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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:
l. To develop networking and protocol standards that meet U.S. gov-
ernment and industry requirements and that will be implemented
in off-the-shelf, commercial products.
2.
To develop testing methodologies to support development and im-
plementation 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 proto-
cols.
Development of Networking and Protocol Standards
l
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 govern-
ment 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
5The 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 stan-
dards, 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 pro-
totypes 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 mes-
sage processing. The primary purposes are to advance the state of the
art in measurement methodologies for advanced computer networking tech-
nologies and determine protocol implementation correctness and perfor-
mance.
The NBS views testing as a cooperative research effort and works with
other agencies, private-sector companies, and other countries in the de-
ve] opment of methodologies. At this time, this cooperat i on i nvo] ves five
network laboratories in other countries and over twenty computer manufac-
turers.
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 en-
gaged in protocol development and implementations.
As s i st i ng Users and Manuf actu rers
The NBS works directly with government agencies to help them use evol-
ving network technologies effectively and apply international and govern-
ment 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 fools, industrywide work-
shops, and cooperative demonstration projects. At this time, the NBS is
working directly with over twenty computer manufacturers in the imple-
mentation 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, mobiliza-
tion, 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 fad] or suffer much loss of capa-
bility because of unpredicted situations, unexpected loads, or
misuse. An international crisis is the strongest test of robust-
ness, since the system must operate immediately and with virtual-
ly full performance when an international situation flares up
unexpectedly.
Availability--Elements of the system needed for operational
readiness or fighting must be continuously available.
InteroperabiJity--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 manage-
rial needs:
l. 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 trans-
port 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 pro-
toco] 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); restora]--the
ability to restore some of the damaged assets to operating status; and
reconstitution--the ability to integrate fragmented assets into a surviv-
ing 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 inter-
operability up to the network layer, but neither TOP nor TP-4 would be
needed. The committee has not considered the extent to WhiCh SUCh in-
creased 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 ~ or 2 nodes of the DDN. For sub-
scribers 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 success-
fully in face of the unexpected. Robustness attempts to avoid or mini-
mize system degradation because of user errors, operator errors, unusual
load patterns, inadequate interface specifications, and so forth. A we11-
designed and tested system will limit the damage caused by incorrect or
unspecified inputs to affect only the performance of the specific func-
tion that is requested. Since protocols are very complex and can be in
very many "states," robustness is an important consideration in evalu-
ating 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 mea-
sures 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 consid-
erably more complex. The ability of computer network protocols to pro-
vide 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 organi-
zations 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, particu-
larly if there is some investment in preplanning, including the nigher-
level protocols that facilitate interoperability. Presidential directives
call for this. This will become a major factor in DOD's need for interop-
erability 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 under-
stood in computer networks. Equally important is the extent of func-
tiona~ity: What jobs will the network do for the user?
The DON 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 pre-
cedence and preemption. Precedence refers to the ability of the system
to adaptively allocate network resources so that the network performance
is related to the importance of the function being performed. Preemption
refers to the ability of the system to remove users (at least temporarily)
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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 communi-
cating parties. (For reliability, additional virtual circuits may be
established to provide an inplace 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 broad-
cast capability (one sender to many receivers); and handle imagery, sen-
sor 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 dif-
ferent autonomous networks of users can communicate with each other.
Interoperability
Presidential and DOD directives place a high priority on interoper-
ability, 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.
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, sup-
port each other, and thereby coordinate and strengthen the management of
forces and other assets. InteroperabiJity at the applications layer can
be achieved through the use of specialized software that performs those
functions of higher-layer protocols (such as TOP or TP-4, file transfer,
_ ~ _
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and virtual terminal) that are needed by the particular application. If
some of the higher-layer transport and utility protocols have been deve-
loped 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 interoperabiJity, is important to specialized
communities of users such as the logistics, command and control, or re-
search and development communities. As these different communities
utilize the DON, 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 TOP or TP-4 within network users, but without
the implementation of higher-level protocols and application interoper-
ability, is not generally an immediate step in increasing interoperabil-
ity. 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; Depart-
ment 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 governmentwide and international
interoperability will be an objective with increasing priority. The NATO
situation is especially important.6
In a somewhat longer time period, DOD will want applications interop-
erability 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
6Europe has been a major force in the development of 150 standards.
Consistent with this is a NATO commitment to adopt ISO standards so long
as they meet military requi remeets.
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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 surviva-
bility 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 increas-
ingly 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 wild place
requirements on the higher-level DOD protocols.
If the DOD chooses to move from TOP 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 net-
work 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 al] networks to be interoperable
since it is not possible to predict when one community will need to com-
municate 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-g-year period with future costs suitably
discounted (lO to 20 percent per year).
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
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protocols can be small since their development cost is amortized by the
commercial vendor over a larger market. Support costs for these proto-
cols tincturing 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 AX in terms of the three options presented in Section VITI.
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 deve-
loping complex information systems if it evolves these capabilities whi
working in concert with the users and the acquiring agencies. In this
light, the following factors are important:
he
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--~t 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 quanti-
tative 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 l9g4. An IP-testing
capability is being added. The Department of Defense is plan-
ning a similar protocol test facility for TOP, 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-
protoco] 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 defi-
ciencies are discovered. It will need a commitment from the
manufacturer that critical problems 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.
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Minimal risks--The DOD needs are so large and important, it
cannot afford to take otherwise avoidable risks.
Maintenance of manageability--The DON is new and is using a new
approach after the cancellation of AUTODIN Il.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. -
7AUToDIN IT 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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Representative terms from entire chapter:
computer networks
