
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

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                                 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













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          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




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            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


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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

 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


































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                                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
























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                                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









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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
 standard

 









-----
(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.

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.)

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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
 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.





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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.

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



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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.

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

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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.

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


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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
achieved.

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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
  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

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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
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










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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
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.

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                 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.

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  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.



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  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.


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 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.

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  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

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  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,

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  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.

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  In a somewhat longer time period, DOD will want applications
  interoperability with many commercial information services.  As
  interoperable computer networks become more common, processing and
  data services will burgeon in the marketplace.  These will include
  specialized data bases and analytic capabilities that all large
  organizations will need in order to be up-to-date and competitive.

  With regard to interoperability at the network level, DOD will want to
  be able to utilize commercially available networks for both
  survivability and operational effectiveness and economy.  In the case
  of a major war in Europe, for example, the United States would want to
  be able to use surviving PTTs (Postal, Telegraphy, and Telephony
  Ministries) for restoral and reconstitution.  During peacetime there
  will be cases where special DOD needs can be best satisfied with
  commercially available capabilities.

  As technology continues to provide less expensive, smaller, and more
  reliable data processing equipment, computer networks will become
  increasingly prevalent at lower levels of the tactical forces--land,
  air, and sea.  It will be important that these tactical networks be
  capable of interoperability with each other (for example, air support
  of ground forces) and with headquarters.  It is likely that the
  tactical network will need a network architecture and protocols that
  are different from the ARPA-\and ISO-derived protocols.  If so, the
  developments will place requirements on the higher-level DOD
  protocols.

  If the DOD chooses to move from TCP to TP-4, this can be done in
  phases for different communities of interest and subnetworks.  In this
  way if there is difficulty in converting one subnet, the rest of the
  network need not be degraded.  Also the different subnets will be able
  to make the transition at the most suitable time in terms of cost,
  risk, and the need to interoperate with other subnets.  As a result if
  DOD uses TP-4 for some new nets or major upgrade of existing nets,
  this will generally not reduce interoperability in the near term
  unless interoperability of applications is needed between two
  communities.  In this case specific interoperability needs may be
  satisfied with specialized gateways for mail or data exchange.

  The DOD points out that it desires all networks to be interoperable
  since it is not possible to predict when one community will need to
  communicate with another or use the resources of the other.  As
  previously indicated, however, unexpected needs for full functional
  interoperability can only be met when appropriate higher-layer
  software is developed.

 Minimize Costs

  The Department of Defense seeks to minimize costs of development,
  procurement, transition (if it decides to move to ISO protocols), and
  support.  Generally the objective is to limit life-cycle costs, that
  is, the total costs over a 5-to-8-year period with future costs
  suitably discounted (10 to 20 percent per year).

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  The Department of Defense has already made a heavy investment in
  protocols, and the investment has paid off in the success of current
  protocols operational in many networks.  On the other hand, the DOD
  acknowledges the potential advantages of using the ISO protocols if
  made available as commercially supported products.  Development costs
  for these protocols can be small since their development cost is
  amortized by the commercial vendor over a larger market.  Support
  costs for these protocols (including minor modifications, integration
  into other products, documentation, and training) are also
  significantly reduced because of vendor-supplied services.  These cost
  factors are further discussed in Section IX in terms of the three
  options presented in Section VIII.

 Ease of Transition and Manageability

  Networks must be manageable and capable of growth and improvement. The
  Department of Defense generally makes the fastest progress in
  developing complex information systems if it evolves these
  capabilities while working in concert with the users and the acquiring
  agencies.  In this light, the following factors are important:

   Minimal interruption of current service--For most DOD networks it is
   essential that they operate continuously.  If there is to be
   transition to new protocol services (whether based on current DOD
   versions or ISO), it is important that these transitions be planned,
   designed, and pretested so that the transition will be nondisruptive.

   Verifiability--It is essential to have a testing capability where new
   protocol implementations can be thoroughly tested to ensure that they
   will interoperate, have full functionality specified, do not contain
   errors, are robust, and meet quantitative performance needs.  The
   National Bureau of Standards has established such a capability, and
   it is being used to verify a number of TP-4 implementations,
   including those demonstrated at the National Computer Conference in
   July 1984.  An IP-testing capability is being added.  The Department
   of Defense is planning a similar protocol test facility for TCP, but
   work is just getting underway.  If the DOD plans to migrate promptly
   to TP-4, there is a question whether this investment is warranted.

   Compatibility with higher protocols--As the transport and
   lower-protocol layers evolve, it is essential that they maintain full
   compatibility with higher-layer protocols.  This is particularly
   important for the DOD because it will increasingly have
   inter-operability at the applications level.

   Responsiveness to evolving DOD needs--Current DOD needs will change
   or new needs may arise.  It is very likely, for example, that subtle
   performance problems may be discovered in a protocol that are unique
   to the strenuous DOD-operating environment and that could have
   serious operational consequences.  If the DOD is using commercial
   protocols products based upon international standards, the DOD will
   need two commitments when critical deficiencies are discovered.  It
   will need a commitment from the manufacturer that critical problems

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   will be promptly fixed and a commitment from the NBS that it will
   move quickly to change federal standards and seek changes in
   international standards.

   Minimal risks--The DOD needs are so large and important, it cannot
   afford to take otherwise avoidable risks.

   Maintenance of manageability--The DDN is new and is using a new
   approach after the cancellation of AUTODIN II (7).  There are
   pressing operational needs and many impatient users.  If the DOD
   delays in moving to ISO protocols and later decides to do so, the
   costs and disruption will be large.  On the other hand, moving now to
   ISO will be less disruptive.

  
































-----
(7)  AUTODIN II was a program to develop a data communications system
for the DOD.  The program envisioned relatively few large packet
switches.  It was cancelled in 1982 in favor of ARPANET-derived designs
because of considerations of security, architecture, survivability, and
cost.

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               III.  COMPARISON OF DOD AND ISO PROTOCOLS

This section presents a general description of the major functional
differences between the ISO and DOD protocol sets at the transport and
network layers and then discusses particular aspects of the protocols:
performance, security, and risk.

COMPARISON OF DOD AND ISO TRANSPORT LAYERS

Differences between the Defense Department's TCP protocol and the
International Standards Organization's TP-4 protocol are described in
terms of items visible to users of the protocol.  Internal differences
in mechanism that have no effect on the service seen by the user are not
considered. A second much simpler protocol, the User Datagram Protocol
(UDP), providing datagram or connectionless service at the transport
layer is also briefly considered.

In summary, the services provided by TCP and TP-4 are functionally quite
similar.  Several functions, however, including data transfer interface,
flow control, connection establishment binding, and out-of-band signals
are provided in significantly different ways by the two protocols.
Neither seems intrinsically superior, but some effort would be required
to convert a higher-level protocol using TCP to make use of TP-4.  The
exact amount of work needed will vary with the nature of the
higher-level protocol implementations and the operating systems in which
they are embedded.  A programmer experienced with the higher-level
protocols would require about six months to design, implement, and test
modifications of the three major DOD higher-level protocols (file
transfer, mail, and Telnet) to work with TP-4.

There are several areas in which the openness and lack of experience
with the TP-4 specification leave questions about just what
functionality is provided and whether incompatibilities are allowed.
These areas include connection-establishment binding, flow control,
addressing, and provision of expedited network service.  The best way to
resolve these questions seems to be to implement and test TP-4 in a
military environment and to further specify desired procedures where
there is unwanted latitude allowed by the standard (see the
recommendations section XI).

There is one area in which the NBS-proposed Federal Information
Processing Standard (FIPS) differs from the ISO specification:  The FIPS
provides a graceful closing service as in TCP, while the ISO does not.











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Data Transfer Interface

TCP is stream oriented.  It does not deliver any End of Transmission
(EOT), but accepts a "push" on the send side which has an effect much
like an EOT causes data being buffered to be sent.

TP-4 is block oriented and does deliver EOT indications.  By indicating
EOT, a sending user should be able to accomplish the same effect as
"push" in TCP in most reasonable TP-4 implementations.

The impact of this is uncertain.  Neither type of interface is
inherently better than the other.  Some applications will find it more
convenient to have a stream-type interface (for example, interactive
terminal handling), while others might prefer a block mode (for example,
file transfer).  It should be possible for TP-4 to approximate the
stream mode by forwarding data without an EOT from the sending user and
delivering data to the receiving user before an EOT is received.  Some
work would have to be done on applications using one type of protocol to
modify them to use the other.

Flow Control

TCP has octet units of allocation, with no EOT and hence no impact of
EOT on the allocation.  The segment size, Transport Protocol Data Unit
(TPDU) size, used by the protocol is invisible to the user, who sees
allocations in units of octets.

TP-4 has segment units of allocation, with a common segment size for
both directions negotiated as part of connection establishment.
Although in some implementations the protocol's flow control is not
directly visible to the users, in others it is.  In the latter case,
users of TP-4 will see allocations in units of segments and will have to
be aware of the segment size for this to be meaningful (for example, to
know that a window of four 100-byte segments seen will be consumed by
two messages of 101 to 200 bytes each).

The impact is uncertain.  Both octet and segment units of flow control
can be argued to have their advantages for different types of
application. The former makes it easy to indicate buffering limits in
terms of total bytes (appropriate for stream transfer), while the latter
makes it easy to indicate buffering limits in terms of messages
(appropriate for block mode).  The way in which flow control is exerted
over an interface is complex and one of the most performance-sensitive
areas of protocols, so a significant conversion and tuning effort would
be required to get an application used with one type of high-level
protocol to be able to perform using another.

Error Detection

TCP applies ones-complement addition checksum.  TP-4 uses an ISO




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algorithm (8).  The error-detection properties of the TCP procedure have
not been studied carefully, but the ISO algorithm is thought to be
somewhat stronger and hence allows fewer nondetected errors in data
passed to users.  It should be noted that the TCP checksum is defined to
include certain fields from the IP level including addresses so that
double protection against misdelivery errors is provided.  The practical
difference in error-detection power is probably not important.

Simultaneous Call Between Same Users

TCP will establish one call.  TP-4 will establish two calls if both
sides support multiple calls, no call if they allow only one call (that
is, see each other as busy), or in very unusual circumstances, one call.
The impact is minor since most applications naturally have an initiator
and a responder side.

Multiple Calls Between Same Addresses_

TCP allows only one call between a given pair of source and destination
ports.  TP-4 allows more than one by using reference numbers.  The
impact is minor since it is easy to generate a new per-call port number
on the calling side in most cases.  This can be a problem in TCP,
however, if both are well-known ports.

Addressing

TCP provides sixteen bit ports for addressing within a node identified
by the internet layer.  Some of these ports are assigned to well-known
applications, others are free for dynamic assignment as needed.

TP-4 provides a variable-length transport suffix (same as Transport
Service Access Point Identifier) in the call-request packet.  The use of
addresses at different levels in the ISO model has not yet been
solidified, but it seems likely that addressing capabilities similar to
TCP's will eventually be provided by TP-4 (or possibly the session
layer) along with standard addresses for common applications.

The impact is likely to be minimal, but this is an open area of the ISO
specifications that may need further definition for use by DOD.

Binding User Entities to Connections

TCP requires a prior Listen Request from a user entity for it to be able
to accept an incoming connection request.  Normally a user entity must
exist and declare itself to TCP, giving prior approval to accept




-----
(8)  For additional information, see Information Processing Systems,
Open Systems Interconnection, Connection-Oriented Transport Protocol
Specifications, ISO DIS 8073, Section 6.17, page 45.

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  a call from a specific or general remote entity.  In some
  implementations it may be possible for a nonresident user entity to
  cause a Listen Request to be posted and an instance of the entity to
  be created when a matching connection request arrives.  TCP does not
  queue an incoming connection request with no matching Listen Request
  but instead rejects the connection.

  TP-4 requires no prior request but passes a Call Indication to a user
  entity whenever a Call Request is received.  It is, however, left open
  as an implementation decision as to how TP-4 finds and/or creates an
  appropriate user entity to give the Call Indication; that is, the
  service does not include or define how user applications make
  themselves available for calls (no Listen Service Primitive).  The
  implementation guidelines indicate that well-known addresses, prior
  process existence, and Call Request queuing are all facilities that
  may or may not be provided at the implementor's choice (9).  This
  would seem to allow for different choices and hence failure to
  establish a connection between standard implementations (for example,
  caller expects requests not to be queued, while callee does queuing,
  and hence never responds).

  The practical impact is uncertain due to lack of experience with how
  the various options allowed by the TP-4 standard will be used in
  practice. TCP seems more oriented to a prior authorization mode of
  operation, while TP-4 most easily supports an
  indication-with-later-acceptance scenario. It is not clear how TP-4
  will support rejecting calls to nonexistent or inactive user entities
  and how user entities could control how many calls they would accept.
  This area may require DOD refinement.

 Out-of-Band Signals

  TCP allows the user to specify an urgent condition at any point in the
  normal data stream.  Several such indications may be combined, with
  only the last one shown to the destination.  There is no limit to the
  number of urgent indications that can be sent.  The TCP urgent
  messages are sent requesting expedited service from the network layer
  so network bottlenecks can be bypassed as well.

