@'jJ University of Colorado at Boulder 

Center for 

Space and Geosciences Policy 

Boulder, Colorado 
FINAL REPORT 

NASA AND THE CHALLENGE OF ISDN: 

THE ROLE OF SATELLITES IN AN ISDN WORLD 

Prepared for: 

The Natiofial Aeronautics and Space Administration, 

Office of Space Science and Applications, 

Communications and Information Systems Division (EC) 

, 

The University of Colorado 

Center for Space and Geosciences Policy 

Principal Investigators: 

Radford Byerly 

Frank Barnes 

George Codding 

Jefferson Hofgard 

NASA Grant NAGW 1105 

May 25, 1988 
TABLE OF CONTENTS 

Executive Summary ................... 3 

Chart Summary ..................... 5 

Introduction ...................... 6 

Organization of the Study ............... 6 

I . 

I1 . 

I11 . IV . 

V . 

VI * 

VI1 . 

VI11 . IX . 

The Concept of ISDN ............... 8 

Organizations Involved in Defining ISDN ..... 11 

The Current Status of ISDN Recommendations ... 14 

Domestic and International Progress 

Current Efforts to Include Satellites in ISDN . . 25 

Towards Implementation .......... -20 

Technical Challenges Ahead ........... 29 

Understanding the Standards Process ....... 40 

Ensuring a Role for Satellites ......... 48 

Summary and Implications for NASA ........ 48 

Glossary ........................ 56 

Bibliography ...................... 58 

References ....................... 61 

i 
EXECUTIVE SUMMARY 

To understand what role satellites may play in Integrated 

Services Digital Networks or ISDN, it is necessary to understand 

the concept of ISDN, including key organizations involved, the 

current status of key standards recommendations, and domestic and 

international progress towards implementation of ISDN. This 

report covers each of these areas. 

The report also contains a summary of the technical 

performance criteria for ISDN, current standards for satellites 

in ISDN, key players in the ISDN environment, and what steps can 

be taken to encourage application of satellites in ISDN. 

ISDN is a developing concept of how telecommunications 

networks should evolve in the future. At the most basic level, 

ISDN is an integrated services network that provides digital 

connections between user-network interfaces. The fact that ISDN 

means "different things to different people" is significant, for 

it indicates that evolution of the concept, and thus the role 

satellites may play, is still ongoing. Therefore, the evolution 

of ISDN and the role that satellites can play in iSDK snouid be 

seen as parallel developments. 

At the same time, standards are being set, which means that 

roles are being defined. In setting standards the major 

international players are the CCITT and the CCIR, both part of 

the ITU. Domestically, ANSI, ECSA, and the COS and the 

(independent) ttT1" standards committee are key players. Ensuring 

a role for satellites in ISDN will require knowledge of, and 

participation in, each of these key groups. 

Considerable work has been done in identifying the basic 

elements of ISDN. These are contained in the so-called "ISeries" Reoomendations from the CCITT. These Recommendations 

cover general aspects of ISDN, service capabilities, overall 

network aspect8, user interfaces, internetwork interfaces, and 

maintenance principles. The CCITT I-Series Recommendations 

compose the initial "boundary conditions" of ISDN, and thus an 

understanding of their requirements and any constraints they may 

pose for satellites in ISDN is important. 

Other new aspects of the ISDN environment are important: 

First, interest seems to be shifting towards emphasis on 

broadband ISDN, which could have far-reaching implications for 

networks in the future. Second, methods of pricing ISDN are 

beginning to emerge as companies begin experimenting with 

different tariff structures. Third, there is an emerging 

consensus that market acceptance of ISDN will not pose a barrier 

to implementation. 

Progress towards implementation of ISDN is occurring at 

domestic and international levels. Within the U.S., Ameritech, 

US West, Nynex, Pacific Telesis and others have initiated or are 
planning field trials. Internationally, Germany, Japan, Sweden, 

and the UK are actively involved in implementation of ISDN. 

Current efforts to include satellites in ISDN have not been 

widespread. INTELSAT has played a active role in encouraging the 

formation of an "ISDN and Satellites Coalition.tt The coalition 

has held several meetings and could serve as a focal point for 

future efforts on behalf of satellites. The CCIR's Study Group 4 

has examined the role of satellites in ISDN, suggesting that the 

major role for satellites will be in long distance, high grade, 

international segments. 

The CCIR and CCITT have issued several Recommendation and 

reports that will impact satellites in ISDN which are covered in 

detail in Chapter VI, "Technical Challenges". The important 

point to note here is that these Recommendation and reports set 

out specific performance standards for satellites in ISDN, some 

of which could, either in their current form or as a result of a 

modification, pose a problem for satellites. Without a thorough 

understanding and continuous evaluation of the implications of 

these technical performance objectives for satellites in ISDN, 

there is a potential for standards to evolve tnat are 

detrimental to satellite involvement in ISDN. 

Thcs, it is important to clearly understand and be able to 

operate within the CCITT and CCIR committees and subcommittees 

involved in ISDN as well as the domestic commmittees that develop 

U.S. consensus positions. The interrelationships between 

different committees are as complex as they are important, making 

complete knowledge of the process a prerequisite to effective 

participation. 

If satellites are to play an important role in ISDN, there 

are several steps that can be taken now. These can be broadly 

grouped into four categories: 1) obtaining the necessary space 

resources; 2) meeting the technical challenges posed by ISDN; 

3) impacting the standards process; and, 4) promoting the 

technical and operational advantages of satellites to users. 

NASA can serve as a facilitator and source of support in a 

manner consistent with the statutory authority granted the 

Agency under the 1958 National Space and Aeronautics Act and in a 

manner consistent with the President's February 1988 National 

Space Policy. Such a role could be pursued under a general 

strategy of technical, supporting, and liaison activities. In 

particular, NASA could work with other national space agencies to 

ensure a coherent posture with regard to the role of satellites 

in ISDN. 
CHART SUMMARY 

What is ISDN? 

- Developing Concept . Integrated Digital Service Networks 

- Will Shape Networks of the Future 

- Satellite Role Can Evolve in Parallel 

Who Are the Major Players? 

- International 

- Domestic 

ITU - CCIT, CCIR 

. ANSI, ECSA, COS, trT1" 

Current Aspects of ISDN Environment 

- CCITT I-Series Recommendations 

- Increasing Interest in Broadband 

- Tariff Structures Emerging 

- Expect Rapid Market Acceptance 

. Basic Elements 

Progress Towards Implementation 

- International 

. UK: Sweden, Germany! Japan 

. Ameritech, Nynex, US West, Pacific Telesis and others 

- Domestic 

Current Efforts to Include Satellites 

- "Satellites and ISDN Coalition" . Initiated by INTELSAT . Could Serve as Focal P 

Set Specific Standards, Performance Criteria 

Important to Nonitor/Check Satellite Ability to Meet 

- CCIR and CCITT Recommendations/Reports 

Understanding Standards Process 

- Particination and Knowledge of Process Key 

Interhational Study Groups, Working Groups at CCITT, CCIR 

Domestic Committees Forming U.S. Consensus Positions 

Ensuring a Role for Satellites 

- Obtain Necessary Resources 

- Meet Technical Challenges 

- Impact Standards Process 

- Promote Technical/Operational Advantages of Satellites 

What Role for NASA? 

- Technical 

- Liaison 

- Supporting 

5 
INTRODUCTION 

In the past few years the tone of discussion surrounding the 

role of satellites in world communications has undergone an 

interesting metamorphosis. The first stage was disbelief that 

satellite applications could be affected by fiber optics. The 

second stage was marked by a fear that a fiber optic vs satellite 

nshowdownn was imminent and that the future of satellites was 

uncertain. The third and current stage recognizes that 

transitions wjll occur, but that each medium has its own ideal 

applications. 

There may be yet a fourth stage, a stage marked by total 

end-to-end digital interconnectivity across virtually all forms 

of user interfaces at extremely high data rates. This concept -- 

integrated services digital networks or ISDN -- is becoming 

synonymous with the future direction of telecommunications. At 

the industry level, interest and participation in field trials 

has been high. Similarly, some foreign governments have already 

made a substantial commitment to testing ISDN technologies. 

Internationally, the ITU, CCITT and CCIR are beginning to set 

standards for LSUN, some of which could impact the r~le sf 

satellites in ISDN. It is this last issue, the role of 

satellites in ISDN, that is the focus of this study. In 

particular, this study seeks to identify the role that satellites 

could play in ISDN and to assist NASA's Communications and 

Information Systems Division in understanding what kinds of 

efforts can help make that potential role into a reality. 

ORGANIZATION OF THE STUDY 

To understand what role satellites can play in ISDN, it is 

first necessary to understand ISDN. 

Chapters I through IV describe the concept of ISDN, 

organizations involved in defining ISDN, the current status of 

key recommendations for standardization, and domestic and 

international progress towards ISDN implementation. These 

Chapters serve as backdrop against which the role of satellites 

is discussed. 

Chapters V and VI focus on current efforts to include 

satellites in ISDN and some of the technical issues involved. 

This section isolates some of the performance criteria that are 

key to including satellites in ISDN, summarizing the importance 

of the major CCITT and CCIR recommendations with respect to 

satellites. 

Chapter VI1 examines the importance of the standards 

process for satellites in ISDN, outlining the key players, the 

relative influence of their roles and how the process of 

standardization works. 

b 
Chapter VI11 examines what steps need to be taken in order 

to ensure a role for satellites in ISDN. These steps are 

discussed in terms of necessary space resources, future 

technical challenges, the standards process, and the comparative 

advantages offered by satellites. 

Chapter IX summarizes the importance of the study's 

findings for NASA's Communications and Information Systems 

Division. Within the context of the study, this Chapter is 

almost a "stand-alone" contribution, as it seeks to meet the 

specific needs of NASA's Code EC in the area of satellites and 

ISDN. 

7 
I. THE CONCEPT OF ISDN 

ISDN is a developing concept related to how existing 

telecommunications networks should evolve in the future. Thus it 

is not now a tangible product or system. ISDN pre-supposes the 

existence of a digital telecommunication network, envisioning a 

variety of services which are accessible to users via a small set 

of multipurpose interfaces. Figure 1 shows schematically how 

users would access such a variety of different telecommunications 

services, presently, and in an ISDN. ISDNs will be characterized 

by the types of services they provide to users, rather than by 

the internal network technology or architecture which permit 

those services to be provided. 

The formal International Consultative Committee on Telephone 

and Telegraph (CCITT) definition of ISDN, adopted in October 

1984, reads: 

Integrated Services Digital Network (ISDN), an 

integrated services network that provides digital 

connections between user-network interfaces. 

This succinct definition specifically mentions the 

interfaces between users and the network, a key component of 

ISDN. A 1981 draft definition stated essentially the same thing 

in a slightly longer and more descriptive way: 

Integrated Services Digital Network (ISDN), a network 

evolved from the telephony IDN [Integrated Digital 

Network] that provides end-to-end digital connectivity 

to support a wide range of services, including voice 

and non-voice services, to which users have access by a 

limited set of standard multipurpose customer 3 interfaces. 

nISDNn is actually a very descriptive acronym, and 

understanding each of the words that make up ISDN will help one 

understand its essence. 

A. Integrated 

There are two ways to look at I1integratedtl, or tlintegration.lt 

First, there is integration of services, which implies a network 

that provides or supports a variety of different telecommunication services, such as telephony, data, and telex, and the 

associated terminal equipment which allows the user access to 

those services. Second, there is integration of access, which 

implies a single connection to obtain access to the network(s) 

which provide the services. 

8 
B. Services 

In ISDN, the word "service" can have several meanings. For 

example, in the CCITT I-Series recommendations defining ISDN, 

there are "bearer services," "supplementary services," and 

"teleservices," each with its own specific definition. In this 

report ttservicett is defined as that which is provided by the 

network to the user (also called a customer or subscriber)4in 

order to satisfy a specific telecommunication requirement. 

C. Digital 

analog to digital technology has been very evident in the field 

of telecommunications; first for transmission, followed more 

recently by digital switching, and now digital user terminals. 

Using digital technology makes possible both storage of messages 

in the network and conversion of the speed, format, protocol or 

medium of the signal, allowing users with different kinds of 

terminals to communicate with each other. Details of the many 

technological and cost advantages of digital teC.liiiGlGgg applied 

to telec3mmunications are discussed at length in many other 

sources. This transition to digital technology is quite 

advanced in many telecommunication networks. According to Mr. 

Richard Hansen of AT&T, for example: 

Within the past ten to fifteen years, the transition from 

Now, in mid 1987, we are well on our way to establishing a completely digital network. We stopped 

adding any new analog transmission systems to our 

network in 1983 and have accelerated our deployment of 

digital systems to meet exploding customer demand. The 

technology that we have right now, and are developing, 

will enable us to build a total digital network. We 

don't need significant technological breakthroughs or 

dramatic cost improvements. 

AT&T, with the largest network in the world, is leading this 

trend, and other U.S. network providers, both public and private, 

are following suit. The situation throughout Europe, Japan, and 

in many other countries, is quite similar. This transition is 

primarily motivated by cost and by the ability to provide new 

services to users (i.e., to generate new revenues). 

