Network Working Group National Research Council Request for Comments: 942 February 1985 TRANSPORT PROTOCOLS FOR DEPARTMENT OF DEFENSE DATA NETWORKS STATUS OF THIS MEMO This RFC is distributed for information only. This RFC does not establish any policy for the DARPA research community or the DDN operational community. Distribution of this memo is unlimited. This RFC reproduces the National Research Council report resulting from a study of the DOD Internet Protocol (IP) and Transmission Control Protocol (TCP) in comparison with the ISO Internet Protocol (ISO-IP) and Transport Protocol level 4 (TP-4). Transport Protocols for Department of Defense Data Networks Report to the Department of Defense and the National Bureau of Standards Committee on Computer-Computer Communication Protocols Board on Telecommunications and Computer Applications Commission on Engineering and Technical Systems National Research Council National Academy Press Washington, D.C. February 1985
NOTICE The project that is the subject of this report was approved by the Governing Board on the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors, according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. This is a report of work supported by Contract No. DCA-83-C-0051 between the U.S. Defense Communications Agency and the National Academy of Sciences, underwritten jointly by the Department of Defense and the National Bureau of Standards. Copies of this publication are available from: Board on Telecommunications and Computer Applications Commission on Engineering and Technical Systems National Research Council 2101 Constitution Avenue, N.W. Washington, D.C. 20418
BOARD ON TELECOMMUNICATIONS -- COMPUTER APPLICATIONS COMMITTEE ON COMPUTER-COMPUTER COMMUNICATION PROTOCOLS Chairman C. CHAPIN CUTLER, Professor of Applied Physics, Stanford University, Stanford, California Members HERBERT D. BENINGTON, Technical Director, System Development Corporation, McLean, Virginia DONALD L. BOYD, Director, Honeywell Corporate Computer Sciences Center, Honeywell Corporate Technology Center, Bloomington, Minnesota DAVID J. FARBER, Professor of Electrical Engineering and Professor of Computer Science, Department of Electrical Engineering, University of Delaware, Newark, Delaware LAWRENCE H. LANDWEBER, Professor, Computer Sciences Department, University of Wisconsin, Madison, Wisconsin ANTHONY G. LAUCK, Manager, Distributed Systems Architecture and Advanced Development, Digital Equipment Corporation, Tewksbury, Massachusetts KEITH A. LUCKE, General Manager of Control Data Technical Standards, Control Data Corporation, Minneapolis, Minnesota MISCHA SCHWARTZ, Professor of Electrical Engineering and Computer Science, Columbia University, New York, New York ROBERT F. STEEN, Director of Architecture, Communication Products Division IBM Corporation, Research Triangle Park, North Carolina CARL A. SUNSHINE, Principal Engineer, Sytek, Incorporated, Los Angeles Operation, Culver City, California DANIEL J. FINK, (Ex-officio), President, D.J. Fink Associates, Inc., Arlington, Virginia JAMES L. FLANAGAN, (CETS LIAISON MEMBER), Head, Acoustics Research Department, AT&T Bell Laboratories, Murray Hill, New Jersey Staff RICHARD B. MARSTEN, Executive Director JEROME D. ROSENBERG, Senior Staff Officer and Study Director LOIS A. LEAK, Administrative Secretary
COMMISSION ON ENGINEERING AND TECHNICAL SYSTEMS BOARD ON TELECOMMUNICATIONS -- COMPUTER APPLICATIONS Chairman DANIEL J. FINK, President, D.J. Fink Associates, Inc., Arlington, Virginia Past Chairman BROCKWAY MCMILLAN, Vice President (Retired), Bell Laboratories, Sedgwick, Maine Members ARTHUR G. ANDERSON, Vice President (Retired), IBM Corporation, San Jose, California DANIEL BELL, Henry Ford II Professor of Social Sciences, Department of Sociology, Harvard University, Cambridge, Massachusetts HERBERT D. BENINGTON, Technical Director, System Development Corporation, McLean, Virginia ELWYN R. BERLEKAMP, Professor of Mathematics, Department of Mathematics, University of California, Berkeley, California ANTHONY J. DEMARIA, Assistant Director of Research for Electronics and Electro-Optics Technology, United Technologies Research Center, East Hartford, Connecticut GERALD P. DINNEEN, Vice President, Science and Technology, Honeywell Incorporated, Minneapolis, Minnesota GEORGE GERBNER, Professor and Dean, The Annenberg School of Communications, University of Pennsylvania, Philadelphia, Pennsylvania ANNE P. JONES, Partner, Sutherland, Asbill and Brennan, Washington, D.C. ADRIAN M. MCDONOUGH, Professor of Management and Decision Sciences (Retired), The Wharton School, University of Pennsylvania, Havertown, Pennsylvania WILBUR L. PRITCHARD, President, Satellite Systems Engineering, Inc., Bethesda, Maryland MICHAEL B. PURSLEY, Professor of Electrical Engineering, University of Illinois, Urbana, Illinois IVAN SELIN, Chairman of the Board, American Management Systems, Inc., Arlington, Virginia
MISCHA SCHWARTZ, Professor of Electrical Engineering and Computer Science, Columbia University, New York, New York ERIC E. SUMNER, Vice President, Operations System and Network Planning, AT&T Bell Laboratories, Holmdel, New Jersey KEITH W. UNCAPHER, Executive Director, USC-Information Sciences Institute Associate Dean, School of Engineering, University of Southern California, Marina del Rey, California JAMES L. FLANAGAN, (CETS LIAISON MEMBER), Head, Acoustics Research Department, AT&T Bell Laboratories, Murray Hill, New Jersey Staff Richard B. Marsten, Executive Director Jerome D. Rosenberg, Senior Staff Officer Karen Laughlin, Administrative Coordinator Carmen A. Ruby, Administrative Assistant Lois A. Leak, Administrative Secretary
