Attachment 41 RECOMMENDATION TO THE A!R STAFF DEVELOPMENT OF THE DISTRIBUTED ADAPTIVE MESSAGE-BLOCK NETWORK August 30, 1965 7 m n d I CAliroitHIA Attachments: 1. Rand recommendation. 2. Letter from the Air Force. 3. Chapter by Paul Baran from recent book on packet switching that discusses rationale for each feature of packet switching and how it came about. ' • 4. P-1995. 5. Calendar pages. 6. IEEE Spectrum Aug. 1964, p. 114. 7. List of RAND depository libraries. 52 L- 17930 R-pnD 30 August 19 65 Deputy Chief of Staff, Research and Development Headquarters, United States Air Force ' • Washington, D. C. 20330 SUBJECT: DEVELOPMENT OF THE DISTRIBUTED ADAPTIVE MESSAGE-BLOCK NETWORK SUMMARY We have reached an appropriate point in our work on "distributed networks" to recommend to the Air Force a specific direction of development. I wrote to you on this subject on August 24, 1964 (L-17082) and General Curtin forwarded a request on December 23, 1964 for evaluation of the eleven RAND Memoranda by AFSC (and RTD, ESD, Lincoln), AFLC, (and GEEIA), and ARCS. Detailed comments were received and forwarded to RAND. A series of briefings and discussions ensued. Some technical difficulties were revealed, but these appear to be correctable v. ,th minor changes in the proposed system. A RAND Memorandum describing theae adjustments is in preparation. In our view it is possible to build a new large common-user communication network able to withstand heavy damage. Such a network can provide a major step forward in Air Force military communication capability. Although there can be no certainty of success because of the complex nature of the required development, the high potential pay-off leads us to recommend that the research and development portions of the following program be undertaken now. We can now purchase an option on lead time at minimum cost. If the research is successful, we will be in a position to move rapidly into implementation of the full network. Only after the preliminary engineering has been completed will there be sufficient information to determine precisely where and how much of such a network should be built. - 2 - 30 August 1965 Deputy Chief of Stuff, Research and Development Although the system is a marked departure from the existing communication system, we believe that after the R and D is proved out the new system can be integrated with the present one on an incremental basis. We v/ill be happy to help in any way as the program evolves_. A further discussion of the problem and the proposed solution is attached. Sincerely, ORIGINAL SIGNS? 3V F. K. COLLLOUM F. R. Collbohm Attachment: Limitations of Present Networks and the Improvements We Seek ATTACHMENT LIMITATIONS OF PRESENT NETWORKS AND THE IMPROVEME NTS WE SEEK *■ l. Most communication networks are highly vulnerable to overt and covert attack. A new, large, highly - Interconnected distributed network, shared amqiig : all military users would offer a major improvement ' in survivability. (See ODC I.) 2. Most military communication is transmitted with negligible protection against loss of critical infor¬ mation to an eavesdropper. Only a small portion of the total military communication load is crypto¬ graphically protected. The military is often highly constrained in subjects that It can discuss over the telephone for fear of eavesdropping. The universal availability of secure communications will be help¬ ful to those having need to transmit classified infor¬ mation. (See ODC IX.) 3. Today, those who connect computers to other comput¬ ers and to the remote entry devices used in command and control systems are not satisfied with the high error rate of a communication network which was not originally designed for digital transmission. Com¬ puters can be intolerant of errors caused by the com¬ munication links. The use of automatic error correc¬ tion features could help achieve the desired, almost error-free user-to-user performance—less than one error in 100 million transmitted bits. (See ODC VI through VIII.) 4. Partially because of high cost, military "hard copy (paper) traffic is primarily limited to center-to-center operation. This produces long delay times between end users. A system that will reduce the cost of digital transmission will help make hard copy facilities more widespread at the action officer level. (See ODC V and VIII.) *ODC is an abbreviation for “On Distributed Communications," the series of memoranda described in Appendix. Attachment - page two [.-17930. 