Although AT&T and other network providers may soon have 

totally digital networks, this does not mean digital end-to-end 

connectivity for all users. Except for larger business users, 

"the last mile" local loop connection to the network is still 

analog, and will remain so for the near future. This will 

influence the feasibility, timing, and costs of providing new 

services to small business and residential users. 

9 
D. Network 

The CCITT defines ffnetworkff as a set of nodes and links that 

provides connections between two or more defined points to 

facilitate telecommunication between them. New telecommunication 

services will be made available by means of networks. Ideally, 

these services would be available from one totally integrated 

network, although initially this will not be possible; public 

networks, private networks and value-added networks will all have 

their roles. 

10 
11. ORGANIZATIONS INVOLVED IN DEFINING ISDN 

There are several domestic and international organizations 

involved in defining standards for ISDN. Without a "road mapV1 of 

sorts, the process of developing standards for ISDN can be 

confusing. This section provides a brief picture of the tlmajor 

players"; information on the many otherj players in this process 

can be found in several other sources. 

The two primary international organizations developing 

digital communications standards are the International 

Telecommunication Union (ITU) and the International Organization 

for Standardization (ISO). Within the ITU, the development of 

standards (called Recommendations) is managed by the International Telegraph and Telephone Consultative Committee (CCITT) 

and the International Radio Consultative Committee (CCIR). Most 

of the work on digital communications networks is confined to 

CCITT. The CCIR is primarily concerned with the technical 

aspects of radio spectrum use. CCITT Study Group XVIII is the 

focal point of international activities related to ISDN, and CCIR 

Study Group IV is responsible for recommendations related to 

fixed satellite service. These two organizations {LCILII aiid 

CCIR) and their sub-groups (Study Group XVIII and Study Group IV) 

are important to note for they appear throughout the study. 

l-l-rmm 

ISO, the largest standards organization in the world, is 

responsible for the development of the Open Systems Interconnection (OSI) Reference Model. The OS1 Model is a seven-layer 

model* which defines a framework for the establishment of 

protocols so that separate systems complying with the model will 

be lVopentt to one another and thus will be able to communicate. 

The model was developed to: 1) accelerate the development of 

computer technology; 2) decrease the cost of computers and 

computer services, 3) address the problems of computer-tocomputer communications; and, 4) meet the steady increase of 

data cgmmunications for an ever-increasing number of applicat ions. 

Layer 1, the physical layer, defines the electrical 

characteristics needed to transmit data across the transmission 

medium such as a transmission wire, microwave, fiber optic or 

satellite link. 

Layer 2, the data link layer, frames the data into packets 

that make up the messages and manages error checking. The next 

layer up, the network layer (3) sets up and manages the routing 

* The "layers" start with the physical hardware at layer (1) and 

progress through (2) data link, (3) network, (4) transport, (5) 

session, (6) presentation, and (7) application layers. 

11 
of data packets to travel across the networks. The standards for 

layers 1-3 also apply to local area network products which are 

primarily made by independent software companies and computer 

companies. Another U.S. standards organization, IEEE, has played 

a principal role in developing specific local area network 

standards. 

The transport and session layers (layers 4 and 5) manage 

the end-to-end connection between machines, multiplexing of 

messages and synchronization of data exchange. These are of 

particular interest to communications companies although they can 

not be considered out of context of the entire model. 

Layer 6, the presentation layer, provides negotiation of a 

common syntax for the transfer of data between programs on 

different computers. It manages the transfer syntax for 

character sets, text strings, data display formats, file 

organization, graphics syntax, videotex, financial information, 

etc. This standard effects any segment of the information 

industry which may be developing information products and 

services for delivery over a computer network. 

At the top, layer 7 is the applications layer which directly 

interfaces to the end user activity. It selects the appropriate 

services for the user application processing and also manages 

the interfacing of user applications with other OS1 layers. It 

provides both generic services such as file transfer and remote 

job control, as well as industry specific protocols such as for 

banking, library, business transactions and others. The OS1 

Model has had a direct impact on the development of certain 

standards for protocols and interfaces in ISDN. 

Within the U.S., the American National Standards Institute 

(ANSI) is the national clearinghouse for voluntary standards. 

ANSI not a standards-developing organization E SA, but rather 

establishes and promulgates full consensus standards (developed 

by other organizations) as American National Standards (ANSs). 

The Exchange Carriers Standards Association (ECSA), formed as a 

result of the breakup of AT&T, develops standards which preserve 

the integrity of nationwide telecommunications and facilit te the 

interconnection and inter-operability of carrier services. 6 

ANSI has promulgated two particularly relevant data 

communication performance standards. These are the American 

National Standard for Information Systems, Data Communication 

Systems and Services; User-oriented Performance Parameters, ANS 

X3.102, and the American National Standard for Information 

Systems, Data Communication Systems and Services; Measurement 

Methods for User-oriented Performance Evaluation, ANS X3.141. 

These standards are being used for measurements serving to 

quantify ACTS system pe~gormance. 

used as hubs in ISDN's. ECSA is both a trade association and 

Satellites like ACTS could be 

12 
sponsor of an independent standards committee, nTl.tl Committee 

Tl is the focal committee for ISDN standards efforts in the U.S. 

and is recognized as such by ANSI. 

Systems (COS). COS does not develop standards, but works in 

conjunction with the National Bureau of Standards (NBS) to 

encourage uniform national implementations of standards for open 

systems, such as those related to ISDN and the OS1 Model. COS is 

also charged with developing test bed and certification 

procedures so that vendors can test compliance with standards 

against an agreed upon reference implementation. 

Another important organization is the Corporation for Open 
111. THE CURRENT STATUS OF ISDN RECOMMENDATIONS 

Since 1980, the development of the necessary standards 

(Recommendations) has taken place within the CCITT with Study 

Group XVIII playing a lead role. One of the Group's most 

significant outputs has been a series of ISDN Recommendations, 

known as the "1-Series Recommendations". These Recommendations 

were adopted at the VIIIth Plenary Assembly in October 1984. 

A. The I-Series Recommendations 

tion describing the principles of ISDN was published in 1980. 

total of 29 Recommendations were prepared and ratified at the 

CCITT Plenary Assembly in 17$4, and work has continued at an even 

more rapid pace since then. Table 1 provides a general 

summary of the I-Series Recommendations adopted in 1984. 

Considerable work has been done since the first recommendaA 

A comprehensive overview of all of the specific recommendations contained in the I-Series is beyond the scope of this 

study. However, a brief discussion of each series serves to 

highlight some of the important aspects of 'cnese ISDN 

Recommendations, providing a context for the identification of 

key issues being discussed in the current study period. 

(1) 1.100 Series - General 

This series outlines the basic principles of ISDN and the 

evolution of ISDNs. The main feature of the ISDN concept is the 

support of a wide range of voice and non-voice applications in 

the same network. A key element of service integration for an 

ISDN is the provision of a range of services using a limited set 

of connection types and multipurpose user-network interface 

arrangements. 

(2) 1.200 Series - Service Capabilities. 

The 1.200 Series is concerned with the identification and 

categorization of services to be offered in an ISDN. This topic 

received considerable attention during the 1981-1984 study 

period. Rather than define specific services, it was decided to 

establish categories of services based on their relationship to 

different levels 94 the OS1 Model. Three categories of services 

were established: 

- Bearer services: those providing the capability for the 

transmission of signals between user-network interfaces. 

- Teleservices: those providing the complete capability for 

communication between users of specified user terminals. 

- Supplementary services: those supplementing or modifying 

a basic telecommunication service. 

14 
TABLE 1 

General Structure of I-Series RecommendatioTg Adopted 

by CCITT at the 1984 Plenary Assembly. 

1.100 SERIES - GENERAL 

- Frame of I-Series Recommendations; Terminology 

- Description of ISDNa 

- General Modelling Methods 

- Evolution 

1.200 SERIES - SERVICE CAPABILITIES 

- Service aspects of ISDNs (Bearer Services and 

Teleservices) 

1.300 SERIES - OVERALL NETWORK ASPECTS AND FUNCTIONS 

- Network Functional Principles 

- Reference Models (Protocoi and F'unciiuiliii Ai-CFiiteCtGTS 

Models; Hypothetical Reference Connections) 

- Numbering, Addressing and Routing Principles 

- Connection Types 

- Performance Objectives (Circuit and Packet Switched 

Connections) 

1.400 SERIES - USER-NETWORK INTERFACES 

- General Aspects of User-Network Interfaces (Reference 

- Applications of User-Network Interfaces (Basic and Primary 

- Layer 1 Recommendations (Basic and Primary Rate 

- Layer 2 Recommendations (LAP D) 

- Layer 3 Recommendations 

- Multiplexing, Rate Adaptation and Support of Existing 

Configurations, Channel Structures and Access 

Capabilities) 

Rate Interfaces) 

Interfaces) 

Recommendations X.21, X.21 bis, X.25, V-Series, 

56 kbit/s 

1.500 SERIES - INTERNETWORK INTERFACES 

1.600 SERIES - MAINTENANCE PRINCIPLES 

- General Maintenance Principles 

- User Related Testing and Maintenance Principles 

15 
(3) 1.300 Series - Overall Network Aspects and Functions. 

The 1.300 Series of Recommendations deal with the network 

itself and how it will provide the services that are part of the 

ISDN. The primary topics related to network aspects include 

architecture, pr?&ocols, connection types, numbering, routing, 

and performance. 

(4) 1.400 Series - User-Network Interfaces. 

At the beginning of the 1981-1984 Study Period, issues were 

prioritized within Study Group XVIII, and high priority was given 

to the 1.400 Series area -- user-network interfaces. Sixteen of 

the 29 I-Series Hecommendations approved in 1984 were in the 

1.400 Series related to user-network interfaces. Of particular 

importance was the definition of a limited set of channel types 

for access to ISDNs through user-network interfaces, and the 

establishment of reference configurations for ISDN user-network 

interfaces. 

Several different channel types have been defined, including 

the llB" and llD1l channels wnicn will Le Use4 ir; the Ir;ltisl 

implementations of ISDN. The lrBrr channel is a 64 kbit/s channel 

intended to carry a wide variety of user information, either 

voice, data, or image. The ltB1l channel does not carry any 

sigiialiiig informati~n, which will he handled by the I1D1l channel 

at either 16 kbit/s for the Basic Rate Interface or 64 kbit/s for 

the Primary Rate Interface. The trD1l channel can also accommodate 

low speed packet data. 

A Basic Rate Interface consisting of f12B+D11 144 kbit/s, 

and a Primary Rate Interface (nominally 1123B+Dt1 (1.544 Mbit/s) or 

"30B+DI1 (2.048 Mbit/s)) have been specified as the fundamental 

arrangements for access into ISDN. 

(5) 1.500 Series - Internetwork Interfaces. 

The 1.500 Series deals with the network-to-network interfaces that will be needed to connect separate ISDNs together, as 

well as connecting ISDNs to existing non-ISDN networks. This 

issue will become more important once actual ISDNs are established, and it is receiving more attention in the current 

study period. 

(6) 1.600 Series - Maintenance Principles. 

The 1.600 Series focuses on maintenance principles, a 

relatively low priority area of study during the 1981-1984 study 

period. This topic is also expected to receive more attention in 

the coming years. 

16 
(7) Summary of I-Series Recommendations 

Some of the basic foundations for ISDN have been 

established in the I-Series Recommendations which set out basic 

principles and specific technical requirements for ISDN. The 

adoption of the I-Series Recommendations is, however, only the 

beginning of an evolving process of standardization. The next 

step is to escablish stable standarqg for first implementations 

(discussed in Chapters I11 and IV). 

B. Increased Emphasis on Broadband ISDN Issues 

The study of broadband ISDN has assumed an important 

position during the 1985-1988 study period. The completion of 

certain I-Series Recommendations may provide for compatible 

implementations of narrowband ISDN by the end of the 1980rs. 

Broadband ISDN topics, however, have far-reaching implications 

for the direction of networks of the future. 

A Broadband Task Group (BBTG) was formed at the beginning of 

the current study period to examine ::broadband aspests af ISEN." 

Since then, the topic has come to dominate the work of Study 

Group XVIII. The focus of the broadband study has shifted from 

distributive services (such as television), to encompass 

rast=~azketburst-switchlng techniques. The work on broadband 

ISDN is divided into three parts: services, user-network interfaces and channels, and transfer modes. A recommendation 

containing the basic principles of ISDN broadband aspects and 

associated evolutionary strategy, and a detailed list of specific 

broadband issues will by6prepared for formal adoption at the 1988 

CCITT Plenary Assembly. 

C. EmerginR ISDN Tariff Principles 

of tariff principles and accounting procedures to guide ISDN 

service providers. Though the CCITT will play an important role 

in the development of ISDN pricing and tariff structures, the 

organization cannot actually set tariffs. As the CCITT's 

director, Theodore Irmer said during an interview with Business 

Communications Review in November, 1986: 

The CCITT has recently 'been involved in the establishment 

The CCITT does not establish tariffs; that is a 

national matter. What we are doing is establishing 

principles for the tariffs and procedures for sharing 

revenue among network providers for an ISDN call. 

Although there are some nations that adopt these 

principles as their national tariff Qfructure, doing so 

is their choice; it is not mandated. 

17 
One ISDN tariff principle emerging from the CCITT is that 

ISDN should provide a reasonable return for network operators and 

that the tariffs must be simple to understand. 

