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Other Titles in the IFAC Proceedings Series AKASHI: Control Science and Technology for the Progress of Society, 7 Volumes ATHERTON: Multivariable Technological Systems BANKS & PRITCHARD: Control of Distributed Parameter Systems CAMPBELL: Control Aspects of Prosthetics and Orthotics Van CAUWENBERGHE: Instrumentation and Automation in the Paper, Rubber, Plastics and Polymerisation Industries CICHOCKI & STRASZAK: Systems Analysis Applications to Complex Programs CRONHJORT: Real Time Programming 1978 CUENOD: Computer Aided Design of Control Systems De GIORGO & ROVEDA: Criteria for Selecting Appropriate Technologies under Different Cultural, Technical and Social Conditions DUBUISSON: Information and Systems ELLIS: Control Problems and Devices in Manufacturing Technology 1980 GHONAIMY: Systems Approach for Development (1977) H AASE: Real Time Programming 1980 HAIMES & KINDLER: Water and Related Land Resource Systems HARRISON: Distributed Computer Control Systems HASEGAWA: Real Time Programming 1981 HASEGAWA & INOUE: Urban, Regional and National Planning — Environmental Aspects HERBST: Automatic Control in Power Generation Distribution and Protection ISERMANN: Identification and System Parameter Estimation ISERMANN & KALTENECKER: Digital Computer Applications to Process Control JANSSEN, PAU & STRASZAK: Dynamic Modelling and Control of National Economics LAUBER: Safety of Computer Control Systems LEONHARD: Control in Power Electronics and Electrical Drives LESKIEWICZ & ZAREMBA: Pneumatic and Hydraulic Components and Instruments in Automatic Control MAHALANABIS: Theory and Application of Digital Control MILLER: Distributed Computer Control Systems 1981 MUNDAY: Automatic Control in Space NAJIM & ABDEL FATTAH: Systems Approach for Development 1980 NIEMI: A Link Between Science and Applications of Automatic Control NOVAK: Software for Computer Control O'SHEA & POLIS: Automation in Mining, Mineral and Metal Processing OSHIMA: Information Control Problems in Manufacturing Technology (1977) RAUCH: Control Applications of Nonlinear Programming REMBOLD: Information Control Problems in Manufacturing Technology (1979) RIJNSDORP: Case Studies in Automation related to Humanization of Work SAWARAGI & AKASHI: Environmental Systems Planning, Design and Control SINGH & TITLI: Control and Management of Integrated Industrial Complexes SMEDEMA: Real Time Programming 1977 SUBRAMANYAM: Computer Applications in Large Scale Power Systems TITLI & SINGH: Large Scale Systems: Theory and Applications Van WOERKOM: Automatic Control in Space 1982 NOTICE TO READERS Dear Reader If your library is not already a standing/continuation order customer to this series, may we recommend that you place a standing/continuation order to receive immediately upon publication all new volumes. Should you find that these volumes no longer serve your needs, your order can be cancelled at any time without notice. ROBERT MAXWELL Publisher at Pergamon Press

DISTRIBUTED COMPUTER CONTROL SYSTEMS 1982 Proceedings Tallinn, of the Fourth U.S.S.R., IF AC Workshop 1982 24-26 May Edited by R. W. GELLIE Commonwealth Scientific & Industrial Research Organization Division of Manufacturing Technology Fitzroy, Australia and R.-R. TA VAST Academy of Sciences of Estonian S.S.R. Institute of Cybernetics Tallinn, U.S.SR. Published for the INTERNATIONAL FEDERATION OF AUTOMATIC CONTROL by PERGAMON PRESS OXFORD NEW YORK TORONTO SYDNEY · PARIS · FRANKFURT

Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 OBW, England U.K. U.S.A. Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. CANADA Pergamon Press Canada Ltd., Suite 104, 150 Consumers Road, Willowdale, Ontario M2J 1P9, Canada AUSTRALIA Pergamon Press (Aust.) Pty. Ltd., P.O. Box 544, Potts Point, N.S.W. 2011, Australia FRANCE Pergamon Press SARL, 24 rue des Ecoles, 75240 Paris, Cedex 05, France FEDERAL REPUBLIC Pergamon Press GmbH, Hammerweg 6, OF GERMANY D 6242 Kronberg-Taunus, Federal Republic of Germany Copyright © 1983 IFAC All reproduced, form or by any means: electronic, mechanical, photocopying, permission in writing from Rights Reserved. stored in a retrieval system or transmitted No part of this publication may be in any tape, without electrostatic, recording the copyright magnetic or otherwise, holders. First edition 1983 Library of Congress Cataloging in Publication Data IFAC Workshop on Distributed Computer Control Systems (4th: 1982: Tallinn, Estonia) Distributed computer control systems 1982. (IFAC proceedings) 1. Automatic control Data processing —Congresses. 2. Electronic data processing - Distributed processing- Congresses. I. Gellie, R.W. II. Tavast, R.-R. (Raul-R.) III. International Federation of Automatic Control. TJ212.2.I34 1982 629.8'95 83-2388 British Library Cataloguing in Publication Data IFAC Workshop DCCS: {4th 1982: Distributed computer control systems 1982. — (IFAC Proceedings) 1. Automatic control Data processing Congresses 2. Electronic data processing- Distribution processing - Congresses I. Title. II. International Federation of Automatic Control. III. Gellie, R.W. IV. Tavast, R R . V. Series 629.8'95 TJ212 Tallinn) ISBN 0-08-028675-5 In order to make this volume available as economically rapidly as possible the reproduced in their original forms. has its typographical limitations way distract the reader. and as been authors' typescripts This method but it is hoped that they in no have unfortunately Printed in Great Britain by A. Wheaton & Co. Ltd., Exeter

FOURTH IFAC WORKSHOP ON DISTRIBUTED COMPUTER CONTROL SYSTEMS Organized by U.S.S.R. National Committee on Automatic Control Institute of Cybernetics, Academy of Sciences of the Estonian S.S.R. Tallinn Technical University Sponsored by IFAC Technical Committee on Computers Co-sponsored by IFAC Technical Committee on Education Wo^hop Chairman Academician B. Tamm International Program Committee R.-R. Tavast, U.S.S.R. (Chairman) V. G. Bochmann, Canada R. W. Gellie, Australia J. Gertler, Hungary T. J. Harrison, U.S.A. Th. Lalive d'Epinary, Switzerland L. Motus, U.S.S.R. K. D. Müller, F.R.G. S. Narita, Japan E. A. Trachtengerts, U.S.S.R.

PREFACE In published in the order in which they were presented. The discussions which took place were recorded transcribed. Some editing was done to improve clarity and avoid repetition but it is hoped that the text retains a sense of spontaneity. The concluded with a panel initial presentations by the panel members and the ensuing discussion included. these proceedings the papers are IFAC Workshops have proven to be a popular and effective forum for presentation and in-depth discussion of ideas by competent experts in emerging areas of automatic control. Indeed, the Workshops on Real Time Programming, which date back to 1971 and have been held annually since that time, have proved so successful that IFAC has published a special booklet "Guidelines for Organizers of IFAC Sponsored Workshops" to assist and encourage more events of this type. and subsequently Workshop session. program The are also The two papers by H.G. Mendelbaum, G. de Sablet., and Wu Zhimei, Zhang Wenkuan, Zhang Yingzhong, Cheng presented at the Workshop because authors were unable to attend. felt that their inclusion would add to the value of this volume. During his term as Chairman of the IFAC Computers Committee, Mr. Charles Doolittle established the Workshops on Distributed Computer Control Systems in recognition of the great interest and activity in this area. The first event in this series was held in Tampa, Florida subsequent events in Ste. Adele, Quebec (1980), Beijing, China Tallinn, Estonia in 1982. this series has been very successful in terms of quality of papers, numbers of participants, and the degree to which the attendees have contributed discusson and exchange of ideas. Yunyi were not the However we (1979) with (1981) and Every event in now I wish to gratefully acknowledge the part played by my co-editor, Raul Tavast, who performed the difficult transcribing and editing the discussions. task of to lively As participants attended by 75 experts from 14 countries. The quality of the papers presented and the discussions which followed may be judged by the reader. can be noted the from Tallinn the Workshop list of was R.W. Gellie. November 23, 1982. Fitzroy, Victoria, Australia. vii

LIST OF PARTICIPANTS IFAC 4th WORKSHOP ON DISTRIBUTED COMPUTER CONTROL SYSTEMS DCCS-82 Olympic Yachting Centre, Tallinn, Estonian S.S.R., U.S.S.R., 24-26 May 1982 C. Dimitrov Institute for Scientific Research in Telecommunications Haidushka Poljana str. 8 Sofia 1612 0. Aarna Tallinn Technical University Ehitajate tee 5 Tallinn 200026 USSR BULGARIA H. Aben Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 D.G. Dimmler Senior Scientist Brookhaven National Laboratory Upton. New York 11973 USA USSR A. Abreu Central Institute of Digital Research 198 No. 1713 Cubanacan Havana CUBA A. Divitakov ZNIKA str. I. Vishovgradsky 46, Room 608 Sofia BULGARIA Z. Apostolova State Committee of Science and Technology, ul. Slavjanska 8 Sofia BULGARIA V.N. Dragunova INEUM Moscow V-334 117812 GSP USSR T.O. Dzjubek Institute of Cybernetics Academy of Sciences Kiev USSR A. Ariste Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 USSR J. Ehrlich Technische Hochschule Leipzig Karl-Liebknecht-Strasse 132 DDR-703 LEIPZIG S.I. Baranov Institute for Analytical Instrumentation Sei. & Techn. Corp., USSR Academy of Sciences Prospect Ogorodnikova 26 198103 Leningrad W. Engmann Technische Hochschule Ilmenau DDR-63 Ulmenau-Ehrenbert USSR B. Becski Technical University of Budapest Visepradi u.30 W. Enkelmann Zentral institut für Hernforschung, Rossendorf 8051 Dresden, P.O. 19 DDR 1132 Budapest HUNGARY G. Bingzhen Research Institute of Electronical Technical Applications Beijing CHINA G. Evstratov Politechnical Institute Kharkov Frunze str. 21. 310002 Kharkov USSR J. Davidson Tecsult International Limite 85, rue Ste-Catherine Ouest, Montreal, Quebec H2X 3T4 CANADA A. Goscinski Institute of Computer Science Stanislaw Staszik University of Mining & Metallurgy al. Mickiewicza 30 30-059 Krakow POLAND DCCS - A* ix

List of Participants χ *,** T.J. Harrison IBM Corporation P.O. Box 1328 Boca Raton Florida 33432 J. Lukacs Central Research Institute for Physics P.O. Box 49, H-1525 Budapest HUNGARY USA U. Luoto Ekono Oy P.O. Box 27 SF-00131 H. Hetzheim Academy of Sciences GDR Helsinki FINLAND I.G. Ilzinya Institute of Electronics & Computer Systems Akademijas 14 Riga 6 226006 G.G. Mask Central Bureau of Statistics Endla 15 Tallinn 200105 USSR USSR * A. Inamoto Computer Systems Works 325 Kamimachiya Kamakura City Kanagawa Prefecture JAPAN 247 M. Mantseva State Committee of Science and Technology ul. Slavjanska 8 Sofia BULGARIA M. Martin Zentral institut für Kybernetik und Informationsprozesse Dresden 8027 Dresden Maeskelstr. 20 M. Maxwell Manager of Control Systems Colgata-Palmolive Co 105 Hudson St. Jersey City New Jersey U. Jaaksoo Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 USSR DDR H. Jinwei System Development Division of China Computer Technical Service Corporation Beijing CHINA USA K.A. Joudu Moscow Institute of Avionics Volokolamskoe 4 Moscow GSP 125871 I. Meiszterics Technical University of Budapest Vérhalom u.29 1025 Budapest USSR HUNGARY ** A. Keevallik Tallinn Technical University Ehitajate tee 5 Tallinn 200026 *,** L. Motus Institute of Cybernetics Akadeemia tee 21 Tallinn * S. Narita USSR 200026 USSR B. Kovacs Computer & Automation Institute Hungarian Academy of Sciences Kende u. 13/17 1111 Budapest *,* Electrical Engineering Dept. Waseda University 3-4-1 Okubo, Shinjuku-ku Tokyo 160 JAPAN L.F. Natiello HUNGARY K. Kralev State Committee of Science & Technology ul. Slavjanska 8 Sofia BULGARIA Exxon Research & Engineering Company P.O. Box 101 Florham Park V. Krüger Academy of Sciences GDR New Jersey 07932 USA D. Nedo Central Institute of Cybernetics & Information Processing Kurstr. 33 1086 Berlin GDR *,** K. Kääramess Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 USSR * M. Ollus Technical Research Centre Electrical Engineering Lab. VTT/SAH SF-02150'Espoo 15 * J. Lan Department of Computer Engineering & Science Qinghua University Beijing CHINA FINLAND

L i s t o f P a r t i c i p a n t s xi Ζ. Pengzu Lab. North-China Institute of Computing Technology Beijing CHINA V. Slivinskas Institute of Mathematics & Cybernetics K. Pozelos 54 Vilnius 232600 USSR A.A. Sternberg INEUM Moscow V-334 117812 GSP D. Penkin Soviet-Bulgar Institute Stambuli nskaja 62-64 Sofia BULGARIA USSR * G.J. Suski Lawrence Livermore National Laboratory P.O. Box 808, Li vermore California 94550 USA V.L. Pertchuk Institute of Automation and Control Processes Suhhanova 5A Vladivostok 690600 USSR * K. Takezawa Toshiba Fuchu Works - Toshiba Corp. 1, Toshiba-cho, Fuchu Tokyo 183 TOKYO B. Petkov Ministry of Communication Computing Centre Sofia BULGARIA K. Petrov State Committee of Science & Technology ul. Slavjanska 8 Sofia BULGARIA ** B. Tamm Tallinn Technical University Ehitajate tee 5 Tallinn 200026 USSR H. Tani Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 J. Pino Central Institute of Digital Research 198 No. 1713 Cubanacan Havana CUBA USSR ** R. Tavast Institute of Cybernetics Akadeemia tee 21 Tallinn 200026 W. Qinsheng Computer Industry of the Ministry of Electronical Industry Beijing CHINA USSR I. Tepandi Tallinn Technical University Ehitajate tee 5 Tallinn 200026 * M.G. Rodd University of the Witwatersrand 1 Jan Smuts Avenue Johannesburg 2000 USSR P. Tianchian Research Institute of Metallurgical Automation Beijing CHINA SOUTH AFRICA L. Rozsa Computer & Automation Institute Hungarian Academy of Science Kendue u. 13 Budapest 1111 *,** E.A. Trakhtengerts Institute of Control Problems Profsoyuznaya 81 Moscow V-279 HUNGARY 117806 USSR * S.M. Rotanov Institute of Electronics & Computer Systems Akademijas 14 Riga 6 226006 I.S. Ukolov Scientific Council of Cybernetics USSR Academy of Sciences 40, Vavilov str. 117333 Moscow USSR USSR I.M. Shenbrot Central Institute of Complex Automation Olhovskaya 25 Moscow B-66 107816 V.l. Utkin Institute of Control Problems Profsoyuznaya 81 Moscow V-279 USSR 117806 USSR A.V. Shileiko Moscow Institute of Railway Engineers F. Engels 36-25 Moscow B-5 107005 T. Vamos Computer & Automation Institute Hungarian of Academy of Sciencies P.O. Box 63 Budapest 112 USSR HUNGARY B.T. Shreiber Central Institute of Complex Automation Olhovskaya 25 Moscow B-66 107816 USSR

xii List of Participants L. Vohandu Tallinn Technical University Ehitajate tee 5 Tallinn 200026 K. Zielinski Academy of Mining & Metallurgy Institute of Computer Science al. Mickiewicza 30 30-059 Krakow USSR POLAND B. Werner VEB PCK Schwedt DDR-1330 Schwedt DDR * G.G. Wood Foxboro Yoxall Redhill Surrey RH1 2HL UK ** A. Work Institute of Cybernetics Akadeemia tee 21 Tallinn * Author ** Program/Organizing Committee 200026 USSR

WELCOME ADDRESS T. Vamos IFA C President sense, due to combinational explosion and due to randomness of parameters. It's nevertheless controllable as a coalition of autonomous system partners, which cooperate through a well-defined information and flow. Flow is understood as anything different from information, e.g. flow of energy, fluids, goods, people, etc. High information technology, high level exchange protocols, reliable well-organized system components are basic requirements and that's the reason why we had to wait until now for this revolution. Several earlier systems like international telephone exchange and some power systems started to realize these ideas long before they were formulated. It's my firm belief that for the future the idea of distributed cooperative systems will be the dominating control principle, for every large-scale system which intends to survive and develop. On behalf of IFAC Council I am happy to address this meeting not only because it is my duty and privilege but also because I can express my satisfaction with IFAC's directions of interest. To tell the truth, we would like to organize not only fashion directed meetings, but such ones which go somehow before the general fashion, which predict from the wel1-estimated trends, stimulate exchange experiences and after that summarise in order to something relevant community. network of transmission provide control to our If this symposium were the first of the distributed control series I would say did we sleep before? 1979 was just the right time to begin and, coming here, it is appropriate to speak about unsolved problems in more depth. about experiences Let me tell you some personal views on the topic which I consider to be even more revolutionary than is generally advertized. Distributed control significant in control decentralized control hierarchical centralized ones. IFAC itself is a cooperative system and it is appropriate to express our gratitude to those who cooperate in IFAC. of information, call for papers and people are organized by our forty organizations by voluntary, groups. Participation is free, without any kind of discrimination, independent of the transients of government policies. Our goals and aims are more global and more stable. is philosophy was after the much more than Distribution national non-profit Decentralized control is mostly a system which is really de-centralized: that means the system as a whole, handled as a black box, is a resolved and reorganized centralized one, not losing the strong central control but only delegating some tasks and some information to the lower subjugated levels. Thanks Committee of this Workshop that shaped the program which is of interest not only for those who could come here at this time, but for all people who look at IFAC's events for information and stimulation. to the International Program Distributed control is a much more liberal solution indicating a highly cooperative philosophy: a coalition of components arranged not hierarchically but in a very democratic coordinative centralization loses its rationality as we consider larger and larger systems, systems which have no rigorous physical limitations but can be augmented adaptively. A very big system is even theoretically uncontrollable in the old way. Any Thanks to the local organizers headed by Vice-President of IFAC, Chairman of our Technical Board, Academician Boris Tamm. or dissolved Soovin koige paremat. Soovin edu. Best wishes and big success. xvii

WELCOME ADDRESS Β . G. Tamm Workshop Chairman, Tallinn Technical University papers from among those submitted. should like to thank everybody who sent contributions and congratulate the authors of the papers selected for the Final Technical Program. I On Committee Committee I am glad to extend a sincere welcome to everybody participating in the 4th Workshop on Distributed Control Systems here in old Tallinn, behalf of the National and Organizing Program International Computer As you know IFAC is a society of volunteers consisting of specialists in automatic control who are ready to undertake personal efforts besides their everyday jobs, in order to promote science and technology. In this respect I should like to thank every member of IFAC, especially the Chairman, Raul Tavast, Tom Harrison, who has had a hand in all four of the workshops, and L. Trachtengerts, members from the USSR NMO, for their outstanding contribution to this IFAC event. Just recently I received two telegrams, one from Dr. W. Gellie, Chairman of the sponsoring committee of this workshop, IFAC TC on Computers, the other from Professor P. Larsen, Chairman of the co-sponsoring committee, IFAC TC on Education sending their best regards for the success of our workshop and asking me to transfer that to you. both Motus and E. Our workshop is already the fourth in the series of Distributed after those held in Tampa (1979, USA) Ste. Adele (1980, Canada) and Beijing (1981, PRC), so we ought to have some kind of experience. Computer Control Dear guests, I should also like to assure you that the volunteers from the Institute of Cybernetics, Academy of Sciences of the Estonian SSR and University have done their best to create a fruitful professional atmosphere as well as to ensure your joyful stay in Tallinn. Tallinn Technical Nevertheless the topic of our interest is developing dramatically and I know the hard efforts of the members of the International Program Committee in selecting the best xviii