8/30/bS 5. We lack complete flexibility of connection between users where secrecy is mandatory. We desire a system in which it will be possible to speak quickly to anyone, anywhere without prior arrangement for the communica¬ tions . (See ODC VIII and IX.) 6. Military communication volume is increasing rapidly, and greater efficiency would result from betternser-to- user communications . We want a system better able to handle larger volumes of traffic than commonly expe¬ rienced today. Better military effectiveness, could result if communications were not treated as a scarce resource that must be highly rationed. (See ODC V and VIII.) 7. Because of the difficulty in assigning costs to commu¬ nications in the military, it is difficult to determine exactly how much we are presently paying. Estimates range from one-half to three billion dollars annually, with this cost increasing about 15 percent annually. In the belief that markedly more military communication is indicated in the future, it becomes mandatory to lay the groundwork upon which to build future communica¬ tion networks that achieve the desired long range demand for.digital and voice communications at minimum cost. The maturity of digital technology allows us to think broadly and differently regarding communications . The concept of an all digital communications network (as opposed to the traditional analog communication net¬ works) allows the designer and user great freedom In survivability, flexibility, growth, secure communica¬ tions and in handling the expected exponential growth in the transmission of digital data. (See ODC X.). HOW THE PROPOSED NETWORK DIFFERS FROM PRESENT DAY NETWORKS The proposed network is described in detail in the OIX3 series of RAND Memoranda. Some of the key differences between it and the present concepts of building communication networks are: sf 1 . Use of digital techniques in lieu of analog circuits throughout the entire network , both in transmission and in switching. . ... !.- ! 7‘J30 , >(/3D/!.S I 2 • Cryptographic techniques designed as an Integral portion of the switching mechanism to provide secrecy for all . network users—whether transmitting classified traffic or nor. 3. The communication network designed as a "bit-transportation system , " rather than a "real-time 11 connection of j series of links. ~ ■ : — .... *■ 4. Integral automatic error detection and repeat (via a dif¬ ferent route) transmission to allow the use of low cost and unreliable links in the network. * 5 . Adaptive routing for high user reliability during peak load periods including enemy attacks. » 6. Provisions to allow each user to "carry his tele phone number" with him. — — -- ir * . hi SPECIFIC RECOMMENDATIONS We recommend that a research and development program be undertaken which can lead eventually to the construction and implementation of the Distributed Adaptive Message-Block Network described in the referenced RAND Memoranda C. We recommend that only the research and development phases be undertaken at this timeTJwith further implementation to follow the successful completion of the preliminary work phases . ,1 P 7 «i. i,-.k *• \ Because of the complex nature of the undertaking and the intricacy of the sub¬ systems, an unusual high level and continuity of technical expertise in digital technology is required In the development and its system management. We suggest that the research and development tasks be divided into separate con¬ tracts, each portion awarded to an organization particularly competent within its own field. This division by task imposes stringent technical competence on the system manager. To aid in this complex and technically difficult effort, we feel that a technical advisory panel should be constituted to review on-going study and development contracts and insure that necessary technical liaison and interaction among the various sub-contractors take place. I because much of the proposed system is based on digital computer techniques, organizations with demonstrated experience in the computer field will probably i-*i fr bring greater pertinent competence to bear in key aspects of the system develop - ( meat than organizations experienced only in traditional analog communication practices 4 • — 1 iiiin'iiiHnnTtfm' L'l'JOU, O/OU/DD DEVELOPy;ElJT COST AND RATE While no definite time-money expenditure rates are enumerated, the order of magnitude of the effort is described in Volume XI of the ODC series. Possibly five million dollars would be an appropriate amount for the initia¬ tion of this development effort. We are not presuming to outline the detailed sequence of actions that might be taken. We have, however, prepared such a list of specific tasks to be performed, in what we believe to be a logical form, and I wiB;be happy to submit it to you for your consideration and action if this would be helpful. The need for a survivable, high data-rate, flexible, user-to-user communi¬ cations is of overriding importance. We do not know of any comparable alternative system proposals to attain this capability and we believe that the Air Force should move swiftly to implement the research and develop¬ ment program proposed herein. The orderly development program outlined offers the promise of a marked increase in communication capability with minimum risk. If the military situation makes it necessary, the research and development program could be accelerated. For highest payoff per dollar risked It should be remem¬ bered that communication system development Is normally a ten year lead- time cycle process. Much better work In this field appears to result from a small number of people working on a project for a long