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RFC 0942

Pages: 88
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Transport protocols for Department of Defense data networks

Part 1 of 3, p. 1 to 29
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Network Working Group                          National Research Council
Request for Comments: 942
                                                           February 1985

                        TRANSPORT PROTOCOLS FOR
                         DEPARTMENT OF DEFENSE
                             DATA NETWORKS


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

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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

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 C. CHAPIN CUTLER, Professor of Applied Physics, Stanford University,
 Stanford, California


 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,

 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

 Department, AT&T Bell Laboratories, Murray Hill, New Jersey


 RICHARD B. MARSTEN, Executive Director
 JEROME D. ROSENBERG, Senior Staff Officer and Study Director
 LOIS A. LEAK, Administrative Secretary

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 DANIEL J. FINK, President, D.J. Fink Associates, Inc., Arlington,

Past Chairman

 BROCKWAY MCMILLAN, Vice President (Retired), Bell Laboratories,
 Sedgwick, Maine


 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,

 ADRIAN M. MCDONOUGH, Professor of Management and Decision Sciences
 (Retired), The Wharton School, University of Pennsylvania, Havertown,

 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

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 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

 Department, AT&T Bell Laboratories, Murray Hill, New Jersey


 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

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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

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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

The committee wishes to thank  Philip Selvaggi of the Department of
Defense and Robert Blanc of the NBS, Institute of Computer Sciences and

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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.

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                           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


(1)  The Advanced Research Projects Agency (ARPA) was reorganized and
became the Defense Advanced Research Projects Agency (DARPA) in 1973.

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 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.


 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.)

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 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

 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.

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  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.


 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

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 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.


 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

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 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.


 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

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  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

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  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

  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

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  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.

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                            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

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

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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

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.

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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).


 The National Bureau of Standards has three primary goals in computer

  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

 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,

Top       Page 24 
  exact statement of DOD functional needs for a particular protocol and
  form a basis for the functions, features, and services of NBS-proposed

  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

  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.

Top       Page 25 
  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.


 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.

Top       Page 26 
 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.

Top       Page 27 
  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

Top       Page 28 
  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

  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.


  Presidential and DOD directives place a high priority on
  interoperability, which is related to the internetworking previously

  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,

Top       Page 29 
  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

   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.

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