The CCITT's Irmer feels that the network providers are 

entitled to a reasonable return but has declined to quantify what 

is a "reasonable return." He pointed to the West German ISDN 

basic access tariff of DM$56 ($28 in the U.S.) per month which is 

double the monthly access charge for basic single line telephone 

service. Irmer said, "...the philosophy is to charge double even 

though the basic (ISDN) access can do much more than two telephone lines in an analog world.tt 

Aside from the CCITT, the Bell operating companies have 

been exploring tariff options. In the initial commercial ISDN 

offerings from the Bell operating companies, the general tariff 

approach is to negotiate single-customer specialized rates for 

the present, and develop generic tariff structur78 later when 

more data is available and demand is sufficient. 

A second emerging principle is a service-independent tariff 

gives the customer these 64 kbps channels, and what the customer 

does with them - their content - should not affect the price of 

service, provided that the equipment needed to provide the 

service does not change..,,This tariff should be related to the 

telephone tariff because ISDN derives from the digital telephone 

network. ... Telephone traffic will be the bulk of the traffic and 

so it is Sggical that the tariff is oriented to telephony 

traffic". 

structure which Irmer described as follrws; WVL- &LAG *n+r.rnnIr L4UW..Y& n. nynwi y Y . ---- AOII 

In the U.S.? there is some early evidence to suggest that 

the price nf an ISDN basic rate access line will be about 1.5 

times the price of basic single line telephone service. The 

rationale follows that a single ISDN line, which supports 

simultaneous voice and data communication, should offer users 

some degree of savings over the cost of two separate, conventional lines needed to 5tjpport voice and data communications 

in non-integrated systems. 

D. Views on Market Acceptance of ISDN 

sufficient revenue can be generated to support any ISDN concept 

prior to 1990. Participants included representatives from 

telephone company service providers, manufacturers, and carriers 

from around the world: the United States, Canada, UK, France, 

Germany, Sweden, Japan, Spain, Italy, Switzerland, Holland, 

Finland, and Norway. During the workshops a number of varying 

viewpoints were eapp-essed and some consensus was reached on a 

number of points. 

At the ISDN '85 conference, participants explored whether 

18 
The first common theme to emerge was that voice and data 

markets are growing -- voice at 3 to 10 percent per year and data 

at 15 to 20 percent per year. 

Second, the ISDN market was recognized as being non-uniform. 

More market research is needed to help determine customer 

acceptance of, and willingness to pay for, the type of services 

available through ISDN. The business sector appears to be the 

market most ready for immediate acceptance of ISDN. In the 

residence sector, cost-effective pricing and easy access to 

services on an integrated basis will determine the degree of 

customer acceptance of ISDN. 

A third area of agreement was that new services and low 

costs will determine the degree of market penetration around the 

world. Many services will meet with wide user acceptance. Yet 

other services may fail if the market willingness to pay is not 

in line with the cost of delivering the service. 

Lastly, a significant conclusion reached by the group was 

that by 1990, the ISDN infrastructure will be the aominarit 

deployment architecture worldwide. 

" 

CI. 

Some network providers and equipment manufacturers have 

already made a strong commitment to ISDN, and are actively 

participating in the creation and adoption of international 

standards to make ISDN a reality. Efforts are occurring 

simultaneously to 1) convert existing analog networks to digital 

permit uniform implementations, and 3) define issues and 

principles for future networks and services in broadband ISDN. 

Few actual standards have been completed and adopted, but it is 

hoped that significant progress will be made so that key issues 

will be resolved in time for the 1988 Plenary Assembly, when 

revisions and additions to the existing I-Series Recommendations 

will be considered for adoption. 

+ ururrrrv*veJ, nnknnl nmit 2) complete key standards for narrowband ISDN to 

19 
IV. DOMESTIC AND INTERNATIONAL PROGRESS TOWARD IMPLEMENTATION 

Several companies and countries are either conducting ISDN 

field trials or have scheduled field trials for 1988. These 

field trials or "tests" are generally seen as an important first 

step towards widespread ISDN deployment. In addition to giving 

vendors and network service providers an opportunity to gain 

valuable experience with ISDN technology, the field trials serve 

as a vehicle to test market acceptance. 

J 

A. U.S. Field Trials 

In the U.S., all seven regional Bell holding companies are 

proceeding with ISDN trials to evaluate the various capabilities 

of the architecture and test the compatibility of network 

equipment supplied by different vendors. Some residential trials 

have 3150 taken place. 

below are representative of the efforts being undertaken by 

the major (Bell) network service providers in the United States. 

(1) US West 

The five field trials summarized 

US West (through the Mountain Bell telephone company) 

conducted a 200-line test that began in November, 1986 in 

Phoenix involving two Arizona state agencies, the Department 

of Administratisn and the Department of Game and Fish. 

Mountain Bell is engaged in three additional ISDN trials in 

the Phoenix area, two of which include Honeywell Information 

Systems and Intel Corp. as customers. These trials used 

switching equipment manufactured by AT&T, GTE, and Northern 

Telecom. 

Ir! Eecemherj ?98hi Mountain Bell began an internal ISDN 

trial using an ISDN switch manufactured by NEC (Japan) to 

provide service between an analog AT&T central office switch 

and US West locations in downtown Denver. Some 96 basic 

rate ISDN lines are involved in this trial which will also 

test high-speed facsimile, integrated voice and data, and 

local area network applications. 

Initiated in March, 1987, a field trial conducted by Pacific 

Northwest Bell will test the feasibility of providing ISDN 

service through a digital Centrex system, which dedicates a 

portion of a central office switch to a customer and acts as 

a private exchange. This test will use a Northern Telecom 

central office switch to provide 200 basic rate (2B+D) 

access lines to the U.S. National Bank of Oregon. 

(2) Ameritech 

Ameritech has disclosed one ISDN trial and one demonstration 

to date. Illinois Bell began providing Centrex service to 

20 
McDonald's corporate headquarters in Oak Brook, Illinois in 

December, 1986. An AT&T digital exchange serves the 

company with 120 ISDN lines. In addition to testing digital 

Centrex, this trial also includes high-speed facsimile and 

asynchronous word processing. The trial is scheduled to run 

through July, 1988. 

Nynex Corp. is conducting or planning ISDN trials in New 

York and Boston. The company is presently evaluating 

switching equipment from both Northern Telecom and Siemens 

(Germany). Nynex hopes to announce commercial ISDN 

customers in 1988. 

New England Telephone began an internal ISDN trial in July 

of 1987. The eight month trial will use an AT&T digital 

switch to connect four of the telephone company's downtown 

Boston locations. Applications to be tested include voice 

and data integration, local area networking and PC-to-PC 

communications. 

(4) Pacific Telasis 

Pacific Telesis Group is conducting a 16 month ISDN trial 

that starts in Sunnyvale, Cal. and will eventually encompass 

San Francisco and San Ramon. The Sunnyvale test, wnicn 

began in September, 1987, provides ISDN service to Lockheed 

Missile and Space Co., Inc., Hayes Microcomputer Products, 

Inc., and AT&T Network Systems through an AT&T switch 

equipped with an ISDN switching module. 

Lockheed will iuse 37 lines in developing applications for 

computer-aided design, engineering and business computing, 

an integrated local area network, video, and telemetry. In 

early 1988 the test will be temporarily interrupted tn 

install the full ISDN feature set on the AT&T switch. 

dayes Microcomputer Products will use two ISDN lines for 

engineering development, accounting administration and 

electronic mail transmission. An interface circuit card 

developed by Hayes will be used to connect personal 

computers at Hayes' facility in San Francisco to the 

telephone company's ISDN network. 

AT&T Network Systems' regional headquarters in Sunnyvale 

will begin using three ISDN lines for office administration 

functions, with additional links to remote locations in San 

Francisco, San Ramon and Palo Alto. 

The combined access lines of these three tests will 

eventually number 250 and involve seven customers. All 

21 
three tests will provide basic rate service with primary 

rate (23B+D) ISDN service scheduled for mid-1988. 

(5) Residential Trials 

The demand for ISDN services from residential subscribers is 

seen as secondary to much larger business markets for ISDN. 

As such, residential ISDN trials have been limited. It is 

worthwhile to note that at least three Bell operating 

companies have installed or are planning to install in the 

very near future fiber optic cables that will extend from 

the local exchange to the subscriber's home. Demonstrations 

of wideband services (such as video) to customers may be a 

precursor to the residential market's acceptance of ISDN. 

In one noteworthy residential offering, Southern Bell has 

plans to offer ISDN services over fiber optic cables to 500 

homes in the Heathrow housing development near Orlando, 

Florida. Foregoing trials, Southern Bell is offering ISDN 

on a commercial basis from the start, confident that 

customers will respond positively. Homeowners have a choice 

of sticking with BOT3 (plain 616 te:eghs;?z service) 5~ 

opting for SDN, which will be priced about 1.5 times higher 

than POTS. 23 

B. International 

There have been numerous field trials and other advances 

outside the U.S. Some of the more notable examples are listed 

below with a brief synopsis of their activities. 

(1) Germany 

The Federal Republic of Germany PTT, the Deutsche 

Bundespost, has2$et the following schedule for ISDN 

implementation: 

1986: ISDN trials. 

1988: Start of' serial ISDN introduction with services 

1989: All digital exchanges prepared for ISDN. 

1990: 100 digital trunk exchanges and 200 local exchanges 

including voice, circuit-switched data, teletex, 

telefax, and videotex. 

installed with access to 50% of the potential ISDN 

subscribers. Also, beginning of introduction of 

broadband ISDN. 

1992: Integration of broadband ISDN. 

1993: Nationwide ISDN coverage. 

22 
Sweden began an extensive network digitalization program in 

1985. At current levels of investment in the telecommunications 

network (about 4.5 - 5 billion SEK (500 - 600 million US$) per 

year), about 40% goes into new digital systems. The proportion 

of digital connections in the inter-exchange network passed the 

50% mark in 1985. At the same time, about 18% of all telephone 

subscribers were connected to digital exchanges. About 250,000 

new lines, or about 5% of the present total, are being connected 

to digital systems every year. A fully digital, synchronized 

long-distance network with common channel signaling* and 

interconnecting about 75 digital exchanges is expected to be in 

place in 1987. 

In Sweden, the ISDN is expected to evolve within the 

framework of the general digitalization of the telecommunications 

network. Within this framework, the first step towards ISDN will 

be a nationwide capability for 64 kbps digital connectivity, 

available in 1987. Technical and commercial ISDN service trials 

are planned during 1987-89. Commercial offerings are expected to 

commence in iy89 ieaaing to fiat' IIWAUG availabilitg tc virtnilly 

any customer by the mid lggOfs. 

(3) United Kingdom 

tr-' - 

In 1985, British Telecom launched its IDA (Integrated 

Digital Access) service as a first step towards a full ISDN. 

Initial service was provided from a single exchange in London 

with remote multiplexers used to serve more distant customers. 

Three additional exchanges were added to the pilot system, each 

with the capability of providing service to 250 single line IDA 

clJ.st.omers e 

In the next few years there will be a rapid increase in the 

number of digital local exchanges in service in Britain, each of 

which will be equipped to provide ISDN service. 

1987 there should be about 180 systems in place. In addition, a 

fully digital SEunk network is planned sometime prior to the end 

of the decade. 

By the end of 

(4) Japan 

Over the last two decades Japan has pushed steadily forward 

in network digitalization. The completion of the nationwide 

* Common channel signaling is a method of signaling between two 

switching centers that uses a connection separate from the voice 

and data channels. 

23 
digitalization of the telephone network is scheduled for 1995. 

The recent annual growth rate of telephone traffic among some 64 

million subscribers has been about 3%. Non-telephone traffic is 

estimated to be growing at a much higher rate. The number of 

facsimile terminals, for instance, is increasing by about 50% a 

year. 

In the past five years NTT, the major provider of domestic 

telecommunication service in Japan, has implemented specialized 

networks dedicated to either circuit switched or packet switched 

data, or to facsimile communication. Both data networks and 

private line services operate at up to 6.3 Mbps on an end-to-end 

digital basis. Other specialized network services, such as 

videotex and video conferencing, are also being widely used in 

large cities. 

NTT hopes to integrate these separate networks into a single 

ISDN. But NTT has a bigger plan in mind than ISDN, which it 

calls INS (Information Network System). The INS concept will 

combine ISDN with communication processing nodes performing 

higher-level function so that a wide range of information and 

communication modes caii be aceo;;;;i;~bated I:: 3 single ~otwnrk 

system. 

An INS pilot is now being operated between Mitaka, a suburb 

of Tokyo; and part of central Tokyo. The pilot offers both 64 

kbps digital communications combined with communication 

processors and wide-band visual services. By 1988, NTT expects 

that it will be able to meet the digital access demands for 

almost all substantial areas in Japan, and when CCITT 

Recommendations are completed, it will @yovide INS access on the 

internationally accepted 2B+D standard. 

24 
V. CURRENT EFFORTS TO INCLUDE SATELLITES IN ISDN 

The foregoing discussion has focussed on introducing the 

general nature of ISDN and some of the basic principles, 

reconmendations and themes that have or are currently emerging. 

This Chapter focuses on how satellites are being perceived within 

the general concept of ISDN. 

