RESEARCH PRIORITIES
IN
NETWORKING AND COMMUNICATIONS
Report to the NSF Division of Networking and Communications Research
and Infrastructure by Members of the Workshop Held
May 12-14, 1994
Airlie House, Virginia
NATIONAL SCIENCE FOUNDATION
Arlington, VA 22230
The opinions expressed in this report are those of the workshop panel and
do not necessarily represent NSF policy.
PREFACE
The Networking and Communications Research Program of the National Science
Foundation supported a two-day workshop at Airlie House, Virginia, May
12-14, 1994. This was the third such workshop, following the second by
slightly more than two years. The focus of the workshop was to identify
major research issues in networking and communications. The goal of the
workshop was to produce a vision of telecommunications for the future and a
research path to implement that vision.
This report defines the context for research priorities and research
initiatives by addressing many important applications of networking and
communications in today's telecommunications and information systems. The
report deals with issues in networking and communications and identifies
and discusses in detail fifteen major research priorities and four research
initiatives that the participants concluded should be pursued over the next
several years. In addition, a number of research areas were identified
that are suitable for collaborative efforts between the various divisions
of NSF and between NSF and other appropriate federal agencies.
RESEARCH PRIORITIES
IN
NETWORKING AND COMMUNICATIONS
Report of a Workshop held May 12-14, 1994, Airlie House, Virginia
Sponsor: NSF Division of Networking and Communications Research and
Infrastructure
Participants:
Richard Blahut, University of Illinois, Urbana
Charles A. Brackett, Bellcore
David D. Clark, Massachusetts Institute of Technology
Donald C. Cox, Stanford University
John N. Daigle, University of Mississippi
G. David Forney, Jr., Codex/Motorola Corporation
Robert G. Gallager, Massachusetts Institute of Technology
Zygmunt Haas, AT&T Bell Laboratories
Bruce E. Hajek, University of Illinois, Urbana
Robert Kahn, Corporation for National Research Initiatives
Simon S. Lam, University of Texas at Austin
Shu Lin, University of Hawaii at Manoa
Robert W. Lucky, Bellcore
W. D. Sincoskie, Bellcore
* William H. Tranter, University of Missouri at Rolla
Jonathan Turner, Washington University, St. Louis
Jack K. Wolf, University of California at San Diego
* Chair
TABLE OF CONTENTS
1. INTRODUCTION 1
2. THE NATURE OF BASIC RESEARCH IN NETWORKS
AND COMMUNICATIONS 3
3. THE NSF PROGRAM 4
Organizational Base of the Program 4
Goals of the Program 5
Relationship of the NCR Program to the NII and HPCC Initiatives 5
Operation and Funding History of the NCR Program 6
4. PRIORITIES FOR BASIC RESEARCH 7
Coding and Coded Modulation 7
Information Theory 8
Communications Signal Processing 10
Protocol Theory, Design, and Engineering 11
Dynamic Network Control 12
Internetworking 14
Optical Networks 15
Security 18
Reliable Networks 20
Switching Systems 20
Wireless Networks and Access 21
Data Storage Systems 23
Video, Speech, Image and Data Compression 25
Mobile and Nomadic Computing 26
Satellite Systems 28
5. RESEARCH INITIATIVES 29
Research Initiative on the Open Data Network 29
Research Initiative on Data Storage Architectures for the NII 32
Wireless Research Initiative 33
National Gigabit Network Research Initiative 35
6. COLLABORATIVE RESEARCH EFFORTS 36
Agents and Filters 37
Navigation Tools 37
Human Interfaces 38
Electronic Publishing 39
Economics 39
Workstation Structure and the Communication Environment 40
Middleware 40
Optical Systems 41
Applications of Gigabit Networks 42
Networking of Applications 42
7. CONCLUSIONS 42
1. INTRODUCTION
The NSF Division of Networking and Communications Research and
Infrastructure was established in 1987, shortly after the creation of the
Computer and Information Science and Engineering Directorate. In 1989, a
workshop was convened to assess the program and to suggest directions for
communications and networking research. A similar group reconvened in
April 1992 to update the suggestions made by the 1989 workshop, to
reconsider the assessment of research directions vis-a-vis research
opportunities and national needs, and to evaluate the educational and
research base in these areas and in the United States.
Since the 1992 workshop the drive toward a National Information
Infrastructure (NII) has captured the attention of the general public as
well as the research community. In view of rapid changes in the fields of
communications and networking, and the pace of policy decisions toward the
NII, NSF convened a third workshop in May, 1994. The purpose of this
workshop was to identify the major issues affecting networking and
communications research for the future, including the NII, and to identify
research priorities.
The workshop participants made the following observations regarding the
environment of networking and communications research:
* The areas of communications, networking, and information storage
constitute major and rapidly growing segments of the U. S. industrial base.
A metric of the importance of networking and communications is the 100%
per year growth rate of Internet traffic. With the introduction of
user-friendly tools, such as MOSAIC (utilization of MOSAIC has initially
been increasing at 11% per week) network traffic and requirements for
bandwidth and storage are certain to increase dramatically.
* During the last several years the technologies for computing,
communications, networking, cable TV, entertainment, and information
storage have been converging at an increasing rate. As a result of this
convergence, many predict a radical and revolutionary change in the way
people live and work.
* Research in communications, networking and information storage has
contributed greatly to the development of the Internet. A substantial new
industry has emerged in the past four years, in the wake of the Internet,
supporting and applying progress in networking technology.
* Critical policy decisions are required to set the stage for efficient,
cost effective, and user friendly implementation of the new information and
communications based society. Informed policy decisions benefit from the
insights generated by networking and communications research.
* The National Information Infrastructure (NII) has been declared a
national goal and objective. There is a growing awareness of its influence
on education, health care, commerce, and government. Networking and
communications are among the core enabling technologies of the NII.
* The increasing level of competition in the telecommunications industry
has led to declining basic research funding in the communications and
networking areas. In addition, industry has turned to more near-term
research and development. These trends have created both an opportunity
and a requirement for NSF to take a more proactive role in guiding basic
research leading to national strategic goals. Increased funding levels at
NSF for research in communications, networking and information storage
would contribute significantly to the rapid realization of the NII.
Future communications networks that are suitable for a National
Information Infrastructure will be expected to support a wide range of
different applications, in a cost-effective manner, with unprecedented
reliability and on a very large scale. They will be expected to:
* support applications with a variety of data rates from a few bits per
second to gigabits per second, and applications whose data rates may vary
widely during a short time period;
* provide a range of quality-of-service options to accommodate different
performance and cost requirements;
* support mobile users and users who access the network from a variety of
locations;
* provide one-to-many and many-to-many communication channels to support
information distribution and collaborative applications.
In addition, the NII will require network architectures that can
accommodate evolution across multiple generations of technology and that
facilitate heterogeneity in applications, end systems, transmission
technologies and switching mechanisms. To allow future networks to be
managed effectively they must provide mechanisms for traffic measurement,
error monitoring, usage accounting and cost recovery.
Workshop participants identified research priorities and recommended four
major research initiatives. In addition, a number of research areas,
suitable for collaborative efforts between various NSF divisions and
between NSF and other federal agencies, were identified. These priorities
and initiatives are detailed in Sections 4, 5, and 6 of this report.
2. THE NATURE OF BASIC RESEARCH IN NETWORKS AND COMMUNICATIONS
The support for basic research in communications and data networks is
decreasing both in industry and in the department of defense. Thus it is
particularly essential for this support to increase at NSF. Part of the
reason for the difficulty in supporting basic research in these areas is a
lack of understanding about the nature of basic research. These
misconceptions characterize basic research as high risk, long term, and
curiosity driven. To the contrary, we maintain that basic research is
often low risk, short term, and vital to national priorities.
In understanding the nature of basic research, it is perhaps better to
call it discipline - oriented research. This is research in which one
builds understanding in a particular discipline by analyzing and studying
successively more complex models, using the insights generated at each
stage to guide further development. Such disciplinary research develops a
body of insights, of generic, well-understood simple problems, of back of
the envelope calculations, and of algorithms and methodologies for coming
to grips with real problems.
Much of modern communications rests on the well established, but still
vital, disciplines of modulation, coding, detection, compression,
equalization, signal processing, etc. As application areas and
technologies change, new models are suggested for these disciplines, but
the new models use and build on the existing discipline, enriching it for
the next set of applications. Thus practical needs, combined with
discipline-oriented research, ideally work in synergy with each other, the
needs enriching the discipline, and the discipline providing the insights
to satisfy the current needs. The existence of disciplinary understanding
permits rapid short-term solutions of new problems, and the possibility of
finding these solutions is low risk because of the existing disciplinary
insights.
Along with the above synergism, discipline-driven research in
communications has often solved important problems almost by chance. For
example, the Lempel-Ziv algorithms (the workhorses of modern data
compression) were developed out of a very theoretical study of data
sequences without stochastic structure. The Viterbi algorithm (one of the
workhorses of modern error correction) was developed out of an effort to
understand theoretical error probability bounds. The Reed-Solomon codes
(another workhorse of modern error correction, used in compact discs) were
developed primarily because of their mathematical elegance. One could view
such chance solutions as "high risk," but in fact these were simply added
bonuses to work that had to be done to maintain the connection between real
problems and discipline-oriented research. Each of these bonuses in fact
created entire industries. Research was an investment with extraordinary
return in these cases. These bonuses were curiosity driven, but in fact
satisfied national needs.
The above picture describes the almost ideal relationship between theory
(discipline-oriented research) and practice as it exists in communications
today, but this is the result of the rich discipline that has been
developed in the past. Because of the past successes of this relationship,
communications theorists continue to enrich the discipline while solving
the immediate problems of the present.
In the network area, theory and practice have had a less satisfactory
relationship than in the communications area. The network area has grown
up more recently than communications, and its disciplines, such as
congestion control, routing, and distributed algorithms, have had a
relatively short gestation period. In addition, the very rapid
technological changes in the last 15 years have never allowed a strong
connection between theory and practice to develop. It is becoming
increasingly apparent, however, that the disciplines of congestion control,
routing, and addressing are generic to all networks. The current practice
of re-solving these problems in an ad hoc way for every new practical
network leads to repeated poor solutions. There is an urgent need for NSF
to support the development of sufficiently strong disciplines that can
interact harmoniously with new network needs.
Maintaining an appropriate balance between discipline-oriented and
application-oriented research is difficult in today's climate. There are
strongly perceived pressures to solve practical problems quickly, and there
is a temptation for discipline-oriented researchers to give up on the
rapidly changing technological scene, and retreat into abstraction and
detail. It is important for both application-oriented and
discipline-oriented researchers to recognize their mutual dependence upon
each other, and to make this dependence clear to administrators and
executives. It is particularly important to cultivate that small group of
individuals who have a deep understanding of both applications and
disciplines. NSF should be proud of its efforts to support both practical
needs and disciplines, and to encourage the linkages between them. A major
challenge for NSF is to draw on the wisdom of the community to continue to
strengthen these linkages.