CONTENTS PREFACE ............................................................ ix EXECUTIVE SUMMARY .................................................. xi I Introduction .................................................. 1 II Review of NBS and DOD Objectives .............................. 3 III Comparison of DOD and ISO Protocols .......................... 13 IV Status of DOD and ISO Protocol Implementations and Specifications .......................... 25 V Markets ...................................................... 31 VI Development of Standard Commercial versus Special Commercial Products .................................. 39 VII Responsiveness of International Standards Process to Change ............................................ 43 VIII Options for DOD and NBS ...................................... 45 IX Cost Comparison of Options .................................. 47 X Evaluation of Options ........................................ 53 XI Recommendations .............................................. 61
PREFACE This is the final report of the National Research Council Committee on Computer-Computer Communication Protocols. The committee was established in May l983 at the request of the Department of Defense (DOD) and the National Bureau of Standards (NBS), Department of Commerce, to develop recommendations and guidelines for resolving differences between the two agencies on a data communications transport protocol standard. Computer-based information and transaction-processing systems are basic tools in modern industry and government. Over the past several years there has been a growing demand to transfer and exchange digitized data in these systems quickly and accurately. This demand for data transfer and exchange has been both among the terminals and computers within an organization and among those in different organizations. Rapid electronic transport of digitized data requires electronic communication links that tie the elements together. These links are established, organized, and maintained by means of a layered series of procedures performing the many functions inherent in the communications process. The successful movement of digitized data depends upon the participants using identical or compatible procedures, or protocols. The DOD and NBS have each developed and promulgated a transport protocol as standard. The two protocols, however, are dissimilar and incompatible. The committee was called to resolve the differences between these protocols. The committee held its first meeting in August l983 at the National Research Council in Washington, D.C. Following this two-day meeting the committee held five more two-day meetings, a three-day meeting, and a one-week workshop. The committee was briefed by personnel from both agencies. In addition, the committee heard from Jon Postel, University of Southern California's Information Sciences Institute; Dave Oran, Digital Equipment Corporation; Vinton Cerf, MCI; David Wood, The Mitre Corporation; Clair Miller, Honeywell, and Robert Follett, IBM, representing the Computer and Business Equipment Manufacturer's Association; and John Newman, Ultimate Corporation. In most cases the briefings were followed by discussion. The committee wishes to thank Philip Selvaggi of the Department of Defense and Robert Blanc of the NBS, Institute of Computer Sciences and
Technology, for their cooperation as their agency's liaison representatives to the committee. The committee appreciates the contributions and support of Richard B. Marsten, Executive Director of the Board on Telecommunications -- Computer Applications (BOTCAP), and Jerome D. Rosenberg, BOTCAP Senior Staff Officer and the committee Study Director. We also wish to thank Lois A. Leak for her expert administrative and secretarial support.
EXECUTIVE SUMMARY Computer communication networks have become a very important part of military and commercial operations. Indeed, the nation is becoming dependent upon their efficiency and reliability, and the recent proliferation of networks and their widespread use have emphasized the importance of developing uniform conventions, or protocols, for communication between computer systems. The Department of Defense (DOD) and the National Bureau of Standards (NBS) have been actively engaged in activities related to protocol standardization. This report is concerned primarily with recommendations on protocol standardization within the Department of Defense. Department of Defense's Transmission Protocol The DOD's Defense Advanced Research Projects Agency (DARPA) has been conducting and supporting research on computer networks for over fifteen years (1). These efforts led to the development of modern packet-switched network design concepts. Transmission between computers is generally accomplished by packet switching using strict protocols for the control and exchange of messages. The Advanced Research Projects Agency network (ARPANET), implemented in the early 1970s, provided a testing ground for research on communications protocols. In 1978, after four years of development, the DOD promulgated versions of its Transmission Control Protocol (TCP) and an Internet Protocol (IP) and mandated their use as standards within the DOD. TCP is now widely used and accepted. These protocols meet the unique operational and functional requirements of the DOD, and any changes in the protocols are viewed with some trepidation by members of the department. DOD representatives have stated that standardizing TCP greatly increased the momentum within the DOD toward establishing interoperability between networks within the DOD. International Standards Organization's Transport Protocol The NBS Institute for Computer Sciences and Technology (ICST), in cooperation with the DOD, many industrial firms, and the International Standards Organization (ISO), has developed a new international standard ----- (1) The Advanced Research Projects Agency (ARPA) was reorganized and became the Defense Advanced Research Projects Agency (DARPA) in 1973.
