Internet was conceived and his team at Network Analysis Corp. worked with Roberts to optimize the and eco- in the era of time-sharing, nomics. Due to Kleinrock’s early development of packet switching theory and his focus on analysis, but has survived into the era of design, and measurement, his Network Measurement Center at UCLA was selected as the first on the personal computers, client/server ARPANET. All this came together September 1969 when BBN installed the first switch at UCLA and the and peer-to-peer computing, first host computer was connected. In December 1970, the Network Working Group (NWG) under Steve and the network computer. Crocker finished the initial ARPANET host-to-host protocol, called the Network Control Protocol (NCP). As the ARPANET sites completed implementing • Each distinct network had to stand on its own, and NCP during 1971–1972, network users finally could no internal changes could be required of any such begin to develop applications. network before being connected to the Internet. In October 1972, a large, successful demonstration • Communications would be on a best-effort basis. If of the ARPANET took place—the first public demon- a packet didn’t make it to the final destination, it would quickly be retransmitted from the source. 3The Advanced Research Projects Agency (ARPA) changed its name to Defense • Black boxes (later called gateways and routers) Advanced Research Projects Agency (DARPA) in 1971, back to ARPA in 1993, and back to DARPA in 1996. We refer throughout to DARPA, the current name. would be used to connect the networks. No infor-

COMMUNICATIONS OF THE ACM February 1997/Vol. 40, No. 2 103 mation would be retained by the gateways about forwarding of individual packets and the separate TCP individual flows of packets passing through them, concerned with such service features as flow control keeping them simple and avoiding complicated and recovery from lost packets. For applications that adaptation and recovery from various failure modes. did not want the services of TCP, an alternative called • There would be no global control at the operations the User Protocol (UDP) was added to pro- level. vide direct access to the basic IP service. In addition to email, , and remote login, Kahn first began work on a communications-ori- other applications were proposed in the early days of the ented set of operating system principles while at BBN Internet, including packet-based voice communication [4]. After joining DARPA and initiating the Internet (the precursor of Internet ), various models of program, he asked Vinton Cerf (then at Stanford Uni- file and disk sharing, and early “worm” programs illus- versity) to work with him on the detailed design of the trating the concept of agents (and viruses). The . Cerf had been deeply involved in the original was not designed for just one application but as a gen- NCP design and development and was already knowl- eral infrastructure on which new applications could be edgeable about interfacing to existing operating sys- conceived, exemplified later by the emergence of the tems. So, armed with Kahn’s architectural approach to Web. The general-purpose nature of the service pro- communications and with Cerf’s NCP experience, vided by TCP and IP makes this possible. these two teamed up to spell out the details of what became the Transmission Control Protocol/Internet Proving the Ideas DARPA funded three efforts to implement TCP: Stan- ford (Cerf), BBN (Tomlinson), and University College The most pressing question for the London (Peter Kirstein). The Stanford team produced a detailed specification, yielding within about a year three future of the Internet is not how independent interoperable implementations of TCP. This was the beginning of long-term experimenta- the technology will change, but tion and development of Internet concepts and tech- nology—along with the constituent networking how the process of change and technologies [3]. Each expansion has involved new challenges. For example, the early implementations of evolution itself will be managed. TCP were done for large time-sharing systems. When desktop computers first appeared, it was thought by Protocol (TCP/IP). some that TCP was too big and complex to run on a The original Cerf/Kahn paper [1] on the Internet personal computer. But David Clark and his research described a protocol, called TCP, providing all the group at MIT produced an implementation first for Internet’s transport and forwarding services. Kahn had the Alto (the early personal workstation devel- intended that TCP would support a range of transport oped at Xerox PARC) and then for the IBM PC, show- services—from the totally reliable sequenced delivery ing that workstations, as well as large time-sharing of data ( model) to a datagram service in systems, could be part of the Internet. which the application made direct use of the underly- Widespread development of local-area networks ing network service, a process that could imply occa- (LANs), PCs, and