3. THE NSF PROGRAM
Organizational Base of the Program
Within the Computer and Information Science and Engineering (CISE)
Directorate, the Division of Networking and Communications Research and
Infrastructure (DNCRI) encompasses two major activities; the Network
Infrastructure and the Networking and Communication Research (NCR)
activities. The infrastructure activity includes the NSF involvement in
the Internet, via the NSFNET and international connections, currently in
transition to a commercially oriented focus involving network access points
(NAP's), a Routing Arbiter (RA), and a very high speed network (vBNS)
serving the research and education community beginning with the
supercomputer centers. In addition, the infrastructure activity includes
special supporting projects, such as the InterNIC, CNIDR, EDGAR and the
Global School House, designed to further the usability and friendliness of
the network. NCR activity focuses on basic research projects furthering
the knowledge base in information theory, networking, and communications.
Where possible and appropriate these two aspects of division activity
complement each other.
Goals of the Program
The long term vision of the Networking and Communications program is seen
as providing the underlying knowledge leading to a national or
international infrastructure with a primarily optical backbone or core,
including satellites as appropriate, with cable, copper twisted pair,
fiber, or wireless access to provide ubiquitous communications and
information services on demand. Transmission links and storage systems
require effective and efficient utilization of spectrum, space, and time
for the communication of voice, video, text, graphics, or other data from
point to point in space and/or time. Distributed or networked
communications requires extensive protocols for seamless and interoperable
information exchange. Privacy, authentication, and intellectual property
rights require expanded attention in a networked environment. Network
management of shared resources is a fundamental requirement. Basic
research required to enable this vision is the goal of the program.
The focus of the program is to find and support, to the extent of
available funding, the very best basic research in the area encompassed by
the program. Since computer science, mathematics, electrical and computer
engineering, and other disciplines are strong contributors to networking
and communications, another goal of the program is to further collaboration
among these communities of interest. Catalyzing an atmosphere in which
multidisciplinary teams can work together across the spectrum from
materials and devices to systems to networking and communications theory is
also a goal of the program. Within these goals there is an objective of
relating to the infrastructure activities of the Division to enhance the
vision of the future and the choice of research projects.
Continuous evolution of educational resources in networking and
communications as technology advances is essential. For DNCRI this
includes not only involvement of graduate students in research projects,
and ongoing curriculum development to include new knowledge developed in
the research program, but also the development and implementation of new
tools for educational delivery systems, including high bandwidth networks,
digital libraries, and networked information resources.
Relationship of the NCR Program to the NII and HPCC Initiatives
The DNCRI activities in creating the NSFNET backbone network, enhancing
its capabilities through higher speed access and wider connectivity
throughout the research and education communities, and through progress in
the development of tools for utilization of network resources focuses
attention on the potential for information exchange and resource sharing
via networking. The recognition of the value of networking is made clear
by the enormous growth rate of network utilization and by the rapid
emergence of new national industries based on networking. The rationale
for the transition from a government sponsored NSFNET backbone to a
commercial focus is the current availability of network services
commercially where none existed previously. NSF will continue to push the
edge of services at the state of the art and contribute to and accelerate
commercial development.
Furtherance of the objective of networking and information exchange has
been pressed forward by the Congress through the High Performance Computing
and Communications (HPCC) initiative in 1990 and by the National
Information Infrastructure initiative of 1993.
Both DNCRI activities in infrastructure development and in research are
central to and provide the very core for these important initiatives. The
entire division is central to the HPCC initiative. Networking and
communications constitute in fact the second "C" and are central to
distributed computing applications. The growth of the Internet is
dependent upon basic research in networking and communications, and the
future NII will also be based on technology developments resulting from
basic research.
Operation and Funding History of the NCR Program
The NCR program was created in 1987 as a part of DNCRI and CISE. The
initial funding level was very small. Funding for the program has
increased from $3.36 M in FY89 to $10.3 M in FY94. The number of active
projects has grown from 42 in 1989 to 102 in 1994. A major research
initiative in gigabit per second networks, led by the Corporation for
National Research Initiatives (CNRI) and jointly funded by DNCRI/NSF and
ARPA and involving five testbeds, began in FY89 and ends its initial phase
in FY94. In FY93, a special solicitation on All Optical Networking in
collaboration with the Engineering Directorate at NSF resulted in jointly
funded interdisciplinary projects.
Networking and communications research is supported under one program
(NCR). The program is administered by a Program Director and a Program
Manager. No a priori division of the program funds is made; the best
proposals from all submissions are selected for award.
The program draws insight as much as possible from the research communities
it serves, including computer science and electrical engineering and
related disciplines, via workshops and symposia, review panel discussions,
and personal interactions. A program goal is to enhance interaction
between computer scientists, electrical engineers, device physicists,
mathematicians, and others to bring about an integrated approach. In
particular, the networking and communications aspects of the program are
treated in an integrated manner rather than separately. A primary thrust
is fundamental theoretical research. Experimental research, drawing upon
the network infrastructure as a tool and at the same time contributing to
the future development of the infrastructure is a secondary thrust, but is
limited by the high cost of such projects compared to available funds.
4. PRIORITIES FOR BASIC RESEARCH
A number of research areas were identified by the workshop participants as
being especially important and timely. The priorities identified in the
following paragraphs will support the development of future systems, both
by providing the underlying theory to guide system development and, more
generally, by strengthening the necessary educational base. While research
in the areas listed below is encouraged by the workshop participants, the
following list of topics is not intended to discourage the submission of
proposals in other areas. The order of topics presented in the following
paragraphs is entirely arbitrary and no priority assignment is implied.
Coding and Coded Modulation
The future communications network will be digital, and will be based on a
fiber-optic backbone with almost unlimited capacity. At the same time, the
use of wireless communications will continue to explode, both to provide
access to the network for people and computers on the move, and in
stand-alone radio networks for specialized applications. Broadcast
television will become digital in HDTV. More and more bits will be sent
down the existing copper wires that go to the individual home or desk. New
satellite systems for high speed digital communications will be developed.
On channels with less than unlimited capacity, it is well understood that
coding is needed to achieve the best efficiency at low error rates.
Powerful error-correcting codes and error control techniques are now used
almost routinely in data communications and storage systems. The recent
invention of coded modulation has revolutionized communications over
bandlimited channels, and is starting to be used in magnetic storage.
As a research field, coding and coded modulation contains both well
explored and newly emerging areas. There are many fundamental problems to
be answered and practical problems to be solved. Important current research
includes the following areas in code structure, code construction,
efficient decoding algorithms, quantization dual of Euclidean-space coding,
and combined coding and equalization:
* A unified structure theory embracing block, convolutional, lattice and
trellis codes has begun to emerge. There have been exciting advances in
developing structural properties of block and lattice codes, such as the
trellis and decomposable structures, which allow the use of soft-decision
decoding to achieve better performance with reduced decoding complexity.
One goal is to have a better understanding of the structural properties of
existing codes so that efficient decoding schemes can be devised, and
another goal is to construct new codes which have good distance properties
and are easy to decode.
* Coding techniques for memoryless channels have been successfully extended
to channels with intersymbol interference. New codes and suitable decoding
algorithms are needed for other types of channels, such as fading and
bursty channels. Application of coding for fading and interference
channels to wireless transmission deserves to be investigated.
* There have been exciting developments recently in Euclidean-space group
and ring codes, and in Hamming-space algebraic-geometry codes. Our
knowledge of these classes of algebraic codes remains far from complete.
* Suboptimal decoding algorithms that can approach optimal or near optimal
performance with significantly reduced decoding complexity are likely to be
the best choice for high-speed and high-performance applications. New
hardware and software architectures are needed for high-speed decoding.
* Work in the past several years on developing quantization duals of
Euclidean-space coding techniques (source coding), and vice versa, has
been promising. Further development of such dual techniques should enrich
both fields.
* Closer ties between synchronization, equalization and coding are needed.
As codes improve, synchronization and equalization must be maintained in
the presence of more severe errors.
Information Theory
Information theory establishes fundamental limits on the performance of
communication systems. In particular, entropy provides an achievable lower
bound on noiseless data compression, and channel capacity provides an
achievable upper bound on reliable data transmission. All data compression
schemes and all coding, modulation, and transmission schemes are bounded by
these limits.
The insights gained from the evolution of this theoretical work now
thoroughly permeate the design of point-to-point communication systems. In
particular, the principles derived from information theory lie at the heart
of the practical design and implementation of modern data compression,
coding, modulation, and detection. Recently, information theoretic
principles have been generating new approaches to magnetic and optical data
storage. In addition, information theory has made central contributions to
cryptography, public key cryptosystems, computer science, statistics, and
pattern recognition.
Multiaccess information theory is by now relatively well established as
the appropriate conceptual tool to study wireless systems in which multiple
sources share a physical medium to access a single receiver. For any given
multiaccess channel, one can compute the capacity region, i.e., the sets of
source rates for which all sources can communicate reliably with the
receiver. One can also calculate achievable error probabilities, as a
function of coding constraint length, for such systems.
For more general networks of sources and receivers, under different types
of feedback conditions, power constraints, and source cooperation, there is
an impressive collection of theoretical results, but, so far, little
cohesive theory and insight about applications exist.
There are a number of areas in information theory that appear to be ripe
for increased coupling to applications. Two of these, compression and
coded modulation, are treated elsewhere in this report. Others areas
include the following:
* Code division multiple access (CDMA or spread spectrum) for cellular
radio has evolved rapidly in recent years and is appropriately modeled in
terms of multiaccess information theory. Information theory is currently
guiding work on multiuser detection, coding, rate allocation, and power
control. Much more work is needed on modelling the time varying multipath
channels, and on developing multiuser decoding algorithms. It is not yet
clear which theoretical results have practical utility, and the theory
itself is still in a rudimentary phase.
* Coding and decoding for channels with unknown probabilistic behavior is a
problem that is relatively well understood theoretically, but there is a
need for applications of this to practice.
There are also many areas where further theoretical development is
necessary. A few of these are as follows:
* There is a need for a more cohesive information theory of networks. This
involves better understanding of broadcast channels, cooperation, feedback,
and interference.
* Formulating information theoretic principles for networks with bursty
sources has long been a perplexing problem which needs progress before
information theory can truly provide a theoretical basis for data networks.
* Many relations between information theory and estimation, classification,
and statistics have been developed over the years, but it appears that
these relations only scratch the surface.
The above research areas are merely suggestions. History suggests that
the most fundamental and important contributions to information theory come
from researchers following their own insights about problems of inherent
and general interest.
Communications Signal Processing
Communications signal processing covers the theory and algorithms for the
recovery of a stream of data from a waveform that may be deeply buried in
noise and interference and may be subject to a variety of degradations and
impairments. Although the subject of communications signal processing is
closely related to other topics in signal processing, it is a highly
specialized topic with many subtopics. This class of signal processing
algorithms is in wide use both in communication systems and, in very
similar form, in magnetic and optical storage systems. A communications
receiver may have limited knowledge of the transmitted waveform, possibly
it must learn even the modulation format only from the received signal.
Equalization is necessary in almost all receivers because of channel
dispersion.
Closely related to equalization is the problem of bit synchronization.
Very powerful codes for error control are now well known that allow for
reliable communication in the presence of very noisy and degraded channels.
It is important that equalization, bit synchronization, and block
synchronization techniques be developed to a similar level of noise
performance.