Transport Protocol (TP-4) and a new Internetwork Protocol (2). These protocols will soon be available as commercial products. Although in part derived from TCP, the new protocols are not compatible with TCP (3). The U.S. standards organizations are supporting TP-4 in international operations, and the Department of Commerce is proposing TP-4 as a Federal Information Processing Standard (FIPS) for use by all federal agencies. DOD OPERATIONAL AND TECHNICAL NEEDS The DOD has unique needs that could be affected by the Transport and Internet Protocol layers. Although all data networks must have some of these capabilities, the DOD's needs for operational readiness, mobilization, and war-fighting capabilities are extreme. These needs include the following: Survivability--Some networks must function, albeit at reduced performance, after many nodes and links have been destroyed. Security--Traffic patterns and data must be selectively protected through encryption, access control, auditing, and routing. Precedence--Systems should adjust the quality of service on the basis of priority of use; this includes a capability to preempt services in cases of very high priority. Robustness--The system must not fail or suffer much loss of capability because of unpredicted situations, unexpected loads, or misuse. An international crisis is the strongest test of robustness, since the system must operate immediately and with virtually full performance when an international situation flares up unexpectedly. Availability--Elements of the system needed for operational readiness or fighting must be continuously available. Interoperability--Different elements of the Department must be able to "talk" to one another, often in unpredicted ways between parties that had not planned to interoperate. ----- (2) The ISO Transport Protocol and ISO Internetwork Protocol became Draft International Standards in September 1983 and April 1984, respectively. Commercial vendors normally consider Draft International Standards to be ready for implementation. (3) Except where noted, the abbreviation TCP generally refers to both the DOD's Transmission Control Protocol and its Internet Protocol. Similarly, the abbreviation TP-4 refers to both the ISO Transport Protocol class 4 and its Internetwork Protocol. (Transport Protocol classes 0 to 3 are used for special purposes not related to those of this study.)
These operational needs reflect themselves into five technical or managerial needs: 1. Functional and operational specifications (that is, will the protocol designs meet the operational needs?); 2. Maximum interoperability; 3. Minimum procurement, development, and support costs; 4. Ease of transition to new protocols; and 5. Manageability and responsiveness to changing DOD requirements. These are the criteria against which DOD options for using the ISO transport and internet protocols should be evaluated. Interoperability is a very important DOD need. Ideally, DOD networks would permit operators at any terminal to access or be accessed by applications in any computer. This would provide more network power for users, integration of independently developed systems, better use of resources, and increased survivability. To increase interoperability, the Office of the Secretary of Defense has mandated the use of TCP for the Defense Communication System's Defense Data Network (DDN), unless waivers are granted. In addition, the Defense Communication Agency (DCA) is establishing standards for three higher-level "utility" protocols for file transfer, terminal access, and electronic mail. Partly as a result of these actions, it has become clear that there is growing momentum toward accepting interoperability and a recognition that it is an important operational need. It is very important, however, to recognize that functional interoperability is only achieved with full generality when two communication nodes can interoperate at all protocol levels. For the DOD the relevant levels are as follows: 1. Internet, using IP; 2. Transport, using TCP; 3. Utility, using file, terminal, or mail protocols; and 4. Specific applications that use the above protocols for their particular purpose. Accordingly, if a network is developed using one transport protocol, it would generally not be able to interoperate functionally with other networks using the same transport protocol unless both networks were also using the higher-level utility and application protocols. In evaluating whether or not to convert to TP-4 and in developing a transition plan, the following factors must be considered: The DOD contains numerous communities of interest whose principal need is to interoperate within their own members, independently. Such communities generally have a specific, well-defined mission.