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 SESSION 1 Chair: R.-R. Tavast SOFTWARE DESIGN FOR MULTIPROCESSOR SYSTEMS COMPUTER CONTROL Ε . A. Trakhtengerts and Yu. M. Shuraits Institute of Control Sciences, Moscow, USSR Abstract. The paper treats t h e specifies of t h e multiprocessor computer systems software d e s i g n , namely the d e s i g n of language m e a n s , translation a n d program parallelization m e a n s , operation systems a n d debug systems. Feasibility of parallel a n d serial program execution, the influence of the execution mode o n t h e useful performance of a computer system a n d t h e reduction of execution time f o r a group of tasks o r m e a n service time f o r a flow of queries are considered. K e y w o r d s . Multiprocessor computer system; parallel computations; automatic parallelization; program branch; usefulness of p a r a - llelization; multiprocessor computer system performance. problems pertaining to the design of parallel algorithms. INTRODUCTION The advent of multiprocessor c o m p u t - er systems capable of performing parallel computations p u t forward new requirements to t h e software w h i c h realizes control algorithms. These requirements m a y b e v e r b a l i z e d i n a single phrase : parallel p e r f o r - mance of t h e computer process. PART I 1. Language means The language means i n multiprocessor systems are intended f o r the o r g a n ! - zation of serial - parallel c o m p u t a - t i o n s . They differ f r o m the " t r a d i - t i o n a l " programming languages i n that they incorporate some additio- n a l u n i t s providing parallel r e a l i z a - t i o n of p r o g r a m fragments a n d i t s t i m i n g . The process of parallelization i m - poses specific requirements o n -language means of programming f o r multiprocessor systems w h i c h should make parallel computations possible and provide their timing; - means of translation w h i c h should provide automatic parallelization of the object program; - means of debug controlling a s y n - chronous performance of certain tasks a n d localizing errors i n r u n n - ing the program o n certain p r o c e s s - ors; - operation system distributing computational resources a n d p r o v i d - ing its o w n parallel operation; - design of algorithms taking full advantage of parallel computations; These include - the introduction of vector a n d m a t r i x operations a n d m e a n s of m a s k - ing t h e operations o n elements of the v e c t o r s ; - the apparatus f o r the creation of sections of parallel p r o g r a m execu- t i o n w h i c h are further referred to as b r a n c h e s , a n d - t h e apparatus f o r b r a n c h synchronization. The expressions o n arrays (vectors, matrices) generally employ t h e same operations a s scalar expressions, u s u a l l y subarrays of various kinds a n d operations o n t h e m are specified. A logical conditional statement p e r - m i t s only those operations w i t h t h e elements of t h e arrays to b e p e r - f o r m e d w h i c h correspond to t h e TRUE value of t h e logical expression f o r conditional statement. Thus masking The first part of t h e p a p e r treats various ways to realize t h e first four requirements. The second part discusses rational combination of t h e parallel a n d serial forms of p r o g r a m e x e c u t i o n , the effect of program p a r a l l e l i z a - tion u p o n the useful capability o f a multiprocessor system a n d some ι

Ε.A. Trakhtengerts & Yu.M. Shuraits 2 least one of the following requirements is satisfied: either it has more than one direct predecessor or its direct predecessor h a s more t h a n one direct follower. of the operations w i t h vectors is performed w h i c h is generally done b y hardware. Special statements f o r branch d e s - cription a n d initialization are i n - troduced f o r parallel b r a n c h o p e r a t - i o n s . In any point of the program one or several branches m a y b e i n i - tialized f o r parallel execution. Usually static a n d dynamic d e f i n i - tions of parallel branches are given. I n the latter case the number of branches i n a given point is d y n a - mically obtained i n the course of the program execution. U s i n g these definitions one may easily construct the linear section search algorithm. A simple cycle is a fragment of the program consisting of one or several cycle a n d cycle body statements not containing transfer-of-control b e y - o n d the cycle boundaries. These boundaries are found b y formed i n d i - cators of cycle description u s e d i n the corresponding programming langu- a g e s . The body of a b r a n c h is specified statically i.e. i n t h e process of translation a n d , generally, m a y n o t be formed dynamically. T h e begining a n d e n d of each b r a n c h are specified b y special statements. This terminates the process of the analysis of a program graph. Parallelization inside linear s e c - t o r s , design of ordered linear s e - quences (OLS) a n d parallelization of simple cycles m a y b e executed i n parallel. The synchronization of the computing process w a s attained t h r o u g h the introduction of variables of the "event" type a n d wait and event termination statements. The operands f o r these statements were the variables or arrays of t h e "event" type. To provide processing of the same data array by several branches statements of the "semapho- r e " type were introduced. To raise the level of synchronizing p r i m i t i - v e s the mechanisms of the conditional critical intervals monitors [2,3,5], sentinels Q6] » control expressions dezvous (in the A d a language) were created. One should note that the above rather complicated synchronization designs m a y b e expressed through the semaphores as w e l l , b u t the u s e of these designs increases software "reliability" a n d lowers the probability of errors i n the program w h e n complex interactions are described. o r arrscps 2·1· Parallelization of linear sections Parallelization inside a linear section is carried out b y statements; inside the statements parallel e x e - cution of arithmetic expressions is possible. (¥} , The variables processed by the statements ρ of the linear section m a y b e categorized i n four groups: 1. Read-only denoted as w. Write-only denoted as X. a f t e r - r e a d denoted as Read-after-write denoted as z. W h e n two statements ?λ w o r k i n parallel memory cells o r , w h i c h i n this case i n the same, iden- tifies of the variables read b y statement PR should n o t be a f f e c t - ed b y writing into them statement P2 . Thus (w1 υ Y1 u z1 )n ( x2 υ Y2 υ z2) = tf> . Changing P1 a n d w e obtain (XluYluzl)n(w2uY2uz2) fi] a n d r e n - ; 2. l; 3· W r i t e - 1 Y. ; a n d 4. . a n d P2 2. Translation means f o r p a r a l l e l ! - zation P2 symmetrically Program analysis a n d its p a r a l l e l i - zation i n the course of the t r a n s l a - t i o n m a y b e carried out as f o l l o w s . = ψ If 1 variables a n d constants of the righthand part of the i-th asignment statement) a n d ο. , output data (i.e. t h e variables i n the lefthand part of the i-th asignment statement) the above requirements informational independence of statement i, j m a y b e w r i t t e n as I.no. = 0, ι . no. = 0, o. no. =0 denotes input data (i.e. the A t the first step linear sections and simple cycles are isolated. A linear section of t h e p r o g r a m is a part of it whose statements are executed i n the natural order sequentially o r i n t h e order determined b y unconditional b r a n c h destructions. A linear section is limited b y the start a n d e n d statements. of Proceeding f r o m these necessary c o n - ditions various algorithms f o r A start statement of t h e linear s e c - t i o n is t h e statement f o r w h i c h a t

3 Design for Multiprocessor Systems Computer Control parallelization of linear sections were suggested. The transformation of scalar arithmetic expressions f o r parallel computation is i n reducing the number of steps necessary to compute the arithmetic expression. For example the computation of the expression a + b * c + d requires two steps. A t the first step ( b * c ) a n d computed. A t the second step the r e - sults obtained at the first step are summed u p . C. I t should not contain any r e f e - rences to the subprograms a n d f u n c - tions whose parameters are generated v a r i a b l e s . D. I t should satisfy restrictions o n the f o r m a n d order of index expressions. c e r t a i n (a + d ) are The structure of the computer system greatly effects the cycle parallelization technique. Thus f o r systems of the ILLIAK-IV type one m a y employ the reference technique systems w i t h a set of asynchronously operating processors, the h y p e r p l a n e technique [g] or the method of p a r a - llelepipeds ftiQ e t c . These methods differ b o t h i n the technique of parallelization a n d i n the strength of restictions imposed u p o n the cycles to b e transformed. (ßj , f o r This parallelization of arithmetic expressions a n d parallel execution of information-uncorrelated linear section statements is possible i n the cases w h e n the computer system permits realization of pipeline processing and/or i s provided w i t h special arithmetical-logical devices for tracking, multiplication, shifting e t c . Thus the computing process m a y be significantly speeded u p . I n a parallel cycle body execution one should determine the range of feasible values f o r each index v a r i - able i n w h i c h the vector operation may b e executed. I n doing so one should provide equivalency of the v e c t o r operation to t h e initial c y c - l e . The solution to this problem is generally that of system of integer equations a n d unequalities Therefore the parameters the cycles to be transformed should b e specified i n terms of constants rather than v a r i a b l e s . 'Then the entire p r e p a - r a t i o n to parallelization should b e carried out i n t h e process t r a n s l a t - i o n rather t h a n i n t h e course of the program*s execution. 2.2. Parallelization of cycles i n the process of translation F o r computer systems employing v e c - tor registers or sets of processor elements vector computations prove highly effective. The operations w i t h the elements of vectors i n such computations are performed one order faster t h a n the same operations w i t h scalars. Consequently the t r a n s f o r - mation of cycle bodies of sequential programs into vector operations m a y make the program execution essentially faster. [9] · It should b e n o t e d that the analysis of cycles u s e d i n FORTRAN programs h a s shown that depending o n the structure of the computer system a n d , consequently, o n t h e p a r a l l e l i - zation technique u s e d , 30 to 60 p e r - cent of cycles i n these programs lent themselves to automatic parallelization. I n the course of transformation of the cycle body of a sequential p r o - gram into a vector operation the latter should b e executed (resulting i n parallel computations) o n those elements of the vector the c o o r d i n a - tes of all points of w h i c h are p a r a l - lel to some plane. F o r instance, such that the condition const holds. T h e value of the c o n s - tant should change after each e x e - cution of the cycle body until all points of the cycle are n o t looked through. Σ a I. = 3. D e t e r m i n a t i o n of branches i n programs A w a y to reduce p r o g r a m execution time is parallelization of it branches i.e. revealing such s e c t i - ons of it w h i c h m a y b e executed s i - multaneously a n d independently. P r o g r a m b r a n c h initialization takes a great deal of time therefore r a - tional branching implies that i n d i - v i d u a l branches b e executed long e n o u g h . W h e n greater program units t h a n linear sections o r simple c y c - les are a n a l y z e d f o r possible p a r a - llelization, the initial program is p r e s e n t e d i n t h e f o r m of linear structures consisting of single- input-single-output n o d e s . I n the i n Lending themselves f o r p a r a l l e l i z a - tion are normally n o t all the cycles but only those w h i c h satisfy restrictions, u s u a l l y the following restrictions are imposed u p o n t h e body of the cycle: some A . I t should n o t contain any i n p u t / output statements. B . I t should not c o n t a i n a n y t r a n s - fer-of-control outside t h e c y c l e .

4 Ε.A. Trakhtengerts & Yu.M. Shuraits this processor results i n a complete failure of the whole g i v e n generalized graph of the p r o g - ram the so-called hammocks are i s o - lated, that i s , subgraphs w i t h a single input a n d single output v e r - tex. Note that a hierarchy of h a m m - ocks is admitted. Orderness a n d hierarchysity of linear structures permit one to reveal time limits of the execution of parallel sections and make their debug easier. W e shall not go into t h e details of h o w h a m - mocks are isolated. Note only that a number of algorithms are available f o r t h e purpose. Proceeding from the p r o g r a m sections, simple cycles a n d 0 1 ß are constructed w h i c h incorporate the above structures. W h e n program branches are shaped all these OLS's are looked through starting w i t h the first one. This i s done after the elements of each O L S are allocated throughout local levels. The initial number of branches i s determined b y the content of the first O L S level. The subsequent analysis of the graph makes u s e of information a n d logical links to unite the branches a n d construct n e w o n e s . system. Alternatively, an operation system m a y function w i t h any of the c o m p u - t e r ^ processors. This results i n a more complicated design of the o p e - r a t i o n system, b u t increases its reliability due to the fact that u n d e r a failure of one processor the system m a y operate o n another. A n operation system m a y , finally, b e decentralized w i t h a part of its functions performed o n one of the central processors a n d the other p a r t , o n peripheral processors. I n this approach central processors are free of performing the functions of the operation system w h i c h results i n a higher efficiency of the c o m - puter. 1s graph consisting of linear fs Assigning individual modules of the operation system to different p r o - cessors i.e. the distribution of the operation system functions among the processors depends on purpose of the system, the characteristics of the central a n d peripheral processors a n d o n t h e topology a n d speed of performance of the interfaces w h i c h provide data exchanges between p r o - cessors. Optimal distribution of functions among the processors m a y significantly increase the overall performance of the computer a n d its tolerance to hardware breakdowns. 1 first I n the process of b r a n c h formation the optimal structure of t h e p r o g - ram should b e obtained i.e. the program of minimal execution time w i t h given finite resources. This is achieved b y means of u n i t i n g some branches together w h i c h results i n the reduction of the b r a n c h f o r m a t i - o n t i m e . The same problem m a y b e stated i n terms of mathematical programming. A n algorithm solving it to a certain extent is designed. 5· The specifics of parallel p r o p - rams debug The major specific features of p a - rallel programs w h i c h make their debug more difficult as compared to serial programs are 4 · The specifics of multiprocessor computers o p e r a - tions systems designing - asynchronous execution of sections of a parallel program, a n d Operation systems f o r multiprocessor computers fulfill the same tasks as i n "conventional" computers b u t b e - sides they [10) -physically simultaneous execution of operations o n several elements of the array. - organize the interaction of p a r a - llel computational processes a n d their timing; The first feature hampers reproduc- t i o n of situations i n w h i c h a n error took p l a c e . Since parallel processes are asynchronous they may access the same data i n different order. The order of processing m a y effect the result a n d the programmer is depri- v e d of any means to restore the order of data processing f o r the l o - calization of the error. This f e a - ture of asynchronous programs adver- sely affects complex debug of c o m p - licated programs. - schedule a n d dispatch computational processes w i t h regard f o r their parallelization; - reconfigure the system whenever necessary; - dynamically reallocate t h e a v a i - lable resources. Multiprocessor operation systems m a y employ enly one specified processor. This makes the design of the system somewhat simpler b u t reduces its reliability since a b r e a k d o w n of The second specific feature offers no special difficulties. To localize a n error i n the course of the debug

5 Design for Multiprocessor Systems Computer Control either all elements of t h e resulting array w h i c h were obtained physically simultaneously or only those specified b y the programmer m a y b e d i s - played. The number of operations performed for a l l tasks i s ι D = Σ D. = c Σ Σ 0..kt? Ρ i=l i=l k=l Assume t h a t t h e execution of I p r o g - rams b o t h i n t h e serial a n d parallel modes goes without idling of t h e processors. ι q 1 k l 1 PART I I . T H E EFFECT O F P A R A - LLELIZATION O N T H E P E R F O R M A N - C E O F MULTIPROCESSOR COMPUTER SYSTEMS I n I programs there a r e D useful instructions where the nominal performance of o n e p r o - cessor. I n a serial r u n of programs the M C S performance i s ι D l sS t ? c c 1 is Parallel execution of some parts of a program reduces i t s r u n time. H o w - ever as a rule parallelization r e - quires certain additional operations to b e executed w h i c h do n o t take place i n its serial execution thus effecting the system performance. The usefulness of parallelization i n multiprocessor computer systems (MC§) may b e treated i n three aspects: 1 cr i n Tl 2tJ/q I n a parallel r u n the time of e x e c u - t i o n of programs w i t h due r e g a r d f o r the expression f o r d I q D Σ Σ |3..kt? up i=i k = i Τ = — - = Ρ cq q I n a parallel mode the useful p e r - formance of a M C S i s i s ρ K l k 1 a)its effect o n t h e m e a n M C S p e r f o r - mance; b) change of execution time f o r a group of programs; 1 / Σ Σ ]3., k t 1 i k p Ρ = qc Σ t ρ (i) lk 1 c) reduction of r u n time f o r a single program. = 1> 0 i k = o w i t h a n d 0i q f o r k = l , . . . , q - l V i e i,i 1. The effect o n the M C S performance cZ tj (18) The first question to arise is that of the conditions of measuring t h e performance. I f one considers t h e average number of instructions e x e - cuted b y processors i n a unit of time he m a y see that w i t h parallel programs it does n o t change u n d e r fault-free operations of the p r o c e - ssors. However if one considers only the number of executed useful instructions i.e. t h e instructions in a serial program such useful p e r - formance m a y b e m u c h less. This r e - sults from the n e e d to execute some extra instructions f o r instance, those of b r a n c h origination a n d i n - tegration. The useful performance of a M C S m a y b e estimated i n the following manner. Let us observe I programs w i t h the degree of p a r a l l e - lization[73 V v where q i s the numb'er of p r o c e s s - ors a n d t. a n d execution times for 'a serial a n d parallel programs respectively. I i s assumed large enough. Note that even without any additional operations Ei m a y b e less than one. L e t us estimate the useful M C S p e r f o r m a n - ce i n execution of parallel programs. Following Γ Γ 33 the part of time t w h i c h i-th task uses cessors ( k < q) number of actions f o r the f u l f i l l - ment of the program i s q D. = c t p Σ t The change of M C S performance i s Ρ q c Σ t i Σ tl 1 Ρ Ν ( 2 ) Ρ ρ P p 1 cq Σ Σ β k t i Σ Σ β.ν k t j k ik ι k «ik ι W i t h a complete parallelization of programs p Ε . / Σ t p Ν = Σ t P i ι ι ' i ' ι (2a) Thus t h e u s e of parallel programs d e - creases t h e useful M C S performance Np times due to the increase of the n u m b e r of operations executed i n parallel. ^ - . i = 1.1 1 p are the t Example. Estimate t h e loss i n t h e performance of a n M C S w i t h 8 p r o c e - ssors f o r a flow of similar tasks w i t h t h e level of parallelization ßx = 0.04, ß3 s 0.27, w i t h that of all t h e rest tasks Let 8* 0.69 ß p « 1 . = 5 a n d t denote p. ßi k a s during k . T h e total Substituting these data into (2) yields p r o - Ν ρ = 0,78 1 - 0,04 + 3 - 0,27 + 8 · 0,69 p Σ ß.vk

6 Ε.A. Trakhtengerts & Yu.M. Shuraits The overall useful performance is thus decreased more t h a n 20 percent. (3) T° = Z x . t ? + max (Σ y., t ) i 1 1 ik ι k i The above considerations were made on the assumption that no limitations were imposed o n t h e volume of m a i n memory. I f program execution requires a larger volume of m a i n m e - mory waiting of data m a y result i n idling of the processors thus a f f e c - ting t h e performance of t h e M C S . Since i n t h e serial processing mode a part of t h e m a i n memory should b e provided f o r each of q run o n q processors while i n the parallel mode t h e entire memory may b e given to a single program if it activates all greater number of exchanges w i t h external memory takes place i n the former case a n d , consequently, the processors i n t h e serial mode of operation m a y idle m u c h longer w a i t - ing f o r data. Using the variable the minimizing function (3) takes u p the form Τ = max (Σ yi kt { ) p + T-> min 1 1 Σ x. t i = l (4) the following conditions should b e met i n this case programs (5) i = 1,1 (6) Ç y .kt P - T < 0 k=l,q q processors a (7) x = 0 , l , yi k= o , i i s t h e Boolean The problem (4-)-(7) problem of integer linear programming. Using the well-known rithms (/]£} i t s solution is quite easy. Note that parallelization of some programs permits the reduction of t h e solution time f o r a package of programs due to greater load of processors during the time τ° . algo- It should b e added that concurrence of data pumping a n d program e x e c u t i - on is more probable under t h e p a r a - llel mode w h i c h also increase of M C S performance. results i n t h e 2. Execution of a group of programs This m a y b e explained w i t h the follo- w i n g example. L e t two processors be employed to execute three identical programs w i t h the time of execution t t see ttiat i n serial processing t h e total execution time amounts to 10 u n i t s , i n parallel 9 units while i n the case of serial execution of two programs a n d parallelization of t h e t h i r d program t h e total time i s 8 u n i t s . Consider two situations possible i n execution of a group of p r o g r a m s : Pj =3# O n e m a y easily 1 =5, a) the group consists of I programs. It i s required to f i n d t h e optimal v e r s i o n of program initialization providing t h e minimal execution time; b) t h e flow of queries f o r each of the tasks i s k n o w n . I t i s required to f i n d t h e v e r s i o n of program e x e - cution providing t h e minimal m e a n waiting time. Similarly o n e m a y treat t h e problem of minimizing execution time f o r a package of programs i n the case w h e n not all of t h e processors operate i n the parallel mode (q. < q) Consider t h e first situation. L e t t h e time of execution of each of t h e programs i n t h e serial mode b e and i n t h e parallel m o d e , ^ (i = 1,1) It i s assumed that i n t h e parallel mode a l l processors a r e b u s y . I n t r o - duce · l t{ Let t h e processors b e presented b y consecutive numbers. T h e n following £12) w e m a y denote l , i f t h e i-th program starts its execution at t h e j-th instant of time a n d keeps busy a l l processors from k-th t O ( k + q . - l ) l > if t h e parallel mode i s u s e d f o r the i-th p r o g - r a m l^o, otherwise - t h . ο, otherwise. If t h e task i s p e r f o r m e d serially denote l , if t h e i-th program i s executed o n t h e k - t h processor ίο, otherwise. The following function i s to be m i n i m i z e d Τ -> min u n d e r t h e constraints T h e n t h e total time f o r t h e e x e c u - t i o n of I programs i s 1,1 k j k ^