Algorithms for channel equalization range from long-standing and
straightforward techniques such as the zero-forcing equalizer to more
recent techniques such as adaptive equalization, either blind or trained.
These are closely related to adaptive filters and may be based on
least-mean-squared (LMS) adaptation. However, VLSI technology now provides
special purpose digital signal processing chips and custom signal
processing chips that can implement sophisticated algorithms. Blind
equalization techniques, which deduce an equalizing filter from a received
unknown data sequence, are necessary for receivers that may dial into a
broadcast waveform in progress.
A variation of the equalization problem is the problem of echo
cancellation which arises in problems of heavy multipath such as wideband
communication in an urban environment. Equalization may also be partially
combined with modulation by means of the modern ideas of prefiltering in
the transmitter to anticipate dispersion in the channel. This method
protects against the unnecessary waste of signal power that would result
from an equalization filter in the receiver. The notions of prefiltering
and of equalization may also interact with modulation in another way; this
through the ideas of Nyquist pulses, partial response signaling, and
intersymbol interference suppression. Maximum-likelihood methods are now
in vogue for combining the ideas of data demodulation and equalization, and
possibly also decoding. The Viterbi algorithm is the algorithm of choice
for implementing the maximum-likelihood demodulator in the presence of all
of these effects provided the number of trellis states is not too high.
Thus there is an interaction between performance at low signal power on a
dispersive channel and the complexity of an affordable Viterbi demodulator.
Signal processing is also important for communication over fading
channels, spread spectrum channels, diversity combining channels, and
interference channels. Demodulators for these channels may employ
nonlinear combining techniques. Waveforms for CDMA applications may
require near/far suppression techniques or transmit power control.
Finally, communication systems may employ space diversity. Multiple
spatial transducers, such as antennas or acoustic devices, may be trained
to create a multitude of individually steered, virtual point-to-point
channels.
Protocol Theory, Design, and Engineering
Today's computer network architectures and protocols are inadequate for
tomorrow's needs, such as gigabit per second communication paths using high
performance fiber-optic links and switching technology. The design and
engineering of high performance networks should be well founded upon
theory. Towards this goal, we need sound and effective techniques for the
design, specification, analysis, implementation, testing, maintenance, and
modification of network architectures and protocols. Recent advances in
protocol theory are beginning to provide understanding into many facets of
protocol behavior and interaction. As the demands for more effective
network communication increase, research on protocol theory must continue
so that we will have a strong foundation upon which to base future designs.
This is especially important when protocols are to be designed and
engineered to accommodate new technologies (e.g., wireless access and
mobility management) and application requirements (e.g., delivery of
variable-bit-rate compressed video for teleconferencing and video servers).
A network, and even more so an internetwork, is necessarily the
composition of a large number of protocols. The communication services
offered by the network are the result of the interaction of its many
protocols which interact with each other through interfaces. To meet the
objectives of network architectures, it is important to understand how
these interfaces should be defined, specified, and satisfied. The
individual protocols should be designed for reuse, portability, efficiency,
modification, and maintainability. Furthermore, to build reliable
networks, it is important not only to prove the correctness of individual
protocols, but also to prove the correctness of the entire collection of
interacting protocols. A complete understanding of protocol interaction
and interfaces is essential to the development of a sound theoretical basis
for composing protocols in the construction of computer networks. We need
to understand how to design and manage such complex software structures, in
which protocol components are typically designed, implemented, modified,
and maintained by different groups of individuals. Most protocols are
designed to perform multiple functions and provide multiple services. This
is done for efficiency but, in many cases, results in very complex
protocols. Usually very little can be proved about their logical behavior.
Methods are needed to synthesize multifunction protocols from relatively
simple ones that implement individual functions. Specifically, techniques
to add new functions to a protocol, without affecting its original
functions or correctness, would be extremely useful. Conversely, methods
to remove specific functions and unnecessary code from an existing protocol
to make it more efficient (lightweight), without affecting the remaining
functions, would let us tailor protocols to specific operating
environments. In this way protocols could ``adapt'' to changes in
underlying switching and transmission technology. The development of such
methods would facilitate the structured implementation of protocols,
improve understanding of interoperability between different protocol
implementations with similar functional components, and address issues of
portability of protocols across implementation platforms.
Formal models are therefore needed that provide a clear understanding of
the relevant theoretical concepts of protocol refinement, projection and
conversion, as well as interface semantics and protocol composition.
Research advances are needed in protocol specification notations, and
semantic models of protocol behavior. Research is also needed to develop
from these notations and models, protocol specification, testing, and
verification methods which can be used in protocol design and engineering
tools. We envision a future in which network protocols, having been
formally verified to work as intended, are cataloged and stored in a
library. Their interfaces would be formally specified in such a way that
their source codes are portable, reusable and easily modifiable.
New high performance fiber optic channels and communication switches are
forcing us to rethink the architecture and structure of computer networks.
Perhaps the old layering paradigm is inappropriate and no longer compatible
with these new high performance networks. As the price/performance ratio of
processors continues to decrease we see more processor capability in
front-end controllers and increasing use of coprocessors. It is necessary
to rethink the decomposition of functions within computer systems and among
their processing elements. Our rethinking should be coupled with
foundational developments in protocol theory and formal models. We need to
understand the interaction among protocols and the resultant engineering
implementation structures. We should also encourage innovative network
architecture and protocol designs. Appropriate metrics for evaluating and
comparing protocols as well as new models for analyzing the performance
characteristics of these architectures and protocols are needed.
Dynamic Network Control
Much research is needed to determine how to configure and control large
high-speed networks of the future. In particular, flow control, admission
control, and routing algorithms need to be developed. New network control
techniques are needed to support new applications with diverse
communication requirements, and to exploit new technology for data links
and switches. The techniques should be dynamic, adapting the network
operating mode in response to changes in network resources or demand.
Future networks approaching gigabit transmission speeds are a driving
force for much of the research on dynamic network control. However a
largely different set of dynamic network control techniques arise in other
contexts, such as in support of ground or satellite-based mobile
information networks, and in support of personal communication systems.
New challenges are posed by the increased ratio of propagation delay to
bit duration. A coast-to-coast gigabit link contains 15 megabits in
transit. Predictive rate control, based on modern automatic control
concepts, needs to be developed. At least in the short run, the increase
in network speed will also cause a large variation in data-rate
requirements. A small number of high-speed sources can generate extremely
bursty traffic loads.
High-speed applications of a network are likely to pose stringent
requirements, including a need for quality of service (QoS) guarantees on
attributes such as end-to-end delay, throughput, support of bursty traffic,
and reliability. "Best-effort'' delivery by networks is not adequate for
some applications, so provisions for negotiating service must be
considered. Research directed towards basic control methods should be
conducted. Some research may be tied to particular new transmission
formats, such as asynchronous transfer mode (ATM). Moreover, some
mechanisms for QoS provisioning in the ATM development serve as useful
examples. However, a better understanding of the network control problem
is also needed for more heterogeneous environments, with a mix of virtual
circuit and datagram traffic, and with the concatenation of multiple
resource control systems, as envisioned for example in the Open Data
Network1. Research is needed in the whole spectrum of switching
techniques, from datagram packet switching to circuit switching, including
a wide variety of virtual-circuit methods.
A closely related issue is the dynamic establishment and management of
special purpose virtual networks over an internet. Execution of
applications over such virtual internets may consume substantial network
resources, especially bandwidth. In addition, transport of the traffic for
these applications may be given priority over "best effort" traffic.
Specific considerations include protocols for specification of resource
requirements of virtual networks, algorithms that access the admissibility
of the virtual network under the network's current operating load,
algorithms that establish the virtual network connection, and algorithms
that manageresources allocated to the virtual network during its lifetime.
At issue are the impact of the existence of the virtual network on
best-effort network traffic and the performance of the virtual network
itself as perceived by the applications.
Cost and complexity considerations may dictate the use of high-speed
switches that occasionally drop packets or block circuits in the face of
high congestion. Traffic modeling, dynamic traffic control, and network
sizing techniques are needed to ensure satisfactory end-to-end performance
in the face of possible packet loss.
Research on network control techniques should be driven in large measure
by an integrated system viewpoint. First, the control techniques should be
designed and ultimately assessed for use in a (possibly large) network, not
just for use on a single link or connection. Secondly, the control
techniques should be suitable for existing or anticipated technology, to
work in conjunction with a complete set of protocols. Implementation
requirements, including communication and computational demands, should be
assessed, whether the techniques are distributed or centralized. Because
of the difficulty in implementing high speed networks, it is unreasonable
to implement every control technique that is evaluated. It is thus
necessary to improve the methodologies for applying such techniques.
However, analyzing implementation requirements, particularly computational
demands, without constructing networks frequently results in inaccurate
results that overlook important aspects of the problems. Therefore, to the
extent possible, analytic work on high speed networks should be performed
in conjunction with physical experiments that verify whether or not the
approach is reasonable.
Internetworking
An internetwork consists of a set of host computers which share a lingua
franca, or common language, for the exchange of information. This common
language, which might be called a bearer service, is mapped onto a set of
lower layer transport networks via a set of mappings from the bearer
service onto a variety of specific networks. An internetwork is created by
concatenation of a set of transport networks, and translation devices,
which then enable end to end provision of the bearer service to hosts
connected to the internetwork. The bearer service must then in turn
support a set of applications which communicate a wide variety of
information via the bearer service. A set of mappings from applications to
the bearer service are required.
Research in internetworking can then be classified in terms of this model
as addressing one or more of the following issues:
* Fundamental internetwork architectural questions deal with the model
itself. These relate to issues such as whether there should be one or more
than one common bearer services, at what protocol layers should the bearer
services exist, how evolvable may a bearer service be, how does one
communicate between networks built around fundamentally different bearer
services, etc.
* There are research questions dealing with the nature of a specific bearer
service. Within the internet community today, the existing bearer service,
IP, is being changed in the context of the IP-next generation work.
Concepts such as larger address spaces, controllable QoS, and provider
selection are being incorporated into the next generation IP. Research is
required to understand what set of characteristics a bearer service should
possess, and what the limitations of any given set of characteristics might
be. Evolvable and non-uniform bearer services are also issues.
* The mapping of bearer services onto specific transport networks is an
area of research. This area includes not only mapping onto new and unusual
local and wide area networks, but also the mappings necessary within the
end systems. Thus, host interfacing issues such as performance and
scalability, as well as issues surrounding the translation of the bearer
service onto specific transport networks, and the requirements the bearer
service may put upon various transport networks are issues. These mappings
must be robust enough that all possible combinations of transport networks
can still be concatenated into a functional end-to-end bearer service.
* Mapping of applications onto bearer services raises research issues about
the applicability of a given bearer service. Today's IP protocol provides
an unreliable datagram service which is not able to support real-time
services such as voice when the network is congested. This has motivated a
body of work which attempts to extend the bearer service to include a
controllable quality of service. Once one has this property, the way in
which applications map onto the service must be extended to allow the
application to specify the service it desires. These type of mappings may
be called application to bearer service signaling issues. Signaling
research may be concerned with issues of internetwork service management,
including naming, addressing, accounting, billing, authentication and
access control, resource discovery and management, and performance/QoS
management, in addition to the recognized need for common internetwork
transport protocols/interfaces.