period of time . than from a large massive crash effort attempting to generate a complete^ system within a short time, i It is hoped that the guidance of the suggested technical advisory panel will provide for flexibility and redirection of this program in the event unforeseen problems or new developments appear. APPENDIX ON DISTRIBUTED COMMUNICATIONS : List of Publications In the Series Introduction to Distributed Communications Networks, Paul Baran, Rivi -3420-PR . , Introduces the system concept and outlines the require-' ments for and design considerations of the distributed ’ digital data communications network. Considers espe¬ cially the use of redundancy as a means of withstanding , heavy enemy attacks.. A general understanding of the proposal may be obtained by reading this volume and Vol. XI. Digital Simulation of Hot-Potato Routing in a Broadband Distributed Communications Network, Sharia P. Boehm and Paul Baran, RM-3103-PR. Describes a computer simulation of the message routing scheme proposed. The basic routing doctrine permitted a network to suffer a large number of breaks, then recon¬ stitute itself by rapidly relearning to make best use of the surviving iinks. Determination o: Path-Lengths in a Distributed Network, J. W. Smith, RM-3578-PR. Continues model simulation reported in Vol. II. The pro¬ gram was rewritten in a more powerful computer language allowing examination of larger networks. Modification of the routing doctrine by intermittently reducing the input data rate of local traffic reduced to a low level the num¬ ber of message blocks taking excessively long paths. The level was so low that a deterministic equation was required in lieu of Monte Carlo to examine the now rare event of a long message block path. The results of both the simulation and the equation agreed in the area of over¬ lapping validity. 1W IV. Priority, Precedence, and Overload, Paul Baran, RM-3638-PR The creation of dynamic or flexible priority and prece¬ dence structures within a communication system handling a mixture of traffic with different data rate, urgency, and importance levels is discussed. The goal chosen is opti¬ mum utilization of the communications resource within a seriously degraded and overloaded network. V. History, Alternative Approaches, and Comparisons, Paul Baran, RM -3 09 7-PR. ;v . A background paper acknowledging the efforts of people in many fields working toward the development of large communications systems where system reliability and survivability are mandatory. A consideration of termi¬ nology is designed to acquaint the reader with the di¬ verse, sometimes conflicting, definitions used. The evolution of the distributed network is traced, and a number of earlier hardware proposals are outlined. VI. Mini-Cost Microwave, Paul Baran, RM-3752-PR. The technical feasibility of constructing an extremely low-cost, all-digital, X- or K^-band microwave relay system, operating at a multi-megabit per second data rate, is examined. The use of newly developed varactor multipliers permits the design of a miniature, all-solid- state microwave repeater powered by a thermo-electric converter burning L-P fuel. VII. Tentative Engineering Specifications and Preliminary Design for a High-Data-Rate Distributed Network Switching Node, Paul Baran, RM-3763-PR. High-speed, or "hot-potato, “ store-and forward mes¬ sage block relaying forms the heart of the proposed Information transmission system. The Switching Nodes are the units in which the complex processing takes place. The node is described in sufficient engineering detail to estimate the components required. Timing cal¬ culations, together with a projected implementation scheme, provide a strong foundation for the belief that the construction and use of the node is practical. ? VIII- The Multiplexing Station, Paul Baran, RiY-3764-PR. A description of the Multiplexing Stations which connect subscribers to the Switching Nodes. The presentation is in engineering detail, demonstrating how the network will simultaneously process traffic from up to 1024 sepa¬ rate users sending a mixture of start-stop teletypewriter, digital voice, and other synchronous signals at various rates. IX. Security, Secrecy, and Tamper-Free Considerations, Paul'Baran, RM -3765-PR Considers the security aspects of a system of the type proposed, in which secrecy is of paramount importance. Describes the safeguards to be built into the network, and evaluates the premise that the existence of "spies" within the supposedly secure system must be anticipated. Security provisions are baaed on the belief that protec¬ tion is best obtained by raising the "price" of espied information to a level which becomes excessive. The treatment of the subject is itself unclassified. X. Cost Estimate, Paul Baran, RM-3766-PR. A detailed cost estimate for the entire proposed system, based on an arbitrary network configuration of 400 Switching Nodes, servicing 100,000 simultaneous users via 200 Multiplexing Stations. Assuming a usable life of ten years, all costs, including operating costs, are estimated at about $60 - 100,000,000 per year. XI. Summary Overview, Paul Baran, RM-3767-PR. Summarizes the system proposal, highlighting the more important features. Considers the particular advantages of the distributed network, and comments on disadvantages. An outline is given of the manner in which future research aimed at an actual implementation of the network might be conducted. Together with the introductory volume, it pro¬ vides a general description of the entire system concept. I r k -n — w department of the air force H{AoaUA*ms UNITtO jtatu ah ;q»ci ' WA1HINOTQN, O.Ci •••. 