workstations in the 1980s allowed sional lost, corrupted, or reordered packets. the nascent Internet to flourish. technology However, the initial effort to implement TCP (developed by Bob Metcalfe at Xerox PARC in 1973) resulted in a version allowing only virtual circuits. is now probably the dominant network technology in This model worked fine for file transfer and remote the Internet and PCs and workstations the dominant login applications, but some of the early work on computers. The increasing scale of the Internet also advanced network applications, particularly packet resulted in several new approaches. For example, the voice in the 1970s, made clear that in some cases was invented (by Paul Mock- packet losses should not be corrected by TCP but left apetris, then at USC’s Information Sciences Institute) to the application to deal with. This insight led to a to provide a scalable mechanism for resolving hierar- reorganization of the original TCP into two proto- chical host names (e.g., www.acm.org) into Internet cols—the simple IP providing only for addressing and addresses. The requirement for scalable

104 February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM approaches led to a hierarchical model of routing, with 1970s computer networks began springing up wher- an Interior Gateway Protocol (IGP) used inside each ever funding was found for the purpose, including the region of the Internet and an Exterior Gateway Proto- Department of Energy’s MFENET and HEPNET, col (EGP) used to tie the regions together. New NASA’s SPAN, the community’s approaches for address aggregation, particularly class- CSNET, the academic community’s BITNET, and less interdomain routing (CIDR), were recently intro- based on Unix UUCP protocols. Commer- duced to control the size of tables. cial networking technologies were being pursued as Another major challenge was how to propagate the well, including IBM’s SNA, Xerox’s XNS, and Digital changes to the software, particularly host software. Equipment Corp.’s DECNET. DARPA supported the University of California at It remained for the British JANET (1984) and U.S. Berkeley to investigate modifications to the Unix oper- NSFNET (1985) programs to explicitly announce their ating system, including incorporating TCP/IP devel- intent to serve the entire higher community, oped at BBN. Although Berkeley later rewrote the regardless of discipline. In 1985, Dennis Jennings came BBN code to more efficiently fit into the Unix system from Ireland for a year to lead the National Science and kernel, incorporation of TCP/IP into the Unix Foundation’s NSFNET program. He helped NSF make BSD system proved a critical element in dispersing the a critical decision—that TCP/IP would be mandatory protocols to the research community. Much of the for NSFNET. And when took over the computer science community began using Unix BSD NSFNET program in 1986, he recognized the need for in their day-to-day computing environments. Looking a wide-area networking infrastructure to support the back, the strategy of incorporating Internet protocols general academic and research community, as well as into a supported operating system for the research the need to develop a strategy for establishing such community was a key element in the Internet’s suc- infrastructure to ultimately be independent of direct cessful widespread adoption. federal funding. TCP/IP was adopted as a defense standard in 1980, Policies and strategies were adopted to achieve that enabling the defense community to begin sharing the end. So while federal agencies shared the cost of common DARPA Internet technology base and leading directly infrastructure, such as trans-oceanic circuits, NSF to the partitioning of the military and non-military encouraged regional networks of the NSFNET to seek communities. By 1983, ARPANET was being used by commercial, non-academic customers. And NSF a significant number of defense R&D and operational enforced an acceptable-use policy, prohibiting Backbone organizations. The transition of ARPANET from NCP use for purposes “not in support of research and educa- to TCP/IP in 1983 permitted it to be split into a MIL- tion.” The predictable (and intended) result of encour- NET supporting operational requirements and an aging commercial network traffic at the local and ARPANET supporting research needs. regional levels, while denying its access to national-scale Thus, by 1985, the Internet was established as a transport, was the emergence and growth of “private,” technology supporting a broad community of competitive, long-haul networks, such as PSI, UUNET, researchers and developers and was beginning to be ANS CO+RE, and (later) others. used by other communities for daily computer com- NSF’s privatization policy culminated in April munications. Email was being used broadly across sev- 1995 with the defunding of the NSFNET Backbone. eral communities, often with different systems, The funds thereby recovered were (competitively) demonstrating