A. Efforts by Intelsat and the Satellite Industry. 

securing a role for satellites in ISDN, hoping not only to 

protect its interest but also to widen the competitive prospects 

for satellites in the future. In early 1986, Intelsat 

established a task force with the goal of ensuring compatibility 

between all aspects of Intelsat digital services and ISDN. 

Intelsat claims to be the only service provider that today can 

offer ISDN capabilities on a global network basis. In addition, 

their IDR (Intermediate Data Rate), IBS (Intelsat Business 

Service) and TDMA (Time Division Multiple Access) services are 

depends on the future direction of ISDN.) 

Intelsat has been active in a number of areas, aiming at 

advertised as being iuiiy n -1 .I -- ~a~k on T uwupaurv*r. hi e (Of cc!rso t.hiS 

Intelsat has also been an active participant in ITU meetings 

focused on the definition of standards for the ISDiu', subrnlttli~g 

contributions to, and heBting a meeting of, the CCITT Study Group 

on ISDN and satellites. 

On an industry-wide level, Intelsat and a number of 

satellite system manufacturers and service providers have formed 

the "Satellite Coalition for ISDN." 

Speaking before the 1987 Satellite VI Conference Dr. Joseph 

Pelton, the Director of Policy at Intelsat, described a situation 

which seems to call for a group to promote satellites: , 

For a number of reasons, the satellite case for ISDN 

has not really been made. What has been missing is a 

unified collective attempt by the satellite industry 

not only to rebut negative perceptions about 

satellites, but also to extol the many advantages of 

satellites in general, and especiallg for 

ISDN-compatible satellite services. 

The Coalition has since addressed a number of issues, 

including standards-making, compatibility between satellites and 

demonstrations, image building, and economic studies of 

satellite versus fiber optic systems. 

, terrestrial-based systems, satellite/ISDN tests and 

1 

25 
The Coalition has recognized the importance of active 

participation in the national and international standards making 

bodies responsible for establishing standards for ISDN. Active 

involvement in these organizations is particularly important in 

light of the Coalition's view that "...the participants (in 

these standards making parties) are almost exclusively comprised 

of operators of national networks and manufactures of equipment 

(central office switches, PBX's, user terminals, etc.) ... and we 

have often found that they are consegHently indifferent to the 

peculiarities of satellite systems." 

At the Coalition's February 1987 -meeting, representatives 

from Comsat assured the group that Comsat has been active in the 

appropriate CCITT forums and that, for the time being, there was 

no grave danger of standards being set resulting in the possible 

exclusion of satellites from the ISDN. Standards making is an 

ongoing $Qsue, they added, and additional support would be 

helpful . 

from Intelsat commented that the CCITT recommendation on 

peri'oruauce erite~ia, zamely cf.521 (Errcr ?erfcraance nn an 

International Digital Connection Forming Part of an Integrated 

Services Digital Network) was quite acceptable for satellite 

transmission links. He also indicated that efforts to revise 

Recommendation G.114 on propagation delay appeared to be 

proceeding well, and that a draft revised recommendation taking 

into account more recent data could be expected in the coming 

months. (Both of these recommendations will be discussed 

subsequently in detail.) 

An important area of concern appears to be switching 

protocols, with the feeling that more emphasis needs to be placed 

On ensuring that signalling and swit59ing standards take 

satellite requirements into account. 

At the coalition's second meeting in May 1987, a member 

Another recent development taking place within CCITT Study 

Group XVIII and discussed by the Coalition concerns standardization for broadband ISDN. The standardization of the transmission rate is likely to be set in the range of 150 to 155 Mbps, 

rather than the previously discussed 140 Mbps. A data rate of 

150 Mbps is just out of the reach of present satellite technology, therefore such a standard would require new planning 

approaches and/or hardware to be developed and implemented to 

allow Intelsat to transmit data at these high ra sgs, and would 

probably affect other satellite systems as well. 

The Coalition's meeting in May 1987 included a discussion 

on the problem of compatibility between satellites and certain 

terrestrial-based facilities. Several members of the Coalition 

suggested that telecommunications equipment and switching 

facilities were frequently incompatible with satellite 

26 
transmissions. One member added that the switching systems of 

certain PBX manufacturers were even incompatible with their own 

units if operated over a satellite circuit. 

To address this situation, it was agreed that a working 

group would be created to: 

a) participate in and contribute to the working parties and 

study groups involved with setting standards affecting satellite 

communications; 

b) prepare a letter to send to manufacturers of digital 

PBXs and other digital communications equipment stressing the 

critical importance of compatibility with satellites; 

c) monitor the developments taking place within the 

definition of Signaling System Number 7 to ensure its full 

compatibility with satellites. Signaling System Number 7 (SS 

No. 71, is a method of common channel signaling and is an 

essential component of the evolving international digital 

networks. 

The use of satellites in ISDN has been demonstrated through 

efforts sponsored jointly by Comsat and British Telecom (BTI) and 

carried by Intelsat. Successful ISDN demonstrations also were 

conducted between London and Washington, D.C., aiid between Lor;d~n 

and New Orleans in early 1987. It was agreed that detailed 

articles on these demonstrations should be placed in the media 

and that targeted letters referring to the success of the 34 

demonstrations be sent to key telecommunications planners. 

It was further agreed that follow-up ISDN demonstrations 

should be pursued. Intelsat promotes the continuation of these 

demonstrations by offering free use of its space segment to its 

signatories for the pur33se of demonstrating the feasibility of 

satellites in the ISDN. 

B. Recommendations from the CCIR on Satellites in the ISDN 

International standards development for ISDN largely takes 

place within various study groups of the CCITT. Recommendations 

dealing with system performance and standards for radio communications, however, are the responsibility of the International 

Radio Consultative Committee (CCIR). Study Group 4 of the CCIR 

is responsible for all matters relating to operation and 

performance criteria of fixed-satellite service.* Within Study 

* The fixed-satellite service relays telephone, data, and radio 

signals from one point to another (point-to-point) or to many 

other ground stations (point-to-multipoint). 

27 ~ 
Group 4, Interim Working Party 4/2 ("IWP 4/2") on Satellites in 

the digital network has addressed several issues critical to 

performance objectives affecting satellites in the ISDN. 

The IWP 4/2 held its fourth meeting from April 6-10, 1987 in 

Tokyo, Japan. The Working Party addressed a number of issues 

central to the development of standards and performance criteria 

necessary for the inclusion of satellites in the ISDN. The 

reports and recommendations produced at this meeting may have an 

important impact on the extent to which satellites are 

incorporated into the ISDN. 

The efforts of the working party produced a new report 

entitled "The Integgated Services Digital Network and the Fixed 

Sat el 1 i t e Se r vi c e . The objective of this report is to 

provide for a broader understanding of ISDN throughout the 

satellite community and to identify the more important aspects 

that impact satellite system design. 

The report sums up the importance of satellites in the 

ISDN, stating that: 

'he major roie expected for?. aate::itcs i: the ISEN is 

as part of the long distance, high grade, international 

segment. In fact, it can be expected that for 

international connections, satellites will be the 

primary transmission medium except for the areas where 

undersea cables are reasonable to install. These are 

also the highest density traffic routes so even in this 

case there will be a significant role to be played by 

satellite systems. 

This is clearly the type of language preferred by the 

satellite community; however, it is no guarantee that satellites 

are assured an important role in ISDN. Doing that will require 

that 1) technical challenges are identified and effectively 

addressed; and, 2) the standards process is well understood and 

effectively utilized. Chapters VI and VI1 focus on these two 

areas. 

28 
VI. TECHNICAL CHALLENGES AHEAD 

This section provides an overview of the most important CCIR 

and CCITT recommendations and reports that will impact satellites 

in ISDN. In general, these are CCITT Recommendation G.821 on 

satellite transmission qualityy objectives; CCIR Recommendation 

614 on allowable error performance; CCIR Report 997 which 

contains detailed information on the characteristics of satellite 

service in ISDN; and CCITT Recommendation G.114 concerning 

limitations on propagation delay and the appropriate use of echo 

control devices for satellites in ISDN. This section ends with a 

list of technical issues that continue to face satellites in 

ISDN. 

A. CCITT Recommendation G.821: International ISDN Transmission 

Qual i ty 0 b j e c t ives . The performance objectives that apply to satellites in the 

ISDN are derived from the overall pe ormance objectives set 

forth in CCITT Recommendation G.821. '' This recommendation, 

entitled llError Performance of an lnternationai Gigiiai 

Connection Forming Part of an Integrated Services Digital 

Network,!' forms the basis upon which performance standards are 

derived fer communication links in an end-to-end ISDN connection. 

Based on the perceived needs of end users, G.821 defines the 

performance objectives for each direction of a 64 kbit/s circuitswitched connection used for voice traffic or as a "Bearer 

Channel" for data-type services. This 64 kbit/s circuit-switched 

(HRX) with a total length of 27,500 km and is a derivative of the 

CCITT's Standard Hypothetical Reference Connection. A digital 

HRX is a model with which studies relating to overall performance 

can be made, t reby facilitating the development of objectives 

and standards. 

The performance objectives of G.821 are given for three 

different performance classifications. International ISDN 

connections -- where satellites are expected play a role -- must 

meet all of these requirements concurrently to be in compliance 

with the objectives. The objectives are: 

(1) Degraded Minutes: Fewer than 10% of ne-minute intervals to 

have a bit error ratio worse than 1 x 10-8 (this is equivalent to 

4 errors or less for 90% of 1-minute intervals for a 64 kbit/s 

HRX) 

I connection is an all digital Hypothetical Reference Connection 

I 

3s 

I 

I 

I 

(2) Severely Errorred Seconds: Fewer than 0.2% of one-second 

intervals to have a bit error ratio worse than 1 x 10-3 (this is 

equivalent to 64 errors or less for 99.8% of 1-second intervals I for a 64 kbit/s HRX) 

I 

I 29 I 
(3) Errorred seconds: Fewer than 8% of one-second intervals to 

have any errors (equivalent to 92% error-free seconds). 

Since these objectives relate to an overall connection it is 

necessary to subdivide these into the constituent parts of 

the HRX. In G.821, the CCITT identifies three different 

components of an end-to-end international connection and 

classifies them as local grade (between the end user and local 

switching center), medium grade (between the local exchange and 

the international switching center), and high grade (the longdistance connection). 

G.821 then describes the strategy used in allocating the 

overall objectives among the constituent parts. The apportionment of degraded minutes and errorred seconds is given as: 

a) Local grade: 15% block allowance to each of two ends; 

b) Medium grade: 15% block allowance to each of two ends; 

c) High grade: 40% (this is a distance-sensitive 

allocation equivalent to a conceptual quality of 0.0016% per 

km for 25,060 kmi. 

Realizing that the error performance of satellites is 

largely independent of distance, the CCIR, in cooperation with 

the CCITTj has undertaken studies to determine the performance 

allocation appropriate for satellites in the HRX. To facilitate 

these studies, the CCIR has developed a model called the 

Hypothetical Reference Digital Path (HRDP), which includes one 

earth-space-earth link and may be used to form part of an HRX. 

permitted degraded minutes and errorred seconds objectives is 

allocated to a single satellite HRDP employed in the high-grade 

portion of the HRX. Given this allocation, the satellite HRDP 

objectives required for compliance with the overall objectives of 

G.821 can be stated as: 

In Recommendation G.821 a block allowance of 20% of the 

a) Degraded minutes: Fewer than 2% of 1-minute intervals to 

have a bit error ratio worse than 1x10'3; 

b) Severely errorred seconds: Fewer than 1x10'3; 

c) Errorred seconds: Fewer than 1.6% of 1-sec intervals to 

have any errors (equivalent to 98.4% error-free seconds). 

B. CCIR Recommendation 614: Allowable Error Performance 

This recommendation, drafted by IWP 4/2 of Study Group 4 of 

the CCIR and accepted by the CCIR at the XVIth Plenary Assembly 

in 1986, specifies the allowable error performance for a HRDP in 

30 
the fixed satellite sefjgice forming part of an international 

connection in an ISDN. It Statas that the bit error ratio at 

the output of a satellite HRDP operating below 15 GHz and forming 

part of a 64 kbit/s connection should not exceed: 

a) 1 x 10-7 for more than 10% of any month; 

b) 1 x for more than 2% of any month; 

c) 1 x 10-3 for more than 0.03% of any month. 

The above objectives were established utilizing the method 

outlined in CCIR Report 997 (Characteristics of a FSS HRDP 

forming part of an ISDN) and are sufficient to meet the required 

FSS HRQE performance objectives given above in Recommendation 

G.821. 

considered available as defined in Recommendation 579. 

The Recommendation applies only when the syskgm is 

In order to provide guidance to the CCITT in determining the 

appropriate performance allocation for a satellite HRDP, the CCIR 

studied the performance requirements of a number of connections 

covering a diverse range of network configurations. In these 

studies it was noted that satellite error performance is 

generally distance-independent, witn a maxiliiuiii siiigle 5s;: 

covering an equivalent terrestrial distance of approximately 

1 6,000 km . se---- vc~al different HRX configurations were studied and it now 

appears reasonable that up to 40% of the total performance 

degradation may be allocated to a FSS HRDP when forming part of 

a Hypothetical Reference Connection (this is compared to the 20% 

block allowance for a satellite element now employed in the highgrade portion of the HRX allowed by Recommendation G.821). 

