Figure 1.9-1: The first Internet Message Processor (IMP), with L. Kleinrock
Sections 1.1-1.8 presented an overview of technology of computer
networking and the Internet. You should know enough now to impress your
family and friends. However, if you really want to be a big hit at the
next cocktail party, you should sprinkle your discourse with tidbits about
the fascinating history of the Internet.
1961-1972: Development and Demonstration of Early Packet Switching Principles
The field of computer networking and today's Internet trace their beginnings back to the early 1960s, a time at which the telephone network was the world's dominant communication network. Recall from section 1.3, that the telephone network uses circuit switching to transmit information from a sender to receiver -- an appropriate choice given that voice is transmitted at a constant rate between sender and receiver. Given the increasing importance (and great expense) of computers in the early 1960's and the advent of timeshared computers, it was perhaps natural (at least with perfect hindsight!) to consider the question of how to hook computers together so that they could be shared among geographically distributed users. The traffic generated by such users was likely to be "bursty" -- intervals of activity, e.g., the sending of a command to a remote computer, followed by periods of inactivity, while waiting for a reply or while contemplating the received response.
Three research groups around the world, all unaware of the others' work [Leiner 98], began inventing the notion of packet switching as an efficient and robust alternative to circuit switching. The first published work on packet-switching techniques was the work by Leonard Kleinrock [Kleinrock 1961, Kleinrock 1964], at that time a graduate student at MIT. Using queuing theory, Kleinrock's work elegantly demonstrated the effectiveness of the packet-switching approach for bursty traffic sources. At the same time, Paul Baran at the Rand Institute had begun investigating the use of packet switching for secure voice over military networks [Baran 1964], while at the National Physical Laboratory in England, Donald Davies and Roger Scantlebury were also developing their ideas on packet switching.
The work at MIT, Rand, and NPL laid the foundations for today's Internet. But the Internet also has a long history of a "Let's build it and demonstrate it" attitude that also dates back to the early 1960's. J.C.R. Licklider [DEC 1990] and Lawrence Roberts, both colleagues of Kleinrock's at MIT, both went on to lead the computer science program at the Advanced Projects Research Agency (ARPA) in the United States. Roberts [Roberts 67] published an overall plan for the so-called ARPAnet [Roberts 1967], the first packet-switched computer network and a direct ancestor of today's public Internet. The early packet switches were known as Interface Message Processors (IMP's) and the contract to build these switches was awarded to BBN. On Labor Day in 1969, the first IMP was installed at UCLA, with three additional IMP being installed shortly thereafter at the Stanford Research Institute, UC Santa Barbara, and the University of Utah. The fledgling precursor to the Internet was four nodes large by the end of 1969. Kleinrock recalls the very first use of the network to perform a remote login from UCLA to SRI crashing the system [Kleinrock 1998].
By 1972, ARPAnet had grown to approximately 15 nodes, and was given its first public demonstration by Robert Kahn at the 1972 International Conference on Computer Communications. The first host-to-host protocol between ARPAnet end systems known as the Network Control Protocol (NCP) was completed [RFC 001]. With an end-to-end protocol available, applications could now be written. The first e-mail program was written by Ray Tomlinson at BBN in 1972.
Once again, with perfect hindsight one might now see that the time was ripe for developing an encompassing architecture for connecting networks together. Pioneering work on interconnecting networks (once again under the sponsorship of DARPA), in essence creating a network of networks, was done by Vinton Cerf and Robert Kahn [Cerf 1974]; the term "internetting" was coined to describe this work. The architectural principles that Kahn' articulated for creating a so-called "open network architecture" are the foundation on which today's Internet is built [Leiner 98]:
These architectural principles were embodied in the TCP protocol. The early versions of TCP, however, were quite different from today's TCP. The early versions of TCP combined a reliable in-sequence delivery of data via end system retransmission (still part of today's TCP) with forwarding functions (which today are performed by IP). Early experimentation with TCP, combined with the recognition of the importance of an unreliable, non-flow-controlled end-end transport service for application such as packetized voice, led to the separation of IP out of TCP and the development of the UDP protocol. The three key Internet protocols that we see today -- TCP, UDP and IP -- were conceptually in place by the end of the 1970's.
In addition to the DARPA Internet-related research, many other important networking activities were underway. In Hawaii, Norman Abramson was developing ALOHAnet, a packet-based radio network that allowed multiple remote sites on the Hawaiian islands to communicate with each other. The ALOHA protocol [Abramson 1970] was the first so-called multiple access protocol, allowing geographically distributed users to share a single broadcast communication medium (a radio frequency). Abramson's work on multiple access protocols was built upon by Robert Metcalfe in the development of the Ethernet protocol [Metcalfe 1976] for wire-based shared broadcast networks. Interestingly, Metcalfe's Ethernet protocol was motivated by the need to connect multiple PCs, printers, and shared disks together [Perkins 1994]. Twenty-five years ago, well before the PC revolution and the explosion of networks, Metcalfe and his colleagues were laying the foundation for today's PC LANs. Ethernet technology represented an important step for internetworking as well. Each Ethernet local area network was itself a network, and as the number of LANs proliferated, the need to internetwork these LANs together became all the more important. An excellent source for information on Ethernet is Spurgeon's Ethernet Web Site, which includes Metcalfe's drawing of his Ethernet concept, as shown below in Figure 1.9-2. We discuss Ethernet, Aloha, and other LAN technologies in detail in Chapter 5;
Figure 1.9-2: A 1976 drawing by R. Metcalfe of the Ethernet concept (from Charles Spurgeon's Ethernet Web Site)
In addition to the DARPA internetworking efforts and the Aloha/Ethernet multiple access networks, a number of companies were developing their own proprietary network architectures. Digital Equipment Corporation (Digital) released the first version of the DECnet in 1975, allowing two PDP-11 minicomputers to communicate with each other. DECnet has continued to evolve since then, with significant portions of the OSI protocol suite being based on ideas pioneered in DECnet. Other important players during the 1970's were Xerox (with the XNS architecture) and IBM (with the SNA architecture). Each of these early networking efforts would contribute to the knowledge base that would drive networking in the 80's and 90's.