the utility of broad-based electronic redistributed to regional networks to buy national- communications between people. scale Internet connectivity from the now numerous, private, long-haul networks. The Backbone had made Transition to Widespread Infrastructure the transition from a network built from routers out of At the same time Internet technology was being exper- the research community (David Mills’s “Fuzzball” imentally validated and widely used by a subset of routers) to commercial equipment. In its eight-and-a- computer science researchers, other networks and net- half-year lifespan, the Backbone had grown from six working technologies were being pursued. The useful- nodes with 56Kbps links to 21 nodes with multiple ness of computer networking—especially 45Mbps. It also saw the Internet grow to more than email—demonstrated by DARPA and Department of 50,000 networks on all seven continents and outer Defense contractors on the ARPANET was not lost on space (with 29,000 networks in the U.S.). other communities and disciplines, so that by the mid- Such was the weight of the NSFNET program’s

COMMUNICATIONS OF THE ACM February 1997/Vol. 40, No. 2 105 ecumenism and funding ($200 million, 1986–1995) infrastructure forward. Community spirit has a long and the quality of the protocols themselves that by history, beginning with the early ARPANET, whose 1990 when the ARPANET itself was finally decom- early researchers worked as a close-knit community missioned, TCP/IP had supplanted or marginalized (the ARPANET Working Group) to accomplish the most other wide-area computer network protocols initial demonstrations of packet switching technology. worldwide, and IP was on its way to becoming Likewise, the packet satellite, packet radio, and other the bearer service for the Global Information DARPA computer science research programs were Infrastructure. multi-contractor collaborative activities that used any available mechanisms to coordinate their efforts, start- Documentation’s Key Role ing with email, and adding , remote access, A key to the rapid growth of the Internet has been free and eventually Web capabilities. and open access to the basic documents, especially the In the late 1970s, recognizing that the growth of specifications of the protocols. The beginnings of the the Internet was accompanied by the growth of the ARPANET and the Internet in the university research interested research community and therefore an community promoted the academic tradition of open increased need for coordination mechanisms, Cerf, publication of ideas and results. However, the normal then manager of the DARPA Internet program, cycle of traditional academic publication was too for- formed several coordination bodies, including the mal and too slow for the dynamic exchange of ideas Internet Configuration Control Board (ICCB), chaired essential to creating networks. In 1969, a key step was by Clark. The ICCB was an invitation-only body taken by S. Crocker (then at UCLA) in establishing the assisting Cerf in managing the burgeoning Internet (or RFC) series of notes activity. [2].These memos were intended to be an informal fast In 1983, when Barry Leiner took over management means of distribution for sharing ideas among network of the Internet program at DARPA, he and Clark rec- researchers. At first the RFCs were printed on paper ognized that the continuing growth of the Internet and distributed via postal mail. As the File Transfer community demanded a restructuring of the coordina- Protocol (FTP) came into use, the RFCs were prepared tion mechanisms. as online files and accessed via FTP. Now, the RFCs are The ICCB was disbanded and replaced by a struc- easily accessed via the Web at dozens of sites around ture of Task Forces, each focused on a particular area of the world. SRI, in its role as Network Information the technology (e.g., routers and end-to-end proto- Center, maintained the online directories. Jon Postel cols). The Internet Activities Board (IAB) included the acted as RFC editor and as manager of centralized chairs of the Task Forces. administration of required protocol number assign- After some changing membership on the IAB, Phill ments—roles he continues to this day. Gross became chair of a revitalized Internet Engineer- The effect of the RFCs was to create a positive feed- ing Task Force (IETF)—at the time only one of the back loop, so ideas or proposals presented in one RFC IAB Task Forces. The growth of the Internet in the would trigger other RFCs. When consensus (or a least mid-1980s resulted in vastly increased attendance at a consistent set of ideas) would come together, a spec- IETF meetings, and Gross had to create substructure ification document would be prepared; such specifica- to the IETF in the form of working groups. tions would then be used as the basis for The expanded community also meant that DARPA implementations by the various research teams. The was no longer the only major player when it came to RFCs are now viewed as