* Current internetworks often lump together the transport of information
(i.e. packet forwarding engines) with the control of this information (i.e.
routing protocols which load the address tables of the forwarding engines).
It may be useful to consider a more structured division between the
low-level information transportation and its control. Signalling then
communicates information from the application to the bearer service
controllers, while a control interface is used to communicate information
between bearer service controllers and the information transport engines.
Research into these topics may enable more flexible and extensible
implementations of internetworks with complex or evolvable bearer services.
* As internets evolve to support billions of users, scalability of nearly
all components of the internetwork become an issue. Research on scaling of
routing protocols is of particular near-term interest. Also, procedures
once done manually or semi-automatically such as fault isolation, cost
accounting, and others require high levels of automation to lower the
operational costs. These, and many other issues of scale deserve
increasing attention.
Optical Networks
Optical fiber has emerged as the medium of choice for point-to-point
transmission systems because the low-loss, low-dispersion properties of
single-mode fiber allow transmission of information at much higher rates
and over much greater unrepeatered distances than does copper wiring of any
form. However, the fundamental architecture of the nationwide
telecommunications infrastructure has remained essentially that which
evolved during the pre-photonic era; point-to-point transmission systems
interconnecting multiplexing / demultiplexing equipment and digital
switches, with fiber simply displacing earlier technologies as the physical
transmission medium. The advances in transmission speeds not withstanding,
the enormous transmission capacity of the fiber remains largely
under-utilized.
Research in optical networks is aimed at answering the question of how
best to take advantage of the bandwidth and other properties of the optical
fiber to enhance the capacity and flexibility of networks. The optical
physical layer may, in addition to bandwidth, provide a degree of
transparency and flexibility which might result in an optical connectivity
layer which is independent of the fiber's physical interconnection
patterns, transparent to the data being transported, and rearrangeable to
meet changing traffic and service requirements. The essential research
issue is to understand the ways in which such an optical connectivity layer
can be used to advantage and the limitations to its use. There are two
principal modes of accessing this bandwidth; wavelength division
multiplexing (WDM) and very high-speed time division multiplexing (TDM).
The cornerstone and key technology that enables optical networks is the
wide-band fiber amplifier, which makes possible transmission spans between
generation and detection far exceeding systems having repeaters, and has a
broadband gain over a spectrum of about 30 nm, or 4 THz, centered around
the low-loss region of the fiber transmission. This broad bandwidth,
together with the very low-noise amplification of the fiber amplifier, have
brought about many proposals for carrying multiwavelength optical signals
end-to-end all-optically, with signals being routed by passive components
that redirect signals according to their wavelengths. For TDM based
networks, optical signals may similarly be directed by processing of
routing headers in the time domain. There are many research issues that
need exploration before such systems can become practical realities. A
number of these research issues are outlined in the following paragraphs.
a. Fundamentals
The are a number of fundamental issues that demand the attention of the
research community. Among these issues are the following:
* Research on the fundamental aspects of multiwavelength and time-domain
all-optical networks including studies of:
- limits to numbers of users
- limits to geographical size
- limits to network capacity
- numbers of wavelengths and switching elements required
- architectures which take maximum advantage of the
properties of, while overcoming the limitations of, the
physical layer.
* Demonstrations of new network concepts at the local, metropolitan, and
wide-area level
* Fundamental limits to physical layer scalability including the following
studies:
- component crosstalk
- fiber nonlinearities
- signal to noise degradation in amplified distributed networks
- multiwavelength amplifier operation
- optical power regulation throughout a distributed network
- optical wavelength or frequency registration and regulation
b. Transparency
An important issue is the need for and the role of transparency in optical
networks. Questions are: What are the benefits and what are the costs?
What are the most severe limitations of transparency and what limits to
network application and performance do they impose? Research issues
include the following:
- limits to transparency
- applications of transparency
- the role for electronic switching in optical networks
c. Network architectures
The following research agenda appears appropriate:
* Research on network architectures to explore the relationship between
connectivity and network performance, and to understand the potential
advantages of network rearrangeability at the optical layer
* Studies of the cost effectiveness of optical networks with regard to
various applications, and the development of network economic models and
tools
* Studies of the potential improvement of network survivability, and
methods of implementation
* Research on the distributed network control algorithms to effect
wavelength assignment, to perform reconfiguration management, routing,
traffic control, signaling and call setup, and to understand the needs and
means for scalable network control algorithms in reconfigurable optical
networks
* Research on network management and operations in a transparent,
reconfigurable network and studies of the interaction of multiple network
management schemes on a reconfigurable transparent optical network
* Studies of the architectural role for wavelength translation, and its
impact on capacity, connectivity, network scale, and network performance.
Is all-optical connectivity required?
* Research to develop an understanding of the role of hierarchy in optical
network architectures, and its impact on network scalability and
survivability
* Research on architectures and technologies for low-cost optical network
access - important questions are: What is the appropriate interface to
all-optical networks? How far towards the end user should all-optical
networks extend, and what means for accessing the network is most
effective? Are the advantages of optical routing maintained if high-speed
network access is done electronically?
* Studies of evolutionary strategy: How are the functions of transmission
and switching best combined in optical networks, and what are the
trade-offs between multiwavelength and multifiber designs? What are the
considerations in making an optical network upgradeable to advancing
technology such as all-optical switching, for example?
* Studies of optical interconnection networks for high-speed switching
fabrics to produce either very high capacity switches or very high
switch-interface speeds
In very high-speed time domain networks, research issues include means for
doing all-optical regeneration, switching, and routing, and the optimal use
of such techniques in networks.
The overall field of optical networking has reached the point where the
first enthusiasm of infinite bandwidth available at zero cost on a global
basis has begun to run into severe practical difficulties. For example, the
notion of end-to-end optical transparency will be difficult to achieve.
Overcoming one of these difficulties will require fundamental advances in
technologies, while others may be solved by new network designs. All of
them will impact that which can be achieved and the extent to which optical
networks will become useful as a part of the broadband network of the
future. The general research questions to be posed at this time relate to
finding the limits of such networks and technologies as imposed by
real-world technology and architectural constraints.
Security
A great deal of research has been directed toward techniques for
encrypting data to ensure confidentiality; however, networks and
communications remain vulnerable. To counter malicious attacks effectively
and provide secure services, a coherent security architecture is needed.
It is envisioned that such an architecture would include the following
components, among others:
* encryption/decryption techniques to ensure data confidentiality, data
integrity, and origin authenticity
* techniques and protocols for access control (authentication,
authorization, firewalls), ensuring anonymity, and countering traffic
analysis and denial of service attacks
* cryptographic protocols to support financial transactions
* electronic money to facilitate the marketing of services
The emphasis here is on open networks with many domains (rather than the
security kernel of a host node or military networks). In this environment,
different domains typically have their own administrative authorities,
different standards of security, and different security mechanisms and
protocols (trusted servers, authentication protocols, authorization
methods). Thus any overall security architecture should be designed to
accommodate heterogeneity.
As more and more hosts are networked together, it is unreasonable to
expect that they will all have the same high standards of security. Once
an intruder has violated a network at a weak point, it can possibly violate
the seemingly more secure parts of the network. To guarantee that the
effects of any security violation will not spread to other parts of the
network, research is needed into protocols and network architectures for
secure information exchange; in particular, protocols for access control
functions such as authentication, authorization, and authority delegation
are important.
Existing techniques for authorization (e.g., protection bits, access
control lists) are highly implementation dependent. Research is needed into
new authorization approaches that allow convenient composition of
authorization requirements specified by a variety of authorities, or for
different authority domains. The formal semantics of such composition must
be well understood. The design of authorization servers that off-load the
authorization function from network services should be investigated.
Smart cards are now available with which human users can carry out the
computations necessary to authenticate hosts. New protocols for
authentication (user-host, peer to peer, interdomain), key distribution,
and authority delegation are needed. The formal semantics of such
protocols must be well understood. In particular, the formal meaning of a
network or protocol being "secure'' is still an open question. The
consequences of security violations are so severe that we should at least
verify that protocols for secure information exchange can survive known
techniques of attack. In order to deal with the complexity of networks,
verification methods founded upon well-defined semantic models are needed.
Reliable Networks
As the role of the communication system in society has grown, user
expectations for reliable and continuous operation have out-paced our
ability to meet those expectations. Successful realization of a National
Information Infrastructure will require a better fundamental understanding
of the sources of failure in networks and more systematic approaches to
combatting failures.
The sources of network failures can be grouped into three categories:
physical device failures, errors in system design and mistakes on the part
of users or network operations staff. Significant improvements are needed
on all three fronts if the emerging information infrastructure is to meet
the demands that will be placed upon it.
The use of redundancy to detect hardware failures and make systems
fault-tolerant has been used successfully in communication systems for many
years. However, we still lack systematic methods for evaluating alternative
redundancy, fault recovery and repair strategies, making it difficult for
system designers to make intelligent choices. The trend toward higher speed
networks can be expected to lead to lower intrinsic device reliability,
making these issues more critical than in the recent past. Intermittent
hardware failures are the most problematical in practice and the least
understood.
Many of the more spectacular failures of communication systems have been
by design errors, usually in system software. Ironically, software intended
to improve reliability tends to be the most error-prone, since it must
guard against events that are difficult to anticipate. There is a clear
need for more systematic approaches to this class of problems.
The increasing sophistication of distributed network control algorithms
can lead to greater opportunities for catastrophic failures. We need more
effective methods for reasoning about distributed algorithms and simulating
them under realistic conditions. Research is also needed on algorithms that
are self-correcting, to minimize the potential for errors to propagate.
Even the best trained operations staff are prone to making mistakes that
lead to system failures. General techniques are needed that minimize the
need for staff interaction with network equipment, and which minimize the
opportunities for errors when intervention is required.
Switching Systems
Effective implementation of a National Information Infrastructure
extending to individual homes and businesses will require switching systems
with tens of thousands of ports operating at gigabit speeds and supporting
a wide range of applications, from low speed telemetry and control to high
resolution images and multichannel HDTV. These systems will need to support
a continuum of channel bandwidths, bursty traffic streams and highly
dynamic multipoint channels. It must be possible to cost-effectively
engineer them so that users' requests for new channels seldom or never
block and so that end-to-end quality of service guarantees can be provided.
They should have a flexible control architecture that separates the higher
level functionality from particular implementations, so as to facilitate
interoperability across multiple switching platforms and evolution over
successive generations of technology.
Realization of these goals require significant new advances in switching
system theory and design. To date, there are no practical architectures for
nonblocking multipoint virtual circuit switches that can meet the
theoretical limits on optimal scaling with respect to all the
characteristics of practical concern (switching network complexity, routing
memory requirements, connection modification cost, delay), and most systems
now being used have poor scaling properties.
Our understanding of blocking in switching networks remains incomplete.
Effective methods for analysis of blocking probability in multipoint
switching systems are only now being formulated. Queueing analyses of large
switching networks have focused on steady-state behavior for simple traffic
arrival models. Engineering of systems for NII applications will require a
better understanding of the transient behavior of large systems in the
context of non-stationary and highly bursty traffic. Both simulation and
analytical approaches are needed to fully explore these issues.