It is also worth noting here that in the 1980's (and even before), researchers (see, e.g., [Fraser 1983, Turner 1986, Fraser 1993]) were also developing a "competitor" technology to the Internet architecture. These efforts have contributed to the development of the ATM (Asynchronous Transfer Mode) architecture, a connection-oriented approach based on the use of fixed size packets, known as cells. We will examine portions of the ATM architecture throughout this book.
Much of the growth in the early 1980's resulted from several distinct efforts to create computer networks linking universities together. BITnet (Because It's There NETwork) provided email and file transfers among several universities in the Northeast. CSNET (Computer Science NETwork) was formed to link together university researchers without access to ARPAnet. In 1986, NSFNET was created to provide access to NSF-sponsored supercomputing centers. Starting with an initial backbone speed of 56Kbps, NSFNET's backbone would be running at 1.5 Mbps by the end of the decade, and would be serving as a primary backbone linking together regional networks.
In the ARPAnet community, many of the final pieces of today's Internet architecture were falling into place. January 1, 1983 saw the official deployment of TCP/IP as the new standard host protocol for Arpanet (replacing the NCP protocol). The transition [Postel 1981] from NCP to TCP/IP was a "flag day" type event -- all host were required to transfer over to TCP/IP as of that day. In the late 1980's, important extensions were made to TCP to implement host-based congestion control [Jacobson 1988]. The Domain Name System, used to map between a human-readable Internet name (e.g., gaia.cs.umass.edu) and its 32-bit IP address, was also developed [Mockapetris 1983, Mockapetris 1987].
Paralleling this development of the ARPAnet (which was for the most part a US effort), in the early 1980s the French launched the Minitel project, an ambitious plan to bring data networking into everyone's home. Sponsored by the French government, the Minitel system consisted of a public packet-switched network (based on the X.25 protocol suite, which uses virtual circuits), Minitel servers, and inexpensive terminals with built-in low speed modems. The Minitel became a huge success in 1984 when the French government gave away a free Minitel terminal to each French household that wanted one. Minitel sites included free sites -- such as a telephone directory site -- as well as private sites, which collected a usage-based fee from each user. At its peak in the mid 1990s, it offered more than 20,000 different services, ranging from home banking to specialized research databases. It was used by over 20% of France's population, generated more than $1 billion each year, and created 10,000 jobs. The Minitel was in a large fraction of French homes ten years before most Americans had ever heard of the Internet. It still enjoys widespread use in France, but is increasingly facing stiff competition from the Internet.
The main event of the 1990's however, was to be the release of the World Wide Web, which brought the Internet into the homes and businesses of millions and millions of people, worldwide. The Web also served as a platform for enabling and deploying hundreds of new applications, including on-line stock trading and banking, streamed multimedia services, and information retrieval services. For a brief history of the early days of the WWW, see [W3C 1995].
The WWW was invented at CERN by Tim Berners-Lee in 1989-1991 [Berners-Lee 1989], based on ideas originating in earlier work on hypertext from the 1940's by Bush [Bush 1945] and since the 1960's by Ted Nelson [Ziff-Davis 1998]. Berners-Lee and his associates developed initial versions of HTML, HTTP, a Web server and a browser -- the four key components of the WWW. The original CERN browsers only provided a line-mode interface. Around the end of 1992 there were about 200 Web servers in operation, this collection of servers being the tip of the iceberg for what was about to come. At about this time several researchers were developing Web browsers with GUI interfaces, including Marc Andreesen, who developed the popular GUI browser Mosaic for X. He released an alpha version of his browser in 1993, and in 1994 formed Mosaic Communications, which later became Netscape Communications Corporation. By 1995 university students were using Mosaic and Netscape browsers to surf the Web on a daily basis. At about this time the US government began to transfer the control of the Internet backbone to private carriers. Companies -- big and small -- began to operate Web servers and transact commerce over the Web. In 1996 Microsoft got into the Web business in a big way, and in the late 1990s it was sued for making its browser a central component of its operating system. In 1999 there were over two-million Web servers in operation. And all of this happened in less than ten years!
During the 1990's, networking research and development also made significant advances in the areas of high-speed routers and routing (see, e.g., Chapter 4) and local area networks (see, e.g., Chapter 5). The technical community struggled with the problems of defining and implementing an Internet service model for traffic requiring real-time constraints, such as continuous media applications (see, e.g., Chapter 6). The need to secure and manage Internet infrastructure (see. e.g., Chapter 7 and 8) also became of paramount importance as e-commerce applications proliferated and the Internet became a central component of the world's telecommunications infrastructure.
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Copyright Keith W. Ross and Jim Kurose 1996-2000