NIEMORANDUM RM-8VBT-PB AUGUST 1934 ON DISTRIBUTED COMMUNICATIONS XI SUMMARY OVERVIEW Paul Baran PREPARED FOR UNITED STATES AIR BAND 74 DQUDW SANTA MEMORANDUM RM-3767-PR AUGUST 1964 ON DISTRIBUTED COMMUNICATIONS XI SUMMARY OVERVIEW Paul Baron This research is sponsored 1'13 the United States Air Forte under Project tract No AF 49r15638 1 $00 monitored by the Directorate of Development Plans Deputy Chief oi Staff Research and Dewhelopment Hq USAF News or contained in this iIemora 1dum should not be interpreted as representing the o ieial opinion or poiiev oi the United States Air Force one MFAELABILITY nortce Quali ed requesters mayr obtain copies of this report from the Defense Documentation Center 1 3-50 '3er ET - - loan Copyright I 9'64 I lu'h P nmn - Want PREFACE This Memorandum is one in a series of eleven RAND Memoranda detailing the Distributed Adaptive Message Block Network a proposed digital data communications system based on a distributed network concept as presented in Vol I in the series Various other items in the series deal with specific features of the concept results of experimental modelings engineering design considerations and background and future implications The series entitled On Distributed Communications is a part of The RAND Corporation's continuing program of research under U S Air Force Project RAND and is related to research in the field of command and control and in governmental and military planning and policy making The present Memorandum the eleventh and final volume in the series summarizes the development of the system proposal The more salient features of the system pre sented in much greater detail in the other Mamoranda in the series are gisted allowing the casual reader to ob tain a general overview of the network A reading of the introductory Memorandum in the series and the present Mame- randum should suffice for a general understanding of the proposed Distributed Adaptive Message Block Network Additionally the advantages and disadvantages of the system are given which will greatly facilitate critical evaluation of the system's feasibility A list of all items in the series is found on p 21 SUMMARY Progress in the Distributed-Adaptive Message Block Network is reviewed in this Memorandum and conclusions are drawn with resPect to its anticipated characteristics The advantages and disadvantages of the proposed system are listed in a comparison with traditional approaches to communication networks An outline of critical key tasks required for further development of these concepts is given Summarizing the last few years' work in this field 1 It appears theoretically possible to build large networks able to withstand heavy damage whether caused by unreliability of components or by enemy attack 2 Highly reliable and error free digital communica- tion systems using noisy links and unreliable components can be built without exceeding the present-day state of- the-art of electronic components--provided we use digital modulation 3 We are beginning to understand or at least to appreciate the cause of time delays and overloading phenomena in communication systems handling competing users with different levels of importance There is a basis for hope that one day we may be able to automate highly so- phisticated priority Systems Such systems may even be so effective as to provide the operational equivalent of-n exercised judgment 4 It appears that a proper direction in which to move in attacking the secrecy problem in large military and commercial communication systems is to design the Vi- provisions as an integral part of the digital switching system 5 Digital cemmunication systems able to serve highly automated sources can be more readily designed from the vieWpoint of bit-transportation systems rather than the con ventional approach of a tandem connection of real time links 6 One day in the future and we are not foolhardy enough to predict an exact date for economic reasons alone in the military environment it may be necessary to break away from existing analog signal communication net work concepts in favor of all-digital networks It is appropriate to redesign user input-output instruments such as telephones and teletypewriters for the deacribed system in order to gain the full benefit that accrues to an all-digital communications network CONTENTS PREFACE SUMMARY Section I INTRODUCTION The Goal II DISADVANTAGES OF THE DISTRIBUTED ADAPTIVE MESSAGE BLOCK NETWORK SOME POSITIVE ATTRIBUTES OF THE TRIBUTED ADAPTIVE MESSAGE BLOCK NETWORK IV SUGGESTED DEVELOPMENT V NEXT-GENERATION RESEARCH VI CONCLUSIONS POSSIBLE PITFALL LIST OF PUBLICATIONS IN THE SERIES hlh h 12 15 1 18 21 I The introductory Memorandum in the series On Distributed Communications described a set of basic concepts the de tails of which have been greatly expanded in the intervening Memoranda in the series The series as a whole is an examination of the feasibility of any digital communications system utilizing hot-potato routing and automatic error detection While preparing the draft of this concluding number it became evident that a distinct and Specific system was being described which we have now chosen to call the Distributed Adaptive Message Block Network in order to distinguish it from the growing set of other dis- tributed networks and systems as described in CDC-V name An electrical communications system can be de- fined as one that permits any person or machine to reliably and instantaneously communicate with any combination of other people or machines anywhere anytime and at zero cost It should effectively allow the illusion that those in communication with one another are all within the same soundproofed roomr-and that the door is locked Almost by definition all electrical communications systems will fall short of meeting these goals the is an abbreviation of the series title 9E Distributed Communications the number following refers to the particular volume within the series A 1ist of all items in the series is found on p 21 shortcomings we are content to live with being determined on the basis of intended application and price Present- day networks are designed to do one particular set of tasks well In the future we shall make even greater demands upon our networks and shall consider new ways of building communications networks taking advantage of the newly emerging computer based technology Let us consider one way we might go about building a new system to meet the requirements of the future We shall attempt to start from scratch and ignore the tra- ditional approach of existing communications systems We shall first focus upon those requirements--particularly military- not being fully satisfied by today's systems For example in their outstanding study of Army communications Bloom Hayfield and Williams of the Franklin Institute conducted a survey among Army Officers on shortcomings of present day Army communications Their findings are shown in Fig 1 We have used the Bloom Hayfield and Williams data as a check list against which the distributed network has been evaluated The separate mechanisms included within the distributed system to match these problems are pre- sented in Table 1 Bloom Joel N Clifton E Hayfield and Richard M Williams People Organizations and Communications Final Report F-A2312 Prepared for Army Communications Systous Division by the Franklin Institute Laboratories for Research and Development Philadelphia January 1962 From Blatant at 31 ibid p 30 1 Fig l--Principal Problus in Army Communications SECURITY SPEED mmunes 5 OVER CONTROL RELJABILITY HQNK Ii r-I 5 4 TRMNING PROCEDURES REDUCE 5 VOLUME VERBOSENESS OVER PERCENT OF CRSES II 45 4w 2 We Table I THE DISTRIBUTED HANDLING OF PRINCIPAL MILITARY COMMUNICATIONS PROBLEMS Problem Number of Cases Possible Solutions Included in Distributed Network Security 16 Built in protection services as an integral part of the system All traffic is treated on a secure base Speed 15 Design for a maximum of two seconds initial con nection time Permit quasi-real time operation- even for store-and-forward traffic Facilities 14 Design for area availability many stations Many tie-in points Over Control Administrative Censorship ll User-to user rather than emphasis on center-to center operation Clarity Error-free end to-end quasi-circuits Clarity may not be a technical problem Reliability Spatially organized parallel redundancy to buy high reliability using lesser-reliability Insufficient Training Capability for unmanned operation automatic fault location Procedures Reduced cost of long-haul communications bandwidth Allows conference calls Reduce Volume Automatic priority control responsive to changing loads and demands 10 Verboseness Fast feedback to user to establish context Verboseness may not be a technical problem 11 Over- classification Allow wider access to user-to-user circuits All network traffic is treated as if it were highly classified From Bloom Hayfield and Williams ibid -4- This list wasn't available at the time the system was initiated and we chose a somewhat different but similar set of criteria Survivability was placed at the top of our list The aim was towards an ideal electrical communica tion system But a real-life system is a collection of compromises and this system is no exception The author believes though that it represents an acceptable price to have to pay for a national communications system able to meet the extreme demands of survivability in the face of a determined enemy Some of the system's disadvantages and advantages are summarized in the next sections together with references to the volumes in the series in which the particular topic is detailed II DTSADVANTAGES OF THE DISTRIBUTED ADAPTIVE MESSAGE BLOCK NETWORK l The system concept is difficult to explain and to comprehend CDC-I 2 There is an almost fired 0 5-sec time delay in voice transmission 3 A E il distributed network is a meaningless entity only large networks are capable of emulating the system's desired properties CDC-I -II 4 No one has ever built or even fully designed all the hardware components required 5 It is an expensive system to simulate CDC-II 6 The concept is eSpecially sensitive to poor System design A brute-force massive-organization approach can easily end up with an expensive fractional-GNP-priced kluge ODE-VII -X An understanding of digital computer design is mandatory to adequately evaluate feasibility ODE-VII 8 The features have not yet been reviewed by those well versed in the secrecy business and reaponsible for determining the acceptability of the pro- posed generaliaed secrecy arrangements The analyses made on secrecy have been limited to information found in the open literature plus a little common sense ODE-IX 9 Analog to-digital conversion is required While such transformation is apparently necessary in conventional its present cost is high 10 The distributed system at this time is de- signed primarily for communications among large key military installations wherein it is possible to maintain secure areas for material adjacent to the Multi plexing Stations A later logical step in the development of the overall approach is to extend pro- tection to