  TP-4 allows users to send expedited data units carrying up to sixteen
  octets of user data.  These are only half synchronized with the normal
  data stream since they may be delivered before previously sent normal
  data, but not after subsequently sent normal data.  Each expedited
  data unit is delivered to the destination, and only one can be
  outstanding at a time.  ISO has indicated its intention to allow
  transport protocols to use network-level expedited service, but this

  
-----
(9)  Specification of a Transport Protocol for Computer Communications,
Vol. 5:  Guidance for the Implementor, Section 2.11.2.  National Bureau
of Standards, Institute for Computer Sciences and Technology,
(Washington, D.C.) U.S. Department of Commerce, January 1983.

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  is not yet defined.

  The impact is primarily for applications like terminal traffic
  handlers that must deal with interrupt-type signals of various types.
  The need to read an arbitrary amount of normal data and recognize
  urgent data in the normal stream are difficulties with TCP urgent
  service, but it has been used successfully by the Telnet protocol.
  The lack of full synchronization of the signal and normal data in TP-4
  may require users to insert their own synchronization marks in the
  normal data stream [as was the case with the old ARPA Network Control
  Program (NCP)], and the limitation of one outstanding signal may be
  restrictive.  Some effort would be required to convert higher-level
  protocols using one transport protocol to using the other.

 Security

  The committee has determined that the TCP and TP-4 are sufficiently
  equivalent in their security-related properties so that no significant
  technical points favor the use of one over the other.

  The DOD protocol architecture assigns the security-marking function to
  the IP layer and provides an 11-byte security option with a defined
  coding in the IP header.

  TP-4 provides a variable-length security option carried in Call
  Request packets.  A variable-length security option field is also
  provided in the ISO IP.  Standard encoding of security markings are
  under consideration but not yet defined and accepted.

  In addition to these explicit security-marking fields, the existence,
  coding, and placement of other header fields have security
  implications. If data is encrypted, for example, a checksum is usually
  used to determine if the decrypted data is correct, so the strength of
  the checksum has security implications.

 Precedence

  TCP supports precedence by using three bits provided in IP headers of
  every packet.  TP-4 provides a 2-byte priority option in Call Request
  packets.  A 2-byte priority option in the ISO IP header is also under
  consideration.  Currently, no implementations make use of precedence
  information (to support preemption, for example).  There should be no
  impact, therefore, of changing from one protocol to the other.

 Type of Service

  The types of network service that can be requested via TCP and TP-4
  are somewhat different.  The impact seems minimal since few networks
  do anything with the type of service fields at present with the
  exception of DARPA's packet radio and satellite nets.  This may become
  more important in the future.



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 Datagram Service

  TCP provides only reliable session service.  A separate User Datagram
  Protocol (UDP) in the DOD architecture supports transaction or
  connectionless-type interaction where individual messages are
  exchanged.  UDP is merely an addition of the port-addressing layer to
  the basic datagram service provided by IP.  No delivery confirmation
  or sequencing is provided (although IP provides fragmentation and
  reassembly).

  The NBS TP-4 specification originally presented to the committee
  provided unit-data-transfer service within the same protocol framework
  as sessions (10).  This material has since been deleted to bring the
  NBS proposal into conformance with ISO work.  A separate ISO datagram
  protocol similar to UDP has been defined and is expected to become a
  draft proposed standard in June 1984.

 Closing

  TCP provides a graceful closing mechanism that ensures that all data
  submitted by users are delivered before the connection is terminated.
  The NBS TP-4 provides a similar mechanism, but is not included in the
  ISO standard TP-4, which provides only an immediate disconnect
  service.  Impact is significant if the ISO version is used because
  users would then have to add their own graceful termination handshake
  if desired.

COMPARISON OF DOD AND ISO INTERNET LAYERS

 The internet protocols of DOD and ISO are much more similar to one
 another than the transport protocols.  This is not surprising since the
 Defense Department's IP was used as the basis for the International
 Standards Organization's IP.  Some reformatting, renaming, and recoding
 of fields has been done.  Hence not only are the services to higher
 layers essentially equivalent, but the protocol mechanisms themselves
 are also nearly identical.  Due to the format changes, however, the two
 protocols are incompatible.

 It should be noted that the IP itself forms only part of the internet
 layer.  For clarity it should also be noted that the internet layer in
 ISO is considered to be the top sublayer within the network layer.

 In DOD, there is an additional Internet Control Message Protocol (ICMP)
 that deals with error conditions, congestion control, and simple
 routing updates to host computers.  There is also a Gateway-to-Gateway
 Protocol (GGP) that deals with internet management and routing updates
 for gateways.  In the ISO, only the IP itself has so far been

 
-----
(10)  National Bureau of Standards, Specification of a Transport
Protocol for Computer Communications, Vol. 3, Class 4 Protocol,
ICST/HLNP-83-3, February 1983.

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 considered, while most error reporting, control, and routing functions
 are considered "management" functions that remain to be addressed in
 the future.

 The only significant differences in the IPs themselves are in the areas
 of addressing and error reporting.  The DOD IP has a fixed-length,
 32-bit source and destination addresses (identifying network and host)
 plus an 8-bit "protocol number" field to identify the higher-level
 protocol for which the IP data is intended.  The ISO IP has
 variable-length source and destination addresses whose format and
 content are not yet specified, although preliminary documentation
 indicates that ISO intends to support a similar level of addressing
 (network/host) in a more global context which would allow use of
 current DOD addresses as a subset.  There is no equivalent of the DOD
 protocol number field, although possibly the tail of the
 variable-length ISO addresses could be used for this purpose.

 Error reporting is provided within the ISO IP by means of a separate
 packet type, while the DOD provides more complete error- and
 status-reporting functions via the separate Internet Control Message
 Protocol (ICMP), including routing "redirect" messages to hosts that
 have sent datagrams via nonoptimal routes.

 In summary, from the functional point of view, DOD and ISO IP can be
 considered essentially equivalent with the provision that the
 ISO-addressing scheme is suitably resolved.  The absence of routing and
 control procedures from the ISO internet layer means that additional
 procedures beyond IP would be needed to produce a complete,
 functioning, internet even if the ISO IP were adopted.  It appears that
 the existing DOD ICMP and GGP or its successors could be modified to
 operate with the ISO IP with modest effort, but this requires further
 study and validation in an operational system.

 A table at the end of this chapter compares DOD and ISO IP packet
 formats.

COMPARISON ON THE BASIS OF PERFORMANCE, SECURITY, AND RISK

 Performance

  The performance of a transport protocol, such as TCP or TP-4, is a
  function of its implementation as well as its inherent design.
  Experience in implementing TCP and other proprietary protocols has
  demonstrated that implementation considerations usually dominate.
  This makes it difficult to compare protocols, since a wide range in
  efficiency of implementations is possible.  Furthermore, there are a
  number of dimensions along which an implementation can be optimized.

  Despite the difficulties, protocol designers have developed several
  metrics for comparing transport protocols.  These view protocol
  performance from a variety of perspectives, including  (1) user
  response time, (2) throughput on a single connection, (3) network and
  host computer resource utilization.  Protocol efficiency can also be

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  significantly affected by the communications environment.  Protocol
  efficiency must be considered in a wide range of communication
  environments, including local area networks, satellite links,
  terrestrial links, and packet-switched networks.

  The critical algorithms most affecting protocol performance are those
  that perform end-to-end error control and end-to-end flow control.
  These algorithms affect the response time, throughput, and resource
  utilization of the protocol during the data transfer phase.  The
  efficiency of the connection management procedures may also be
  important in applications involving frequent connections of brief
  duration.

  The committee compared the algorithms and message formats specified
  for each protocol for critical functions, including flow-and
  error-control and connection management.  They concluded that since
  the two protocols were sufficiently similar there would be no
  significant difference in performance of TCP or TP-4 implementations
  of equal quality optimized for a given environment.

  The committee compared the error-and-flow-control algorithms of TCP/IP
  and TP-4.  Both employ window-based techniques using large-sequence
  number spaces and both permit large window sizes.  Their differences
  are minor. TCP performs its error-and-flow-control in units of octets,
  rather than the protocol data units employed by TP-4.  This adds a
  small amount of overhead to TCP calculation in return for a finer
  control over host buffer memory.  The committee did not consider the
  difference significant, assuming that appropriate buffer management
  strategies are implemented by transport and higher-level protocols.
  TP-4 employs more sophisticated techniques to ensure that flow-control
  information is reliably transmitted than does TCP.  These more
  sophisticated techniques may reduce TP-4 protocol overhead during
  periods of light load in some applications, possibly adding slightly
  more CPU load in other cases.  The committee did not consider these
  effects significant.

  Both protocols employ a three-way handshake for establishing a
  transport connection.  The differences between the TCP and TP-4
  handshake are related to the addressing conventions employed for
  establishing connections and do not affect protocol efficiency.  In
  the common cases where a client process requests a connection to a
  server process, the TCP and TP-4 operations are equivalent.

  Both protocols permit a range of policy decisions in their
  implementation. These include (1) selection of timer values used to
  recover from transmission errors and lost packets, (2) selection of
  window sizes at the receiver and transmitter, and (3) selection of
  protocol data unit sizes.  Both permit substantial reduction in
  control message overhead by expanding window sizes.  Both permit
  credits to be granted "optimistically," permitting receiver buffers to
  be shared over several transport connections and permitting credit
  reduction in the event of buffer congestion. Both permit optimizing
  protocol efficiency by delaying control message traffic when it does

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  not need to be transmitted, combining it with later data or control
  traffic.

  The most significant difference between TCP and TP-4 flow control
  derives from slight differences in expression of flow control at the
  transport layer service interface.  TCP employs a stream model while
  TP-4 uses a message model.  These two models are equivalent in
  function; however, some higher-level applications protocols may be
  more naturally expressed in one model than the other.  The committee
  considered the possibility that current ARPA protocols might require
  some adaptation to operate more efficiently with TP-4.  For this
  reason the committee recommends that the DOD study the operation of
  current DOD higher-level protocols on TP-4 (recommendation 5, Chapter
  XI).

 Security

  The committee considered the impact of security requirements on
  transport protocols primarily and also on overall protocol hierarchies
  in the DOD, The American National Standards Institute (ANSI), and ISO.
  Based on the information the committee received, it finds that:

   The current TCP-4 and TP-4 are sufficiently equivalent in their
   security-related properties that no significant technical points
   would favor the use of one over the other.

   There is no technical impediment to their equivalent evolution over
   time in the security area.

 Risk

  There are several risks in implementing a new protocol or protocol
  family.  These include (1) fatal flaws in protocol design not easily
  rectified, (2) errors in protocol specification, (3) ambiguities in
  protocol specification, (4) errors in protocol implementation, (5)
  performance degradation due to inefficient implementation, (6)
  performance degradation due to "untuned" implementation, and (7)
  performance degradation due to untuned application protocols.

  This list of risks comes from experience in implementing computer
  networks based on the DOD protocols and proprietary commercial
  protocols. Considering that it took more than ten years for the
  current TCP protocols to reach their current state of maturity and
  that the TP-4 protocol is only about two years old, the committee
  devoted considerable attention to the maturity of TP-4.

 Fatal Flaws in Protocol Design

  Early ARPANET protocols had a number of "fatal" design errors that
  resulted in deadlocks or other serious system failures.  Commercial
  networks had similar problems in early design phases.  The committee
  considered the possibility that TP-4 could suffer from similar faults
  and concluded that this was unlikely.  TP-4 employs design techniques

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  similar to those of TCP and proprietary transport protocols.  The
  faults encountered in the ARPANET are now well known.  Indeed, the
  state of the art in transport protocol design is now quite mature.
  The developers of the TP-4 protocol were familiar with the earlier
  protocols and their problems.

 Errors and Ambiguities in Protocol Specification

  Early in the development of TP-4, NBS developed a formal protocol
  specification and a test environment based on this specification.  A
  protocol implementation can be partially compiled automatically from
  the formal specification.  Other implementations can be tested against
  this master implementation.  The NBS protocol laboratory was used to
  debug the formal specification of TP-4 and is currently being used to
  certify other implementations of TP-4.  The laboratory has also
  developed and employed tools to analyze the specification for possible
  problems.  The existence of this laboratory and the results obtained
  to date led the committee to conclude that there is no substantial
  risk associated with the TP-4 protocol specification.

  In contrast TCP has only recently received a formal specification. To
  the committee's knowledge most existing TCP implementations predate
  the formal TCP specification and have not been derived from the formal
  specification.  In the committee's opinion the formal TCP
  specification is likely to have more bugs or ambiguities than the TP-4
  specification.

  At the present time NBS has developed the only formal specification
  for ISO TP-4.  ISO is currently developing standards for formal
  specification techniques that are similar to those used by NBS.  When
  these specifications are complete ISO will update the TP-4
  specification to include a formal description.  In translating the
  current informal ISO specification into the formal specification there
  is a risk that the ISO specification may be changed such that it is no
  longer consistent with the current NBS specification.  The National
  Bureau of Standards is playing a key role in developing the ISO formal
  specification techniques and formal specification.  It plans to
  generate automatically an implementation of the ISO formal
  specification and verify it against the NBS specification using the
  NBS test tools.  In the committee's opinion this makes the risk of
  unintentional changes in the ISO specification quite low.