Recent advances in optical device technology have created new
opportunities for novel switching architectures. While the classical tools
of switching system theory can be applied to such systems, new issues, such
as cross-over minimization and wavelenth re-use require extension of the
standard models.
In the last decade, the research community has witnessed a wide variety of
proposed switching system architectures, but little definitive evaluation
or comparisons. It is time for the community to create evaluation criteria
that factor in both performance and cost measures, where
technology-dependent and technology-independent factors are clearly
separated.
Control architectures for large switching systems have yet to receive
adequate attention from the research community. Architectures that can
support a variety of switching platforms, can support very high rates of
connection configuration, and in which the control processing capacity can
be engineered separately from the switching system capacity are clearly
needed for NII applications, and equally clearly, are well beyond the
current state of the art.
Wireless Networks and Access
Wireless local area data networks are needed to provide high data rates (>
10 MB/s) to low speed and stationary terminals within campus and building
environments, and wireless personal communications systems (microcellular
systems) are needed to provide voice and moderate data rates (~ 1 MB/s) to
moving terminals within all populated areas. These different wireless
access applications require different optimizations in the integration into
efficient wireless access systems of the large numbers of complex and
diverse techniques that make up these systems. These systems need to cope
with the contention and mutual cochannel interference among multiple
randomly positioned terminals that share frequency spectrum, and access
multiple spatially separated access points to fixed networks. The
techniques must work together in harmony to maximize spectrum utilization
(overall system capacity) and system performance in the time-varying
frequency-selective multipath fading environment while minimizing power
consumption in battery operated portable terminals.
Fundamental research to optimize these systems is needed on the following
topics:
* Combined multi-carrier and coding to mitigate delay spread. Effective
implementations of these techniques for time-invariant wireline
transmissions need to be extended and advanced for effective use in the
multiple-access time-varying wireless environment.
* Interference nulling techniques for increasing the reuse of frequencies
and to increase system capacity and improve performance.
* Algorithms and criteria used to determine when handoff from one access
point to another is required. Pattern classification and recognition
techniques should be applied to identify local signal characteristics to
aid in handoff execution.
* Low complexity signal processing algorithms and implementations are
needed to reduce power consumption in battery powered terminals.
* Assessments of system capacity and performance of competing access
technologies are needed in the time-varying dispersive multipath
environment. In order to be useful, these assessments of FDMA, TDMA and
CDMA must be done for the same environmental conditions, and must include,
for each, the same capacity enhancing techniques, e.g., power control,
dynamic channel assignment, optimum handoff algorithms, diversity, and
interference nulling.
* Research on new techniques for improving the performance and capacity of
wireless access systems should be supported.
* Measurements and modeling of radio propagation between a terminal
location and multiple base station locations for different propagation
environments.
Large integrated networks that support wireless access must include
capabilities not required to support fixed point-to-point or
point-to-multipoint communications. Research is needed in large network
protocols, signaling, data based management and routing algorithms to
provide the following:
* Management of large scale mobility. This includes recognition of the
location of mobile terminals away from home, registration of the current
location with the network, and efficient routing from data initiation
locations to new away from home locations.
* Management of small scale mobility. This requires accommodation of
handoff from one network access point to another as terminals move and
efficient routing to the new attachment point.
* Accommodation of the wide range of variability of wireless circuits.
These circuits are often good (low error rates), but occasionally become
bad (bursty errors) with terminal motion or changes in the environment, and
may disappear as a terminal moves out of range, or interference becomes
excessive. Network intelligence must cope with these realities of wireless
access, since mobility is an important feature.
* Security and privacy of the inherently not-secure wireless link.
Provisions for encryption of data, security of identification and
authentication, and resistance to unauthorized users must be provided in
wireless network protocols and signaling.
Networks supporting wireless access must accommodate different wireless
technologies with different mobility characteristics including: a) cellular
vehicular mobile and high tier PCS (terrestrial and satellite) providing
low data rates (<10 kB/s) and high-speed, wide-ranging mobility, b)
low-tier personal communication systems (low-power access) providing
moderate data rates (~ 1 MB/s) and mobility throughout populated areas and
c) wireless local area data networks providing high data rates (>10 MB/s)
with limited mobility in buildings and campus environments.
Data Storage Systems
For many years, the growth in linear and areal bit densities in magnetic
and optical data recording devices showed a steady but predictable
increase. These density increases were largely due to scaling (e.g.,
lowering the flying height of the head in a magnetic hard disk drive) but
keeping the signal processing the same. Within the last year or two,
however, this rate of growth in density has shown a dramatic increase.
This change in the slope of the growth curves has at least partially been
due to the introduction of modern techniques of communications signal
processing to these products. An example is the introduction of a so
called PRML (partial response, maximum likelihood) system whereby instead
of trying to eliminate intersymbol interference by linear equalization
(with the concomitant noise enhancement), one accepts but shapes the
intersymbol interference into the form of a Class IV partial response
channel and then uses Viterbi detection to search for the most likely
transmitted data pattern.
The applications of the principles of modern communications to magnetic
and optical storage devices is still in its infancy and a multitude of
challenging research topics exist in this area. Although research in this
area has shown a steady growth, the breadth and depth of research topics to
be solved could support a larger number of investigations.
Although magnetic and optical storage systems share many similarities with
the more classical communication channels, there are sufficient differences
from the classical channel models. For example, in a high density thin
film magnetic disk, it is observed in the laboratory that magnetic transitio
ns (which carry the information) tend to partially destroy each other.
Furthermore one type of noise (due to the zig-zag nature of these
transitions) is only present where transitions exist and thus should not be
considered as additive and independent of the signal. Thus, new channel
models must be obtained from experimental investigations.
Since classical channel models do not apply, neither do the classical
modulation, coding and signal processing solutions. For example, magnetic
and optical media usually confine their write waveforms to take on only a
small number of values (two, for saturation recording in magnetic media).
This precludes the use of the usual bandwidth efficient modulation
techniques such as QAM. Yet, we know that these channels should be able to
support signals carrying many information bits per unit bandwidth. How to
achieve this remains an unsolved problem.
Furthermore storage surfaces are fundamentally multi-dimensional. The
idea of a track is an artificial constraint that introduces new problems of
tracking and track to track interference.
In addition to the usual implementation constraints, recording channels
have some severe additional ones. In order to record and retrieve at rates
to support today's high speed computers or networks, one needs to read and
write at extremely high data rates (which stresses the capability of the
read-write electronics). Furthermore, many storage devices are intended
for portable use where power consumption is a severe requirement. Finally,
there is the ever present cost pressures which are particularly severe in
commodity products.
With the coming capability to transport enormous quantities of information
at ever increasing speeds, there will be a corresponding growth in the
capacity to store this information. Special purpose storage devices will
be needed for particular types of information (e.g., video). Higher
input-output speeds will be required to accept data from this information
superhighway. Furthermore, it is to be expected that radically different
new storage systems will evolve (e.g., holographic memories).
The storage industry is one of the most successful industries in the
United States. Although the U.S. is still the dominant force in this very
lucrative field, its dominance is under constant threat. It is essential
that we aggressively pursue research in this area.
Video, Speech, Image and Data Compression
With the expected onslaught of multi-media traffic on the national data
superhighways, the need for the efficient digital transmission of video,
speech, images, and data becomes ever more important. Although other NSF
programs treat both speech and video compression techniques, the proper
choice and marriage of these techniques to the peculiarities of data
networks need special attention.
Data compression, for voice, images, video, and data, are old and well
established disciplines within information theory, and at the same time are
applied to constantly shifting application areas. One might think that the
need for compression should disappear with the decreasing cost per bit of
communication and storage, but in fact commercial interest is growing. One
reason for this is that the cost of computation in compression algorithms
is decreasing at about the same rate as communication and storage costs are
decreasing. Another reason is that communication capacity is likely to
remain limited in wireless communication systems such as cellular radio,
personal communication, emergency and military communication systems, and
broadcast video. Yet another reason is that one can temporarily avoid
adding additional storage to personal computers through data compression.
A final reason, for voice, images, and video, is that one can reduce
congestion on packet networks by throwing away less important data. The
segregation of important from less important data is best done by
compression techniques.
Compression can be separated into lossless and lossy compression. In
lossless compression, the original data must be exactly retrievable from
the compressed form; this is usually required for digital data. In lossy
compression, the original data need only be retrieved within some allowable
distortion; this is the case with voice, video, and images.
If speech is to be transmitted over a digital communication system, it is
necessary to convert the speech into a digital format before transmission.
Many methods are available for digitizing speech, and it is desirable to
achieve high efficiency while satisfying the user requirements and the
communication system constraints. User requirements may be concerned with
intelligibility, speaker recognition, and natural voice quality. Some
communication systems require a constant data rate into the digital system.
Other communication systems benefit from a variable data rate format. For
example, CDMA wireless systems take advantage of the voice activity factor
(i.e., the fact that user are not speaking 100% of the time.) to decrease
interference and increase the maximum number of simultaneous users. ATM
networks take similar advantage of variable data rates.
It is to be expected that digitized video will provide a large percentage
of the traffic in future high speed integrated networks. The public's
present addiction to broadcast video will be enhanced by increasing the
number of available channels and the introduction of interactive video.
The worldwide adoption of digital standards for higher definition TV is
expected and electronic cinema is also on the horizon.
A variety of schemes have been proposed for achieving data compression for
video. Both intraframe and interframe coding schemes have been devised and
built. Presently, real time compression systems based upon variations of
the two dimensional cosine transform exist in hardware that can achieve
almost perfect reproduction of video with less than one bit per pixel.
Much higher compression ratios have been promised by other techniques.
Image compression and video compression are closely related, of course,
and advances in one can usually be applied to the other. It is important
in both areas to develop better compression techniques in which important
data can be segregated from less important data in such a way that
reasonable image quality can be retrieved in the absence of the less
important data. This is important in integrated networks where congestion
might require eliminating the less important data. It is also important
for browsing, where one needs to rapidly acquire a large number of less
detailed images, and then focus more closely on very high quality images.
Although much progress has been made in both video and speech
digitization, many fundamental questions still remain. New and more
efficient means for compressing both speech and video are sought. High
priority should be placed on the synthesis and analysis of compression
systems that match the requirements of the new emerging communication
technologies such as digital cellular, PCN and high speed data networks.
Lossless compression is a mature science, and the sliding window type of
Lempel-Ziv algorithm and the adaptive dictionary type of Lempel-Ziv
algorithm have become the workhorses of commercial lossless compression.
These algorithms will adapt in principle to any source statistics with any
kind of memory. In practice, these algorithms are less adaptive because of
the fixed window or dictionary size. These limitations, however, allow the
commercial algorithms to rapidly adjust to changing statistics. There is a
need for a better understanding of adaptive data compression of sources
whose statistics occasionally change (or, more generally, sources with
multi time scale statistics). There is also need for a better
understanding of the relationships between lossless compression and
estimation.
Mobile and Nomadic Computing
The technological advances in hardware miniaturization (e.g., portable
computers) coupled with the advances in wireless technology have led to the
introduction of new computing paradigms - the Nomadic and Mobile Computing.