Although a distance related approach did not appear to be 

applicable to satellites, the need to allocate a portion of the 

overall performance objectives gave rise to the concept of a 

"satellite equivalent distance" (SED) that could be assigned to 

the satellite HRDP. 

The value of this hypothetical distance was determined from 

a study of real situations and HRXs. These studies resulted in 

a distance of 10,000 km for a "traffic weighted" SED and 13,000 

km based on examinations of actual international busy hour 

traffic. Both of these values are close to the 12,500 km figure 

currently allocated to a FSS HRDP in CCITT Recommendation G.821. 

Models involving two satellite hops were also studied. The 

use of dual satellite hops may lead to problems in user 

acceptance due to propagation delay and network synchronization 

due to variations in delay. Connections of this type should 

therefore only be used in exceptional cases were alternatives are 

not practical. The number of satellite hops, including those 

involving inter-satellite links, continues to be studied by the 

CCIR. 

31 
The study of satellite HRDPs continues to be important 

because of the rapid evolution in the design and application of 

satellite networks. Trends towards the use of smaller earth 

stations have resulted in decreasing terrestrial distances from 

the earth station to the end user. Consequently, different 

performance allocations may need to be considered in these cases. 

C. CCIR Report 997: Satellite Characteristics in ISDN 

Providing the basis for and supporting Recommendation 614 

(above), this report, ltCharacteristics of a Fixed-Satellite 

Service Hypothetical Reference Digital Path Forming Part of an 

Integrated Services Digital Network," first appeared in the CCIR 

1986 "Green Book". A draft revision of the report, including new 

material on various topics which bear on the development of ISDN 

performance criteria, was prepared by IWP 4/2 of the CCIR and 

presented at their meeting in Tokyo in April of 1987. 

The report provides some insight into the ISDN HRX requirements as specified in Recommendaiiun G.52;. IIGpw~ 997 

translates the performance requirements in G.821 into terms 

useful to a satellite system designer and provides the necessary 

background information. In addition, it describes the method 

that has been used for converting from the CCITT specification to 

the form of performance objective used for satellite systems, and 

gives the satellite HRDP performance requirements that result 

from applying this method to the values quoted in Recommendation 

G.821. Report 997 notes that, "...the performance of a satellite 

I any performance specification. However, the use of forward error 

correction, power control and site diversity which can significantly improve system performance has penalties of decreased 

capacity and/or increased cost. 

therefore requires suitable justification.11 

n----C 

, digital transmission channel can be designed to meet virtually I 

The use of43uch techniques 

Report 997 then goes on to discuss other technical aspects 

affecting the performance of satellites in the ISDN. 

I 1. Availability 

The performance objectives of G.821 apply only when a link 

is considered to be available. Availability can be affected by 

atmospheric conditions (e.g. heavy rain) causing high bit error 

rates. The generally accepted definition of unavailable time, as 

stated in Report 997, is: 

A period of unavailable time begins when the it error 

rate (BER) in each second is worse than 1x10-3 for a 

period of 10 consecutive seconds. These 10 seconds are 

32 
considered to be unavailable time. The period of 

unavailable time terminates when the BER in each second 

is better than 1x10'3 for a period of 10 consecutive 

seconds. These 10 seconds are considered to be 

available time and would contribute to the severely 

errorred second performance objective. Excessive BER 

is only one of the factors contributing towards the 

total unavailable time. Definitions concerning 

availabslity can be found in CCITT Recommendation 

G.106. 

2. Error Causing Mechanisms 

error in digital satellite systems. The NASA Propagation Program 

has played a fundamental role in understanding such adverse 

effects.44 The wide bandwidths available at higher frequencies 

make them attractive for high-capacity digital systems, but rain, 

clouds, and atmospheric gases tend to degrade Earth-space 

transmissions severely with increasing frequency. 

Propagation and interference effects are major causes of 

CCIR Report 997 provides information on error mechanisms 

other than propagation and interference. The following error 

causing mechanisms have been identified: 

- signal path switching in earth-station IF and RF 

- signal path switching in earth-station baseband equipment; 

- power supply transients at earth stations; 

- signal path switching in the satellite. 

equipment; 

Estimates of the frequency and duration of error bursts due 

to the above mechanisms can be found in Annex I11 of Report 997. 

3. Interference and Sharing Constraints 

fixed-satellite service were obtained from CCIR recommendations 

written for systems using pulse code modulation (PCM) for 

telephony (non-ISDN). Depending on the method used to improve 

performance (e.g. higher output power per channel), the improved 

performance levels required of ISDN satellite connections can 

cause higher levels of interference into other FSS networks and 

represent a higher percentage of total noise than anticipated for 

satellite circuits designed to meet CCIR recommendations. One 

study refered to in Report 997 indicates that the level of 

interference caused by radio-relay and fixed-satellite service 

systems will account for 34% of the total noise at the input to 

systems forming part of an ISDN. Further difficulty with the 

effects of interference is anticipated in that many systems are 

expected to be constrained by the severely errorred seconds 

performance standard. 

Prior to G.821, performance standards for systems in the 

33 
The CCIR further believes that urgent and extensive study of 

the effect of interference on satellite ISDN connections is 

necessary and that new recommendations relating to allowable 

interference into ISDN satellite circuits may need to be 

developed. Propagation plays an important role in interference. 

Tropospheric ducts and scatter from precipitation are the two 

most important propagation phenomena contributing to 

interference. 

4. Error Performance at Higher Transmission Bit Rates - 

The error performance objectives currently specified by the 

CCITT and CCIR are based on a communications channel operating at 

the standard 64 kbit/s rate. It is necessary to consider how 

these objectives can be applied to higher transmission rates. A 

method for translating the BER criteria to transmission rates 

higher than 64 kbit/s is proposed in Annex IV of Report 997. 

This matter will be the subject of further study within the CCIR. 

D. Echo ~ and Delay in Satellite Communications 

High altitude communication satellites, such as those in 

geostationary orbit, are often subject to criticisms directed at 

ezhz and delay associated with satellites. 

It is well known that the effect of echoes in voice 

communications, when accompanied by a substantial transmission 

delay, can be detrimental to the quality of communications. In 

data communications as well, the propagation delays imposed by 

satellite connections may require special considerations. Yet 

there are techniques available today that effectively deal with 

the adverse effects of echo. 

The results of subjectid8 tests performed by AT&T45 and the 

TransCanada Telephone System provide substantial evidence that 

through the proper use of echo control devices, voice 

communications carried via satellite can be equivalent in 

quality to those carried by terrestrial-based radio and cable 

systems. 

The problems associated with long transmission delays in 

certain data communication applications can be minimized through 

the use of protocols that effectively compensate for the delay. 

The principal recommendations concerning limitations on 

propagation delay and the appropriate use of echo control devices 

are contained CCITT Recommendation G.114. 

34 
1. CCITT Recommendation G.114: Limits on Propagation Delay 

and Use of Echo Control Devices 

G. 114 states: 

"The times in this Recommendation are the means of the 

propagation times in the two direction of transmission 

in a connection. When opposite directions of transmission are provided by different media (e.g. a 

satellite channel in one direction and a terrestrial 

channel in the other) the two times contributing to the 

mean may differ considerably.I? 

1. Limits for a connection 

It is necessary in an international telephone 

connection to limit the propagation time between two 

subscribers. As the propagation time is increased, 

subscriber difficulties increase, and the rate of 

increase of difficulty rises. As a network performance 

objective, the CCITT therefore recommends the following 

iimitation on mean one-way propagation iimea wiiari echo 

sources exist and appropriate echo control devices, 

such as echo suppressors and echo cancelers, are used: 

a) 0 to 150 ms, acceptable; 

b) 150 to 400 ms, acceptable, provided that increasing 

care is exercised on connections when the mean 

one-way propagation time exceeds about 300 ms, and 

provided that echo control devices, such as echo 

suppressors and echo cancelers, designed for 

long-delay circuits, are used; 

c) above 400 ms, unacceptable. Connections with these 

delays should not be used except under the most 

exceptional circumstances. 

The Recommendation continues: 

2. Values for circuits 

2.3 International Circuits: 

The magnitude of the mean ne-way propagati 

for circuits on high altitude communication 

n time 

satellite systems makes it desirable to impose 

some routing restriction on their use. Details of 

these restrictions are given in Recommendation 

4-13. 

35 
And, from the conclusion of Annex A to the Recommendation: 

In public telephone networks, only connections 

which do not contain more than one satellite hop 

should be permitted. Two hops can only be 

tolerated in special cases. Connections with more 

than two hops are totally unsuitable for 

telephony. 

The fact that this Recommendation suggests limitations on 

the mean values for one-way propagation times is significant and 

implies certain limitations on the use satellites. 

When used to carry transmissions for both directions of a 

connection, the use of satellites would be limited to one 

up-link, one down-link, and one intersatellite link. The use, 

for instance, of a satellite link to carry the international 

portion of a call, combined with another satellite in the 

domestic long-distance network, would be prohibited. This does 

not mean, however, that a double-hop satellite link is always 

prohibited. For example, if a double-hop satellite link is used 

for transmission in one direction, and a ie~~e~t~i~l ohannel i: 

the other, the limitations on mean one-way propagation time can 

be met. This is effective because the total round-trip time is 

significant, not only the one-way delay. 

2. Implications for Data Communications 

Communication system designers must take the delay 

characteristics of satellites into account when establishing 

timing limits on acknowledgements, handshaking*, count-down 

timers, etc. These limits must not be less than some reasonable 

minimum amount of time required for the transmission of data via 

satellite. A reasonable value might consist of: a) the best case 

minimum propagation time possible with satellites (earth stations 

in close proximity); b) some time for additional transmission 

delay due to earth stations located far apart from each other; 

c) some small allowance for variations in transmission delay due 

to orbital perturbations; d) some allowance for an intersatellite 

link; e) some allowance for on-board switching or signal 

processing; and f) some allowance for the delay encountered in 

terrestrial-based switching and transmission facilities. Items b) 

*"Handshakingvt describes a mode of communication between two 

electronic devices. One device sends a signal (extends its hand) 

to a second device in an effort to initiate communications. If 

the second device does not assert the appropriate response 

(extends its hand to the first device) within a specified amount 

of time, the communication is terminated. 

36 
through f) above will be relatively small compared with the 260ms 

single-hop one-way transmission delay and may not be applicable 

in all cases but must be taken into account. 

In the ISDN, the communications protocols are currently 

being designed around the seven-layer Open Systems 

Interconnection (OSI) reference model. Complete specifications 

for the OS1 model are currently undergoing development within 

the ISO. At this time, it appears that the protocols can be made 

to accommodate satellites in compliance with the OS1 model. It 

is essential, however, that the interests of the satellite 

industry be represented, through continued participation in the 

appropriate standards making bodies, to ensure total 

compatibility with developing protocols and standards. 

Therefore, a thorough understanding of the standards making 

process (as discussed in Chapter VII) is essential in forming an 

ISDN environment receptive to a strong satellite presence. 

E. Areas for Further Study 

In setting an agenda for study, the CGlH nas listed a 

number of areas. 

three general areas for study: 

Contained in4question 29/4, for example, are 

(1) What are the preferred satellite system characteristics 

significant for digital transmission networks? 

(2) What are the implications of multiple satellite hops and 

inter-satellite links on various types of digital services? 

(3) What are the optimum interface characteristics for the 

transmission of various kinds of digital traffic (e.g. telephony, 

television and data)? 

The CCIR has further recommended that a number of additional 

more specific studies should be conducted in areas such as: 

(1) determination of the impact that Low Rate Encoding and 

Digital Speech Interpolation might have on the characteristics of 

voice and data communications in digital satellite systems; 

(2) identification of the various points at which digital 

satellite systems might interface with a digital network and 

determination of the characteristics of such interfaces; 

(3) determination of availability and performance criteria (e.g. 

phase jitter, slips, bunched digital errors) at the relevant 

interfaces; and what coding/decoding techniques for error 

correction, if any, may be needed to meet the performance 

criteria; 

37 
(4) determination of how best to accommodate elastic buffering 

to compensate time delay variations due to satellite movement; 

(5) determination of the impact, if any, of ISDN services on 

satellite system design; 

(6) determination of satellite system characteristics which are 

of significance for data transmission and the similarities with, 

and differences from, terrestrial networks; 

(7) the impact on current data networks or services of factors 

relating to satellite systems, in particular the transmission 

delay and its periodic daily variation; 

(8) solutions which might offset the potential unfavorable 

effects of satellite systems on existing data services; 

(9) error-correction systems better suited to data transmission 

by satellite (coordination with CCITT Study Group VI1 is 

required); 

( IUI the means of' integl%aiiiig sstellite systems izto 

international data networks; 

,--. 

(11) high-speed services that can be provided by satellite and 

are comparable with the facilities offered by terrestrial 

networks; 

(12) the effect of multi-destination and multiple access 

satellite characteristics on data network topology; and 

(13) determination of the extent to which ~atellit~~system design 

may need to take account of OS1 layered protocols. 