Design for Multiprocessor Systems Computer Control 7 problem (8)-(12) one m a y u s e the a l - gorithm w h i c h brings the solution close to optimal. I t s essence is i n the following. A s s i g n all the p r o g - rams executed serially to the p r o - cessors i n such a manner that the most durable program takes u p a free processor i n t h e first place. o n processor k* est total program execution time r* transfer a program w i t h t h e maximal value Ej into the parallel processing quality h o l d s : xi +( 1- xi ) tÎ X T tï f f y « k < k = l,q 1J1 C 1 1 = ^ 1 Then Jl=J w i t h the g r e a t - j + X j t ? - l k + q . - x y (Σ Σ 1 ^ Σ k ^ k - q . y. l J l = 0 k J l k ij j.=j +1 l 1 mode if the following i n e - yi jk = 0,l , x.= 0,1 (r - r k) > q tP (1 (13) V k=*k* The 3rd a n d 4-th of these constraints determine the condition of concurrence of assigning the entire p r o c e s s - or resource to the program. This problem i s nonlinear, integer a n d i t s accurate solution i s very h a r d t o f i n d . The program employing the parallel mode m a y b e transferred onto free processors starting w i t h the least b u s y . I n doing so time decreases. This transformation of programs into the parallel mode m a y be carried out until the condition (13) i s true f o r at least one program. T* The problem however w i l l b e essentially simplified if one assumes that the program i s regarded to b e e x e c u - ted w h e n it i s given the processor time i n the parallel mode a n d tj , i n t h e serial m o d e . L e t us'introduce the variable zi k characterizing t h e processor time assigned to t h e i-th program o n the k-th processor. T h e l o a d time far the k-th processor i s It i s necessary to minimize p E x a m p l e . f i l l e d o n three processors, each task of duration ( t = ( 6 . 3 | 10.4; 8 . 3 ; 15.6; 11.5)· Employing t h e above algorithm w e o b - t a i n t h e following assignment of serial tasks to t h e processors: (4; 5 a n d 1; 2 a n d 3) w i t h the execution time (15, 17 parallelization of the 2nd a n d 3rd tasks realized o n the t h i r d p r o c e - ssor are 5/6 a n d &/$ . Condition (13) i s true f o r the 3rd task since (18-15M18-17) > 3.8 /9 execution of t h e 3rd task i n the p a - rallel mode requires processor time of w h i c h 7 units i s provided o n t h e t h i r d processor a n d 2 u n i t s , o n t h e first. T h e total execution time f o r the package of programs is thus reduced b y 1 a n d amounts t o 17 time u n i t s . i f 5 tasks are to b e f u l - q t of 1 , t\ )= τΐ ς= Σ ζΐ ik ? 18)· T h e degrees of Τ min (g) under the constraints imposed o n t h e assignment of the processor time . The 9 units of the ( 9 ) The time of executing programs o n each of t h e processors should n o t exceed , i.e. T Similarly one m a y treat the problem of time minimization f o r the execu- t i o n of program packages i n other statements. H o w e v e r the above statement sufficiently proves that one should thoroughly consider whether parallelization is really necessary i n h i s stacked operation. (10) Σ z.k - Τ < 0 k= l,q Besides if the program i n the s e r i - al mode m a y b e executed only o n o n e specified processor Consider n o w t h e second of the two situations given at the beginning of this p a r t . i f flows of queries are coming f o r execution of various programs (which is often t h e case i n computer-aided management a n d control s y s t e m s ) . T h e major attention has to be p a i d t o t h e time o f serving the q u e - r i e s . L e t u s analyze this situation f r o m t h e viewpoint of possible p a r a - llelization of programs. Assume that all t h e programs have equal p r i o r i - z Σ z = 0 k=l,q-l · i = (11) i k * i k k ^ k The condition that the variables are integers leads to the following: xi = 0> 1 > z .keN (12) To find an approximate solution for

Ε.A. Trakhtengerts & Yu.M. Shuraits 8 t i e s . L e t P o i s s o n query flows reach programs w i t h the time constant 'S a n d the times of serial a n d parallel execution t 1 1 = 1/u p = ΐ/μ ρ , a n à t respectively of t h e analysis of such system d e - p e n d o n the discipline of service accepted f o r t h e case w h e n query queues occur. ( i = U ) . The results Comparing (14) to (16) or (15) to (17; depending o n the distribution of t h e program execution time one mgy f i n d o u t w h i c h of the service modes is preferable. H o w e v e r w h e n a single program i s served i n either t h e serial o r t h e parallel mode a n analytical study i s possible. E x a m p l e . Let t w o processors realize a P o i s s o n flow of queries o n some problem characterized b y the expo- nentially distributed execution time The parallel mode a situation similar t o serving a flow of queries b y a single device. Let u s u s e t h e Pollachek-Khinchin formula £nj f o r the m e a n time of presence of a query i n t h e system p r o v i d e d t h e service law i s a r b i t r a - ry: operation presents W ± th ( " l V - (1,1.6) ' Substituting these values into (14) and (16) yields Ε = W 1 + - 1 . 5 - λ The parallel mode turns to b e better w h e n Ε < w tely w i t h tems load i n the parallel mode i s ρ Ε =bj ( 1 + ρ ( l + c\ ) / ( 2 ( l - p ) ) ) i # e . approxima- q λ < =0.77· The s y s - F o r a n exponential time of service we shall have 2 = λ / μρ =0.51. The limit value of t h e load also depends o n the efficiency of parallelization E . ^ / q t above example Ε =0.75· Note that w i t h Ε =1 parallel execution mode is always preferable. Εωρ=1/μ ( 1 + λ / ( μ - λ ) ) (14) 1 3 * I n the F o r a permanent service t i m e , w i t h due regard f o r w e shall have Analytical analysis i n t h e general case of I flows of queries f o r programs i s v e r y difficult a n d m o d e - lling m a y b e suggested instead. ρ = t ( 1 + X t / 2 ( 1 - X t ) ) (15) Ε ω O n the w h o l e it m a y b e concluded that w i t h equal priorities of programs t h e parallel mode effectively i n systems w i t h small loads where waiting times are little a n d t h e m a j o r part of service times are t a k e n u p b y program execution. I t should b e said also that t h e parallel mode turns more f o r lengthy programs. H o w e v e r f o r programs w i t h intensive query flows the more effective mode i s serial. The serial p r o g r a m execution presents a situation similar t o serving a f l o w o f queries b y q a n exponential service time t h e expression f o r t h e m e a n time of p r e - sence of a auery i n t h e system i s as follows Cvj) : works more d e v i c e s . F o r effective q 1 , M X / M ) qM. q ! ( 1 - λ /ςμ ) W - q 2 (16) " S ' i ^ n=0 q W h e n programs w i t h different p r i o r i - ties are h a n d l e d those w i t h h i g h priorities should b e executed i n p a - rallel w h i l e those w i t h low p r i o r i - ties serially since generally the system is little loaded b y h i g h priority programs a n d t h e m a j o r s e r - vice time i s t h e time of execution w h i c h should b e reduced. + (λ /Μ )" n! q! ( l - X / qM) F o r a permanent service time t h e m e a n waiting time . [ill i s qe 1 X t/ q ! l - Ç X t / q r q ( X t ) q Wq - q +l ' i - ( \ t / q ) ' ( q / t ) d - X t / q ) q 3· Parallelization of a single p r o g - r a m (17) qe " -— - X t. q — X t ( X t ) i / ( + 2 _ ) A s i t w a s n o t e d above program p a r a - llelization decreases the performance of a M C S . H o w e v e r the useful speed q ! /<*-*t) k/ k ! Xt l-e Σ ( X t ) k=q

9 Design for Multiprocessor Systems Computer Control systems techniques. Academic P r e s s . N e w Y o r k , 1972, pp.220-230. 5· H o a r e , C.A.R. M o n i t o r s . A n operating system structuring concept. Comm. of the A C M , v o l . 17 (197*0, N o . 10, p p . 549-557· 6. K e l l e r , R . M . Sentinels: A language construct f o r multiprocess coordination. Unpublished M e m o , Dept of Computer Science, Univ* cf U t a h , Salt C i t y , 1978· 7· K u c k , D . J . , M a r u o k a Υ · , a n d Chen S.-C. O n the number of operations simultaneously executable i n Eortran-like programs a n d their resulting speedup. IEEE T r a n s , o n Computers., V o l . 0-21(1972), N o . 1 2 , p p . 1293-1310. 8. L a m p o r t , L . The parallel executi- o n of Do loops. Comm. of the A C M , v o l . 17(197*5t N o . 2, pp.83-93· 9. Lebedev, V . G . a n d Shuraits, Y u . M# Parallelization of cycles w i t h arbitrary steps. Avtomatika i T e - lemekhanika, N o . 9(1979), pp.158- 167 (in R u s s i a n ) . 10· R a b i n o v i c h , V . M . Specifics of the design of operation systems for u n i f o r m M C S * s w i t h variable structure. I n "Problems of cyber- n e t i c s . Multiprocessor computer systems w i t h variable structures. VINITI, Moscpw, 1981, pp.58-64- (in Russian) · 1 1 · S a a t y , T# Elements of quçu-eing theory w i t h applications •McGraw- H i l l , N e w York-Toronto-London, 1961· 1 2 . Shuraits, Y u . M . Optimal resourse allocation i n multiple execution of a complex of jobs. I n "Urgent problems of t h e control theory and applications". N a u k a P u b l . , M o s c o w , 1977, pp.122-125 (in R u s s i a n ) . 13· Trakhtengerts, E.A. Some estima- tes of the essectiveness of c o m - putation parallelization. I n "Computer-Aided Control System D e s i g n " . Statistika Publ.,Moscow, 1981, p p . 88-100 (in Russian). 14· Val'kovsky, V . A . , a n d Kotov,V.Ye. Automatic design of parallel programs. Preprint N o . 14-6, SO A N SSSR, Novosibirsk, 1979 (in R u s s i a n ) . 15· W a g n e r , H . Principles of o p e r a - tions research w i t h applications to managerial decisions. P r e n t i - ce-Hall, Englewood C l i f f s , N e w Jersey, 1969· of computation estimated i n terms of the number of instructions of a parallelprogram executed b y a M G S i n a unit of time increases times. L e t u s enumerate tne cases w h e n , i n our opinion, program p a r a - llelization is preferable: 1/ t p p = t s - w h e n service time f o r a program operating i n control systems under time limitations is to b e reduced; - w h e n the system*s main memory o r its reliability characteristics are restricted, a n d - to provide a flexible load of processors w i t h sharp variations i n the flows of t a s k s . To some extent the first a n d the third cases where treated i n the previous parts of t h e paper. R e l i a - bility of individual M O S devices effects the selection of the program operation mode so that program r e s - tarts or duplication of computations may b e necessary w h i c h m a y significantly increase the program e x e c u - tion time i n the serial mode a n d r e - duce the overall efficiency of the M C S . Indeed if the failure p r o b a b i - lity f o r some device is nonlinear time dependent w h i c h is practically always the case the increase of program execution time m a y d r a m a t i - cally raise the probability of f a i - lure. This makes program restart n e - cessary w h i c h takes extra time δ · I n this case the efficiency of parallelization is (t w h i c h already m a y b e close or even more than unity. The effective i m p - lementation of M C S thorough analysis of the goals of parallelization should b e made a n d criteria estimating the usefulness of this parallelization pointed o u t . It is desirable that alternate variants b e developed w i t h b o t h a parallel a n d a serial v e r s i o n of the program execution a n d either of them be activated depending o n the concrete situation i n the M C S . 1 + δ) / qt p 1s implies that a REFERENCES 1 . Campbell, R . H . , a n d Haberman,A.H. The specification of process synchronization b y p a t h expressions. Lecture notes i n computer science, Springer-Verlag, B e r l i n , 1974· 2. H a n s e n , P.B. Operating system principles. Prentice-Hall, 1973· 3· Hansen,P.B. The programming language concurrent Pascal IEEE Trans, o n Software Engineering, Vol. 1 (1975), N o . 2. 4. H o a r e , C.A.R. Towards a theory of parallel programming. Operating

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 DISCUSSION Shi 1 eiko: you stated that at present there were no discussions on the possibility of the realization of parallel processing. At the beginning of your talk usefulness parallelization highly depends on hardware, and it is possible to show that some algorithms that are very effective on one structure of a parallel absolutely ineffective structure. It is possible to make a relevant analysis to understand whether it is useful to parallelize on some particular hardware, but no algorithm exists for that, either. and effectiveness of system, are on another Trakhtengerts: were no discussions about whether parallel processing is necessary or not. agrees that it is necessary to create parallel processing processors. The question is how to create them. Well. I said that there Everybody and parallel Inamoto: system architecture. question concerning multiprocessing on some sort of a computer system. idea of the optimum processors in case you parallelize, for instance, the FORTRAN compiler? I'm looking at the computer I'd like to ask a Shi lei ko: processing is impossible but necessary. I'll ask you a very simple question. Let us have a problem to generate a sequence of natural numbers, 1,2,3. parallelize this process? Then I understand that parallel Have you any number of the Can you Trakhtengerts: answer this question, but I think it is possible. I can answer another question, that is, I know parallelizing the computation of all simple numbers, and how to create all integers. I am not ready yet to Trakhtengerts: I have no idea of how many processors are needed for parallelizing a compiling process. should be stated vice versa: if we have a particular hardware, how to organize an effective compiler? I think the problem an algorithm for Harrison: analytically at a rather general case of determining parallelism in a given problem or expression. I think you demonstrated correctly that this is a very difficult problem. If you arbitrarily take all problems one may wish to solve and you want to parallelize them, that's very difficult. Later on you proposed and discussed a computer system consisting of separate multi-processors, stating that designing the operating system for that kind of system is difficult. But this is a much more constrained example than that of a general analytical expression. applied your method specifically related systems? Have you taken an OS and attempted through your algorithmic method to determine where the parallelism exists and how it is best implemented? You started by looking Shi lei ko: Can you tell us what the measure of effectiveness of the processes, either sequential or parallel, is? Trakhtengerts: measures of effectiveness. simple: the time to perform a task, not considering the cost. Another approach is well known - the cost of operations per second: the cost of the task divided by the time to perform the task. Usually two joined processors work less effectively than two separate processors. multiprocessor is a processors it may be very ineffective. A multiprocessor contains processors and many ALU's. The latter are much cheaper than control devices. In this case cost per task time may be the proper measure of effectiveness. parallel processing is less universal than sequential processing. There may be several One is very If the unity of simple Have you functions operating to to several control Besides, Trakhtengerts: I think that up to now it has been impossible to create such an algorithm which would show when parallelism is useful and when it is not. The 11

12 Discussion Joudu: debugging parallel programs, so that we'll have to test all depending on whether the program is for parallel or sequential work? Will there be any difficulties in Dragunova: depend on the number of processors, and if yes, then how? Does complexity of algorithms the branches, not Trakhtengerts: difficulty, but that's a big one: not impossible that after having made a mistake, one may have the same situation again. Parallel processing is asynchronous processing and, as soon as you parallelize synchronous processing, you will have the same situation as in sequential processing. I can see only one Trakhtengerts: oT the computer. for example Scientific Processors), the complexity of algorithms does not depend on the number of processors. For other multiprocessors, say, Burroughs 7000, that dependence may exist. It depends on the structure For vector processors, CRAY-1 or PSP it is (Parallel

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 SESSION 2 Chair: L. F. Natiello IEEE PROJECT 802: LOCAL AREA STANDARD - NETWORK A March 1982 Status Report T . J . H a r r i s o n Advanced Software Engineering Technology, IBM Corporation, FL 33432, USA Boca Raton, A b s t r a c t . ty of t h e I n s t i t u t e ( I E E E ) P r o j e c t 8 0 2 is d e f i n i n g n e t w o r k s in w h i c h m i c r o p r o c e s s o r d e v i c e s a r e c o u p l e d o n a p e e r - t o - p e e r b a s i s . T h e p a p e r p r o v i d e s a b r i e f h i s t o r y a n d r a t i o n a l e for t h e e f f o r t a n d a n o v e r v i e w of t h e c u r r e n t d r a f t s t a n d a r d . T h i s p a p e r d e s c r i b e s P r o j e c t 8 0 2 of t h e C o m p u t e r S o c i e - for E l e c t r i c a l a s t a n d a r d for local c o n t r o l l e d t e r m i n a l s a n d o t h e r a n d E l e c t r o n i c E n g i n e e r s 1. a r e a K e y w o r d s . c a t i o n ; c a t i o n s c o m p u t e r a p p l i c a t i o n s . P r o j e c t t o k e n 802 ; local p a s s i n g ; a r e a n e t w o r k ; LAN ; t e l e c o m m u n i - C S M A / C D ; 0 5 1 ; r e f e r e n c e m o d e l ; c o m m u n i - D i s c l a i m e r a n d C a u t i o n not p o s i t i o n m e m b e r s . t h i s the " w o r k i n g g r o u p " level p a r t i c i p a n t s a c t as i n d e p e n d e n t " e x p e r t s » " t h e i r p o s i t i o n s , a n d t h o s e of t h e a u t h o r * m a y n o t r e p r e s e n t t h o s e of t h e i r s o r i n g o r g a n i z a t i o n s . n e c e s s a r i l y r e p r e s e n t t h e o t h e r c o m m i t t e e a d d i t i o n , of In It is p r u d e n t to r e m i n d t h e r e a d e r of s e v e r a l c a u t i o n s a n d c o n v e n t i o n s a p p l y to t h e c u r r e n t s t a t u s of P r o j e c t 802 a n d , in f a c t , to t h e t e n t a t i v e r e s u l t s of a n y s t a n d a r d s - d e v e l o p i n g o r g a n i zat i on i s i n c e t h a t a c t i v i t y is b e i n g d o n e at w h e r e s p o n - T h i s p u b l i c a t i o n of IEEE P r o j e c t 8 0 2 or of a n y o t h e r d i s c u s s e d , a n d it h a s n o t b e e n a p p r o v e d by t h e s e b o d i e s . It is b a s e d p r i m a r i l y o n p u b l i c i n f o r - m a t i o n a v a i l a b l e l i t e r a t u r e a n d t h e m i n u t e s of m e e t i n g s . T h e m o s t r e c e n t m e e t - ing of t h e c o m m i t t e e w a s h e l d 1982 M a r c h 8-12 a n d m i n u t e s a r e not a v a i l a b l e as t h i s p a p e r is w r i t t e n . As d e s c r i p t i o n s r e s u l t i n g d e c i s i o n s a t t h a t b a s e d o n t h e a u t h o r ' s n o t e s . p a p e r is n o t a n o f f i c i a l o r g a n i z a t i o n s T h e u n d e r g o i n g r e p o r t is p r o v i d e d f o r c u r r e n t i n f o r m a t i o n o n l y . It s h o u l d n o t be u s e d as t h e b a s i s for d e c i - s i o n s a f f e c t i n g d e s i g n » s p é c i f i c a t i o n » or s a l e s a c t i v i t y . T h e f i n a l p r o c e s s h a s n o t y e t b e g u n a n d c h a n g e s , p e r h a p s m a j o r in s c o p e » m a y b e m a d e b e f o r e a p p r o v a l as a n IEEE» A m e r i c a n i n t e r n a t i o n a l s t a n d a r d is a c c o m - p1i s h e d * p r o p o s e d s t a n d a r d c h a n g e s t i l l is a n d t h i s in t h e f u t u r e p r o d u c t a p p r o v a l a r e s u i t » f r o m N a t i o n a l or m e e t i n g a r e O p i n i o n s a n d s p e c u l a t i o n as t o the c o n t e n t of t h e f i n a l a r d , t h e c u r r e n t c o n s e n s u s , a n d f u t u r e are t h o s e of t h e a u t h o r a n d do T h e a u t h o r is n o t a m e m b e r of t h e I E E E 8 0 2 c o m m i t t e e b u t h a s b e e n i n d i r e c t l y a s s o c i a t e d p r o j e c t a n d r e l a t e d t h r o u g h h i s i n v o l v e m e n t n u m b e r of n a t i o n a l a n d i n t e r n a - t i o n a l s t a n d a r d s o r g a n i z a t i o n s . s t a n d - g r o u p a c t i o n s w i t h t h e p r o j e c t s w i t h a 1 T h i s p a r t of t h e p a p e r b o r r o w s h e a v i - ly f r o m p r e v i o u s p a p e r s a u t h o r e d or c o - a u - t h o r e d by t h e a u t h o r ( l , 2 ) .