the “documents of record” in funding the Internet. In addition to NSFNET and the the Internet engineering and standards community various U.S. and international government-funded and will continue to be critical to future net evolution activities, interest in the commercial sector was begin- while furthering the net’s initial role of sharing infor- ning to grow. And in 1985, when both Kahn and mation about its own design and operations. Leiner left DARPA, there was a significant decrease in DARPA's Internet activity. The IAB was left without Formation of a Broad Community a primary sponsor and so increasingly assumed the The Internet is as much a collection of communities as mantle of leadership. a collection of technologies, and its success is largely Continued growth resulted in even further sub- attributable to satisfying basic community needs as structure within both the IAB and IETF, while growth well as utilizing the community effectively to push the in the commercial sector brought increased concern

106 February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM “In the future, computers will shop for us. You will log into a virtual supermarket and order food, they will send it to you the next day. School will change too. You could have school at home and your homework in, but you won’t make any friends that way. We will have to make friends on the Internet. Libraries will still be there, but not many people will visit them anymore and they will be knocked down. —Nicholas Phibbs, age 12 ” Surrey, UK regarding the standards process. The twin motivations technology. In the early 1980s, dozens of vendors were of making the process open and fair and the need to incorporating TCP/IP into their products because they win Internet community support eventually led in saw buyers for that approach to networking. Unfortu- 1991 to formation of the , under the nately, they lacked real information about how the auspices of Kahn’s Corporation for National Research technology was supposed to work and how their cus- Initiatives (CNRI) and the leadership of Cerf, who was tomers planned to use the approach. then with CNRI. In 1985, recognizing the lack of available informa- In 1992, yet another reorganization took place. The tion and appropriate training, Daniel Lynch in cooper- IAB was reorganized and renamed the Internet Archi- ation with the IAB arranged a three-day workshop for tecture Board. A more peer-like relationship was all vendors to learn how TCP/IP worked and what it defined between the new IAB and Internet Engineer- still could not do well. Speakers were mostly from the ing Steering Group (IESG), with the IETF and IESG DARPA research community where they had devel- taking greater responsibility for approving standards. oped these protocols and used them in day-to-day Ultimately, a and mutually supportive work. Approximately 250 vendor representatives heard relationship was formed among the IAB, IETF, and the 50 inventors and experimenters. Internet Society. The first Interop trade show, September 1988, The Web’s recent development and widespread demonstrated interoperability between vendor prod- deployment brings a new community, as many of the ucts and was attended by 50 companies and 5,000 people now working on the Web didn’t view them- engineers from potential customer organizations. selves primarily as network researchers and developers. Interop has grown immensely since then, and today is Therefore, in 1995, a new coordination organization an annual event in seven locations around the world for was formed—the World-Wide Web Consortium an audience of more than 250,000 who want to learn (W3C), initially led from MIT’s Laboratory for Com- which products seamlessly work with which other puter Science by Al Vezza and Tim Berners-Lee, the products and about the latest technology. Web’s inventor. Today, the W3C is responsible for In the last few years, we have seen a new phase of evolving the various protocols and standards associated commercialization. Originally, commercial efforts with the Web. mainly comprised vendors providing the basic net- working products and service providers offering Commercialization connectivity and basic Internet services. The Inter- Commercialization of the Internet has involved not net has now become almost a “commodity” service, only development of competitive, private network ser- and much of the latest attention has been on the use vices, but commercial products implementing Internet of this global information infrastructure as support