F. Summary Technical Aspects 

any international connection that is part of an ISDN whether or 

not satellites are involved. CCIR Recommendation 614 establishes 

the performance objectives for satellite systems forming part of 

an international connection in an ISDN necessary to comply with 

the overall quality standards required by CCITT Recommendation 

G.821. Report 997 provides supporting material to Recommendation 

614. CCITT Recommendation G.114 sets generally applicable 

standards for echo and delay which satellites must meet and which 

present a challenge to satellite designers. 

CCITT Recommendation G.821 sets performance standards for 

These recommendations have been formulated to serve as 

guidelines in the design and planning of satellite communication 

systems. The constraints on system design imposed by these 

recommendations do not appear to be overly stringent and could 

result in the realization of economical satellite systems 

38 
ensuring the role of satellites in the ISDN as it develops in the 

future. At the same time, it is clear that there remain numerous 

technical issues to be addressed. In seeking the appropriate 

role for satellites in ISDN, it will be important for the 

satellite community to be actively involved in meeting the 

current technical objectives (as contained in the above 

Recommendations and Reports) as well as to anticipate future 

technical requirements (as suggested by areas for future study). 

39 
VII. UNDERSTANDING THE STANDARDS PROCESS 

This section examines the ISDN standardization effort and 

the primary factors influencing its pace and direction. 

Standards for ISDN will define the system, determine 

equipment that can be used, and set protocols for use of the 

system: thus they are a critical part of ISDN and important with 

respect to the inclusion of satellites. The process itself is 

dynamic and still taking shape. Standards that are too rigid may 

delay adoption of the system while standards that are too loose 

may preclude the needed degree of integration. Early standards 

may freeze immature technology while late ones may face too many 

existing systems. It is important, therefore, to have a clear 

understanding of the process of standardization since it has a 

direct bearing on the utility of satellites in ISDN. 

A. CCITT as the Focal Point of International Activities 

The CCITT has had the responsibility of providing standards 

and operating guidelines for international telephony networks 

technology began to be implemented in the national networks of 

member countries participating in CCITT, the transition of 

telephone networks from analog to digital technology was a 

natural area for further study. As early as iy72, CCITT naa 

formulated two definitions describing this development: First, 

"An integrated digital network (IDN) is a network in which 

connections established by digital switching are used for the 

transmission of digital signals." The second definition read: 

since its inception. IA the 4nLn*- I)uv 3) as UAeAUUI A:-:t-l +msnamiaainn VAU.&VY.&Y-.--~-- 

An integrated services digital network (ISDN) is an 

integrated digital network (IDN) in which the same 

digital switches and digital paths are used tqg* 

establish connections for different services. 

With these initial definitions as a foundation, work 

continued throughout the 19701s, resulting in an expanded list of 

conceptual principles that were accepted at the 1980 Plenary 

Assembly. Study Group XVIII was created by the Plenary Assembly 

to carry this work forward, and to coordinate ISDN related work 

of other groups during the 1981-1984 Study Period. The other 

groups with a particular interest in ISDN are Study Groups VII, 

XI, and XVII. A complete list of CCITT Study Groups is shown in 

Table 2. 

* This definition has since been superceded by the definitions in 

Chapter I . 40 
SG-I : 

SG-11: 

SG-111: 

SG-IV: 

SG-V: 

SG-VI: 

SG-VlL: 

SG-VIII: 

SG-IX: 

SG-X: 

--- .

SG-XI: 

SG-XII: 

SG-XV: 

SG-XVII: 

Table 2 

CCITT Study Groups (SG), 1985-1988 Study Period5' 

Definition, operation and quality of service aspects 

of telegraph, data transmission and telematic services 

(facsimile, Teletex, Videotex, etc.) 

Operation of telephone network and ISDN 

General tariff principles including accounting 

Transmission maintenance of international lines, 

circuits and chains of circuits; maintenance of 

automatic and semi-automatic networks 

Protection against dangers and disturbances of 

electromagnetic origin 

Outside plant 

Terminal equipment for telematic services 

Telegraph networks and terminal equipment 

Languages and methods for telecommunications 

applications 

ISDN and telephone network switching and signalling 

Transmission performance of telephone networks and 

terminals 

Transmission systems 

Data transmission over the telephone network 

SG-XVIII: Digital networks including ISDN 

41 
As a result of intensive effort during the 1981-1984 Study 

Period, the I-Series Recommendations were created, establishing 

the general principles of ISDN, as well as detailed specifications of the user-network and internetwork interfaces (see 

pages 13-18). Building on the initial I-Series Recommendations, 

Study Group XVIII of the CCITT has continued to be the focal 

point for international ISDN standardization during the 1985-1988 

Study Period. Work within the Study Group for the current study 

period has been divided among eight Working Parties listed in 

Table 3. 

Table 3 

Study Group XVIII Working Pasties for the 

1985-1988 Study Period 

XVIII/l 

XVIII/2 

XVIII/3 

XVIII/4 

XVIII/Ej 

XVIII/6 

XVIII/7 

XVIII/8 

Service aspects 

NetworK aspects 

User-network interfaces, layer 1 

Architecture and models 

Maintenance and general aspects 

Performance aspects 

Transmission aspects 

Speech processing 

During the current study period, many of the interim 

standards which carried over from the 1981-1984 period have been 

enhanced and expanded. There has also been a considerable amount 

of work done on standards for broadband ISDN. Many of the more 

important draft Recommendations that have been completed are 

being submitted to an accelerated procedure for provisional 

approval prior to the 1988 Plenary Assembly. CCITT instituted 

this accelerated procedure to accommodate the fast changing 

na.ture of the technology and to allow completed Recommendations 

to be approved and put into use as needed between Plenary 

Assemblies which occur at four year intervals. 

In addition to participation by the more than 160 member 

countries of the ITU, CCITT enjoys participation from numerous 

recognized private operating carriers (RPOAs, e.g. ATAT), 

scientific and industrial organizations (SIOs, e.g., IBM) and 

international organizations (e.g.,Intelsat). As an incentive to 

participate, membership rates for these groups are only one-fifth 

those of member countries, resulting in the cooperation of 

42 
practically the entire telecommunications industry. Presently, 

there are 147 pufacturers and 56 network operators 

participating. This high level of industry participation is 

one of CCITT's greatest strengths, resulting in considerable 

influence in the international arena. 

Given this broad international support, and the potential 

ramifications of international standards developed by CCITT, many 

countries have established national standards organizations 

designed to follow the progress of CCITT very closely. In the 

U.S., this is done through ECSA's Tl committee which has the 

technical expertise, and a group, the YJ.S. CCITT", which 

coordinates various contributions from U.S. participants in an 

attempt to present unified U.S. positions at CCITT meetings. 

industry support that CCITT has on an international level. T1 

committee membership categories include: exchange carriers, 

inter-exchange carriers and re-sellers, manufacturers and 

vendors, and general interest, which includes government 

agencies, consultants, user groups and liaisons with other 

committees. The Tl committee currently has six taciiiilcal 

subcommittees, listed in Table 4. 

Within the U.S., the T1 Committee enjoys the same level of 

TlCl Carrier-CPE Interfaces 

T1D1 ISDN 

T1M1 Internetwork Operations, Administration, 

T1Q1 Performance 

TlX1 Carrier-Carrier Interfaces 

TlY 1 Specialized Subjects 

Maintenance and Provisioning 

Subcommittee TlDl is concerned with all aspects of ISDN, and 

prepares positions on ISDN matters for submission to the U.S. 

CCITT and other standards organizations. TlDl has three Working 

Groups : 

* The T1 technical subcommittees have since been restructured. 

TlCl and TlDl.3 have been merged to form TlEl. Similarly, TlX1, 

TlD1.1, and TlD1.2 now form TlS1. The net result has been to 

integrate ISDN across the subcommittee structure, indicating a 

further degree of growth in ISDN. 

43 
TlD1.1 - ISDN Architecture and Services 

TlD1.2 - Switching and Signalling Protocols 

TlDl.3 - Physical Layer 

Although the Tl committee is less than four years old, it has 

already assumed the position of the most important U.S. 

standards committee related to ISDN, with subcommittee T1D1 

leading this effort. 

B. The Influence of Other Standards Organizations on ISDN 

Given the large scope of ISDN standards development, the 

CCITT cannot and has not worked in isolation from other standard's 

organizations that are either directly or indirectly impacted by 

ISDN standards. The input of these other standards organizations 

has had an influence on the evolution of ISDN standards 

development. 

ISO's input regarding compliance with the Open Systems Interconnection rioaei (ua~ Xodeij are two exaiiigles ~f t~is icfluezce. 

CCIR's expertise in fixed satellite services and 

,--- 

As a result of cooperation between the CCITT and CCIR 

several recommendations have been changed to document explicitly 

the recognition of satellites as a possible component in the 

implementation of ISDN. This cooperation has been formalized by 

the creation of CCIR's Interim Working Party 4/2, and by liaison 

representation from CCITT. Good progress has been made, although 

not all of the issues have been resolved (see pages 54-57), and 

this working relationship is likely to be maintained as ISDN 

standards continue to evolve. 

In the case of the OS1 Model (which is in the domain of ISO) 

the CCITT has taken several steps to ensure that ISDN standards 

are developed in accordance with the concepts of the model. Most 

importantly, CCITT has taken ISO's International Standard #7498, 

which describes the OS1 Reference Model, redrafted it using its 

own terminology, and adopted it as standard of its own, known as 

Recommendation X.200. Aside from minor differences in 

terminology, these two standards are virtually identical. 

Consequently, CCITT is giving due consideration to how the OS1 

Model affects ISDN, since CCITT tries to coordinate all of its 

own standards so as to minimize contradictions or areas of 

conflict. 

Beyond procedural considerations, the ISDN standards 

themselves reflect an effort to fit ISDN into the OS1 Model 

wherever it makes sense to do so. For example, definition of 

user-network interfaces in ISDN comprise the first three layers 

Of the OS1 Model. Specific protocols, such as the LAP-D protocol 

for ISDN signaling on the D channel, conform closely to the 

44 
HDLC* protocol of the OS1 Model. 

The OS1 Model is evolving in much the same way that ISDN 

standards are evolving, and there will be a continued mutual ---- 

influence between the two efforts in the future. Formal liaison 

agreements now in place should facilitate the necessary exchange 

of planning and technical information so that this parallel 

evolution could take place in a smooth and efficient manner, and 

so that the evolution for both systems would be complementary. 

C. The Debate over Dominant Vendors 

Dominant vendors (i.e., AT&T, IBM) obviously have an 

interest in the standards process. There is however, some debate 

over the degree of influence they may have vis-a-vis small 

vendors. 

One the one hand, there has been some concern that large 

companies with dominant positions in the marketplace may exert 

undue influence because they are able to send more people to more 

meetings, thus ensuring that the company's interests are 

expressed and protected. In addition, tne larger, estabiisned 

companies may enjoy an advantage due to the de -- facto standard 

which their product already may have set in the market place. 

On the other hand, the potential for undue influence 

appears to be largely neutralized through the voting structure of 

committees like CCITT and T1, which allow only one vote per 

vendor. In some cases, such as AT&T and GTE, two votes are 

allowed; one as a network provider and one as an equipment 

manufacturer. However, there is no weighted voting process built 

into the system and thus a small vendor's vote counts the same as 

a large vendor. 

D. The Role of the ITU 

Once a particular question or project comes to the ITU for 

study, a determination must be made as to which Consultative 

Committee and which Study Group or groups should be involved. 

In determining which organization should be responsible for 

which areas of standardization, differences are resolved at a 

high level between the administrations of the standards 

organizations, presumably with a certain amount of negotiation 

and compromise. Although all of the organizations involved in 

this activity have an international scope, the ITU is the only 

* HDLC- High Level Data Link Control. A bit-oriented 

synchronous transmission protocol defined at the data link layer 

of OS1 model. See page 9 for layers of the OS1 Model. 

45 
organization established by formal government-to-government 

treaty; both IS0 and IEC may defer to the decision of the ITU in 

areas where national governments are directly involved. 

Within both CCITT and CCIR, questions and projects are 

assigned to study groups at the Plenary Assembly which takes 

place every four years. At the study group level, working 

parties follow ITU procedures for the submittal of 

I1contributionsn to the full study group. Consensus must be 

achieved among the working group doing the work before draft 

recommendations can be passed up for approval by the Study Group 

and ultimately by the Plenary Assembly. 

E. Interpretation and Implementation of Standards 

standard can lead to problems of interpretation and 

implementation. Reconciliation at this stage often occurs 

outside the context of the standards-making body that produced 

the standard. 

Ambiguity in the language or various options written into a 

The problem of interpretation and implementation is being 

addressed in the U.S. and in Europe. The Corporation for Open 

Systems (COS), in conjunction with NBS, is working to establish 

common interpretations of standards so that their full benefit 

can be realized by users, carriers and equipment manufacturers. 

In Europe, the common market has passed a nrecommendationtl (not 

to be confused with CCITT Recommendations) which defines 

deadlines and specifications of what services will be offered 

throughout the 12 countries that comprise the European ComTwnity, 

to encourage the introduction of a single version of ISDN. 

Prior to the Parliamentary recommendation, each European PTT 

would comply with international standards for connecting 

networks, while implementing country-specific user interfaces and 

services not specified by the standards. This was done 

intentionally to maintain relationships with preferred equipment 

suppliers. Although the PTTs favored the old approach, 

multinational users in Europe found the practice very frustrating 

and expensive. 