  One possible risk remains.  The ISO specification for TP-4 that was
  approved is an informal document subject to the ambiguities of
  informal protocol specifications.  The formalization may remove
  ambiguities that have gone undetected and that were the basis of its
  approval.  It is conceivable that once these ambiguities are exposed,
  the current consensus for TP-4 may dissolve.  The committee considers
  this risk to be very low. The areas of ambiguity in protocol
  specifications are typically only of concern to protocol implementors.
  The current protocol implementors through much of the world are
  typically using the NBS formal specifications as a basis of their
  implementations of TP-4 and have access to the NBS test tools for

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  certifying their implementations.  In the event of a possible
  conflict, the majority of implementors could be expected to support
  resolution of ambiguities in favor of the current NBS formal
  specification, making it unlikely that ISO would approve an alternate
  resolution.

 Errors in Protocol Implementation

  Several factors influence the likelihood of errors in a protocol
  implementation.  These include the complexity of the protocol, quality
  of the protocol specification, the experience of the implementors, and
  the availability of test tools.  Based on the availability of the NBS
  test tools and formal protocol specification for TP-4, the committee
  did not see any significant risk of errors in implementing TP-4.

 Performance Issues

  The largest risk in implementing TP-4 concerns the performance of the
  implementations.  This risk is not inherent in the protocol as
  specified, but is present in new implementations of any transport
  protocol.  Experience has shown that performance can often be improved
  by a factor of two or more by careful attention to implementation
  details and careful performance measurement and tuning.  The committee
  considered it likely that some initial implementations of TP-4 will
  have significantly lower performance than the current mature
  implementations of TCP.  Evidence to support this conclusion may be
  found in data supplied by the DOD which show a wide range of
  performance of TCP implementations.

  Some members of the committee expressed the belief that over the long
  term, TP-4 will afford better performance due to widespread commercial
  support.  Vendors will be highly motivated to optimize performance of
  their TP-4 implementations, since a large number of users will
  benchmark implementation performance.  Many individuals will become
  familiar with implementations of TP-4 and with configuring and
  operating networks based on TP-4.  Initially, this expertise will be
  found in organizations developing TP-4 implementations and
  installation.

  The committee believes that the largest performance risks are short
  term.  The performance of existing DOD high-level protocols may be
  affected by subtle differences between TP-4 and TCP interfaces.
  Highlevel DOD implementations and protocols may require retuning to
  attain some high-level efficiency using TP-4.  Another short-term risk
  is potential lack of experience in configuring and operating
  TP-4-based networks.  The committee believes that a program of testing
  and development would minimize these risks, ensuring that the current
  high-level DOD protocols run effectively on TP-4-based networks.

  There is a possibility that the equivalent, but different, protocol
  mechanisms and interfaces in TP-4 may manifest some undesirable
  behavior that is not expected and which cannot easily be removed by
  tuning.  In this event ISO may find it necessary to make some

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  modifications to TP-4. It is unlikely that such problems will be
  serious enough to prevent an early transition to TP-4.  If such
  problems are discovered, it is expected that they can be handled
  through the normal standards process of periodic enhancement.  A
  number of proprietary commercial networking protocols are similar in
  operation to TP-4 and do not have serious performance problems. Any
  enhancements that may be desirable can probably be added to TP-4 in a
  compatible fashion, permitting interoperation of enhanced and
  unenhanced implementations.

TABLE:  Comparison of DOD and ISO IP Packet Formats

 DOD                               ISO (not in correct order)
 ----------------------------------------------------------------------

 Protocol version:  4 bits         Version:  8 bits
 Header Length (in 32-bit words):  [Header] Length (in bytes):  8 bits
    4 bits
 Type of service:  8 bits          Quality of service**:  8 bits
    (includes 3-bit Precedence)    Precedence**:  8 bits
 Total Length:  16 bits            Segment Length:  16 bits
 ID:  16 bits                      Data Unit ID*:  16 bits
 Don't Fragment flag               Segmentation Permitted flag
 More Fragments flag               More Segments flag
 Fragment offset:  13 bits         Segment offset*:  16 bits
 Time to live (sec):  8 bits       Lifetime (.5 sec):  8 bits
 Protocol number:  8 bits          ---
 Header checksum:  16 bits         Header checksum:  16 bits
    (provided by subnet layer)     Network Layer Protocol ID:  8 bits
 ---                               [Generate] Error flag
 (in ICMP)                         Type:  5 bits
 ---                               Total Length*:  16 bits
 .............                     .............
 Source address:  32 bits          Source address length:  8 bits
                                   Source address:  var.
 Dest. address:  32 bits           Dest. address length:  8 bits
                                   Dest. address:  var.
 .............                     .............

 OPTIONS: NOP, Security,           OPTIONS: Padding, Security
 Source Route, Record Route,       Source Route, Record Route,
 Stream ID, Time Stamp             Quality of service, Precedence,
                                   Error reason (only for error type)
 .............                     .............
 DATA                              DATA
 ......................................................................

  *  only present if segmentation is in use
  ** in options





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 IV.  STATUS OF DOD AND ISO PROTOCOL IMPLEMENTATIONS AND SPECIFICATIONS

DEPARTMENT OF DEFENSE

 The DOD internetting protocol was first introduced in 1974 and later
 split into separate TCP and IP specifications.  From 1974 until 1978,
 when they were adopted as DOD standards, the protocols underwent a
 number of major revisions.  These revisions were largely a result of
 extensive experience gained by researchers working on the DARPA
 Internet project. The DARPA "Request for Comment" and "Internet
 Experimental Note" technical report series document the conclusions of
 numerous protocol-related studies and discussions.  Successive
 specifications of TCP and other internet protocols are also given by
 reports in these series.  Most of these specifications were informally
 presented and were accompanied by discussions that affected design
 choices.  The most recent TCP documents introduce a more formal style
 of presentation (11).

 The first experimental TCP implementations were completed in 1974 at
 Stanford University and Bolt Beranek and Newman, Inc., for the
 PDP-11/ELF and DEC-10/TENEX systems, respectively.  Today
 implementation exists for numerous computer systems.  While many of
 these were implemented at and are supported by university and other
 research groups, several are available as commercial products.

 Testing of TCP was done on the ARPANET (12), other DOD networks
 (Satellite net, packet radio), and a variety of local networks. For
 several years a number of DARPA contractors used TCP in parallel with
 the old ARPANET transport protocol (NCP).  In addition, for about six
 months preceding the January 1, l983, ARPANET cutover from NCP to TCP,
 these hosts were joined by additional TCP-only hosts (for a total of
 approximately thirty).  This extensive testing prior to the cutover to
 TCP enabled the networks involved to maintain operational capability
 throughout

 







-----
(11)  Transport Control Protocol, DOD MIL-STD-1778, August 1983.

(12)  The ARPANET is a data communications network established in 1969
by the DOD's Advanced Research Projects Agency to interconnect the
computer resources at selected research centers at substantially lower
costs than systems then available.  The ARPANET is a fully operational
80-node network that interconnects over 200 host computers in the United
States, the United Kingdom, and Norway.  ARPA became the Defense
Advanced Research Projects Agency (DARPA) in 1973.

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 the transition and to achieve normal service levels in a few months.
 Today the TCP-based DOD networks includes hundreds of hosts (over 300
 on DDN alone) and serves thousands of users.  Traffic on just the
 ARPANET component is now approximately 500 million packets per month.

 TCP is also extensively used on local area networks including Ethernet
 and Pronet, as well as on CSNET, the Computer Science Research Network
 (Telenet hosts).

 In addition to TCP, the DOD protocol architecture includes internet
 layer protocols for communication between hosts and gateways (ICMP) and
 between gateways (GGP).  Experience indicates that the design of robust
 and powerful gateways that internet numerous networks and provide
 survivability is a complex challenge.  DOD is developing new gateway
 protocols that could be adapted to work with either DOD's or ISO's IP.

 The higher-level protocols currently used on DDN for electronic mail
 (Simple Mail Transfer Protocol), file transfer (File Transfer
 Protocol), and remote log-in (Telnet) are TCP-specific.  Their
 specifications are stable, and numerous implementations exist.  The DOD
 has indicated its intent to adopt ISO higher-level protocols when they
 are specified and implementations are available.

 The committee has concluded that the DOD transport and internet
 protocols are well tested and robust.  It is unlikely that major
 problems with their design or specifications will be uncovered.  No
 comprehensive facility or procedures for testing new implementations of
 TCP now exist, although efforts in this area are being started at
 Defense Communications Agency (DCA).

INTERNATIONAL STANDARDS ORGANIZATION

 Standardization and development of the ISO IP and ISO TP-4 are
 proceeding in a relatively independent fashion.  Currently, TP-4 is
 further along in the standardization process.  The local area network
 communications environment has created an immediate need for TP-4
 functions; however, communications within a single Local Area Network
 (LAN) do not need an internet capability.  A "null" IP has been defined
 to enable TP-4 to be used on a single LAN without the necessity of a
 complete IP.  It is quite likely that some early TP-4 products will
 implement this null IP, leaving implementation of the complete IP for
 future product development. In the following discussion, TP-4 and IP
 will be treated separately due to this potential independence.

 TP-4 Status and Plans

  The ISO TP-4 became a Draft International Standard in September 1983.
  The final stages in standardization are primarily procedural.  The
  committee expects products that implement TP-4 to be widely available
  in the market within about two years.  It normally takes twelve to
  eighteen months for implementations and testing prior to product
  announcement. Some vendors apparently began implementation and testing
  the protocol

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  soon after it became a draft proposal in June 1982, because the
  protocol was essentially frozen at that time.

  At present, INTEL and Able Computer have announced the availability of
  products that implement TP-4 for use over LANs.  The committee does
  not know, however, whether these products have been delivered or
  incorporated into systems.  In addition, more than twenty companies
  have indicated their support of TP-4 and their intention to
  incorporate TP-4 into future products, without announcing specific
  products or availability dates.  Most companies do not make specific
  product announcements until relatively late in the product development
  process.

  In December 1982 six vendors and network users interested in early
  development of TP-4 products requested NBS to hold a series of
  workshops on the operation of TP-4 in a LAN environment.  To date,
  four workshops have been held, with more than thirty companies in
  attendance.  The first workshop set a goal of demonstrating
  multivendor networking at a major U.S. national computer conference.
  The second workshop, held in April 1983, determined that
  demonstrations would include a file transfer application and would be
  developed on two local area network technologies currently
  standardized by the Institute of Electrical and Electronics Engineers
  (IEEE).  These technologies are the Carrier Sense Multiple Access with
  Collision Detection, which is standardized by IEEE committee 802.3,
  and the Token Bus, which is standardized by IEEE committee 803.4.  The
  workshop selected the National Computer Conference in July 1984 for
  the demonstrations.

  Vendors committed to the demonstration developed and tested TP-4
  implementations using the NBS test tools.  The workshops defined a
  schedule that called for individual testing through April 1984 with
  multivendor testing commencing thereafter.  While the vendors that
  participated in the demonstration have emphasized that participation
  in the demonstration is not a commitment to product development, a
  number of large customers have indicated that there will be an
  immediate market demand for TP-4 implementation as soon after the
  demonstration as practical.  The committee considers it highly likely
  that many commercial vendors will announce commitments to deliver TP-4
  products shortly after the demonstration.

 Internetwork Protocol Status and Plans

  The ISO Internetwork Protocol (IP) became a Draft International
  Standard (DIS) in May 1984 (13).  The DIS was out for ballot for the
  previous eight months.  Attaining DIS status freezes the technical
  approach, permitting implementations to begin.

  
-----
(13)  ISO Draft Proposal, Information Processing Systems -- Data
Communications -- Protocol for Providing Connectionless Network
Services, DP 8473, May 1984.

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  The ISO IP specification is only one of several specifications needed
  to completely specify the Network Layer.  A number of other
  specifications are needed, including a Gateway-to-Host error protocol,
  a network wide addressing plan, and a Gateway-to-Gateway Protocol for
  managing routing information.  A complete specification is needed
  before an internetwork, consisting of gateways and hosts, can be
  deployed.  Most of the complexity of the Network Layer, however, is
  confined to the gateways.  A complete standardization of the Network
  Layer is not required to develop and deploy host systems.

  The International Standards Organization is currently developing
  proposals for conveying error information between hosts and gateways.
  It is expected that responses to the Draft Proposal by ISO members
  will include proposals to provide these functions.  The committee does
  not consider this a controversial area and expects that these
  capabilities will be included in the ISO standard by the time it
  reaches Draft International Status.

  Addressing is a more complex issue.  The addressing structure of a
  computer internetwork depends on complex trade-offs between
  implementation complexity, flexibility, network cost, and network
  robustness.  Addressing structure in a large network can influence the
  range of possible policy decisions available for routing network
  traffic.  The trade-offs for a military environment may be
  significantly different from those of a commercial environment.  The
  ISO has considered these factors in its existing IP.  A flexible
  addressing scheme is provided, permitting implementation of a variety
  of addressing structures.  Host computers need not be concerned with
  the internal structure of addresses.  The committee considers that the
  IP-addressing scheme has sufficient flexibility that host
  implementations can be constructed that will support the full range of
  addressing philosophies allowed by ISO, including those needed by DOD.

  Routing algorithms, like addressing, are complex and often
  controversial. For this reason ISO has not yet attempted
  standardization of routing algorithms.  A routing algorithm is a key
  part of a Gateway-to-Gateway Protocol.  A single network must
  implement a common routing algorithm.  In the absence of an ISO
  routing algorithm, a network must be based on either proprietary
  routing algorithms or on other standards.