Nomadic Computing refers to the ability of a user to compute, communicate
and access information regardless and independent of the user's location;
we refer to this feature as "personal mobility." Mobile Computing
introduces the element of "terminal mobility" into the working environment;
i.e., a user's terminal may be moved while engaged in a communication
session or computation processing. Combined, Mobile and Nomadic Computing
allow computing and communication from anywhere and at anytime. A mobile
and nomadic user may need to communicate with other users, to download
files, or to obtain some other network services while accessing the network
intermittently, from different locations, and sometimes while on the move.
In order to communicate, a mobile terminal requires tetherless access to
local-, metropolitan-, and wide-area networks. Thus, Mobile Computing can
be implemented through the wireless technology, allowing the users to
maintain constant connectivity while in the area covered by the wireless
communication. A nomadic user connects (possibly infrequently) to a fixed
network and may use different network attachment points and different
terminal equipment. The challenge in implementing a Mobile and Nomadic
Computing environment is to reduce the effects of personal and terminal
mobility on supported services and applications. In other words and for
example, the performance of applications running on a mobile platform
should only be minimally affected by the terminal mobility. Similarly,
nomadic user interfaces should be preserved when subject to personal
mobility.
Some of the networking issues falling under the subject of Mobile and
Nomadic Computing are:
* effects of the limitations of portable hardware and the effects of
mobility on the performance of applications; e.g., how the limited
computing power and limited throughput of portable machines, or the
frequent changes of associations between mobiles and the fixed network,
affect the performance of applications and what needs to be done to reduce
(or hide) these effects.
* design of applications for portable and mobile hardware
* novel applications and services for the mobile environment (e.g.,
location-dependent services)
* effects of mobility on communication protocols
* design of networking protocols for mobile networks (e.g., Mobile IP)
* consistency of data bases and file systems in the disconnected computing
environment
* location management and user tracking algorithms for nomadic users
* seamless performance across heterogeneous networks
* preservation and transparency of user interfaces to the connection
network and connection hardware (e.g., using different terminal types)
* security in the mobile environment
Some additional non-networking issues, related to the topic of Mobile and
Nomadic Computing, are:
* hardware supporting the portable and mobile environment (e.g., portable
computers, long-life and large-capacity batteries, low-power subsystems,
hardware reliability)
* user interfaces for nomadic computing (e.g., pen-based interfaces,
handwriting recognition, voice recognition)
* economical and social implications of Mobile and Nomadic Computing
Satellite Systems
More than a quarter of a century of research has been directed to the
development of satellite communication systems. Advances in computer,
data, and optical communications have, however, left satellite
communications behind in terms of transmission speed, protocol
compatibility, and time delay performance. Because of this a number of
challenges lie ahead due to changes in satellite applications. A sample of
these changes include the following:
* Satellite applications have evolved from point-to-point (trunk traffic)
to point-to-multipoint (broadcasting), multipoint-to-point (data
collection), and to multipoint-to-multipoint (personal communications).
* Satellite applications have evolved from fixed earth stations to moving
earth stations (personal communications).
* In contrast to early satellite applications, a significant change is from a small number of satellite user networks to a very large number of satellite user networks.
From a scientific point of view, communication by satellite involves
multi-disciplinary areas with many facets. These include the space
segment, the ground segment, orbital dynamics, power sources and the
efficient use of power, launch vehicle technology, transponder
optimization, and the operational strategy of the system. Within the realm
of communications and networking the following research topics are
suggested:
* New innovative concepts, ideas, and applications of network theory,
access strategies, channel coding techniques, modulation alternatives,
techniques for equalization and synchronization are needed for application
to satellite systems. Especially important are applications aimed at mobile
satellite communication systems, personal satellite communication systems,
and very small aperture terminals.
* Asynchronous Transfer Mode (ATM) has been recommended for multimedia,
multi-link, and multi-purpose transmission applications. How can satellite
networks be compatible with ATM?
* The GPS (Global Position System) is basically for location
identification. What are new potential GPS applications?
* Without reference to any particular system, what are the basic underlying
principles which impact the design of all low-earth-orbit and
medium-earth-orbit satellite communication systems. Of particular
importance are low-cost architectures, effective handover procedures,
optimal coverage, performance improvement, and reliability enhancement.
* How should new space segments, new earth segments, and the new
communication infrastructure be developed in order to meet the rapidly
changing user environment?
As can be seen from the preceding list, the optimal design and
implementation of a satellite communication system draws from many areas of
communications and networking, and therefore profits from research in many
of the priority areas previously discussed.
5. RESEARCH INITIATIVES
The following four projects were recommended by the workshop committee as
research initiatives for the NSF. Unlike research projects resulting from
proposals submitted by individuals or single institutions, the initiatives
described in the following paragraphs will require larger funding and will
require a significant level of coordination.
Research Initiative on the Open Data Network
There are many visions of the NII, ranging from 500 channels of TV on
demand to an open, universal network marketplace of ideas, products and
services. This section describes an initiative to explore one particular
vision for the NII, the Open Data Network, or ODN, which emphasizes the
open nature of the interfaces, and open access by service and network
providers. The defining development of this vision can be found in a recent
report from the National Research Council, which served as a motivation for
this initiative proposal1.
While there are a number of aspects to the ODN vision, the most central
idea is that of a protocol layer called the technology independent bearer
service, which is an abstract definition of the basic network service
provided by the various technologies out of which the network is built. The
bearer service is a low-level protocol layer; current examples include the
IP layer of the Internet, or the 3 kHz circuit of the telephone system.
The NRC report identifies the key features that such a bearer service
should have; it should be an open interface, it should be implementable as
a separately priced service, it should be as independent as possible of
technology, it must support a range of quality of service (QoS), and it
should include only those service aspects that cannot be exported to
another layer.
The ODN vision of the NII is a broad one; it includes the services and
objectives of the Internet community, the cable, the telephone and the
entertainment industries. The precise technical details of an integrated
bearer service that can serve all these communities is unproven. One effort
to produce an advanced bearer service is within the Internet community,
which is developing a next generation of the IP protocol, but it remains to
be shown if this effort will be broad enough to meet the needs of this
diverse set of players. This initiative is intended to provide a testbed
for the development and evaluation of any bearer service proposal with this
broad set of objectives.
To meet this set of objectives, a successful bearer service must have a
range of technical features. For example, it will presumably have to
support a range of QoS, it must provide a framework for dealing with
congestion, it must provide building blocks for security, it must provide
for change and evolution, and so on. This list is not meant to be
definitive, but to suggest the range of issues that a suitable bearer
service must address.
a. Core research
Because of the range of issues that the bearer service must address,
successful definition of such a service must depend on research in a number
of areas which were discussed earlier in the report. Most of the Research
Priorities discussed in the previous section of this report impact in some
way the architecture, implementation, and performance of a data network.
b. Architecture
Integration of all these issues into a unified proposal for a service is
an effort in its own right, as can be seen by the level of effort in the
development of the next generation of IP. Architectural efforts of this
sort are very important, and should be separately recognized from the core
research discussed above.
c. Testbed
The key objective of this initiative is to develop a rich enough
experimental context, both in the technology options over which the bearer
service is implemented and as well in the applications it in turn supports,
so that the resulting experiments and demonstrations provide a valid
assessment of the breadth of the proposed bearer service. The testbed
could be realized as a collection of separate experiments, addressing
different technologies and application areas, so long as they are tied
together by an unified vision of a common bearer service architecture. The
manner in which this unified vision can be articulated and imposed on a set
of separate testbed components remains to be defined.
d. Technology in the testbed
For example, the range of technology below the bearer service might
include ATM, very high speed networks, wireless, LANs, and emerging
subscriber loop technology. These specific technologies are suggested both
for their importance and because they have specific technical issues
relevant the breadth of the bearer service. Wireless technology raises
issues of the management of mobility within the network, intermittent
connectivity and variable bandwidth, and the trade-off in function between
the wireless technology and the bearer service. Very high speed networks
raise issues of achieving real throughput, dealing with high delay,
implementation of cost-effective, high performance forwarders, interfacing
to end-nodes and so on. Subscriber loops raise special issues, as discussed
below.
e. Applications in the testbed
Applications should be selected to illustrate the service requirements of
the communities discussed above. Thus, they might include video on demand,
interactive multi-media, telephony, and traditional best effort data
access. Attachment to the testbed of high-performance video servers, for
example, would at the same time demonstrate issues in storage servers, high
speed networking, and effective integration of video into a general
network, as well as the specifics of the bearer service. Attachment of
other application experiments is a validation of the objective of openness,
and should be facilitated. One component of the testbed should be the
construction of a virtual network over the Internet to support the bearer
service, a capability that would permit wide access to the testbed
environment.
f. Objectives of the testbed
At a high level, the objective of the testbed must be to demonstrate real
interoperation among the technologies and services. The key issues are
generality of the bearer service, the cost-effective delivery of key
application data (for example voice and video) and scalability of the
resulting solution. Related issues such as security should also be
demonstrated.
g. Routers for the bearer service
As a part of this testbed, the different technologies must be
interconnected, as is done with IP routers today. To allow experimentation,
it would preferable if the interconnection and forwarding function could be
realized in a changeable manner (e.g., software or programmable hardware),
so that different proposals for bearer services could be explored on the
testbed, and the proposals could evolve as experiments proceed. A key to
experimentation at this level is flexible experimental apparatus, which
must include the interconnection devices or routers.
h. Technology development
As a part of this testbed, new applications and new network technology
could be developed and evaluated. A particular technology example at the
present time is new equipment for subscriber loops. Current commercial
proposals for a next generation subscriber loop seem to specialize on video
delivery and telephony, but do not seem to recognize the potential value of
a general service such as is provided by the Internet. Development and
deployment of advanced subscriber loop technology would at the same time
validate that concept as well as the ability of the proposed bearer service
to integrate this technology into the overall network framework. The NRC
report identifies a number of specific technical options that might be
incorporated into an ODN subscriber loop, including a flexible means to
allocate transmission capacity from the subscriber into the network, the
integration of transport for specialized and for general sorts of data
traffic, and the statistical aggregation of bursty traffic.
Research Initiative on Data Storage Architectures for the NII
Most data storage devices, data storage systems and data storage
architectures have been designed for either stand-alone computers (e.g.,
for PC's or for workstations), for a cluster of computers (e.g., a file
server for a cluster of stand-alone computers) or for computer centers
(e.g., the disks and tape systems that take up all the space in a super
computer center).
The enormous number of users that will be interconnected via the NII, the
tremendous data rates at which traffic will flow over the NII, the mismatch
of data rates which will occur where the NII interconnects lower bandwidth
communication channels and the diversity of services that will be offered
over the NII all will impose an entirely new set of requirements for data
storage systems. If this important issue is not faced early on, the
communications portion of the NII will be designed without properly taking
into account the interplay between the storage and the communications
network.