The DOD Intelligence Information System (DODIIS) and the World Wide Military Command and Control System (WWMCCS) are examples. Interoperability is needed primarily between the higher layer applications programs initially unique to each community of interest. There are many different kinds of operations needed between communities of interest. Examples of such operations are headquarters' need for access to several subordinate communities and the communities' need for some minimum functional interoperability with each other (such as mail exchange). The need for functional interoperability can arise, unexpectedly and urgently, at a time of crisis or when improved management opportunities are discovered. Widespread standardization of TP-4 and higher-level protocols can readily help to achieve these needs. Often, special development of additional applications that cost time and money will be necessary. The DOD needs functional interoperability with many important external agencies that are committed to ISO standards: The North Atlantic Treaty Organization (NATO), some intelligence and security agencies, and other parts of the federal government. The same objectives that have prompted the use of standardized protocols at higher-level headquarters will lead to their use by tactical groups in the field. SOME COMPARISONS A detailed comparison of the DOD Transmission Control Protocol and the ISO Transport Protocol indicates they are functionally equivalent and provide essentially similar services. Because it is clear that a great deal of care and experience in protocol development have gone into generating the specifications for TP-4, the committee is confident that TP-4 will meet military requirements. Although there are differences between the two protocols, they do not compromise DOD requirements. And, although in several areas, including the data transfer interface, flow control, connection establishment, and out-of-band, services are provided in different ways by the two protocols, neither seems intrinsically superior. Thus, while existing applications may need to be modified somewhat if moved from TCP to TP-4, new applications can be written to use either protocol with a similar level of effort. The TCP and TP-4 protocols are sufficiently equivalent in their security-related properties in that there are no significant technical points favoring the use of one over the other. While TCP currently has the edge in maturity of implementation, TP-4 is gaining rapidly due to the worldwide support for and acceptance of the
Open System Interconnection (OSI) international standards. Experimental TCP implementations were completed in 1974 at Stanford University and BBN Communications Corporation. Between 1974 and 1982 a large number of implementations were produced. The Defense Advanced Research Projects Agency (ARPA) network switched to a complete use of TCP in January 1983. Operations have been satisfactory and its use is growing. A number of TCP implementations are also in commercial use in various private networks. In contrast, TP-4 has not yet been implemented in any large operational system. It has been tested experimentally, however, and has received endorsement by many commercial vendors worldwide. In addition, substantial portions of TP-4 have been demonstrated at the National Computer Conference in July 1984. The Internet Protocol (IP) part of the standards is not believed to be a problem. The ISO IP is not as far along as TP-4, but it is much less complex. The ISO IP, based very strongly on the DOD IP, became a draft international standard in April 1984. The rapidity of the progress in ISO and the results achieved over the past two years have surprised even the supporters of international standards. The reasons for this progress are twofold: strong market demands stemming from the growing integration of communications and data processing and the progress in networking technology over the past years as the result of ARPA and commercial developments. Although the DOD networks have been a model upon which the ISO transport standards have been built, the rest of the world is adopting TP-4. Because the DOD represents a small fraction of the market and because the United States supports the ISO standard, it is not realistic to hope that TP-4 can be altered to conform with TCP. This raises the question as to what action should be taken by the DOD with respect to the ISO standard. SOME ECONOMIC CONSIDERATIONS The DOD has a large and growing commitment in operational TCP networks, and this will increase by 50 to 100 percent in the next eighteen months. This rate of investment will probably continue for the next five years for new systems and the upgrading of current ones. The current Military Network (MILNET) and Movement Information Network (MINET) systems are expanding and will shortly be combined. The Strategic Air Command Digital Information Network (SACDIN) and DODIIS are undergoing major upgrading. When these changes are completed, there are plans to upgrade the WWMCCS Intercomputer Network (WIN) and to add separate SECRET and TOP SECRET networks. There are plans to combine these six networks in the late 1980s, and they will become interoperable and multilevel secure using an advanced technology now under development. If these plans are implemented on schedule, a delay of several years in moving to TP-4 would mean that the DOD networks in the late 1980s would be virtually all TCP-based. Subsequent conversion to international standards would be very expensive
if hastily attempted in order to maintain established DOD interoperability and gain interoperability with a large body of users. As the Department of Defense policy recognizes, there are significant advantages in using commercial vendor products if they meet the department's operational needs. The major advantages are as follows: Costs to the DOD for development, production, and maintenance are significantly lower because (1) vendors spread the cost over a much larger user base, (2) commercial vendors are generally more efficient in their operations, and (3) vendors look for ways to improve their product to meet competition. The department generally gets more effective products because vendors integrate the protocol functions into their entire software and hardware product line. Thus the DOD may be able eventually to use commercial software products that are built on top of, and thereby take advantage of, the transport protocols. By depending on industry to manage the development and maintenance of products, the department can use its scarce management and technical resources on activities unique to its mission. Because the costs of transport and internet protocol development and maintenance are so intertwined with other factors, it is impossible to give a precise estimate of the savings that would be achieved by using commercial products. Savings will vary in individual cases. The marginal savings should range from 30 to 80 percent. RECOMMENDATIONS The ISO protocols are now well specified but will not generally be commercially available for many months. Nevertheless, this committee believes that the principles on which they are based are well-established, and the protocols can be made to satisfy fully DOD's needs. The committee recommends that the DOD move toward adoption of TP-4 as costandard with TCP and toward exclusive use of TP-4. Transition to the use of the ISO standards, however, must be managed in a manner that will maintain DOD's operational capabilities and minimize risks. The timing of the transition is, therefore, a major concern. Descriptions of two options that take this requirement into account follow. A majority of the committee recommends the first option, while a minority favors the second. A third option--to defer action--is also described but not recommended. Option 1 The first option is for the DOD to immediately modify its current transport policy statement to specify TP-4 as a costandard along with TCP. In addition, the DOD would develop a military specification for
TP-4 that would also cover DOD requirements for discretionary options allowed under the NBS protocol specifications. Requests for proposals (RFPs) for new networks or major upgrades of existing networks would specify TP-4 as the preferred protocol. Contracts for TP-4 systems would be awarded only to contractors providing commercial products, except for unique cases. Existing networks that use TCP and new networks firmly committed to the use of TCP-based systems could continue to acquire implementations of TCP. The DOD should carefully review each case, however, to see whether it would be advantageous to delay or modify some of these acquisitions in order to use commercial TP-4 products. For each community of users it should be decided when it is operationally or economically most advantageous to replace its current or planned systems in order to conform to ISO standards without excessively compromising continued operations. United States government test facilities would be developed to enable validation of TP-4 products (4). The Department of Defense would either require that products be validated using these test facilities or that they be certified by the vendor. The test facilities could also be used to isolate multivendor protocol compatibility problems. The existing NBS validation tools should be used as the base for the DOD test facilities. Because under this option networks based on both TCP and TP-4 would coexist for some time, several capabilities that facilitate interoperability among networks would need to be developed. The Department of Defense generally will not find them commercially available. Examples are gateways among networks or specialized hosts that provide services such as electronic mail. The department would need to initiate or modify development programs to provide these capabilities, and a test and demonstration network would be required. Option 2 Under Option 2 the Department of Defense would immediately announce its intention to adopt TP-4 as a transport protocol costandard with TCP after a satisfactory demonstration of its suitability for use in military networks. A final commitment would be deferred until the demonstration has been evaluated and TP-4 is commercially available. The demonstration should take at most eighteen months and should involve development of TP-4 implementations and their installation. This option differs from Option 1 primarily in postponing the adoption of a TP-4 standard and, consequently, the issuance of RFPs based on TP-4 until successful completion of a demonstration. The department, ----- (4) Validation means a systematic and thorough state-of-the-art testing of the products to assure that all technical specifications are being achieved.