The European shift towards standardized user interfaces is 

in marked contrast to the ongoing struggle to include a 

specification for the rtUtl reference point interface into the 

CCITT Recommendations for ISDN. The essence of the problem is 

shown in Figure 2. 

46 
FIGURE 2 

DRXXXAE PAGE IS 

OF POOR QUALITY 

Curtour Prcnires 

SERVICE PROVIDER 

IIt**t~tI*t*IIt*t**tII t*t*ItI**t*I*t****tIt*ttttl 

8 m 

Dircc TE1 Inter t acc 140KBIT/S (2E+D) ! I I# I 160KBIT/S~ 

(R-Reference (S-Rrfrrmcr) 

Point ) Point ) 

ll CENTRAL 

I OFFICE LINE 

TERMINALS 

REFERENCE I REFERENCE 

1 

PO I NT 8 POINT I 

~ FCC DEFINED CPE 

ISDN User-Network Interface Reference Model showing the location of the 

U Reference point. 

by most countries. 

Equ i pment boundary. 

Asterisk line denotes ISDN network boundary as interpreted 

Solid line denotes FCC-defined Customer Premises 

46a 
As a result of an FCC ruling, in the U.S. competitive 

telecommunications marketplace the network termination equipment 

(NT1) is considered to be customer premises equipment and not 

part of the network. Consequently, there is a need to standardize 

the U interface on the network side of the NT1 for the U.S. 

market. In virtually every other country in the world, the NT1 

is considered part of the network and is owned by the service 

provider, not by the customer. The interface between the central 

office nd the NT1 is therefore not subject to ISDN Recommenda- tions. 53 

The U reference point interface is a good example of the 

importance that a particular standard can have and how, subject 

to interpretation, a part or parts of a network can be considered 

either subject or not subject to applicable Recommendations. 

47 
VIII. ENSURING A ROLE FOR SATELLITES 

If satellites are to play an important role in ISDN, there 

are several steps that can be taken now. These can be broadly 

grouped into four categories: 1) obtaining the necessary space 

resources; 2) meeting the technical challenges; 3) impacting the 

standards process; and 4) promoting the technical and operational 

advantages of satellites to users. 

A. Obtaining the Necessary Space Resources 

Space resources, in this context, includes pri-marily both the 

appropriate bands of radio frequencies that permit the 

transmitting signals to satellites and re-transmitting the 

signals to ground receivers and the appropriate geostationary 

orbital positions in which to station communication satellites. 

Making certain that the necessary radio frequencies are allocated 

to the various satellite communication services is only one part 

of the challenge facing satellites. Obtaining the right to use 

frequencies in the allocated bands, and the accompanying 

geostationary orbital position, without suffering harmful 

interference from other satellite communicaiiuri systems is 

another area of importance concerning resources. 

For governmental or private entities that intend to provide 

a satellite communication system, the process of obtaining 

resources has two parts, both of which are important to 

understand. 

First, the right to use the space resources in question must 

be recognized and approved by an agency of the userls own 

government. Second, the use of the space resource must be 

recognized by an agency of the International Telecommunication 

Union, the International Frequency Registration Board (IFBB). 

Two different procedures for obtaining this right to use 

certain frequencies and the associated geostationary satellite 

orbital position have evolved: the first-come, first-served 

procedure and the a_ priori procedure. The first-come, 

first-served approach is based on national telecommunication 

administrations notifying the ITU's International Frequency Board 

of frequencies to be used by domestic radio stations if: 1) the 

frequencies in question are capable of causing harmful 

interference to any other radio service; 2) the frequencies are 

to be used for international communication; or 3) the 

administration desires 11t05Bbtain international recognition of 

the use of the frequency." This process is still the 

prevailing rule though there has been continuing pressure from 

the developing world for an a priori assignment process. Such an 

approach, if adopted by the ITU, would involve the allotment of 

space resources to countries according to a pre-arranged formula, 

perhaps through the medium of a formal treaty. 

48 
Assured access to necessary space resources is an obvious 

prerequisite if satellites are to play a role in ISDN. The next 

ITU World Administrative Radio Conference at which the allotment 

process will be discussed and possibly altered, will be held in 

1988. With respect to satellites in ISDN, this is the forum 

within which the "raw resources11 for satellite operations will be 

determined. Thus, the importance of the process of allocation 

cannot be over-emphasized for without these base resources, 

satellites will have no firm foundation for a future within ISDN. 

Two additional resource areas are worth noting. First, 

satellite operators must be able to launch and correctly orbit 

their satellites. Availability of launch services and related 

support (including insurance) cannot be ignored as a resource 

issue. Second, operators will be faced with the increasing 

potential for damage by space debris. These two real problems 

are outside the scope of the present report but neither can be 

overlooked as an issue. 

B. Meeting the Technical Challenge 

A vitally important part of encouraging a role for 

satellites in ISDN will be the ability to meet the technical 

challenges that evolving standards may pose. As a point of 

departure, the list of CCIR "Areas for Further Study?! presented 

earlier in this report (see pages 37-38) should be fully studied. 

Though this initial list may not be comprehensive, it does 

illustrate the scope of technological efforts needed to ensure a 

role for satellites in ISDN. 

C. Impacting the Standards Process 

It is important for representatives of the satellite 

industry to expand and strengthen current efforts aimed at 

participating directly in the development of standards for ISDN. 

Impacting the standards process however, will require more than 

just organizational representation. 

The llSatellite Coalition & ISDNfl has already identified 

areas that need to be addressed if satellites are to impact the 

standards process more effectively. The coalition has identified 

the prominent standards-making bodies and agreed that their 

efforts should be focused on participation in the key national 

and international groups57in particular subcommittee T1Dl and 

CCITT Study Group XVIII. 

To be effective, the strategy of participation must be 

driven or guided by clear objectives, each aimed at enhancing the 

perceived value of satellites in ISDN. Part of the problem may 

stem from the lack of visibility of the satellite community in 

the definition of the network architecture and models of the 

ISDN. In an effort to enhance the recognition of satellite 

49 
capabilities in the ISDN a number of contributions were submitted 

to the CCITT meeting in July, 1987 suggesting modifications to 

appropriate ISDN-related recommendations in order to more 

adequately reflect the advantages of satellites in the ISDN 

(e.g., their natural point-to-multipoint ability, and the 

possibility of non-hierarchical networks with distributed earth 

stations extending to locations relatively close to the end 

user). 

successful but more are needed. 

The contributions were sysidered to be relatively 

Two other standardization efforts paralleling the 

development of ISDN that require particular attention are the 

OS1 reference model and Signaling System No. 7. 

The OS1 reference model is an architecture that describes 

how data communications protocols should be structured. The OS1 

model is well on its way to becoming an internationally accepted 

standard, along with the HDLC protocol. It was noted by the 

coalition that while presently, both the OS1 reference model and 

Signalling System No. 7 can be made to be essentially satellite 

compatible, attention must be given to assure that they continue 

to remain so. For example, only the first tilret: UP the OS1 

modelts seven layers are well defined. As the other layers are 

defined, principally under the direction of users, cyje should be 

taken to ensure their compatibility with satellites. 

Signaling System No. 7 is the common channel signaling 

system that will be an integral part of ISDN. The system as 

designed should work well with both land-based and satellite 

links, provided that the delay characteristic of satellites is 

taken into account when the transport protocols are established. 

A member of the satellite coalition commented that in the videoconferencing area, a move towards certain standards, including 

standards for delay, could discriminate against satellites. The 

coalition has agreed to monitor these developments in an effort 

to ensure ful&Ocompatibility between satellites and Signaling 

System No. 7. 

An important underlying issue that the satellite and ISDN 

coalition has identified is that satellite communications suffers 

from a poor public image - primarily in regards to echo and 

delay, security, and overall transmission quality. Though the 

use of echo cancelers and other advances in technology can be 

successful in solving the fundamental problems of echo and noise, 

this is generally not perceived as such by users. This Itimage 

problem" has been seen by many members of the satellites and ISDN 

coalition as the most serious obstacle6qacing satellites in their 

attempt to assume a full role in ISDN. 

The coalition has taken some specific steps towards meeting 

the challenge of ISDN. They have, for example, agreed that the 

collection of additional data on satellite echo and delay would 

50 
be helpful and that further studies on rrpurelt delay (without 

echo) may be required. They further agreed that a public 

relations campaign emphasizing the positive aspects of 

satellites, including their flexibility and digital transmission 

capabilities, would be beneficial in strengthening the image of 

satellites held by users and systems planners. In addition, 

the need for better studies of the relative strengths of fiber 

optic vs. satellite has been recognized. 

D. Promoting the Use of Satellites 

In order for satellites to enjoy widespread acceptance and 

application in an ISDN world, they must do more than merely 

achieve technical compatibility with ISDN standards. The 

satellite industry should strengthen efforts aimed at promoting 

the inherent operational, technical, and economic strengths that 

satellites have over fiber optic and other terrestrial-based 

communication systems. A strategy of promoting the use of 

satellites can be built around areas where satellites are 

competitive or have a distinct comparative advantage. These 

would include, but may not be limited to: 

-- point-to-multipoint communications. 

-- high quality, high capacity international point-topoint communications. 

-- thin-route applications for low volumes of traffic. 

-- mobile-satellite communications and related 

applications such as RDSS (Radio Determination 

Satellite System)*. 

-- inherent flexibility that can be used to adjust 

network configurations dynamically or to accommodate 

sudden increases in demand for transmission capacity. 

-- the fact that satellite networks are easily and 

quickly implemented. If the proper satellite is in 

operation and available a system can be brought on 

line almost immediately after installing the necessary 

earth station user equipment. 

-- the ability, through VSATs, to bypass local telephone 

company access charges. 

* RDSS allows the tracking of, and message dispatch to, mobile 

fleets that may be air, land, or sea-based. 

51 
-- satellites are only system today that can offer a 

capability for global connectivity in ISDN. 

-- broadcast 

52 
IX. SUMMARY AND IHPLICATIONS FOR NASA 

The National Space Act of 1958 gives NASA broad statutory 

authority to engage in space applications research and 

development. Section 102(c)(5) of the Act calls for NASA to 

preserve 'Ithe role of the United States as a leader in 

aeronautical and space science and technology and in the 

application thereof to the c@duct of peaceful activities within 

and outside the atmosphere." In addition, The President?s 

February 1988 National Space Policy clearly supports NASA's 

institutional role in assisting commercial efforts in space as 

long as direct subsidies are not involved. These two instruments 

give NASA the authority to do space applications related to ISDN. 

How that authority can be used to define an effective role for 

NASA in ISDN is addressed here. 

Efforts aimed at an Integrated Services Digital Network 

global telecommunication system are currently underway on various 

national and international levels. To some extent, ISDN is 

still a concept though some significant pilot projects have been 

initiated, plans are being made, and detailed discussions on the 

expected standards have already taken place. Within this 

setting, the future role of satellites in ISDN is being determined. 

ISDN per se is not a threat to the satellite communications 

industry; optical fiber is the technology that could take much of 

the business. However, ISDN -- apparently a neutral concept -- 

could be the tool used to give traffic to optical fiber at the 

expense of satellites. As part of its statutory role to support 

the application of space technology, NASA should work towards 

ensuring that satellites evolve in parallel with ISDN and that 

appropriate standards are developed. 

moving to add the Advanced Communications Technology Satellite 

(ACTS) to that record. However, NASA may be entering a new era 

in which (i) funds for major flight projects will be hard to 

find; and (ii) the communications program is being given a new 

mission -- helping science and applications programs. It is thus 

important that a new selective strategy be developed -- a 

focused effort -- through which the agency may best achieve its 

various goals synergistically. 

NASA has a history of successful flight projects, and is 

The "Satellites and ISDN Coalitionff is potentially a key 

actor for its existence gives NASA a place to interact strongly 

and effectively with industry while remaining within the proper 

role for a government agency. 

independent but complementary, mutually reinforcing programs to 

ensure that satellites have their proper place. 

The coalition and NASA can have 

Three kinds of activities seem appropriate in a program to 

support satellite communications: They could be called technical, 

53 
supporting, and liaison. All of these will interact, e.g., the 

results of technical activities might determine which supporting 

activities are carried out, and be disseminated through liaison 

activities. 

Technical activities would include attacking the problems 

listed on pages 33-34 of this study, perhaps by putting 

experiment packages on NOAA or DoD satellites. There is also a 

need to review the situation to see if other technical problems 

have become more pressing. Experiments need to be conducted to 

test the feasibility of proposed standards. In addition, field 

trials involving satellites and ISDN must be supported. Such 

research may reveal that new technology needs to be developed. 

In all these activities (i) ground equipment should be 

considered, perhaps even more strongly than satellites; and (ii) 

the use of ACTS should be considered. 

Supporting activities encompass those activities needed to 

make the standard setting process work for satellites instead of 

being negative or neutral. This must involve active, strategic 

support of the whole process. For example, it is necessary first 

to know in detail the players and the timetable. Often the U.S. 

position taken to an international standard meeting is 

coordinated only at the last minute. In this situation it is 

easy for specific considerations -- for example, the need to 

account for satellite characteristics -- to be overlooked. Thus 

there is a need to convene meetings at the appropriate time to 

exchange information and develop consensus. There is also a need 

to attend and support meetings. The National Bureau of Standards 

for years has encouraged its staff to support voluntary standards 

organizations, for example by becoming the secretary to a 

committee; they have found this to be an effective way to 

advance their goals. Overall, in these supporting activities 

there is need for consultation and coordination with industry. 