Thomas J. Harrison 14 T h e r e a l s o m u s t b e a g r e e m e n t o n c e r t a i n p r o t o c o l s a n d c o n v e n t i o n s t h a t i n f o r m a t i o n b e e x c h a n g e d . u s e r s p e a k s C h i n e s e s p e a k s E n g l i s h , t h e r e p r o b a b l y m u s t b e a g r e e m e n t o n w h i c h u s e d s o t h a t i n f o r m a t i o n , a s o p p o s e d t o m e r e s i g n a l s , a r e e x c h a n g e d . u s e r s d o n o t s h a r e a c o m m o n a l t e r n a t i v e s s u c h t r a n s l a t o r m u s t b e u t i l i z e d , b u t t h i s i m p o s e s a c o s t a n d , p o s s i b l y , a n u n d e - s i r a b l e l o s s C o n v e n t i o n s , s u c h a s u s i n g i n i t i a t e i n f o r m a t i o n " g o o d - b y " t o t e r m i n a t e a g r e e d u p o n a n d o b s e r v e d b y a l l u s e r s . I N T R O D U C T I O N i n o r d e r I f o n e o t h e r L o c a l u c t a n d c o m p u t e r s e n s e , " a n i d e a I n t h e e a r l y d a y s o f c o m p u t i n g , i c s a n d t h e s p e c i a l i z e d s u p p o r t i z e d s y s t e m s i n w h i c h t h e u s e r c a m e t o t h e h a r d w a r e t o u s e i t . A s t e c h n o l o g y a d v a n c e s , c o m p e t i t i o n , p r o d u c t i o n c o m b i n e d t o r e d u c e i n g c o s t s , t h e a l t e r n a t i v e o f d i s t r i b - u t i n g c o m p u t i n g p o w e r b e c a m e a t t r a c t i v e p r o c e s s i n g " ( w h i c h h a d b e e n a r o u n d f o r a l o n g t i m e ! ) e m e r g e d c o n c e p t . T h e i n t r o d u c t i o n s o - c a l l e d " m i c r o p r o c e s s o r " a n d " m i c r o - c o m p u t e r " n o w p r o m i s e t h e p o s s i b i l i t y o f e a c h u s e r h a v i n g c o m p u t i n g p o w e r a t w o r k s t a t i o n ( 3 ) . m i c r o p r o c e s s o r i s s p a w n i n g a w h o l e n e w c l a s s o f s o - c a l l e d d e v i c e s " t h a t p r o v i d e c a p a b i l i t y w i t h o u t t i m e - s h a r e d p o w e r o f a c e n t r a l e r . a r e a n e t w o r k s o f r e c e n t t h e c o n t i n u i n g s y s t e m s . ( L A N s ) a r e a p r o d - a d v a n c e s i n e v o l u t i o n T h e y w h o s e t i m e h a s c o m e . " a n d t h e t e c h n o l o g y o f a l a n g u a g e w i l l b e a r e » i n I f t h e l a n g u a g e , e c o n o m - r e q u i r e m e n t f a v o r e d f o r a s i n t e r p o s i n g a c e n t r a l - o f e f f i c i e n c y . " h e l l o " t o t r a n s f e r i t , m u s t a n d m a s s c o m p u t - a n d b e t o " d i s t r i b u t e d t h e u s e r a n d T h e s i g n i f i r a n t a n d t h e e c o n o m i c s u c h a s t h e c o s t o f a t r a n s l a t o r , m u s t e v a l u a t e d . I n a d d i t i o n , m u s t b e a n t i c i p a t e d f u r t h e r a d v a n c e s a v o i d , w h e n e v e r o f r e p l a c e m e n t e q u i p m e n t a n d d a t a . n u m b e r o f n e c e s s a r y a g r e e m e n t s i s e f f e c t s , C h i n e s e - E n g l i s h u n d e r s t o o d f u t u r e t o p r o v i d e i n t e c h n o l o g y a n d t o p o s s i b l e , f u t u r e a n d c o n v e r s i o n a s a p o p u l a r o f t h e b e a n d n e e d s f o r s i g n i f i c a n t i n d i v i d u a l a d d i t i o n , t h e I n t h e c o s t s o f " i n t e l l i g e n t s i g n i f i c a n t u t i l i z i n g t h e T h e r e c o g n i t i o n o f t h e s e n e e d s a n d t h e t e c h n o l o g i c a l e n v i r o n m e n t f o r m a t i o n o f t h e I E E E S t a n d a r d s C o m m i t t e e , P r o j e c t 8 0 2 , i n F e b r u a r y t a s k w a s r e c o g n i z e d c o m p l e x , v e r y l a r g e , a n d c o m m e r c i a l l y s i g n i f i c a n t . A n u r g e n c y w a s p e r c e i v e d t o q u i c k l y e s t a b l i s h m i n i m u m s e t o f r e q u i r e m e n t s a n d p r o t o - c o l s b e f o r e a i n c o m p a t i b l e d e v i c e s e x a m i n a t i o n , i t b e c a m e n o s i n g l e s t a n d a r d n e e d s o f a l l a p p l i c a t i o n s . l i m i t e d " f a m i l y o f a d d r e s s e d a b r o a d r a n g e o f a n t i c i p a t e d a p p l i c a t i o n s c o u l d s a v i n g s t h r o u g h a r e d u c t i o n o f u n n e c - e s s a r y p r o l i f e r a t i o n d e s i g n s a n d t h r o u g h c o m p e t i t i o n a n d m a s s l a r g e - s c a l e - i n t e g r a t e d d e v i c e s . I n r e t r o s p e c t , t i o n w a s a c c u r a t e y e a r s h a v e s e e n t h e c o m m e r c i a l d u c t i o n o f m a n y L A N s , s o m e b y t h e I E E E w o r k . c o m p u t - l e d t o t h e L o c a l N e t w o r k f o r m a l l y k n o w n a s 1 9 8 0 . T h e i r a s b e i n g I n f o r m a t i o n p r o v i d e d b e e x t e n d e d d e v i c e s c o n v e n i e n t b e t w e e n a n d e v e n a n t i c i p a t i n g f u r t h e r u l a r a d v a n c e s p e r f o r m a n c e a n d f u n c t i o n , i t i s h a r d t o v i s u a l i z e t h e d a y c o m p u t i n g p o w e r o f t h e l a r g e i z e d " m a i n f r a m e s " w i l l n o t b e r e q u i r e d a s a p a r t o f t h e t o t a l r o n m e n t . D i s t r i b u t e d a n o t h e r c o m p u t i n g c a p a b i l i t y , n o t r e p l a c e , b u t r a t h e r t h e u s e o f c e n t r a l i z e d s o l v e i n f o r m a t i o n p r o c e s s i n g s h a r i n g , i n h e r e n t l y s y s t e m s , c a n b y c e n t r a l i z e d t o t h r o u g h c o m m u n i c a t i o n s u c h d e v i c e s . v e r y m i c r o p r o c e s s o r - b a s e d t h e d e v e l o p m e n t o f p r o t o c o l s N o n e t h e l e s s , s p e c t a c - m i c r o p r o c e s s o r a g r e e m e n t o n s o m e l a r g e n u m b e r o f i n e m e r g e d . a p p a r e n t c o u l d U p o n t h a t t h e w h e n t h e i m m e n s e c e n t r a l - s e r v e H o w e v e r , a s t a n d a r d s " w h i c h c o m p u t i n g c o m p u t i n g i s b u t e n v i - r e s u l t i n e c o n o m i c i t d o e s c o m p l e m e n t s , c o m p u t e r s p r o b l e m s . o f t h e p r o m o t i o n o f p r o d u c t i o n e l e c t r o n i c t h e a n d t h e p a s t i n c o m p a t i b l e t o o f T h e i n g s m a l l a c o s t c o n s i s t e n t w i t h t h e d e v i c e T h i s n e e d w a s a n t i c i p a t e d b y r e s e a r c h - e r s a s l o n g a s t e n e x p e r i m e n t a l l o c a l e s t a b l i s h e d . W i t h i n c r e a s e i n t h e n u m b e r m i c r o c o m p u t e r s , t h e s e n e t w o r k s a r e n o w o f c o m m e r c i a l i n t e r e s t . n e e d f o r L A N s c o m e s d e s i r e t o m i c r o p r o c e s s o r - b a s e d f r o m t h e g r o w - c o m m u n i c a t e p e r c e p - b e t w e e n d e v i c e s a t t w o i n t r o - c o s t . i n f l u e n c e d years n e t w o r k s t h e o f a g o a n d w e r e T h e b y t h e i n t e n s i t y o f t h e c o m m i t t e e S i n c e t h e f i r s t t h a n t w o y e a r s a g o , t h e c o m m i t t e e h a s m e t e l e v e n t i m e s , t y p i c a l l y f o r f o u r o r f i v e d a y s e v e r y t w o o r t h r e e I n a d d i t i o n , s u b c o m m i t t e e s b e t w e e n c o m m i t t e e m e e t i n g s . o f t h e c o m m i t t e e a n d i t s s u b c o m m i t t e e s i n v o l v e o v e r o n e h u n d r e d p e o p l e . i s a l e v e l o f a c t i v i t y a m o n g t h e h i g h e s t o f a n y s i m i l a r a r d i z a t i o n e f f o r t . m e e t i n g w a s h e l d 1982 M a r c h u r g e n c y c o n t i n u e s a s d e m o n s t r a t e d t r e m e n d o u s a v a i l a b l e w o r k . m o r e m e e t i n g a l i t t l e m o n t h s . o f t e n M e e t i n g s E f f e c t i v e a g r e e m e n t p o i n t s . b e a g r e e m e n t m e d i u m , s y s t e m , o f c o n n e c t o r s , e t c m u s t b e s u c h r e c e i v e d c o m m u n i c a t i o n o n a n u m b e r F i r s t , f o r e x a m p l e , t h e r e o n t h e s u c h a s t h e p u b l i c i n w h i c h t h e i n t e r c o n n e c t i n g t h a t s i g n a l s r e q u i r e s t e c h n i c a l m e e t o f m u s t c o m m u n i c a t i o n t e l e p h o n e c h a r a c t e r i s t i c s T h i s r a n k s s t a n d - r e c e n t w h i c h l i n e s T h e m o s t 8-12. t r a n s m i t t e d a n d a r e c o m p a t i b l e .

IEEE PROJECT 802 15 e x i s t e n c e n e t w o r k s a n d b u t d i f f è r e n t i a t e s t h e I E E E c o m m i t t e e s w o r k i n g o n a s e r i a l e x t e n s i o n t o t h e I E E E - 4 8 8 b u s a n d o n s e v e r a l b o a r d - l e v e l b u s e s . o f o t h e r h a v e t y p e s d i f f e r e n t I n r e f e r e n c e , i t s w o r k o f d a t a g o a l s S C O P E A N D O R G A N I Z A T I O N w h i c h c h a r a c t e r i s t i c s . w i t h o u t p a r t i c u l a r , T h e r e w a s n o g e n e r a l l y n i t i o n o f a s t i l l is n o t h a s e v o l v e d a d e f i n i t i o n a s t h e b a s i s f o r t h e i r e f f o r t . T h a t d e f i n i t i o n , a s i n c o r p o r a t e d i n t o p r o p o s e d ( 5 ) s t a n d a r d i s : a c c e p t e d d e f i - t h e r e s p e c i f i c it L A N a n d , i n d e e d , N e v e r t h e l e s s , t h e g r o u p 2. f r o m t h a t o f m i c r o c o m p u t e r D r a f t Β o f t h e W i t h r e g a r d t o v a l u e s f o r a r e a , n u m b e r o f s t a t i o n s i n t e r c o n n e c t i o n t o p o l o g y , t h e a p p r o v e d f u n c t i o n a l r e q u i r e m e n t s c o m m u n i c a t i o n m e d i u m k i l o m e t e r s i n l e n g t h , l e a s t t w o h u n d r e d p r o p o s e d s t a n d a r d p h y s i c a l t o p o l o g i e s t r a n s m i s s i o n r a t e s . l e n g t h , a n d L o c a l i s t y p e s c o m m u n i c a t i o n c o n f i n e d g e o g r a p h i c o f f i c e b u i l d i n g , a w a r e h o u s e , o r a c a m p u s . T h e n e t w o r k c a n d e p e n d o n a p h y s i c a l c h a n n e l o f m o d e r a t e t o h i g h r a t e w h i c h h a s a l o w e r r o r r a t e . o w n e d a n d u s e d b y a s i n g l e i z a t i o n . T h i s i s i n c o n t r a s t t o l o n g d i s t a n c e i n t e r c o n n e c t f a c i l i t i e s d i f f e r e n t p a r t s o r a r e u s e d a s a p u b l i c T h e L o c a l N e t w o r k d i f f e r e n t f r o m i n t e r c o n n e c t d e v i c e s o n a t o p o r c o m p o n e n t s s i n g l e p i e c e o f e q u i p m e n t . N e t w o r k » ' A d i s t i n g u i s h e d o f d a t a L o c a l f r o m N e t w o r k o t h e r i n t h a t u s u a l l y s i z e d s u p p o r t e d , n e t w o r k s i s a m o d e r a t e a r e a s u c h a s a s i n g l e s p e c i f y a o f a t l e a s t t w o s u p p o r t i n g s t a t i o n s . s u p p o r t s a n d a v a r i e t y o f t o a t T h e s e v e r a l c o m m u n i c a t i o n d a t a c o n s i s t e n t l y T h e n e t w o r k I t f o c u s o n a m i n i m u m s e t o f t h a t w i l l a l l o w m e s s a g e s a t a c o m m i t t e e r e c o g n i z e s o f i n f o r m a t i o n , d a t a b y t e s , r e q u i r e s a g r e e m e n t s t h o s e b e i n g d i s c u s s e d . a d d r e s s e d s i n c e c o n s i d e r i n g t h e m i n t e r n a t i o n a l l e v e l . i s a l s o t h e c o m m i t t e e ' s i n t e n t t o r e q u i r e m e n t s t o e x c h a n g e l e v e l . t h a t t h e e x c h a n g e o p p o s e d t o i s o r g a n - d e v i c e s v e r y b a s i c T h e n e t w o r k s w h i c h i n a s m e r e l y b e y o n d o f t h e c o u n t r y u t i l i t y . i s n e t w o r k s T h e s e a r e n o t c o m m i t t e e s a r e a t t h e n a t i o n a l a n d a l s o w h i c h d e s k - o t h e r w i t h i n a T h e S y s t e m t h e n i t i o n s a n d a g r e e m e n t s s e t o f " l a y e r s " t h a t f u n c t i o n s w h i c h , i n t h e g e n e r a l a r e r e q u i r e d f o r t w o u s e r s t o i n f o r m a t i o n . T h e D r a f t S t a n d a r d f o r t h e O S I R e f e r e n c e c a n b e o b t a i n e d m o d e l c o n s i s t s o f s e v e n l a y e r s a s s h o w n i n F i g . 1 . T h e b o u n d a r i e s l a y e r s a r e d e f i n e d p a r a m e t e r s a n d p r o c e d u r e s n e c e s s a r y f o r o n e l a y e r i n f o r m a t i o n w i t h i t s a d j a c e n t T h e p a r a m e t e r s a n d a l l o w t h e t w o c o r r e s p o n d i n g t w o c o m m u n i c a t i n g t i v e l y e x c h a n g e i n f o r m a t i o n a r e c a l l e d " p r o t o c o l s . " I S 0 / T C 9 7 / S C 1 6 I n t e r c o n n e c t f r a m e w o r k f o r a c o m m o n s e t o f d e f i - w o r k o f o n p r o v i d e s " O p e n T h i s t h e n e t w o r k c o n c e r n f o r c o s t . d e f i n i t i o n c o m m i t t e e ' s w i l l i m p l i c i t l y c o n c e p t b e u s e d i n c l u d e s w h a t t h e a n d i t s (0 S I ) " o f f o r o r g a n i z e d a s a p r o v i d e s p e c i f i c c a s e , e x c h a n g e S p e c i f i c a l l y , o f f i c e c a m p u s , s i g n a l s i t s p r i m a r y u s e i n t h e e m e r g i n g " o f f i c e a u t o m a t i o n " i n d u s t r y , a l t h o u g h t h e e v o l v i n g a r d c l e a r l y h a s a p p l i c a t i o n a r e a s , s u c h a s s o m e a p p l i c a t i o n s a n d u n i v e r s i t y e n v i r o n m e n t . a b o u t g e o g r a p h i c r e s t r i c t i o n t o m o d e r a t e - t o - h i g h r a t e s r e c o g n i z e s t h e c o s t s w i t h v e r y h i g h s p e e d d a t a o v e r l o n g d i s t a n c e s . r a t e i m p l i e s a h i g h l y m e d i a , a n d e x t r a o r d i n a r y d e t e c t a n d c o r r e c t l i n k a n d p h y s i c a l l e v e l s a r e a v o i d e d . F i n a l l y , t h e d e f i n i t i o n r e c o g n i z e s t h e i t s r e f e r e n c e w a r e h o u s e , t o a n d a a n I n t e r n a t i o n a l b u i l d i n g , a M o d e l f r o m A N S I ( 5 ) . T h e a r e a i n s t a n d - i n o t h e r c o n t r o l b e t w e e n t h e a g r e e d - u p o n t h a t t o e x c h a n g e l a y e r s . p r o c e d u r e s l a y e r s i n s y s t e m s t o b y i n d u s t r i a l t h e a r e r e s e a r c h I t s s t a t e m e n t a r e a a n d o r i t s d a t a t h a t a s s o c i a t e d t r a n s m i s s i o n T h e l o w n o i s e - i m m u n e m e a n s e r r o r s a t t h e d a t a e f f e c - e r r o r t o APPLICATION APPLICATION PRESENTATION PRESENTATION T h e I S 0 / T C 9 7 o n C o m p u t e r s a n d I n f o r m a - t i o n P r o c e s s i n g a v o i d e d a d e f i n i t i o n a t t h e i r m e e t i n g a n d m e r e l y p r i m a r y d i f f e r e n c e s b e t w e e n D a t a N e t w o r k s N e t w o r k s a r e t h a t t h e P u b l i c N e t w o r k s a r e n o t r e s t r i c t e d t o t h e u s e r p r e m i s e s a n d t h a t t h e p r o t o - c o l s a n d f a c i l i t i e s a r e n o t u n d e r u s e r c o n t r o l " (4). i n t e r n a t i o n a l c o m m i t t e e p r e c i s e TRANSPORT TRANSPORT D e c e m b e r 1 9 8 1 n o t e d : Boundary " T h e P u b l i c A r e a D a t a DATA LINK a n d L o c a l iPHYSICAL PHYSICAL TRANSMISSION MEDIA Fig.l: OSI Reference Model

Thomas J. Harrison 16 p r o c e s s i n g d i s t r i b u t i o n m i s s i o n c o n t r o l . s h o u l d v a r i e t y c o m p u t e r s a n d t e r m i n a l s t o g a t e w a y s t o o t h e r n e t w o r k s . a n d t o a n d I n a d d i t i o n , p r o v i d e f o r t h e a t t a c h m e n t o f a o f d e v i c e s e l e c t r o n i c d i g i t a l i n d u s t r i a l / p r o c e s s t h e d o c u m e n t t r a n s - T h e f u n c t i o n s l o w e s t a n d t h e s e r v i c e s ( N e t w o r k ) t h e c o m m i t t e e m e n t i n g w i l l r e q u i r e t i o n s o l e l y f o r t h e p u r p o s e s o f s a t i s - f y i n g l o c a l n e t w o r k L i a i s o n h a s b e e n e s t a b l i s h e d m a j o r g r o u p s d e a l i n g l a y e r s t o e n s u r e , t o t h e d e g r e e b l e , t h a t t h e 8 0 2 c o n s i s t e n t w i t h o t h e r a r d s . I E E E e f f o r t r e p r e s e n t e d l a y e r s ( P h y s i c a l a n d D a t a p r o v i d e d t o t h e t h i r d l a y e r . I t i s t h e f e e l i n g o f t h a t s t a n d a r d s l a y e r s t h r e e l i t t l e * if a n y , m o d i f i c a - i s c o n c e r n e d w i t h t h e t h e L i n k ) v o i c e b y t w o s t a n d a r d s r a n g i n g f r o m i m p l e - s e v e n t h r o u g h T h e s o m e w h i c h S p e c i f i c d i s c u s s i o n a r e t h e u s e o f H D L C ( 7 ) a s a m o d e l ( i f , a n d t o t h e e x t e n t , a p p r o p r i a t e t o d o s o ) , a n d i n d e p e n d - e n c e f r o m t o p o l o g y , t r a n s m i s s i o n a n d s p e c i f i c t r a n s m i s s i o n v a r y i n g d e g r e e s , t h e s e m e t b y t h e e v o l v i n g d i v e r s i t y o f t h e g o a l s , l e d t o t h e r e q u i r e m e n t f o r a n u m b e r o f o p t i o n s i n t h e p r o p o s e d s t a n d a r d m a y s e e m l a r g e a t f i r s t g l a n c e . e r , n o t a l l o p t i o n s a r e i n d e p e n d e n t . F o r e x a m p l e , s e l e c t i n g m e d i a a c c e s s c o n t r o l t h e c h o i c e o f m e d i a a n d t r a n s m i s s i o n m e t h o d t o t w o o u t o f t h e m o r e t h a n s i x i n c l u d e d i n t h e s t a n d a r d . s t a n d a r d r e q u i r e s t h a t t h e m a n u f a c t u r - e r s p e c i f i c a l l y s t a t e a r e i n c o r p o r a t e d i n a g i v e n d e v i c e . a l s o d e f i n e s t h e c r i t e r i a f o r c l a i m i n g c o m p l i a n c e t o t h e s t a n d a r d . s u b c o m m i t t e e s s p e c i f i c h a v e g o a l s a l s o e a r l y t h e i r i n t e r e s t e s t a b l i s h e d i n i t s w o r k e f f o r t . i n r e q u i r e m e n t s . w i t h t h e w i t h t h e h i g h e r g o a l s g u i d e d o f t h i s p o s s i - w i l l s t a n d - s t a n d a r d e m e r g i n g b e it i s r a t e , m e d i a . I n I n m o d e l * t h a t a d o p t e d b y t h e c o m m i t t e e , t h e m o d e l i t s e l f . t e e , c h a i r e d b y M a r i s G r a u b e o f T e k t r o - n i x , h a s b e e n o r g a n i z e d s u b c o m m i t t e e s * l i g h t o f t h e s t r u c t u r e o f t h e O S I t h e n a t u r a l o r g a n i z a t i o n , a n d g o a l s a r e b e i n g s t a n d a r d . h o w e v e r , h a s T h e m i r r o r s c o m m i t - T h e o v e r a l l w h i c h H o w e v - i n t o t h r e e t h e C S M A / C D n a r r o w s T h e M e d i a j o i n t l y b y C h r i s W a r g o o f R C A a n d N a t h a n T o b o l o f s c o p e r o u g h l y c o r r e s p o n d i n g L a y e r 1, o r P h y s i c a l t h e O S I R e f e r e n c e S u b c o m m i t t e e , c h a i r e d m e t h o d C o d e x , h a s a t o T h e p r o p o s e d L a y e r , o f M o d e l . w h i c h o p t i o n s I t T h e C o n t r o l c h a i r e d H o n e y w e l l , 2 ( L i n k ) o f t h e O S I m o d e l . D a t a L i n k ( D L M A C b y c o r r e s p o n d s t o a n d M e d i a S u b c o m m i t t e e ) G e r a l d A c c e s s , C l a n c y o f L a y e r A r e s u l t o f t h e s e c o n f o r m i n g b e a b l e t o c o m m u n i c a t e w i t h e a c h I n s o m e c a s e s , a b l e t o c o e x i s t n e t w o r k . T h a t c o n n e c t e d t o c o m m u n i c a t e w i t h d e v i c e s , a n d d e v i c e s h a v i n g i n c o m p a t i b l e o p t i o n s i s t h a t t w o p i e c e s o f e q u i p m e n t m a y n o t o t h e r . m a y b e p h y s i c a l T h e H i g h m i t t e e , L a d i n s k y H a r v e s t e r u n d e r s t a n d i n g l o c a l f i v e l a y e r s o f t h e O S I m o d e l , , L e v e l I n t e r f a c e c h a i r e d o f i s r e s p o n s i b l e t h e n e t w o r k s S u b c o m - W i l l i a m h o w e v e r , i n t h e s a m e i s , t h e y t h e p h y s i c a l o t h e r n o t i n t e r f e r e t h e y b y I n t e r n a t i o n a l c a n b o t h b e f o r o f m e d i a , e f f e c t t h e c o m p a t i b l e o n h i g h e r w i t h o p t i o n s . R E Q U I R E M E N T S A N D G O A L S T h e g u i d e d t i o n a l e v o l v e d f i r s t f e w m e e t i n g s . a s a n a p p e n d i x D r a f t Β p r o p o s a l (6). c o m m i t t e e i n t h e i r w o r k b y a s e t o f r e q u i r e m e n t s a n d w e r e a n d s u b c o m m i t t e e s a r e f u n c - w h i c h O V E R V I E W O F T H E P R O P O S E D S T A N D A R D a n d g o a l s a p p r o v e d T h e s e a r e i n c l u d e d t o C h a p t e r T h e p r o v i d e s a f r a m e w o r k f o r u n d e r s t a n d i n g t h e 8 0 2 a c t i v i t y . c o n c e r n e d w i t h t h e l o w e s t t w o l a y e r s o f t h e O S I / R t f , t h e p h y s i c a l a n d d a t a l a y e r s . T h e O S I / R M a l l o w s t h e c r e a t i o n g r o u p i n g r e l a t e d f u n c t i o n s . p r o v e d c o n v e n i e n t p r i m a r i l y d u e t o t h e d i f f e r e n t f o r m e d i a a c c e s s c o n t r o l c h a r a c t e r i s t i c s o f t h e M A C h o w e v e r , a r e s u c h s u b l a y e r s i n c l u d e s a t e d w i t h b o t h t h e p h y s i c a l a n d d a t a l i n k l a y e r s o f t h e O S I / R M . s u b l a y e r s t r a d d l e s b e t w e e n L a y e r s 1 a n d 2 i n t h e O S I / R M . O S I R e f e r e n c e M o d e l ( O S I / R M ) d u r i n g t h e P r o j e c t 8 0 2 i s I o f t h e l i n k a n d b y r e c o g n i z e s o f s u b l a y e r s T h e l a y e r e d a r c h i t e c t u r e k e y r e q u i r e m e n t i s t o w h i c h : p r o v i d e a T h i s h a s f o r P r o j e c t 8 0 2 , o p t i o n s ( M A C ) . o p t i o n s , o n e o f t h e f u n c t i o n s • C o r r e s p o n d s S y s t e m s M o d e 1 ; t o t h e I S O R e f e r e n c e O p e n I n t e r c o n n e c t i o n T h e t h a t • P e r m i t s o f m o d e r a t e l y p r i c e d d e v i c e s ; a n d e f f i c i e n t i n t e r c o n n e c t i o n a s s o c i - T h u s , t h e b o u n d a r y • C a n m o d e r a t e i t s e l f b e i m p l e m e n t e d a t t h e p r i c e . T h e f u n c t i o n a l s u p p o r t s t a n d a r d i s a l s o t o p r o v i d e a p p l i c a b i l i t y a p p l i c a t i o n s b r o a d s h o u l d w o r d T h e m a p p i n g o f t h e O S I / R M p h y s i c a l a n d d a t a l i n k l a y e r s i n t o t h e t h r e e a n d l a y e r e d r a n g i n g f r o m

17 IEEE PROJECT 802 L A N / R M L A N / R M N e t w o r k ) L o g i c a l M e d i a A c c e s s i c a l L a y e r s . A c c e s s P o i n t s p o r t s a t t h e 3 / 2 l a y e r t h e O S I / R M N e t w o r k L a y e r . c a l l e d t h e p r o v i d e l o g i c a l a n d M A C l a y e r s , a n d t h e M A C a n d P h y s - i c a l L a y e r s , r e s p e c t i v e l y . i s s h o w n l a y e r s i n F i g . 2 . a r e c a l l e d L i n k C o n t r o l C o n t r o l T h e m u l t i p l e L L C S e r v i c e ( L - S A P s ) p r o v i d e b o u n d a r y T h e t h r e e t h e ( L o c a l ( L N L L C ) , ( M A C ) , a n d P h y s - l o g i c a l w i t h S A P s , P - S A P , S i n g l e t h e M A C - S A P p o r t s a n d b e t w e e n t h e L L C Fig.2: Mapping of OSI and LAN Reference Models T h e l i n k T h e a l l o w s u n i t s r e q u i r e m e n t f o r e s t a b l i s h i n g a l o g i c a l l i n k . T h e s e f r a m e s e d g e d i n t h e L L C l a y e r m i g h t b e a t a h i g h e r e r r o r r e c o v e r y o r p r ο ν i d e d . L N L L C s e r v i c e s T y p e t h e e x c h a n g e b e t w e e n p r o v i d e s t w o t y p e s o f t o t h e N e t w o r k 1 o r C o n n e c t i o n l e s s o f p r o t o c o l t w o L - S A P s l a y e r L a y e r . s e r v i c e d a t a LAN F R A M E S T R U C T U R E M a n y p r o p o s e d L A N c a n b e d i s c e r n e d f i e l d s i n t h e t r a n s m i s s i o n s t a t e d e a r l i e r , S u b c o m m i t t e e w a s H D L C t h e d e g r e e p o s s i b l e . t h e H D L C a n d t h e p r o p o s e d is s h o w n i n Fi g . 3 . o f t h e c h a r a c t e r i s t i c s o f t h e f r o m t h e f r a m e . o f t h e c o n f o r m a n c e t o A c o m p a r i s o n o f L N L L C w i t h o u t t h e A s a r e n o t a c k n o w l - ( a l t h o u g h l a y e r ) f l o w c o n t r o l a g o a l D L M A C t h e y a n d n o a r e f r a m e s T y p e 2 o r c o n n e c t i o n - o r i e n t e d r e q u i r e s t h e l o g i c a l l i n k b e t w e e n t w o L - S A P s t o t h e e x c h a n g e o f u s e r d a t a . t h e d a t a t r a n s f e r t r a n s m i t t e d ( o r s e q u e n c e . B o t h e r r o r r e c o v e r y a n d f l o w c o n t r o l a r e p r o v i d e d . d e v i c e m a y p r o v i d e T y p e 2 s e r v i c e ; h o w e v e r , i n t h e l a t t e r c a s e , i t m u s t a l s o w e l l . s e r v i c e o f p r i o r W h e n i n f r a m e s d e l i v e r e d ) I n c o m p a r i n g t h e H D L C a n d L A N f r a m e s , a n u m b e r o f d i f f e r e n c e s f i e d . T h e f i r s t i s t h a t b o u n d a r i e s a r e d e l i m i t e d " f l a g " f i e l d c o n s i s t i n g s e q u e n c e o f b i t s . d a t a o r a d d r e s s b i t s e q u e n c e t o t h e F f i e l d , d e v i c e s p r o v i d e " b i t t e c h n i q u e t h a t i n s e r t s p r e s c r i b e d m a n n e r t o p r e v e n t t h e f l a g p a t t e r n f r o m r i n g w i t h i n t h e f r a m e . n o t d o n e , a n e r r o n e o u s w o u l d b e d e t e c t e d . e s t a b l i s h m e n t a c a n b e i d e n t i - f r a m e H D L C b y a n F o r o f a m o d e » a r e i n u n i q u e I n o r d e r t o a v o i d a i d e n t i c a l A c o n f o r m i n g T y p e H D L C - c o m p a t i b l e s t u f f i n g , " b i t s w h e n e v e r e i t h e r 1 o r a a i n p r o v i d e T y p e 1 a s n e c e s s a r y o c c u r - I f t h i s f r a m e b o u n d a r y w e r e A t h i r d t y p e o f l i n k s e r v i c e , b e i n g r e f e r r e d t o a s T y p e 1 . 5 , i s b e i n g c o n s i d e r e d b u t i s n o t y e t i n c l u d e d i n t h e p r o p o s a l . I t c o n n e c t i o n l e s s - a c k n o w l e d g e d t h a t p r o v i d e s a s i m p l e w i t h o u t e r r o r r e c o v e r y ( e . g . , ic r e t r a n s m i s s i o n ) o r f l o w c u r r e n t l y w o u l d p r o v i d e s e r v i c e a c k n o w l e d g e m e n t a u t o m a t - c o n t r o l a A f t e r s u b c o m m i t t e e t h a t t h e H D L C t h e h i $ h - s p e e d f o r t h e L A N . T h i s s t e m s f o r n o n - l i n e a r s m i s s i o n ond c o n s i d e r a b l e d i s c u s s i o n , t h e t h e r e a c h e d f l a g s a r e u n d e s i r a b l e i n e n v i r o n m e n t f r o m t h e n e e d c o d i n g d u r i n g t h e t r a n - r e c e i p t o f d a t a a n d i t s c o n c l u s i o n 3. e n v i s i o n e d T h e f u n d a m e n t a l l y a p p l i c a t i o n - e n t i t y " c a p t u r e " t h e p h y s i c a l u s e . T h r e e p r o v i d e d i n C a r r i e r - S e n s e C o l l i s i o n T o k e n — P a s s i n g » a n d B u s T o k e n - P a s s i n g . M e d i u m A c c e s s C o n t r o l p r o v i d e s w i t h t h e a b i l i t y t o m e d i u m f o r i t s c o n t r o l m e t h o d s t h e p r o p o s e d M u l t i p l e - A c c e s s D e t e c t ( C S M A / C D ) , ( M A C ) l a y e r a n a r e s t a n d a r d : INFORMATION (I) FCS F w i t h R i n g F s Flag (Frame Delimiter) A = Address (Destination) C = Control FCS = Frame Check Sequence T h e t i o n s r e c e i v e P - S A P s . a r e p r o v i d e d i n t h i s i n c l u d i n g c o a x , a n d s y s t e m s . C o n s i d e r a t i o n i s b e i n g t o a f i b e r o p t i c m e d i u m a s w e l l . P h y s i c a l n e c e s s a r y b i t s S e v e r a l L a y e r p r o v i d e s t h e f u n c - t o t r a n s m i t b e t w e e n p e e r - e n t i t y t r a n s m i s s i o n i n i t i a l b r o a d b a n d a n d b a s e b a n d s h i e l d e d t w i s t e d a n d s c h e m e s s t a n d a r d , DA = Destination Address SA = Source Address DAP = Destination SAP Address SSAP = Source SAP Address Preamble Length Count : Padding Octets = Start Frame Delimiter = End Frame Delimiter PAD SFD EFD b o t h p a i r g i v e n TOKEN—PASSING METHOD FRAME I n a c c e s s t h i s p r o v i d e d " a d d r e s s r e c o g n i z e d " t h e r i n g m e t h o d t y p e t o k e n - p a s s i n g d i s c u s s e d s e r v i c e t h e m e d i a l a t e r , AC1 = Access Control 1 (Ring Only) AC2 - Access Control 2 IDL = Idle Time Fill (Ring Only) o f b y f u n c t i o n i s " c o p y " i n d i c a t o r s . a n d Fig.3: HDLC and 802-LAN Frame Structures

Thomas J. Harrison 18 s t a t i o n s o n a n y g i v e n l i n k m u s t u s e t h e s a m e l e n g t h a d d r e s s e s . e q u i p m e n t i s n o t r e q u i r e d t o i m p l e m e n t b o t h 2 a n d 6 o c t e t a d d r e s s e s . i m p l i c a t i o n s p e r f o r m a n c e , s u s c e p t i b i l i t y t o e r r o r . a d o p t e d f o r f r a m e , p r e a m b l e , t a k e a d v a n t a g e n i q u e s u t i l i z e d T h e y p r o v i d e , F C S , a H a m m i n g d i s t a n c e o f a t l e a s t A . i n t e r m s i m p l e m e n t a t i o n , o f h a r d w a r e C o n f o r m i n g a n d T h e p a t t e r n s f r a m e , a n d i d l e d e l i m i t e r s o f t h e e n c o d i n g f o r t r a n s m i s s i o n . t o g e t h e r w i t h a s t a r t i n g e n d i n g 4 e W i t h a 6 o c t e t p o s s i b l e a d d r e s s e s . t h i s h u g e t h e d e s i r e " U n i v e r s a l a d d r e s s i n g E t h e r n e t * . p i e c e o f e q u i p m e n t c o u l d h a v e a u n i q u e a d d r e s s t h r o u g h o u t e x a c t m a n n e r i n w h i c h a d m i n i s t e r e d h a s n o t b e e n b u t i s b e i n g p u r s u e d b y t h e c o m m i t t e e . T h e s e c o n d b i t o f t h e S A a n d D A is s e t t o z e r o t o i n d i c a t e a d d r e s s a n d t o o n e t o i n d i c a t e a d m i n i s t e r e d a d d r e s s e s . t h e r e f o r e , t h e r e a d d r e s s s p a c e s , e a c h a d d r e s s e s . T h e l a r g e t e r e d a d d r e s s i n g r a n g e a l s o o f f e r s t h e u s e r t h e p o s s i b i l i t y t h e a d d r e s s f o r s o m e a s s o c i a t i n g a b l o c k o f a d d r e s s e s w i t h a p a r t i c u l a r b u i l d i n g i n a m u 1 t i b u i 1 d i n g c o m p l e x . a d d r e s s , t h e r e a r e 2 T h e r a t i o n a l e f o r a d d r e s s i n g r a n g e t o a c c o m m o d a t e P r o d u c t C o d e c o n c e p t i n t r o d u c e d T h e i d e a i s t e c h - c o m e s f r o m t h e ( U P C ) " 3 2 - b i t b y A s e c o n d d i f f e r e n c e t h e H D L C a n d L N L L C f r a m e s i s t h e i n c l u - s i o n o f a d d i t i o n a l t h e L A N . H D L C p o i n t - t o - p o i n t l i n k s , w h e r e o n l y t w o s t a t i o n s m u l t i p o i n t u n b a l a n c e d t r a n s m i t t i n g s t a t i o n a p r i m a r y s t a t i o n s t a t i o n r e s p o n d i n g t h e p e e r m u l t i p o i n t p r o v i d e d b y t h e L A N , p e r m i s s i o n t r a n s m i t i s n o t r e q u i r e d a n d m u l t i p l e s o u r c e s c a n b e c o n c u r r e n t l y m e s s a g e s t o t h e s t a t i o n . A s a r e s u l t , s t a t i o n s m u s t b e t o l d t h e i d e n t i t y o f t h e s e n d i n g s t a t i o n o u t t h e t r a n s m i s s i o n s . t h e c o n c e p t o f c o n c u r r e n t m u l t i p l e h i g h e r - l a y e r n o t e d i n c o m p a r i n g t h a t e v e r y a d d r e s s f i e l d s f o r p r o v i d e s t h e r e a r e o n t h e l i n k , a n d l i n k s , w h e r e t h e i s a l w a y s o r a t o a p r i m a r y . e n v i r o n m e n t t h e w o r l d ! t h i s d e t e r m i n e d , T h e b e f o r w i l l e i t h e r s e c o n d a r y " u n i v e r s a l " l o c a l l y E f f e c t i v e l y , t w o d i s t i n c t c o n t a i n i n g l o c a l l y a I n a r e t o 4 fe 2 a d m i n i s - s e n d i n g s a m e d e s t i n a t i o n t h e r e c e i v i n g o f p u r p o s e p a r t i t i o n i n g s u c h a s i n o r d e r t o I n s o r t a d d i t i o n , a c c e s s p r o t o c o l s t o S e r v i c e A c c e s s P o i n t ( S A P ) A d d r e s s e s t h r o u g h m e a n s h e n c e , t h e S A P a d d r e s s ) b e i n g b y t h e s o u r c e s t a t i o n s . T h e r e s u l t , t h e a d d i t i o n o f t h e S A , D S A P , a n d S S A P f i e l d s a s , if y o u l i k e , t h e H D L C a d d r e s s i n g t h e u s e o f t o i d e n t i f y S A P s t h e p r o t o c o l ( a n d , r e q u i r e s a I n a c c o r d a n c e w i t h t h e O S I / R M , S A P s a r e i d e n t i f i e d b y a d d r e s s e s . t h e f i r s t b i t I n d i v i d u a l / G r o u p i n d i c a t o r s e c o n d i s s e t t o b i n a r y 1 a n d r e s e r v e d f o r f u t u r e , b u t u n s p e c i f i e d , u s e . T h i s l e a v e s a d d r e s s e s t h a t c o u l d i n d i v i d u a l p r o t o c o l s b e t w e e n t h e D L C a n d N e t w o r k F o r t h e S S A P , t h e c o n c e p t d o e s n o t m a k e f i r s t b i t i s u s e d a s a C o m m a n d / R e s p o n s e ( C / R ) b i t , a s i n H D L C u t i l i z e d d e s t i n a t i o n t h e r e f o r e , I n t h e D S A P , p r o v i d e s a n d t h e a n d t h e i s e x t e n s i o n s o f c o n c e p t . c o m m i t t e e f o r S A P s i x b i t s c o r r e s p o n d a t t h e b o u n d a r y t o L a y e r s . A d d r e s s ι η g i n d i v i d u a l / g r o u p s e n s e s o t h e S o u r c e a n d D e s t i n a t i o n A d d r e s s e s D e s t i n a t i o n i n d i v i d u a l a d d r e s s e s . u n i q u e l y a n d , f r o m H D L C a d d r e s s i n g . i d e n t i f y m o r e d e s t i n a t i o n o f t h e m e s s a g e . in t h e f i r s t o c t e t o f t h e D A a d d r e s s a n d z e r o v i d u a l a d d r e s s . a d d r e s s ( a l l o n e s ) i s d e s i g n a t e d a s a n " a l l s t a t i o n " a d d r e s s , a l l c o n n e c t e d s t a t i o n s . a d d r e s s h a s n o m e a n i n g f i r s t b i t o f t h e f i r s t o c t e t i s a l w a y s z e r o s o a s t o m a i n t a i n a d d r e s s a s s i g n m e n t . g r o u p a d d r e s s e s c a n n o t b e u s e d i n t h e c o n n e c t e d c l a s s o f s e r v i c e ( T y p e 2 ) a n d g r o u p t r a n s m i s s i o n s e d g e d a t t h e L N L L C l e v e l . a d d d e s s e s o r I n d i v i d u a l i d e n t i f y s t a t i o n s o n t h e l i n k c o n c e p t u a l l y , r e m a i n m a y b e e i t h e r g r o u p ( m u l t i c a s t ) a d d r e s s e s C o n t r o l F i e l d s u n c h a n g e d a d d r e s s e s G r o u p t h a n o n e s t a t i o n a s t h e T h e s i n g l e - o c t e t C c o n t r o l i n F i g . 3 i s u s e d t o d e s i g n a t e a n d r e s p o n s e f u n c t i o n s L L C l a y e r . I n a d d i t i o n , f r a m e s e q u e n c e T h e g e n e r a l f o r m a t s i d e n t i c a l t o a l t h o u g h t h e r e a r e d i f f e r e n c e s d e f i n e d c o m m a n d f o r m a t s p r o v i d e f o r n u m b e r e d t i o n t r a n s f e r n u m b e r e d s u p e r v i s o r y b e r e d c o n t r o l , i n f o r m a t i o n t r a n s f e r T h e a v a i l a b l e c o m m a n d s a r e a s u b s e t o f t h o s e a s s o c i a t e d w i t h f i e l d s h o w n c o m m a n d A o n e b i t o f t h e i n d i c a t e s i d e n t i f i e s a n A s p e c i a l p o s i t i o n f i r s t g r o u p i n d i - g r o u p i n v o k e d a t t h e i t c o n t a i n s w h e n r e q u i r e d . o f t h e f i e l d a r e u s e d i n a n u m b e r s t h o s e H D L C r e c o g n i z e d b y S i n c e a g r o u p a s a S A , t h e i n t h e T h r e e i n f o r m a - s e r v i c e ) , u n n u m - u n n u m b e r e d f u n c t i o n s . ( T y p e 2 c o n s i s t e n c y i n I n a d d i t i o n , t r a n s f e r , a n d ( T y p e 1 s e r v i c e ) . a r e n o t a c k n o w l - H D L C w i t h a d d i - T h e S A a n d D A a r e o f e q u a l m a y b e e i t h e r 2 o r 6 o c t e t s l e n g t h a n d l o n g . A l l E t h e r n e t C O R P O R A T I O N . i s a t r a d e m a r k o f X E R O X