however, should proceed with those provisions of Option 1 that may be completed in parallel with the demonstration. Early issuance of a TP-4 military specification, development of validation procedures, and implementation of means for interoperability would be particularly important in this regard. Option 3 Under the third option the DOD would continue using TCP as the accepted transport standard and defer any decision on the use of TP-4 indefinitely. The department would be expected to stay well informed on the development and use of the new protocol in the commercial and international arena and, with the National Bureau of Standards, work on means to transfer data between the two protocol systems. Testing and evaluation of TP-4 standards by NBS would continue. The DOD might eventually accommodate both protocol systems in an evolutionary conversion to TP-4. Comparison of Options The committee believes that all three options equally satisfy the functional objectives of the DOD, including matters of security. It believes the two protocols are sufficiently similar and no significant differences in performance are to be expected if the chosen protocol implementation is of equal quality and is optimized for the given environment. The primary motivation for recommending Option 1 is to obtain the benefits of standard commercial products in the communication protocol area at an early date. Benefits include smaller development, procurement, and support costs; more timely updates; and a wider product availability. By immediately committing to TP-4 as a costandard for new systems, Option 1 minimizes the number of systems that have to be converted eventually from TCP. The ability to manage the transition is better than with Option 2 since the number of systems changed would be smaller and the time duration of mixed TCP and TP-4 operation would be shorter. Interoperability with external systems (NATO, government, commercial), which presumably will also use TP-4, would be brought about more quickly. Option 1 involves greater risk, however, since it commits to a new approach without as complete a demonstration of its viability. As with Option 1, a primary benefit of following Option 2 would be obtaining the use of standard commercial products. Unit procurement costs probably would be lower than with Option 1 because the commercial market for TP-4 will have expanded somewhat by the time DOD would begin to buy TP-4 products. Risk is smaller, compared to Option 1, because testing and demonstration of the suitability for military use will have preceded the commitment to the ISO protocols. Transition and support costs would be higher than for Option 1, however, because more networks and systems would already have been implemented with TCP. Also this is perhaps the most difficult option to manage since the largest number of system conversions and the
longest interval of mixed TCP and TP-4 operations would occur. In addition, interoperability with external networks through standardization would be delayed. The principal benefit of exercising Option 3 would be the elimination of transition cost and the risk of faulty system behavior and delay. It would allow the most rapid achievement of full internal interoperability among DOD systems. Manageability should be good because only one set of protocols would be in use (one with which the DOD already has much experience), and because the DOD would be in complete control of system evolution. Procurement costs for TCP systems would remain high compared with standard ISO protocol products, however, and availability of implementations for new systems and releases would remain limited. External interoperability with non-DOD systems would be limited and inefficient. In summary, Option 1 provides the most rapid path toward the use of commercial products and interoperability with external systems. Option 2 reduces the risk but involves somewhat greater delay and expense. Option 3 involves the least risk and provides the quickest route to interoperability within the Defense Department at the least short-term cost. These are, however, accompanied by penalties of incompatibility with NATO and other external systems and higher life-cycle costs.
I. INTRODUCTION For the past two decades industry and government have experienced an increasing need to share software programs, transfer data, and exchange information among computers. As a result, computer-to-computer data communications networks and, therefore, communication formats and procedures, or protocols, have proliferated. The need to interconnect these networks is obvious, but the problems in establishing agreements among users on the protocols have heightened. The Department of Defense (DOD) has been conducting research and development on protocols and communication standards for more than fifteen years. In December 1978 the DOD promulgated versions of the Defense Advanced Research Projects Agency's (DARPA) Transmission Control Protocol (TCP) and Internet Protocol (IP) as standards within DOD. With the participation of major manufacturers and systems houses, the DOD has implemented successfully over twenty different applications of these standards in DOD operational data communications networks. The Institute for Computer Sciences and Technology (ICST) of the National Bureau of Standards (NBS) is the government agency responsible for developing network protocols and interface standards to meet the needs of federal agencies. The Institute has been actively helping national and international voluntary standards organizations develop sets of protocol standards that can be incorporated into commercial products. Working with both industry and government agencies, the ICST has developed protocol requirements based, in terms of functions and services, on the DOD's TCP. These requirements were submitted to the International Standards Organization (ISO) and resulted in the development of a transport protocol (TP-4) that has the announced support of twenty computer manufacturers. Although the ISO's TP-4 is based on the DOD's TCP, the two protocols are not compatible. Thus manufacturers who wish to serve DOD, while remaining able to capture a significant share of the worldwide market, have to field two product lines that are incompatible but perform the same function. The Institute for Computer Sciences and Technology would like to have a single set of protocol standards that serves both the DOD, other government agencies, and commercial vendors. It would be to the advantage of the DOD to use the same standards as the rest of the world. The dilemma, however, is understandable: The DOD
has well satisfied its requirements by its own tried and proven protocols, the agency has invested heavily in systems operating successfully with TCP, and the Armed Forces is increasingly adopting the protocol. Thus, although DOD's policy is to use commercial standards whenever suitable, it is hesitant about converting to the ISO TP-4 protocols. In addition, the DOD is not certain whether the ISO TP-4 completely satisfies military requirements. In 1983 both DOD and the ICST agreed that an objective study of the situation was needed. Each requested assistance from the National Research Council. The National Research Council, through its Board on Telecommunications and Computer Applications (BOTCAP), appointed a special Committee on Computer-Computer Communication Protocols to study the issues and develop recommendations and guidelines for ways to resolve the differences in a mutually beneficial manner. The six items composing the committee's scope of work are as follows: 1. Review the technical aspects of the DOD transmission control and ICST transport protocols. 2. Review the status of the implementation of these protocols. 3. Review the industrial and government markets for these protocols. 4. Analyze the technical and political implications of the DOD and ICST views on the protocols. 5. Report on time and cost implications to the DOD, other federal entities, and manufacturers of the DOD and ICST positions. 6. Recommend courses of action toward resolving the differences between the DOD and ICST on these protocol standards. The committee devoted considerable effort to reviewing the objectives and goals of the DOD and NBS that relate to data communications, the technical aspects of the two protocols, the status of their implementation in operating networks, and the market conditions pertaining to their use. This process included hearing government and industry presentations and reviewing pertinent literature. The results of this part of the study are presented in Sections II through VII. Concurrent with this research and analysis, the committee developed ten possible options that offered plausible resolutions of the problem. These ranged from maintaining the status quo to an immediate switchover from one protocol to the other. From these ten initial options three were determined to hold the greatest potential for resolving the problem. Section VIII describes the three options, Section IX provides a cost comparison, and Section X provides an overall evaluation of the three options. Section XI presents the committee's basic and detailed recommendations for how best the DOD might approach the differences between its protocol and the ISO protocol.
II. REVIEW OF NBS AND DOD OBJECTIVES The National Bureau of Standards and the Department of Defense are such disparate organizations that the committee felt it needed to begin its study with a definition of the roles and expectations of each with regard to the protocol issues in question. The following provides a review of each organization's objectives (5). NBS OBJECTIVES The National Bureau of Standards has three primary goals in computer networking: 1. To develop networking and protocol standards that meet U.S. government and industry requirements and that will be implemented in off-the-shelf, commercial products. 2. To develop testing methodologies to support development and implementation of computer network protocols. 3. To assist government and industry users in the application of advanced networking technologies and computer and communications equipment manufacturers in the implementation of standard protocols. Development of Networking and Protocol Standards The Bureau accomplishes the first objective through close coordination and cooperation with U.S. computer manufacturers and communications system developers. Technical specifications are developed cooperatively with U.S. industry and other government agencies and provided as proposals to voluntary standards organizations. Because the Department of Defense is potentially the largest government client of these standards, DOD requirements are carefully factored into these proposals. In addition, protocols for computer-to-computer communications developed within the DOD research community are used as an ----- (5) The objectives were reviewed by representatives of NBS and DOD, respectively.