COMMUNICATIONS OF THE ACM February 1997/Vol. 40, No. 2 107 for other commercial services. managed. Internet architecture has always been driven This activity has been accelerated by the widespread by a core group of designers, but the form of that group and rapid adoption of browsers and Web technology, has changed as the number of interested outside parties giving users easy access to information linked around has grown. With the success of the Internet has come a the globe. Products are available for finding, sending, proliferation of stakeholders—now with an economic as and retrieving that information, and many of the latest well as an intellectual investment in the network. We developments seek to provide increasingly sophisti- see, for example, in the debates over control of the cated information services on top of basic Internet data domain and the form of the next-generation communications. IP addresses a struggle to find the next social structure to guide the Internet. However, that structure is more History of the Future difficult to define, given the large number of stake- The Internet was conceived in the era of time-sharing, holders. The industry also struggles to find the eco- but has survived into the era of personal computers, nomic rationale for the huge investment needed for client/server and peer-to-peer computing, and the net- future growth to, for example, upgrade residential work computer. It was designed before LANs existed, access to more suitable technology. If the Internet but has evolved to accommodate LANs as well as more stumbles, it will not be because we lack technology, recent ATM and -switched services. It was envi- vision, or motivation but because we cannot set a direc- sioned as supporting a range of functions—from file tion and march collectively into the future. C sharing and remote login to resource sharing and col- laboration, and has spawned email and more recently References the Web. But most important, it started as the cre- 1. Cerf, V.G., and Kahn, R.E. A protocol for packet network . IEEE Trans. Comm. Tech 5 (May 1974), 627–641. ation of a small band of dedicated researchers and has 2. Crocker, S. Host software. RFC 001. Apr. 7, 1969. grown to be a commercial success with billions of dol- 3. Kahn, R. guest ed., Uncapher, K., van Trees, H., assoc. guest eds. Special Issue on Packet Communication Networks. Proceedings of the IEEE 66, 11 lars invested annually. (Nov. 1978). One should not conclude that the Internet is com- 4. Kahn., R. Communications Principles for Operating Systems. Internal plete. The Internet is a creature of the computer, not BBN memorandum, Jan. 1972. 5. Kleinrock, L. Information Flow in Large Communication Nets. RLE the traditional networks of the telephone or Quarterly Progress Report, July 1961. industries. It will—indeed it must—continue chang- 6. Licklider, J.C.R., and Clark, W. On-Line Man-Computer Communica- tion. Aug. 1962. ing at the speed of the computer industry to remain rel- 7. Roberts, L. Multiple Computer Networks and Intercomputer Communi- evant. It is now changing to provide such new services cation. In Proceedings of the ACM Gatlinburg Conference (Oct. 1967). as real-time transport, supporting, for example, audio 8. Roberts, L., and Merrill, T. Toward a Cooperative Network of Time- and streams. The availability of pervasive net- Shared Computers. In Proceedings of the Fall AFIPS Conference (Oct. 1966). working—that is, the Internet itself—along with pow- erful affordable computing and communications in Barry M. Leiner ([email protected]) is Vice President of portable form (e.g., laptop computers, two-way , Microelectronics and Computer Technology Corp. Vinton G. Cerf ([email protected]) is Senior Vice President, PDAs, cellular phones) makes possible a new paradigm Internet Architecture and Engineering, at MCI Communications of nomadic computing and communications. Corp. This evolution will bring us new applications— David D. Clark ([email protected]) is a senior research scientist Internet telephone and, further out, Internet televi- at the MIT Laboratory for Computer Science. Robert E. Kahn ([email protected]) is President of the sion. It will also permit more sophisticated forms of Corporation for National Research Initiatives. pricing and cost recovery, a perhaps painful require- Leonard Kleinrock ([email protected]) is a professor of computer ment in this commercial world. It is changing to science at the University of California, Los Angeles. Daniel C. Lynch ([email protected]) is Chairman of accommodate yet another generation of underlying CyberCash Inc. and founder of the Interop networking trade show network technologies with different characteristics and and conferences. requirements—from broadband residential access to Jon Postel ([email protected]) is the Director of the Computer satellites. New modes of access and new forms of ser- Networks Division of the Information Sciences Institute of the vice will spawn new applications that in turn will University of Southern California. Lawrence G. Roberts ([email protected]) is the President drive further evolution of the net itself. of ATM Systems Division of Connectware Inc. The most pressing question for the future of the Stephen S. Wolff ([email protected]) is with , Internet is not how the technology will change, but Inc. how the process of change and evolution itself will be Copyright held by the authors

108 February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM