Advanced Network Technology

June 1993

OTA-BP-TCT-101

NTIS order #PB93-203735
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Advanced Network

Technology--Background Paper, OTA-BP-TCT-1O1 (Washington, DC:

U.S. Government printing Office, June 1993).

For sale by the U.S. Government Printing Office

Supcl IIIILWIICIII (If [k)c ulllLlll\. \lAll stop $s01’, \$ Allllg((u. [)(’ 2(141? () ~?x

ISBN 0-16 -041805-4
-— . .

Foreword

c

omputer networks are having dramatic impacts on our lives. What were

once esoteric tools used only by scientists and engineers are becoming

more widely used in schools, libraries, and businesses. At the same

time, researchers are working to develop even more capable networks

that promise to change fundamentally the way we communicate.

This background paper analyzes technologies for tomorrow’s information superhighways. Advanced networks will first be used to support scientists

in their work, linking researchers to supercomputers, databases, and scientific

instruments. As the new networks are deployed more widely, they will be used

by a broader range of users for business, entertainment, health care, and education applications.

The background paper also describes six test networks that are being

funded as part of the High Performance Computing and Communications

Program. These test networks are a collaboration of government, industry, and

academia, and allow researchers to try new approaches to network design and to

attack a variety of research questions, Significant progress has been made in the

development of technologies that will help achieve the goals of the HighPerformance Computing Act of 1991.

This is the third publication from OTA’s assessment on information

technology and research, which was requested by the House Committee on

Science, Space, and Technology and the Senate Committee on Commerce,

Science, and Transportation. The first two background papers, High

Performance Computing & Networking for Science and Seeking Solutions:

High-Performance Computing for Science, were published in 1989 and 1991,

respectively.

OTA appreciates the assistance of the National Science Foundation, the

Advanced Research Projects Agency, the Department of Energy, the National

Aeronautics and Space Administration, and many experts in industry and academia who reviewed or contributed to this document. The contents of this paper,

however, are the sole responsibility of OTA.

h- -

Roger C. Herdman, Director

. . .

Ill
Reviewers

Rick Adams

CEO

UUNET Technologies

Robert Aiken

Department of Energy

Raymond Albers

Assistant Vice President

Technology Planning

Bell Atlantic

Alan Baratz

Applications Solutions Director

High Performance Computing and

Communications

IBM

Adam Beguelin

Research Scientist

School of Computer Science

Carnegie Mellon University

Richard Binder

Principal Scientist

Corporation for National Research

Initiatives

John Cavallini

Deputy Associate Director

Office of Scientific Computing

Department of Energy

Bruce Davie

Member of Technical Staff

Broadband Packet Switching

Research

Bellcore

Darleen Fisher

Associate Program Manager

Division of Networking and

Communications Research and

Infrastructure

National Science Foundation

Linda Garcia

Senior Associate

Office of Technology Assessment

Tom Hausken

Analyst

Office of Technology Assessment

Milo Medin

Deputy Project Manager

NASA Science Internet Office

NASA

Paul Messina

Director

Caltech Concurrent Supercomputer

Facility

California Institute of Technology

Craig Partridge

Senior Scientist

Bolt Beranek and Newman

Daniel Stevenson

Director

Communications Research

MCNC

Richard Thayer

Director

Federal Government Affairs

AT&T

Bo Thomas

Senior Federal Account Manager

sprint

Philip Webre

Principal Analyst

Congressional Budget Office

AlIan Weis

President

Advanced Network & Services

Joan Winston

Senior Analyst

Office of Technology Assessment

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the reviewers. The

reviewers do not, however, necessarily approve, disapprove, or endorse this background paper OTA assumes full responsibility for the background paper and the accuracy of its contents.

iv
ALAN BUZACOTT

Project Director

Administrative Staff

Liz Emanuel, Office Administrator

Barbara Bradley, Secretary

Karolyn St. Clair, PC Specialist

Preject Staff

John Andelin

Assistant Director, OTA

Science, Information, and

Natural Resources Division

James W. Curlin

Program Manager OTA

Telecommunication and

Computing

Technologies Program
contents

1 Introduction and Summary, 1

Federal Support for Gigabit Networking, 1

summary, 8

2 The Internet, 15

Applications, 21

Protocols, 24

Network Components, 26

The Internet and the Public Switched Network, 31

3 Broadband Network Technology, 35

Broadband Applications, 35

Fast Packet Networks, 42

Network Component Development-Current Status, 44

Application of Broadband Technologies, 47

4 Gigabit Research, 51

Research Objectives, 52

Testbed Progress, 56

5 Application of Testbed Research, 65

Application to the NREN, 65

Application to Other Networks, 70

INDEX, 75

,

‘$?

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I I 1

vii
—

T

Introduction

and

Summary 1

he vision of the Nation’s future telecommunications

system is that of a broadband network (see box l-A) that

can support video, sound, data, and image communications. Toward this end, the High-Performance Computing Act of 1991 called for the Federal computer networks that

connect universities and Federal laboratories to be upgraded to

“gigabit networks” (see box l-B) by 1996.1 This background

paper reviews technologies that may contribute to achieving this

objective, and describes the six prototype gigabit networks or

“testbeds” that are being funded as part of the Federal High

Performance Computing and Communications Program. These

prototype networks are intended to demonstrate new communications technologies, provide experience with the construction of

advanced networks, and address some of the unresolved research

questions.

FEDERAL SUPPORT FOR GIGABIT NETWORKING

The High Performance Computing and Communications

Program (HPCC) is a multiagency program that supports The HPCC

research on advanced supercomputers, software, and networks.2

In part, these technologies are being developed to attack the program funds

“Grand Challenges”: science and engineering problems in

climate change, chemistry, and other areas that can only be the development

solved with powerful computer systems. Network research is one of new of four components of the HPCC program, and represents about

15 percent of the program’s annual budget of close to $1 billion.3

communications

1 High-Perfo rmance Computing Act of 1991 (HPCA), PL 102-194, Sec. 102(a).

2 Office of Science and Twhnology Policy (OSTP), “Grand Challenges 1993: High technologies.

Perfo rmance Computing and Communications, ’ 1992.

3 Ibid., p. 28.
2 I Advanced Network Technology

Box l-A–Broadband Networks

Computers and networks handle informa- Figure l-A-l—Digital Data

tion as patterns of electronic or optical signals.

Text pictures, sound, video, and numerical Electrical or optical signal

data can then be stored on floppy disks, used

in computations, and sent from computer to

~

1

I

1

J

“ 1

computer through a network In digital/computers or networks, the electronic or optical signals

that represent information can take on one of Binary representation

two values, such as a high or a low voltage,

which are usually thought of either as a “l” or “1” “o” “o” “l” “l” ,,(),, H,,, “o” “l” “o”

a “O” (figure l-A-l). These 1s and 0s are called

bits. SOURCE: Office of Technology Assessment, 1993.

Different patterns of 1s and Os are used to represent different kinds of data Inmost computers, the letter ”A”

is represented by the pattern of electronic signals corresponding to “01 000001 .“ To represent images, different

patterns of bits are used to represent different shades (from Iight to dark) and odors. Sound is represented in much

the same way, except that the patterns of bits represent the intensity of sound at points in time.

The number of bits required to represent information depends on a number of factors. One factor is the quality

of the representation. A good quality, high-resolution image would require more bits than a low-resolution image.

Also, some kinds of information inherently require more bits in order to be represented accurately. A page of a book

with only text might contain a few thousand characters, and could be represented with a few tens of thousands

of bits. A page of image data on the other hand, could require millions of bits.

Because images and video, which is a sequence of images, require many more bits to be represented

accurately, they have strained the capabilities of computers and networks. Images take up too much space in a

computer’s memory, and take too long to be sent through a network to be practical. The new high-capacity network

technologies described in this background paper have the ability to support two-way digital, image, and video

communications in a more efficient manner.

Digital Networks

In the past, networks designed for video or sound used anabg transmission. In the old analog telephone

network, for example, the telephone’s microphone converted the spoken sounds into an electrical signal whose

The other three components of the program target Network (NREN). The gigabit research program

supercomputer design, software to solve the

Grand Challenges, and research in computer

science and mathematics.

The HPCC program is the most visible source

of Federal funds for the development of new

communications technology. The networking component of the program is divided into two parts:

1) research on gigabit network technology, and 2)

developing a National Research and Education

supports research on advanced network technology and the development of the six testbeds. The

NREN program supports the deployment of an

advanced network to improve and broaden network access for the research and education

community. The High-Performance Computing

Act of 1991 specfies that the NREN should

operate at gigabit speeds by 1996, if technically

possible. 4

4 HPCA, op. cit., footnote 1.
Chapter I—Introduction and Summary | 3

strength corresponded to the loudness of the sounds. This signal then traveled through the network’s wires until

it reached its destination, where it was used to make the telephone’s speaker vibrate, recreating the spoken

Sounds.

Digital/ networks transmit information in digital form, as a series of bits. Digital networks are required for

high-speed communications between computers-computers work with digital data. However, digital networks

can also transmit real-world information such as sounds and pictures if special digital telephones or video cameras

are used to represent the information in digital form. A digital telephone, for example, generates a series of patterns

of Is and 0s, corresponding to the loudness of the sounds. At the destination, these 1s and Os are interpreted by

the digital telephone and used to recreate the original sounds. Digital networks are quickly replacing analog

networks. They are needed to transmit the growing amount of computer data They also transmit voice and video

information more cleanly, without interference and distortion. More importantly, digital networks allow a single

network to carry all types of information. Today, separate networks are used for voice traffic (the telephone

network), computer communications (data networks such as the Internet) and video (broadcast or cable television

or other specialized networks). Because these different kinds of information can all be represented in digital form,

a single digital network can potentially be used to transmit all types of information. This is not the only requirement,

however (see ch. 2 and ch. 3).

Broadband Networks

The Capacity of a digital network is often described in terms of the number of bits that the network can transmit

from place to place every second. A digital telephone network can transmit 64,000 bits every second. This is

sufficient capacity to carry a telephone conversation with acceptable quality, but is not enough to carry video.

Although some videotelephones can use regular telephone lines, users of videoconferencing systems usually

prefer to use special services that can transmit at 384,000 bits per second or more. VCR-quality television needs

about 1.5 million bits per second, and high-definition television needs about 20 million bits per second--about 300

times the capacity of a digital telephone line.

The Capacity of a network, measured as the number of bits it can transmit every second, is called “bandwidth.”

Engineers often talk about “narrowband” networks, which are low bandwidth networks, and “broadband”

networks, which are high bandwidth networks. The dividing line between the two is not always clear, and changes

as technology evolves. Today, any kind of network that transmits at more than 100 million bits per second would

definitely be considered a broadband network. Chapter 3 describes fiber optics and other technologies that will

be used to build broadband networks.

SOURCE: Office of Technology Assessment, 1993.

Broadband networks such as the NREN will removed as a bottleneck, the computers will be

both improve the performance of existing applications and accommodate new types of applications. There will likely be a shift to image- and

video-based communications, which are not adequately supported by currently deployed network

technology. “Multimedia” applications that use

images and video, as well as text and sound, look

promising in a number of areas, e.g., education,

health care, business, and entertainment. Broadband networks will also allow a closer coupling of

the computers on a network; as the network is

able to form an integrated system that performs as

a single, more powerful, computer.

Broadband networks will require a fundamental rethinking of network design. Several new

concepts have been proposed and are being

investigated by the testbeds. Fiber is a highly

touted technology for constructing broadband

networks, but it alone is not sufficient. Switches

(see box l-C) and the components that link

computers to the network will have to be upgraded at the same time in order to keep pace with
4 I Advanced Network Technology

Box l-B-Gigabit Networks

Much of the research described in this background paper is aimed at the development of gigabit networks,

broadband networks that can transmit data atone billion bits per second or more (a “gigabit? is one billion bits;

“gigabit per second” is abbreviated as Gb/s or Gbps). This represents a 20-fold increase over the most capable

links in the networks that currently serve the research and education community. The current National Science

Foundation network uses Iinks that transmit data at 45 million bits per second (megabits per second or Mb/s), and

even this capacity has not been fully utilized because of bottlenecks in the network’s switches. The development

of a gigabit network is an ambitious target-most current industry technology planning targets broadband networks

with lower bandwidths, in the 150 million bits per second range.

The basic outlines of the technology evolution of the DOD, NASA, DOE, and NSF networks that serve

research and education were established in 1987 and 1989 reports issued by the Office of Science and

Technology Policy. In the late 1980s, link bandwidths in the Federal networks were 1.5 Mb/s or less. The OSTP

reports outlined a three-stage plan for the evolution of these networks to gigabit networks by the mid-to-late 1990s

(see figure l-B-l). The gigabit target was also specified by the High-Performance Computing Act of 1991. The

OSTP report envisioned that each generation of technology would move from an experimental phase in the

Federal networks to commercial service.

Figure l-B-l—Timetable for the National Research and Education Network

Stage 3 –.- -—.--.– —-- ---- Experimental networks

Gbits/sec 1 -

Research and development —.———— I

Revolutionary to commercial

technology

changes

/

Stage 2

45 mbps

h

Operational network

.-

Evolutionary

changes

Stage 1

1.5 mbps

F’”-

r–-‘-:::= Stages 1 & 2 R&D

89 90 91 92 93 94 95

services

. . . . . . . . . . .

. . . . . . . . . .

96

SOURCE: Office of Science and Technology Policy, "The Federal High Performance Computing Program,” September 8, 1989.

Currently, the Federal agency networks are in the middle phases of the second stage, the operation of

networks with 45 Mb/slinks. At the same time, research and development for the third stage, the deployment of

gigabit networks, is underway. In practice, the network capacity will not jump directly from 45 Mb/s to gigabit rates.

The next step will be to 155 Mb/s, then to 622 Mb/s, and then to greater than one gigabit per second. The

bandwidths used in computer networks (1.5 Mb/s, 45 Mb/s, 155 Mb/s, and 622 Mb/s) correspond to standards

chosen by manufacturers of transmission equipment.

SOURCES: Office of Science and Technology Policy (OSTP), “A Research and Development Strategy for High Performance Computing,”

Nov. 20, 1987; OSTP, “The Federal High-Performance Computing Program,” Sept. 8, 1989; High-Performance Computing Act of 1991

(HPCA), Public Law 102-194, Sec. 102(a).
—.

Chapter I–Introduction and Summary | 5

Box l-C-Computer Network Components

A computer network has three main components: computers, links, and switches (figure 1 -C-l). The web of

links and switches carry data between the computers. Links are made of copper (either “twisted pair” or “coaxial

cable”) or fiber optics. Transmission equipment at each end of the fiber or copper generates the electrical or optical

signals. There are also satellite and microwave links that send radio waves through the air. Fiber has several

advantages over other types of Iinks--most notably its very high bandwidth. The fiberoptic links needed for gigabit

networks are already commercially available. However, gigabit networks will not be deployed until research issues

in other network components are addressed.

Figure l-C-l—A Simple Computer Network

{ \

Link m -

1

(

+15A .

El -

-

!54

-53

SOURCE: Office of Technology Assessment, 1993.

For example, new high-capacity switches are needed to keep pace with the higher bandwidth of fiber optic

links. Just as railroad switches direct trains from track to track, the switches in computer networks direct information

from link to link. As the information travels through the network, the switches decide which link it will have to traverse

next in order to reach its destination. The rules by which the switches and users’ computers coordinate the

transmission of information through the network are called protocols.

While most computer networks are limited in their ability to carry high-bandwidth signals such as video, cable

television networks are widely used to distribute television signals to homes. However, cable networks usually do

not have switches. For this reason, they only permit one-way communications: the signal is simply broadcast to

everyone on the network. Much of the network research today is devoted to the development of switches that would

allow networks to support two-way, high-bandwidth communications.

SOURCE: Office of Technology Assessment, 1993.

the faster flow of data. Broadband networks will sufficient flexibility to carry all types of informabe more than simply higher bandwidth versions of tion efficiently.

today’s networks, however. Networks will also be

redesigned so that a single type of network can B The NREN

carry video, sound, data, and image services. The One objective for the NREN is that it serve as

existing telephone and data networks do not have an enabling technology for science and engineer-
6 I Advanced Network Technology

ing researche5 The gigabit NREN will be able to

handle the very large data sets generated by

supercomputers. Scientists could use the gigabit

NREN to support “visualization,” the use of a

computer-generated picture to represent data in

image form. For example, ocean temperatures

computed by a climate model could be represented by different colors superimposed on a map

of the world, instead of a list of numbers.

Visualization is an essential technique for understanding the results of a simulation. Currently,

much of the data

B

periments and

roadband computed by simnetworks will require ulations goes un-

,

a fundamental used because of

the time needed

rethinking of to compute imnetwork design. ages on conventional computers.

Supercomputers could perform the computations

more quickly, but few laboratories have supercomputers. With a high-speed network, a scientist

could send the data to a distant supercomputer,

which would be able to quickly compute the

images and send them back through the network

for display on the scientist’s computer.

A second objective for the NREN program is

that it demonstrate and test advanced broadband

communications technologies before they are

deployed in commercial networks. The NREN

program will upgrade federally supported networks such as the National Science Foundation’s

NSFNET, the Department of Energy’s Energy

Sciences Network (ESnet), and the National

Aeronautics and Space Administration’s NASA

Science Internet (NSI).6 These networks form the

core of the “Internet” a larger collection of

interconnected networks that provides electronic

mail services and access to databases and supercomputers for users in all parts of the United States

and around the world.7 During 1992, Federal

agencies announced plans for upgrading their

current networks as part of the NREN program.8

The NREN program can be viewed as a

continuation and expansion of the Federal support

that created the Internet. The Internet’s technology evolved from that of the Arpanet, a research

project of the Advanced Research Projects Agency.

Beginning in 1969, the Arpanet served to demonstrate the then-new technology of ‘packet switching." Packet switched networks were able to

support computer communications applications

that could not be efficiently accommodated by the

telephone network’s ‘‘circuit switched” technology (see ch. 2, p. 29). Packet switched networks

are now widely deployed, Internet services are

being offered by the private sector, and the

Internet protocols are becoming world standards.

In much the same way, the NREN program is

intended to catalyze the deployment of a new

generation of network technology.

Past government programs have also been

successful in broadening access to networks for

the larger research and education community. The

Internet is increasingly essential to users in the

academic community beyond the original core

group of users in engineering and computer

science. It is now estimated that over 600 colleges

5 For a &~ptiOn of the goals and darackxistics of the NREN see HPCA, op. cit., footnote 1, Sec. 102(a)-(c); OSTP, op. cit., footnote

2, p. 18; U.S. Congress, Office of ‘Rxhnology Assessmen~ High Performance Computing & Networking for Science, O’lA-BP_-59

(Washington DC: U.S. Government Printing Of!Ice, September 1989), p. 25.

6 OSTP, op. cit., footnote 2, p. 18; Office of Science and ‘IMmology Policy, “The National Research and Education Network Program:

A Report to Congress, ” December 1992, p. 2.

7 Robert E. Cale~ “The Network of AU Networks,” The New York Times, Dec. 6, 1992, p, F12.

s National Science Foundation “Public Draft: Network Awess Point Manager/Routing Authority and Very High Speed Backbone Network

Services Provider for NSFNET and the NREN Program,” June 12, 1992; James F. Leightonj Manger of Networking and Engineering, National

Energy Research Supercomputer Center, Lawrence Livermore National Laboratory, ‘ESnet Fast-Packet Services Requirements Specification

Document” Feb. 20, 1992.
Chapter 1–Introduction and Summary | 7

and universities and an estimated 1,000 high

schools are connected to the Internet.9 As the

Internet user community becomes more diverse,

there is a growing need for simplifying the

applications and their user interfaces.

This background paper primarily describes

gigabit NREN applications and network technologies. There are, however, several controversial

policy issues related to the NREN program.10

First, the scope of the NREN is uncertain. As a

key component of the HPCC program, a clear role

of the NREN is to serve scientists and engineers

at Federal laboratories, supercomputer centers,

and major research universities. This objective

will be met primarily by upgrading the networks

operated by the National Science Foundation

(NSF), Department of Energy (DOE), and the

National Aeronautics and Space Administration

(NASA). However, there are several different

visions of the extent to which the NREN program

should also serve a broader academic community,

such as libraries and schools.

A second major issue concerns the “commercialization" of the NREN. The NREN will

develop from the current Internet, which is

increasingly used by government and businesses,

not only by the research and education community. Several new commercial providers have

emerged to offer Internet services to this market,

which is not served by Federal agency networks.

One of the goals of the NREN program is to

continue this commercialization process, while at

the same time achieving the science and network

research goals of the NREN program. There has

been considerable uncertainty about the mechanisms by which this objective is to be achieved.

The High-Performance Computing Act does

not clearly specify the scope of the NREN or the

mechanism for commercialization. NSF has had

to address these issues in the course of developing

a plan for the development of its network, which

will be a central component of the NREN. These

debates have slowed considerably the process by

which NSF will select the companies that will

operate its network. NSF’s original plan, released

in the summer of 1992, is undergoing significant

revisions (see box 5-A). As of May, 1993, a new

plan had not been issued. It is increasingly

unlikely that NSF will be able to deploy its

next-generation network by the Spring of 1994, as

was originally planned.

In addition, the growing commercial importance of networking is leading to greater scrutiny

of the agencies’ choices of contractors to operate

their NREN networks. DOE selected a contractor

for its component of the NREN in thessummer of

1992, planning to deploy the new network in

mid-1993. However, a losing bidder protested

DOE’s selection to the General Accounting

Office (GAO). In March, 1993, GAO overturned

DOE’s choice of contractor and recommended

that DOE revise its solicitation, conduct discussions with potential contractors, and allow contractors a new opportunity to bid.ll DOE has

g Darleen Fisher, Associate Program Manager, National Science Foundation, personal comrnunicatio% Feb. 11, 1993.

10 For ism= relat~ to tie NREN program, see Hearings before the House Subcommittee on Science, W. 12, 1992, Seti No. 120.

11 me dispute concem~ tie pmies’ interpretation of certain provisions in DOE’s Request for fiOfXMdS WV. ATM’ protested DOE’S

selection of Sprint to be the contractor for the DOE network arguing successfully that the RFF had specified more fully-developed switches

than had been proposed by Sprint as part of its bid. GAO ruled that the switches that Sprint planned to use did not comply with a provision

in the RFP that proposals had to “conclusively demonstrate cument availability of the required end-to-end opemtional capability,” DOE, by

contrast, was satisfkd that the switches had been developed to the level envisioned by the RFP and were appropriate to a program designed

to explore leading-edge technology.

DOE’s RFP had speci.fkd the use of “cell relay’ technology, which is the basis for both synchronous Transfer Mode (Am and Switched

Multimegabit Data Service (SMDS) services. ATM is expected to play an important role in the future development of computer networking

and the telecommunications industry, while SMDS is viewed primarily as an intermediate step towards ATM. DOE selected Sprint in large

part because Sprint proposed to begin ATM services immediately, while AT&T bid a service based on SMDS and evolving to ATM only in

1994. Early deployment of ATM would have provided a valuable opportunity to evaluate and demonstrate a key telecommunications industxy

technology. Comptroller General of the United States, Decision in the Matter of AT&~ File B-250516.3, March 30, 1993.
8 I Advanced Network Technology

asked GAO to reconsider its decision. The DOE

example raises questions about the effect of

government procurement procedures on the ability of federal agencies to act as pioneers of

leading-edge network technology. The additional

time that would be required to comply with

GAO’s recommendations, added to the sevenmonth GAO process, would delay deployment of

DOE’s network by over a year.

9 The Testbeds

The HPCC program’s six gigabit testbeds

(table l-l) are intended to demonstrate emerging

high-speed network technologies and address

unresolved research questions. While each

testbed involves a different research team and is

emphasizing dif-

~ f“nttoP@~=

s

is similarity in

ignificant their approach.

progress has been The testbeds typmade toward the ically consist of

development of

gigabit technology.

a high-speed network connecting

I three or four sites

-universities, industry laboratories, supercomputer centers, and

Federal laboratories-with high-bandwidth optical fiber. Located at each of the testbed sites are

computers, prototype switches, and other network

components. Each research group has both network and applications researchers-the applications will be used to test different approaches to

network design.