exact statement of DOD functional needs for a particular protocol and form a basis for the functions, features, and services of NBS-proposed standards. To further the development of commercial products that implement standards, the NBS gives priority to the needs of U.S. computer manufacturers who wish to market their products nationally and internationally, not just to the U.S. government. The NBS participates, therefore, in national and international voluntary standards organizations toward the development of an international consensus based on United States needs. Specifications, formal description techniques, testing methodologies, and test results developed by the NBS are used to further the international standardization process. Development of Testing Methodologies The National Bureau of Standards has laboratory activities where prototypes of draft protocol standards are implemented and tested in a variety of communications environments supporting different applications on different kinds and sizes of computers. Communications environments include, for example, global networks, local networks, and office system networks. Applications may, for example, include file transfer or message processing. The primary purposes are to advance the state of the art in measurement methodologies for advanced computer networking technologies and determine protocol implementation correctness and performance. The NBS views testing as a cooperative research effort and works with other agencies, private-sector companies, and other countries in the development of methodologies. At this time, this cooperation involves five network laboratories in other countries and over twenty computer manufacturers. The testing methodologies developed at the NBS are well documented, and the testing tools themselves are developed with the objective of portability in mind. They are made available to many organizations engaged in protocol development and implementations. Assisting Users and Manufacturers The NBS works directly with government agencies to help them use evolving network technologies effectively and apply international and government networking standards properly. When large amounts of assistance are required, the NBS provides it under contract. Assistance to industry is provided through cooperative research efforts and by the availability of NBS testing tools, industry wide workshops, and cooperative demonstration projects. At this time, the NBS is working directly with over twenty computer manufacturers in the implementation of network protocol standards.
Consistent with overall goals, NBS standards developments, research in testing methodologies, and technical assistance are characterized by direct industry and government cooperation and mutual support. DOD OBJECTIVES The DOD has unique needs that could be affected by the Transport and Internet Protocol layers. Although all data networks must have some of these capabilities, the DOD's needs for operational readiness, mobilization, and war-fighting capabilities are extreme. These needs include the following: Survivability--Some networks must function, albeit at reduced performance, after many nodes and links have been destroyed. Security--Traffic patterns and data must be selectively protected through encryption, access control, auditing, and routing. Precedence--Systems should adjust the quality ot service on the basis of priority of use; this includes a capability to preempt services in cases of very high priority. Robustness--The system must not fail or suffer much loss of capability because of unpredicted situations, unexpected loads, or misuse. An international crisis is the strongest test of robustness, since the system must operate immediately and with virtually full performance when an international situation flares up unexpectedly. Availability--Elements of the system needed for operational readiness or fighting must be continuously available. Interoperability--Different elements of the Department must be able to "talk" to one another, often in unpredicted ways between parties that had not planned to interoperate. These operational needs reflect themselves into five technical or managerial needs: 1. Functional and operational specifications (that is, will the protocol designs meet the operational needs?); 2. Maximum interoperability; 3. Minimum procurement, development, and support costs; 4. Ease of transition to new protocols; and 5. Manageability and responsiveness to changing DOD requirements. These are the criteria against which DOD options for using the ISO transport and internet protocols should be evaluated.
Performance and Functionality The performance and functionality of the protocols must provide for the many unique operational needs of the DOD. The following paragraphs discuss in some detail both these needs and the ways they can impact protocol design. Survivability includes protecting assets, hiding them, and duplicating them for redundancy. It also includes endurance--the assurance that those assets that do survive can continue to perform in a battle environment for as long as needed (generally months rather than hours); restoral--the ability to restore some of the damaged assets to operating status; and reconstitution--the ability to integrate fragmented assets into a surviving and enduring network. The DOD feels that an important reason for adopting international and commercial standards is that under cases of very widespread damage to its own communications networks, it would be able to support DOD functions by using those civil communications that survive. This would require interoperability up to the network layer, but neither TCP nor TP-4 would be needed. The committee has not considered the extent to which such increased interoperability would increase survivability through better restoral and reconstitution. Availability is an indication of how reliable the system and its components are and how quickly they can be repaired after a failure. Availability is also a function of how badly the system has been damaged. The DDN objective for system availability in peacetime varies according to whether subscribers have access to l or 2 nodes of the DDN. For subscribers having access to only one node of the DDN, the objective is that the system be available 99.3 percent of the time, that is, the system will be unavailable for no more than 60 hours per year. For subscribers having access to 2 nodes, the objective is that the system be available 99.99 percent of the time, that is, the system will be unavailable for no more than one hour per year. Robustness is a measure of how well the system will operate successfully in face of the unexpected. Robustness attempts to avoid or minimize system degradation because of user errors, operator errors, unusual load patterns, inadequate interface specifications, and so forth. A well designed and tested system will limit the damage caused by incorrect or unspecified inputs to affect only the performance of the specific function that is requested. Since protocols are very complex and can be in very many "states", robustness is an important consideration in evaluating and implementing protocols. Security attempts to limit the unauthorized user from gaining both the information communicated in the system and the patterns of traffic throughout the system. Security also attempts to prevent spoofing of the system: an agent attempting to appear as a legitimate user, insert false traffic, or deny services to users by repeatedly seeking system services.