remote telephones a facility not included in the present design Some preliminary work has been started on this problem 11 Another possible difficulty is that our present voice telephone plant usually provides excellent service for peacetime civilian communications and the need for Special communications capabilities for the military has not always been widely appreciated Many tend to evaluate potential performance under combat conditions from_the standards of their own civilian voice telephone experience This is not the best measure for realistically determining the suits- bility of a military communications system -8- SOME POSITIVE ATTRIBUTES OF THE DISTRIBUTED ADAPTIVE MESSAGE BLOCK NETWORK l The system uses automatic learning to obtain perfect switching in its fully-distributed network con- figuration Thus it is less vulnerable to enemy attack than conventional networks ODC-I -II 2 The system has been designed completely from scratch to meet future requirements of military security physical survivability digital data flexibility and ease of adding new services -IV -IK 3 The system handles start stop teletype as well as standard high-speed binary-stream data rates of 600 2400 4800 9600 and 19 800 bits sec It could easily be adapted to handle very-high-Speed data if required 4 Each of the up to 1024 Multiplexing Stations simultaneously handles some 128 telephone subscribers together with 866 other simultaneous subscribers using other data input devices -IX 5 Automatic user-to-user is integrated into the network switching apparatus to eliminate the need for slow manual ODC-VII -IX 6 User-to-user information flows through the network only during actual transmission of information For ex ample after a pseudo-circuit is established blank Spots lasting longer than lf20 sec in Speech modes are See one-Iv p 12 not transmitted Thus high quality Speech need only load the transmission plant to an average equivalent data rate of about 5000 bitsfsec The system is readily amenable to the use of satellites as links ODC-VII 8 The system is able to withstand heavy network damage without interruption of on-going end-toeend traffic ODC-I -IX 9 From the user's viewpoint the system appears to be virtually noise- and error-free when handling data -IX 10 No cumulative distortion occurs on voice circuits whether 1 mi or 10 000 mi long other than a fixed initial quantization noise -IX 11 Undetected digital errors are expected to be extremely rare -IX 12 The network is designed to handle a broad mixture of inputfoutput devices -IX 13 Automatic error detection and repeat transmission is built into the System_on a linkaby-link basis simpli- fying the design of highly automated low-cost digital input devices -VII 14 Multi-level and automatic error- tracking procedures make the system far more immune to sophisticated sabotage than any other known communications system -IX 15 Instantaneous multi-station secure conference calls can he set up even after the con- versation is underway 16 The potentially high degree of security protec- tion provided permits a mixing of classified and uncles sified traffic both military and civilian over the same facilities DDC-VII -IX 17 As Message Blocks usually travel by different routes it appears impossible for an eavesdropper to de- traffic unless Ell preceding Message Blocks are received CDC-II -IX 18 The system appears to be highly resistant to overload--even when subjected to heavy damage ODC-V 19 The overall system reliability offers hopes of being far better than today's systems and it can be built of elements of lower-reliability than presently used ODC-I -VII -X 20 The system uses regenerative saturated amplifi- cation to circumvent the effects of cumulative distortion thereby permitting the use of inexpensive high data-rate links -X 21 The system uses the mini-cost microwave to build new high-data-rate links at very low cost 4 5- megabit sec rates appear feasible at a link cost a decimal order of magnitude lower than in conventional systems ODE-VI 22 Cost even on a per-subscriber basis appears'f roughly comparable to that of present-day conventional networks -X 23 Signaling symbols are transmitted as repetitive binary patterns at the same bit rate as the data informa- tion permitting additional signaling if desired while the receiver is off-hook This feature can be used to -11- simplify future automatic computer to computer conversation 24 Automatic error detection and analysis is easily implemented by virtue of the all-digital nature of the equipment facilitating the locating of possible sources of trouble CDC-VII -IX 25 This system has the security speed and low-error characteristics to make it useful as a signaling network to set circuit switches for possible extremely-high-data-rate circuit-switched systems in the far future 26 The system allows ready implementation of sophis- ticated automatic priority precedence and overload controls ODC-IV IV SUGGESTED DEVELOPMENT To this point we have spoken primarily of a system concept In order to evolve a hardware system more study and prototype development is indicated Only after this series has been carefully scrutinized and only after we have ironed out possible flaws in the concept should such further development be considered Such a development program might include the follow- ing items These items are merely guesstimates based on the writer's judgment of what work must be done Study and Research Phase in millions 1 Investigate new problems that may 25 be encountered in a bit-trans- portation communications system 2 Perform a traffic analysis