19 IEEE PROJECT 802 p r o p o n e n t s m e t h o d s t h a t s i n g l e t e c h n i c a l e n c e s . i n t o t w o g r o u p s , n e i t h e r o f w h i c h " o u t v o t e " t h e o t h e r . a n d i t s d e p r e c a t o r s . w e r e o r t h o g o n a l t h e y c o u l d n o t b e m e r g e d p r o p o s a l d u e t o a n d p h i l o s o p h i c a l T h e c o m m i t t e e T h e t i o n a l T h e y r e a d y e x c h a n g e c o m m a n d s i n c l u d e ( n o t i d e n t i f i c a t i o n . u n i q u e t h i n g s r e a d y ) . t o t h e L A N . a s r e c e i v e r e j e c t , i n t h e s e n s e i n t o a f u n d a m e n t a l d i f f e r - b e c a m e p o l a r i z e d s u c h a n d T h e A C a n d L C f i e l d s c a n b e c o n s i d e r e d a s s p e c i a l i z e d c o n t r o l t o k e n - p a s s i n g a n d C S M A / C D m e d i a m e t h o d s . C S M A / C D r e q u i r e s f r a m e s i z e f o r p r o p e r o p e r a t i o n s o t h a t s o m e p a d d i n g o f t h e i n f o r m a t i o n is n e c e s s a r y w h e n b y t e s is s m a l l ( o r z e r o ) . i n d i c a t e s t h e t o t a l n u m b e r o f o c t e t s i n t h e D S A P , S S A P , C , a n d I ( I n f o r m a t i o n ) f i e l d s s o t h a t t h e r e c e i v e r c a n s t r i p o f f t h e p a d d i n g b i t s . a s a s e p a r a t e f i e l d , t h e P A D f i e l d i s r e a l l y a v a r i a b l e p a r t o f t h e I - f i e l d . c o u l d f i e l d s f o r t h e a c c e s s m i n i m u m a D e s p i t e s i n g l e m e t h o d , i t b e c a m e c l e a r t h a t t h e a d v a n t a g e s o f e a c h t a n t f o r p a r t i c u l a r F e a r i n g t h a t f u r t h e r r e s u l t i n a p r o l i f e r a t i o n o f i n c o m p a t - i b l e e q u i p m e n t c o m m i t t e e a d o p t e d p r a g m a t i c c o m p r o m i s e . b e t t e r t o a g r e e o n t w o m e t h o d s d e l a y o r d e f e a t t h e e n t i r e F o r t u n a t e l y , t h e d e c i s i o n t o t h e L i n k L a y e r o f t h e O S I / R M b o t h m e t h o d s t o u t i l i z e the s a m e s o that a h i g h d e g r e e o f s t i l l exists. a s t r o n g d e s i r e t o h a v e a f i e l d d a t a m e t h o d w e r e a p p l i c a t i o n s . d e l a y w o u l d i m p o r - t h e n u m b e r o f T h e L C f i e l d o n l y o f f e r i n g s , b o t h m e t h o d s I t t h e a s a f e l t A l t h o u g h s h o w n w a s t h a n t o s t a n d a r d . s u b l a y e r a l l o w s L N L L C , c o m m o n a l i t y ( i n c l u d i n g z e r o ) T h e A C f i e l d s p r o v i d e c o n t r o l t i o n f o r t h e M A C t o k e n - p a s s i n g T h e r i n g t o k e n - p a s s i n g m e t h o d b o t h A C 1 a n d A C 2 » s i n g l e o c t e t . s t a t e i n d i c a t o r p r i o r i t y a n d s i n g l e b i t i s r e s e r v e d f o r u s e b y t h e o p t i o n a l c e n t r a l i z e d m o n i t o r i n f o r m a - i n t h e m e t h o d s . u t i l i z e s s u b l a y e r a c c e s s m e d i a e a c h o f w h i c h i s a A C 1 c o n t a i n s t h e t o k e n a n d t h e r e s e r v a t i o n o p t i o n a l b i t s . C a r r i e r - S e n s e C o l l i s i o n D e t e c t ( C S M A / C D ) M u l t i p l e A c c e s s u i t h A f u n c t i o n . T h e d e s i g n D E C , c o n c e p t f o r s h a r i n g t h e p h y s i c a l s m i s s i o n m e d i a l i s t e n s b e f o r e t r a n s m i t t i n g t o d e t e r - m i n e if t h e l i n e i s i d l e . t h e s t a t i o n d e f e r s i d l e f o r a c e r t a i n e n s u r e t h a t t h e m e d i a a n d s t a t i o n s r e c o v e r e d . O n c e t h e t r a n s m i t t i n g i t s f r a m e , t o l i s t e n f o r a s i m i l a r t o m a k e s u r e t h a t a s i g n a l h a s n o t o c c u r r e d . e s s e n t i a l l y e q u a l t o t h e m a x i m u m t r i p p r o p a g a t i o n d e l a y t h e c o l l i s i o n d e t e c t i o n c o l l i s i o n w i l l o c c u r d o w " if t w o s t a t i o n s d e t e r m i n e t h e l i n e is i d l e a n d b e g i n t r a n s m i s s i o n , o n l y t o h a v e t h e t r a n s m i s s i o n s c o l l i d e s t a t i o n s . T h e n e e d f o r t h e s t a t i o n t o r e m a i n a c t i v e d u r i n g t h e e n t i r e s i o n w i n d o w a l s o e s t a b l i s h e s a m i n i m u m f r a m e s i z e , g i v i n g r i s e t o t h e r e q u i r e - m e n t f o r t h e L C ( L e n g t h T h e m i n i m u m f r a m e s i z e i s d e p e n d e n t o n b o t h t h e t r a n s m i s s i o n p h y s i c a l e x t e n t o f t h e n e t w o r k . C S M A / C D f o r E t h e r n e t I n t e l , a n d X e r o x m e t h o d i s 4 a s a n n o u n c e d b y ( 8 ) . T h e b a s i c b a s e d o n t h e T h e A C 2 f i e l d i n t h e r i n g m e t h o d c o n t a i n s ( r e s e r v e d f o r f u t u r e c a t i n g if t h e f r a m e is t o b e u s e d b y t h e M A C o r L N L L C s u b l a y e r , a n d 6 b i t s t o e n c o d e M A C c o m m a n d s . t o k e n - p a s s i n g m e t h o d , A C 2 i s u s e d f o r c o n t r o l f u n c t i o n s b u t n o t a l l i d e n t i c a l , t o t h o s e u s e d o n t h e r i n g . t o k e n - p a s s i n g e x t e n s i o n u s e ) » a b i t i n d i - a n b i t t r a n - s t a t i o n i s t h a t a I f it i s n o t , u n t i l t h e l i n e i s p e r i o d o f t i m e t o I n t h e b u s t h a t a r e s i m i l a r , h a v e s t a t i o n i t p e r i o d o f t i m e " c o l l i s i o n " T h i s p e r i o d b e g i n s c o n t i n u e s T h e t r a n s m i t f o r a m i n i m u m a p p r o x i m a t e l y e q u a l t o t h e p r o p a g a t i o n a n d p r o c e s s i n g d e l a y p h y s i c a l r i n g . F o r s h o r t l a r g e r i n g , t h i s r e q u i r e m e n t i s s a t i s - f i e d b y t r a n s m i t t i n g a n i d l i n g a s i n d i c a t e d b y t h e o p t i o n a l I D L f i e l d . r i n g m e t h o d r e q u i r e s a s t a t i o n t o l e n g t h o f t i m e i s r o u n d ( l a t e n c y ) o f t h e f r a m e s o r a d e l a y s i n h a r d w a r e . d u r i n g t h i s p l u s A " w i n - s i g n a l t r a i l i n g b e t w e e n S e q u e n c e ) i s four T h e F C S ( F r a m e o c t e t s l o n g i n a l l t h e a c c e s s T h e c h e c k s e q u e n c e b e i n g c y c l i c r e d u n d a n c y u t i l i z e s t h e χ 3 2 + χ2 6 + χ2 3 + χ2 2 + χ1 É > + χ1 2 + χ1 1+ C h e c k c o l l i - m e t h o d s . u t i l i z e d i s a c h e c k ( C R C ) a n d g e n e r a t o r C o u n t ) f i e l d . p o l y n o m i a l r a t e a n d t h e χ1 0 + χ8 + χ7 + χ5 χΑ + χ2 + χ + 1 , + I f a c o l l i s i o n i s d e t e c t e d , t h e s t a t i o n r e i n f o r c e s t h e c o l l i s i o n b r i e f p e r i o d o f t i m e ( t h e " j a m t i m e " ) t o e n s u r e t h a t a l l s t a t i o n s E a c h t r ar>sm i 1 1 i n g q u i e s c e s a n d d e l a y s m i s s i o n a t t e m p t s b y a t i m e p e r i o d . T h e s e t o f n u m b e r s w h i c h t h e r a n d o m i z a t i o n d o u b l e s t h e t i m e t o e a c h r e t r y ( k n o w n a s b i n a r y e x p o n e n t i a l s i g n a l f o r a M E D I A A C C E S S C O N T R O L M E T H O D S d e t e c t i t . s t a t i o n s u b s e q u e n t p s e u d o - r a n d o m T h e a c c e s s c l a s s i c a l a r e , a n d m u s t b e , d e v e l o p e d . t h e a c t i v i t y , t w o p o t e n t i a l m e t h o d s w e r e p r o p o s e d . a d v a n t a g e s a n d c o m m i t t e e c o n t r o l d e c i s i o n s m e c h a n i s m s e x a m p l e r e g a r d i n g r e p r e s e n t a h o w s t a n d a r d s E a r l y i n c a n d i d a t e E a c h h a d i t s d i s a d v a n t a g e s , t h e n t r a n s - o f o n b a s e d a t t e m p t b a c k o f f ) . i s i t s

20 Thomas J. Harrison i f i e d r e l a t i v e l y d a t i o n s c a b l e f o r s i g n a l f r o m t h e c a b l e t a p p o i n t . r e q u i r e m e n t t i o n r e q u i r e m e n t s i f , f o r e x a m p l e , t h e t a p p o i n t i s l o c a t e d i n a c e i l i n g o r w a l l c a v i t y s i n c e it i m p l i e s t h e n e e d f o r a c t i v e e l e c t r o n i c t h e t a p l o c a t i o n . a l o n g t h e c a b l e ; 3 ) a s t r i n g e n t s e t o f r e g a r d i n g c a b l e s e g m e n t l e n g t h s ; a n d 4 ) t h e n e e d a m p l i f i c a t i o n d o w n t h e d r o p l o c a t i o n s C M S A / C D P r o p e r t i e s . r e c o m m e n - c o u p l i n g a n d T h e C S M A / C D a r e t h a t i t i s c o m p l e t e l y in t h e s e n s e t h a t e v e r y s t a t i o n c o n t e n d s f o r a c c e s s ; it i s a s i m p l e a n d e a s i l y i m p l e m e n t e d a n d it i s q u i t e e f f i c i e n t l o a d i n g i s l o w i m p o r t a n t c h a r a c t e r i s t i c s o f f a i r e q u a l l y T h i s l a t t e r m a y c o m p l i c a t e i n s t a l l a - a c c e s s a l g o r i t h m , w h e n t r a f f i c 5. c o m p o n e n t s a t C S M A / C D w h i c h m a y b e u n d e s i r a b l e i n s o m e c a t i o n s . T h e m e t h o d s o t h a t > if i t i s n e c e s s a r y l o a d , it c a n n o t d e s i r a b l e f e a t u r e o f h i g h e r p r i o r i t y . t h e r e f o r e , r e s p o n s e t i c a l r a t h e r t h a n d e t e r m i n i s t i c . i s o f t e n c o n s i d e r e d r e a l - t i m e e n v i r o n m e n t . t i m e s a t u r a t i o n f u r t h e r m o r e , i s a s y m p t o t i c t o i n f i n i t y a t a r e l a t i v e l y l o w l o a d i n g v a l u e e x p r e s s e d b y s o m e p e r f o r m a n c e d e p e n d e n c e o n d e l a y m a y l i m i t t h e s y s t e m e v o l u t i o n a s f u t u r e e n h a n c e m e n t s d i s t a n c e o r t r a n s m i s s i o n c o n s i d e r e d . T h i s i s b e c a u s e t h e m i n i - m u m a c c e p t a b l e f r a m e w i t h e i t h e r a n i n c r e a s e l e n g t h o r t h e t r a n s m i s s i o n C S M A / C D i s d i r e c t l y a p p l i c a b l e b u s t o p o l o g i e s a n d , t h e r e f o r e , n o t s a t i s f y a p p l i c a t i o n s t o p o l o g i e s m a y b e m o r e a l s o h a s s o m e c h a r a c t e r i s t i c s a p p l i - u n f a i r t o s h e d c a n n o t b e T o k e n A c c e s s M e t h o d s b e d i s c r i m i n a t o r y , a w h e n s o m e t r a f f i c i s A c c e s s t i m e is C o n c e p t u a l l y , t h e t o k e n a c c e s s a r e a s s i m p l e a s C S M A / C D , a l t h o u g h t h e m e d i a m a n a g e m e n t f u n c t i o n s c o m p l e x a n d i m p l y c a p a b i l i t y i n t h e a t t a c h e d d e v i c e . T h e b a s i c c o n c e p t i s t h a t t h e s t a t i o n s o n t h e L A N a r e f o r m e d w h e t h e r o r n o t t h e p h y s i c a l t o p o l o g y i s a r i n g . C o n t r o l o f t h e t r a n s m i s s i o n m e d i u m i s p a s s e d b e t w e e n s t a t i o n s i n a n o r d e r e d s e q u e n c e b y m e a n s o f a " t o k e n " . T h e t o k e n r e p r e s e n t s a " p e r m i s s i o n t o t r a n s m i t " t h a t g r a n t s e x c l u s i v e u s e o f t h e t r a n s m i s s i o n m e d i u m f o r a t i m e d e t e r m i n e d b y a t i m e r . " D e p e n d i n g t o k e n - h o l d i n g t i m e l e n g t h , t h e s t a t i o n m u l t i p l e f r a m e s d u r i n g " w i n d o w , " a s o p p o s e d f r a m e i n h e r e n t i n t h e C S M A / C D A t t h e c o m p l e t i o n o f t h e w i n d o w o r w h e n t h e s t a t i o n h a s t r a n s m i t t e d a l l w a i t - i n g f r a m e s ( p o s s i b l y t h e t o k e n t o t h e n e x t l o g i c a l r i n g . m e t h o d s t i m e a n d , s t a t i s - a r e m o r e T h i s i n a g r e a t e r l o g i c a l u n a c c e p t a b l e T h e c h a r a c t e r i s t i c , n o n l i n e a r , r e s p o n s e i n t o a l o g i c a l r i n g b e c o m i n g f e. C o n c e r n t h a t i s a l s o s y s t e m t h e p r o p a g a t i o n t o i n c r e a s e s p e e d m a x i m u m a r e " t o k e n - h o l d i n g o n a n d t h e m a y t r a n s m i t t h i s t r a n s m i t t o t h e t h e f r a m e s i z e i n t h e m e d i u m i n c r e a s e s r a t e . o n l y t o d o e s o t h e r s i n g l e m e t h o d . w h e r e a p p r o p r i a t e . n o n e ) , s t a t i o n i n t h e i t p a s s e s D e s p i t e m e t h o d w h e n c o m p a r e d t o t h e p r o c e d u r a l a s p e c t s o f t h e t o k e n i c a l i m p l e m e n t a t i o n p l a c e a d d i t i o n a l d e m a n d s o n a n d i n s t a l l a t i o n l i s t e n - w h i l e - t r a n s m i t t i n g m e a n s t h a t t h e d y n a m i c m u s t b e l i m i t e d . D E C / I n t e 1 / X e r o x d e f i n i t i o n , t h i s is a b o u t 1 0 - 1 2 d B . T h i s , a n d t h e n e e d f o r i m p e d a n c e m a t c h i n g r e f l e c t i o n s , l e a d s t o : 1) t h e u s e o f 5 0 o h m c o a x i a l c a b l e f o r b a s e b a n d m i s s i o n r a t h e r t h a n t h e m o r e u s e d 7 5 o h m c a b l e ; 2 ) t h e r e q u i r e m e n t t o p l a c e t r a n s c e i v e r s t h e s i m p l i c i t y o f t h e a c c e s s a p p r o a c h , o f C S M A / C D p h y s - m a y T h e m o r e C S M A / C D . r e q u i r e d t o i n i t i a l i z e t h e t o k e n p a s s - i n g s e q u e n c e i n t h e c a s e o f t o p o l o g i e s , a s w e l l a s f o r a d m i n i s t r a - t i v e ( m o n i t o r i n g ) e r r o r c o n t r o l t o d e t e c t f a u l t s , e . g . , t h e l o s s o f t h e t o k e n o r t h e e x i s t e n c e o f m u l t i p l e s t a n d a r d p r o v i d e s t h a t t h e m o n i t o r i n g f u n c t i o n b e r e p l i c a t e d in a l l s t a t i o n s c a p a b l e o f p a s s i n g t h e t o k e n , c e n t r a l i z e d c o n t r o l i s n o t p r e c l u d e d . c o n t r o l c o m p l e x o f a t o k e n t h a n S p e c i f i c a l l y , a c c e s s L A N i s t h e c a s e m e a n s e q u i p m e n t i n o f a r e p r a c t i c e s . T h e r e q u i r e m e n t s i g n a l I n t h e c a s e o f t h e r a n g e n o n - r i n g l i m i t f u n c t i o n s s u c h c o r r e c t a s a n d t o a v o i d t o k e n s . T h e t r a n s - c o m m o n l y a l t h o u g h o n l y a t p r e s p e c - 5 D u e t o t h e s t a t i s t i c a l t h e m e t h o d , l a t i o n s d e p e n d o n t h e s t a t i s t i c a l a s s u m p t i o n s r e g a r d i n g m e s s a g e l e n g t h s , t h e r e i s c o n t i n u i n g t h e s e c a l c u l a t i o n s , s o u r c e ( 9 ) s u g g e s t g o o d u p t o a t r a f f i c 4 0 % o f t h e t o t a l b u s c a p a c i t y . U n d e r a s e t o f s t a t e d t h e a s y m p t o t e o c c u r s m a t e l y 5 5 % o f o f f e r e d a n d 1 0 M b p s ( 9 ) n a t u r e o f c a l c u - B u s T o k e n - P a s s i n g O p e r a t i o n e f f i c i e n c y T h e a c c e s s m e t h o d s d i f f e r p h y s i c a l t o p o l o g y o f t h e n e t w o r k . t h e s o - c a l l e d n o n - p h y s i c a 1 - r i n g t h e b u s a n d s t a r , t h e M A C l a y e r t a i n s a r e c o r d o f t h e p r e d e c e s s o r a n d s u c c e s s o r n o d e s i n t h e l o g i c a l I t a l s o h a s m e a n s l o g i c a l r i n g , a d m i t t i n g n o d e s w i t h t h e n e c e s s a r y a d j u s t m e n t o f d e t a i l s o f t h e t o k e n - p a s s i n g d e p e n d i n g o n t h e l o a d i n g , A l t h o u g h d e b a t e a t l e a s t o n e e f f i c i e n c y l o a d i n g o f e t c . I n o r a s o v e r " b r o a d c a s t " t o p o l o g i e s s u c h m a i n - a b o u t r i n g . t h e fe a s s u m p t i o n s , a t a p p r o x i - l o a d a t 2 k m f o r c r e a t i n g o r d e l e t i n g