In the past, users satisfied their storage requirements either by owning
sufficient storage to satisfy their needs or by sharing storage with others
within some organization (such as with others at the same workplace). If
the NII is to reach a majority of the households in the US, the former
approach would be exceedingly wasteful and unduly expensive. The
alternative is to create "sharehouses" of storage which would serve a
community of users. These users would rent storage space as needed
("storage on demand"). There would probably be a basic monthly charge for
this service plus a charge based upon usage. Indeed many users might share
the same storage space if they were sharing common information but such a
scenario would require the standardization of data formats. Lurking in the
background are the issues of privacy, authentication, etc. Models of user
storage requirements would have to be developed in order for the storage on
demand provider to ensure a specified quality of service.
It is likely that buffering of information will be required to accommodate
the high bandwidths of the NII and the lower bandwidths of the "last mile"
into the household and/or mobile users connected by a wireless service.
Here temporary storage will be required for the information at these
interfaces, just as warehouses are used to temporarily store goods
delivered by trucks which travel on our superhighways before they are
delivered to consumers (or retailers who sell to consumers). The storage
devices that interface with the largest bandwidth data channels will have
to have the ability to record at much higher data rates than what is
available in present storage systems. Indeed a hierarchy of temporary
storage devices might be needed with the device closest to the high
bandwidth network being a large capacity device with high bandwidth and
where devices closer to the consumer would have less capacity and lower
bandwidths.
The development of specialized storage devices for specialized
applications is an important part of the NII. For example, video on demand
will impose an entirely different set of requirements on storage devices
than our present requirement for millisecond access for data to a computer.
Alternatively, a general purpose, cheap, and easily deployable storage
might be developed (say from microdisks) which could accommodate a wide
variety of uses.
Although most of the above discussion is concerned with issues of storage
architecture, equally important is the need for the continued development
of storage systems with increased capacity, lower cost, decreased power,
etc.
The following structure is suggested to launch this initiative. First, an
advisory panel of experts which span all aspects of this problem should be
convened to discuss and refine the scope of the initiative. Then a Call
for Proposals should be put forth that encourages response from teams of
investigators which are comprised of experts in both storage and data
communication networks. Responses from both industry and universities
should be sought. Since the problem needs to be attacked both from the
standpoint of basic principles and experimental research, proposals for one
or more testbeds should be sought.
Wireless Research Initiative
Two objectives of the Wireless Initiative testbed are to: a) configure and
demonstrate a high performance wireless data system with technology
prototypes that can provide reliable wireless access at rates greater than
10 MB/s to an open data network testbed, and b) exercise mobility
management and wireless access capabilities of a prototype open data
network testbed that has been built to be compatible with the wireless
access system and technology prototype. The accomplishment of these
objectives will require the installation in a testbed of several prototype
wireless base stations attached to the open data network testbed in at
least two geographically separated locations and construction of several
portable wireless terminal prototypes that can be moved among base stations
within a location and between locations. This is the minimum size
experiment needed: a) to exercise the wireless access system and technology
and both the small scale and large scale mobility management capabilities
of the open data network, and b) to demonstrate their combined performance.
Current research activities (e.g., ARPA sponsored projects at UCLA and
UCB) and commercial products aimed at wireless data networking have been
hampered by the previously limited choices of radio spectrum available for
their use. The focus of these current activities has been on use of
Industrial, Scientific and Medical (ISM) frequency bands that restrict use
to direct sequence or frequency hopping spread spectrum techniques, and
that contain many sources of ISM interference. These techniques are not
optimum for wireless transmission of bursty data at rates of 10 MB/s and
greater. Also, the available spectrum bandwidths cannot support enough
spreading to provide significant spreading gain for such high data rates.
Short-burst data-transmissions are not compatible with the tight power
control and additional degrees of freedom needing initial synchronizing
that are required by high-capacity multiple base-station spread-spectrum.
The FCC has recently allocated 20 MHz of frequency spectrum near 2 GHz for
unlicensed wireless data systems that must be designed to operate without
jamming each other. Also, for time invariant wireline applications,
multi-carrier modulation and coding have been combined to provide high
capacity and multipath mitigation for data transmission over those
bandlimited channels. Research to extend these multipath mitigation
techniques for application to time-varying multiple-access wireless
multipath channels in the newly allocated frequency bands provides
opportunities for advances in the performance and capabilities of
high-speed wireless access to open data networks.
The challenge for wireless local area information networks is to integrate
into an efficient wireless access system a large number of complex and
diverse techniques. Many different techniques are required to cope with
the contention and mutual co-channel interference among multiple randomly
positioned terminals that share frequency spectrum and access multiple
spatially separated access points (base stations) to the fixed network.
The techniques must work together in harmony to maximize spectrum
utilization efficiency (overall system capacity) and system performance in
the time-varying frequency-selective multipath fading environment while
minimizing power consumption in battery operated portable terminals.
Global optimization of the techniques together is required; optimizing each
technique individually does not result in a good overall system solution.
Diverse techniques to be harmoniously integrated to accomplish these
objectives include interference nulling, multipath mitigation
(multi-carrier, diversity or adaptive equalization), radio link level
packet data protocols, handoff criteria and algorithms, frequency
assignment (dynamic assignment algorithms), error control and modulation,
adaptive power control, time and frequency division multiple access, and
encryption for privacy, security and authentication.
Challenges for large integrated fixed networks that support wireless
access are: 1) to provide large scale mobility management (recognition of
terminal location, registration of location, and routing) for terminals
used away from home, 2) to provide small scale mobility management for
handing off terminals from one fixed wireless access point to another as
terminals move, and 3) to accommodate the widely varying error performance
of wireless circuits as terminals move.
A workshop should be held to configure some wireless access systems for
trial in open network testbeds. Research, planning, and implementation of
prototypes for use in the testbed should be supported, along with
experiments using the wireless access techniques in an open data network
testbed. These experimental prototypes should make use of the new
frequency spectrum near 2 GHZ, recently allocated by the FCC for these
wireless communications applications. New wireless access information
networks will take advantage of the opportunity provided by this new
frequency spectrum dedicated for this use, as well as advances in
techniques and technologies resulting from research on wireless access
technologies.
National Gigabit Network Research Initiative
The NSF/ARPA sponsored project on gigabit testbeds has significantly
advanced the field of very high speed networking. The initiative created
five relatively small scale, disjoint testbeds to focus attention on
distributed high performance scientific computing applications and the use
of gigabit networks to support such applications. The Corporation for
National Research Initiatives played a very important role in organizing
this unique collaboration among academia, industry and government. The
visionary, technically ambitious nature of the project appealed to
stakeholders in industry and government, as well as academic researchers,
and the three communities were able to come together to construct a
research project which jointly far exceeded the capabilities of any single
community.
The completion of the gigabit testbed projects in 1994/95 leaves open the
question of how to maintain the research momentum, and capitalize on the
opportunities available for collaborative research in high speed networking
in the 1995-2000 timeframe. One of the main contributions of the gigabit
testbed project was the development of a unique
academia/industry/government collaboration. The landscape has changed
significantly, the research agenda is somewhat different, but the
opportunity for building upon the unique collaboration already established
is, if anything, far more promising than it was in 1988 when the gigabit
testbeds project was formed.
NSF has restructured the NSFNET program along the lines of NSF 93-52, to
create the very high speed backbone network service (vBNS), the Network
Access Points (NAPs), and a Routing Arbiter (RA), and to fund Regional
Network Providers (RNPs) for the purchase of inter-regional connectivity on
the open market. The NAPs, the RA, the RNPs, and the private-sector
inter-regional IP carriers will constitute a coordination mechanism for
commodity networking. There will be 4 NAPs deployed, one each in
California, Chicago, New York, and Washington, DC. The vBNS will be, in
1995, a high speed backbone service connecting the NSF supercomputer
centers operating at 155 Mb/s or greater speeds, with connections to each
of the NAPs, initially at 45 Mb/s. The vBNS and the NAPs are likely to
employ ATM technology, although some of the NAPs will begin with LAN
technology. While the NAPs and vBNS might be used to provide
interconnection among experimental subnets, they cannot serve as viable
research networks for development of the next generation of network
technology, since they must be extremely reliable, and cannot be disrupted
for purposes of experimentation.
Members of the telecommunications industry are quite interested in
contributing towards a national gigabit research network. Many researchers
currently developing applications over limited scale gigabit testbeds could
benefit greatly from access to other research sites with end to end gigabit
speeds. Achievement of this goal will require a wide range of research
activities. Greater gigabit network connectivity through a national
gigabit research network which complements the government investment in
NSFNET would enable a much richer set of collaborations for network and
applications research, and allow a large set of research groups to
participate. A national gigabit network complementing and interconnected
with the new NSFNET can provide an effective basis for continued
advancement of NSFNET capability as well as the technology transfer
necessary to accelerate the NII.
A joint ARPA/NSF workshop was convened July 20-21, 1994, to articulate the
research agenda for high performance networking and applications and
determine the requirements for a gigabit network infrastructure. The
workshop was attended by a broad cross-section of researchers in both
networking and gigabit applications and the workshop report is expected to
present a strong consensus position that carries the endorsement of key
research leaders. NSF should work with ARPA and the research community to
formulate specific plans for creating a gigabit research network
infrastructure that will support the applications and network technology
research agenda outlined in the workshop report.
6. COLLABORATIVE PROJECTS
As the power and extent of communications networks have increased, issues
in networking have become intertwined with issues having to do with the
usage of these networks by human users for the advancement of social and
business purposes. The National Information Infrastructure initiatives
recognize that issues in networking far transcend the technical and
scientific problems usually associated with the communications theory
field. If the great breakthroughs in optical transmission, image
compression, data network protocols, and in other comparable areas
championed by the National Science Foundation in past years are to
contribute significantly to the attainment of national goals, then this
formative work must be augmented by conceptual advances in the
applications, usability, and economics of networks.
Most of the issues in the higher layers of networking, i.e., the
"middleware" and applications layers, involve multi-disciplinary
considerations cutting across the National Science Foundation organizations
and across other government agencies. It is often unclear which
organization has the ultimate responsibility to champion these issues, but
the work itself is vital. Not only are these issues energizing to the
communications field, but it is often true that the applications user
interfaces and middleware needs determine the philosophy of network design
for the lower layers. The committee strongly recommends that the Division
of Networking and Communications Research undertake collaborative efforts
with other divisions of the NSF, and with other government agencies, to
ensure the development of appropriate research in these areas.
Agents and Filters
Agents are intelligent programs that act on a user's behalf to carry out
actions in an autonomous fashion. An example of an agent would be a
program that went into the network in search of a particular piece of
information, such as the address of another user. In carrying out this
task the agent might well clone itself to search out different
substructures of the network. In a highly heterogeneous network of
networks with ever-changing, locally-maintained directories, this is an
important and difficult problem. Since the agent itself has many of the
characteristics of a virus, a high priority area of research is the
incorporation of protection against harm to the network and user resources.
A useful instance of simple agents is executable email. An electronic
mail message could, for example, act as an automated polling mechanism with
built-in return forms and statistical analysis of these returns. An
executable email message could also serve for catalog ordering of items
wherever the recipient clicked his mouse. The uses are obvious, but the
protection concerns are paramount.