11, OCT 1955 Attachment #2 * ■ Mr F • H. Collbohm The. RAND Corporation 1700 Main Street Santa Monica, California 90U06 'Dear Mr Collbohm: necomraend oW°n to the Air Staff - Development of the • + h S 1 Ut ? d Ad a P tiva Message-Block Network has been reviewed by * he Ai 3> 5 tTsrrr^ v Major James Singleton of my Command and Control Grou^/\AFRDQPC) has been designated as Project Monitor. are to direc ^velopment Plan Cor review to soli f to DDR&E. AFSC.to prepare a Preliminary Technical IDF). 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Q ; “ J. “■ , o P® «o 2 2o « ft. Q. a •* C (N ^ -o^o^yd- ^ .5 £ so* 5 a -- " S H I •? < a P g-u ^ o s g g = « u? S > f &• § — c J "i. §. O 5 °- £ s :> i e u T e “ M°c?uS E ^ 5 ^ v r* 3 E ^ 5 v r*.' 2 "IcS C3 f U C r o ec c ^ H -i 2 1- s » n , — ® 3 - oC cu 2 5 J. c. ^ jJ 5« O O p ■-. -Z 0. > u • c co ^ <r* r* o t .^CJ ,' l — r« o E 3 -:?! jj oa> £ 5 q ^ § 4 .2 = Ki. ^ v ^2’ TO ~-v O O rn lT* ^ O'” ■i R i £ 0 b K y 0 T3 . f - W S « S- 5 « B- ^ °! g.s.gl 8^<S — ^ o E c • . H . 5 5 -§ V) re g : 2 'E o; o - o - S’ E ■ 5 -o | o a p < • c t: , -J a u c. j cd z re — o TO , , ~ w kl § “ UJ E d iif 3 Attachment #4 Reproduced by The RAND Corporation • Santo Monica • California Corporation views expressed in this paper are not necessarily those of the P-1995 1 RELIABLE DIGITAL COMMUNICATIONS SYSTEMS UTILIZING UNRELIABLE NETWORK REPEATER NODES INTRODUCTION The cloud-of-doom att itude that nuclear war spells the end of the earth Is slowly lifting from the minds of the many. Better quantitative estimates of post-attack destruction to¬ gether with a less emotional discussion of the alternatives may mark the end of the "what the hell--what's the use ?" era. A new view emerges: the possibility of a war exists but there is much that c an be done to minimize the consequences. rt---- - -- ‘ “ *-----1 If war does not mean the end of the earth in a black and white manner, then it follows that we should do those things that make the shade of grey as light as possible: to plan now to minimize potential destruction and to do all those things necessary to permit the survivors of the holocaust to shuck their ashes and reconstruct the economy swiftly. PURPOSE This paper Is directed toward the communications system designer in the hope that he will not neglect, these problems of survival in the design of his future systems. Unfortunately, no panacea can be presented. P-19S5 2 There Is none. Only a single limited technique is described, that of using one form of distributed redundancy to minimize vulnerability. A detailed examination demonstrates that the problem is not an unscivabie one, but that much money and much wor'.-c are necessary to provide all- the elements needed for the true solution to the vulnerability problem. The timing for’suc h thinking is particularly app ro priate now, for we are Just beginning to design and lay out designs for the digital data transmission systems of the future. We are J-ust approaching the initi ation state of the designs of systems where computers speak to one another. When this day comes, the digital communications system capacity needed will be orders of magnitude greater than our chief present-day digital transmission technique; namely, teletype. For example, a cO WPM teletype channel would take about two weeks, operatin g 24 hours per day without breakdown, to transmit a single standard size reel of magnetic tape used on a digital computer. This may be compared to a writing time of about 6 minutes on the computer. Millimicrosecond clock rate data links will be needed in the future. Our present communications plant will not suffice. As ohere does not seem to be any fundamental technical problem thau prohibits the operation of digital communications links at the cl o ck rate of digital computers, the view is taken that it is only a matter of time before such design requirements be¬ come hardware. The systems designs of the next few years will ce uhe systerns-in-being of the next few decades. It is hoped P-1995 3 that these systems will be foresighted enough to Include an I nsurance policy purchasing Invulnerability. CONTENTS This first paper of this series describes a rationale for the use of redundancy in networks and the payoff fori varying degrees of such redundancy. The second paper, by Frank Yates and Paul 3aran, describes a nigh speed automatic switching technique for digital messages. In this paper the time of arrival of messages is used to determine the shortest.routing paths over a severely