  The committee has studied the current ISO IP and the current ISO
  addressing structure.  It believes that it will be possible to map the
  current DOD IP-addressing structure and routing algorithm into the ISO
  network layer.  In practice this means that the Gateway-to-Host
  Protocols and addressing formats will fully comply with the ISO
  standards, while gateways will need to include additional DOD
  capabilities.  (This is addressed in recommendations, section IX.)
  This approach will enable DOD to procure commercial host
  implementations, while retaining the need for procuring DOD-specific
  gateways.  The committee believes these hybrid DOD-ISO gateways can be
  readily developed by modifying existing DOD gateway implementations.
  Since the majority of systems in a network are hosts and not gateways,

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  the committee considers this approach worthwhile.

  To the committee's knowledge no vendor has yet announced plans to
  support the ISO Internetwork Protocol.  This is not surprising, since
  the ISO IP attained Draft Proposal status only recently.  The
  committee has considered the possibility that the ISO IP may not
  attain the same wide level of market demand and vendor support
  anticipated by TP-4.  Since host support of IP is necessary for DOD to
  migrate to ISO protocols, the committee has considered this question
  in some depth.

  While it is possible to operate TP-4 directly over a LAN or directly
  over an X.25-based, wide-area network, some form of internetwork
  capability or alternative approach is needed to interconnect systems
  attached to multiple LANs via Wide Area Networks (WANs).  In the
  current ISO open systems architecture, this function is to be provided
  by the Network layer. There are two possible Network layer services,
  connectionless and connection oriented.  The ISO architecture permits
  both of these services, leaving it to the market place to determine
  which approach is to be selected.  The DOD believes that the
  connectionless approach best suits their needs.

  Developing a connection-oriented network that operates over a mixed
  LAN and WAN environment is considerably more difficult than developing
  a connectionless one.  Existing LANs are inherently connectionless and
  existing (X.25) WANs are inherently connection oriented.  A protocol
  to provide internetwork service between these LANs must arrive at a
  common subnetwork capability.  It is a relatively simple matter to
  adapt a connection-oriented to a connectionless service since it can
  be done by ignoring unneeded functions of the connection-oriented
  service.  Adapting a connectionless subnetwork to the needs of a
  connection-oriented network service is much more difficult.  Many of
  the functions provided by TP-4 would be needed in the network layer to
  build such a service.

  Some work is currently going on in European Computer Manufacturer's
  Association (ECMA) to interconnect WANs and LANs in a
  connection-oriented fashion.  There is considerable controversy
  surrounding several proposals, since some participants in the
  standards process do not believe the proposals conform to the ISO
  Reference Model for Open Systems Interconnection. This, plus their
  complexity, makes it unlikely that a connection-oriented network
  standard will gain support in ISO in the immediate future.

  There is an immediate need for users to build networks consisting of
  interconnected LANs and WANs.  Such networks are currently in place
  using vendor proprietary architectures.  Market pressures to build
  multivendor LAN and WAN networks make it quite likely that vendors
  will adopt the immediate solution and implement the connectionless ISO
  IP.  The committee believes that DOD can enhance the early
  availability of ISO IP by announcing its intention to use it.
  Commercial availability of IP is an important part of a migration
  strategy, as described in the section on recommendations. The

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  committee believes that vendors would be responsive to DOD requests
  for IP, since IP is quite simple to implement in comparison with TP-4
  and since they foresee the need to operate in mixed LAN-WAN
  environments.


















































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                              V.  MARKETS

The committee reviewed the market demand and its potential with respect
to both TCP and TP-4 to provide an indication of the likelihood and
rapidity with which competition and its benefits will develop.  The
committee concludes that the market demand for TCP protocols will be
small outside the United States.  The demand for TP-4, on the other
hand, is expected to be worldwide.

In this report we use the term market demand to indicate the potential
or actual demand for products using the protocols under discussion.  A
large market is characterized by a broad demand from all sectors of the
marketplace:  consumers, businesses, and governments.  The broadest
demand is an international demand in all sectors.  We distinguish the
demand for products from the supply that usually develops as a result of
the demand. It is assumed here that a broad market demand will result in
a broad range of products, competitive in price, quality, function, and
performance.

The demand for products implementing computer communication protocols is
discussed in relation to the requirements placed on the potential
customer. Specifically, the customer may be required to acquire products
that meet one or the other of the standards under discussion or may have
no obligation to use either of the two.  That is, customers will fall
into one of the following classes with respect to these standards:

 1.  DOD standards required.

 2.  International or National standards required.

 3.  No requirement with respect to standards.

Although customers in the third class may be under no formal obligation
to use standards, they may still prefer a standard solution for several
possible real or perceived benefits.  They may, for example, obtain a
broader selection of products using the standard solution or may obtain
a more competitive price.  They may also require a specific
communication protocol in order to share information with products that
are required by fiat to implement certain standard protocols.  This need
for compatible protocols to communicate is a powerful driving force
toward communication standards.

DEPARTMENT OF DEFENSE NETWORKS MARKET STATUS AND PLANS

 The major networks of the Defense Data Network include the following:









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  Military Network (MILNET)--operational and growing.

  Advanced Research Projects Agency Network (ARPANET)--operational and
  growing.

  WWMCCS Intercomputer Network (WIN)--to be upgraded.

  DOD Intelligence Information System (DODIIS)--to be upgraded.

  Strategic Air Command Digital Information Network (SACDIN)--to be
  upgraded.

  Movement Information Network (MINET)--to be established in 1984.

  Sensitive Compartmented Information (SCI) net--to be established in
  1985.

  TOP SECRET (TS) net--to be established in 1985.

  SECRET net--to be established in 1986.

 Initially, each of these networks has its own backbone.  The networks
 will be integrated into a common Defense Data Network in a series of
 phases starting in 1984 with the integration of MILNET and MINET.  It
 is planned that by 1988 they will all be integrated but communities of
 interest will operate at different security classifications
 interconnected with Internet Private Line Interfaces (IPLIs).  When
 appropriate technology becomes available in the late 1980s, the network
 will have the capability for multilevel security, including end-to-end
 encryption, and will achieve interoperability between all users.

 The following observations are relevant to the TCP and TP-4 issue:

  The DOD currently has two major networks, MILNET and ARPANET,
  currently comprising the DDN.  About sixty subnets and hundreds of
  hosts are internetted and most use TCP.

  This year a European network, MINET, will be activated and integrated
  into the DDN.  It uses TCP.

  In the second half of 1983, fifteen additional subscribers have been
  added to MILNET and current planning estimates hundreds more
  additional subscribers in 1984 and 1985.

  For the many DDN users that are, or shortly will be, interconnected
  over common backbones, there are groups of users that need
  interoperability within the group.  These groups are determined by the
  military department they are part of as well as by functions such as
  logistics, maintenance, training, and many others.

  The Air Force and the Army are both committed to the use of TCP for
  some of their networks or subnetworks (including Local Area


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  Networks) and active acquisition programs are underway, or will be
  initiated, during the next twelve to eighteen months.

  The DDN Program Office has procured, or shortly will procure, devices
  to facilitate terminal and host access to DDN hosts and terminals.
  These devices employ TCP.

  NATO has discussed protocol standards and has selected ISO as an
  approach, subject to its being adapted to meet military requirements,
  if such adaptation is necessary.  There is no definitive planning
  underway, however, to develop a NATO computer network.

  The Mail Bridge that will allow traffic to pass between the classified
  segment and the unclassified segment will use TCP and is scheduled for
  a 1987 Initial Operational Capability (IOC).

  In general, the backbone in the various networks provides functions at
  layers below TCP and TP-4.  As a result a backbone (such as MILNET)
  could support users of either protocol set.  The users of one set
  could not, however, interoperate with the users of another unless
  additional steps are taken.

 In summary, there is a large TCP community operational today and the
 community is growing rapidly.  In addition, there are, or shortly will
 be, procurements underway that plan to use TCP.  The rate of growth
 cannot be precisely estimated in part because of uncertainties in
 demand and availability of trunks and cryptographic equipment.  On the
 other hand, interconnection of several major networks will not take
 place until 1987 or later; and for those elements that are
 interconnected, there are many groups of users that primarily require
 interoperability with each other.

 System Descriptions

  MILNET is a network for handling the unclassified operational data of
  the DOD.  It was created after the decision in 1982 to cancel the
  AUTODIN II system by dividing the ARPANET into two nets, MILNET and
  ARPA Research Net.  The majority of the capacity of ARPANET was
  assigned to MILNET, and the number of subscribers is growing rapidly.
  The network backbone does not require the use of TCP but its use is
  generally mandated for subscribers. To achieve TCP functions, the DDN
  will procure some interface devices and thereby take the burden off
  some subscribers.

  ARPANET supports most of the research organizations sponsored by
  DARPA.  It generally uses TCP but some users continue to use NCP.

  MINET is a European network scheduled for Initial Operational
  Capability (IOC) in 1984 to handle unclassified operational traffic,
  mostly logistical, and tie into the MILNET.  It will have 8 nodes, 8
  TACs, and 3 hosts to process electronic mail.  These hosts and others
  to be added to the net will use TCP and the File Transfer Protocol
  (FTP).

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  The Department of Defense Intelligence Information System currently
  uses a home-grown protocol.  Sometime after 1984 its plans are to
  upgrade it to TCP.  It will be a 3-node, 3-host net with plans to
  upgrade it to 20 to 30 nodes and about 50 hosts.  The net is run at a
  high-security level (SCI) for communicating compartmented data.  The
  SCI network consists of those users of SCI who are outside of DODIIS.

  SACDIN is an upgrade of the digital communications system of the
  Strategic Air Command.  The IOC is planned for about 1985.  At
  present, TCP is not planned initially as a protocol.  SACDIN will
  operate with multilevel security up to Top Secret sensitive
  information.

  WIN is the WWMCCS Information Network.  It is currently operational
  and uses NCP as a transport protocol. There is a major effort underway
  to modernize the WWMCCS, including upgrading or replacing current
  computers, providing Local Area Networks at major centers throughout
  the world, and providing common software packages for utilities and
  some applications. The upgrading of the transport protocols is part of
  this effort.  Schedules are still uncertain but there is a target of
  1986 for the protocol upgrading.

  TOP SECRET is a network that will support top secret users other than
  WIN and SACDIN.

  SECRET net is a network that will operate at the Secret level.  It
  should be very useful for a large community that does not routinely
  need top secret or compartmented information.  This is a community
  primarily outside the command and intelligence communities and
  includes missions such as logistics, procurement, and research and
  development.  DOD will start the system as soon as there is sufficient
  cryptographic equipment; by 1986 they hope to have a 90-node network
  with several hundred subscribers.

  The Army plans to establish a Headquarters Net tying together major
  headquarters with an IOC of 1986.  It will use TCP.

  The Air Force has established a Program Office to help in the
  development of Local Area Networks at major Air Force installations.
  These could be internetted using the DDN and thereby also gain access
  to other nodes. TCP has been mandated.  Initial procurements are
  underway.

  Mail Bridge will provide gateways between ARPA Research Net and other
  elements of the DDN.  These would use TCP and are scheduled for IOC in
  1987.

  During 1984 the DDN is procuring two capabilities that will facilitate
  use of the network and higher-level protocols.

  The first capability will be provided shortly by Network Access
  Controllers (NAC).  The NACs provide three elements all based on TCP:


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   1.   Terminal Access Controllers (TACs) allow a cluster of terminals
        to access hosts on the DDN.  Many are in operation today as a
        legacy of the ARPANET developments.  New ones will be
        competitively procured.

   2.   Terminal Emulation Processes (TEP) allow the connection of a
        high-capacity host to the DDN through a number of terminal-like
        lines.

   3.   Host Front-End Processors (HFP) allow high-capacity host
        connection to the DDN through use of a Network Front End that
        off loads much processing capacity from the host.

  The second capability will be provided by software the DDN is
  currently procuring for up to seventeen families of specific
  combinations of hosts and their commercially available operating
  systems.  The software packages will include 1822 or X.25, TCP, and
  utility protocols for terminal access, mail, and file transfer.
  Initial operational capability is planned for late 1985.

 Integration

  MINET will be connected to MILNET in 1984.  This will be an
  unclassified network.

  WIN, DODIIS, SECRET, and SACDIN will be integrated as a classified
  network in 1987 at the earliest.  Since they all operate at different
  security levels, they will be able to use the same DDN backbone but
  will be cryptologically isolated.

  Integration and interoperability of all the networks will not be
  possible until the late 1980s at the earliest, since this will require
  successful implementation of an advanced technology for end-to-end
  cryptological networking and the development of techniques for
  multilevel security in individual and netted computer systems.

  The use of gateways as elements to integrate networks is under
  consideration.  Gateways are currently operational to interconnect
  MILNET with (l) ARPANET (six gateways primarily used to exchange mail
  between authorized users), (2) MINET (one gateway for use prior to
  integration of the two networks into one), and (3) eight
  developmentally oriented networks. There are many more gateways
  internetting ARPANET with other research nets.  Most of these gateways
  use the ARPA-developed Gateway-to-Gateway Protocol.  It is now
  realized that this protocol is deficient for widespread use and ARPA
  has been investigating alternatives.

  The earliest requirement for additional gateways in the operational
  elements of the DDN will be to internet Local Area Networks into
  global networks of the DDN.  A new "stub" protocol has been developed
  that might meet this need.  The DDN is reviewing its requirements for
  available gateways and approaches.