Finally, Security is also concerned with making sure that electronic measures cannot seriously degrade the system, confuse its performance, or cause loss of security in other ways. Encryption of communication links is a relatively straightforward element of security. It is widely used, fairly well understood, constantly undergoing improvement, and becoming less expensive. On the other hand, computer network security is a much newer field and considerably more complex. The ability of computer network protocols to provide security is a very critical issue. In the past decade much has been learned about vulnerability of computer operating systems, development of trusted systems, different levels of protection, means of proving that security has been achieved, and ways to achieve multilevel systems or a compartmented mode. This is a dynamic field, however, and new experience and analysis will probably place new requirements on network protocols. Crisis-performance needs are a form of global robustness. The nature of a national security crisis is that it is fraught with the unexpected. Unusual patterns of communication traffic emerge. Previously unstressed capabilities become critical to national leaders. Individuals and organizations that had not been communicating must suddenly have close, secure, and reliable communications. Many users need information that they are not sure exists, and if it does, they do not know where it is or how to get it. The development of widely deployed, interoperable computer networks can provide important new capabilities for a crisis, particularly if there is some investment in preplanning, including the higher-level protocols that facilitate interoperability. Presidential directives call for this. This will become a major factor in DOD's need for interoperability with other federal computer networks. The DOD, as one of the most affected parties, has good reason to be concerned that its network protocols will stand the tests of a crisis. In addition, there are performance and functionality features that are measures of the capability of the network when it is not damaged or stressed by unexpected situations. Performance includes quantifiable measures such as time delays, transmission integrity, data rates and efficiency, throughput, numbers of users, and other features well understood in computer networks. Equally important is the extent of functionality: What jobs will the network do for the user? The DDN has established some performance objectives such as end-to-end delays for high-precedence and routine traffic, the probability of undetected errors, and the probability of misdelivered packets. Such objectives are important to engineer a system soundly. The DOD must place greater emphasis on more complex performance issues such as the efficiency with which protocols process and communicate data. The DOD has stated a need for an effective and robust system for precedence and preemption. Precedence refers to the ability of the system to adaptively allocate network resources so that the network performance is related to the importance of the function being
performed. Preemption refers to the ability of the system to remove users (at least temporarily) until the needs of the high-priority user are satisfied. The ARPANET environment in which the protocols were developed did not emphasize these capabilities, and the current MILNET does not function as effectively in this regard as DOD voice networks. The DOD has also stated a need for connectionless communications and a broadcast mode. In the majority of network protocols, when two of more parties communicate, virtual circuits are established between the communicating parties. (For reliability, additional virtual circuits may be established to provide an in place backup.) DOD needs a connectionless mode where the message can be transmitted to one or more parties without the virtual circuit in order to enhance survivability; provide a broadcast capability (one sender to many receivers); and handle imagery, sensor data, and speech traffic quickly and efficiently. If intermediate nodes are destroyed or become otherwise unavailable, there is still a chance that the data can be sent via alternate paths. The broadcast capability is particularly important in tactical situations where many parties must be informed almost simultaneously and where the available assets may be disappearing and appearing dynamically. The Department of Defense requires an internetting capability whereby different autonomous networks of users can communicate with each other. Interoperability Presidential and DOD directives place a high priority on interoperability, which is related to the internetworking previously discussed. Interoperability is primarily important at two levels: network access and applications. To achieve interoperability at the level of network access,users of backbone communications nets must utilize the same lower-level protocols that are utilized by the network. Generally these protocols are layers 1, 2, and 3, up to and including part of the IP layer. In other words, interoperability for network access does not depend on either implementation of the transport layer (TP-4 or TCP) or of all of the internet (IP) layer. The primary advantages of network access interoperability are twofold: 1. Significant economies of scale are possible since the various users can share the resources of the backbone network including hardware, software, and development and support costs. 2. Network survivability for all users can be increased significantly since the network has high redundancy and, as the threat increases, the redundancy can also be increased. Interoperability at the applications layer allows compatible users at different nodes to talk to each other, that is, to share their data,
support each other, and thereby coordinate and strengthen the management of forces and other assets. Interoperability at the applications layer can be achieved through the use of specialized software that performs those functions of higher-layer protocols (such as TCP or TP-4, file transfer, and virtual terminal) that are needed by the particular application. If some of the higher-layer transport and utility protocols have been developed for particular hosts or work stations, their use greatly reduces development, integration, and support costs, although with a potential sacrifice of performance. Interoperability at the applications level, that is, full functional interoperability, is important to specialized communities of users such as the logistics, command and control, or research and development communities. As these different communities utilize the DDN, they have the advantages of shared network resources. Within each community there is full functional interoperability but generally there is much less need for one community to have functional interoperability with members of another community. The implementation of TCP or TP-4 within network users, but without the implementation of higher-level protocols and application interoperability, is not generally an immediate step in increasing interoperability. It does have these immediate advantages: It represents an important step in investing in longer-term interoperability. It generally represents an economical near-term investment on which communities of interest can build their own applications. It facilitates the development of devices for general network use such as Terminal Access Controllers (TACs). Interoperability at the applications level will become increasingly important among the following communities: Worldwide Military Command and Control Systems, including systems of subordinate commands; Department of Defense Intelligence Information Systems; U.S. tactical force headquarters (fixed and mobile); NATO force headquarters; other U.S. intelligence agencies; the State Department; and the Federal Bureau of Investigation and other security agencies. Although interoperability of applications within the DOD has the highest priority, it is clear that government wide and international interoperability will be an objective with increasing priority. The NATO situation is especially important (6). ----- (6) Europe has been a major force in the development of ISO standards. Consistent with this is a NATO commitment to adopt ISO standards so long as they meet military requirements.