IEEE PROJECT 802 21 s t a t i o n c l a i m i n g t o h a v e t h e t o k e n , t h e s t a t i o n m u s t " d r o p t h e t o k e n " a n d e n t e r t h e w a t c h i n g m o d e . c a t e t o k e n s a r e e v e n t u a l l y p r e d e c e s s o r a d d r e s s e s , a n d h a n d l i n g l o s t o r m u l t i p l e a r e c o n n e c t e d l i n e a n d r e c e i v e S t a t i o n s n o t c a p a b i l i t i e s c a n c o e x i s t o n t h e p h y s - i c a l n e t w o r k a n d c a n r e s p o n d t o q u e r i e s f r o m t h e t o k e n - h o l d i n g a s t h e r e s p o n s e i s w i t h i n t h e p r i m a r y s t a t i o n ' s t o k e n h o l d i n g t i m e . t i o n , i t s r e s p o n s e o t h e r s t a t i o n s . p r i m a r y - s e c o n d a r y r e l a t i o n s h i p . a n d s u c c e s s o r s t a t i o n f a u l t s s u c h a s t o k e n s . A l l s t a t i o n s i n p a r a l l e l a l l t r a n s m i s s i o n s . h a v i n g t o k e n - h a n d l i n g I n t h i s w a y , d u p l i - e l i m i n a t e d . a c r o s s t h e P r o c e d u r e s a r e p r o v i d e d f o r i n i t i a l i z - i n g t h e l o g i c a l r i n g , t o r i n g ( a d m i n i s t r a t i v e r e s p o n s i b i l i t y , a n d a d d i n g a n d d e l e t - i n g s t a t i o n s . T h e p r o c e s s i n v o l v e s a " c o n t e s t " i n w h i c h t h e w i n n i n g s t a t i o n h a s t h e r i g h t t o b e t h e i n i t i a l i z e r . i n v o l v e s t h e u s e o f a " d e m a n d t h r o u g h w h i c h s t a t i o n s e n t r y i n t o t h e l o g i c a l s u b s e q u e n t a l g o r i t h m s i m u l t a n e o u s r e q u e s t s s t a t i o n s . a s s i g n i n g m o n i - c o n t r o l ) s t a t i o n a s l o n g i n i t i a l i z a t i o n I n a d d i - c o n f u s e a l l o w s t y p e m u s t T h i s n o t A d d i n g s t a t i o n s w i n d o w " r e q u e s t r i n g a n d a w h i c h s o r t s o u t b y m u l t i p l e a o f c a n A m o d e s : t o k e n , p a s s i n g t h e t o k e n , i n i t i a l i z i n g t h e r i n g , c l a i m i n g t h e t o k e n , o r s e n d - i n g a n i m m e d i a t e r e s p o n s e t o t h e t o k e n h o l d e r . Wfien i n t h e w a t c h i n g m o d e , t h e s t a t i o n l i s t e n s t o m e d i u m . W h e n t h e s t a t i o n v a l i d f r a m e a d d r e s s e d f u n c t i o n s p r o c e s s d i r e c t l y o r b y p a s s i n g t h e i n f o r m a t i o n t o t h e L N L L C l a y e r . f r a m e r e q u e s t s a n i m m e d i a t e t h e s t a t i o n s e n d i n g - r e s p o n s e r e c e i v e d f r a m e i s t o k e n , t h e s t a t i o n e n t e r s t h e u s i n g - t o k e n s t a t i o n m a y b e W a t c h i n g t h e m e d i u m , u s i n g t h e i n o n e o f s e v e r a l B u s A t t h e M a r c h 1 9 8 2 m e e t i n g , t h e c o m m i t - t e e i n c o r p o r a t e d a n w h e r e b y a s e t o f s t a t i o n s i s g u a r a n t e e d a c e r t a i n p e r c e n t a g e n u m b e r o f o c t e t s t h a t m i t t e d o n a r o t a t i o n a r o u n d t h e l o g i c a l t h e p r e s e n c e o f t i m e r , t h e m a x i m u m ( o r m a x i m u m o c t e t s t i o n ) i s k n o w n c o r r e s p o n d i n g m a x i m u m c a n b e c o n s i d e r e d a s t h e b a n d w i d t h o f t h e r i n g . I n t h e a d o p t e d m e t h o d , c l a s s e s o f s t a t i o n s t h e s e a r e d e s i g n a t e d ( S ) , A s y n c h r o n o u s c h r o n o u s 2 ( A S 2 ) . T i m e d - T o k e n B a n d w i d t h A l l o c a t i o n . o p t i o n a l m e t h o d o n t h e r e c e i v e s a t o i t , t h e M A C t h e f r a m e a c t i v i t y o f t h e c o u l d b e t r a n s - o f t h e r i n g (10). t h e t o k e n - h o l d i n g t o k e n r o t a t i o n a l l o w e d p e r r o t a - a n d f i x e d . o c t e t s m a x i m u m e i t h e r t o k e n D u e t o I f t h e r e c e i v e d r e s p o n s e , e n t e r s m o d e . t i m e t h e t h e I f T h e a l l o w e d m o d e . t h r e e If t i m e p e r i o d ) t h e s t a t i o n m a y i n f e r t h a t r e s t a r t o f t h e l o g i c a l E i t h e r t h e s t a t i o n c l a i m s t h e t o k e n a n d r e s t a r t s i t a r o u n d t h e o l d l o g i c a l o r i t a t t e m p t s t o l o g i c a l r i n g , d e p e n d i n g o n i t s s t a t e a t t h e t i m e t h e s i l e n c e w h i c h j u s t p a s s e d t h e t o k e n h a s p r i m a r y r e s p o n s i b i l i t y t o r e c l a i m t h e t o k e n i f it i s l o s t . I f t h e t o k e n i s n o t r e c o v - e r e d , o t h e r s t a t i o n s r e i n i t i a l i z a t i o n . t h e s t a t i o n ( g r e a t e r w i t h o u t g o e s t h a n h e a r i n g a n y a c t i v i t y , f o r a a d e f i n e d p r o l o n g e d t i m e o u t a r e a l l o w e d a n d a s S y n c h r o n o u s ( A S 1 ) , a n d A s y n - 1 r e c o v e r y o r r i n g i s n e e d e d . A n p r e d e f i n e d n u m b e r ( N S ) o f o c t e t s e v e r i t r e c e i v e s t h e t o k e n . t h e m a x i m u m n u m b e r a l l o w e d a n d t h e s u m o f c o m p a r e d t o t h e b a n d w i d t h ( i n o c t e t s ) , it c a n b e s e e n t h a t t h e S s t a t i o n s a r e g u a r a n t e e d a m i n i m u m p e r c e n t a g e o f t h e b a n d w i d t h . F u r t h e r m o r e , t h e b a n d w i d t h a l l o c a t e d t o t h e S s h a r e d e q u a l l y a m o n g S s t a t i o n m a y t r a n s m i t u p t o a w h e n - B y k n o w i n g s t a t i o n s t h e i r N S s a s r i n g t h e r e i n i t i a l i z e o f S o c c u r s . T h e n o d e w i l l a t t e m p t s t a t i o n s t h e m . w i l l b e W h e n a s t a t i o n p e r f o r m s f u n c t i o n s s t a t i o n s s m i t s a n y i n f o r m a t i o n . n a n c e f u n c t i o n s a g a i n s t i t s " t o k e n h o l d i n g t i m e . " a l l o f t h e i n f o r m a t i o n h a s b e e n s e n t o r t h e m a x i m u m t o k e n e x c e e d e d , t h e s t a t i o n p a s s e s t h e t o k e n t o t h e n e x t s t a t i o n r i n g . T h e t o k e n is p a s s e d b y a n a b b r e v i a t e d f r a m e ( S F D A C 2 D A S A F C S E F D ) t h a t e x p l i c i t l y t r a n s f e r s t o t h e s u c c e s s o r s t a t i o n . t h e n w a t c h e s f o r a c t i v i t y o n t h e l i n e . A s s o o n a s a n y t h i n g i s h e a r d , i t r e s e t s i t s r e s p o n s i b i l i t y t o k e n a n d r e e n t e r s t h e w a t c h i n g If t h e t o k e n p a s s i s u n s u c c e s s f u l , t h e n o d e a t t e m p t s t o r e c o v e r t h e r e m a i n i n g l i n k a g e s . I f , w h i l e t h e t o k e n , t h e s t a t i o n r e c e i v e s t h e t o k e n , i t l o g i c a l r i n g ( s u c h a s a c c e p t i n g i n t o t h e r i n g ) b e f o r e i t t r a n - s o m e m a i n t e n a n c e T h e g u a r a n t e e d a c t u a l l y t o s e n d , A S 2 s t a t i o n s . e s s e n t i a l l y a c o u n t i n g A S 1 s t a t i o n s a r e a s s i g n e d a n u m b e r w h i c h i s t h e m a x i m u m e a c h s t a t i o n c a n s e n d d o s o . T h e A S 2 s t a t i o n s a r e a s s i g n e d a s i m i l a r n u m b e r N A S 2 . a l l o w e d t o s e n d F S = N A S I - T F S o c t e t s , w h e r e T F S i s t h e t o t a l n u m b e r o f o c t e t s s e n t b y a l l s t a t i o n s i t s e l f ) o n t h e r o t a t i o n . I f F S i s z e r o o r t h e s t a t i o n m a y n o t s e n d a n y f r a m e s . S i m i l a r l y , A S 2 s t a t i o n s m a y s e n d F S = N A S 2 - T F S o c t e t s i f F S i s g r e a t e r z e r o . r e m a i n i n g b a n d w i d t h , p l u s t o t h e S s t a t i o n s b u t n o t u s e d d u e t o a l a c k o f i s s h a r e d a m o n g t h e A S 1 a n d T h e s h a r i n g a l g o r i t h m i s s c h e m e t h a t n e w o c t e t s T h e s e n o t m a i n t e - c h a r g e d W h e n a r e w h e r e b y N A S I o c t e t s a l l o w e d t o h o l d i n g t i m e i s n u m b e r o f w h e n i n t h e l o g i c a l s e n d i n g A S 1 s t a t i o n s a r e c o n t r o l T h e s t a t i o n ( i n c l u d i n g t o k e n n e g a t i v e , p r e v i o u s f o r r e c o v e r i n g t h e m o d e . t h a n i n p o s s e s s i o n o f h e a r s a n o t h e r

22 Thomas J. Harrison ( a s s u m i n g s p a c e " a d d r e s s r e d u n d a n t s e c o n d r e t r a n s m i t s s t a t i o n o n t h e r i n g . i s c o n g e s t e d a n d c a n n o t c o p y t h e f r a m e , it s e t s o n l y t h e A b i t s . Ε b i t s p r o v i d e t h e S A i n f o r m a t i o n n e e d e d f o r e r r o r p r o c e d u r e s . T h e A a n d C b i t c o m b i n a - t i o n e s s e n t i a l l y p r o v i d e s t h e T y p e 1 . 5 c o n n e c t i o n l e s s - a c k n o w l e d g e d m e n t i o n e d e a r l i e r . d a n t b i t s f o r t h e A a n d C p r o v i d e s e r r o r p r o t e c t i o n E F D i s n o t c o v e r e d b y t h e F C S . i t h a s t h e n e c e s s a r y a v a i l a b l e ) , r e c o g n i z e d " ( A ) b i t s a n d t w o " c o p i e d " ( C ) o c t e t o f t h e E F D t o o n e , a n d t h e f r a m e I f t h e D A s t a t i o n b u f f e r T h e d i v i d e t h e b a n d w i d t h a n d A S 2 s t a t i o n s a c c o r d i n g t o t h e r a t i o N A S 1 / N A S 2 . T h e f r a c t i o n a l a s s i g n e d t o A S 1 s t a t i o n s e q u a l l y a m o n g t h e m . l o a d e d c o n d i t i o n s , s t a t i o n s m a y n o t r e c e i v e a f a i r o f t h e b a n d w i d t h s t a t i o n s d e p e n d i n g in t h e l o g i c a l r i n g . c o n s i d e r e d a s e r i o u s h e a v y l o a d i n g p r e s u m a b l y o n l y i n f r e q u e n t l y r e q u i r e m e n t s a r e l e s s t h o s e o f A S 1 a n d S s t a t i o n s . e f f e c t o f t h i s a l g o r i t h m a v a i l a b l e t o A S 1 i s t o s e t s t w o r e d u n d a n t b i t s i n t h e b a n d w i d t h i s s h a r e d U n d e r h o w e v e r , t o t h e n e x t h e a v i l y s o m e A S 2 s h a r e f o r t h e A S 2 o n t h e i r T h i s p r o b l e m w i l l a n d A S 2 d e m a n d i n g T h e A , C , a n d s t a t i o n r e c o v e r y l e f t w i t h p o s i t i o n i s n o t s i n c e o c c u r s e r v i c e t h a n s e r v i c e r e d u n - i n d i c a t o r s s i n c e T h e u s e o f t h e I n ( S A ) o r a n " i d l e " l e a s t t h e f i r s t f r a m e it s e n t t h e r i n g . W h e n i t r e c o g n i z e s i s o w n S A i n t h i s f r a m e , i t n a y s e n d t o k e n " a b b r e v i a t e d E F D ) t o t h e n e x t s t a t i o n o n t h e r i n g . O p t i o n a l l y , it m a y r e c e i v e s t h e l a s t f r a m e i t s e n t . o p t i o n r e d u c e s t h e r i n g p r o v i d e s e a r l i e r a s s u r a n c e s u b s e q u e n t f r a m e s r e c e i v e d c o r r e c t l y . t h e s t a t i o n m e a n t i m e , c o n t i n u e s p a t t e r n o f b i t s t h e t o k e n - h o l d i n g s e n d i n g u n t i l a t t r a v e r s e s R i n g T o k e n - P a s s i n g O p e r a t i o n f r a m e s T h e p h y s i c a l d i f f e r e n t . in s e r i e s n o t i n t e n d e d r e l a y e d a f t e r b y p a s s i n a c t i v e p r e s e r v e a r e p a s s e d w i t h o u t c e s s o r a n d s u c c e s s o r s t a t i o n s i n c e t h e s e a r e i n h e r e n t i c a l c o n n e c t i o n . a c t i o n , a n u n c l a i m e d c i r c u l a t e o n t h e p h y s i c a l s o f r a m e r e m o v a l s a r y . T h e f r a m e i t y b e l o n g s s t a t i o n b u t f a u l t d e t e c t i o n r e m o v e f r a m e s s t a t i o n m a l f u n c t i o n s . o p e r a t i o n o n s e q u e n t i a l m e d i a ( i . e . , s o m e w h a t r i n g ) T h e s t a t i o n s a r e c o n n e c t e d w i t h t h e m e d i u m a n d f r a m e s f o r a g i v e n t o t h e n e x t p h y s i c a l s h o r t p r o c e s s i n g r e l a y f u n c t i o n ( i . e . , o f f l i n e ) c i r c u i t c o n t i n u i t y . f r o m o n e s t a t i o n t o t h e n e x t e x p l i c i t k n o w l e d g e i s a " f r e e f r a m e ( S F D A C 1 A C 2 s t a t i o n a r e s t a t i o n d e l a y . i s p r o v i d e d f o r s t a t i o n s t o w a i t u n t i l i t a A T h i s c a p a c i t y b u t t h a t s e n t a l l a n d T o k e n s w e r e o f a d d r e s s e s i n t h e p h y s - p r e d e - P r e e m p t i v e M a r c h a d o p t e d p r e e m p t i o n m e t h o d . p r o v i d e d c u r r e n t r e s e r v e t h e n e x t f r e e t o k e n a t a h i g h e r p r i o r i t y l e v e l . A h i g h e r p r i o r i t y t h a n t h e t o k e n - h o l d i n g s t a t i o n s e t s t h e r e s e r v a t i o n i t s h i g h e r p r i o r i t y p a s s e s t h r o u g h t h e s t a t i o n . A C 1 f r a m e r e t u r n s t o t h e t o k e n - h o l d i n g s t a t i o n , t h e n e x t f r e e t o k e n i s i s s u e d w i t h i t s p r i o r i t y r e s e r v e d p r i o r i t y l o w e r p r i o r i t y a r e c l a i m i n g t h e t o k e n s o i t p a s s e s t o t h e r e q u e s t i n g s t a t i o n o r a n s t a t i o n o f e q u a l p r i o r i t y f r a m e s t o s e n d . P r i o r i t y m e e t i n g , a n o p t i o n i n t h e r i n g T w o t h r e e - b i t i n A C 1 p r i o r i t y O p t i o n . t h e f o r t o k e n - p a s s i n g f i e l d s t o d e s i g n a t e o f t h e t o k e n a n d t o A t t h e c o m m i t t e e p r i o r i t y 1 9 8 2 D u e t o t h e r e p e a t i n g m e s s a g e r i n g p r o c e d u r e s a r e n e c e s - r e m o v a l r e s p o n s i b i l - t o t h e t r a n s m i t t i n g w o u l d f o r e v e r a r e t h e a l g o r i t h m s t o k e n - h o l d i n g s t a t i o n h a v i n g a if t h e b i t s t o l e v e l a s t h e f r a m e I n t h e r i n g c o n t a i n s t h e t o k e n w h i c h m a y b e e i t h e r f r e e o r b u s y . W h e n o p t i o n a l p r i o r i t y i s n o t u s e d , t r a n s m i t a v a i l a b l e r e c e i v e s a f r e e t o k e n . m e r e l y s e t s t h e t o k e n b u s y , a p p e n d s t h e f r a m e ( D A ... E F D ) , a n d s e n d s i t t o t h e n e x t s t a t i o n o n t h e p h y s i c a l r i n g . T h e t r a n s m i t t i n g s t a t i o n m a y s e n d f r a m e s , a l l m a r k e d u p t o a l i m i t t o k e n - h o l d i n g t i m e r t o k e n - p a s s i n g m e t h o d , A C 1 W h e n t h e p r e e m p t i v e s t a t i o n m a y w h e n e v e r T h e s t a t i o n i n d i c a t o r r e m a i n d e r a b i t s l e v e l . p r o h i b i t e d s e t t o t h e S t a t i o n s o f f r a m e s i t f r o m t o o f t h e i n t e r m e d i a t e t h a t n o w h a s m u l t i p l e t o k e n , b y w i t h a b u s y i m p o s e d ( c o u n t e r ) . t h e T h e t h e b i l i t y o r i g i n a l p r i o r i t y a v a i l a b l e s t a t i o n p r i o r i t y , p r i o r i t y a n d b e f o r e p a s s i n g i t t o t h e n e x t T h i s g u a r a n t e e s r e s t a r t e d a t t h e p o i n t r u p t e d . S i n c e o f p r i o r i t y , t h e t o k e n m a y b e u p g r a d e d o r i g i n a l p r i o r i t y t o s t a t i o n l e v e l d o w n g r a d e p r i o r i t y s t a t i o n s f r a m e s . s e e s a f r e e t o k e n a t t h e h i g h e r i t a s s u m e s t h a t t h e h i g h e r s t a t i o n s h a v e i t d o w n g r a d e s t h e t o k e n w h i c h h a s t h e r e s p o n s i - t h e t o k e n t o i t s w h e n a l l h a v e s e n t W h e n t h e u p g r a d e d h i g h e r t h e i r o r i g i n a l I n t e r m e d i a t e i d e n t i f i e d m e s s a g e , r e t r a n s m i t i t t o t h e n e x t s t a t i o n a f e w b i t - t i m e d e l a y s f o r p r o c e s s i n g . If t h e i n t e r m e d i a t e e r r o r , i t s e t s t h e f i r s t o c t e t o f t h e E F D t o o n e b e f o r e i t is t r a n s m i t t e d . s t a t i o n s b y S A a n d D A r e c e i v e c h e c k i t f o r b e t w e e n t h o s e e a c h a n d a f t e r e r r o r s , b e e n s a t i s f i e d p r i o r i t y s t a t i o n . s t a t i o n d e t e c t s a n l a s t b i t o f t h e t h a t t h e t o k e n p a s s i s i t w a s i n t e r - t h e r e a r e e i g h t l e v e l s W h e n s t a t i o n , t h e s t a t i o n t h e f r a m e a r r i v e s c o p i e s t h e f r a m e a t t h e D A