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INTERNATIONAL AND NATIONAL STANDARD MARKET DEMAND FOR TP-4

 In the United States and most countries of the world, national
 standards organizations adopt international data communication
 standards.

 In the United States the standards for the transport protocols are
 established by the American National Standards Institute (ANSI).  The
 same standards for the federal sector are established by the NBS with
 an exception for DOD's military needs which may be established by MIL
 standards. Market demand for the latter was previously discussed.

 Outside the DOD there are numerous government agencies and
 organizations such as the Federal Aviation Agency, Internal Revenue
 Service, the Federal Bureau of Investigation, and the Federal Reserve
 Banks which have, or will have, networks that fall under the guidance
 of the NBS and will probably use the NBS-specified standard protocols
 when the NBS standard is issued.  Already the Federal Reserve is
 procuring its computer networking products using the X.25 protocol.

 National Support of International Standards

  The earliest evidence of demand for TP-4 products is in countries that
  give strong support for ISO standards.  Most countries outside of the
  United States give the international standards much stronger
  governmental support than the United States does for a variety of
  reasons. First, in most cases these governments own the postal and
  telecommunication monopolies.  Frequently, the responsibility for
  these organizations is at a ministerial level in the government.
  Furthermore, many of the modern countries have concluded that the
  information industry is a national resource and one of the growth
  industries of the future.  International standards that are neutral,
  in the sense that no manufacturer has a head start, give the companies
  in these countries the additional margin they feel is necessary to
  compete in the worldwide market.  It is also recognized by many that a
  worldwide market is much better than a market demand fragmented by
  national geographic and political considerations. Finally, the PTTs
  have traditionally provided information services equivalent to those
  for which some of the ISO computer communication protocols are
  designed.  The best example is Teletext, which is an upgraded version
  of the Telex system used widely outside the United States.

  Consequently, government networks in many countries use the
  international ISO standards or the national standards derived from the
  international standards.  Bid requests for government networks in
  France and Germany, for example, have required support for ISO
  protocols for over a year even though the standards are not yet fully
  approved.  These bids ask the respondent only to state support for the
  protocols.  No doubt, as the ISO protocols become stable, these
  countries will require the protocols for their networks.  These
  government networks will further influence the implementation of
  networks not actually required to use the international and national
  standards.

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MARKET SEGMENTS NOT REQUIRED TO USE TCP OR TP-4

 Most of the demand for communication protocols comes from potential
 customers who are under no government fiat to use either TCP or TP-4
 protocols in their networks or network products.  Many of these will
 use existing supplier-specified protocols.  Such protocols have been
 embedded in products for over ten years and are well tested both
 formally and through field experience in thousands of networks.
 Continuing demand for these protocols will not contribute to the
 relative demand for either TCP or TP-4.

 There are widely recognized advantages in using international standard
 protocols for computer communications.  First, there is tremendous
 value in exchanging information with other information users.  As the
 standard protocols become widely used, the value of the information
 accessible through networks using these protocols is normally greater
 than the value of information accessible through less widely used
 networks protocols. This is the reason that industry groups such as
 airlines, banks, and insurance companies band together to set up common
 networks.  Similarly, it is recognized that there are economies of
 scale for widely used networking protocols both in the sense that
 equipment can be obtained at lower cost and in the sense that the
 manufacturer's improvements in performance, function, and cost will be
 repaid by market demand.  In addition, many network protocol users wish
 to have the option to procure equipment from a wide variety of vendors.
 Sometimes international standards encourage this environment.  Finally,
 international organizations would prefer to have common procurement of
 equipment and software for worldwide operations.  Thus international
 standards are preferred for operational as well as logistic
 considerations.

 In the United States much of the demand for TP-4 will develop in the
 industries that exchange information regularly with entities of the
 federal government.  If the Federal Reserve were to use the TP-4
 standard for exchanging information with member banks, for example,
 there would be pressure on the banks to use TP-4.  Similarly, if DOD
 suppliers wish to have easy access to DOD employees using a system
 based on TCP, they would need to use TCP.  Also many of the
 university-oriented networks use the ARPANET protocols to exchange
 information with other university ARPANET users.

 The committee concludes that the demand for TP-4 in the United States
 will significantly out weigh the demand for TCP independent of DOD's
 adoption of TP-4.  If DOD adopts the ISO TP-4 immediately or if DOD
 adopts TP-4 after a demonstration, the U.S. market demand for TCP
 protocols will disappear as the current networks are converted to TP-4.
 If DOD chooses to use the DOD TCP indefinitely, clearly the DOD and
 ARPANET demand for TCP will continue.

 A similar set of market forces operates outside the United States
 except that the foreign governments are more strongly in favor of
 international and national standards and have smaller investments in
 nonstandard equipment.  Thus there are even more industries drawn to

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 the standards in order to share information.  This is illustrated by
 the extremely strong support for ISO efforts.  The European Computer
 Manufacturers Association has been active in the TP-4 standardization
 effort.  NATO appears committed to TP-4 implementations, and there is
 likely to be intense competition in this arena.  Lacking the federal
 government support of two different protocol suites, there is a
 stronger force to adopt a single international standard in most
 countries.  There are other countries with a similar problem, however.
 Germany is beginning to install systems based on its unique national
 standard but has committed to convert eventually to ISO protocols.

 The committee concludes that there will be little market demand for the
 TCP protocols outside the United States.  The strong international
 demand will be for ISO protocols, including TP-4.








































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   VI.  DEVELOPMENT OF STANDARD COMMERCIAL VERSUS SPECIAL COMMERCIAL
PRODUCTS

DOD has expressed a desire to use off-the-shelf commercial products
because they are expected to be less costly.  It is expected that
performance of commercial products will be optimized to increase
competitiveness. User cost will be lower because of a large commercial
customer base over which to amortize costs for development, continuous
improvements, and maintenance.  Furthermore, the DOD may benefit from
having more vendors compete for their business.  This section examines
the way vendors select standard products for development and the
implications in cost, continuing supports, and improvements.

PRODUCT DEVELOPMENT VERSUS SYSTEM INTEGRATION

 It is assumed in this discussion that off-the-shelf commercial products
 can be used through system integration to construct system solutions.
 Most vendors supply both standard products and system integration
 services.  Some vendors supply only the integration functions, using
 other vendors' products.  System integration adds value to the product
 and in some cases results in modifications of the product to meet
 system requirements. When standard products are used, the
 responsibility for continuing maintenance and improvements almost
 always can be passed to the product developer.  Thus in this discussion
 we assume that off-the-shelf commercial products are standard products
 supplied by vendors to implement one or more transport-level protocols
 for the DOD.

CRITERIA FOR SELECTION OF STANDARD PRODUCTS

 The product vendor's choice to develop a standard product is governed
 by market requirements, economic opportunities, and other design
 considerations. In the case of data transmission products, market
 requirements include competition, connection to the installed base of
 products, market growth, and satisfaction of the standards requirements
 of customers.

 Often the vendor will develop a product that supports several protocols
 as options.  Usually only one or two protocols will be selected for
 primary support, and all other options are considered for secondary
 support. The primary protocols selected for implementation are based
 upon the largest potential market for the vendor.  These protocols
 become the vendor's standard products.  Standard products are announced
 for sale and supported on a continuing basis.  Implementations of
 secondary protocols are often adaptations of the implementations of
 standard protocols and may be suboptimal with respect to performance
 and continuing vendor support. Often secondary implementations are
 created when an RFP is issued and the vendor who wishes to respond to
 the RFP must create a special product to do so.  This committee
 believes that, in general, future standard data transmission products
 will be either TP-4 or vendor-unique protocols and TCP will be a
 special product.


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STANDARD VERSUS SPECIAL PRODUCT

 Within the OSI architectural model, seven layers are defined, each of
 which will have protocols defined for interconnection of systems.
 These protocols are controlled by standards.  TP-4 is an example of a
 protocol for the transport layer.  These protocols will be implemented
 on many vendor systems that have different systems architecture,
 different operating system architectures, and, therefore, differences
 in the specifics of the layer interface.  The vendor systems will be
 designed to optimize the specific environments that each vendor has
 determined are most important to satisfy the major market objective for
 that vendor's particular computer architectures.  This determines the
 vendor's standard system and architecture. Support of special
 requirements will frequently be designed as modifications to a standard
 system, using translators and other techniques to bridge the
 differences in layer interface definitions, operating systems
 structure, and protocols.  Most support activity, optimization of
 performance and resource usage will be directed at the standard system
 architecture selected by the supplier.

 Special-Product Process

  Special-product development is initiated to meet customer
  specifications. The specifications, schedule, and cost assume that
  special products are released using an existing version of the
  software system (operating system, language, communications, and data
  manager).  Support for the special product is conditioned on a support
  contract.  The special product is tested and released with that
  system.  This provides the fastest availability of the product, since
  the schedule will only include the time to develop the product and
  test it with the selected system.  It is likely that by the time a
  product and its software system are delivered, a newer version of the
  software system containing code corrections and added functions and
  other new products will have been released.  Additional cost to the
  customer is required if the vendor is to modify the special product to
  operate on this new version of software.  This occurs frequently in a
  rapidly developing technology.  If the special product is not
  modified, operational and maintenance expenses may increase.

 Standard-Product Process

  A standard product is developed to meet the market requirements of a
  market area.  The development of a standard product generally has a
  target date that is used as a basis for scheduling system development,
  fabrication, and testing into a planned software system release.  The
  product then is included in the test and integration plan for the
  system release and integration into a systems test procedure to assure
  operation with the other parts of the software system.  The standard
  product then becomes a part of the software system, and as new
  releases of the system are made, the product is tested as a part of
  the integrated system to assure that it still operates with the
  revised, new system.  The product may also be enhanced to satisfy new
  requirements or resolve problems of the earlier version.  The product

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  then will operate with the latest software system release.

  The integration process complicates the development process.  The
  increased complexity may result in a longer development schedule or
  may require more resources than special products require since (1) the
  cycle may involve a longer product requirement definition, (2)
  additional planning and integration testing may be needed to
  coordinate the product design with other system activities, and (3)
  there is the possibility of up to twelve months' delay in scheduling a
  software system release, which for most vendors generally occurs at 6-
  to 12 month intervals.  The product may be maintained with a
  corrective code released in intermediate system fabrication and
  integrated into the following software release. Different categories
  of support may be available and these categories may vary by product.
  The support categories may range from no support to full unlimited
  warranty.

CONCLUSION

 The committee concludes that there are significant benefits for the
 Department of Defense in using standard commercial products that meet
 the department's operational needs:

  Costs to the DOD for development, production, and maintenance are
  significantly lower because (l) vendors spread the cost over a much
  larger user base, (2) commercial vendors have to be efficient in their
  operations in view of the competition in the market, and (3) vendors
  look for ways to upgrade their product to meet competition.

  The department may get additional useful products because vendors
  integrate the protocol function into their corporate software and
  hardware product lines.  Thus the DOD may be able eventually to use
  standard commercial software application products that are built on
  top of, and thereby take advantage of, the transport protocols.  The
  DOD will thereby have a wider selection of standard commercial
  application products to choose from.  By depending on industry to
  manage the development, maintenance, and upgrade of products, the DOD
  can use its scarce management and technical resources on activities
  unique to its mission.















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   VII.  RESPONSIVENESS OF INTERNATIONAL STANDARDS PROCESS TO CHANGE

The international standards process has proven its ability to respond
quickly to new requirements and protocol problems uncovered during
standardization. The United States, through organizations such as the
NBS, the ANSI, and IEEE has a leadership role in this process.  The
committee concludes that the process can be responsive to DOD's needs.

The DOD will benefit from active participation in the international
protocol standardization efforts.  This will ensure that the DOD's
evolving computer communications needs will be met in future commercial
products. Also the DOD will have access to a broad spectrum of protocol
experts and have access to those developing future commercial products.
These benefits will far out weigh the costs of participation.

There will probably be very few high-priority instances where DOD will
require immediate changes to its operational commercial software. These
may relate to security or survivability.  In order to accommodate these
changes in the short run, the DOD will need agreements with its
commercial suppliers for quick fixes to be made while the standard is
being changed.

































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                     VIII.  OPTIONS FOR DOD AND NBS

The committee believes that the Department of Defense is committed to
adopting commercial standards when they are suitable and available and,
therefore, will adopt the ISO standards eventually as the military
standard for transport-level communication protocol.  Further, the DOD
realizes the benefits in cost and reliability of obtaining its data
communications equipment from vendors who offer it as standard products.
Of the three options identified by the committee, the first two are ways
for the DOD to realize these benefits while the third option would
withhold the benefits from the DOD indefinitely.

The primary difference between Option l and Option 2 is in the timing of
the transition from TCP to TP-4.  This timing difference has
implications in risk, cost, and manageability of the transition.  (This
is discussed in Chapter X in greater detail.)

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.  The Department of Defense would either
 require that products be validated using these test facilities or be
 certified by the vendor.  The test facilities could also be used to











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 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
 should, however, 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 of
 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.











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                    IX.  COST COMPARISON OF OPTIONS

There are so many variables affecting cost, it is impossible to compare
precisely the cost for each option over time.  The estimates in this
section are, therefore, mostly qualitative.  They are based on the wide
experience of several committee members in commercial networking (14).