The testbed program is administered by NSF

and the Advanced Research Projects Agency12

(ARPA). Five of the testbeds are jointly funded

for 3 years by NSF and ARPA under a cooperative

agreement with the Corporation for National

Research Initiatives (CNRI). The principals of

CNRI, a nonprofit organization, played significant roles in the development of both the Arpanet

and the Internet.13 CNRI is responsible for

organizing the testbeds and coordinating their

progress. Funding for the testbeds is modest,

when compared to their visibility and the overall

HPCC budget. The cooperative agreement with

CNRI is for $15.8 million over 3 years. Most of

the cost of building the networks has been borne

by industry, in the form of contributions of

transmission capacity, prototype switches, and

research personnel.

The testbeds are investigating the use of

advanced network technology to match the needs

of the NREN. There is an emphasis on delivering

the highest bandwidths possible to the users and

demonstrating the range of applications that

would be used by leading-edge users of the

NREN. Most of these applications are supercomputer-based. For example, some applications

use the network to link several supercomputers,

allowing their combined processing power to

compute complex simulations more rapidly. Many

of the applications being investigated also use the

network to enable visualization of the results of

simulations or experiments.

Initially, only a few users would have computers powerful enough to need a gigabit network.

However, the processing power of lower cost

workstations and ordinary desktop computers is

likely to continue to increase rapidly, as a result

of advances in microprocessor technology. Gigabit networks and the lessons learned from the

testbeds will then be used more widely.

SUMMARY

I Progress

Significant progress has been made toward the

development of gigabit network technology since

1987, when the Office of Science and Technology

Policy (OSTP) noted that considerable research

would be needed to determine the design of

12 Fo~erly the Defense Advanced Research Projects Agency (DARPA).

13 Dr. Row )?. ~is fie~id~t of ~;Dr. Vtiton G. Cerf is Vim ~sident.
Table l-l-Gigabit Testbed Participants

o

I

u)

Ld

I

Iv

g

Testbed Location Industry Federal Supercomputer centers Universities &

laboratories other

AURORA Northeast IBM MIT

Bellcore University of Pennsylvania

Bell Atlantic

NYNEX

MCI

BLANCA Nationwide AT&T Lawrence Berkeley National Center for University of Illinois

Laboratory Supercomputing University of Wisconsin

Applications University of CaliforniaBerkeley

CASA Southwest MCI Jet Propulsion San Diego Supercomputer California Institute of

Pacific Bell Laboratory Center Technology

U.S. West Los Alamos National

Laboratory

NECTAR Pittsburgh Bellcore Pittsburgh Supercomputer Carnegie Mellon University

Bell Atlantic Center

VISTAnet North Carolina Bell South North Carolina University of North

GTE Supercomputer Center (at Carolina-Chapel Hill

MCNC) North Carolina State

University

MCNC

MAGIC South Dakota Sprint U.S. Army Future Battle Minnesota Supercomputer University of Kansas

Kansas MITRE Laboratory Center

Minnesota Digital Equipment U.S. Army HighCorp. Performance

Southwestern Bell Computing Research

Northern Telecom Center

Split Rock Telecom U.S. Geological Survey

SRI International Lawrence Berkeley

Laboratory

A

SOURCE: Corporation for National Research Initiatives (CNRI), Advanced Research Projects Agency (ARPA).
10 I Advanced Network Technology

gigabit networks.14 There has been growing consensus within the technical community on many

issues, and the development of the optical fiber

links, switches, and other network components is

underway. The testbeds represent the next step in

the research-integrating the hardware and software components into a working network system

and testing it with applications.

The basic characteristics of the design of

broadband networks began to emerge in the

mid-1980s, supported by the results of simulations and small-scale experiments. Researchers’

objective was to develop networks that could

support high band -

widths and were

T

also sufficiently

he testbeds have flexible to supestablished a useful port a range of

model for network services. One

research. characteristic of

these networks is

the use of optical fiber links, which have the

necessary capacity to support many new services,

including bandwidth-intensive video- and imagebased applications. The second major characteristic of the proposed designs for advanced networks

is the use of ‘‘fast packet switches, ’ a new type

of switch that has both the processing power to

keep up with increases in link bandwidth and the

flexibility to support several kinds of services.

As these ideas began to emerge, computer and

telecommunications companies initiated the development of the network components required

for broadband networks. There appear to be no

significant technological barriers to the development of the components required for the gigabit

NREN. Transmission equipment of the type that

would be required for the gigabit NREN is

already becoming available commercially and is

being used in the testbeds. Some fast packet

switches are also becoming commercially available. Versions of these switches that operate at

gigabit rates are in prototype form and will be

incorporated in the testbeds over the coming year.

The testbeds are looking to the next step in the

research-the development of test networks. This

is a systems integration task-developing the

individual components is only part of the process

of building an advanced network. There is often

much to be learned about making the components

work together and solving unforeseen problems

in the implementation. In addition, there are

research questions that can only be investigated

with a realistic test network. The testbeds will

provide a way to test various proposed approaches to network design.

Progress on the testbeds has been slower than

expected, due to delays in making the transmision equipment available and in completing work

on the switches and other components. Switches

are complex systems, requiring the fabrication of

numerous electronic circuits. It was originally

hoped that the optical fiber links could be

deployed and the gigabit switches and other

components finished in time to have a year to

experiment with the working testbed networks

before the end of the program in mid-1993. It now

appears that the testbeds will not be operational

until the third quarter of 1993. The testbed

program has been extended to permit a year’s

research on the testbed facilities once they

become operational.

H Testbed Concept

The testbeds have established a useful model

for network research. The design and construction

of a test network fills a gap between the earlier

stages of the network research-small scale

experiments and component development—and

the deployment of the technology in production

14 OfflW of Science and ‘lkchnoIo~ policy, “A Research and Development Strategy for High Performance Computing,” NOV. 20, 1987,

p. 21.
networks. The testbed networks model the configuration in which the technology is expected to be

deployed—the test sites are separated by realistic

distances and the networks will be tested with

applications of the type expected to be used in the

gigabit NREN. In addition, the participants in the

testbeds will play important roles when the

networks are deployed.

The testbed research contributes in a number of

ways to a knowledge base that reduces the risks

involved in deploying advanced network technology. First, there are a number of research issues

that are difficult to address without a working

network that can be used to try different approaches. Second, the systems integration process

provides experience that can be applied when the

production network is constructed. In many ways

the experience gained in the process of getting the

testbeds to work will be as valuable as any

research done with the operational testbeds.

Third, the testbeds serve to demonstrate the utility

of the technology, which serves to create interest

among potential users and commercial network

providers.

The relatively small amount of government

money invested has been used primarily to

organize and manage the testbeds and to encourage academic involvement. The testbeds have

mainly drawn on other government and industry

investment. The organization of the testbeds as a

collaborative effort of government, academic, and

industry groups is essential, because of the many

disciplines required to build and test a network.

Industry has contributed expertise in a number of

areas. For example, it would be too difficult and

expensive for academic researchers to develop

the high-speed electronics needed for the switches

and other components. Academic researchers are

involved in the Internet community, and have

contributed ideas for new protocols and applications. Other applications work has come from a

Chapter I-Introduction and Summary I 11

number of scientific disciplines and the supercomputer community.

One of CNRI’s main contributions was to

encourage the involvement of the telecommunications carriers in the testbeds. The transmission

facilities required for the testbeds are expensive

because of the long distances between the testbed

sites and the demands for very high bandwidth.

Most experimental work in the past was on small

scale networks in a laboratory, due to the prohibitive cost of linking distant test sites. However, the

carriers are installing the required transmission

capacity and making it available to the testbeds at

no cost. All three major interexchange carriers

(AT&T, MCI, and Sprint), and most of the

Regional Bell Operating Companies (RBOCs)

are playing a role in the testbeds.

The testbed research overlaps with industry

priorities in some areas and not in others. The

basic design of the networks—the types of

switches and transmission equipment—reflects

emerging industry concepts. However, much of

the research agenda focuses on higher bandwidths

and more specialized applications than will be

used with commercial broadband networks in the

near term. Only a few users will use the types of

supercomputer-based applications being emphasized by the testbeds. Of greater near-term commercial importance to industry are medium bandwidth ‘‘multimedia’ applications that require

more bandwidth than can be supported by current

networks, but significantly less than the gigabit

speeds required by the supercomputer community.

1 Application of Testbed Research

The testbed research is applicable both to the

NREN and to other networks. The NREN will

serve only the research and education community

and is best viewed as only part of the broader

national information infrastructure. 15 The scope of

the national information infrastructure will inlfI For one view of tie relatiomtip ~Ween the NREN and the ‘‘National kfOMKitiOnmasmcti~,’ see Michael M. Roberts, “Positioning

the National Research and Education Network” EDUCOMRcview, vol. 26, No. 3, summer 1991, pp. 11-13.
12 I Advanced Network Technology

elude both the United States’ part of the Internet

and a wide array of other services offered by the

computer and information industries, the carriers,

the cable television industry, and others.

APPLICATION TO NREN

During 1992, DOE, NASA, and NSF published

plans for the future development of their networks, a key component in the evolution to the

gigabit NREN.l6 Some aspects of these plans are

still unclear; for example, NSF has left to

prospective bidders the choice of switching technology, from among those being investigated by

the testbeds and

T

elsewhere. Howhe rate of NREN ever, the agency

evolution is less plans appear to

be consistent with

dependent on the target estabtechnology issues lished by the

than on delays testbeds. Initially,

in the selection the agency netof service providers. I works will operate at lower bandwidths than the testbed networks, but they will

incorporate more of the testbed technology as

they evolve over time to meet the goal of the

gigabit NREN.

Today, the highest bandwidth of the agency

networks is 45 Mb/s; it appears that they will

move to 155 Mb/s in 1994, with 622 Mb/s the

highest rate that is realistically achievable by

1996. The rate of evolution is less dependent on

technology issues than on delays in the process by

which the Federal agencies select suppliers of

NREN network services. Because agency choices

of technologies and suppliers have broad implications for the Internet and the national information

infrastructure in general, there have been several

disputes over agency plans (see p. 7). While the

NREN program has created a high level of

interest in advanced networks, further delays in

the deployment of agency networks may reduce

the degree to which they will play the role of

technology pioneers.

The agency networks’ evolution depends in

part on the timely deployment of the necessary

high bandwidth transmission infrastructure by the

telecommunications carriers. Computer networks

generally use links supplied by the carriers-the

network operators do not normally put their own

fiber in the ground. The carriers’ networks

already have gigabit-capacity fiber installed, but

today the capacity is usually divided among

thousands of low-bandwidth channels used for

telephone calls. New transmission equipment, the

electronics at each end of the fiber, is required to

allow the fiber’s capacity to be divided into the

high-bandwidth channels needed by the gigabit

NREN. This equipment is being used in the

testbeds and is becoming available commercially,

but is very expensive.

The testbed applications research helps researchers to understand how the NREN would be

used to achieve the science goals of the overall

HPCC program. For example, some of the testbed

applications show how networks can be used to

bring greater computer power to bear on complex

simulations such as the Grand Challenge problems. They may also show how networks can be

used to help researchers collaborate-the Grand

Challenge teams are expected to involve scientists at widely separated locations. In 1992, the

NSF supercomputer centers proposed the concept

of a ‘‘metacenter, which uses a high-speed

network to link the computing power of the four

NSF supercomputer centers.

The testbeds do not address all of the technology issues that are key to the future development

of the NREN. Because the NREN will develop

from the federally funded segment of the current

Internet, it is affected by issues related to the

growing number of users of the Internet. This

growth in the number of users is straining some of

the Internet protocols, and their future development is a topic of intensive study and debate

16 NSF, Op. cit., footnote 8; Leightow op. cit., foo~ote 8.
Chapter I-Introduction and Summary 113

within the Internet community. Also, the testbeds

are not looking at applications that would be used

by a broad range of users in the near term, or at

issues related to making the Internet applications

easier to use.

OTHER NETWORKS

One of the roles of the NREN is to serve as a

testbed in itself, demonstrating technology that

will then be deployed more broadly in the

national information infrastructure. The testbed

program will also impact the evolution of the

national information infrastructure more directly,

bypassing the intermediate stage of deployment

in the NREN. This is because the network

technology used in the testbeds reflects near-term

industry planning. While the testbeds have emphasized higher bandwidths and more specialized

applications than are of immediate commercial

importance, the testbed networks reflect ideas

that figure prominently in industry plans and,

wherever possible, use equipment that conforms

to emerging standards.

For example, many of the testbeds use a

switching technology called Asynchronous Transfer Mode or ATM. This technology has become

central to telecommunications industry planning

because it is designed to support many different

kinds of services-today’s telephone network

switches are limited mainly to carrying ordinary

telephone calls. ATM can support Internet-type

services such as will be used in the NREN, and

also video, voice, and other data communications

services-the carriers plan to use ATM to enter a

variety of markets. Although ATM has been

widely accepted by the telecommunications industry and progress has been made towards its

implementation, there are a number of unresolved

research issues. The testbeds are providing a

large-scale opportunity to test this technology and

possibly provide input to the standards process.
—— —.-.———.

T

he gigabit National Research and Education Network

(NREN) is to develop from the current Internet, a

‘‘network of networks” that connects users in all parts

of the United States and around the world. The Internet

allows users to communicate using electronic mail, to retrieve

data stored in databases, and to access distant computers. The

network began as an Advanced Research Projects Agency

research project to investigate computer networking technology,

and in slightly over 20 years has grown into an essential

infrastructure for research and education. The NREN initiative

and associated research programs are intended to support the

further evolution of research and education networking, broadening access to the network and enabling new applications through

the deployment of advanced technologies.

Federal support to further the development of networks that

support research and education communications is directed

primarily at upgrading the Federal “backbone” networks that

have formed the core of the Internet.l These networks include the

National Science Foundation’s NSFNET backbone, the NASA

Science Internet (NSI) (figure 2-l), the Department of Energy’s

Energy Sciences Network (ESnet), and the Department of

Defense’s DARTnet and Terrestrial Wideband Network

(TWBnet). The NASA and DOE networks are primarily intended

for traffic related to the mission of the supporting agency, while

the current NSFNET backbone serves users in a broader range of

disciplines in universities, supercomputer centers, and industry

research laboratories. The DOD networks support research and

development of new communications technologies. The Federal

The

Internet 2

Federal agency

networks will

f orm the core

of the gigabit

NREN.

1 Office of Science and lkchnology Policy (OSTP), “Grand Challenges 1993: High

Performance Computing and Communications, ’ p. 18.

15
16 I Advanced Network Technology

&

a)

5

u)

i i
Chapter 2–The Internet | 17

NYSERNet

Logical Topology

Figure 2-2—Regional Network

/ \

Plattsburgh

Potsdam

( //

m

Rome/Utica

Oswego

~

Rochester m Saratoga

z

Buffalo Syracuse

~1

Troy

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m

k

\ -in Albany

Freedonia Alfred \ Ithaca

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IT

Olean \ Corning Binghamton

To NSFNET/lnternet

— T1 (1 1.5 Mbsps) NYSERNet Backbone

El Core Point-of-Presence (POP)

■ Future Core POP

>if NSFNET/lnternet Gateway

= Dialup Services

0 Future Dialup Services

= NSF NET Backbone — — — .- —

SOURCE: NYSERNet.

\

Kingston

White Plains/Yorktown

r

networks are interconnected at FIXes (Federal

Internet Exchanges) at NASA’s Ames Research

Center in California and at the University of

Maryland.

Upgrading the agency-supported backbones is

not the only thing needed to improve research and

education networking. The majority of users in

universities, schools, and libraries do not have

direct access to one of the backbone networks.

These users rely on thousands of other networks

that, together with the Federal agency backbones,

form the Internet. These networks are interconnected, and information typically travels through

several networks on its way from one user to

New York City

Germany vi%!5-

‘d ~-Gaden Cit y

Israel

CIXnet

another. In order to provide good performance

end-to-end, all of the Internet’s networks will

need to evolve in a coordinated fashion, matched

in capability and performance.

Most of the Internet’s networks are “campus”

or ‘corporate networks, connecting users within

a university or a company. Campus and corporate

networks may in turn be interconnected by

“regional” networks. For example, NYSERNet

(New York State Education and Research Network) connects campuses and industrial customers in New York State (figure 2-2) and

BARRNET (Bay Area Regional Research Network) does the same in northern California.
18 I Advanced Network Technology

-G!@

-@53

Y“< \ ‘N

SOURCE: National Science Foundation (NSF).

Regional networks also provide a connection The Internet also includes several networks

between campus networks and the national that provide service on a for-profit basis.4 The

NSFNET backbone that carries traffic to other government investment in developing and demonregions. 2 The regional networks, and the resulting strating Internet technology during the 1970s and

three-tier structure of campus, regional, and 1980s has created opportunities for the private

backbone networks (figure 2-3), evolved with sector to sell Internet services. The effectiveness

support from the National Science Foundation.3

of the Internet technology has been proven, and a

2 NASA and DOE sites are connected directly to the agency networks. However, NASA and DOE rely on the regional networks and the

NSFN@T backbone to connect to university researchers participating in NASA and DOE projects.

3 For a description of evolution of the regional networks and the threetier structure, see Richard A. Mandelbaurn and Paulette A.

Mandelbaurn, “The Strategic Future of the Mid-Level Networks,” Brian Kahin (cd.), Building Information Zn@structure (New YorlL NY:

McGraw Hill Primis, 1992).

4 fic ArnuIU “The Internet Dil emnxu Freeway or Tollway,” Business Communications Review, December 1992, vol. 22, No. 12, p. 31.
——.

Chapter 2–The Internet 19

growing number of companies are now using the

Internet to conduct business. Even though the

NREN program continues government funding

for the agency backbone networks, in order to

upgrade them to gigabit speeds, gov ernment

support is becoming less central to the Internet as

a whole. New commercial providers of nationwide Internet services have emerged. In addition,

NSF has been reducing subsidies to the regional

networks, which are increasingly being asked to

recover costs from users.

The availability of commercial services is

leading to a change in the makeup of the users of

the Internet. Until recently, corporate use of the

Internet was restricted to scientists and engineers

in research laboratories or engineering departments. In part, this was due to the history of the

Internet as an experimental network. The limited

use of the Internet by the private sector was also

due to an “Acceptable Use” policy that reserved

the federally supported backbones for research

and education traffic.5 The new commercial

providers have no traffic restrictions, allowing the

Internet to serve a wider range of users. Today’s

Internet users can have different security requirements6 their technical sophistication varies, and

the demands they place on the network’s capacity

differs.

One of the goals of the NREN program is to

continue the trend towards provision of Internet

services on a commercial basis, rather than solely

as the result of a government subsidy.7 The

NREN program continues government support

for networking, but the emergence of commercial

providers is leading to changes in the mechanisms

by which this support is provided. NSI and ESnet

will continue to support agency missions, but the

next-generation NSFNET backbone will be considerably different from the current NSFNET

backbone. As part of its NREN plans, NSF has

decided that much of the trafic that is currently

carried by its NSFNET backbone will in the

future be handled by commercial providers,

encouraging the further development of this

segment of the Internet.

The next-generation NSFNET backbone will

support a narrower range of users and serve fewer

sites. Today NSFNET backbone serves many

sites nationwide, connecting regional networks

and supercomputer centers (figure 2-4). It is a

“general purpose” backbone, carrying traffic

ranging from ordinary electronic mail to advanced supercomputer applications. In the future,

the backbone will primarily be used by the NSF

supercomputer centers, in Ithaca, New York,

Pittsburgh, Pennsylvania, San Diego, California,

and Champaign, Illinois.* Other users, with more

routine applications, will use services available

from commercial providers. Without the current

national backbone, the regional networks will

have to make new arrangements for their interconnection (see ch. 5, p. 67).

The next-generation NSFNET backbone will

continue to contribute to the objective of developing advanced network technology. The new

backbone, together with the next-generation NSI

and ESNET, will be one of the frost networks to

use the technologies studied by the gigabit

testbeds described in chapter 4. The Federal

networks will provide ‘‘experimental” services,

not yet available from commercial providers.

They will demonstrate and test new network

s For issues re~ted to NSF’S Acceptable Use Policy, see Hearings before the House !$ubcornmittee on Science, Space, ~d wko@Y,

Mar. 12, 1992, Serial No. 120.

6 Gary H. Anthes, ‘Internet Security Risks, ” Compuferworld, VO1. 26, No. 48, NOV. 30, 1992, p. 55.

7 “[Tlhe NREN Program has a series of synergistic goals [including] stimulating the availability, at a reasonable cost of the required

services from the private sector,’ OffIce of Science and lkchnology Policy (OSTP), “The National Research and Education Network Program:

A Report to Congress,” December 1992, p. 2.

8 For a description of the NSF supercomputer centers, see U.S. Congress, OffIce of Technology Assessment, High Pe@ormance Computing

and Networkingfor Science, OTA-BP-CIT-59 (Washington DC: U.S. Governm ent Printing Office, September 1989), pp. 9-10.
20 I Advanced Network Technology

Figure 2-4--NSFNET Backbone

-

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7

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SOURCE: Merit, Inc.

technologies and applications before they are

deployed more widely by operators of commercial networks.

Federal agencies may subsidize access to

network services for users not at one of the

backbone sites.9 Today, NSF lowers the cost of

networking for many users by directly subsidizing a general-purpose backbone and by providing

subsidies to the regional networks. This strategy

has contributed to broadening network access

beyond major universities and supercomputer

centers, to include many colleges and schools. In

the future, many of these users will no longer be

able to use the subsidized NSF network. Instead,

Federal agencies may subsidize users’ purchases

of services from the commercial providers.

w

The NREN can then be viewed as many

interconnected networks, developing from components of the current Internet, Some networksthe agency backbones-will be funded directly

by the government. This part of the NREN is

sometimes referred to as the ‘Interagency Interim

NREN" or “NREN proper," and will use advanced network technologies to support high-end

users, agency missions, and the science objectives

of the I-WCC program. Other Internet networkssuch as existing regional networks or new commercial providers-may also carry NREN traffic,

from users subsidized by the government, but

would carry commercial traffic as well. These

networks will likely use less sophisticated network

technology than the agency backbone networks.

g ‘‘Overtime, NSF will target its funding to those campuses which have fwcial impedirmmts to comecting into the U.S. Internet.” Robert

A.ikenet al,, “NSFImplementation Plan for I.nteragency Interim NREN,’ May 1992, p. 4; “Federalfunds. , will also support users that serve

Federal missions whether or not they aeeess NREN through the agency networks,’ OSTP, op. cit., footnote 7, p. 3.
Chapter 2–The Internet | 21

This two-part strategy-agency operation of

advanced networks combined with subsidies for

Internet access for certain groups of end users—

represents a more detailed framework than the

general NREN concepts and goals outlined in the

High Performance Computing Act of 1991. It is

expected to form the basis of NSF’s forthcoming

solicitation for the operation of its component of

the NREN. It is also outlined in recently introduced legislation, the High Performance Computing and High Speed Networking Applications Act

of 1993 (H.R. 1757), which would amend the

High Performance Computing Act of 1991. However, there is concern in parts of the user

community most affected by the change to an

environment in which there is no longer a general

purpose government operated network about the

cost of commercial services and about the timing

and management of the transition.

The remainder of this chapter describes the

technology used in the current Internet. Chapter 3

provides an overview of emerging concepts that

address some of the limitations of current network

technology and might be used to construct gigabit

networks. Chapter 4 describes the gigabit

testbeds, NSF- and ARPA-funded prototype networks that are investigating these new technologies. Chapter 5 outlines NSF, NASA, and DOE

plans for the deployment of the testbed technologies in their networks.