Filters are programs that select and prioritize information according to
the instructions, needs, or customs of a given user. Simple filters today
sort and prioritize electronic mail based on subject, author, key words,
etc. Other experimental uses include the selection of news items from a
passing stream of information. At issue is the effectiveness of user
profiles, whether these are pre-selected by the user or learned over time
by the filter itself based upon the accumulation of instances. The
problems are greatly compounded when the information is in the form of
digitized sound or images, as opposed to text. In a world increasingly
filled with a flood of information, and with users ever more strained for
available time, filters will assume an important role in the acquisition of
information.
Navigation Tools
Arguably the most important development the past year in the evolution of
the Internet was the introduction of Mosaic, a hypermedia information
navigator that has opened up the network both to untrained users and to new
and non-traditional information suppliers. Mosaic presents the user with a
"point and click" interface that relieves the user from having to know
where on the network the information sources are located and how these
resources can be obtained. Mosaic also incorporates sound and both still
and video images. It was originated at the University of Illinois National
Center for Supercomputing Applications under funding in the gigabit testbed
program. Through 1993 its use grew at the incredible rate of 11% per
week, exceeding one million users by the beginning of 1994.
Mosaic is the latest in a succession of information navigators, or front
ends, that includes Gopher, World Wide Web, and the Wide Area Information
System. It is now very clear that the expansion of Internet into
electronic commerce and into the nation's homes will be critically
dependent upon its ease of use as perceived at the customer interface.
Although the Mosaic program is currently serving as the model for this
interface, and is in fact being rapidly commercialized, there is the
likelihood that further exploration of the principles of information
navigation might result in new breakthroughs in the application and use of
networks. It is recommended that collaborative efforts be undertaken
towards establishing models, techniques, and behaviors in the navigation of
heterogeneous networks of disparate and ever-changing information bases.
Human Interfaces
Information navigation is one aspect of the user interface to computer
networks. In Apple's influential advertisement featuring the "knowledge
navigator" the user engages in a spoken dialog with his palmtop computer.
"Show me the amount of rainfall in Brazil by year," he speaks to the
computer, which responds with charts that exemplify the desired
information. Subsequently, the computer negotiates video calls and
conferences, relieving the user of the responsibility of placing and
administering these multimedia connections.
One of the highly contested and debated areas of network interface today
is in the set-top box that connects the user to video-on-demand services.
Principles relating to how average users will interact with these highly
intelligent appliances are not well understood, yet the utility and
economics of broadband services will depend on how well accepted these
interfaces become. It took many years, for example, for widespread
acceptance of the mouse/windows interface to become nearly universal in
personal computing.
Another paradigm for naive user interaction with a network is being
pioneered today by General Magic, with an interface that perhaps owes more
of its antecedents to the world of video games. In conducting electronic
shopping using this interface, the user effectively "walks" down a street
filled with shops. Doors can be opened, shops entered, and purchases made.
It remains to be seen what level of acceptance this interface can achieve
among the untrained populace, as compared with the the point-and-click
hyperlinks of the Mosaic interface.
Research problems in the human interface to networks include issues in
behavioral science, computer science, speech and handwriting recognition,
image understanding, language understanding, and other allied fields. Some
of these issues will affect the network design, while others may be
regarded as incidental to the philosophy of networking. All of them will
determine how and how much networks are used in the future.
Electronic Publishing
Electronic publishing is a field that has its genesis in the emergence of
wide scale public networking, but at the moment it is still in an
experimental phase. A number of journals and information providers are now
offering free or subscription versions of their conventional publications
through Internet. Others are inventing new multimedia forms of their
journals that take advantage of the unique capabilities of computer
networks. All of these efforts seem tentative and experimental at present,
establishing a presence for the time when a suitable infrastructure for
electronic publishing becomes a reality.
Perhaps the most important issues in electronic publishing lie outside the
conventional technological domain. Certainly, copyright and intellectual
property protection are at the forefront of discussion and controversy in
this field. There are technical considerations that affect these issues
however. One important capability in the network is the efficiency of
billing. Can the network support the collection of a very small charge per
unit of information accessed, or will the cost of billing itself swamp the
small charge? Achieving a reliable, secure, and inexpensive billing system
will be essential to foster the new electronic publishing industry.
The techniques developed in cyptology for privacy and security have direct
applicability to electronic publishing. For example, it may be necessary
to ensure privacy or anonymity in the access of information. Copyright
protection is another problem that may be amenable to technological
solution through the use of cryptographic techniques.
Scientists and engineers themselves have much to gain by building an
infrastructure for electronic publishing. Advances in science are
dependent upon a fast, efficient, and open publication system. The rate of
advancement of technology has now outstripped the conventional publication
system, and many scientists and engineers look to Internet to provide the
latest information. However, the current culture in network news groups is
so inefficient that many knowledgeable users have quit reading these
bulletin boards altogether. Collaborative experiments for the publication
of technical information might be an especially fruitful area for National
Science Foundation participation.
Economics
It is difficult to consider many of the most important issues in
networking without confronting issues in economics. In considering the
National Information Infrastructure, for example, what is the cost of
installing broadband capability? How does this compare with the cost of
ISDN? How much more does it cost to make this capability two-way, as
opposed to broadcast (and low speed control) only?
Why does Internet appear to be free to industrial users? Is it because
Internet has discovered a more cost-efficient architecture for networking,
through the philosophy of pushing complexity and cost to the periphery? Is
it because Internet has a simple fixed-cost billing algorithm? Or is it
because Internet has avoided the regulatory controls that have through many
years achieved a socially-accepted distribution of the costs of the
telephone infrastructure among the many classes of users?
It is frustrating to technologists that the costs of communications
networks are so poorly understood, and seem only weakly dependent upon
technology. Where are the economic bottlenecks, and how can technology be
used to make network access and services inexpensive?
Collaborative efforts in the economics of networking would only be
fruitful for communications technologists if real wisdom bearing on design
philosophy was likely to emerge. The track record here does not encourage
optimism, but some of the most critical national issues in networking
depend on a better understanding of economics. Possibilities for
collaboration are worth exploring, but must be carefully assessed.
Workstation Structure and the Communication Environment
Current workstations and personal computers are not designed with the aim
of supporting very high speed network interconnections. With the exception
of the fastest supercomputers, internal bus structures typically cannot
support interfaces that run at speeds much above a few hundred megabits per
second or less. Gigabit network speeds will require internal computer bus
speeds that are at least several times that rate. Even at speeds of a few
hundred megabits per second, the workstation software imposes a set of
further bottlenecks for the data to contend with. Operating systems are
not designed to handle large data flows in very short time intervals or
those with real-time constraints. Applications programs often interface
the operating systems in ways that provide barriers to high speed operation
to the end application. The applications themselves may need to be
rewritten or reconceived to allow such high speed operation, even if all
the underlying software can support high data rates. Architectural
approaches to the design of workstation hardware and software are needed
that will alleviate these limitations and enable the transition from the
slower existing network environments to the higher speed network
environments of the future.
Middleware
The National Information Infrastructure (NII) will consist of a large
number of application specific capabilities that are provided in a
nationwide networking environment consisting of many interconnected
physical elements. While a user could write software applications for a
given piece of hardware without the need for operating system software,
there is great advantage in not requiring each such user to separately
invent or reinvent file management conventions, memory management
techniques, scheduling, and resource allocation procedures. Further, by
having common software services that all the applications can share,
independent applications have a better chance of being able to
interoperate, and multiple processes may even run essentially at the same
time.
A similar set of intermediate software services (to be known as
middleware) is needed in the NII to assist applications developers in
creating applications and systems efficiently. Independent applications
development groups may have the ability to interwork their applications
over the NII without having to do joint development. Examples of generic
middleware capabilities are persistent storage in the network, locator
services, and global resource allocation. Examples of application specific
middleware capabilities would include codified definitions of common terms,
mappings between common terms and discipline specific terms, and widely
used application specific functions. Research is needed to define the
taxonomy and framework of the middleware and to explore specific instances
of middleware in a collaborative network environment.
Optical Systems
Optical networking and communications is very much interdependent on
optical devices and systems. This includes the development of integrated
optical components, the integration of these components into optical
systems, and the integration of optical components and systems with
electronic systems and components. Optical interconnects for computer
systems and optoelectronic computing systems are closely related topics.
In 1993 the Networking and Communications Research (NCR) program, in
collaboration with the Electrical and Communications Systems Division in
the Engineering Directorate and the Cross Disciplinary Activities Division
in the Computer and Information Science and Engineering Directorate,
conducted a special solicitation on all-optical networking, with a focus on
the interaction of device, systems, and networking researchers. A workshop
was held, white papers were solicited and received, followed by a smaller
number of full proposals, and five awards to three universities were made.
Subsequently a Foundation-wide committee was established to facilitate
collaborative efforts in optical systems and NCR is a participant is this
effort. Small group research integrating optical networking and
communications with optical devices and systems should continue to be
supported. Also, it will be especially necessary to encourage partnerships
among academic and industrial researchers if progress is to be realized in
this field.
Applications of Gigabit Networks
While the technology of gigabit networks enables the interaction of
multiple machines at very high speeds, not all network applications require
high bandwidth. Applications per se do not normally fall largely within
the network research area. Uses which do require very high bandwidth often
involve supercomputers and scientific grand challenges; these generally lie
at the heart of other scientific disciplines. Design and manufacturing
applications are often engineering enterprises and computer intensive.
Most tools for collaboration, including those that are specially designed
for very high speed networks, are as much a distributed computing activity
as they are a networking activity. Thus, we expect that most efforts to
apply gigabit networks will require the joint support of multiple divisions
of NSF and possibly multiple agencies of the government. These kinds of
collaborative activities are encouraged.
Networking of Applications
Techniques are sought that enable scientific research applications that
have been developed for operation on a single computer to be made
operational in a distributed computing environment on the network. These
include techniques for describing how to partition a given computation to
run on multiple machines, tools for recrafting software for this
environment and for distributing the components to other machines, and
mechanisms for linking the components together and for instrumenting the
resulting system. Where administrative control of the machines and their
software environments cannot be provided easily, techniques need to be
developed to locate and negotiate for network resources. Systems that
facilitate the dynamic implementation of a shared computational environment
are likely to provide implementation and execution efficiencies, but the
use of standard execution environments will also be necessary.
7. CONCLUSIONS
This report identifies and describes a number of important research
priorities (15 in all) central to the communications and networking area.
These areas must be supported if a firm scientific base is to be provided
for the design, development and deployment of future communication systems
and networks. Many of these priorities represent enabling technologies for
the National Information Infrastructure (NII). The four research
initiatives, which are broader in scope and will require greater funding
than single investigator projects, relate directly to the design and the
deployment of future large-scale systems. It is now clear that development
of future communication systems and networks is very much an
interdisciplinary activity requiring expertise from the fields of
electrical engineering, computer science, materials science, mathematics,
and a number of other fields. In recognition of this interdisciplinary
nature a number of activities are described in this report, which are
suitable for collaborative efforts between several NSF divisions and for
collaborative efforts between the NSF and other federal agencies.
1Realizing the Information Future, National Research Council, 1994.
1 Realizing the Information Future, Computer Science and
Telecommunications Board, National Research Council, National Academy
Press, Washington D.C., May, 1994, a study commissioned by the NSF.