Cost comparisons among the three options are difficult for two reasons:

 1.   There are an unlimited number of scenarios that can be considered
 for the growth of DOD's data communication networks in the next fifteen
 to twenty years, involving questions such as (a) How many different
 implementations will there be? (b) What economies of scale can be
 achieved? (c) How much software will be shared between different
 implementations? (d) How much will the standards change for greater
 effectiveness or to accommodate higher-layer standards? and (e) What
 will happen to manpower costs in this high-skill area?

 2.   It is difficult to isolate the costs attributable to developing,
 implementing, and maintaining the protocols at issue.  This is
 especially true if we assume DOD continues to use its own unique
 protocols.  For both in-house and contractor efforts, the costs
 associated with TCP are folded into many other efforts. If DOD moves to
 commercial protocols, the marginal costs may be more visible.


















-----
(14)  The committee has had some access to a study recently conducted by
the Defense Communication Agency that compares the costs of commercially
maintained versus government-maintained operating systems for the
Honeywell computers used in WWMCCS.  Although the WWMCCS example has
many fewer dimensions and systems than are covered by this analysis, the
committee urges the DOD to review this study as a good example of
potential savings from commercially vended software.  (WWMCCS-ADP System
Software Economic Analysis.  J. Stephens and others, Joint Data Systems
Support Center, Defense Communications Agency, Technical Report, in
draft.)

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A major motivation expressed by the DOD for using commercial protocols
is that the commercial protocols are significantly cheaper.  If this is
the case, then many in the DOD would like to know the savings over the
next ten to twenty years if DOD adopts TP-4.  This is not a question we
will try to answer in this report, but the concept of opportunity costs
is significant.  If DOD can successfully move to commercial standards,
then it will eventually be able to use DOD's scarce management and
technical resources to strengthen its efforts in other areas of
information communications and processing that are more unique to the
DOD.  Given the finite pool of such resources available to the DOD, the
value of this transfer may be significantly greater than the dollars
saved by adopting the international standards.

The following assumptions have been used in trying to estimate the cost
factors if DOD moves toward adopting TP-4 using either Option 1 or 2:

 No major subsystem of the DDN (which includes MILNET, DODIIS, WWMCCS,
 and so forth) would use both protocols at the same time except possibly
 for a brief transition period.

 In only a few selected cases would a capability be required to handle
 both protocols.  These cases could include select hosts that use both,
 special servers (most likely mail servers) that could provide functions
 between several communities of interest using both protocols, or
 translating gateways between networks.

 Within the DDN both sets of protocols would be used for a period of
 five to ten years starting eighteen months after the DOD approves the
 use of TP-4 in a new system.

 In virtually all cases, the phase-over from TCP to TP-4 in a subsystem
 of the DDN would be performed at a time when there is a major upgrade
 of subsystem elements that include TCP as a part. In other words, the
 transition is not merely a substitution of transport or internet
 software except in cases where the hardware currently being used is
 from a vendor who has started to offer TP-4 as a commercial product.
 Where this is not the case, the transition includes the substitution of
 new hardware whose vendor provides TP-4 commercially.

COST FACTORS AND MODEL

 Four major factors must be considered in evaluating the costs of the
 three options:

  1.   How much lower will be the cost of commercial, standard-product
       protocols compared to those developed and acquired by the DOD?

  2.   If DOD decides to adopt TP-4, how quickly can it start using it
       in new systems, and how quickly will it phase TCP out of older
       systems?




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  3.   What will be the one-time cost of management and test before DOD
       is prepared to start using TP-4?

  4.   What will be the marginal costs of maintaining the two standards
       over the 5- to 10-year transition period?

 Savings Using Commercial Software

  Commercial software providing TP-4 will tend to be cheaper than DOD
  provided TCP because commercial one-time and recurring costs
  (especially the former) can be apportioned over a larger consumer
  base, and the commercial supplier will tend to be more efficient.  As
  in most cases where one compares the cost of one product provided by
  two vendors, there will be situations where a DOD vendor providing TCP
  can do it more cheaply than a commercial vendor providing TP-4.  These
  occurrences will be rare but they illustrate the difficulty of
  developing detailed quantitative models that compare the costs.
  Factors relating to competing suppliers go far beyond the transport
  protocols themselves and distort such models.

  The first argument relating to the size of the consumer base has many
  factors.  For the time period under consideration, DOD represents
  about 3 percent of the commercial U.S. computer base.  It would follow
  that DOD should pay much less in development and support costs for the
  commercial products.  But there are other factors.  The number of
  commercial suppliers is larger than the number of DOD suppliers by a
  factor of 5-10. The DOD's need for transport and internet protocols
  will be greater than the average commercial user in the time period
  under consideration.  If commercial vendors break out the costs of
  developing these protocol features earlier than planned, DOD will pick
  up a larger share of the tab. This could be by a factor of 2 or more.
  A good deal of the one-time development and production costs of TCP
  have already been spent by the DOD or partly written off by DOD
  vendors.  This factor would be extremely difficult to estimate, but we
  do not think it is very significant since the major costs in
  implementation relate to processes down-the-line from getting a
  C-language version.  These down-the-line processes must be repeated in
  great part as families of hardware and software are upgraded with
  system and technology improvements to meet DOD directives for standard
  TCP products.  There are also factors that cut in the other direction;
  if the DOD is only 3 percent of the U.S. commercial user market, it is
  an even smaller fraction of the international user market.  This
  latter market is growing;  its need for ISO protocols will be
  relatively higher than the U.S. market, and market share for U.S.
  manufacturers, including foreign subsidiaries, is large and holding
  its own.

  The situation is equally complex when it comes to comparing the
  efficiency of commercial vendors with DOD vendors when it relates to
  developing, installing, and maintaining transport and internet
  protocols.  The elements that favor increased efficiency of the
  commercial supplier include the following:


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   The commercial marketplace is much larger, less regulated, and is
   forced, therefore, to seek greater efficiency and innovation.

   Transport and internet protocols represent functions that interact
   very closely with operating systems, the largest portion of which are
   commercial.  The major sources of expertise for dealing with these
   operating systems are in the commercial marketplace, primarily with
   the vendors who supply the hardware as well as with vendors who
   specialize in related products.

   The commercial sector is in the business of managing the interplay
   between operating systems, protocols, related software and hardware
   products, new technology and architecture, and the relationship
   between all these and the market.  If DOD adopts TP-4, it will be
   delegating many of these management functions to a marketplace that
   will generally make better and faster decisions.

  For every dollar that the DOD might invest in TCP, how much would it
  cost to gain comparable capability with TP-4 procured as vendor
  standard products?  The many factors involved make a precise estimate
  impossible. We believe, however, that TP-4 can be procured at
  substantial savings and with virtually no economic risk if the market
  develops as we believe it will, with many vendors offering it as a
  commercial product by mid-1986. On the average, we judge the savings
  to be 30 to 80 percent including initial installation, field support,
  and maintenance.

 How Soon Will TP-4 Be Used?

  The sooner that DOD decides to use TP-4, the greater will be DOD's
  savings.  These savings can offset the adverse cost factors discussed
  in the next two sections:  the cost to decide to use TP-4 and the
  added cost for the period when two standards (TCP and TP-4) are in
  use.

  Currently, TCP is generally used in MILNET, MINET, and ARPANET.  As
  previously stated in the assumptions, even if DOD decides to move
  aggressively toward TP-4, there are no evident, strong economic or
  operational reasons for converting these users to the new standards
  until a major upgrade of the users' communications and processing
  subsystems is planned. Also in the next twelve to eighteen months new
  uses of these nets are planned that will expand existing subnets and
  these new users would use TCP in order to be interoperable with the
  current users in their community of interest.

  In some cases the planning for new subnets for new communities of
  users is well along.  DODIIS is a primary example.  Some of these
  subnets should very likely proceed with TCP, but others appear to be
  prime targets for TP-4 if DOD is to move in the direction of adopting
  TP-4. The WWMCCS and its WIN are probably good examples of the latter.
  Planning and implementation for all of these subsystems must move
  ahead, however, and if DOD does not make a firm commitment to TP-4 by
  mid-1985, the number of systems that will move ahead with TCP will

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  probably constitute almost half of the growth of the DDN in the next
  five years.  In other words, delay of a decision to move to TP-4 until
  1986 would mean that most of the DDN subnets that will exist in the
  late 1980s will be based on TCP, whereas a decision for TP-4 a year
  earlier could significantly reduce this number.

 Cost of Decision to Use TP-4

  The costs of the decision to use TP-4 include the one-time management
  and test costs that DOD decides are needed before a TP-4 commitment
  and policy can be approved.  Under Option 1 these costs are small.
  Under Option 2 they are significantly higher, although the amount will
  depend on the extent and duration of the testing needed.  Under Option
  3 there will be no management and test costs.

 Marginal Costs of Maintaining Two Standards

  If DOD moves toward the gradual introduction of TP-4, both standards
  will have to be maintained for five to ten years.  The additional
  costs of maintaining two standards include the following:

   Management costs of dealing with two standards.

   Costs for developing and maintaining capabilities for limited
   intercommunication between systems using the different transport and
   internet protocols.  These include costs for gateways,
   dual-capability hosts, and special servers such as mail.

   Parallel validation capability.  The DOD is implementing a validation
   capability for DOD TCP.  This is similar to the currently operational
   NBS facility for TP-4 testing.  If DOD selects Option 1, there is a
   question whether this DOD facility should be completed for TCP
   (because the number of new implementations of TCP would be small
   several years from now).  If DOD selects Option 2, the facility is
   probably desirable.

   Costs for maintaining research and development (R&D) programs to
   improve the standards.  A part of the DARPA and DCA research and
   development programs in information technology is directed at system
   issues related to TCP.  This includes work on internet issues,
   gateways, and higher-level protocols.  The committee has not reviewed
   the research program for details and cost; however, a commitment to
   move toward ISO standards should affect the program.  Costs would
   increase to the extent that the program would be involved with
   interactions with both protocols.  There would be some decreased
   requirements for R&D in light of potential dependence on commercial
   R&D to improve the standards.  In the next several years, however,
   the committee concludes that dual standards would, on balance,
   somewhat increase R&D costs because of the DOD's unique operational
   requirements.

  These costs are roughly the same for Options 1 and 2 and depend on how
  DOD manages the transition.  Under an austere transition, which does

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  not provide extensive interoperability between TP-4 and TCP-based
  systems and minimizes costs in other areas, the overall costs could be
  low in comparison with potential savings.

 Evaluation of Options by Cost

  In terms of the previously discussed factors, savings can develop in
  two ways:  by using TP-4 instead of TCP in new systems and by
  replacement of TCP with TP-4 in existing systems when this can be done
  smoothly and efficiently.  The earlier that TP-4 is introduced, the
  greater these savings.

  In contrast costs will be incurred in two ways:  in one-time planning
  to use TP-4 and in continuing costs of operating two standards.

  The following is a summary of the cost evaluation of the three options
  in the near term:

  Option 3 is least expensive.  It achieves no commercial savings but
  has no costs for one-time planning and maintenance of dual standards.

  Option 1 is at most only slightly more expensive than Option 3 since
  one-time planning costs (which are much lower than for Option 2) and
  maintenance costs can be significantly offset with commercial savings
  in the following several years.

  Option 2 is most expensive since it does not realize significant
  offsetting commercial savings.

  In the longer term (beyond the next several years) commercial savings
  for Options 1 and 2 should overtake costs of transition, and both
  these options should cost the same.

  There is a concern on the part of some members of the committee
  whether the higher near-term costs of Option 2 are adequately offset
  by the Option's long-term savings to warrant the transition.


















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                       X.  EVALUATION OF OPTIONS

We present a summary of the strengths and weaknesses of each option,
followed by a detailed evaluation for each set of criteria.

SUMMARY

 Option 1's primary benefit is that it would allow the DOD to obtain the
 benefits of standard commercial products in the communication protocol
 area at an early date.  These 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, and commercial), which presumably will use TP-4,
 would also be brought about more quickly.  Option 1 involves greater
 risk, however, since it commits to a new approach without 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 since 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 since
 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/or delay.
 It would allow the most rapid achievement of full internal
 interoperability among DOD systems.  Manageability should be good,
 since only one set of protocols would be in use (one with which the DOD
 already has much experience) and the DOD would be in complete control
 of system evolution. Procurement costs for TCP systems would remain
 high compared to 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.







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 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 provides a quicker route to interoperability within the
 Defense Department and at the least risk, but at a higher life-cycle
 cost and incompatibility with NATO and other external systems.

DEFENSE DEPARTMENT OBJECTIVES VERSUS OPTIONS

 The committee has identified a set of DOD objectives for transport
 protocols, discussed in Section II of this report.  In this section we
 discuss the potential of each of the three options for achieving those
 objectives.  The objectives have been grouped into five major
 categories that serve as criteria for evaluation of options.

 Functional and Performance Objectives

  There are certain functional and performance objectives that standard
  DOD transport protocols must satisfy.  Key objectives include security
  capabilities, the ability to establish message precedence in crisis
  situations, and survivability of continuing operations when failures
  occur and portions of the network become inoperable.  This implies
  continuous availability of the primary data transmission network and
  the ability to reconfigure the networks to operate after some of its
  nodes are lost.

