2ème OCR BBN

Report No. 4799 Soit Bolt Beranek and Newman Inc.

1. EXECUTIVE SUMMARY

In fiscal year 1969 a DARPA program entitled "Resource Sharing Computer Networks" was initiated. The research carried out under this program has since become internationally famous as the ARPANET.

This DARPA program has created no less than a revolution in computer technology and has been one of the most successful projects ever undertaken by DARPA. The program has initiated extensive changes in the Defense Department's use of computers as well as in the use of computers by the entire public and private sectors, both in the United States and around the world. Just as the telephone, the telegraph, and the printing press had far-reaching effects on human intercommunication, the widespread utilization of computer networks which has been catalyzed by the ARPANET project represents a similarly far-reaching change in the use of computers by mankind. The full impact of the technical changes set in motion by this project may not be understood for many years.

In 1975 the ARPANET was successfully transferred to the Défense Communications Agency which has operated it since that time.

CHAPTER II: THE ARPANET PROJECT - OBJECTIVES AND RESULTS

1. PROGRAM OBJECTIVE AND TECHNICAL NEED

1.1 Defense Program Addressed

The DARPA program had the following objectives:

(1) To develop techniques and obtain experience on interconnecting computers in such a way that a very broad class of interactions are possible, and

(2) To improve and increase computer research productivity through resource sharing. It was envisioned that by establishing a network tying computer research centers together, both goals would be achieved.

In fact, the most efficient way to develop the techniques needed for an effective network was thought to be by involving the research talent at these centers in prototype activity. Just as time-shared computer Systems permitted groups of hundreds of individual users to share hardware and software resources with one another, it was thought that networks connecting dozens of such Systems would permit resource sharing between thousands of users. Each System, by virtue of being time-shared, could offer any of its services to another computer System on demand. The most important criterion / for the type of network interconnection desired was that any user or program on any of the networked computers be able to utilize any program or subsystem available on any other computer without having to modify the remote program.

This objective was an entirely new and different approach to an extremely serious problem which existed throughout both the Défense Department and society at large. The many hundreds of computer centers in the Défense Department and the many other thousands of computer centers in the private and public sectors operate almost completely autonomously. Each computer center is forced to recreate ail the software and data files that it wishes to utilize. In many cases this involves the complete reprograming of software or reformatting of data files.. This duplication and redundant effort is extremely costly and time consuming.

In fiscal year 1969 DARPA estimated that such duplicative efforts more than double the national costs of creating and maintaining the software. There had been, other completely different attempts to address this problem, such as attempts at language standards for computers, attempts at standardizing the types of hardware, and attempts at automatic translation between computer languages. Although each such approach had some value and utility, the problems of trying to share computer software resources or files was truly enormous.

In addition to the general problem shared with the rest of the scientific community, the Défense Departmer.t also faces certain special problems having to do with training. Military personnel trained to use one manufacturer's equipment must often be trained 'again to use another's. Machines procured from different manufacturers require as many different user training programs as there are machines, thus inhibiting positive transfer of training that could accumulate through the rotation of military personnel. Those data files and programs which have common utility to many military organizations and installations must be stored, created and maintained separately at each different machine. Military Systems interconnected in a distributed interactive network obviate such constraints.

Another objective of the program was to permit the linking of specialized computers to the many general-purpose computer centers. It was thought that with the then recent improvements in the hardware area, it would become most cost effective to design and construct computers efficient at specialized tasks (e.g., compiling, list processing and information retrieval).

Making such machines available to ail the computer research establishments would significantly increase the capability at these other centers.

This program was addressed to no less than changing the use of computers by the entire Defense Department. It was clearly intended that the use of such a computer network would permit resource sharing within and across the military services and throughout the Defense research community.

1.2 State of the Art at Program Inception

By the date of the program plan in the late 1960s most of the specific technologies required for a computer network had individually been achieved in some form. For example, there had been many connections of phone lines to computers (e.g., the SAGE System, Air Line reservations systems, and time-sharing Systems).

However, there had been only a very small number of attempts to connect computers together for the purpose of experimenting with the sharing of resources. : In the early 1960s an attempt was made to link computers together at the Western Data Processing Center at UCLA for the purpose of enabling similar computers to perform load sharing. A similar experiment was also performed at Bell Laboratories and achieved reasonable success for several years.

A number of networks were constructed for the primary purpose of message handling, including a Westinghouse inventory control System and several airline reservations networks. The SITA network for airline reservations was surprisingly advanced in concept in the mid-1960s, but details about SITA were generally not known in the U.S. Computing community. In any case, the techniques used for such message Systems were special purpose in nature and were not readily transferable into the general area of inter-computer communications.

A direct progenitor of the ARPANET was an effort made in the mid-1960s to achieve a coupling between academic Computing expertise and the operation of the SDC Q32 computer. This effort led to a phone line connection between the Q32 at SDC and the TX2 at Lincoln Laboratory, and demonstrated the relative ease of modifying time sharing Systems to permit network interactions .

Aside from the technical problems of interconnecting computers with communication circuits, the notion of computer networks had been considered in a number of places from a theoretical point of view. Of particular note was work done by Paul Baran and others at the Rand Corporation in a study "On Distributed Communications" in the early i960"s. Also of note was work done by Donald Davies and others at the National Physical Laboratory in England in the mid-1960's.

In turn, at the time of the initiation of the ARPANET program in fiscal year 1969 many of the requisite ideas had been considered and many of the requisite technical bits and pièces a had been attempted in some form, but no significant attempt had ever been made to put them together into a resource sharing computer network.

1.3 Specific Technological Problems Addressed

The technological problems of building the ARPANET can be considered at many different levels of detail. At the top level, there were really two problems:

1. To construct a "subnetwork" consisting of telephone circuits and switching nodes whose reliability, delay characteristics, capacity, and cost would facilitate resource sharing among the computers on the network.

2. To understand, design, and implement the protocols and procedures within the operating Systems of each connected computer, in order to allow the use of the new subnetwork by those computers in sharing resources.

Within these two major technological problems, there were, of course, a large number of sub-problems; including the engineering of the phone circuit connections, the topology of the network, the selection of switching node equipment, the design of line disciplines to work through phone line errors, the routing problem, and many others.

1.4 Expected Payoff/Time-Frame/Costs

The goals for the ARPANET project were very broad and envisaged a significant eventual impact on the use of computers in both the public and private sectors. However, in addition to these long-range goals, DARPA visualized some quite specific initial payoff in the form of improved productivity of the DARPA research program itself, and a resulting cost/performance benefit to the services from DARPA research. In fiscal year 1969, a number of computer research centers throughout the country were supported in whole or in part by DARPA's Information Processing Techniques Office (IPTO). The installation of an effective network tying these locations together would substantially reduce duplication and improve the transfer of scientific results, as well as develop the network techniques needed by the military.

The research output of these projects was important to ail three Services and it was expected that this output could be substantially increased for the same dollar cost if a portion of the funds were utilized for the network.

In addition, initial payoff was anticipated in the form of technology transfer from the ARPANET project in three ways :

• By dissemination of new scientific knowledge through conferences and the appropriate literature.

• By transfer of management of the ARPANET to a common carrier, and the resulting availability of ARPANET services to other groups (such as Office of Education Regional Laboratories, NSF-supported universities, and various user groups supported by the NIH) .

• By adoption of the network technology by specific military groups (such as the National Military Command System Support Center . and other military centers affiliated to them e.g., CINCPAC, CINCEUR, and HACV).