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 RFCis distributed for information only. This RFCdoes not
establish any policy for the DARPA research community or the DDN
operational community. Distribution of this memo is unlimited.
This RFCreprodUCes 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.
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(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.
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(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).