  As previously stated, the two protocols are functionally equivalent.
  TCP and TP-4 have equivalent reliability characteristics and are able
  to detect and recover from failures.  The committee also concludes
  that robustness, availability, and performance in crises are
  equivalent using either protocol.  The committee concludes that all
  three options equally satisfy the functional objectives that DOD
  requires.

  Since the performance characteristics of TCP versus TP-4 will be a
  function primarily of the particular implementations, the committee
  concludes that the two protocols are sufficiently alike that there are
  no significant differences in performance of a TCP or a TP-4
  implementation of equal quality when each is optimized for a given
  environment.

  If Option 1 is selected, early implementations may result in
  suboptimal performance.  Option 2 specifies that there be a
  demonstration network established that will provide time for
  adjustment, testing, and gaining experience.  Option 3 would result in
  no reduction in performance of current networks.  The maturity of TCP
  has resulted in many implementations that have demonstrated good
  performance.  This experience provides a knowledge base for future
  implementations of either TCP or TP-4. In either case, however,
  initial implementations of TCP or TP-4 may be suboptimal and require
  additional development to optimize performance.



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 Maximizing Interoperability

  A high-priority DOD objective is interoperability among its internal
  networks and among internal networks and non-DOD, external networks,
  including NATO.  Interoperability allows users of a network to have
  access to applications on the same or other networks.

  Option 3 would allow the DOD to increase internal interoperability
  most rapidly by continuing to mandate use of TCP for all new systems.
  Interoperability with external systems, however, the vast majority of
  which are expected to use ISO standard protocols, will remain limited.

  The more quickly DOD moves to use TP-4, the more rapidly external
  interoperability will improve.  In the short run internal
  interoperability will be reduced due to the existence of both TCP and
  TP-4 protocols by different subnets.  This problem is greater with
  Option 2 then Option 1 since the number of systems and the length of
  time both protocols are in use is greater.  In both options the
  problem can be reduced by providing special servers and translating
  gateways to provide limited interoperability where needed among
  subnets using different protocols.

 Minimizing Procurement, Development, and Support Costs

  A DOD goal is to assure availability of commercial-grade transport
  systems from vendors and minimize development, procurement, and
  continuing support costs.  Both Option 1 and, after demonstration,
  Option 2 result in DOD adopting the TP-4 standard that has the
  endorsement of both national (ANSI) and international (ISO) standards
  organizations.  Further, this protocol has been endorsed for use by
  NATO, the European Computer Manufacturer's Association, the Computer
  and Business Equipment Manufacturer's Association (CBEMA), and the NBS
  Institute of Computer Sciences and Technology for the information
  processing community of the federal government.

  The result of the endorsements will be widespread use of the standard
  protocol in worldwide networks and a large number of vendors supplying
  commercial grade products supporting TP-4.  As previously noted, many
  vendors have already stated they plan to develop TP-4-based products
  and many are already doing this in-house.  Thus a large market and
  large vendor base will assure the availability of commercial grade
  TP-4 products.

  A large market and supply of commercial-grade products will give DOD a
  large competitive base from which to select its data transmission
  systems. The effect will be to reduce DOD acquisition cost because
  large markets allow vendors to amortize development and support cost
  over a large base.  This favors adoption of either of the options that
  results in DOD using TP-4 as its standard.

  With the availability of commercial-grade products, vendors will take
  the responsibility for continuing maintenance and enhancements of the
  product.  Transmission products are tightly coupled to the operating

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  systems on the host computer systems in which they operate.  With
  vendor support of the products, evolution of both the host computer
  operating system and transmission system will occur in
  synchronization.  This again favors the adoption by DOD of either the
  Option 1 or Option 2 that results in TP-4.  In these options much of
  the support cost is covered by the vendors and spread over the large
  market base.  This reduces the development and maintenance cost passed
  on to the DOD.

  The committee does not believe that a large market beyond the DOD will
  develop for TCP because worldwide markets for products will be based
  on the ISO standards.  Consequently, if the DOD chooses Option 3, only
  the DOD-dedicated vendors would supply TCP as standard products
  resulting in a smaller market and supply for TCP products and limited
  availability of TCP products.

  If DOD remains with TCP, many commercial vendors will be forced to
  develop and support both the commercial standard products (TP-4) and
  DOD standard special products (TCP) to stay in both markets.  In many
  cases only the large market-based products such as TP-4 will be
  considered standard and TCP products will be considered special
  products.  The effect is higher development and support cost to the
  vendors which would be passed on to DOD.  Thus the incentive for
  continuing enhancement to the special product, TCP, would be reduced.
  This responsibility would be passed to DOD, also resulting in higher
  costs.

 Ease of Transition

  The DOD is concerned with the ease and risk associated with transition
  from the current network architecture using TCP to its future network
  architecture.  The objectives for DOD are to reduce the interruption
  of data communication services supplied by its active networks;
  minimize the risk of using an immature, untried protocol; and maximize
  the use of the critical skills, knowledge, and experience of the
  engineers who develop the communications products.

  The maturity of TCP and the momentum that exists in the DOD community
  for implementing future systems using TCP would favor Option 3.
  Selection of Option 3 would minimize interruption of service and
  minimize risk. With this option there would be no transition; the DOD
  would remain with its current policy.  There would be no conversion
  costs and the only risks for DOD would be associated with poor
  implementations of new TCP-based products.

  The committee believes that much of the technical risk is associated
  with implementations.  Therefore, given the relative state of their
  specifications and implementations as discussed earlier, the committee
  feels that the risks are comparable for implementing new products for
  either TCP or TP-4.  Since DOD is acquiring many new networks the
  implementation risk of either TCP or TP-4 will be equal.

  If DOD chooses Option 1, it will display confidence in the TP-4

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  specifications and in the vendor's implementations through its
  immediate commitment for TP-4 use in new military networks.  DOD will,
  in effect, be making a commitment similar to that of vendors who are
  planning this protocol for their standard products.  Since most new
  networks would not use a transport protocol other than TP-4, this
  minimizes the number of networks and therefore the cost of converting
  and maintaining TCP networks to TP-4.

  Since the standard TP-4 products from vendors are not available today,
  DOD endorsement of TP-4 may have the effect of accelerating vendor
  development of standard products.  These products are expected to be
  generally available by 1986.  Thus Option 1 can be consistent with the
  manufacturers' expected product plans.  Option 1 provides, therefore,
  the least conversion cost but with higher risk for DOD conversion.

  If DOD chooses Option 2, then the risk that TP-4 will not meet DOD
  needs is reduced since there is no commitment to use this protocol
  until a successful demonstration is completed.  In the interim, many
  networks will have been committed using TCP, resulting in higher
  conversion costs than with Option 1.  In summary, Option 2 provides a
  lower risk approach for DOD to convert to TP-4, but will encounter the
  higher conversion cost.

  There is a great deal of experience with TCP and thus there is an
  engineering community that is highly knowledgeable about it.  As
  previously noted, however, if DOD remains with TCP, some DOD vendors
  will be forced to support multiple protocol products.  The functional
  equivalence and similarities between TCP and TP-4 permit an easy
  transition for the experienced engineer to move from TCP to TP-4.
  Option 2 allows more time for this transition to occur, and thereby
  minimizes the risk associated with a complete switch to TP-4.

  In addition to the transport protocols, a transition from TCP to TP-4
  also involves the conversion of applications.  The committee has
  concluded that the services provided by TCP and TP-4 are comparable
  and applications software can be moved from TCP to TP-4 without loss
  of functionality.  Obviously, Option 3 requires no conversion to
  existing applications on current implementations.  Option 2 will
  result in more applications interfacing to TCP than Option 1, thus
  potentially increasing conversion costs. In the future DOD could
  minimize the cost of conversion by standardizing the services provided
  by the transport layer to the applications.

 Manageability and Responsiveness to DOD Requirements

  The final set of objectives is concerned with the degree of difficulty
  that DOD will experience in managing its installed networks and future
  networks.  As communications requirements evolve, DOD must have the
  ability to alter specifications so they will satisfy new requirements.
  Finally, DOD requires facilities for validation of protocol
  implementations as they are added to their networks.

  Since Option 3 is to maintain the status quo, no additional management

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  difficulty is anticipated.

  Both Option 1 and Option 2 will cause some additional management
  difficulties since they require that the current momentum for adopting
  TCP to be redirected toward TP-4 without loss of intensity.  In
  addition to this change, DOD must manage both TCP and TP-4 networks.
  This will add to its management difficulties.

  Option 2 will result in greater management difficulties than Option l
  due to the larger number of TCP systems that must eventually be
  converted and the larger time period over which both protocols must be
  supported.

  There are benefits from each option.  If Option 3 is selected, DOD and
  its vendors have sole responsibility for determining what changes are
  needed, implementing the change, validating the change and the ongoing
  maintenance of the standard.  If either Option 1 or Option 2 is
  chosen, then DOD may encounter difficulty in persuading the standards
  groups to adopt its proposals; however, DOD would gain the experience
  and knowledge of the industry standards-making bodies.  The industry
  standards bodies should be receptive to good technical arguments for
  correction of errors or apparent major deficiencies in the protocol.
  The standards bodies that maintain the standard should become a
  technical resource for DOD to develop its military specifications.

  Since TP-4 will be a commercial standard, those vendors who adhere to
  the standard will insure that validation facilities are in place.  The
  National Bureau of Standards has a test facility for TP-4.  No such
  facility exists for TCP.  If Option 1 or Option 2 is chosen, DOD can
  use this facility to validate vendor implementations.  DOD should work
  with NBS to develop a similar facility for TCP.  This is particularly
  important for new implementations of TCP.  DOD should continue working
  with and through NBS in getting needed protocol revisions introduced
  into the appropriate standards bodies.

  In summary, Option 3 results in no new management difficulties while
  Option 2 causes the greatest difficulties.  Option 1 allows DOD to
  move toward commercialized standard products with the smallest
  addition of management tasks.

EFFECT OF PROPOSED OPTIONS ON MARKET SHARE

 Option 1 would quickly reduce the market held by TCP products as TP-4
 products begin to take hold in the marketplace.  In addition, it would
 enhance the ability of U.S. manufacturers to compete in the world
 networks market based on ISO standards because they would not have to
 engage in parallel development nor support two sets of protocols for
 very long. Option 2 could have a comparable but less pronounced effect
 in the marketplace and it would be delayed.  Because of the very
 probable rapid deployment of TCP-based systems in DOD networks while
 the TP-4 is still in the demonstration phase, however, many more
 networks than in Option 1 would probably end up using TCP.  This would
 tend to reduce the U.S. manufacturer's competitive edge in the world

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 market because their need to develop and maintain both TCP products as
 well as TP-4 products would dilute their skill resources.  The same
 thing would happen with Option 3.  Although none of the options would
 affect the world market for TP-4 greatly, Option 3 would result in a
 residual market for TCP products in the DOD and related networks.

 Products made specifically for this market would continue to exist, but
 with functions limited to this specific market, the products would lack
 some of the advantages of large-scale production and product
 development.












































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                          XI.  RECOMMENDATIONS

We first present our basic recommendation and then provide detailed
recommendations on aspects that require amplification.  These are
followed by additional considerations in several important areas
relating to the transition plans.  Many of our recommendations are
closely related to each other, and care should be taken not to consider
any single recommendation in isolation.

BASIC RECOMMENDATION

 The committee unanimously recommends that DOD should adopt the ISO TP-4
 (and IP) as DOD costandards with its TCP (and IP) and move toward
 eventual exclusive use of TP-4.  Transition to use of the ISO
 standards, however, must be managed to maintain operational
 capabilities and minimize risks.  The timing of the transition to use
 of these protocols is, therefore, a major concern, and the committee
 was divided on the best schedule to recommend.

 A majority of the committee favored immediate adoption of the ISO
 protocols as costandards with TCP, giving major procurements in 1984-85
 the option of using these standards (Option 1).  A minority favored
 deferring adoption of the ISO protocols by the DOD until after a
 demonstration of commercial quality implementations supporting military
 applications (Option 2).  This difference is reflected in detailed
 recommendations 2-4 below.  The reasons for the two viewpoints are
 based on differences within the committee on the extent of the risk
 associated with adopting a protocol, TP-4, that has not been
 implemented on operational networks.

DETAILED RECOMMENDATIONS

 In the following recommendations the committee provides details about
 actions that should be taken to implement the basic recommendations.
 Most of the recommendations involve actions that require the DOD to
 take the lead role, with occasional support from the NBS Institute for
 Computer Sciences and Technology.  Some recommendations are directed
 more toward NBS.  Other government agencies and parties interested in
 using DOD protocols or in their future evolution may also find these
 recommendations applicable.














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 (1).  DOD should rapidly identify "open areas" of the ISO TP-4
 specifications where various options for implementation are allowed and
 define a required subset for use in DOD systems (a MIL-SPEC version of
 the standards, for example).  In doing this, the DOD should work with
 the NBS with the goal of developing a Federal Standard, that has
 relatively few options for implementation, facilitates maximum federal
 interoperability, and makes it clear to vendors which functions are
 required in their commercial products.

 (2).  DOD should aggressively develop and implement a plan for
 integration of TP-4 as a costandard with TCP and for migration toward
 its eventual exclusive use.  The plan should include provision for
 rapid completion of a MIL-SPEC (detailed recommendation 1), either
 validation or demonstration facilities (detailed recommendation 3),
 timing for procurement of systems with the new protocols (detailed
 recommendation 4), development of equipment and procedures to support a
 period of joint operation with both TCP and TP-4 protocols in use, and
 guidelines for eventual conversion of TCP systems to the new protocols.