APPLICATIONS

From the users’ perspective, an “application”

is a task that the combination of the computer and

the network enables them to perform. For example, a science teacher might use the Internet to

locate information that can be used in a class, such

as images stored in NASA databases, or databases

containing tailored educational materials. Researchers use the Internet to track developments in their

field, by exchanging information or drafts of

papers and collaborating with other scientists.10

In the business world, networks are increasingly

used to track inventory or manage activities

throughout a large company. In the future, networks may be used to help provide medical

services to distant locations.

From a network engineering perspective, an

‘‘application ‘‘ is a computer program that builds

on the basic network service to allow a user to

perform tasks. The application program provides

interaction with the user; it does not handle the

details of moving a message through the network

to its destination. These functions are performed

by communications software-a second program

running on the computer—and specialized hardware that converts the computer’s digital data to

the format used by the network. When an

applications program wants to send information

to another computer, it hands the message to the

communications software, which then formats the

message and sends it over the network.

There are four major Internet applications—

electronic mail (e-mail), file transfer, remote

login, and news. Electronic mail is used to send

messages to other users of the Internet, and for

most users it is probably the application they use

the most frequently. File transfer (File Transfer

Protocol or FTP) is used to retrieve a "file" from

another computer; a file could be a computer

program, an article, or information from a commercial database. “Remote login” (Telnet) is

used to control a distant computer; this is the

application used to access a supercomputer or one

of the other specialized computing resources on

the Internet. “News” is a kind of bulletin board

or discussion group-thousands of “newsgroups”

address a wide range of different topics.

The current Internet applications are difficult to

use. For example, it is difficult to find information

resources on the network. First, the user has to

know that the information exists somewhere

reachable on the network, then where to find it,

and, having found the database, how to locate the

information in the database. A number of new

10 For an ovemiew of the wide -e of uses for the Internet, see Daniel P. Dem, ‘‘Applying the Internet, ” Byte, February 192, P. 111.
22 | Advanced Network Technology

applications assist this process by acting as

indexes or catalogues. Second, the user interface

for most applications is often difficult to use,

requiring a user to recall obscure commands. The

difficulty in use is partly due to the Internet’s

heritage as an experimental network used mainly

by scientists and engineers who were comfortable

with arcane computer languages.

The existing Internet applications programs are

beginning to be replaced by more sophisticated

versions.11 Today, for example, the Internet file

transfer program, FTP, is used to retrieve a file

from a distant computer, but a different program

is used to retrieve a file stored on the ‘‘home’

computer. Newer versions of these applications

are ‘‘transparent, ’ so that the user will not know

whether a file is located on a distant computer, or

that a program is executed on a different machine.

These new applications are the beginnings of a

foundation for ‘distributed computing,’ in which

the computers on a network form an integrated

system that performs as a single computer.

I Applications and Network Technology

Some limitations of current applications are

due to the applications software itself, but other

limitations are due to the underlying network

technology. One problem with current network

technology is a shortage of bandwidth. Bandwidth is a measure of the amount of data that can

be moved through the network in a given period

of time, and is typically specified in terms of ‘bits

per second.” Because of the limited capacity of

today’s network, it is often impractical to move

large amounts of data across the network—

examples of large files are images (see box 2-A)

and the data sets used in supercomputer applications.

A second limitation of current Internet technology is that it is best suited for applications that

handle text or numerical data. The Internet is less

effective when supporting applications that make

use of ‘‘real-time’ media such as video and

sound.12 In the case of video, this is due in part to

the bandwidth limitation- high-quality video needs

to move large amounts of data, and the necessary

bandwidth is not available throughout the Internet. Support for video and sound is also limited

because the performance of the Internet is highly

variable. Because video creates the illusion of

motion by sending a “stream” of pictures at

regular intervals, a longer delay in the time it

takes one of the pictures to get through the

network interrupts the video information that is

being displayed on the user’s computer.13 A new

technology called “fast packet switching,” discussed in detail in chapter 3, may provide the

more consistent network performance that video

applications need. Digital transmission and high

bandwidth alone are not always sufficient to

enable a network to carry video.

The limited capacity of the current Internet and

the variability of its performance also constrain

the use of sophisticated ‘distributed computing”

applications. In distributed computing, one is able

to treat the computers on a network as a single,

more powerful computer. For example, two

computers, exchanging data through the network

as necessary, might be able to complete a

computation in half the time needed by one

computer working alone. If data takes too long to

travel between the computers, however, the

advantages of dividing a computation among

several computers are lost. In the current Internet,

the local area network (LAN) technology used in

campus networks often performs better than wide

area network (WAN technology used in the

11 For example, “distributed fde systems” are beginning to replace the traditional File Transfer Protocol (FIT) application.

12 Jeffrey Schwartz, “A Push for Packet Video,” ConununicarionsWeek, Aug. 3, 1992, p. 1.

13 ~ problemis &inga~&~ inan~~rof ways. Newnetworkarchitectures, described in Chi3pkr 3, try tO rdua the dew= of vfition

in network performancee. Other researchers are investigating mechanismsthat would compensate for the variable performan ce. For example,

the receiving computer could “even out” some of the variation before the data is displayed to the user.
.—— .—

Chapter 2–The Internet | 23

Box 2-A-images and Video

Images

The screen of a computer’s display is made up of many individual picture elements or “pixels,” like the little

dots that can be seen on television screens. By displaying each pixel with a different shade and different color,

the computer forms an image on the screen. The greater the density of pixels, the higher the “resolution” of the

image, The displays used for ordinary desktop computers usually have a few hundred pixels in both the horizontal

and vertical directions, while a high-definition television display would have about 1,000 pixels vertically and about

2,000 horizontally. Even higher resolution displays are being developed for specialized medical, publishing, and

defense-related applications.

The use of high-resolution images places considerable demands on computers and networks. Typically, each

pixel on a screen is represented by 24 bits. A high-resolution display with 2,000 pixels horizontally and 2,000 pixels

vertically has 4 million pixels (2,000x2,000=4,000,000). This means that 96 million bits are needed to represent

the image (4 million x 24 = 96 million).

In the telephone network, voice conversations are sent through links that transmit 64 thousand bits per

second. Using these links, an image represented by 96 million bits would take 25 minutes to send through the

network. By contrast, it would take less than one-tenth of a second to send the same image through a gigabit

network.

Video

Video is a series of images, sent many times a second at regular intervals in order to create the illusion of

motion. Typically, 30 or 60 images are sent every second. In a low bandwidth network, in order to send this many

images every second, the images have to be of very low resolution.

Two strategies have been adopted for accommodating image and video transport in networks. The first is

to use compression techniques that reduce the number of bits needed for each image. Often, some parts of a

scene do not have to be shown in great detail. Compression schemes for videotelephones sometimes rely on the

fact that users are only interested in the “talking head,” not the background. Sometimes little changes from one

image to the next (if there is no movement in the scene), in which case the image data does not need to be sent

again.

These techniques are being applied to the new high-definition television systems that are being studied by

the Federal Communications Commission for selection as a U.S. standard. An uncompressed high-definition

television signal that sends 30 images or “frames” every second, with a resolution of 1,000 pixels vertically and

2,000 pixels horizontally, needs about 1.5 gigabits per second. By contrast, new compression algorithms support

high-definition television at bandwidths of 30 Mb/s or less, one-fiftieth the bandwidth required for the

uncompressed signal.

The second strategy for accommodating video or images is to increase network capacity. Fiber optic

technology can transport many more bits every second than the “twisted pair” copper wires that are used for

today’s telephone service. This background paper outlines some of the research being done on very high-capacity

networks that can carry high-resolution video and images. However, even a “gigabit network” is not sufficient for

certain kinds of very high-resolution video, and compression techniques might still be used.

SOURCES: Peng H. Ang et al., “Video Compression Makes Big Gains,” IEEE Spectrum, vol. 28, No. 10, October 1991, pp. 1519; Bernard

Cole, “The Technology Framework,” IEEE Spectrum, vol. 30, No. 3, March 1993, pp. 32-39; J, Bryan Lyies and Daniel C. Swinehart, “The

Emerging Gigabit Environment and the Role of Local ATM,” IEEE Communications, vol. 30, No, 4, April 1992, pp. 52-58.
24 | Advanced Network Technology

Figure 2-5-Growth in NSFNET Traffic

December ’92 Packets

\

22 billion total packets (In

~A

billions)

24

,

July

Sep.

Nov.

SOURCE: Merit. Inc.

regional and national backbone networks and thus

distributed computing applications are used more

widely in the local environment.

Limitations in network performance are becoming more apparent as computer technology

advances. First, advances in computer power

have resulted in demands for more bandwidth

(figure 2-5). The size of the files that users would

like to send through the network is increasing as

a result of greater processing power and larger

memories.14 Some of the new “massively parallel" computers being studied as part of the HPCC

Program may accelerate this trend (see box 2-B).

Furthermore, the declining cost of computing

power has allowed more users to connect to the

network, creating more demand for the limited

amount of capacity .15 Second, computers are

increasingly equipped with display technology

that supports video-based applications. As video

and sound begin to be processed by computers,

there will be greater demand for networks that

support this stream-type traffic. Today’s networks were designed for an environment in which

computers were restricted to working with ordinary text and numerical data.

In response to the limitations of today’s networks and the trends in computer design, there is

now a general vision of the type of services that

future computer networks will have to support—

larger, possibly image-oriented files, greater use

of stream-type services such as video and sound,

and more distributed computing. However, there

are a number of issues that must be solved, and

researchers are trying to learn more about the

applications that users will need in the future.

Because most network technologies support some

types of applications better than others, arguments in the technical community about the best

way to build broadband networks can often be

traced to different assumptions about the expected mix of applications. One of the objectives

of the NSF/ARPA gigabit testbeds discussed in

chapter 4 is to learn about applications for

advanced networks by encouraging collaboration

among applications developers and network engineers.

PROTOCOLS

The Internet is a “packet-switched’ network—

a very different design from that used by the

telephone network.l6 Data travels through the

network as a “packet,” a block of digital data

consisting of the application’s data and some

extra information added by the communications

software and hardware.17 This information is sent

either before the applications data in a‘ ‘header, ’

or after the data, in a “trailer,” and tells the

network the packet’s destination address or instructs the receiving computer as to what to do

with the applications data in the packet (figure

2-6). For example, the sending computer could

14 T~Studg ‘‘can High-Perforrnan ce Networks Meet Future R&D Needs?’ R&D h4aguzine, October 1992, pp. 3034.

15 Tfi~c on & NS~T~k~ne ~ ~~at a ~te of 1~ p monti. OSTP, op. Cit., fOOtnOte 7, p. 31.

16 Vfiton G, Cefi, ‘iNe~o&,” s~entific A~fica~, VO1, 265, No. 3, sepwm~ 1991, pp. 72-81.

17 ~eq pwke~ ~compw~ t. tie Cnvelows ~~~ or-m~ servic~~e ~~info~tion in b packet performs much the same

function as the address on an envelope.
Chapter 2–The Internet | 25

Box 2-B—Massively Parallel Computers

The conventional computers found on most desktops use a single processor. Programs for these computers

consist of a list of instructions, to be executed one after another by the processor. Parallel computers are based

on the idea that a computer with several processors can solve a problem more quickly than a computer with a single

processor. Much of the HPCC Program’s supercomputer design research focuses on the development of

“massively parallel” computers with thousands of processors.

Supercomputers are expensive, high-performance machines that have been used mainly for numerical

simulations in science and engineering. The first commercially important supercomputer, the CRAY-1, was first

sold in 1976. It used a single processor, and achieved its high performance by careful attention to processor design

and the use of specialized electronics. Over the next decade, supercomputer designers followed this basic model,

trying to achieve the highest possible performance with a single processor.

By the mid-1980s, however, it became increasingly difficult to squeeze better performance out of traditional

supercomputer designs, even as more exotic technologies were applied to the task. As a result, supercomputer

designers began trying a different route to improved performance-the use of several processors. One approach

involved a relatively small number of traditional high-performance supercomputer processors. For example, in

1983, Cray shipped a supercomputer that used four processors to speed up performance.

By contrast, the massively parallel approach to supercomputer design uses hundreds or thousands of

low-cost microprocessors (processors that fit on a single semiconductor chip). The greater the number of

processors, the more powerful the computer. In many cases, the microprocessors are the same as those used

in high-end workstations. The performance of microprocessors increases every year, creating the potential for

even more powerful massively parallel supercomputers.

Supercomputer centers and Federal laboratories have purchased several massively parallel supercomputers

and are exploring their use in a number of applications. A major challenge for users of massively parallel

supercomputers lies in the area of software. Massively parallel computers have to be programmed in new ways,

because programs can no longer be thought of as a simple list of instructions. New algorithms, efficient ways of

solving numerical problems, will have to be developed. Research on algorithms and software tools that take

advantage of the potential of massively parallel supercomputers is one focus of the HPCC program.

SOURCES: Glenn Zorpette, cd.,“Special Report: Supercomputers,” IEEE Spectrum, vol. 29, No. 9, September 1992; pp. 26-41; Office

of Science and Technology Policy, “Grand Challenges 1993: High Performance Computing and Communications,” 1992, pp. 13-17; Carl

S. Ledbetter, “A Historical Perspective of Scientific Computing in Japan and the United States,” Supecomputing Review, vol. 3, No. 12,

December 1990, pp. 48-58.

put a short code in the header to tell the receiving address and determines which link the packet

computer that the data belongs to an electronic

mail message—this allows the receiving computer to process the data appropriately after

receiving the packet.

Once the packets have been formatted they are

sent out of the computer and through the network’s web of links and switches. Switches

receive packets coming in on one link and send

them out on the next link in the path to their

destination (figure 2-7). When the packet arrives

at a switch, the switch scans the destination

should transit next. The Internet packet switches

or ‘routers’ are special computers that have been

provided with connections to a number of links

and programmed to carry out the switching

functions.

The software in the routers and the users’

computers implement ‘protocols, ’ the rules that

determine the format of the packets and the

actions taken by the routers and networked

computers. The Internet protocols are often referred to as TCP/IP (the acronyms refer to the two

330-073 0 - 93 - 3 QL 3
26 I Advanced Network Technology

Figure 2-6-Packet

!

I I I I

I I 1 I

Header

Trailer ~ Applications data To: Computer #-- ‘“ >

I From: Computer #–

A packet is a block of digital data, consisting of data from the user’s application and extra informationused by the network

or receiving computer to process the packet. For example, the “header” might contain the “address” of the destination

computer. A real packet would be several thousand bits long.

SOURCE: Office of Technology Assessment, 1993.

most important Internet protocols, the Transmission Control Protocol and the Internet Protocol.)

Special protocols called “routing protocols” are

used by the routers to keep a current map of the

Internet and to determine the best path to a

destination computer—for example, to choose a

path that avoids heavily loaded networks.

One of the most important characteristics of the

Internet is that the thousands of linked networks

are independently operated; there is no central

control of the Internet. However, by sharing the

Internet protocols, the networks are able to

exchange traffic. One of the functions of the

Internet protocols is to mask differences in the

technology used by the networks that makeup the

Internet. The campus networks’ local area network technology differs from the wide area

network technology used in the regional and

national backbone networks, and there are many

different local area network standards. The term

“Internet” is short for “internetworking,” the

practice of linking technologically different and

independently operated networks.

The future of the current Internet protocols is

the subject of considerable debate in the Internet

community. The most significant problem is that

today’s routing technologies are being strained by

rapid growth in the number of connected networks and users. 18 The management of a complex

and growing network has been one of the major

challenges faced by the current NSFNET. A

number of different proposals that would simplify

the routers’ task of finding paths through today’s

more complex Internet are being considered. The

effect of increases in bandwidth on TCP/IP has

also been debated in the technical community,

and new protocols have been proposed. Many

now believe that TCP/IP can continue to provide

good service over gigabit networks, but internetworking in high bandwidth networks is a research

topic in itself.

NETWORK COMPONENTS

A network is a complex system, consisting of

many computer programs and hardware components such as links, computers, and switches. The

overall performance of the network depends on

how well these components work together. There

are a number of potential bottlenecks-the rate at

which data can be transferred from the computer’s

memory to the network, the rate at which data can

be transmitted through the links, and the amount

of time the switches need to decide where to send

data next. Simply removing one of these bottlenecks does not guarantee that the overall performance of the network will improve. The emergence

of fiber optics has removed the links as a

bottleneck for the foreseeable future; the research

projects described in chapter 4 show that this has

exposed research issues in other parts of the

network.

18 men LyDc& ‘‘Internet Wtioqhosk, ’ CommunicationsWeek International, Aug. 10, 1992, p. 1.
Chapter 2–The Internet I 27

Figure 2-7—Packet Switching

N?&. (a) Packet-switched communication

I

v

As a packet travels through the network, the switches decide where to send the packet next. 1“

The links in a packet network are shared by several users. Network designers choose

the link capacity or bandwidth to match the expected amount of traffic.

SOURCE: Office of Technology Assessment, 1993.

I Computers

Many different kinds of computers are attached

to the Internet, ranging from desktop personal

computers costing a few hundred dollars to

supercomputers that cost millions of dollars.

Among scientists and engineers, the type of

computer that is most widely used is the ‘‘workstation," a powerful desktop computer with

enough processing power to support graphical

user interfaces and high-resolution displays. For

most of today’s applications, almost any computer has enough processing power to attach to

the Internet. The low bandwidth of the current

Internet places few demands on computers for

handling the communications functions, leaving

much of the processing power free to run the

applications.
28 | Advanced Network Technology

One of the reasons for the creation of the

NSFNET backbone was to provide access to

NSF’s four supercomputer centers. Recently,

these supercomputer centers have begun to install

“massively parallel’ supercomputers. This new

type of supercomputer attempts to achieve very

high processing speeds by combining the processing power of thousands of smaller processors.

Other supercomputers use a more traditional

design, and are referred to as ‘vector’ supercomputers. Each design may work best with certain

kinds of computations; one of the objectives of

the gigabit testbed research is to explore the use

of networks to divide up problems in a way that

takes advantage of the strengths of both vector

and massively parallel supercomputers.19

I Links

The digital links in computer networks usually

use copper or fiber, but satellite and microwave

links are also used. At each end of the copper or

fiber is the transmission equipment, electronics

that convert data into the optical or electrical

signals that travel through the network. The

capacity of the wires or strands of fiber depends

on the characteristics of the material used and on

the capabilities of the transmission equipment.

Today’s Internet uses both low bandwidth links

that operate over copper at a few thousand bits per

second (kilobits per second or kb/s), and high

bandwidth links that operate over fiber with a data

rate of about 45 million bits per second (megabits

per second or Mb/s). The test networks described

in chapter 4 will use links that operate at a rate of

one billion bits per second (a gigabit per second

or Gb/s).

Typically, a single wire or strand of fiber

carries many links at the same time. Through a

process called “multiplexing,” several lowbandwidth links can be aggregated into a higher

bandwidth link. Gigabit-capacity fiber, for example, can be used either to carry several thousand

low-bandwidth links used for telephone calls, or

a single high-bandwidth link needed for a gigabit

network.

The required link bandwidth depends on both

the bandwidth requirement of each user and on

the number of users sharing the link One of the

main reasons for upgrading the links in the

NSFNET backbone from 1.5 Mb/s to 45 Mb/s in

1991 was to accommodate growth in the number

of users. Growth in the use of routine applications

can also be supported by simply adding more

low-bandwidth links. However, new applications

that need very large amounts of bandwidth to

themselves require the deployment of higher

bandwidth links. By increasing the link bandwidth to gigabit rates, the gigabit NREN will be

able to support new classes of advanced applications, not just growth in the number of users.

Operators of wide area computer networks,

such as the regional networks and the agency

backbones, typically lease their links from the

telephone companies. The telephone companies

have already obtained the rights-of-way and have

installed the transmission facilities for use in their

core business, voice telephone service. Because

of the reliance on telephone company facilities,

discussions of computer network link bandwidth

often use telecommunications industry designations of link capacity. For example, the current

NSFNET backbone is often referredtoasa‘‘T3°

network, after the industry designation of 45 Mb/s

links. ‘‘Tl links, which operate at 1.5 Mb/s, are

used in the current Department of Energy and

NASA networks and in the regional networks. As

the Federal networks are upgraded to bandwidths

above the 45 Mb/s T3 rate, they will use a new

family of transmission standards designed for

high-capacity fiber optic links, called Synchronous Optical Network (SONET) (see table 2-l).

Universities and corporations install their own

links in their buildings for use in local area

networks. Local area networks can provide users

with higher bandwidth than wide area networks—

19 IfA u~on of sup~Owe~, “ IEEE Spectrum, vol. 28, No. 6, June 1991, p. 18.
Chapter 2–The Internet I 29

Figure 2-8-Access Link

(7*“f’ ‘2

( 1

• 1

0

Access link K! 0 ❑ n

\w““)

SOURCE: Office of Technology Assessment, 1993.

Table 2-l—Transmission Rates

Industry designation Transmission rate

DSO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 kb/S

T1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Mb/s

T3 . . . . . . . . . . . . . . . . . . . . ..0. . . . . . . . . . . . 45 Mb/s

SONET OC-3 . . . . . . . . . . . . . . . . . . . . . . . . 155 Mb/s

SONET OC-12 . . . . . . . . . . . . . . . . . . . . . . . 622 Mb/s

SONET OC-48 . . . . . . . . . . . . . . . . . . . . . . . 2.4 Gb/s

SOURCE: Office of Technology Assessment, 1993.

this is due in large part to the high cost of high

bandwidth wide area links. Because of the higher

bandwidth available on local area networks, they

have been used for experimentation with highbandwidth distributed computing and video applications. In the future, however, users will want

wide area networks that match the performance of

local area networks; one of the objectives of the

testbed project outlined in chapter 4 is to investigate high-speed wide area networking.

When campus networks arrange to be connected to the closest regional or national network,

they obtain an ‘‘access’ link (figure 2-8). This is

usually leased from the telephone company, just

as the links inside wide area networks are leased

from the telephone company. The cost of the

Internet service depends on the access bandwidth;

high bandwidth access is extremely expensive. It

is common to find local area networks operating

at 10 Mb/s or 100 Mb/s, while the access link to

the rest of the Internet operates at 56 kb/s or less

(some organizations have 1.5 Mb/s access links,

but these are considerably more expensive). Most

individuals, schools, and small businesses are

required to use their ordinary analog telephone

line to access Internet services-a device called a

‘‘modem’ is needed to send digital computer

data over these lines, usually at 14.4 kb/s or less.

9 Switches

Packet switches in the Internet, also known as

routers, direct packets to the next link in the path

to their destination. Packet switched networks

emerged to handle data communications, services

not well supported by the “circuit switches’ used

for ordinary telephone calls (figure 2-9). Packet

networks are more efficient for typical computer

communications traffic-short transactions or

“bursts” separated by periods of no traffic (box

2-C). In a packet network, several users share the

same link-during the period in which one group

of users is not using the link, other users can send

their packets. In a circuit switched network, by

contrast, each communication gets its own link.

For this reason, circuit switches are most efficient

when a communication involves a relatively long,

steady stream of data such as video or voice.

While the Internet networks use telephone

company links, the packet switches are usually

not operated by the telephone companies. Instead,

a second organization plans the network and

installs the packet switches at the sites it has

chosen—the involvement of the telephone company is usually limited to providing the links

between the sites. From the perspective of the
30 I Advanced Network Technology

Figure 2-9-Circuit Switching

(a) Telephone network

In the telephone network, circuit switches are interconnected by several links.

No communication can take place until a “circuit” is established.

(b) Circuit-switched call

I

First, a number is dialled by one of the users. The network then checks to make

sure that there are unused links in the path between the two users. If there are

unused links, the switches establish connections between each of the links in the

path, thereby creating a “circuit.”

has to be established for each pair of users. Network designers try to ensure

that the number of available links matches the expected level of usage. w

SOURCE: Office of Technology Assessment, 1993.
Chapter 2–The Internet | 31

telephone company, the computer network traffic

is just “bits” traveling over its links-the telephone company’s equipment does not make

decisions about where to send the packets.

Beginning in the mid- 1970s, the telephone companies began installing some packet switches in

their networks in order to support the growing

data communications market, but their efforts to

enter this market were considered to be unsuccessful.

The processing power required of a packet

switch depends on the link bandwidth and the

complexity of the network. As the link bandwidth

increases, switches must be able to process

packets more quickly. The processing power

needed will also increase as the network gets

larger and more complex, because it becomes

more difficult to determine the best path through

the network. Currently, the NSFNET backbone’s

router technology does not allow the use of

applications that need more than 22.5 Mb/s, half

the potential maximum of a 45 Mb/s T3 network.20 This shows how the overall performance

of the network depends on many different components; increasing the link bandwidth is not the

only requirement for an advanced network.

THE INTERNET AND THE PUBLIC

SWITCHED NETWORK

In some ways, the Internet and the “public

switched network” that is operated by common

carrier telephone companies are separate. They

differ in the services they provide-the telephone

network mainly provides ordinary voice communications services, while the Internet provides

data communications services such as electronic

mail and access to remote computers. They also

differ as to the communities that they servealmost everyone has a telephone, while the

Internet and other computer networks primarily

serve users in the academic community or in

industry. Finally, they differ in their network

technology-the Internet is a packet-switched

network, while the telephone network is a circuitswitched network. However, the Internet and the

telephone network are related in a number of

ways. Any discussion of the evolution of networking has to consider both the traditional

telecommunications companies and the Internet

community.

First, the Internet and the public switched

network are related in that the links in wide-area

computer networks are usually supplied by the

telephone companies--computer network operators do not usually put their own fiber in the

ground. As a result, the availability of new

computer network capabilities can depend on the

extent to which the telephone companies deploy

advanced transmission facilities, and on the cost

of leasing the links.

The availability of advanced transmission fadepending on whether a com- cilities varies21,

puter network will operate over the telephone

network’s ‘‘interoffice’ or “local loop” segments. Most of the links required for a wide area

network such as the NSFNET backbone operate

over the interoffice core of the telephone network,

which has largely been upgraded to optical fiber

and digital transmission. The telephone companies upgraded this part of their networks in part to

achieve operational savings, even when delivering existing services.

However, access links, such as those between

a campus and a regional network, need to use

local loop facilities. For the most part, this

segment of the telephone network still consists of

copper, analog lines. Large users are able to avoid

this bottleneck by making special arrangements

with the local exchange carrier for higher bandwidth digital lines. However, individuals,

schools, and small businesses generally have to

m Mm B~a@ IBM, personal cornrnunicatioq Feb. 3, 1993.

21 Natio~ ~l=om~catiom ad ~o~tion Administration Department of Commerce, “’lklecommunieations in the Age of

Information” October 1991, pp. 97-109.
32 I Advanced Network Technology

Box 2-C-Packet Switching and Circuit Switching

Computer networks such as the Internet use packet switches, which direct packets from link to link through

a network. Today’s telephone network by contrast, uses circuit switches. Each type of switching technology works

best with different kinds of communications. Packet switching is more efficient for the transfer of typicai computer

communications traffic such as files of text or numerical data (figure 2-C-1). Circuit switching, on the other hand,

Figure 2-C-l—Packet Switching More Efficient for Data

(a) Data communications does not use circuits fully

Circuit switching can be used for computer communications. Here, circuits have been set up between two pairs

of computers. However, computer communications often have a “bursty” character -- periods in which data IS

sent followed by periods of “silence.” When no data is sent, the circuit’s capacity goes unused. The capacity IS

used more efficiently when the communications Involve a steady flow of Information, such as video

or voice transmission.

(b) Link sharing makes packet networks more efficient for data

‘L

In a packet-switched network, several users’ traffic shares the same link. If one user IS not using the link’s

capacity, it can be used by others. The figure shows bursts of data assembled into packets and travelling

through the network on the same link. Here, one link’s capacity is sufficient to handle communications between

both pairs of users, freeing the second link for other uses.

SOURCE: Office of Technology Assessment, 1993.

use the combination of a modem and their telecommunications providers are beginning t o

telephone line to access computer networks. The offer data communications services, including

bandwidth of such an arrangement is relatively Internet services. In the past, efforts by the

low--only a few kb/s—and is clearly a bottleneck industry to enter this market have not been

that limits widespread use of sophisticated serv- successful. This has been attributed to a ‘‘culture

ices. clash’ —a lack of understanding of computer

The telephone network and computer networks network technology and of the needs of users of

are also related in the sense that the traditional computer networks. However, the telephone com-
Chapter 2–The Internet | 33

can provide the consistent performance needed by video or voice traffic (figure 2-C-2). One of the objectives of

the research described in chapter 3 and chapter 4 is to develop switches that combine the efficiency and flexibility

of packet switching with the consistent performance of circuit switching.

Figure 2-C-2—Circuit Switching Better for Voice or Video

(a) Variable performance due to packet network link sharing

If two packets arrive at a switch at the same time and need to use the same outgoing Iink (I), one of the packets

wiII have to wait (II). It IS difficult for a user to know in advance what the network performance wiII be. The

packet may experience no delay (the dark gray packet), or it may have to wait at each switch (the light gray

packet). This variation in delay has limited the use of packet networks for time-sensdive communications such

as video or voice.

(b) Circuit switched performance is predictable

1 - – 1

>

[

1 1

>

(ii)

In a circuit-switched network, each communication has Its own circuit. Users’ information travels through the

network without being affected by the characteristics of other communications (1)–(11). The time needed for

information to travel through the network wiII always be the same.

SOURCE: Office of Technology Assessment, 1993.

panics hope to play a more active role in this their network without any further involvement

market. from the telephone companies, sharing their

The telephone companies have two main com- network’s capacity among different groups of

petitors in this venture. First, there are already a users for a fee. The current T3 NSFNET backbone

number of commercial providers of Internet is obtained as a service from one of these

services and other data communications services. commercial Internet providers.

These providers lease lines from the telephone Second, many users choose to operate ‘private

companies, install packet switches, and operate networks’ ‘—they build a network of their own
34 | Advanced Network Technology

using leased lines and bypass the public network.

Most corporations use this strategy to interconnect local area networks at different sites within

their organization. Equipment used in private

networks is provided by computer companies and

others, who have taken advantage of the telephone companies’ lack of success in providing

data communications services. United States

firms that specialize in the development of routers

and other equipment for private networks are

world leaders and are among today’s fastest

growing companies.22

The telephone companies have introduced a

number of new packet-switched services that are

intended to encourage users to abandon their

private networks.23 One of these services is called

Switched Multimegabit Data Service (SMDS);

another is called Frame Relay.24 The SMDS and

Frame Relay switches do not understand the

Internet protocols, but they can still be used to

carry Internet traffic. The Internet packets are

‘‘encapsulated, ’ or put inside an SMDS or Frame

Relay ‘envelope,’ and sent through the network;

at the other end the Internet packet is extracted

and delivered to the computer. The carriers view

SMDS and Frame Relay as transitional steps to a

new technology called Asynchronous Transfer

Mode (ATM), described in chapter 3. They can

potentially be used to provide data communications services up to 45 Mb/s.

Because of the interrelationship between the

Internet and the public switched network, the

evolution of the Internet is affected by two

different sets of standards committees. The telecommunications industry standards affect mainly

low level issues, such as transmission standards,

but some of the standards for new telecommunications industry packet switched services may

play a role as well. The most important international standards group is the CCITT (International Telegraph and Telephone Consultative

Committee). The CCITT is a technical committee

of the International Telecommunications Union

(ITU), a specialized agency of the United Nations

that is headquartered in Geneva.25 United States

telecommunications standards are the responsibility of Committee Tl, which is accredited by the

American National Standards Institute (ANSI)

and sponsored by the Exchange Carriers Standards Association (ECSA).26 Telecommunications

industry standards setting has often been criticized as excessively bureaucratic and slow.

By contrast, the Internet standards community,

which addresses higher level issues related to

routing, the TCP/IP protocols, and applications, is

more informal. Much of the work is done by

electronic mail, and there is a greater emphasis on

proving that something works before it is standardized.27 The two groups responsible for Internet

standards are the Internet Engineering Task Force

(IETF) and the Internet Activities Board (IAB).

The IETF has a number of different working

groups, each looking at a different aspect of the

Internet’s operation.

22 G. p=~ fic@, “U.S. Hi@.Mh Firms Have Begun Staging Littie-Noticed Revival,” Wall Street Journal, Dec. 14, 1992, p. 1; G.

Pascal Zachaq and Stephen Kreider Yoder, “Computm Industry Divides Into Camps of Winners and Liners,” Jan. 27, 1993, p. 1; Alan

Deutschmaq “America’s Fastest-Growing Companies, ” Fortune, vol., 126, No. 7, Oct. 5, 1992, p. 58.

23 ho~a met for the= semic~ is the smaller companies that cannot currently jus~ private newO*.

~ Tim Wikoq “bca.1 CarrieJS by Out Data Service Agendas,” CommunicationsWeek, my 25, 1992.

~ G.A. Codding ~d A.M. Rut.lcowsld, The International Telecommunications Union in a Changing Worki~, MA: Artech House,

1982).

26 ]*M. Lfichu5, ~ ~s~~ds commit@ T1—~l~omm~~tio~,” “ IEEE Communications, vol. 23, No. 1, January 1985, pp. 34-37.

27&l Malamud, “Stacks: Interoperabil.ity in Today’s Computer Networks,” (Englewood Cliffs, NJ: Prentice Hall, 1992), p. 223.
Broadband

Network

Technology 3

A

dvances in computer technology are driving the requirements for broadband networks. Because of increases in

the processing power of computers, there is a need for

higher bandwidth networks. Computers are increasingly

able to execute ‘‘multimedia” applications, so it is expected that

future networks must be able to carry several kinds of traffic.

Broadband networks will lead to applications that are used for a

wider range of problems, with more emphasis on image-based

communications.

The computer and telecommunications industries have conceived broadband network designs for these requirements. Fiber

optic links are a key component of these networks. However,

replacing the smaller capacity links in current networks with

higher bandwidth fiber optic links is not all that is needed:

Improvements in protocol and switch design must also follow.

Future switches will have more processing power, in order to

keep pace with the faster flow of traffic through the links. They

will also be designed in a way that allows them to handle

different types of traffic. Today’s switching technologies do not

have this capability-packet switches only handle text and

numerical data efficiently, the telephone network’s circuit

switches are best suited to voice traffic, and special networks are

needed for video. The ‘‘integrated services’ concept envisions Broadband

networks that use the same links and switches for all types of

traffic, instead of different technologies for video, data, and networks use

voice. new switch

BROADBAND APPLICATIONS technologies.

The new high bandwidth integrated services networks would

improve the performance of existing applications and enable new

applications. Existing applications, such as electronic mail or

35
36 | Advanced Network Technology

databases, could be augmented though the use of

image files and video clips; higher bandwidth

networks would also allow the faster transfer of

large files of supercomputer data. Support for

real-time high-resolution video would expand

possibilities further, allowing videoconferencing

or the display of output from a scientific instrument, such as a telescope. More generally, the

combination of more powerful computers and

integrated services networks will permit wider

use of two new categories of applications—

multimedia applications and distributed computing.

1 Multimedia Applications

Multimedia applications take advantage of the

capability of high-bandwidth integrated services

networks to deliver many different kinds of

data-video, image, audio, and text and numerical data. They also take advantage of the processing power of advanced workstations and other

devices attached to the network, allowing users to

edit, process, and select data arriving from a

variety of sources over the network.l Multimedia

applications have been suggested for a large

number of areas2

, including education and health

care. There are many different concepts for

delivering multimedia services to the home, such

as multimedia catalogues for home shopping,

information services, entertainment video, and

videotelephone services. Many segments of both

service and manufacturing industries are increasingly using image-based applications-for example, computers are widely used in the publishing

and advertising industries to compose pages

using high-resolution images.

Multimedia is also the foundation for a new

category of applications that use the combination

of computing and communications to create a

‘‘collaborative’ work environment in which

users at a number of scattered sites are able to

work together on the same project.3 For example,

an application might allow several researchers to

work on the same set of experimental data at the

same time-any processing done by one researcher would automatically be shown on the

other researchers’ displays. Videoconferencing

and collaborative applications might allow closer

interaction between researchers in different places.

It is expected, for example, that the teams

working on the Grand Challenges will include

scientists at many locations.

For researchers, “visualization” provides a

way to represent large amounts of data in a more

understandable form; it uses images and video to

show the results of simulations or experiments

(box 3-A). For example, the results of a simulation of a city’s air quality could be shown as an

image, with the concentration of a particular

chemical indicated by different colors and color

intensity. If a researcher wanted to review the

evolution of the air quality over time, a series of

images could be used to create a video segment

showing the change in pollutant concentration.

Other programs running on the workstation could

be used to process the data further, perhaps by

examining one part of an image more closely or

by comparing the simulation data to experimental

data.

In education, multimedia could be used in

computer-based instructional materials. Multimedia databases would give students and teachers

access to image and video data. Videoconferencing and collaborative applications could enable closer interaction between teachers and students at multiple locations. For example, it might

1 Special Issue: Multimedia Communications, IEEE Commun icutions, vol. 30, No. 5, h@ 1992.

Z Michael L. Dertouzos, Director, MIT Laboratory for Computer Science, testimony at hearings before the Joint Economic Committee, June

12, 1992.

J Sara A. Bly et al., “Media Spaces: Bringing People Together in a Video, Audio, and Computing Environment,” Commuru”cations of the

ACM, vol. 36, No. 1, January 1993.

4 Matthew Arrott and Sara La@ “Perspectives on Visualization” IEEE Spectrum, vol. 29, No. 9, pp. 61-65,
Chapter 3-Broadband Network Technology | 37

As part of the CASA testbed research described in chapter 4, a gigabit network will be used to combine data from

a variety of sources, such as satellites and digital elevation models, to create three-dimensional views.

be possible to better emulate the classroom

environment by allowing more two-way communication than is currently possible. Students

might also be able to select a particular view of an

experiment being demonstrated by a teacher. In

health care, transfer of high-resolution images,

such as x-ray and MRI data, combined with

videoconferencing and other collaborative applications, could allow doctors to consult with

specialists in other areas of the country.5

I Distributed Computing

Other researchers have begun to consider the

relationship between computers and communications in a more general way. “Distributed computing’ uses the network to combine the processing power and memory of multiple computers. It

is then possible, for example, to combine several

low-cost workstations to achieve performance

comparable to that of a supercomputer--a very

expensive machine to purchase and operate.

Computations can also draw on data stored in

many different locations. Distributed computing

becomes feasible as the network connecting the

computers becomes less of a bottleneck, allowing

them to work more closely together.

It may also be useful to do distributed supercomputing—using the network to provide proc5 M. Niel Ransom and Dan R. Spears, “Applications of Public Gigabit Networks,’ IEEE Nehvor~ vol. 6, No. 2, March 1992, p. 31.
38 I Advanced Network Technology

Box 3-A-interactive Visualization Using Gigabit Networks

Scientists at the University of Wisconsin’s Space Science and Engineering Center have developed a software

package that allows “interactive” visualization of data computed by a model. This photograph of a workstation’s

display shows both a computed forecast of cold fronts moving across the North Atlantic and the “control panel”

that the scientist can use to control the images displayed.

computers generate new kindss -$ g

of images, that change in response

~ , .-

to their users’ needs. If the scientist

selects the command “animate,” in

the upper left hand corner of the

control panel, the workstation will

display a succession of images that

show the evolution of the storm over

time. Other commands allow the ~ .

user to rotate and “zoom” the

images, to look at them from any

angle.

The time required for a workstation to compute a new image, in

response to a user command, can

be significant. A supercomputer ., ‘1 would be able to reduce the re- .

sponse time and allow interactive

exploration of the data computed by the model. However, like many research institutions, the University of

Wisconsin does not have a supercomputer.

The Internet could be used to send data to one of the NSF’s supercomputercenters. However, the data rate

of today’s Internet is too low-the advantages of speeding up the computation by using a supercomputer are

outweighed by the time needed to transfer the model data to and from the supercomputer. With a gigabit network,

the communication time would no longer be a bottleneck.

As part of the BLANCA testbed’s applications research (see oh. 4, p. 56), University of Wisconsin scientists

will use a gigabit network to support interactive visualization of large data sets. The user’s commands would be

sent from the workstation through the network to a supercomputer at the National Center for Supercomputing

Applications, in Champaign, Illinois, which would do most of the visualization processing and send the image data

back to the workstation for display. This testbed research may serve to demonstrate away for the majority of

research institutions that do not have supercomputers to do interactive visualization.

SOURCES: William Hibbard, University of Wisconsin--Space Science and Engineering Center, Mar. 11, 1993; William Hibbard, David

Santek and Gregory Tripoli, “lnteractive Atmospheric Data Access Via High-Speed Networks,” Computer Networks and ISDN Systems,

vol. 22, pp. 103-109.

essing power that exceeds that of a single not need to build a model of an airplane and test

supercomputer (see box 3-B). Supercomputer

—

it in a wind tunnel, but can simulate the flow of air

applications are often simulations of real-world around the airplane on a supercomputer. Unfortuphenomena; for example, airplane designers do nately, for many interesting problems the process6 Charles E. Catlett, ‘‘In Search of Gigabit Applications, ’ IEEE Communications, vol. 30, No. 4, April 1992, pp. 43-45.
Chapter 3-Broadband Network Technology | 39

—.— —-- — .- — The CASA testbed will use a gigabit network to link supercomputers at the California Institute of Technology

(CIT), Jet Propulsion Laboratory (JPL), Los Alamos National Laboratory (LANL), and the San Diego

Supercomputer Center (SDSC).

ing time required with even the fastest supercomputer can be significant.7 Researchers hope to

reduce this time by using multiple computers in

parallel and linking them through a network. The

network could also connect the supercomputers to

scientific instruments or massive remote databases that would provide data to be used in the

calculations.8

1 Applications and Network Requirements

Two requirements will be placed on future

networks. First, they will need to have much

higher bandwidth than today’s networks, in order

to keep pace with advances in computer technology and support bandwidth-intensive videobased and distributed computing applications.

Distributed supercomputing applications would

require even greater increases in network bandwidth. Second, the networks will have to be more

flexible than today’s networks-they will be

supporting a more diverse range of services, with

a wider range of bandwidth requirements.

HIGHER BANDWIDTH

The bandwidth requirement for each type of

application depends on a number of factors.

7 OffIce of Science Technology Policy, “Grand Challenges 1993: High Performan ce Computing and Communications, ’ p. 15.

8 Catlem op. cit., footnote 6, pp. 4649.
40 I Advanced Network Technology

Box W-Distributed Supercomputing

Supercomputer-based simulations are becoming essential tools for science and engineering. Often,

scientists are able to study problems that would be difficult or impossible to study theoretically or experimentally.

For example, a number of researchers are developing climate models that can be used to predict the evolution

of the Earth’s climate over the coming decades. Computational science is becoming more widely used as the

increasing power of new supercomputers brings more problems within reach.

One of the goals of the HPCC program is the development of computer technology that will allow scientists

to tackle problems that are beyond the capabilities of today’s machines. Some problems simply take too long to

compute-some current models of the ozone depletion process take 10 hours of supercomputer time to compute

the complex chemical reactions that take place in everyday of “real” time. Other problems cannot be studied at

a useful level of detail-computer power might limit a climate model to tracking the evolution of temperatures at

only a limited number of points on the globe.

Greater processing power is also required for “interactivity,” completing a computation in time to allow a user

to take some action to control an instrument, change the parameters of a simulation, or “browse” other data sets

in a database (see box 3-A). This requires that the computation of the model and the visualization processing be

done in a fraction of a second. Today, images can take a considerable amount of time to compute, and are

generally processed “off line” after the computation has been completed. Because of the time required to process

newly computed or collected data much of the data often goes unused.

The testbed program is investigating the use of gigabit networks to help address difficult computational

science problems. High-speed networks may enable increased processing power, by linking several computers

through the network. For example, a model could be computed on a supercomputer and then sent to a special

graphics processor for the visualization processing, or a model could be split into two parts, with two

supercomputers working in parallel to solve the problem. Networks also allow data from multiple sources to be used

in a computation--large databases and scientific instruments, for example.

In the testbeds described in chapter 4, distributed supercomputing is used to increase processing power to

study long-term weather models (part of the CASA testbed research), molecular dynamics (NECTAR), and

chemical modeling (CASA). The use of networked computers to speed up the visualization process in an

interactive fashion is being explored as part of applications for medical treatment planning (VISTAnet) and radio

astronomy (BIANCA). Navigation of multiple large databases and associated visualization are used for terrain

visualization (CASA), atmospheric sciences (BLANCA), and terrain navigation (MAGIC).

The testbeds are also working on the systems software and “tools” that will support these applications.

Today, implementing distributed applications requires detailed knowledge of the behavior of the network and the

characteristics of different computers. Distributed supercomputing will only be widely used by scientists if they can

be freed of the need to learn these details, and can concentrate on the science aspects of their simulations. The

testbeds are developing software modules that implement commonly used functions, and programs that automate

parts of the applications development process. In the long run, the objective is to create software support and

distributed operating systems for a “metacomputer,” which would hide the complexity of networked computers and

appear to the programmer as a single computer.

SOURCES: Gary Stix, “Gigabit Connection,” Scientific American, October 1990, p. 118; Matthew Arrott and Sara Latta, “Perspectives on

Visualization,” IEEE Specftum, vet. 29, No. 9, September 1992, pp. 61-65; Larry Smarr and Charles E. Catiett, “Metacomputing,”

Communications of the ACM, vol. 35, No. 6, June 1992, pp. 46-52; office of Science and Technology Policy, “Grand Challenges 1993:

High Performance Computing and Communications,” p. 54.
Chapter 3-Broadband Network Technology | 41

Because of advances in ‘‘compression” technology, it now appears that relatively modest increases in bandwidth can accommodate many

simple video and multimedia applications. There

are many ways to convert a video signal to a

digital stream of bits; new compression algorithms are able to squeeze the information content

into fewer bits without significantly affecting

picture quality.9 These improvements have resulted from a better understanding of the mathematics of signal processing and also from research on how people perceive images .10 In

addition, increased processing power due to

advances in microelectronics has allowed sending

and receiving computers to do more complex

signal processing.

Advances in compression technology have

been dramatic. While it was once believed that a

155 Mb/s fiber optic link could carry only a single

high-definition television (HDTV) signal, it is

now believed that such a link can carry five or six

HDTV signals. 11 In addition, it now appears that

many simple video and multimedia applications

will not require broadband fiber access to the

network. New compression techniques are able to

compress VCR-quality video to a few megabits

per second, bandwidths that can be supported by

new schemes for converting the telephone companies’ existing copper local loops to digital

service12 There are a number of emerging viola

and image compression standards-the most

prominent of these will be the HDTV standard to

be chosen by the Federal Communications Commission in 1993.13

However, there are still many possible applications that would more fully use the capacity of

fiber. 14 These are the kinds of applications that are

being investigated by the testbeds described in

chapter 4. One possibility is distributed supercomputing-the use of high-bandwidth links to

combine the processing power of multiple supercomputers. There are also applications that require images or video of a quality that can be only

supported by fiber, despite advances in compression technology. In some cases, such as some

medical applications, compression cannot be

used because it destroys vital data. Other applications may demand very high bandwidths because

many medium bandwidth streams of data are

delivered to the user at once, allowing the user to

select, combine, or process the streams at the

workstation. 15 “Telepresence” or “virtual reality’ applications require the delivery of large

amounts of data in order to create the illusion of

a user being in a distant location.

FLEXIBILITY

The second requirement the envisioned applications place on advanced networks is flexibility.

First, new network technologies should be sufficiently flexible to carry all kinds of traffic. The

integrated services concept envisions a network

in which the same links and switches are used, to

the extent possible, for all types of traffic.

Integrated services networks may be more efficient than separate networks, and would also

match advances in computer technology that

allow computers to run multimedia applications.

Today, different network technologies are used

for voice, video, and ordinary data traffic. As new

services were required, new types of networks

were constructed. The telephone network was

s Mark Robichaux, ‘‘Need More TV? TCI May Offer 500 Cbannels,” Wall Street Journal, Dec. 3, 1992, p. B1.

10 P. H. Ang et al., ‘‘Video Compression Makes Big Gains,” IEEE Specfrum, October 1991, pp. 16-19.

1 I See, for a table of bandwidth m@rernents for compressed signals, J. Bryan Lyles and Daniel C. SwiDeh@ “ne EmW@g Gigabit

Environment and the Role of Imcal AT~” IEEE Communications, vol. 30, No. 4, p. 54.

12 ~]es F. IWSOq “Bell Atlantic Stretches Copper for Video TM*’ Telephony, CM. 26, 1992, P. 10.

13 ~k hw ‘‘Swatig Out the HDTV Contest,’ Business Week, No. 3306, Feb. 22, 1993, pp. 92-94.

14 mom and Spears, op. cit., footnote 5, pp. 3~.

IS Lyles and swine- op. cit., footnote 11, p. 55.
42 | Advanced Network Technology

augmented first by packet switched networks for

data and then by a variety of specialized networks

for video communicationl6 and distribution, such

as cable television networks. Separate networks

were required in part because no switching

technologies worked equally well with all services.

Broadband networks should also be able to

accommodate a range of applications bandwidths, from the very small amount of bandwidth

required for ordinary electronic mail to the gigabit

rates needed for distributed supercomputing.

Some kinds of switching technologies are more

flexible than others in accommodating different

bandwidths in the same network. Circuit switches,

the type used in the current telephone network,

limit applications to a small number of predetermined bandwidths, while packet switches are

more flexible.

Flexibility is also important from a network

planning standpoint. While there are some general ideas about the ways in which broadband

networks will be used, there is no real operational

experience. Ideally, the network technology that

is deployed would be able to accommodate a

range of different scenarios, and its effectiveness

would not depend on network planners knowing

the exact mix of future applications in advance. In

addition, future networks will have to support a

more diverse range of users, each with different

bandwidth and service requirements. Network

operators would like to deploy network technology that could provide services to a diverse range

of users with a minimum amount of customization.

FAST PACKET NETWORKS

A number of new concepts for network design

may meet the requirements for flexible broadband

integrated services networks.17 There is general

agreement that these networks will rely on fiber

optic transmission, which has sufficient bandwidth to carry video and other types of bandwidthintensive services. There is also general agreement that future networks will use a concept

called “fast packet switching,” which provides

the necessary processing power to keep up with

increases in link bandwidth and the necessary

flexibility to support different kinds of services

and a range of bandwidth requirements.

Fast packet networks overcome the main weakness of traditional packet networks by using

special control mechanisms to provide the consistent network performance required for video

and other real-time services. In traditional packet

networks such as the current Internet, the network

could become heavily loaded in a way that

degraded these services. Researchers are looking

at a number of different schemes to either prevent

networks from becoming too heavily loaded, or to

minimize the effects of a heavily loaded network

on traffic such as video that is sensitive to

network performance. Fast packet switches can

then act as the foundation for integrated services

networks.

Both the computer and telecommunications

industries are investigating fast-packet approaches.

In response to the emerging consensus for these

technologies, considerable work has been done

on the development of the necessary network

components such as switches. However, until

recently most experience with these networks had

been confined to relatively small-scale experimentation with local area networks, or simulation

and mathematical modeling. One of the main

purposes of the testbeds described in chapter 4 is

to demonstrate these networks in a realistic

environment. In addition to the testbeds, a number

of other experimental fast packet networks are

now being planned or are operational.

Two different kinds of fast packet switching

are being studied by the testbeds. The most

16 For ~mple, he C_jN~R’r network ~ Nofi CWoliM uws ~@-~dwid~ m.ic~wave bks to SUppOfi videoeonferencing ~d

“teleelaases.’

17 Nim K. Cheung, “The Infrastructure for Gigabit Computer Networks, ” IEEE Communications, vol. 30, No. 4, April 1992, p. 60.
—

Chapter 3-Broadband Network Technology | 43

prominent of the fast packet switching concepts

was first championed by the telephone companies

and is called Asynchronous Transfer Mode, or

ATM.18 ATM has been chosen by the telecommunications industrys international standards group,

the CCITT, as the foundation for the Broadband

Integrated Services Digital Network (B-ISDN), a

blueprint for the future development of the

telephone network.19 B-ISDN envisions the provision of 155 Mb/s or 622 Mb/s fiberoptic access

links to each customer, which would then be used

to carry voice, video, and data traffic to support a

range of applications.20

One of the most significant aspects of ATM is

that it has subsequently been adopted by many

companies in the computer industry, and by

manufacturers of equipment for local area networks and private networks. This convergence

with telecommunications industry plans21 may

simplify the task of connecting different kinds of

networks—in the past, local and wide area

networks have used different technologies. However, technologies other than ATM have also been

proposed for local area networks. Most of the

testbeds described in the next chapter are using

supercomputer industry networking standards

that require the construction of modules that

convert between the supercomputer network format and ATM.

While most packet networks use packets that

can be very long and vary in size depending on the

data being carried, ATM networks use short

packets called ‘‘cells’ that are always the same

length (figure 3-l). If an ATM network is being

used to carry Internet traffic, the Internet packets

would be broken into a series of cells (figure

Figure 3-1—ATM Cell

I

Data I

Header

(48 bytes) (5 bytes) I

International standards specify that ATM cells are 53 “bytes”

long, 48 bytes to carry the applications data and 5 bytes for

the header, which is used to carry such information as the

destination’s address. By contrast, the packets used in

traditional packet networks can be several thousand bytes

long. A “byte” is the computer science term for eight bits.

SOURCE: Office of Technology Assessment, 1993.

3-2(a)). After traveling through the network, the

cells would be reassembled into the Internet

packet and delivered to the destination computer.

The same network could also carry video or

sound: as the video or sound was digitized, the

computer would load the bits into a cell (figure

3-2(b)-(c)). As soon as the cell was filled, it would

be sent into the network and the user would begin

filling the next cell. The cells carrying the video

and Internet packet data would travel through the

network together, sharing the same links (figure

3-3) and being processed by the same switches.

The second approach to fast packet switching

being studied by the testbeds is called Packet

Transfer Mode or PTM. The version being

studied in the testbeds has not been adopted by

standards committees. PTM does not use short

cells, but more traditional packets that can be

longer if necessary. This may simplify the task of

carrying long Internet packets, because the computer does not have to break up the packet into

many cells. ATM may also encounter problems at

very high bandwidths-because the cells are so

18 ROM w. Luc~, Ex~tive D~@r, comm~~tiIxM sciences R~~ch Divisiq AT&T Bell timtorics, testimony at hearhgs

before the Joint Economic Committee, June 12, 1992.

19A. Day, “International Standardization of B-ISDN,” IEEE L/S, vol. 2, No. 3, August 1991.

20 peter Broke ~dHefi~h~bmster, ‘CBm~~d Sewices: ~~~~,” Te/ecom~nicarions, VO1. 25, No. 12, DaCXIIIXX 1991, pp.

24-32.

2.1 Jo~ J. Ke~m, “AT&T Sets Alliance to Make - to Provide Multimedia ServiwS, ’ Wall Street Journal, Jan. 13, 1993, p. B6; John

McQaillan, “Who’s Who in Am” Business Communications Review, August 1992, p. 10.
44 I Advanced Network Technology

Figure 3-2—ATM

(a) Data communications using

Es Packet

->~“

,,

ATM

,,

-> ITI . . . . . . . Q ‘m

ATM cells

Packets are broken into several ATM cells. After traveling through the network, the cells are reassembled into packets.

(b) Video communications using ATM

RI Digital video

> - ...... ~

,,

,! /’” \ ( ‘ ‘ “ ‘

ATM cells

The digital video bits are put in cells and sent through the network. At the destination, the bits are removed from the cells.

(c) Voice communications using ATM

kid Digital voice

> ,M ““” ”” ”1—UUUU%

,,

r,

ATM cells

Voice is handled in the same way as video.

SOURCE: Office of Technology Assessment, 1993.

short, there is little time to process each cell NETWORK COMPONENT

before the next one arrives. However, ATM CURRENT STATUS

DEVELOPMENTproponents believe that the use of cells makes it The telecommunications and computer induseasier to develop the control mechanisms that tries have been working intensively to develop

support real-time traffic such as video, and to be components for fast packet networks. The compobetter suited to voice traffic. One purpose of the nents are in varying stages of development. Fiber

testbed research is to compare the two approaches optic transmission links are the most advanced in

to fast packet switching with realistic traffic. their development—very high bandwidth optical
Chapter 3-Broadband Network Technology | 45

Figure 3-3-integrated Services Using Fast Packet switching

(a) Today, separate networks for each service

[m’] i~”’1 Packet switched network

(b) Fast packet switched network supports all services

/

SOURCE: Office of Technology Assessment, 1993.

transmission systems are now commercially available. Fast packet switches are the subject of

considerable industry research and development;

most of the major telecommunications industry

suppliers have had intensive ATM switch development efforts since 1987 or 1988, when it

became clear that standards groups were going to

adopt ATM. Some fast packet switches are

becoming available commercially, but switches

are less advanced in their development than the

fiber optic links. Important work also remains to

be done on

hardware that

computer and

the design of the software and

handle the connection between the

the network.

1 Optical Fiber

Optical fiber has clearly emerged as an enabling technology for broadband networks. With

increased bandwidth the links will be able to

move data more quickly and support the transport

of bandwidth-intensive traffic such as video. The

development of the transmission equipment that

handles gigabit rates is no longer a research issue.

Although configured to support voice telephone

calls, many fiber optic links in today’s telephone

network operate at more than one gigabit per

second. Furthermore, the fiber cable is already

widely deployed in much of the telephone network, especially in the interoffice portions of the

network that will provide most of the transmission facilities for the agency backbones and

regional networks.

For the telephone company fiber links to

support the gigabit NREN and other broadband

services, new transmission equipment will have

to be deployed. This equipment is expected to
46 I Advanced Network Technology

conform to a new standard called Synchronous

Optical Network (SONET), and is now becoming

commercially available. While fiber has been

used in the telephone network for a number of

years, the link capacity was mainly configured to

carry thousands of low bandwidth telephone

calls. SONET transmission links, on the other

hand, can be configured to support the highbandwidth channels required for advanced networks. For example, the transmission facilities to

be used in the testbeds employ a 2.4 Gb/s SONET

link, which can be divided into four 600 Mb/s

channels.

1 Switches

The development of fast packet switches is less

advanced than the development of transmission

links. However, there has been considerable

theoretical work done on switch design, prototypes have been developed, and some early

commercial products are becoming available. By

the end of 1993 or early 1994, several suppliers

should have ATM products on the market. The

early products are designed primarily for private

networks or carrier networks operating at 45 Mb/s

or 155 Mb/s, not gigabit rates. 155 Mb/s is the

bandwidth specified by the telecommunications

industry’s standards group, the CCITT, for the

Broadband Integrated Services Digital Network

(B-ISDN) service.

There are many different ideas for how to build

fast packet switches-the “best” design depends

on assumptions about the number of users, the

bandwidth of the network, and the mix of traffic.

However, all of the proposed switch designs rely

on hardware, in order to speed the processing, and

are usually based on ‘‘parallel’ designs that

allow many packets or cells to be processed at

once.

If ATM switches do become central to telephone company networks, then there will be

demand for large switches to replace the current

‘‘central offices’ that handle tens of thousands of

lines. Most of the ATM switches now becoming

available only handle a small number of lines16 or 64 lines are common configurations.

Initially, ATM switches will probably be introduced to support new services, rather than as a

replacement for existing central office switches .22

Building an ATM switch that can serve thousands

of lines is a difficult task, requiring further

research on switch design and device technology

and packaging. The move to ATM switching has

the potential to change the market positions of

telecommunications equipment manufacturers,

much as the transition from analog to digital

created market opportunities in the late 1970s.23

Switches control the flow of packets using

considerable software “intelligence.” For example, if the network is heavily loaded, a switch may

decide to handle video or other performancesensitive traffic first. Switches may also help

prevent the network from becoming too busy—

they may prevent a user from sending traffic, or

verify that users are not using more than their

share of the network capacity. These aspects of

the control of the network are still important

research issues, however; there are many different

proposals for managing fast packet networks. As

a result, some of the prototype switches used in

the testbeds described in chapter 4 are flexible

enough to allow researchers to reprogram the

network control mechanisms.

I Computers

The use of high-bandwidth links and switches

will expose new bottlenecks inside many computers.

24 New computer designs may have to be

22 ~~d -M,“Am@~h ~~es End-to-end ATM RFP,” Telephony, vo~. 224, No. 9, ~. 1, 1993, p. 14.

m Jo~ J. Kellm, “~lepho~ Switching Moves ‘lbward Increased S-” Wall Street Journal, NOV. 4, 1992, p. B4; St-m TNc&

“Northern Keeps ATM Details S@” Telephony, Sept. 28, 1992, p. 13; “NEC Lands ATM Pact for Wiltel,” TeZephony, Oct. 26, 1992, p.

8.

~ H.T. Kung, “Gigabit Local Area Networks: A Systems Perspective,” IEEE Communications, vol. 30, No. 4, April 1992, pp. 86-88.
Chapter 3-Broadband Network Technology | 47

developed to improve the rate at which data can

be transferred from the network, through the

computer’s internal circuitry, and into memory,

where it can be used by the applications software.

Both the internal circuitry and the memory of

today’s computers are limited in the rate at which

they can transfer data. In the past, the design and

operation of computers has focused on the task of

maximizing the processing power once the data is

in memory, not the larger problem of maximizing

the performance of networked applications.

Computers may also require additional processors or hardware to process protocols. With low

speed networks, the computer’s main processor

was powerful enough to handle the communications functions and still have enough time left to

run applications. This may continue to be the case

as the processing power of computers continues

to increase. However, in some cases it may be

necessary to relieve the processor of some of the

burden of handling the communications functions. This is likely to be the case with ATMbased networks-because the cells are so short,

there are many cells to be processed in a given

amount of time. Special ‘‘network interfaces’

that speed the protocol processing are being

developed for a number of different computers as

part of the testbed project discussed in the next

chapter.

APPLICATION OF BROADBAND

TECHNOLOGIES

The broadband technologies discussed in this

chapter will be used in both the Internet and in

other networks, such as private networks or the

public switched network. The use of broadband

technologies in the Internet is linked to their

deployment in the public switched network in two

respects. First, the Internet will probably continue

to rely on the public network’s transmission

infrastructure. As a result, it is dependent on the

rate of deployment and the cost of SONET links.

Second, the carriers may use their new ATMbased infrastructure as a way to play a more active

role in the computer communications business

and offer Internet services.

1 Application to the Internet

The links in the high-speed networks in the

core of the Internet are expected to use the

SONET-based transmission infrastructure that

the telephone companies are planning to deploy.

SONET is actually a family of transmission

rates-there is 155 Mb/s, 622 Mb/s, and 2.4 Gb/s

SONET equipment becoming available now.

Users that need access to the Internet at broadband rates will also use SONET for their access

links. Large universities and commercial users of

the Internet would be able to make special

arrangements with their local exchange carrier for

the provision of fiber access. The rate at which the

carriers will more broadly deploy optical fiber in

the local loop depends on the resolution of

complex economic and policy issues.

However, many users of the Internet will not

require fiber optic access links in the near term.

The carriers have proposed several new technologies that would convert existing copper local

loops to digital service. These technologies do not

support true broadband capabilities, but still

represent a significant improvement over the

existing analog local loop. They include the

Integrated Services Digital Network (ISDN) (see

box 3-C for a description of ISDN), High-bit-rate

Digital Subscriber Line (HDSL)25, and Asymmetric Digital Subscriber Line (ADSL) standards.

ISDN provides access at 144 kb/s; HDSL provides access at 768 kb/s. These technologies are

available on a limited basis from the carriers and

are the subject of a number of trials and demonstrations.26 The pace of their deployment depends

~ ~d A. Greenen and William R. Murphy, ‘ ‘HDSL: ~athe Utility of Copper-Based Transmission Networks, Telecommunications,

August 1992, p. 55.

26 -on, op. cit., footnote 12.
48 I Advanced Network Technology

Box 3-C--ISDN

ISDN (Integrated Services Digital Network) is a telecommunications industry standard for upgrading local

loops to digital service. This “last mile” of the network, the wire that connects a telephone network to its customers,

is less sophisticated than other parts of the network The core of the telephone network uses high-capacity, digital,

fiberoptic links. The local loop, by contrast uses Iow-capacity, analog, copper wires. This technology is acceptable

for ordinary telephone service, but more sophisticated services will require upgraded local loops.

When work began on the ISDN standards in the mid-1970s, it was believed that ISDN would soon be

deployed to all of the telephone network’s customers. Today, ISDN is used only on a very limited basis, due to

delays in completing the standards and several regulatory and economic questions. Because of the delays in

deploying ISDN, large business customers found more capable technologies. More importantly, a new vision of

the future of the local loop emerged-the wiring of homes with fiberoptic Iinks--and ISDN was no longer viewed

as a technology with an important role to play.

There is now renewed interest in ISDN, however, as an “intermediate” step between the current analog local

loop and the use of fiber optics. Because of the cost of deploying fiber, it may be many years before significant

numbers of homes are connected. ISDN is cheaper than fiber, can be deployed sooner, and, while its capacity

is only a fraction of fiber’s, represents a significant improvement over the current analog local loop. While ISDN

will not become the universal network standard once envisioned, it may play a role in providing better network

access to certain groups of users.

For example, one possible application might be telecommuting, which allows employees to work at a desktop

computer at home. To connect to the office computers, workers today would need a device called a modem, which

lets them send digital computer data over the analog local loop. Common modem standards transmit data at 2,400

or 9,600 bits per second; ISDN, by contrast, provides two 64,000 bits per second (64 kb/s) channels. This would

allow videoconferencing of reasonable quality, faster transfer of graphics information, and better quality fax

transmission. It would also permit much-improved access to the Internet for home users. Today, good-quality

access to the Internet is usually only available to large customers who are able to arrange for special digital access

lines to be provided by their local telephone company.

ISDN allows the existing copper local loops to be used for digital service. However, it requires users to buy

new equipment for their end of the line, which converts their data to the ISDN format. It also requires that the

telephone company’s equipment, such as the “central office” switches, be upgraded. Currently, the user

equipment is expensive and only one-third of the telephone lines are connected to switches that are “ISDN ready.”

In addition, ISDN communications are hampered by the fact that different equipment manufacturers have

implemented their own versions of ISDN, despite the fact that it was developed to be a standard. In most of the

United States, ISDN is not available as a regular service.

However, some progress is being made toward overcoming ISDN’S problems. The industry has a number

of initiatives that are intended to encourage the development of ISDN equipment that conforms to a common

specification. The Regional Bell Operating Companies, which provide local telephone service in most of the United

States, have announced that they are planning to make 56 percent of their lines ISDN-ready by the end of 1994.

In addition, the cost of users’ ISDN equipment may decline as it becomes more widely used.

Broadband ISDN, which is discussed on p. 46, uses very different technology from “ordinary” or

“narrowband” ISDN. Narrowband ISDN is best viewed as a digital upgrade of the telephone network’s copper local

loop. Broadband ISDN, by contrast, requires fiber optics and Asynchronous Transfer Mode (ATM), a new approach

to network design discussed in detail in this background paper. ISDN and Broadband ISDN have little in common

other than their names.

SOURCES: James N. Budwey, “h’s Time to Get Off the ‘POTS’,” Telecfommunications, August 1992, p. 4; Cindy Skrzycki, ” ‘Data Highway’

Plan Costs May Decline,” The Washington Post Jan. 20, 1993, p. G1; Bob Wallace, “Study Raises Concerns About National ISDN,”

Network World, June 29, 1992, p. 27; Mitchell Kapor, President, Electronic Frontier Foundation, testimony at hearings before the House

Subcommittee on Telecommunications and Finance, Jan. 19, 1993; Steve Lohr, “Computer Makers Told to Get Involved In Rules,” The

New York Times, Feb. 23,1993, p. D2.
Chapter 3-Broadband Network Technology | 49

on resolving standards issues and on business

decisions made by the carriers. 27

Internet traffic may be handled by some of the

new fast packet switching systems. As was noted

above (p. 43), fast packet networks can carry

Internet traffic if the Internet packets are first

converted to the appropriate fast packet format—

for example, if the Internet packets are broken up

into a series of ATM cells. It is likely that other

types of switching technologies will also be used.

The success of the Internet is due in substantial

part to the commonality of protocols that support

the technological diversity of the interconnected

networks. Some networks will continue to use

‘‘routers," similar to those used in today’s

backbone networks, while others may employ the

new fast packet switching technologies or some

of the new data communications services that the

carriers may offer, such as Frame Relay or SMDS.

9 Public Network

In many ways, the most significant aspect of

ATM is that it was first championed by the

telephone companies and is now a key component

of telephone company planning. ATM represents

a dramatic change in the design of telecommunications industry networks. Traditionally, the industry has not used packet switches. It used the

circuit switches that were ideally suited to carrying voice telephone traffic. The industry standards group, the CCITT, chose ATM because it

believed that simply upgrading the existing circuit switched network to higher bandwidths

would not provide the necessary flexibility to

support future services. ATM is a central component of carrier strategy; they hope to use ATM as

the basis for a range of future services, including

video, Internet services, and other data communications services such as Frame Relay or SMDS.28

ATM’s flexibility offers the carriers an opportunity to enter a variety of markets and quickly

offer new services with a common infrastructure.

However, some believe that ATM’s flexibility

also means that it is a compromise technology,

and that more specialized network technology

will continue to play a role.29 Moreover, there are

still important economic considerations for the

telephone companies as they determine the best

way to evolve from the current network to an

ATM-based infrastructure.30 Both service providers and manufacturers are facing difficult decisions about the timing of their investments and

the appropriate migration scenarios.31 Deployment decisions depend on estimates of future

revenues, equipment costs, the viability of competing technologies, and the carriers’ investment

in their existing networks.

27 *mdL. Andrews, ‘‘‘Baby Bells’ Rift Threatens An Advanced Phone Service,’ The New York Times, Dee. 1, 1992, p. D1.

28 Ben Lisows~ and Louise Reingold, ‘ ‘Sprint’s Evolution to Broadband ISDN,’ IEEE Communications, August 1992, vol. 30, No. 8, pp.

28-30; John Williamson and Steven Titc4 “Gazing Toward the Broadband HonzorL” Telephony, Oct. 5, 1992, p. 38.

29 ~-Tau ha, CCwt Shotid Be the Goal for ATM?’ IEEE Communications, September 1992, vol. 6. No. 59 PP. Ofi.

30 Stephen M. W~~rS, “A New Direction for Broadband ISDN, ” IEEE Communications, vol. 29, No. 9, September 1991, pp. 39-42.

31 caol WTilSom 1‘It’s Not mt You DO IL But HOW YOU DO It That Counts, ’ Telephony, June 15, 1$% P. 9.
Gigabit

Research

A

s was discussed in chapter 3, the limitations of current

networks and advances in computer technology led to

new ideas for applications and broadband network

design. This in turn led to hardware and software

development for switches, computers, and other network components required for advanced networks. This chapter describes

some of the research programs that are focusing on the next

step-the development of test networks.1 This task presents a

difficult challenge, but it is hoped that the test networks will

answer important research questions, provide experience with

the construction of high-speed networks, and demonstrate their

utility.

Several “testbeds” are being funded as part of the National

Research and Education Network (NREN) initiative by the

Advanced Research Projects Agency (ARPA) and the National

Science Foundation (NSF). The testbed concept was first

proposed to NSF in 1987 by the nonprofit Corporation for

National Research Initiatives (CNRI). CNRI was then awarded

a planning grant, and solicited proposals or white papers" from The HPCC

prospective testbed participants. A subsequent proposal was then

reviewed by NSF with a focus on funding levels, research program’s six

objectives, and the composition of the testbeds. The project,

cofunded by ARPA and NSF under a cooperative agreement with testbeds will

CNRI, began in 1990 and originally covered a 3-year research

program. The program has now been extended by an additional demonstrate

fifteen months, through the end of 1994. CNRI is coordinat- gigabit

1 Corporation for National Research Initiatives, ‘‘A Brief Description of the CNRJ

Gigabit lkstbed Initiative,” January 1992; Gary StiX, “Gigabit Conn=tiom” Sci@@

net-working.

4

American, October 1990, pp. 118-1 19; John Markoff, “Computer Project Would Speed

Dam” The New York Times, June 8, 1990, p. Al; “Gigabit Network ‘I&tbeds,” IEEE

Computer, vol. 23, No. 9, September 1990, pp. 77-80.

51
52 | Advanced Network Technology

ing five testbeds; a sixth testbed, funded by

ARPA alone, was announced in June of 1992.

The testbeds are investigating gigabit networks, very high-speed broadband networks that

represent the limit of what can be achieved today.

Most current work on broadband networks is

looking at lower bandwidths, such as the 155

Mb/s rate that will be used for the telephone

companies’ B-ISDN service. Because of the focus

on gigabit rates, some aspects of the testbeds’

research agenda are unique. In other respects,

however, the testbeds are one of a number of

research programs whose work will impact the

NREN-fast packet switching technologies, for

example, are being studied as part of many

industry research projects.

RESEARCH OBJECTIVES

In general, the objective of the testbeds is to

speed the deployment of advanced network technology, in the NREN and elsewhere. The networks are designed to provide a realistic test

environment for the technologies outlined in the

previous chapter. The switches and transmission

equipment conform to emerging industry standards wherever possible. More speculative concepts such as optical switching are not being

investigated by the testbeds—the focus is on the

network technologies that are central to near-term

industry planning. One purpose of the testbeds is

to look at unresolved research questions. However, the most valuable aspect of the testbeds will

be to demonstrate the feasibility of these networks

and provide experience with their construction.

While much of the research is related to

near-term industry plans, the testbeds are also

looking into the future. The testbed networks

achieve the highest bandwidths possible, given

the constraints of emerging industry standards,

current technology, and the time horizon of the

program. The equipment used in the testbeds had

to be such that it could reasonably be expected to

be working in time to integrate the components

and begin testing the networks by the end of the

project. The applications are the most bandwidthintensive possible, “gigabit applications” that

require a full gigabit of bandwidth for each user.

For the most part, these are distributed supercomputing applications that use the network to

combine the processing power of multiple supercomputers.

The research is also related to the expected use

of the network technology in the NREN environment. This emphasizes the use of Internet protocols with the new fast packet switching technologies, because the NREN program is linked to the

evolution of the Internet. In addition, supercomputer-based applications of the type being investigated by the testbeds will play an important role

in the gigabit NREN. However, not all issues

relevant to the future development of the NREN

are addressed by the testbeds: because of the

emphasis on high-speed applications there is little

work being done on applications that will be used

outside the supercomputer community. Nor is

there significant work being done on topics

related to the growing size and complexity of the

Internet (see ch. 2, p. 26, and ch. 5, p. 70).

Given the objective of demonstrating the feasibility of the emerging network design concepts,

the testbeds are emphasizing the construction of

working networks-much of the prior network

research used modeling or simulation in “paper

studies. Because there is little real experience

with broadband networks, these models and

simulations are based on assumed traffic patterns

that may not be accurate. The testbeds are

addressing this problem by building test networks

and investigating both network and applications

research simultaneously. The applications will

provide a source of traffic with which to test the

network components and protocols.

In addition, there is a focus on overall systems

performance. The overall performance of a network depends on how well the individual components work together, not solely on the performance of any single component. In the past,

researchers have tended to focus on the design of

individual components; for example, some have
Chapter 4-Gigabit Research | 53

looked mainly at switch design, others at transmission systems, and others at protocol issues. In

part, this has been due to the complexity of

organizing research programs such as the testbeds

that draw on the collaboration among several

disciplines.

The five CNRI testbeds are AURORA, BLANCA,

CASA, NECTAR, and VISTAnet, and are discussed in more detail in boxes 4-A to 4-E. The

sixth testbed, MAGIC, is described in box 4-F.

1 Testbed Design

Each testbed is building a high-speed network

that addresses wide area networking issues. The

networks connect three or four sites—industry

research laboratories, universities, Federal laboratories, and supercomputer centers-separated

by anywhere from about 30 to many hundreds of

miles. The focus on wide area networks provides

a realistic testbed for the agency backbones and

the public switched network. In the past, much of

the research done on advanced networks has

involved small “local area networks. ” These

served to demonstrate the basic concepts and

could be investigated by a small research group

within a laboratory. The development of highspeed wide area networks is much more difficult,

both technically and organizationally.

The testbed networks reflect the basic technology trends outlined in the previous chapter. The

networks all use optical fiber transmission and

fast packet switching. There is major emphasis on

the use of the telephone companies’ Asynchronous Transfer Mode (ATM) concept—five of the

six testbeds use ATM in some fashion. One of the

testbeds also uses Packet Transfer Mode (PTM),

a second kind of fast packet switching, and is

investigating the relationship between ATM and

PTM. Industry standard equipment is used wherever possible-the transmission links conform to

the current version of the Synchronous Optical

Network (SONET) standard, and the switches and

other components that process the ATM cells

conform as closely as possible to the current

versions of the international standards.

In order to focus on the systems issues, an effort

was made to draw on component development

work that was already underway when the testbed

program started in 1990. This would limit the

extent to which components had to be specially

developed and allow more time to experiment

with protocols, applications, and other issues

related to the operation of the overall network.

Because fiber optic technology is the most

advanced part of the system, the testbeds are able

to use early production models of SONET transmission equipment, operating at 622 Mb/s or 2.4

Gb/s. The switches, on the other hand, are mainly

prototypes, as are the interfaces between the

computers and the networks-before the testbed

work focused attention on the issue of interconnecting different network elements, network interfaces received less attention than such areas as

switch or protocol design.

At each testbed site are computers, switches,

and network equipment. Computing resources

available on the testbeds include workstations,

vector supercomputers, massively parallel supercomputers, and some specialized processors. In

some cases this equipment is connected directly

to the wide area network; in other cases it is

connected through a local area network. The local

area networks are using newly emerging gigabitper-second standards such as the supercomputer

community’s High Performance Parallel Interface (HIPPI) or pre-standard experimental technologies. A number of different interface devices

are being developed to handle the conversion

between the local area and wide area network

protocols, especially the HIPPI to ATM conversion.

Of particular interest is the investigation of the

use of networks to enable collaboration between

scientists and bring to bear increased processing

power on a scientific simulation. Many of the

applications also use the network to support

visualization or interactive control of a simulation

executing on a distant computer. Scientists and
54 I Advanced Network Technology

Box 4-A–AURORA

The AURORA network links four sites in the Figure 4-A-l—AURORA

Northeast: the University of Pennsylvania in Philadelphia; Bell Communications Research (Bellcore) in

Morristown, NJ; IBM’s T.J. Watson Research Center,

in Hawthorne NY; and the Massachusetts Institute of

Technology (MIT), in Cambridge, MA (figure 4-A-l). MIT

Bellcore is the research arm of the Regional Bell

Operating Companies (RBOCS) that provide local

telephone service in much of the United States.

t~

IBM

The testbed sites are connected by 622 Mb/s H

SONET channels. The transmission facilities are University of Bellcore

Pennsylvania

provided by three different carriers: interexchange

links are provided by MCI, local exchange links to IBM

and MIT are provided by NYNEX, and local exchange

links to the University of Pennsylvania and Bellcore are SOURCE: Office of Technology Assessment, 1993.

provided by Bell Atlantic.

Each node will have experimental fast packet switches, which can either route traffic to a local area network

on the testbed site or to another node. The local area networks will then distribute traffic to workstations, video

monitors, and other devices. A number of network interfaces have been built to allow the workstations to connect

to the local area networks and SONET transmission links. Bellcore and IBM are also supplying equipment for use

in multimedia and videoconferencing applications.

AURORA is unique in two respects. First, it will employ two different switching technologies. Bellcore is

contributing an ATM switch, based on the telecommunications industry standard that uses small, fixed length

packets called cells. IBM is contributing a switch based on a second fast packet switching technology called Packet

Transfer Mode (PTM) (part of IBM’s “plaNET” network architecture). The PTM switch was designed to support a

network architecture based on variable sized packets; it can, however, also handle ATM cells.

One of the research issues will be to compare the two types of switching technologies and to explore ways

in which the two technologies can work together. In the current Internet, networks based on a wide variety of

underlying technologies are used. Because both PTM and ATM maybe used in future networks, it is important

to gain understanding of how traffic could best be exchanged between these two networks. This work represents

an initial step towards gigabit inter networking.

AURORA is also unique in that it is not investigating distributed supercomputing applications. Instead, it

emphasizes experimentation with high-speed “multimedia” applications. Because video streams do not in general

require a full gigabit of bandwidth, one concept is to deliver a gigabit stream consisting of a large number of

medium-bandwidth video signals. For example, the network could be used to support an electronic classroom in

which a user could select from different views of a classroom demonstration.

SOURCES: Biereck et al., “Gigabit Networking Research at Bellcore,” IEEE Network, vol. 6, No. 2, March 1992, pp. 42-48; Cidon et al.,

“Bandwidth Management and Congestion Control in plaNET,” IEEE Communications, vol. 29, No. 10, October 1991, pp. 54-64.

other researchers are developing applications in a details of the network and computers’ operation,

number of areas, such as climate modeling, a number of modules and programs are being

chemical modeling, and space science. Because, developed that simplify the task of applications

in the long run, scientists will want to develop development in a distributed computing environapplications without having to learn all of the ment.
Chapter 4--Gigabit Research | 55

The protocols generally conform to the existing

Internet protocols, the protocols that will be the

most widely used in the NREN. The use of

well-understood, standard protocols also allows

applications researchers to concentrate on applications development. The testbeds will provide a

way to test the behavior of the Internet protocols

in high-speed networks and to explore their use in

a fast-packet-switched environment. However,

the testbeds will also be testing a number of

experimental protocols that may perform better

with new network technologies. This research

may serve to test ideas that will be incorporated

in the Internet protocols in the future.

I Testbed Organization

One of CNRI’s key roles has been to assemble

the testbed teams. The testbeds draw on researchers in industry, universities, supercomputer centers, and Federal laboratories. Some researchers

within the groups have experience with traditional telecommunications issues, while others

are more familiar with issues related to the

Internet or supercomputer networking. The

testbed research is necessarily multidisciplinary.

In particular, each research group involves both

network and applications researchers. The applications researchers have experience with supercomputers, visualization, graphics, and a variety

of scientific disciplines. Network researchers

draw on expertise with switches, transmission

equipment, protocols, signal processing, and computer architecture.

While regular meetings are held between CNRI

and program managers at ARPA and NSF, most

of the responsibility for the management of the

testbed program lies with CNRI. For example,

one of CNRI’S functions was to help develop the

spectifications for the transmission equipment that

would be used in the testbeds. CNRI has also been

responsible for maintaining the technical direction of the project, and has held a number of

meetings on specific technologies. In addition,

there have been annual meetings, which include

attendees from a wider group than just the testbed

participants, such as workstation manufacturers

and government agencies, in an attempt to relate

the testbed research to other industry activities

and the broader NREN program.

One of CNRI’s main contributions has been to

ensure the participation of the carriers and other

industrial partners. Participation of industry is

essential to meeting the research goals of the

project. First, the expertise required to develop

many of the components required for high-speed

network research is only available in industry.

These components are complex, and their development involves the fabrication of custom integrated circuits and high-speed circuit design.

Second, industry involvement has lowered the

cost to the government of the program. The

components developed by industry and the transmission capacity between the testbed sites have

been contributed at no cost. Because of the

contributions of industry, ARPA and NSF’s

support through the cooperative agreement with

CNRI only covers a small part of the total cost of

the project.2

There are a number of issues associated with

the participation of industrial partners in the

research venture. Some of these concerns are

legal-there are antitrust issues, and further

regulatory constraints govern the telecommunications industry. Another factor has been the

competitive relationship among the testbed participants-while participating in the same research

project, they are also competitors in various lines

of business. For example, the wider use of more

sophisticated telecommunications industry services may not necessarily be in the interests of

companies that have emerged to offer computer

networking services.

Moreover, some aspects of the research do not

reflect industry priorities. Because of the cost of

true gigabit access, it has been estimated that it

2 Stix, op. cit., footnote 1, p. 118.
56 | Advanced Network Technology

Box 4-B–BLANCA

The sites on the BLANCA network Figure 4-B-1 —BLANCA

are more widely separated than those of

the other testbeds. The network links

AT&T Bell Laboratories in New Jersey, the

University of Wisconsin and the University

of Illinois, and the University of CaliforniaBerkeley and Lawrence Berkeley Laboratories (figure 4-B-l). Because of the cost of

gigabit transmission facilities, high-speed

links will initially be used only for some

parts of the network. The cross-country

segments of the network will use 45 Mb/s

T3 links. While this bandwidth is not /’

sufficient for distributed Supercomputing SOURCE: Office of Technology Assessment, 1993.

applications, the BLANCA network will still

provide an environment for researching the behavior of new protocols in a large network

BLANCA is an ATM-based network. The experimental ATM switches and other hardware are being supplied

by AT&T Bell Labs, the main industrial partner for BLANCA. BLANCA builds on preexisting research relationships

between Bell Labs and the University of Wisconsin, University of Illinois, and UC-Berkeley. The switches are

designed in such away as to allow researchers at the universities to ’’take over’’ the network, to control the switches

with computer programs that implement their experimental protocols. The network research interests are similar

to those of others Iooking at ATM-based networks, such as congestion control and the behavior of internet

protocols in an ATM-based network, and is being carried out primarily at UC-Berkeley, the University of Illinois,

and the University of Wisconsin.

BLANCA emphasizes distributed supercomputing applications, as do most of the other testbeds. The

applications work is being done at the National Center for Supercomputing Applications (NCSA), the University

would not be generally available to commercial cations industry’s ATM-based Broadband Intecustomers until about 2005.3 Much of the research agenda focuses on higher bandwidths and

more specialized applications than are expected

to have near-term commercial significance for the

telecommunications industry. Industry planning

is oriented more towards medium-bandwidth

multimedia applications-applications that require more bandwidth than can be supported by

current networks, but significantly less than the

gigabit/second rates required by the supercomputer community. For example, the telecommunigrated Services Digital Network (B-ISDN) standard envisions 155 Mb/s channels to each customer

in the near term. Furthermore, many of the

interesting issues related to the operation of fast

packet networks can be studied with lower

bandwidth networks, although a few issues may

only become apparent at gigabit/second speeds.4

TESTBED PROGRESS

The major research results of the testbeds are

still to come. Most of the networks are not

3 M. Niel Ransom and Dan R. spews, “Applications of Pablic Gigabit Networks, ’ IEEE Network, vol. 6, No. 2, March 1992, p. 30.

4 Leonard ICleinrocL ‘‘The Latency/Bandwidth Tradeoff in Gigabit Networks, ” IEEE Communications, vol. 30, No. 4, April 1992, pp.

36-40.
— .-

Chapter 4-Gigabit Research |57

of Wisconsin, and Lawrence Berkeley Laboratories. A significant part of the work involves the development of

software packages and modules that make it easier for scientists to use distributed supercomputing applications.

For example, NCSA has been developing modules that handle many of the networking functions; these free

scientists of the need to learn all the details of t he network’s operation-they can simply incorporate the modules

in their applications. Another project is developing a digital library that allows the user to control the retrieval and

processing of data--one of the programs that can be accessed by this digital library handles visualization

processing, for example.

The applications under development as part of BLANCA could be viewed as prototypes for the Grand

Challenge problems to be investigated under the HPCC program. One important aspect of these problems is that

they will require collaboration between geographically dispersed researchers. The network and computing

environment could support this collaboration by providng facilities for videoconferencing. On a more sophisticated

level, researchers at NCSA have developed a program that permits collaborative investigation of data. It permits

a researcher to highlight a feature in the data displayed on a workstation screen; researchers at other sites would

then see the same feature highlighted on their displays.

The Grand Challenge problems will also involve very large data sets. Processing the data into image form

is computationally intensive, especially when it is necessary to view the data interactively. The University of

Wisconsin and NCSA are investigating the use of high-bandwidth connections from a scientist’s workstation to a

supercomputer to provide the necessary computational resources for visualization processing.

A radio astronomy application being studied as part of the BLANCA project is looking at issues involved in

visualizing large data sets. Arrays of radiotelescopes collect the data, which is then sent through the network to

a supercomputer. A user at a workstation connected through a high-bandwidth network to the supercomputer can

control the processing of the raw data into images, which are then sent through the network to the workstation for

display.

SOURCES: BLANCA Annual Report Charles E. Catlett, "In Search of Gigabit Applications,” IEEE Communications, vol. 30, No. 4, April

1992, pp. 42-51; Larry Smarr and Charles E. Catlett, “Metacomputing,” Communications of the ACM, vol. 35, No. 6, June 1992, pp. 45-52;

Carolyn Duffy Marsan, “Gigabit Network at Siggraph Proves Need, Reveals Limits,” Federal Computer Week, vol. 6, No. 22, Aug. 3,1992,

p. 1.

expected to be operational until the third quarter original 3-year program. Because most of the

of 1993. After the initial planning stage, the

testbed work during 1990-92 was mainly devoted

to completing hardware development for the

switches and interfaces, theoretical and simulation work on protocols, and development of the

applications software and tools. The next step will

be to integrate these components into a working

network; this will occur in stages over the next

few months. As the networks become operational,

researchers will be able to begin addressing the

unresolved research questions.

Work on the testbeds has been proceeding

more slowly than expected. It had been hoped that

there would be about a year to experiment with

functioning networks before the end of the

networks were not yet operational, a 15-month

extension was granted in order to allow time to

look at network-level issues and test the networks

with applications. The delay has been due to the

late availability of the transmission equipment

and problems with the fabrication of switches and

other hardware components.

# Component Development

During the first 2 years of the testbed project,

the participants have been working mainly on the

completion of the individual network components. The SONET transmission equipment has

taken longer than expected to become available,

but is currently being tested and, in some cases,
58 I Advanced Network Technology

Figure 4-C-1 -CASA

Box 4-C--CASA

The CASA network connects four sites--the San

Diego Supercomputer Center, Los Alamos National

Laboratory, and the Jet Propulsion Laboratory and

Caltech in Pasadena (figure 4-C-1 ). The links between

the testbed sites are provided by MCI, Pacific Bell, and

US West. Also participating in the project is the UCLA

Atmospheric Sciences Department.

The main emphasis of the CASA project is on

applications development-using the network to combine the processing power of multiple supercomput- Los Alamos

National Laboratory

ers. The three main applications under investigation

are modeling of climate change, modeling of chemical

reactions, and interactive visualization of data describ San Diego

ing the Earth’s crust. These applications all require Supercomputer

Center more processing power than is available from a single

supercomputer. For example, the CASA climate SOURCE: office of Technology Assessment, 1993.

change model is limited to simulations of a decade or

less in the current computing environment One of the research issues concerns the partitioning of a computation

among multiple supercomputers. While in theory multiple computers can be combined in order to solve a problem

more quickly, the best way to allocate parts of the computation to different computers depends on a number of

factors. it maybe necessary, for example, to arrange the computation in such away as to hide the time it takes

for data to travel between the computers-even when traveling at speeds dose to the speed of light, data can take

a significant amount of time to travel from one computer to another. Efficient implementations would arrange the

computation so that the supercomputer would be able to proceed with other calculations while waiting for data to

arrive.

Efficient implementations may also be able to take advantage of the strengths and weaknesses of different

supercomputer architectures. For example, researchers have determined that the climate modeling application

can be split into a number of parts, each of which executes fastest on a particular kind of supercomputer. The part

of the simulation that models oceans could be executed on a massively parallel computer, while the atmosphere

would be modeled by a more conventional vector supercomputer. The two models would then exchange

temperature information and other data at regular intervals. The CASA network provides access to a wide variety

of supercomputer architectures, including different types of Cray Y-MPs, and massively parallel machines from

Thinking Machines and intel.

SOURCES: The CASA Gigabit Network Testbed, brochure; Charles E. Catlett, “In Search of Gigabit Applications,” IEEECornrnun/cat&rrs,

vol. 30, No. 4, April 1992, pp. 43-44; Elizabeth Smith, “NREN-Computer Expressway of the Future,” Gather/Scatter, p. 3.

installed in the carrier networks. While the to the equipment that vendors expect to be the

development of this equipment did not present bulk of early demand. In addition, some aspects

any research issues, its availability was subject to of the SONET standard have taken longer to

factors affecting vendor development schedules. complete than expected.

In part, these were hardware and software engi- The development of the switch prototypes had

neering issues. However, other factors have been underway when the testbed work began, but

played a role; for example, the SONET equipment in some cases the testbeds presented a more

is very expensive and it is “high end’ compared aggressive research target. The interfaces that
Chapter 4-Gigabit Research | 59

Box 4-D-NECTAR

The NECTAR network consists of a high-speed Iink that connects two local area networks, at Carnegie Mellon

University and the Pittsburgh Supercomputer Center. The fiber links are being supplied by Bell Atlantic, and

Bellcore and CMU are collaborating on the hardware design.

One area of research focuses on the interconnection of high-speed local and wide area networks. The

NECTAR local area networks conform to anew standard called HIPPI (High Performance Parallel Interface), while

the wide area connection between the two sites will use ATM cells over a SONET link. Research on this

configuration is important because HIPPI is expected to be widely used by the supercomputer community, and

the telephone companies are expected to deploy ATM- and SONET-based networks. A better understanding of

the interactions between the two kinds of networks is expected to support future distributed supercomputing

applications. As part of the research, a special interface circuit that converts between the HIPPI and ATM/SONET

formats is being developed.

Another area of research is the implications of new high-speed networks for computer design. Most of today’s

computers were not designed in such a way as to optimize the task of moving data to and from the network.

Applications may not be able to take advantage of improvements in the network bandwidth without improvements

in the internal hardware or systems software of the computer. The NECTAR researchers are investigating different

approaches to delivering data from the network to applications at high speed. Part of this effort has involved the

construction of special “interface” circuits that free the computer’s main processor of some of the protocol

processing tasks.

Software development for the applications has been proceeding in parallel with the development of the

hardware components. The applications have been tested in the local environment and it is hoped that the

applications can be made to work on the gigabit network with a minimum of modifications when it becomes

operational. The applications are distributed supercomputing applications that take advantage of the combined

power of multiple supercomputers to reduce the time needed to solve a problem, The NECTAR network will

connect a number of different computers, including the workstations, the experimental iWarp parallel computer,

and a variety of machines at PSC.

SOURCES: NECTAR annual report; H.T. Kung, “Gigabit Local Area Networks: A Systems Perspective,” IEEE Communications, vol. 30,

No. 4, April 1992, p. 79.

connect the computers to the network, or connect the other switches and interfaces should be

local and wide area networks, were designed

specifically for the testbeds. Delays in the development of these components are due to their

complexity and the demands of high-speed electronic design. A switch, for example, consists of

a number of subsystems, each with a large number

of standard and newly designed integrated circuits.5 At the end of 1992, the custom integrated

circuits had been designed, and most of the

subsystems tested. The PTM switch to be used in

the AURORA testbed has been completed, and

completed shortly.