Liaison activities can ensure a broadly coordinated effort 

in support of satellites. 

achieved through the ISDN coalition, if its membership remains 

broad, but more is needed. Specifically: (i) There is a need to 

coordinate with foreign space agencies. They should have an 

influence on their national PTTs which should in turn facilitate 

the adoption of international standards friendly to satellites; 

(ii) There is a need to work with other agencies interested in 

satellite communications, e.g., DoD and NOAA, and with other 

parts of NASA (Code T). It may be possible to use TDRSS for some 

technical activities. The DoD may be able to influence foreign 

defense ministries to support satellite-friendly standards. 

Some coordination with industry can be 

Overall, the goal is to selectively promote satellites where 

they are strongest, and if necessary to do the work to prove 

their strength and improve their image. There are two inherent 

54 
advantages to a NASA-ISDN strategy based on technical, 

supporting, and liaison efforts. 

flight projects are required in order to make significant nearterm progress on technical ISDN/satellite questions. Similarly, 

supporting and liaison are comparatively low-cost and low risk 

investments on NASA's part. 

First, the strategy is relatively low cost, e.g., no new 

The second advantage concerns NASA's traditional role in 

serving the communications satellite industry. The rapid pace of 

changes in the ISDN environment and the complexity of 

participants in the standards process has created a need for a 

focused source of information and support for satellites in ISDN. 

Fulfilling that role through technical, support, and liaison 

activities affords NASA a timely opportunity to take the 

initiative and reach out to effectively support the needs of the 

communications satellite industry. 

For NASA and the future of the communications satellite 

industry, ISDN can either be a problem or an opportunity. 

Failure to recognize and adapt to the changes of an ISDN world 

will clearly lead to problems for satellites. On the other hand, 

the question of ISDN and satellites creates a unique opportunity 

for NASA to effectively support the satellite communications 

industry and, from a broader perspective, assist in maintaining 

U.S. technological and economic preeminence in an emerging new 

field of communications. 

55 
GLOSSARY 

B. Channel: 64 Kbps. The basic user channel used to carry 

digital data. 

Cos: Corporation for Open Systems. An American organization 

whose main objective is to promote compatible 

implementation of standards for open systems. COS is not 

a standards making organization and works closely with the 

National Bureau of Standards. 

CCITT: International Consultative Committee on Telephone and 

Telegraph. An international committee established to 

promote standard for the development of telephone, 

telegraph systems and data networks, and to create the 

environment of interworking between the networks of the 

different countries of the world. This committee is set 

up under the International Telecommunication Union (ITU). 

CCIR: - International Consultative Committee on 

Radiocommunications. An international committee 

established to promote standards for the development of 

radio communication and set up under the International 

Telecommunication Union (ITU). 

D Channel: 16 Kbps (basic access) and 64 Kbps (primary access). 

Carries signaling information to control circuitswitched calls and is also used for packetswitching or low speed telemetry. 

ECSA: Exchange Carriers Standards Association. An American trade 

association and independent standards committee whose main 

objective is to develop and promulgate standards to enhance 

the existing nationwide telecommunications service and to 

encourage compatibility of carrier services. 

ECS: - European Fixed-Service Satellite System. A communication 

satellite system established by the Interim Eutelsat to 

provide service between fixed earth terminals. 

FSS: - Fixed-Satellite Services. 

HRDP: - Hypothetical Reference Digital Path. A CCIR digital model 

to assist in proper allocation of circuits. 

HRX: - Hypothetical Reference Connection. A CCITT digital circuit 

model which allows for extensive performance monitoring. 

IDA: Integrated Digital Access. The first step towards full ISDN, 

IDA permits uniform connection to telecommunications 

services. 

56 
- INS: Information Network System. INS combines ISDN with 

intelligent communication processing nodes, allowing a wide 

range of information and communication modes to be 

accommodated in a single network system. 

ISO: - International Standards Organization. An international 

committee whose main objective is to provide a standard for 

open systems architecture via a reference known as OS1 (Open 

Systems Interconnect), first published in November 1978. 

- ITU: International Telecommunication Union. A special agency of 

the United Nations whose main objectives are: 

1. The promotion of international cooperation for 

efficient use of telecommunication service; 

2. Creation of the widest possible public access to 

communications facilities; 

3. Coordination of activities between national interests 

in the telecommunication field. 

- TSnN: Tntegrated Services Digital Network. A planned worldwide 

telecommunication service that will use digital 

transmission and switching technology to support voice and 

digital data communication. 

IWP 412: Interim Working Party. A group within the CCIR, under 

Study Group 4, dealing specifically with fixedsatellite services operations and performance criteria. 

ss %7: Signaling System #7. A specification of the protocol 

and network for ISDN signaling, the SS #7 is a method 

of common channel signaling. 

IrU1* interface: The notion that a transmission line from the local 

telephone company is essentially interfaced with 

the customer premise as bare wires. 

57 
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58 
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59 
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60 
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1 . A.M. Rutkowski, !'Beyond Fiber Optics versus Satellites". 

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2. A.M. Rutkowski, Integrated Services Digital Networks. 

Artech House, Inc. Dedham, MA, 1985, p. xxi. 

3. Ibid. 

4. Ibid. 

5. See James Martin, Telecommunications and the Computer. 

Prentice Hall, Inc., 1976. See also Bellamy, John C., Digital 

Telephony, John Wiley and Sons, Inc., 1982. 

6. Richard C. Hansen, ItAT&Tts Digital Network Evolution." 

Proceedings, IEEE International Conference on Communications, 

October 1985, pp.120-128. 

- 

- 

7. See D.M. Cerni, Standards in Process: Foundations and 

Profiles of ISDN and OS1 Studies. NTIA Report 84-170. U.S. 

1984. 

8. Hal Folts, "Open Systems Standards." IEEE Network Magazine. 

Vol. 1, No. 1 July 1987, p.54. 

9. Ian M. Lifchus, "Standards Committee T1--Telecommunications.!? IEEE Communications Magazine. Vol. 23, No.1. January 

1985, p.34. 

10. R.D. Cass, "Quantifying ACTS Communication System 

Performance," 12th AIAA International Communication Systems 

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11. Kit Fung, "ISDN Standards and Issues." Telesis, Volume 13, 

No. 3, 1986, p.28. 

12. Irmer, op. cit., p.5. 

13. Theodor Irmer, "CCITT and the ISDN.II Proceedings, International Conference on ISDN and its Impact on Information 

Technolo Institution m7F- of Electrical Engineers. January 14-16, 

14. Fung, op. cit., p.26. 

15. H.K. Pfyffer, "Overview of ISDNII. Proceedings of the 1986 

IEEE International Communications Conference. Institute of 

Electrical and Electronic Engineers, Vol. 1, pp.ll.l.l-11.1.5. 

61 
16. A.M. Rutkowski, "ISDN After Brasilia: Part l.?? Telecommunications, April 1987, p.53. 

17. Fred K. Knight, ttCCITTts Director on the Evolution of ISDN." 

Business Communications Review, January/February, 1987. 

18. Paul Kemezis, "What Price ISDN? First Cost Details Bared." 

Data Communications, August, 1987. 

19. Ibid. 

20. Kemezis, 01. G., p. 51. AT&T is reportedly planning to 

offer ISDN services for a one time charge of $3,000-$4,000 in 

select test locations. See MIS Week, '?AT&T, a Little Late, 

Debuts ISDN PRI", (Vol. 9, Nompril 11, 1988, p.36. 

21. Richard K. Snelling and Katherine W. Kaplan, "Services and 

Revenue Requirements." IEEE Communications Magazine, March 1986. 

22. Ellis Booker, "A Look at Existing Trials and Whatvs in Store 

for 1988.l' Telephony, October 5, 1987. 

23. "This is Not a Test: Southern Bell Sells Home ISDN." Data 

Communications, October 1Y87. 

24. Adrian Morant, "ISDN in Europe: Trying it out in Germany." 

Telephone Engineer & Management, December 1, 1966. 

25. Trends of Change in Telecommunications Policy, OECD, Paris, 

1987- 

26. John Griffiths, "British Telecomm's ISDN Experience," 

Proceedings of the IEEE International Communications Conference, 

1986. 

27. S. Hashimoto, H. Ishikawa. and K. Ikimi, "INS Trial and 

Future Network Evolution in Japan." 

International Communications Conference, 1986. 

Proceedings of the IEEE 

28. INTELSAT Report, 1986-87. 

29. Joseph N. Pelton. "Joining the Global Village: Linking LowCost Domestic Satellite Networks in the Global ISDN." Statement 

of the International Telecommunications Satellite Organization. 

February 19, 1987, p.22. 

30. Minutes of the ISDN and Satellites Coalition Working Group. 

July 15, 1987. INTELSAT Headquarters, Washington, D.C. 

Attachment No. 1, p.2. 

62 
31. Minutes of the ISDN and Satellites Coalition, February 17, 

- 1987. Crystal City, VA. 

32. Minutes of the ISDN and Satellites Coalition Meeting, May 

29, 1987. INTELSAT Headquarters, Washington, D.C. 

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34. Minutes of the ISDN and Satellites Coalition Working Group, 

July 15, 1987. Crystal City, VA. 

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Cost Domestic Satellite Networks into the Global ISDN." 

Statement of the International Telecommunications Satellite 

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36. Report of IWP 4/2 to Study Group IV: Implementation of 

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Red Book, Vol. 111, Malaga-Torremolinos, 1984. 

39. CCIR Recommendation 614, "Allowable Error Performance for 

Hypothetical Reference Digital Path in the Fixed-Satellite 

Service Operating Below 15 GHZ when Forming Part of an 

International Connection to an ISDN." Green Book, Vol. IV, 

Dubrovnik, 1986. 

40. CCIR Report 997, "Characteristics of a Fixed-Satellite 

Service Hypothetical Reference Digital Path Forming Part of an 

ISDN." Green Book, Vol. IV, Dubrovnik, 1986. Revised, Tokyo, 

1987 . 41. CCIR Recommendation 579, "Availability Objectives for a 

Hypothetical Reference Circuit and a Hypothetical Reference 

Digital Path When Used for Telephony Using Pulse Code Modulation, 

or as Part of an ISDN Hypothetical Reference Connection." Green 

Book - (Fixed-Satellite Service), Vol. IV, Dubrovnik, 1986. 

42. CCIR Report 997, "Characteristics of a Fixed-Satellite 

Service Hypothetical Reference Digital Path Forming Part of an 

ISDN." Green Book. Vol. IV, Dubrovnik, 1986. 

43. Report 997, op. cit., p.70. 

63 
44. NASA, Science Review of the NASA Radio Propagation Program, 

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Subjective Evaluation of Echo Control Methods," Proceedings - 

IEEE National Telecommunications Conference, Vol. 3, 1979. 

46. J.A. Post and R.D. Silverthorn, "Results of a Subjective 

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Trunks," Proceedings - IEEE National Telecommunications 

Conference, Vol. 3, 1979. 

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Intearation of Satellite Systems into Digital Transmission 

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48. Ibid; IlStudy Programme 29A/4, "Interface Characteristics for 

International Digital Transmission Links in the Fixed Satellite 

Service.?I and, ?'Study Programme 29B/4, "Integration of Satellite 

Systems in Data Transmission Networks." 

49. Theodor Irmer. "CCITT and ISDN." Proceedings, 

International Conference on the ISDN ana its Impaci UI~ 

Information Technology. Institution of Electrical Engineers. 

January 14-16, 1985. 

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Committee. "List of Study Groups and Questions Under Study." 

Red Book, Vol. 1, VI11 Plenary Assembly, Malago-Torremolines, 

October 8-19, 1984. ITU, Geneva, 1985. 

51. H.K. Pfyffer, "CCITT News: Meeting of Study Group XVIII." 

Telecommunications Journal, Vol. 53, December 1986, pp.678-680. 

52. Eckart Hummel, "The CCITT." IEEE Communications Magazine, 

Vol. 23, No. 1, January 1985, pp.10-11. 

53. Ian M. Lifchus, "Standards Committee T1 - Telecommunications.!? IEEE Communications Magazine, Vol. 23, No. 1, pp.35-37. 

54. Peter Heywood, tvCommon ISDN Game Plan, Schedule Adopted by 

Major Nations in Europe." Data Communications, February, 1987, 

p.69. 

55. Pauline Boorsook, Marks the Critical Spot for User 

Interface to ISDN." Newsfront, DATA Communications, July 1987, 

p.84. 

56. See Radio Regulations, Edition of 1982, Art. 12 for most 

recent version of this process. 

64 
57. Minutes of the "ISDN and Satellites Coalition." Working 

Group, July 15, 1987, INTELSAT Headquarters, Washington, D.C. 

58. Ibid. - 

59 Ibid. 

60. Ibid. 

61. Ibid. - 

j 

I 

I - 

62. Space Law: Selected Basic Documents, Prepared for the 

Committee on Commerce, Science, and Transportation. United 

States Senate. 95th Congress, 2nd Session, 2nd ed., 1978. pp. 500. 

65