damaged network. The third paper, by Paul Baran and Robert Hameriy, describes a lower speed digital system using a tag containing the number of times a message has been relayed to provide a method for authenticating point of origin. These two separate systems exhibit different properties; it is possible to multiplex them together to utilize the ad¬ vantages of both and devise a third system. It Is thus possible to visualize a new set of systems based upon a distributed organization. Automatic route selection is not new, b ut t hese papers seek as a common goal synthesis of systems where the intelligence required t o swi tch signals to surviving limes is at the llnk_ nodes and not at one or a few centralized switching centers. This paper thus describes what we choose to call distributed organization as compared to the more familiar centralized switching center type organization. T I *mj LmJ LJ ieJ Attachment #6 . IEEE publications scanning the issues advance abstracts translated journals special publications Scanning the issues Distributed Communications. A great deal of thought has necessarily been given m recent years to the question of the survivability oT communications systems in the event of attack. Un¬ pleasant though such a prospect may be, the studies themselves have led to some interesting suggestions as to what form our future networks might take. Of particular interest is the distributed communication network concept in which each station is connected to all adjacent stations rather than to a few switching points, as in a centralized system. Although one can draw a wide variety of networks, they all factor into two components: centralized (or star) and distributed (or grid or mesh). (See 'pes (A) and (C), respectively in Fig. U The centralized network is obviously Pig. 1. (A) Centralized, (B) Decentralized, (C) Distribution networks. rig. 2. Definition of redundancy level. R = 3 R = 4 1 U vulnerable, as destruction of a single central node destroys communication between the end stations. In practice, a mixture of star and mesh components is used to form communications net¬ works. For example, type (B) in Fig. 1 shows the hierarchical structure of a set of stars connected in the form of a larger star with an additional link forming a loop. Such a network is sometimes called a "decentralized" network, because complete reliance upon a single point is not always required. Since destruction of a small number of nodes in a decentralized network can. destroy communications, the properties, problems, and hopes of building “dis¬ tributed" communications networks are of paramount interest. In a recent study of the effects of an attack on a distributed network, an investigation was made of the per¬ centage of surviving linked stations versus the probability of station de¬ struction for various levels of network redundancy. Redundancy level is a measure of connectivity and is used here as defined in Fig. 2. A key point revealed by the study is that extremely survivable networks can be built with the use of a moderately low redundancy of connectivity level. Redundancy levels on the order of only three permit the withstanding of ex¬ tremely heavy level attacks with neg* ligiblc additional communications loss. In addition, when one studies what happens when the links rather than the nodes of the network are destroyed, it becomes evident that highly reliable networks can be achieved with low-cost unreliable communication links, even links so unreliable.as to be unusable in present networks. Our future systems design problem is that of building at lowest cost very reliable systems out of the described set of unreliable elements. For communi¬ cations of the future, digital links appear increasingly attractive by permitting low-cost switching and low-cost links. In any event the network must be built with the expectation of heavy damage. Powerful error removal methods exist. Some of the communication con¬ struction methods that look attractive for the near future include pulse regenerative repeater line, minimum- cost or “mlmcost" microwave, TV broadcast station digital transmission, and satellites. In communications, as in irunsporta- Fig. 3. All-digital network composed of mixture of links. tion, it is most economical for many users to share a common resource rather than for each to build his own system, particularly when intermittent or occasional service is supplied. This intcrmiltency of service is highly char¬ acteristic of digital communication re¬ quirements. Therefore, we would like to consider one day the interconnection Of many all-digital links to provide a resource optimized for the handling of data for many potential intermittent users: a new common-user system. • Fig. 3 demonstrates the basic notion: A wide mixture of different digital transmission links is combined to form a common resource divided among many potential users. (P. Baran, "On Distributed Communications Net¬ works, IEEE Trans, on Cnn\numica~ lions Systems, March 1964.) Repetition in Learning. 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