 Whatever timing is chosen for the introduction of ISO protocols, an
 extended period must be expected when both TCP and TP-4 are in use in
 different systems.  Hence equipment and procedures must be developed to
 provide limited communication between systems using the two protocol
 sets.  This will include dual protocol operation for some gateways,
 relay hosts, service hosts, and terminal concentrators.  A secondary
 purpose of the test system described in detailed recommendation 3
 should be to aid in development of this transition support equipment.

 Both a general transition strategy and specific transition plans for
 each existing system should be developed.  The switchover from old to
 new protocols will take place at different times as appropriate for
 each system during an overall transition period of many years.

 (3).  As soon as possible, the DOD should develop a protocol test
 facility. If Option 1 is followed, this facility would serve primarily
 to validate implementations of both old and new protocol sets.  If
 Option 2 is followed, the facility would initially focus on
 demonstrating the suitability of the new protocols for use in a
 military environment as rapidly as possible and then provide for
 testing of commercially supplied protocol implementations.

 For validation purposes, the NBS protocol-testing facility developed
 for ISO protocols should serve as a good basis, but extensions to deal
 with any DOD-specific option for the ISO protocols, performance, and
 DOD protocols would be necessary.  DOD is now beginning such a program.









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 For a more complete demonstration, commercial-quality implementations
 of the ISO protocols must be obtained and shown to support military
 applications in an operational subnetwork such as such as ARPANET or
 DODIIS. In both cases the facility should also be used for development
 and demonstration of the transition support equipment mentioned in
 detailed recommendation 2.

 (4).  Procurements of new networks and major upgrades of existing
 networks should favor use of ISO TP-4 as rapidly as possible.  If
 Option 1 is followed, RFPs may specify the new protocols immediately.
 If Option 2 is followed, this must await successful completion of the
 demonstration discussed in recommendation 3.  Procurements for existing
 networks using TCP may continue to require TCP-based equipment until an
 appropriate conversion point is reached (see detailed recommendation
 2).

 The purpose of this recommendation is to minimize spending on new TCP
 implementations and their subsequent conversion to TP-4 where possible,
 while recognizing that some additions to TCP-based systems will also be
 needed.  If Option 2 is followed, immediate requirements for new
 systems may force new implementations of TCP in these cases also
 because the demonstration is not completed at the time RFPs must be
 issued.

 (5).  As part of a transition plan, a transport service interface to
 higher-level protocols more like that of TP-4 should be developed for
 TCP and tested with existing higher-layer protocols.

 This should serve as a rapid test of whether existing DOD protocols can
 make effective use of the somewhat different style of service that TP-4
 provides.  It should also allow higher-level protocols to be modified
 to make use of TP-4 in parallel with the implementation of TP-4 itself,
 making the ultimate transition to TP-4 more rapid and certain of
 success.  Finally, it may allow use of a single version of the
 higher-level protocols to be used on both TCP and TP-4 equipment.

 (6).  DOD should continue using existing DOD-specific, higher-level
 protocols for operational purposes (Telnet, FTP, and Simple Mail
 Transfer Protocol, for example) but minimize effort on their further
 development and plan to adopt suitable ISO protocols as they are
 developed.  Research on protocols providing new services (multimedia
 mail, compressed video, and voice store-and-forward, for example)
 should continue.  The committee is pleased to find that DOD is already
 pursuing this course of action.

 (7).  The NBS Institute for Computer Sciences and Technology should
 maintain close liaison with DOD to ensure that DOD needs for new
 protocols and modifications to existing standards are effectively
 represented to appropriate standards bodies.  This should include
 research areas such as multimedia mail where there is significant
 commercial as well as military interest.



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 The committee is pleased to find that this is already being done
 through contracts from DOD for ICST to represent its interests in
 standardization activities.  Further cooperation (in demonstrating and
 testing protocols, for example) could occur.

 (8).  The NBS and DOD should collaborate from the outset in the
 development of new protocols for use as federal standards.  This will
 ensure early agreement on functions, features, and services of the
 protocols under development. The NBS should present the developing work
 early to the ISO standardization activities to expedite convergence on
 internationally acceptable standards.

 Such collaboration could help ensure that future protocol standards
 will be developed in a single, coordinated process that results in a
 single standard accommodating both DOD, other federal agencies, and
 commercial needs.

 (9).  DOD and NBS should develop additions to protocol specifications
 to support preemption of limited resources by high-precedence users.
 Such capabilities are needed during high-load situations such as might
 develop during wartime or other crisis situations.  They are not yet
 part of either the TCP or TP-4 specifications or existing
 implementations.  This should be an example of the sort of
 collaboration mentioned in detailed recommendations 7 and 8.

 This is important to avoid possible incompatibilities between different
 implementations of the same specification as discussed in Section III.
 It is likely that vendors would welcome guidance on how to deal with
 open areas of the specifications, and early action by DOD could result
 in their mandated subset becoming the de facto standard for most
 commercial implementations as well, with consequent benefits to DOD.
 This is a good area for cooperation between DOD and NBS.

ADDITIONAL CONSIDERATIONS

 Transition Plan

  This section describes the major elements of a transition plan from
  use of TCP to use of TP-4 in DOD systems.  The plan will vary
  depending on the option chosen.  Both Option 1 and Option 2 share a
  number of common elements that are discussed first, including
  development of a MIL-SPEC, protocol-testing facilities, and transition
  support equipment. If Option 2 is followed, a demonstration of TP-4
  must also be undertaken.

  MIL-SPEC.  As noted in recommendation 1, several open areas and
  options in the ISO TP-4 must be specified in order to have complete
  and compatible protocol implementations.  Completion of this
  specification by the DOD should be a top priority objective.





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  Protocol-Testing Facilities.  As noted in recommendation 3, test
  facilities for protocol implementations are essential.  Under Option
  1, this facility should serve primarily to validate implementations of
  both old and new protocol sets.  If Option 2 is followed, the facility
  should initially focus on demonstrating the suitability of the new
  protocols for use in a military environment as rapidly as possible,
  and provide for testing of commercially supplied protocol
  implementations.

  For validation purposes, the NBS protocol-testing facility developed
  for ISO protocols should serve as a good basis, but extensions to deal
  with any DOD-specific options for the ISO protocols, performance, and
  DOD protocols would be necessary.  The DOD has stated that such a
  program has been started.

  Transition Support Equipment.  In any transition plan it must be
  assumed that the large body of systems with existing TCP
  implementations will take a substantial period of time to switch
  completely to the use of the ISO protocols.  Some networks will
  include many different communities sharing a common communications
  backbone.  Members of one community communicate primarily among
  themselves, but occasionally outside their community.  While members
  of one community are likely to change over as a group, different
  communities will change to use the new protocols at different times.

  Hence an interim period must be anticipated when some systems are
  using the old protocols and others, the new protocols.  The transition
  plan must provide some means of allowing interaction between old and
  new systems where required during this period.  Toward this end, a
  number of relay hosts may need to be developed that support both old
  and new protocols.  These will allow automatic-staged forwarding of
  electronic mail between old and new systems and manually set up file
  transfer or remote terminal access via the relays.  Performance
  through these relays will not be as good as with direct connections,
  but the relays should provide an adequate level of service for
  occasional interactions among different communities of the internet
  system.

  When more frequent interaction is anticipated and better service is
  needed, major service hosts should support both old and new protocol
  sets concurrently so they can provide service directly without
  requiring the use of relays.  Such service hosts include widely used
  time-sharing machines, file servers, and special servers such as
  Network Information Centers, Network Operations Centers, and
  Administrator Machines (providing mailboxes of network administrators,
  for example).  Some dual protocol servers
  may also act as relays where the load of both functions can be
  supported.

  Terminal concentrators for general use must also support both protocol
  sets so that connections to both old and new hosts can be made
  directly.


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  Gateways must support both old and new IPs so hosts using either one
  may send internet traffic.  This requirement could be relaxed in the
  case of entire networks that will switch over simultaneously and hence
  will only need one type of IP traffic.  Gateways should not have to
  translate between old and new IPs--it will be assumed that both source
  and destination hosts are using the same protocols or going through an
  explicit relay intermediate host.

  This latter point requires some elaboration.  If one type of IP packet
  arrives at a destination host or gateway that only handles the other
  type, it must be discarded.  It would be good if, in addition, a
  suitable ICMP error packet could be returned in the unsupported
  protocol so it would be meaningful to the source.  To avoid this
  situation the internet-host name table maintained by the Network
  Information Center should indicate which protocol(s) each host
  supports.  Then when a source host looks up the address of a
  destination, it will also determine which type protocol to use or if a
  relay is required.

 Demonstration Plan

  If Option 2 is followed, a major demonstration of the ISO protocols in
  a military environment must be undertaken.  Any such demonstration
  should proceed by stages beginning with the implementation of TP-4 in
  one network (15).  Then the demonstration would be extended to include
  internetting (still with DOD IP) to validate the suitability of TP-4
  as a replacement for TCP.  The demonstration would then be further
  extended to employ the ISO IP in place of DOD IP.

  Stand-Alone TP-4 Network Demonstration.  The first stage of any
  transition plan must be to establish a demonstration network or
  subnetwork using TP-4 in place of TCP under existing higher-level
  protocols. This step will require selection of a suitable network (or
  subnetwork), procurement of TP-4 implementations for hosts and
  terminal access controllers on that network, and modification of
  higher-level protocols to use TP-4.  The demonstration should include
  sufficient use of real applications to test the protocols in an
  operational environment.

  To limit the amount of change attempted at one time, the DOD IP may be
  retained and used under TP-4.  Alternatively, if ISO IP development
  status seems to warrant it, ISO IP may be installed along with TP-4.

  



-----
(15)  For the remainder of this chapter, the use of TCP and TP-4 to
include their respective IPs will no longer hold.  The four
entities--Transmission Control Protocol (TCP) and its Internet Protocol
(DOD IP) and the Transport Protocol (TP-4) and its Internetwork Protocol
(ISO IP)--will be treated individually.

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  In the latter case, all TP-4 hosts would be on the same network
  anyway, so that IP will only be used between hosts and no gateways
  will be involved and no gateway modifications will be needed.

  The hosts involved could be dedicated to the demonstration and hence
  only support TP-4 and only be able to interact with other
  demonstration network hosts or be concurrently supporting TCP and DOD
  IP for operational traffic to other "normal" hosts.  In the latter
  case, no forwarding or relaying of traffic by hosts between normal and
  ISO logical networks would be allowed or performed (the demonstration
  network would be logically closed).

  Stand-Alone TP-4 Internet Demonstration.  The next step would be to
  expand the demonstration to include more than one network (at least
  logically) and hence involve gateways.  If only TP-4 is involved, this
  is a simple extension to test TP-4 over longer internet paths with
  more variable performance.  If ISO IP is also being tested at the same
  time, modification of the gateways involved will also be required as
  indicated in the next section.

  Stand-Alone ISO IP Demonstration.  Once TP-4 has been tested,
  introduction of the ISO IP to replace DOD IP may commence.  In
  addition to simply replacing one IP with the other in hosts and
  gateways, this will require modification of the gateways to perform
  ICMP and GGP on top of the ISO IP.

  These gateways could either be dedicated to the demonstration and
  hence have only ISO IP, or could be concurrently supporting normal
  operational traffic via DOD IP.  In the latter case, once again, no
  forwarding of traffic between ISO demonstration internet and normal
  systems would be allowed.

  At the conclusion of these three steps, the ISO TP-4 and IP could be
  deemed to have demonstrated their basic functional suitability in a
  military environment.  The transition support equipment described
  above should have been developed in parallel, providing the capability
  to smoothly and successfully switch operational systems using the old
  protocols to use of the new protocols.

 Switchover of User Systems

  Once the above preparations have been made and the demonstration
  completed, if Option 2 is being followed, the switchover of user
  systems can commence.  Each network or community within a network
  should be able to switch at its convenience and maintain the ability
  to interact with other systems.  The user systems will not be required
  to support operational use of both protocol sets simultaneously at any
  time unless they wish to do so for their own reliability purposes.






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  Switchover of user systems also requires a personnel-training effort.
  While earlier steps involved a relatively small number of specialists
  and support staff at major sites, this step will affect all user
  sites, and their network support staff must be trained in the new
  procedures.

  Once switchover of all systems to the new protocol set is complete,
  support for the old protocols by TACS, service hosts, and gateways can
  be removed.

 Lessons Learned from the ARPANET NCP-to-TCP Transition

  The following points summarize some important lessons learned during
  the ARPANET transition from NCP to TCP (16).

   Conversion of TACs and service hosts to support both protocols before
   the transition of user hosts starts is essential.

   Relay capabilities were heavily used for mail, but used little for
   other purposes.

   The Network Information Center was not ready to support the new
   protocols and this caused problems in distributing the host name
   table.

   There were significant performance problems that required careful
   analysis and parameter tuning after the transition.  These were
   unavoidable because no service host had been stressed prior to the
   switchover, with a full user load over a long time period using the
   new protocols.

  

















-----
(16)  For additional information, see ARPANET Request for Comments:
NCP/TCP Transition Plan, J. Postel, (Menlo Park, California: SRI
International Telecommunications Sciences Center, November 1981).

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