To the extent possible, much of the work on

protocols has been proceeding in parallel with the

hardware development. This is expected to lead to

faster research results once the networks become

operational. Some of the work on protocols is

conceptual and theoretical, and is done by simulation or by mathematically modeling the flow of

data through a network. One of the main reasons

for building the testbed networks is to test the

assumptions that underlie these models and

5 For a description of the components of one prototype switch see Biersack et. al., ‘‘Gigabit Networking Research at Bellcore, ” IEEE

Communican’ens, vol. 6, No. 2, March 1992, p. 47.
60 | Advanced Network Technology

Box 4-E-VISTAnet

One of the VISTAnet objectives was to use emerging public network technology and standards wherever

possible. The switches and transmission equipment were supplied by the local telephone companies, Bell South

and GTE, and are early production models from major equipment vendors. In contrast to the other testbeds, the

switches are located not at one of the research sites but in telephone company central offices.

The VISTAnet network research involves Bell South, GTE, MCNC, North Carolina State University, and the

computer science department at UNC-Chapel Hill. As with the other testbeds, a number of interface circuits have

been developed. One of these boards also has the capability to collect data on traffic patterns, which will be used

to develop more accurate traffic models for network research. This technology has been licensed, and may soon

be available as a commercial product.

VISTAnet differs from the other testbeds in its focus on a single application. MCNC and UNC are collaborating

on the development of an application that uses a network of powerful computers to help doctors plan cancer

treatments. In radiation therapy, a number of treatment beams are used to deliver radiation to a tumor. Planning

the orientation and strength of these beams is essential, because of the need to deliver radiation precisely and

avoid the surrounding tissue. Planning involves calculating the distribution of radiation patterns forgiven beam

strengths and orientations.

One limitation of existing technology is that the treatment planning is typically done only in two

dimensions --doctors are only able to look at the distribution of radiation on a “slice” of the patient’s body. The

VISTAnet system, on the other hand, would be able to display data in three dimensions, giving doctors a much

better view of the distribution of radiation.

Another limitation of current technology is that the planning process is not “interactive.” Using today’s

technologies, interactivity is possible only at low resolution-generating a high-resolution image takes too long

and is done “off-line.” VISTAnet is developing a system in which doctors can immediately seethe effects of varying

a parameter such as beam strength, allowing doctors to examine a greater range of treatment plans.

The interactive display of 3-D images of radiation distribution is computationally intensive. VISTAnet is using

a high-bandwidth network to combine the processing power of a supercomputer, medical workstations, and a

PixelPlanes machine, a special graphics processor developed at the University of North Carolina. A user at the

workstation sends a description of the proposed beam strengths and orientation to a Cray supercomputer at

MCNC, which then calculates the corresponding distribution of radiation. Data resulting from this computation is

then sent to the PixelPlanes graphics processor at UNC-CH, which generates the image data that shows the

radiation distribution as a 3-D image superimposed on the patient’s body. The image data is then sent to the

workstation for display. Much of the software has been developed and tested on low-speed versions of the

VISTAnet network.

The VISTAnet application is a good example of the many different disciplines required to developadistributed

computing application. The medical component draws on expertise at the School of Medicine at UNC-CH. The

application also requires the development of a user interface that allows doctors to rotate the image or highlight

certain features. The graphics algorithms required to interactively generate 3-D volumes are themselves an

important research area

SOURCES: Dan Stevenson, ed., “VISTAnet Annual Report” April 1992; B.E. Basch et al., “VISTAnet: A BISDN Field Trial:" IEEE LTS,

vol. 2, No. 3, August 1991, pp. 22-30; M. Nisi Ransom and Dan R. Spears, “Applications of Public Gigabit Networks,” IEEE Network, vol.

6, No. 2, March 1992, p. 32; Daniel S. Stevenson and Julian G. Rosenman, “VISTAnet Gigabit Testbed,” IEEE Journal on Selected Areas

in Telecommunications, vol. 10, No. 9, December 1992, pp. 1423-1420.
Chapter 4-Gigabit Research 161

Box 4-F-MAGIC

The MAGIC testbed is similar in many respects to the five CNRI testbeds, in that a high-speed network is used

to provide access to supercomputing resources. As in the CNRI testbeds, there is considerable involvement of

industry, the Internet protocols will be used, and the telecommunications services will conform to emerging industry

standards like SONET and ATM. The application that will be used to test the network technology is of direct interest

to the Department of Defense.

The participants in MAGIC are the Earth Resources Observation Systems Data Center, U.S. Army

High-Performance Computing Research Center, the U.S. Army’s Future Battle Laboratory, U.S. Geological

Survey, Minnesota Supercomputer Center, SRI International, Lawrence Berkeley Laboratory, U.S. Department of

Energy, MITRE, Digital Equipment Corp., the University of Kansas, Sprint, Southwestern Bell, Northern Telecom,

and Split Rock Telecom.

The MAGIC network will connect four Figure 4-F-1 —MAGIC

sites, the University of Kansas in Lawrence,

Kansas, the U.S. Geological Survey in Sioux

Falls, South Dakota, the U.S. Army’s Future

Battle laboratory in Fort Leavenworth, Kansas,

and the Minnesota Supercomputer Center in

Minneapolis, Minnesota (figure 4-F-l). In the

first phase of the project, the sites will be

connected with point to point, 155 Mb/s or 622

Mb/s SONET circuits. In the second phase of

the project, the network will use an ATM switch.

The SONET and ATM services will be provided

by Sprint.

One of the research issues is the interconData Center High-Performance

Research Center

nection of different types of gigabit local area SOURCE: Office of Technology Assessment, 1993.

networks. Three different types of local area

networks will be connected through the ATM wide area network. As part of the research effort, new modules will

be built that convert from the local area network technology to ATM, and allow the interconnection of the different

networks.

The application will investigate remote visualization of data drawn from a number of different sources.

Information from a database at the U.S. Geological Survey will be sent through the network to a massively parallel

supercomputer at the Minnesota Supercomputer Center. The supercomputer will compute images based on t his

data, and send the image data through the network to the Future Battle Laboratory, where it will be displayed on

a workstation. The supercomputer provides the necessary processing power to select and view the images

interactively (see the discussion of the VISTAnet application in box 4-E).

The test application will allow the simulation of walking or flying through a representation of a landscape. The

Army believes “that field officers could benefit from this capability, and that the application could be used for

planning and educational activities. The landscape images are created from aerial images, satellite data, and

geographic elevation data. Researchers will also study user interfaces to this type of application.

SOURCES: Anita Taff, “Sprint to Provide Services for DARPA Research Net,” Network World, vol. 9, No. 27, July 6,1992, p. 9; Tim Wilson,

“Group Plots Gigabit Networking,” Communications Week International, July 6, 1992, p. 35.
62 I Advanced Network Technology

simulations. The protocol research also involves

evaluating the behavior of existing networks like

the Internet and writing software that will be used

to program the switches, computers, and interfaces.

Work on the distributed supercomputing applications has also been proceeding in parallel with

the hardware development. Much of the software

development for the applications has been completed. In many cases, it has been possible to test

these applications to a limited extent using

existing high-speed local area networks or lowspeed wide area networks like the Internet. Before

writing the software, extensive analysis was done

of the required computations, to determine how

best to divide up the computations among the

multiple computers that make up the overall

system. Other important software development

has involved the development of user interfaces

and software tools that would make it easier to

program distributed computing applications.

1 Systems Integration

The next objective of the testbed project will be

to combine the network components into an

operational network. This will begin once the

transmission equipment is in place and work on

the switches and other hardware has been completed. The systems integration task will proceed

in stages, beginning with the simplest network

possible, to minimize the number of sources of

possible problems. VISTAnet began the integration process in the fall of 1992; the other testbeds

should be in position to start this work by the third

quarter of 1993. Over time, the networks will be

expanded into more complex configurations.

The issues addressed in the early part of the

systems integration phase are the low-level details of making sure that components designed by

different groups work together or that a signal

arrives in the format expected by a component’s

designer. These are the kinds of problems that are

difficult to find when components are tested

individually. For example, when the NSFNET

backbone was upgraded from T1 to T3 links

during 1990-92, the technical staff of the

NSFNET backbone provider found that some

components did not behave as expected under

certain conditions, or unexpected traffic patterns

required changes to the software and hardware.6

Similar problems will probably be encountered as

the testbeds begin to work through this stage with

prototype or newly developed network components.

1 Network Research

One research issue concerns the algorithms

used to control fast packet networks. These

mechanisms are used to enable fast packet networks to support many different kinds of services

using the same links and switches; one of the

weaknesses of traditional packet networks was

that they could not guarantee the kind of performance required for real-time applications such as

video. In a fast packet network, software in the

users’ computers and in the switches will have to

cooperate in managing the flow of traffic through

the network in a way that supports all kinds of

services. There have been many different mechanisms proposed for accomplishing this objective,

but it is regarded as the most difficult problem

with fast packet networks. The testbeds will

provide an opportunity to test different control

algorithms.

Another research issue is related to the development of distributed supercomputing applications. In these applications a computation is

divided among multiple supercomputers; the

network is then used to exchange data as the

computation proceeds. Deciding how to allocate

different parts of the computation to different

supercomputers is a difficult problem. The best

strategy depends in part on the characteristics of

the network and the strengths and weaknesses of

6 + (T3 up-s ~ ~S Ne~ork NW Completion’ ANS Updute, VO1. 1, No. 1, 1991, P. 1.
. .

Chapter 4-Gigabit Research | 63

different computers connected to the network— computer. In order to maximize processing power,

for example, some parts of a computation maybe computers shouId not be idle while they are

executed fastest on a massively parallel com- waiting for one of the other computers to finish its

puter, while other parts may run faster on a vector task or for data to be sent through the network.
Application of

Testbed

Research 5

T

he networking component of the High Performance

Computing and Communications (HPCC) Program funds

both research on gigabit technology and the deployment

of this technology in the National Research and Education Network (NREN). One of the NREN’s roles is to provide

additional experience with advanced network technologies

before they are deployed more widely in the national information

infrastructure. However, the testbed research will also be applied

directly to other networks, such as the common carriers’ public

switched network, without intermediate deployment in the

NREN.

APPLICATION TO THE NREN

There is no overall NREN development plan; however, the

National Science Foundation (NSF) is to coordinate the evolution of the Federal agency networks that are the core of the

NREN.l During 1992, NSF, the Department of Energy (DOE),

and the National Aeronautics and Space Administration (NASA)

announced plans for the future development of their networks.2

Based on these plans, the next-generation agency networks will The testbed likely be similar to the testbed networks, with an emphasis on

Synchronous Optical Network (SONET) fiberoptic transmission research can be

and fast packet switching. These broadband technologies are

applied to

1 Hlce of Science and llxhnology Policy, ‘‘Grand Challenges 1993: High

Performanw Computing and Communications,” p. 33. networks other 2 NatiO~ Science Foundation, “Public Draft: Network Access Point Manager/

Routing Authority and Very High Speed Backbone Network Services provider for

NSFNET and the NREN Program,” than the NREN.

June 12, 1992; James F. Leighto~ Manager of

Networking and Engineering, National Energy Research Supercomputer Center, Lawrence Livermore National Laboratory, “ESnet Fast-Packet Services Requirements

Specification Document, ” Feb. 20, 1992.

65
66 I Advanced Network Technology

being studied in a large number of research

programs, but the testbed research is unique in its

emphasis on building wide area gigabit networks

and testing them with applications.

1 Agency Plans

The Federal agencies will not build their own

‘‘private’ networks, but will obtain services from

a network service provider. In effect, NSF, DOE,

and NASA will act as early, large customers for

advanced services. While industry has developed

the switches and transmission equipment required

for advanced network services, the agency backbones will be one of the first opportunities to

integrate these components into a system that

provides services to real users. Users of the

agency backbones are knowledgeable about networking and will assist in integrating new network services with computers and applications to

create useful systems.

The agency backbone services could be provided by a number of different organizations—

the carriers, computer companies, or some of the

emerging providers of commercial Internet services-or consortia. Provision of services for

agency backbone networks provides valuable

experience that the network operator may be able

to translate into earlier availability of advanced

services on a commercial basis.3 For prospective

players, the decision to participate in the provision of services to the agency networks weighs

the experience gained and long-term strategic

considerations against the cost of providing the

service, which is greater than the money available

from the Federal agencies.

To help stimulate market interest, DOE and

NASA had originally decided to combine their

NREN-related programs. A single supplier would

have provided network services to both agencies,

connecting sites such as DOE’s Los Alamos

National Laboratory or NASA’s Ames Research

Center. However, the General Accounting Office

(GAO) overturned DOE’s choice of contractor in

March, 1993 (see ch. 1, p. 7). The steps that the

agencies will take in response to this decision

were still unclear at the time of publication, but it

is possible that DOE and NASA will now decide

to proceed separately. The procurement process

has been significantly delayed, and will likely not

be completed before the fourth quarter of 1993.

Before the GAO decision, NASA and DOE had

planned to begin connecting sites to the new

network in mid-1993.

NSF issued a draft solicitation for its nextgeneration network in mid-1992. NSF plans to

publish a final version of the solicitation and

award a cooperative agreement during 1993. The

new network is scheduled to begin operation in

mid-1994. NSF’s plans for the evolution of its

network have greater implication for the evolution of the NREN and the Internet than do those

of DOE and NASA. The current NSFNET backbone carries much more traffic than the other

agency backbones 4 and serves a broader range of

users. However, many of those users will not be

able to use the next-generation backbone.

The new NSF network’s Primary purpose will

be to connect the NSF supercomputer centers,

enabling advanced distributed supercomputing

applications. By contrast, today’s NSFNET backbone is a‘ ‘general-purpose’ network that carries

all types of research and education traffic. NSF

envisions that in the future routine research and

education traffic will be handled by commercial

providers, not by the agency-operated backbone.

There are a number of emerging commercial

providers, and the network technology required to

support routine traffic is sufficiently stable and

reliable. This strategy would also free capacity on

the backbone for experimental applications.

The transition to the new environment resulting from the changed role of the NSFNET

3 h H. Linfitrom, “Sprint Blasts Ahead With ATM Deployment, “ Telephony, vol. 223, No. 8, Aug. 24, 1992.

4 Stephen S. Wolff, Director, Division of Networking and Communications Researeh and Infrastructure, National Scienee Foundation

testimony at hearings before the House Subcommittee on Science, Mar. 12, 1992, Serial No. 120, p. 155.
Chapter 5-Application of Testbed Research | 67

backbone will require careful management to

ensure stability. NSF’s plan will affect significantly the existing three-level hierarchy of the

NSFNET. The regional networks were designed

to provide connections to sites on the current

backbone, which in turn provides inter-regional

connectivity. Under NSF’s new plan, the backbone will serve many fewer sites and will no

longer play the same central role in research and

education networking. The regional networks

will have to make new arrangements for interconnections and will be operating in a more competitive environment.

1 Agency Backbone Technology

The collaborative nature of the testbeds makes

it more likely that the network technologies

developed by industry will be suitable for operation in the agency backbone environment. The

testbeds are emphasizing the technologies’ use

with the Internet protocols used by the agency

networks, and are studying the interaction between fast packet networks and supercomputer

network standards and applications. In addition,

they emphasize the gigabit bandwidths required

to support the Grand Challenge applications that

are a key component of the overall HPCC

program. The involvement of the carriers in the

research program may also lead the carriers

toward a more active role in providing NREN

services.

While the plans for the evolution of the agency

backbones are consistent with the target established by the testbeds, the agency networks will

initially operate at lower bandwidths than the

testbeds. The agency backbones will incorporate

more of the technology from the testbed research

as they evolve over time to meet the goal of the

gigabit NREN. However, some issues cannot be

addressed by the testbeds, or may be discovered

only as the agency networks are deployed. Many

of these issues are related to the more complex

topologies (greater number of sites), larger number of users, and more diverse sources of traffic

that will be present on the production networks.

TRANSMISSION TECHNOLOGY

The agencies envision the use of SONET

equipment similar to that used in the testbeds, and

have indicated that they hope to use 155 Mb/s

SONET equipment in 1994 and then upgrade over

time to 622 Mb/s (the next transmission rate in the

SONET family) by 1996, the High Performance

Computing Act’s target year for the use of gigabit

links. The 622 Mb/s rate, less than a full gigabit

per second, is sometimes referredtoasa‘‘goverment gigabit."5

The rate at which the agency backbones will

evolve depends on the timely deployment of a

high-bandwidth SONET transmission infrastructure by the carriers. While much of the carriers’

existing network uses fiber, SONET transmission

equipment is required in order to support computer networking above the current T3 rates-it

allows the fiber to be configured to carry high

bandwidth channels. However, this equipment is

extremely costly at this time and the carriers’

deployment schedules have been slipping from

earlier estimates.

The testbed networks will have also provided

experience with the connection of supercomputers to high speed networks. ‘‘High end” users

will require fiber links connecting their sites to

the NREN. Only fiber is able to carry the large

amounts of data needed for supercomputer-based

applications. The testbeds are one of the first

large-scale deployments of SONET to end-users,

and considerable work has been done on interface

devices to connect supercomputers and highspeed local area networks to fast packet switched

networks. However, widespread use of highspeed networks will depend in part on the degree

to which computer companies design their workstations to be fully integrated into a high-speed

network. Today, bottlenecks encountered in mov5 Carpenter et al., “Where Are We With Gigabits?” IEEE Network, vol. 6, No, 2, March 1992, p. 10.
68 I Advanced Network Technology

ing data from the network into the computer’s

memory, where it can be used by the applications

software, can limit the performance of the overall

system.

SWITCHES

The next-generation backbone networks will

use fast packet switching technology similar to

that used in the testbeds. Initially, the switches

will not be as sophisticated, because of the lower

link bandwidths. The network operator’s choice

of switching technology, from among those being

investigated in the testbeds and elsewhere, depends in part on long-term strategic considerations. If a carrier were to provide services for an

agency network, it would probably use Asynchronous Transfer Mode (ATM) switches. ATM has

been chosen as the foundation for the future

development of carrier networks, and the provision of services for the agency backbone would

provide an opportunity to gain experience with its

use. Other providers might also choose to use

ATM switches, or strategic considerations may

lead to the choice of an alternate switching

technology.

The DOE Reqest for Proposals issued in early

1992 specified the use of fast packet “cell relay’

technology. “Cell relay” is a term used to

describe both ATM and Switched Multimegabit

Data Service (SMDS), a data communications

service developed by the telephone companies. In

the summer of 1992, DOE and NASA selected a

contractor that proposed to use ATM. This

DOE/NASA program would have been the frost

large-scale deployment of ATM. One of the goals

of DOE and NASA is to encourage the development of commercial services by evaluating and

demonstrating emerging technologies such as

ATM. The agencies’ effectiveness in performing

this function may be reduced by any further

delays resulting from GAO’s decision overturning their choice of contractor.

The National Science Foundation’s draft solicitation describing the evolution of its backbone

network did not specify a particular type of

switch. 6 NSF will allow prospective bidders to

propose their choice of switching technology.

The most likely option that would be proposed

would be an ATM-based approach. Another type

of fast packet technology, such as the PTM

approach developed by one of the participants in

the Aurora testbed, might also be used. The

approach of ‘overlaying’ an Internet network on

a network that uses fast packet technology is not

unique to ATM. However, ATM has broad

support from industry standards committees.

OTHER NREN NETWORKS

The regional networks and other commercial

providers of Internet services may also carry

NREN traffic. Operators of these networks are

faced with the same technology choices as those

for the backbone networks. However, because

many of these networks will require lower bandwidths than the backbones, they may continue to

use ‘‘router-based” networks or use new “prebroadband” services being offered by the carriers

and other service providers. Two examples of

these pre-broadband services are Frame Relay

and SMDS.7 These are packet switching services

that can also be used to carry Internet traffic (see

ch. 2, p. 34). Because the Internet protocols are

able to hide differences in network technology

from the users of the network, the NREN’s

networks can be based on a variety of different

technologies.

Campus networks and other networks based

primarily on local area networks will also become

more capable. Local area network research is not

currently a focus of the testbeds, although the

interconnection of local and wide area networks

6 N~ti~~ science F~~&tion, ‘cRqest for public Commmt: sohci~tion Concwt NSNT Backbone Network Services, ” June 12,

1992.

7 ‘Wry Sweeney, “TCP/IP-SMDS Trial Completed, ” CommunicationsWeek, Aug. 17, 1992, p. 25.
—--—

is being studied. One of the most important trends

in local area network design is that there is a

growing amount of support for ATM-based local

area networks and products for ATM local area

networks are beginning to appear. Other kinds of

high-bandwidth local area network standards are

also being studied by standards committees.

1 Applications

Because of the emphasis on gigabit applications, the testbed applications research is primarily applicable to high-end users of the NREN. The

testbeds have been one of a small number of

research programs to address supercomputerrelated networking issues. These applications are,

in general, of little concern to industry and would

receive less attention without the testbeds. The

testbeds’ gigabit applications research will have

important impacts on the overall HPCC initiative.

Distributed supercomputing maybe an important

tool for bringing more processing power to bear

on the Grand Challenge problems. In addition, the

Grand Challenge teams will be scattered about the

country and could use networks to support

collaboration. The sizes of the data sets used in

Grand Challenge problems will be very large,

requiring high-bandwidth networks to move them

from place to place within a reasonable period of

time.

High-speed network support of supercomputing is important to the missions of the NSF

supercomputer centers and the Federal laboratories. Ied by testbed participants, the NSF supercomputer centers have proposed a concept that

would make use of the distributed supercomputing ideas investigated by the testbeds.8 They

envision a ‘‘metacenter’ ‘—the use of the new

high-speed backbone to integrate the computational and intellectual resources of the supercomputer centers.9 In effect, it would be possible for

the four supercomputer centers to act as a single

Chapter 5-Application of Testbed Research 169

center, distributing a computation among several

machines as the computation required.

High-end users of the agency backbones are

only part of the user community addressed by the

NREN program. Few users will have access to a

full gigabit/second of bandwidth, and the supercomputer applications studied by the testbeds are

by definition highly specialized. For most users

the primary result of improving network capability will be better performance with existing

applications and the wider use of video and

image-based communications. Because these capabilities may have considerable significance in

commercial applications, much work is being

done on these types of applications by industry.

Some types of applications development, however, may require added support. Legislation

introduced in the 103rd Congress (S.4 and H.R.

1757) seeks to expand support for applications

development in a variety of education, medicine

manufacturing, and library settings.

I Internetworking

The NREN is closely linked to the evolution of

the Internet protocols that enable the thousands of

independently operated networks that make up

the Internet to exchange traffic. The testbeds are

providing an opportunity to investigate the use of

the Internet protocols in fast packet switched

networks. The collaborative nature of the testbed

program may be encouraging the Internet community to influence the ATM standards process to

better support Internet protocols. In addition, the

testbeds are investigating the behavior of the

Internet protocols at high speeds, and comparing

them to some new concepts in protocol design. In

the past few years, a number of protocols have

been proposed that may perform better in highspeed networks and are better suited to the new

fiber-based, fast packet switched networks. For

example, today’s Internet protocols are designed

8 John Markoff, “A Crucial Linkup in the US Data Highway,” New York Times, Sept. 30, 1992, p. D8.

g Carolyn Duffy Marsoq “NSF Pursues Computing Without Walls,’ Federal Computer Week, vol. 6, No. 35, NOV. 30, 1992, p. 1.
70 | Advanced Network Technology

Figure 5-l-Growth In NSFNET Networks

Number of foreign, regional, state and local networks

December 1992

9,000

P

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

Total Networks: 8,561 /

01--- , r r , I , r , , , r

Dec. ’90 Dec. ’91 Dec. ‘92

SOURCE: Merit, Inc., 1992.

to handle the types of transmission errors that

occur with poor-quality copper lines, but rarely

occur with new fiber-based transmission systems.

Other issues related to the evolution of the

Internet protocols are not being studied by the

testbeds. The main issue confronting the Internet

community today is the growing size and complexity of the network—not increases in bandwidth. The growth in the number of users and

networks that make up the Internet is putting

pressure on current ‘‘routing” technology (figure

5-l). Routing is the process by which a path from

one computer to another through a series of

intermediate networks is determined. Calculating

these paths using current algorithms demands a

considerable amount of processing power; the

problem is getting worse as the Internet continues

to grow and become more complex. Routing

issues have not been studied by the testbeds,

which only connect a few sites.