for 1 00 this future system and recommend a detailed system growth plan 3 Study the precise degree of 50 secrecy required in future Systems 4 Amplify the detailed description of 50 the mechanisms used for automating - precedence 5 Simulate entire system operation 2 00 in maximum depth with emphasis 0n reliability 6 Investigate some of the better 25 analog-to-digital modulation schemes such as High Information Delta Modulation applicable to this system 7 Perform cost-comparison studies 50 Total 5 00 -13- Design Phase 1 Design a low-cost all-digital telephone with push-button signaling Design the Switching Node in full detail Design the Multiplexing Station in full detail Design the Mini-Cost micro- wave in full detail Design of low-cost high-data rate plowed cable line in full detail Design low-cost graphic and text inputfoutput devices suitable for user-to-user service in this system Total Hardware Test Phase 1 2 Build and test mini cost microwave Build and test low-cost plowed cable line Build and test critical assemblies proposed for the Switching Node Build and test critical assemblies proposed for the multiplexing Station Build and test low-cost text handling devices Build and test teletype and voice High Information Delta Modulation data modems Total Cost 3 in millions 20 1 50 20 20 25 20 50 2 00 40 Cost Development Phase in millions 1 Build and test three Switching 2 00 Nodes 2 Build and test three Multiplexing 4 00 Stations Total 6 00 Final Test Phase 1 Evaluate performance of test 2 00 units before proceeding Total 2 00 The expenditure milestone points that can be ear- marked for system evaluation would occur at about the $1 25 million level during the Study and Research Phase after the $5imillion point at the conclusion of the entire Study and Research Phase at the $11 6 million level at the end of the Design Phase at the $15 7- million mark at the end of the Test Phase at the million level at the end of the Development Phase and at the $23 7emillion point at the end of the Final Test Phase Thus there are many early opportunities to re- evaluate and redirect this program upon discovery of un- foreseen difficulties or better alternative approaches -15- V NEXT-GENERATION RESEARCH Even though the system has yet to be studied in actual implementation detail it is felt appropriate to start thinking about further development of the system notion Consideration today of a next-generation system will simplify orderly system evolution tomorrow New areas for research for example might include the investigation of the feasibility of using links in the 15- to lSU-megabit sec range Or we might study the possibility of forming links of low-cost infrared lasers Very-low-cost microwave is also a possible avenue to reduce the feeder network cost The technology upon which the system is based is developing at an explosive rate For instance our de- sign examination of the Switching Node ODS-VII indicated a physical size of about 2 cu ft using late-1962 digital computer technology Autonetics Division of North American Aviation Inc however has announced a new microminiaturi iaed computer see Table II in late stages of development This unit appears to have a computing capacity almost as great as that we have proposed package of about 0 3 cu ft--and at a comparable cost The implication of what the changing computer tech nology offers the communications designer has not always been fully appreciated in the past Therefore we should strive to become better prepared to take advantage of this deveIOping technology by continuing the research Table II COMPARISON OF THE MONICA-C COMPUTER WITH THAI PROPOSED FOR THE SWITCHING MODES Proposed a Switching Monioeec Node Words oore 8192 4000 storage were length bits 30 32 Memory cycle useo Main memory 6 Scratch pad 1 256 words Clock rate me 1 0 1 5 mash hr 19 500 no Size cu ft 0 3 72 Power kwl_ 0 19 5 Temperature DC 65 40 Cost in pro- $100 000 $100 000 to duotion quantities $150 000 North American Av1at1on Ino Antonetlos D1v131on Mean-Time Between Failures effort even while b ilding the hardware In retrospect the designs described in and are now somewhat out of date in light of the mierominiature developments of the past year VI CONCLUSIONS A new system has been described offering much promise in solving many military communications problems It is however a difficult system to understand and further re search is necessary in order to achieve sufficient con fidence in the notion to permit investment of large sums for its construction Some paths leading to further ex- aminations of these concepts have been described The amount of work and its nature is such that it is beyond the scope of work appropriate to RAND Thus the majority of the future work will have to come from other organizations and agencies Now the hard work must begin -18 POSSIBLE PITFALL There is the human tendency for those who would sug- gest new systems to overstate the value of their projects and to understate the problems The writer believes that he has called attention to the individual technical problems as they have arisen within each of the Memoranda describing the system How- ever there are still a few problems that are not so Specifically elucidated These are not technical problems in the usual sense but will probably be the key problems which will set the upper bound upon the speed of development of the proposed system They include the limited diffusion of technical competence in the computer communications art a very human fear of complicated systems the right of free access between existing communications networks