Work on issues related to managing the growth

of the Internet is being done primarily within the

Internet community’s technical organizations,

such as the Internet Activities Board (IAB) and

the Internet Engineering Task Force (IETF). The

IETF consists of a number of working groups, one

of which addresses routing issues. Currently,

within the technical community there are many

different proposals; some only address immediate

problems, while others attempt to solve the

problems in a way that will be satisfactory for a

number of years. Besides addressing issues related to growth, some of the new routing algorithms may also take into account the growing

diversity of service providers and network capabilities. Routing and management problems associated with the growing Internet are a major

research area that requires more study .10

NSF’s plan for the evolution of its network as

part of the NREN program is linked closely to

changes in routing technology. Today, the

NSFNET backbone operator plays an especially

important role in determining routes for research

and education networks. As the Internet becomes

more commercialized, however, it becomes less

appropriate for NSF to be responsible for this

aspect of its operation. NSF envisions reducing

the reliance of Internet networks on the NSFNET

backbone’s operator for routing information.ll

NSF has proposed that the routing function be

handled by a separate organization, the “routing

authority,’ not by the operator of NSF’s network.

NSF’s plan also calls for the creation of a number

of Network Attachment Points (NAPs), where

commercial networks and agency networks could

obtain routing information and interconnect with

each other (see box 5-A).

APPLICATION TO OTHER NETWORKS

The testbed program will also impact the

evolution of the national information infrastructure more directly, without the intermediate stage

of deployment in the NREN. This national

information infrastructure includes the larger

U.S. Internet-the NREN program targets only

one part of the U.S. segment of the Internet (see

10 ARPA is supporting research in these areas, such as through its DA.R’I’net IX’Ogr1 I Row mm et al., NatiO~ stien~ Foundatio~ ‘‘NSF Implementation Plan for Interagency bterim m,” MIIy 1992.
Chapter 5-Application of Testbed Research | 71

figure 5-2).12 It also includes a wide array of other

services and technologies to be offered by the

carriers, cable television companies, computer

hardware and software companies, information

service providers and others.

1 Application to the Internet

The Internet is increasingly expanding to serve

communities other than the core research and

education community that is the focus of the

NR.EN program. The regional networks and new

commercial providers now carry business traffic.

The trends towards broader use of the Internet and

growing numbers of users seem likely to continue. These will be driven in part by the advances

in switching and transmission technology described in chapter 3. They depend to a greater

extent on addressing the security concerns of

commercial customers, the degree that use of

Internet applications can be simplified, and the

deployment of advanced digital local loop technologies.

It is possible that the switches and fiber optic

links deployed by providers of agency backbone

services will also carry commercial traffic. Some

of the capacity would be used for the agency

backbone network and some would be used to

provide services to commercial customers. The

Federal agency backbone would be the network’s

most important customer, acting as a catalyst for

the deployment of the required switches and

transmission equipment, while commercial customers would help to recover that portion of the

costs of operating the network not covered by the

Federal agencies’ funding.

D Other Services

The network technology studied by the

testbeds is equally applicable to services other

than Internet services. The research will also be

Figure 5-2—Relationship Between NREN,

Internet, and National Information Infrastructure

National

information

infrastructure

SOURCE: Office of Technology Assessment, 1993.

applied directly to private networks, the common

carriers’ public switched network, and possibly

cable television networks.13 This is because the

network technology used in the testbeds reflects

near-term industry planning. While the testbeds

have emphasized higher bandwidths and more

specialized applications than have immediate

commercial importance, the basic design of the

testbed networks-such as the use of fast packet

switching and SONET-reflects ideas that figure

prominently in industry plans.

The carriers and other network operators could

use the new advanced technologies to provide

Internet services, or an array of other voice, video,

and data communications services. Switch and

transmission technologies, though advancing at

different rates, are making substantial progress.

Because of their commercial importance, fast

packet and fiber optic technologies are being

12 For a disc~sion of the relationship of the Internet to the NREN, s= c~ptm 2, p. 31.

13 For ~ de~ption of ~ ~le ~ovid~’s pl~ to we~~Wckd Kqj~@ ‘ ‘Time w~m to LECS: Here we Come, ’ Te/ephony,

vol. 224, No. 5, Feb. 1, 1993, p. 8. IBM is testing its plaNET (PTM) fast packet switch in a cable network in Toronto, CaM&. See ‘ ‘IBM’s

1.2 Gigabit/sec. Networking Scheme, ” Cab[e-Telco Report, August 1992, p. 9.
72 | Advanced Network Technology

Box 5-A-NSFNET Backbone Recompetition

The National Science Foundation’s plans for the future development of its backbone network have attracted

considerable scrutiny. The NSFNET backbone plays an especially important role in the Internet and in the National

Research and Education Network program. Currently, NSF has a cooperative agreement with Merit Network, a

not-for-profit organization of nine Michigan universities. However, Merit does not operate the NSFNET backbone

“in-house.” A second organization, Advanced Network& Services (ANS), operates the network-Merit obtains

the services for the NSFNET backbone from ANS.

The cooperative agreement with Merit for the NSFNET backbone was announced in November 1987, and

covered the 5-year period to November of 1992. Merit’s proposal was submitted in partnership with IBM and MCI.

The relationship between Merit and its partners changed in September of 1990, when Merit, IBM, and MCI

announced the formation of ANS, as a not-for-profit corporation. ANS received capital from MCI and IBM at its

formation, and IBM and MCI provide switches, transmission capacity, and other services to ANS. Overtime, more

of the responsibilities for the NSFNET backbone have been shifted from Merit to its subcontractor, ANS.

Over the life of the 5-year cooperative agreement with Merit, there have been three important changes in the

Internet First, Merit and ANS have Increased the NSFNET backbone’s link bandwidth from 56 kb/s, to 1.5 Mb/s

(T1), to 45 Mb/s (T3). Second, the Internet has become a much more important part of the U.S. information

infrastructure--the amount of traffic and the number of users has grown rapidly. Finally, the past 2 years have seen

the emergence of commercial Internet service providers. In particular, ANS has created a for-profit subsidiary.

While the T1 network was used only by NSFNET backbone traffic, the T3 network operated by ANS is shared by

the NSFNET backbone and ANS’s commercial customers.

The relationship between NSF, Merit, ANS, and other commercial providers was the subject of hearings

before the House Subcommittee on Science in March of 1992. Concern was expressed by some witnesses that

the current arrangement benefited ANS unduly, and had not been foreseen by the 1987 cooperative agreement

with Merit. Other witnesses pointed to the success of the NSFNET backbone, the growth in the number of users,

and the value of the equipment and services contributed by Merit and its partners.

Recompetition

In preparation for the expiration of the cooperative agreement with Merit in November of 1992, NSF studied

a number of options for the future development of the NSFNET backbone. In studying these options, NSF had

to take into account several factors that did not apply in 1987. One factor was the emergence of commercial

providers. Any new plan for the backbone could not favor the incumbent, ANS, and would have to provide equal

opportunity for all firms wishing to provide services to the NSFNET backbone. A second factor was the need for

stability. The Internet is now an essential infrastructure for many more users than in 1987, and stability would have

to be ensured during the transition to any new arrangement. Finally, NSF had to take into account the NSFNET

backbone’s central role in the NREN program.

One option studied by NSF was to discontinue direct funding o fa backbone network. Instead, NSF could fund

the regional networks and allow them to choose among commercial providers of interconnections, encouraging

further development of the commercial networks. According to testimony of the director of the NSF division

responsible for NSFNET, this plan was opposed by the regional networks and by other Federal agencies, in part

because of concerns about stability during the transition to this environment.

As a result, NSF decided that it would continue to operate a backbone network. NSF’s timetable called for

extending the arrangement with ANS for up to 18 months beyond November 1992, to the middle of 1994. This

eighteen month period was intended to allow time to 1) select the provider of the next-generation NSFNET

backbone, and 2) install the required links and switches. Originally, NSF planned to make the awards in the middle

of 1993, allowing a year for the transition to the new network,
Chapter 5-Application of Testbed Research | 73

The NSFNET Solicitation Concept

The Project Development Plan for the continued provision of NSFNHET backbone services after the expiration

of the agreement with Merit was published by NSF in November of 1991. This development plan stated the

requirements for stability, fair competition, and support of NREN objectives. The Development Plan also presented

the concept of splitting the current NSFNET backbone provider’s tasks into two parts, and awarding each part to

separate organizations.

NSF published a more detailed version of this plan in June of 1992 and requested public comments.

According to the plan, one of the two awards would be for the provision of very high speed Backbone Network

Services (vBNS). The vBNS provider would operate the i inks and switches and be responsible for moving packets

through the NSFNET backbone. Among other requirements, the vBNS provider would establish a network that

would operate at 155 Mbps or higher and would “provide for real-time multimedia services, including multicasting

and video teleconferencing.” NSF did not specify a switching or transmission technology; however, the reference

to 155 Mbps implies the use of SONET transmission equipment

The second award would be for the Routing Authority (RA). The routing authority would be responsible for

the routing functions that had previously been performed by the backbone operator. The RA would also operate

Network Access Points (NAPs), which would facilitate the connection of other networks to the vBNS and to each

other. These could be other Federal networks, or commercial networks. The routing information required in order

to facilitate the coordination of these networks would be stored in a database accessible at the NAPs. A total of

about $10 million annually would be available for the two awards.

Changes to the Draft Solicitation

The public comments received by NSF in response to the draft proposal reflect the degree to which NSF's

plans affect more than just the NSFNET backbone. NSF's proposed NAP/RA structure could best be characterized

as an “architecture” for the NREN and the internet, with significant implications for the larger information

infrastructure. As such, the NSFS plans affected users, interexchange and local exchange carriers, regional

networks and other current and prospective providers of Internet services, and other federally supported networks.

As of May, 1993, a revised version of the NSF solicitation had not been released. However, in December

1992, NSF outlined its intention to change its original plan in a number of ways. While the basic vBNS/NAP/RA

structure was maintained, NSF indicated that it would make three awards, not two. The NAPs would not have to

be operated by the Routing Authority, as had been specified in the draft solicitation, but could be operated by a

separate organization.

More importantly, NSF announced that the new backbone would be used primarily to connect the NSF

supercomputer centers. The draft solicitation had indicated t hat the new network would continue to be a “general

purpose” backbone, serving a large number of sites and carrying both routine and high-end traffic. By Iimiting the

scope of the backbone, NSF’s new approach would require more routine services to be obtained from commercial

providers.

SOURCES: Robert Aikan et al., “NSF Implementation Plan for Interagency Interim NREN,” May 1992; National Science Foundation,

“Project Development Plan: Continuation and Enhancement of NSFNET Backbone Services,” November 1991; National Science

Foundation, “Network Access Point Manager/Routing Authority and Very High Speed Backbone Network Services Provider for NSFNET

and the NREN Program: Program Solicitation,” June 1992; Ellen Hoffman, “NSFNET Backbone Service Restructured,” Link Letter, vol.

5, No. 3, November 1992, p. 1; Douglas E. van Houweling, Merit Network Inc., testimony at hearings before the House Subcommittee on

Science, Mar. 12,1992, pp. 36-41; Stephen S. Wolff, Assistant Director, Directorate for Computer and Information Science and Englneerlng,

National Science Foundation, testimony at headings before the House Subcommittee on Science, Mar. 12,1992, pp. 133-136, pp. 148-156;

William L. Schrader, President and CEO, Performance Systems International, Inc., testimony at hearings before the House Subcommittee

on Science, Mar. 12, 1992, pp. 87-98; Ellen Messmer, “NSF Changes Course On Its Internet Plan,” Network World, vol. 9, No. 51, Dec.

21, 1992, p. 1; Office of Inspector General, National Science Foundation, “Review of NSFNET,” Mar. 23, 1993.
74 | Advanced Network Technology

studied by a large number of research programs in

addition to the testbeds. The issues affecting the

deployment of these technologies in commercial

settings are mainly concerned with trading the

costs associated with the existing infrastructure

against the potential of future markets for the new

technologies. Regulatory and economic factors

affecting the pace of deployment are beyond the

scope of this background paper.

The involvement of the carriers in the testbeds

was an important result of the visibility afforded

by the HPCC program and the Corporation for

National Research Initiatives’ organization. All

three major interexchange carriers and most of the

Regional Bell Operating Companies are involved.

The focus on ATM-related issues serves to

provide experience with the construction of these

networks and demonstrate their feasibility on a

significant scale. Despite the carriers’ stated

commitment to ATM, the degree to which the

transition to ATM represents a true paradigm shift

for the telecommunications industry should not

be underestimated. The testbeds will have served

to help advance the carriers beyond the stage of

standards-setting, component development, and

small-scale experiments. There are many who

believe that a nationwide gigabit network is not

possible without basing it on the ongoing investments of the carriers.14

The testbeds may also be helping to provide

input to the ATM standards process. Currently,

there is some concern in the telecommunications

industry that elements of ATM are being standardized before there is sufficient understanding of

the tradeoffs. In particular, there is uncertainty

about the best way to control the traffic in ATM

networks, a key component in the use of ATM to

support integrated services. The testbeds will

provide experience with real traffic, due to the

involvement of applications researchers. The

academic researchers are also contributing to the

solution of these problems; while algorithms for

the control of packet networks area longstanding

topic of theoretical research, the testbeds may

serve to focus the work of academic researchers

on topics of concern to industry to a greater

extent.

14 Vkton G. Cefi, “~o~a Rea&g of tie_hgislatio~” TeZecommuru”cations, VO1. 25, No. 11, November 1991, p. 29.
Index

A

Access link Internet, 29

Advanced Research Projects Agency

administration of testbeds, 8, 55

Arpanet development, 6

Internet, 15

Algorithm, fast packet network, 62

American National Standards Institute, 34

Analog network, digital network, contrasted, 2-3

ANSI. See American National Standards Institute

Application, defined, 21

Arpanet, Internet evolution from, 6

Asymmetric Digital Subscriber Line, 47

Asynchronous Transfer Mode (ATM) switching technology, 13, 43-46, 49

future applications, 68-69,74

ATM. See Asynchronous Transfer Mode (ATM)

AT&T, contribution to testbed research, 11

AURORA network, 54,59

B

‘‘Backbone network”

Federal agency future direction, 67-70,72

Internet, 15-17

Bandwidth

of agency networks, used presently, 12

defined, 3

link, multiplexing, 28

requirement, broadband network technology, 39,41

shortage of, Internet, 22

BARRNET, 17

Bay Area Regional Research Network. See

BARRNET

Bit, defined, 2

BLANCA network, 56

Broadband Integrated Services Digital Network

(B-ISDN), 46,56-57

Broadband network technology, 35-49

Asymmetric Digital Subscriber Line, 47

Asynchronous Transfer Mode (ATM) switching

technology, 4346,49

bandwidth requirement, 39,41

classroom utilization, 36-37

component development, 44-47

compression technology, 41

computer development, 46-47

distributed computing, 37-39

flexibility of, 41-42

High-bit-rate Digital Subscriber Line, 47

high-definition television signal, 41

Integrated Services Digital Network, 47-48

interactive visualization, 36, 38

Internet application, 47-49

multimedia applications, 36-37

National Research and Education Network research,

objective of, 6

network requirements, and applications, 39-42

optical fiber, 45-46

overview of, 2-5

public network, 49

simulation, 36-39

switch development, 46

video, 36-38

Bulletin board, Internet, 21
76 | Advanced Network Technology

c

Cable television network testbed research technology

application to, 71, 74

Campus network, and Internet, 17

CASA network, 58

Circuit switch, 6,29,32

Classroom, broadband network technology utilization,

36-38

Climate change, and network research, 1

Coaxial cable, computer link, 5

Color representation, bit patterning, 2

Commercial availability, of broadband network transmission equipment, 10

Commercial provider, Internet service, 19

Commercialism, of National Research and Education

Network, 7

Compression technology, broadband network technology, 41

Computer network. See Network

Contractor, for National Research and Education

Network, 7-8

Copper link computer network, 5

Corporate network, Internet, 17

Corporation for National Research Initiatives, 8

Cost, network research component, of High Performance Computing and Communications program,

1-2

D

DARTnet, Internet, 15-16

Data, pattern of electronic signal, 2

Delay, in testbed operation, 10

Department of Energy. See U.S. Department of Energy

Digital computer, signal, 2

Digital network

analog network, contrasted, 2-3

defined, 2

Distributed computing

broadband network technology, 37-39

Internet, 22

Distributed supercomputer, 38,40,6243

DOE. See U.S. Department of Energy

E

E-mail, Internet, 21

Electronic mail. See E-mail

Electronic signal, digital computer, 2

ESnet, Internet, 15-16

Exchange Carriers Standards Association, 34

F

Fast packet switching, 42-45

algorithm, 62

Asynchronous Transfer Mode (ATM) switching

technology, 4346

for broadband network, 10

Packet Transfer Mode (PTM), 43-44

Federal Internet Exchange (FIX), Internet, 17

Fiber optic link, 5

transmission standards, Synchronous Optical Network, 28-29

File Transfer Protocol, Internet, 21

Frame Relay, 34

FIP. See File Transfer Protocol

Funding, testbed

under Corporation for National Research Initiatives

agreement, 8

overview, 11

G

General Accounting Office, protest to, by National

Research and Education Network contract bidder, 7-8

Gigabit research

AURORA, 54,59

BLANCA, 56-57

Broadband Integrated Services Digital Network

(B-ISDN), 56-57

CASA, 58

MAGIC, 61

network

fiber optic link, 5

overview, 4

technology, progress of, 8, 10

objectives of, 52-56

standard, High Performance Parallel Interface, 53

supercomputing research, 62-63

Synchronous Optical Network (SONET), 65,67

testbed design, 53-55

testbed progress in, 56-63

VISTAnet, 60,62

Government funding, of testbeds, 11

“Grand Challenges’ network research and, 1
H

High-bit-rate Digital Subscriber Line, broadband network technology, 47

High-definition television signal, compression technology, 41

High-Performance Computing Act of 1991, legislative

purpose, 1

High Performance Computing and Communications

program, network research component

gigabit network technology research, 51-63

overview of, 1-13

High Performance Computing and High Speed Networking Applications Act of 1993, 21

High Performance Parallel Interface, gigabit-persecond standard, 53

HIPPI. See High Performance Parallel Interface

I

Image, bit patterning, 2

Industry investment, in testbeds, 11

Information handling, by computer network, overview, 2

Information pattern, voltage, 2

Integrated Services Digital Network broadband network technology application, 47-48

Interactive visualization, broadband network technology, 36, 38

Interagency Interim National Research and Education

Network 20

Interface, with Internet, 22

International Telecommunications Union, standards,

establishment of, 34

International Telegraph and Telephone Consultative

Committee, standards, establishment of, 34

Internet, 15-34

access link, 29

Advanced Research Projects Agency, 15

applications, 21-24

“backbone” networks, 15-17

bandwidth, shortage of, 22

BARRNET, 17

broadband network technology application, 47-49

bulletin board, 21

campus network and, 17

commercial providers, 19

composition of, overview, 6-7

corporate network and, 17

DARTnet, 15-16

distributed computing, 22

e-mail, 21

ESnet, 15-16

Federal Internet Exchange (FIX), 17

File Transfer Protocol, 21

Frame Relay, 34

Interagency Interim National Research and Education Network, 20

LAN, 22,24

“massively parallel” computer, 24-25

modem, 29

National Science Foundation, 18

network components, 26-31

computer, 27-28

link, 28-29

switch, 29-32

network technology, and applications, 22-24

newsgroup, 21

NSFNET, 15-16

backbone, 19

hierarchical structure, 18

NSI, 15-16

NYSERNet, 17

packet switching, 24-26,32

private sector opportunity, 18-19

protocols, 24-26

public switched network, 31-34

regional network and, 17-18

sound, limitations of, 22

Switched Multimegabit Data Service, 34

technology used in, 21-34

telephone company, 28-29,31-34

Telnet, 21

testbed research application, 71

transmission rates, 28-29

transparent application version, 22

TWBnet, 15-16

users of, increase in number of, 12-13

video, limitations of, 22-23

WAN, 22,24

Internet Activities Board, standards, 34,70

Internet Engineering Task Force, standards, 34,70

Internetworking, National Research and Education

Network 69-70,72-73
78 I Advanced Network Technology

L

LAN, Internet, 22,24

Link, Internet, 28-29

Local area network. See LAN

M

MAGIC network 61

“Massively parallel’ computer, 24-25

MCI, contribution to testbed research, 11

Modem, Internet, 29

Multimedia applications, of broadband networks, 3,

36-37

Multiplexing, bandwidth Iink 28

N

Narrowband network, defined, 3

National Aeronautics and Space Administration

NASA Science Internet. See NSI

National Research and Education Network

commercialism of, 7

internetworking, 69-70,72-73

objective of, 5-8

scope of, 7

testbed research application, 65-70

National Science Foundation, Internet, 18

National Science Foundation Network. See NSFNET

NICTAR network, 59

Network, components of, 3,5

Internet, 26-31

Network design, broadband network, 3

Network technology, Internet applications, 22-24

New York State Education and Research Network. See

NYSERNet

Newsgroup, Internet, 21

NREN. See National Research and Education Network

NSFNET

future developments, 65-67,70

Internet, 15-16

backbone, 19

hierarchical structure, 18

testbed research application, 65-67

NSI

future development, 65-66,68

Internet, 15-16

NYSERNet, 17

0

Optical fiber, 45-46

link, of broadband network, 10

signal, digital computer, 2

P

Packet switching, 6

Internet, 29,31-32

Packet Transfer Mode (PTM), fast packet switching,

4 3 4

Private network

establishment of, 33-34

Federal agency, future development, 66

private sector opportunity, Internet, 18-19

Procurement procedure, and National Research and

Education Network 7-8

Protocols, Internet, 24-26

Prototype gigabit network. See testbed

Public network

broadband network technology, 49

Internet, 31-34

R

Regional Bell Operating Company, contribution to

testbed research, 11

Regional network and Internet, 17-18

Remote login. See Telnet

Router. See Packet switch

s

Shade, bit patterning, 2

Simulation

broadband network technology, 36-39

and visualization, 6

SONET See Synchronous Optical Network

Sound, Internet limitations, 22

Sprint, contribution to testbed research, 11

Standards, establishment of, for Internet, 34

Supercomputer

distributed, 38,40,62-63

arid National Research and Education Network, 8

and visualization, 6

Switch

circuit, packet, contrasted, 29, 32

development, broadband network technology, 46

future application of testbed research, 68
Index | 79

Internet, 29-32. See also Packet switching

technology. See also circuit switch, Fast packet

switching, Packet switching

Asynchronous Transfer Mode (ATM, 13

overview, 35

Switched Multimegabit Data Service, 34

Synchronous Optical Network, 58,65,67

transmission standards, fiber optic link, 28-29

T

Telecommunications carriers, testbed research, contribution to, 11

Telephone company

Internet, 28-29,31-34

link lease from, 28

Telnet, Internet, 21

Testbed

concept of, 10-11

design, gigabit research, 53-55

gigabit, National Research and Education Network,

8-9

organization, gigabit research, 55-56

Testbed research

advantages of, 11

application, National Research and Education Network, 65-70

application of, 65-74

Asynchronous Transfer Mode (ATM), 13

National Research and Education Network application, 12-13

Transmission

rates, Internet, 28-29

standards, fiber optic link, Synchronous Optical

Network, 28-29

technology, future application of testbed research,

67-48

Transparent application version, Internet, 22

TWBnet, Internet, 15-16

Twisted pair cable, computer link, 5

u

U.S. Department of Energy, testbed research application, 65-66

User community, Internet, 6-7

v

Video

bit patterning, 2

broadband network technology, 36-37

Internet limitations, 22-23

Videoconferencing system, bit transmission, 3

VISTAnet, 60,62

Visualization, by gigabit National Research and Education Network, 6

Voltage, information pattern, 2

w

WAN, Internet, 22, 24

Wide area network. See WAN