etc We would like to discuss briefly one of these key problems In this series we have proposed a radically different communications system--one that started with a difficult military goal and has been shown to require com plex equipment to satisfy a large set of military needs We have discussed a new large communication system one markedly different from the present in both concept and in equipment and one which will mean a merging of Ltwo different technologiesi _Ebmputers and communications People with competence in both these fields are not numerous Our concern is whether we will have enough well-trained people capable of understanding both the this venture a success Here may lie the real question of feasibility Our present-day components are fully adequate The difficult problems lie in hooking them together This is not to say that there will be a dearth of organizations happy to bid on providing such a system on a cost-plus-fixed-fee basis There may even be some fool hardy enough to have a go at a fixed cost banking on the returns from the inevitable engineering changes to bail them out The skills that we need are exactly those which are most heavily advertised in the help-wanted pages of our new5papers and magazines Thus where we can go and what we can do may be substantially limited by the breadth and extent of our computer technology manpower base Historically we upgrade the level of resPonsibility of each of the engineers on a BigdL military electronics project--or fracture the project into enough small pieces in hopes that sheer numbers of warm bodies alone will make up for an acknowledged lack of technical foundations But in the development of a system_of this type numbers alone will not substitute for competence -21- ON DISTRIBUTED COMMUNICATIONS M_List of Publications in the Series I Introduction to Distributed Communications Networks Paul Baran Introduces the system concept and outlines the requirements for and design considerations of the distributed digital data communications net- work Considers especially 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 II Digital Simulation of Hot-Potato Routing in a Broadband Distributed Communications Network Sharla P Boehm and Paul Baran 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 reconstitute itself by rapidly relearning to make best use of the surviving links Determination of in a Distributed Network J W Smith RM-3578-PR Continues model simulation reported in Vol II The program 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 number 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 overlapping validity -22- IV Priority Precedence and Overload Paul Baran RM-3638-PRI The creation of dynamic or flexible priority and precedence structures within a communication system handling a mixture of traffic with dif- ferent data rate urgency and importance levels is discussed The goal chosen is optimum utiliza- tion of the communications resource within a seriously degraded and overloaded network V History Alternative Approaches and Comparisons Paul Baran A background paper acknowledging the efforts of people in many fields working toward the develop ment of large communications systems where system reliability and survivability are mandatory A consideration of terminology is designed to ac- quaint the reader with the diverse 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 The technical feasibility of constructing an extremely low-cost all digital X- or Ku 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 High-speed or hot-potato store-and-forward message block relaying forms the heart of the proposed information transmission system The Switching Nodes are the units in which the com- plex processing takes place The node is de- scribed in sufficient engineering detail to estimate the components required Timing calcu- lations together with a projected implementation -23- scheme provide a strong toundation for the belief that the construction and use of the node is practical The Multiplexing Station Paul Baran A description of the Multiplexing Stations which connect subscribers to the Switching Nodes The presentation_is in engineering detail demonstrat- ing how the network will simultaneously process traffic from up to 1024 separate users sending a mixture of start-stop teletypewriter digital voice and other signals at various rates IX Security Secrecy and Tamper-Free Considerations Paul Baran 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 or spies within the supposedly secure system must be anticipated Security provisions are based on the belief that protec- tion is best obtained by raising the price of espied information to a level which becomes ex- cessive The treatment of the subject is itself unclassified K Cost Estimate Paul Baran A detailed cost estimate for the entire proposed system based on an arbitrary network configura- tion of 400 Switching Nodes servicing 100 000 simultaneous users via5200 MUltiplexing Stations Assuming a usable life of ten years all costs including operating costs are estimated at about $60 000 000 per year XI Summary Overview Paul Baran RMF3761-PR Summarizes the system preposal 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 imple _mentation of the network might be conducted To- gether with the introductory volume it provides a general description of the entire system concept                     National Security Archive    Suite 701  Gelman Library  The George Washington University    2130 H Street  NW  Washington  D C  20037    Phone  202 994‐7000  Fax  202 994‐7005  nsarchiv@gwu edu