IEEE PROJECT 802 23 F o r C S M A / C D a n u m b e r o f t i m e s b e f o r e i t r e t u r n s t o i t s o r i g i n a l v a l u e a r o u n d t h e r i n g . a n d i s r e s t a r t e d A b a s e b a n d c a b l e s e c o n d r a t e . p r o v i d e 5 , a n d 2 0 M b s . s y s t e m a 1 0 ( M b s ) F u t u r e a d d i t i o n a l u s i n g 5 0 o h m m e g a b i t t r a n s m i s s i o n e x t e n s i o n s r a t e s o f 1» a t p e r T o k e n M e t h o d P r o p e r t i e s w i l l T h e t o k e n - p a s s i n g t h e y c a n . w i t h t h e p r o v i s i o n f o r p r i o r - i t y o r b a n d w i d t h a l l o c a t i o n , b e f a i r o r u n f a i r , a s t h e s i t u a t i o n T h e y a r e a l s o d e t e r m i n i s t i c t h e y c a n p r o v i d e p r e d i c t r b l e t h u s m a k i n g t h e m m o r e s o m e r e a l - t i m e a p p l i c a t i o n s . m e t h o d s p r o m i s e t o b e v e r y w i t h t h e e f f e c t i v e s y s t e m p e r h a p s e x c e e d i n g 9 0 % o f t h e r a w c a p a c i t y o f t h e m e d i u m . t h e e f f i c i e n c y i s r e l a t i v e l y t i v e t o b o t h t h e n u m b e r o f s t a t i o n s a n d t h e l e n g t h o f t h e m e d i u m . i m p o r t a n t p r o p e r t i e s a c c e s s o f t h e m e t h o d s a r e t h a t A b r o a d b a n d t h a t u s i n g 7 5 o h m c o a x i a l c a b l e a t a 10 M b s r a t e . T h e t i o n f o r t h i s i s s u e d f o r t e c h n i c a l r e v i e w i n M a y 1 9 8 2 a n d m a y o r m a y n o t b e in t h e i n i t i a l s t a n d a r d . s y s t e m i n s i m i l a r t o C A T V s y s t e m s u s e d r e q u i r e s . s o r e s p o n s e , t h a t s p e c i f i c a - s y s t e m w i l l b e a t t r a c t i v e f o r T h e e f f i c i e n t , o f t h e c a p a c i t y • F o r t h e R i n g T o k e n - P a s s i n g M e t h o d F u r t h e r m o r e , i n s e n s i - A o h m c a b l e a t r a t e s o f 1 a n d 4 M b s . b a s e b a n d s h i e l d e d s y s t e m u s i n g t w i s t e d - p a i r 1 5 0 O n t o k e n - p a s s i n g a b l y m u c h C o m m i t t e e d e s i g n o f c o m p l e x b e l i e v e chips i s a c h i e v a b l e i n c u r r e n t o g y . T h e d e - s i g n s t a n d a r d d o e s n o t r e p r e s e n t a n e x i s t - i n g p r o d u c t , a l t h o u g h s y s t e m s h a v e b e e n y e a r s . A s a r e s u l t , e f f o r t t o v e r i f y t h e d e s i g n s i m u l a t i o n a n d p r o t o t y p i n g w i l l b e r e q u i r e d p r i o r t o i n d u s t r y a c c e p t a n c e . t h e n e g a t i v e m e t h o d s a r e u n q u e s t i o n - m o r e c o m p l e x m e m b e r s e x p e r i e n c e d V L S I c h i p s , t h a t t h e d e s i g n s i d e , t h e A b a s e b a n d s y s t e m c o a x i a l c a b l e a t 4, 2 0 , a n d 4 0 M b s . T h e l a t t e r r a t e i s n o t i n t h e o r i g i n a l 8 0 2 a n d i t s i n c l u s i o n h a s n o t b e e n a p p r o v e d b y t h e 8 0 2 C o m m i t t e e , a l t h o u g h t h e M e d i a t e e h a s a p p r o v e d i t . u s i n g 7 5 o h m t h a n C S M A / C D . i n t h e h o w e v e r , s u i t a b l e t e c h n o l - a s r e q u i r e m e n t s o f S u b c o m m i t - e v o l v i n g t h e m a n y s i m i l a r • F o r t h e B u s T o k e n - P a s s i n g M e t h o d i n u s e f o r s e v e r a l a s i g n i f i c a n t t h r o u g h p r o b a b l y w i d e s p r e a d A p h a s e - c o n t i n u o u s u t i l i z i n g 7 5 o h m c o a x i a l f o r r a t e s u p t o 1 M b s . s i n g l e c h a n n e l , F S K s y s t e m c a b l e F i v e c h a n n e l , s y s t e m s c a b l e . a n d 1 0 M b s s i n g l e F S K p h a s e - c o h e r e n t u s i n g 7 5 o h m c o a x i a l P H Y S I C A L L A Y E R I M P L E M E N T A T I O N T h e t h e o n e s i g n a l t e s t i n g f o r d e t a i l s a r e i n d e p e n d e n t o f t h e a c t u a l t r a n s m i s s i o n m e d i u m d e p e n d o n t h e e x a c t t y p e o f m e d i u m a n d t r a n s m i s s i o n t e c h n i q u e . s o m e t r a n s m i s s i o n s y s t e m s s u i t e d f o r p a r t i c u l a r m e t h o d s . F o r e x a m p l e , t r a n s m i s s i o n s c h e m e s a r e n o t a p p l i c a - b l e t o t h e r i n g t o k e n - p a s s i n g p h y s i c a l d e t a i l s o f t r a n s m i t t i n g s y s t e m t o l e v e l s , m o d u l a t i o n c i r c u i t s , t h e i r c o n t r o l . l a y e r i s c o n c e r n e d w i t h f r o m b i t s i n v o l v e s t e c h n i q u e s , p r o t o c o l s S o m e o f A m u l t i l e v e l d u o b i n a r y A M / P S K a t 1, 5 , 1 0 , a n d 2 0 M b s o n 7 5 o h m c o a x i a l c a b l e . b r o a d b a n d s y s t e m u s i n g a n o t h e r . I t e t c a n d t h e s e I n p u r s u i n g , t r o n i c c o m m i t t e e s , a n d r i n g t o p o l o g i e s . r a t e s h a v e n o t b e e n a d d i t i o n , t h e c o m m i t t e e w i t h A s s o c i a t i o n o p t i c m e d i a f o r s t a r T h e t r a n s m i s s i o n d e t e r m i n e d . i s b u t m a n y o t h e r s i n c o o p e r a t i o n E l e c - ( E I A ) I n d u s t r i e s f i b e r I n a d d i t i o n , a r e b e t t e r m e d i a t h e b r o a d b a n d a c c e s s m e t h o d . S T A T U S A N D P L A N I t p r o v i d e a v a r i e t y o f m e d i a a n d t r a n s - m i s s i o n r a t e s w h e r e d o s o . D u e t o t h e e f f o r t p r e p a r e t h e s p e c i f i c a t i o n s , t h e i n i t i a l s t a n d a r d a l l t h e s e l e c t e d a l t e r n a t i v e s . a n t i c i p a t e d t h a t t h e f i r s t t h e s t a n d a r d w i l l i n c l u d e t h e f o l l o w - i n g : i s t h e i n t e n t o f t h e c o m m i t t e e t o T h e w a s t h e D r a f t d o c u m e n t . t h e m e e t i n g , s u c h a s t h e i n c o r p o r a t i o n o f s p e c i f i c o p t i o n s a l l o c a t i o n a n d p r e e m p t i v e t h e t o k e n - p a s s i n g p u r p o s e o f t h e M a r c h 1 9 8 2 m e e t i n g t o c o n s i d e r c o m m e n t s r e s u l t o f t h e c o m m i t t e e Β a n d t o c o n t i n u e M a j o r c h a n g e s i t m a k e s s e n s e t o r e q u i r e d t o h o w e v e r , w i l l n o t r e c e i v e d a s b a l l o t o n r e f i n i n g t h e w e r e m a d e a t i n c l u d e I t i s v e r s i o n o f f o r b a n d w i d t h p r i o r i t y i n a n d t h e m e t h o d s DCCS - B*

24 Thomas J. Harrison R E F E R E N C E S d e c i s i o n t o u s e t h e L C a n d P A D f i e l d s in C S M A / C D . I t i s t h e i n t e n t o f t h e c o m m i t t e e t o i s s u e ( D r a f t C ) i n M a y 1 9 8 2 f o r a 3 0 d a y c o m m i t t e e b a l l o t . A s i m p l i e d n o t a l l s e c t i o n s a r e c o n s i d e r e d f o r a f o r m a l b a l l o t a n d t h e s e i n c l u d e d f o r t e c h n i c a l r e v i e w (1). G e r a l d J . C l a n c y , J r . a n d T h o m a s J . H a r r i s o n , " L o c a l S t a n d a r d s - - A 3 r d I F A C W o r k s h o p o n D i s t r i b u t e d C o m p u t e r C o n t r o l B e i j i n g , C h i n a , 1 9 8 1 ( P r o c e e d i n g s t o b e p u b l i s h e d b y P e r g a m o n P r e s s ) . T h o m a s J . H a r r i s o n , " I E E E 8 0 2 L o c a l A r e a N e t w o r k S h a r e 5 8 , P a p e r C 2 1 2 , S h a r e I n c . , ( I l l Ε . W a c k e r D r . , C h i c a g o , I L 6 0 6 0 1 ) , L o s A n g e l e s , 1 9 8 2 . ( 3 ) · T . M a n u e l , " M i c r o c o m p u t e r - s i z e d u n i t s h a n d l e i n s t r u c t i o n s p e r s e c o n d , " t r o n i c s , F e b r u a r y p p . 3 9 - 4 0 . ( 4 ) . " R e s o l u t i o n s T a k e n a t T C 9 7 i n g , " P a r i s , I S O / T C 9 7 / n l 0 4 6 , T C 9 7 , A m e r i c a n N a t i o n a l I n s t i t u t e , N e w Y o r k . ( 5 ) . " D a t a P r o c e s s i n g I n t e r c o n n e c t i o n - B a s i c M o d e l , " I S O / D P I S 0 / T C 9 7 / S C 1 6 , A u g u s t 6 , 1 9 8 1 . ( 6 ) . I E E E 8 0 2 L o c a l D r a f t Β , I n s t i t u t e o f arid E l e c t r o n i c Y o r k , O c t o b e r 1 9 , 1 9 8 1 . (7)· " D a t a C o m m u n i c a t i o n s H i g h - l e v e l D a t a P r o c e d u r e s - I S O S t a n d a r d 3 3 0 9 - 1 9 7 9 ( 2 n d E d . ) , I S O C e n t r a l S e c r e t a r i a t , S w i t z e r l a n d . ( 8 ) . " T h e E t h e r n e t , N e t w o r k : D a t a P h y s i c a l L a y e r ( V e r s i o n 1 . 0 ) , " j o i n t l y b y D i g i t a l E q u i p m e n t I n t e l C o r p o r a t i o n , C o r p o r a t i o n , S e p t e m b e r 3 0 , 1 9 8 0 . ( 9 ) . W . B u x , " L o c a l - A r e a A P e r f o r m a η c e C o n f e r e n c e o n Z u r i c h , S w i t z e r l a n d , 1 9 8 0 · t h e n e x t r e v i s i o n A r e a N e t w o r k R e p o r t , " S t a t u s e a r l i e r , r e a d y w i l l b e o n l y . S y s t e m s , 1 5 - 1 7 , A u g u s t C o m m e n t s b a l l o t in A u g u s t w i l l b e b a l l o t e d t h a t t h e r e q u i r e d 7 5 % p l u r a l i t y w i l l b e a c h i e v e d a t t h e c o m m i t t e e p r o p o s e d s t a n d a r d w i l l t h e T e c h n i c a l C o m m i t t e e C o m m u n i c a t i o n s ( T C C C ) a p p r o v a l p r i o r t o i t s s u b m i s s i o n t o t h e I E E E S t a n d a r d s B o a r d . s i g n i f i c a n t a s p e c t o v e r l o o k e d , o n e w o u l d v e r s i o n s e n t t o t h e T C C C , c h a n g e s o f a n e d i t o r i a l n a t u r e , w i l l b e t h e i n i t i a l v e r s i o n I E E E s t a n d a r d . T h e c o m m i t t e e t o e x t e n d t h e r e v i s i o n s w h i c h , d e t a i l r e q u i r e m e n t s r a t e s a n d m e d i a n o t i n c l u d e d i n i t i a l s t a n d a r d . r e s u l t i n g w i l l b e d i s c u s s e d a t a 1 9 8 2 . R e s u l t i n g w i t h t h e e x p e c t a t i o n f r o m t h e D r a f t C ( 2 ) . P r o j e c t S t a n d a r d , " m e e t i n g r e v i s i o n s M a r c h 1 7 , l e v e l . T h e t h e n b e s e n t t o o n C o m p u t e r f o r o n e m i l l i o n E l e c - 1 9 8 2 , t h e i r 2 4 , U n l e s s h a s s o m e b e e n M e e t - e x p e c t t h a t t h e e x c e p t f o r 2 - 4 D e c e m b e r 1 9 8 1 , S e c r e t a r i a t S t a n d a r d s f o r o f t h e r e s u l t i n g i n t e n d s t h r o u g h w i l l - O p e n S y s t e m s R e f e r e n c e S e c r e t a r i a t N e w s t a n d a r d f o r f o r e x a m p l e , t r a n s m i s s i o n 7 4 9 8 , A N S I , Y o r k , i n t h e N e t w o r k S t a n d a r d - E l e c t r i c a l I t i s e x p e c t e d b e c o n s i d e r e d t i o n a l t i o n ) t h r o u g h i t s s u b c o m m i t t e e o n d a t a c o m m u n i c a t i o n s , I S 0 / T C 9 7 / S C 6 . i n t r o d u c t i o n i n t o I S O p r o b a b l y t h r o u g h o n e o f t w o r o u t e s . a n C o m p u t e r s M a n u f a c t u r e r s ( E C M A ) c u r r e n t l y i s c o n s i d e r i n g o f d o c u m e n t s d e r i v e d s e c t i o n s o f t h e I E E E 8 0 2 p r o p o s a l . a l i a i s o n m e m b e r o f I S O , E C M A r e q u e s t c o n s i d e r a t i o n d o c u m e n t s . I t i s a l s o E C M A w i l l c o n s i d e r m e t h o d s a t i t s f u t u r e a l t e r n a t e r o u t e . d i s t r i b u t e d t o m e m b e r s N a t i o n a l S t a n d a r d s T h i s s u b c o m m i t t e e , a s t h e b o d y s i b l e f o r U . S . I S 0 / T C 9 7 / S C 6 , c o u l d s u b m i t a l l o r p a r t o f D r a f t C ( o r i t s s u c c e s s o r s , i f a n y ) a s a U . S . c o n t r i b u t i o n . a p p r o a c h i s u s e d , t h a t t h e p r o p o s a l a p p r o v e d a s a n I S O S t a n d a r d . t h a t t h e s t a n d a r d b y t h e I S O O r g a n i z a t i o n w i l l E n g i n e e r s , N e w ( I n t e r n a - S t a n d a r d i z a - f o r L i n k C o n t r o l I t s F r a m e S t r u c t u r e , " w i l l b e T h e E u r o p e - A s s o c i a t i o n G e n e v a , a s e t A L o c a l L a y e r S p e c i f i c a t i o n p u b l i s h e d C o r p o r a t i o n , a n d A r e a a n d f r o m t h e C S M A / C D L i n k A s c o u l d i t s t h a t o f e x p e c t e d t o k e n - p a s s i n g m e e t i n g s . D r a f t C o f S u b c o m m i t t e e X e r o x t h e A s a n S u b n e t w o r k s Î C o m p a r i s o n , " L o c a l w i l l A m e r i c a n X 3 S 3 . r e s p o n - b e I F I P N e t w o r k s , A u g u s t , p a r t i c i p a t i o n i n (10). R . M . G r o w , " A T i m e d - T o k e n c o l f o r L o c a l b e p r e s e n t e d a t I E E E E l e c t r o ' 8 2 , B o s t o n , M a y 1 9 8 2 . P r o t o - A r e a N e t w o r k s , " T o W h i c h e v e r e x p e c t e d w i l l b e i t c a n b e e v e n t u a l l y A C K N O W L E D G E M E N T w o u l d l i k e t o a s s i s t a n c e D o n n a n , R i c h G a r y R o b i n s o n v e r s i o n o f t h i s p a p e r . r e m a i n , a n d t h e r e m a y b e s o m e , a r e t h e r e s u l t o f t h e a u t h o r ' s n o t e s t a k e n d u r i n g a t y p i c a l , b u t v e r y h e c t i c , m e e t i n g o f t h e 802 T h e t h e a u t h o r a c k n o w l e d g e C l a n c y , B o b o f G e r r y F a b b r i , T o m P h i n n e y , a n d i n r e v i e w i n g a n T h e e r r o r s e a r l i e r t h a t i n c o m p l e t e C o m m i t t e e .

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 DISCUSSION Narita: simi Tar speech at the next meeting or do you expect any major changes in the content you have just mentioned? will there be the first silicon chip for the token-passing method? Dr. Harrison, will you make a the token. it receives a frame with a free token at the level it had assigned. For example, if priority 4 is higher than 3 and I am the token holding station, and at level 3 I'm asked to release the token at 4, that's what I do. Now that token may go around and get jacked up to 5 and 6 but then is returned to 5 and then back to 4. When I see it again at 4 and it is free, I know that all the four and higher priority requests have been satisfied. that token, return it to 3 and send it on to the next station. transmission time, be immediately jacked up again to 4. But the algorithm says that when I see a free token at the level I assigned to it, then I grab it and bring it back down to where it was. So it is automatic, but it may go through several steps before you get there. It does it automatically when Secondly, when Harrison : both: I don't know the answer to either! I have the feeling that the committee itself is anxious to complete its work. In fact, I spent many hours writing a paper before the March 1982 meeting, figuring that I wouldn't have to change it, and then after that meeting I spent three rather hectic days totally rewritting the paper, because the changes were major. that there will be further changes of that magnitude, but I would not recommend to anyone that they go out and start, as we say, pouring silicon, based on what is in the May draft. If I am back next year, perhaps I can give a report on the final standard and I hope there will not be too many changes. I'll answer very briefly to So I grab It may, because of I don't expect Your synchronous AS1 and AS2. I sat down and attempted to write an analytical expression probability of any given station getting service under any given conditions. It is a non-linear function because every time the token comes to you, you reset your counter. If you take a six-station case you have six non-linear resettings taking place. could predict ahead of time how my network would act is to write a simulation program which by the way, the author of the scheme R.M. Grow has done. He, however, has used the system so much that he has a heuristic sense of how it works. I found it took me several days of playing with charts of numbers, not having my computer with me, before I really began to understand how it worked. I might point out that R.M. Grow is presenting a paper this week at IEEE Electro '82. It is the last reference in my paper, and he has a complete explanation of his scheme, using somewhat different terms from mine. I had to simplify it for this brief presentation. second question was about the Well, In Phoenix to predict the As far as chips are concerned, I have no information on that. nobody has publicly announced their plans with respect to a chip which will implement a media access method, with the exception of the ETHERNET-1 ike chip from DEC, INTEL and XEROX. Within the committee, however, the discussion is such that one would believe that there are several semiconductor manufacturers (in the United States and Japan, in particular) who are very interested in the activity. or not they are designing something, they have not stated publicly. To my knowledge functions or The only way I other Whether Vohandu: make your ring token priority downgrading automatically or by free will? that game with AS1 and AS2 seem to be like poker where three different classes of people are playing and only the people in money can play it really? I have two questions. Do you Doesn't Harrison : downgrading. such interrupted is responsible for downgrading Number one - on the token The ring token algorithm is the station that originally 25

Discussion 26 response, I invoke the monitor function and assume that the token has been lost. then attempt to reinitialize the logical ring. Rodd: monitor function. I think from the process control point of view the big worry is what happens when a token gets lost. where does your monitor exerci sed? You mentioned just in passing the I How and function get As another example, if a station gets on the line and hears no activity for some period of time, the monitor function is activated and it assumes that the token is lost and will attempt to restart token. If two stations attempt to start the token simultaneously and they hear each other, they are both obligated to back off. So, eventually somebody is going to start the token again using whereby you essentially go out and ask who wants to be in the logical ring. distributed monitor function is defined by state diagrams in Draft C of the proposed standard. It is worked out in quite some detai1. Harri son: function centralized. depends on whether it is the bus or the ring scheme. Each station has a monitoring facility, so in the example, when sending the token on to the next station, I'm responsible for that token until I hear the next station come on line, take it, and do something with it; either send a message or pass it on to the next station. At that time I drop my monitor responsibility. However, if I send it and after a time period I hear no As I indicated, the monitor can be centralized The exact way or it works non- the bus scheme, for a system This

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 STANDARDIZATION WORK FOR COMMUNICATION AMONG DISTRIBUTED COMPUTER CONTROL SYSTEMS G. G. Wood European Market Research & Product Planning, Foxboro Yoxall, Redhill, Surrey RH1 2HL, UK ABSTRACT: local area communications are discussed and compared with the needs of Distributed Computer Control Systems in industry. The standards groups are International Electrotechnical Commission ( I EC), International Standards Organization (ISO) and Institute of Electrical and Electronic Engineers (IEEE). The current position of some standardization groups working in The paper then introduces the following issues which may affect further evolution of the work on these standards:- (1) The need and direction for services and protocols in the higher levels. (2) The impact of fibre optics which favour a change from the passive "T bus" to a network of point-to-point links for communication. (3) The economic arguments for the application areas with numerically small markets to adopt subsets of the standards developed for large markets. KEYWORDS: 625. Industrial Data Highways, Communication sub-systems. Local Area Networks, Communications, PROWAY, IEEE 802, IEC Di sei aimer. This paper is not an official statement by any standardization body. The information is drawn from individual discussions and working documents which are subject to change, consequently it should not be relied upon for decisions about product design or commercial activity. The opinions are those of the author and do not necessarily represent his employer, any other committee member or their sponsoring organizations. The author has been a member of the IEC Working Group on PROWAY since its inception and Chairman of the Coupler Sub-Group. He is a liaison member of the IEC Working Group on Interface Systems for Programmable Measuring Instruments. INTRODUCTION of these evolving standards could support industrial Distributed Systems (DCCS). These applications are characterised by up to 100 microprocessor based stations separated by distances up to 2 KM. Such systems are the industrial equivalent of a Local Area Network (LAN). Computer Control The age of the microprocessor has arrived and microprocessors interconnected for application purposes and environments. The most critical factor in these multi-micro systems is the communication structure. User concern for this subject is reflected in committees seeking to produce standards for communication microprocessor based standards are unusual in that they seek to define a standard before industry usage has created a "de facto" standard which can then be tidied up and documented. Several are being many different This paper covers the author's view of the present status among standards which could support a DCCS or Industrial LAN in the future:- among devices. distributed These - Process Plant Communications (PROWAY formats) 1 and Process Application 27

28 G.G. Wood - Laboratory Communications: (Serial extension of IEC 625-1) - Office Communications: (IEEE S02 - Post and Telegraph Communications (CCITT X 25) The 625-Serial and IEEE 802 groups are working on several standards with various optional choices in Layers 1 and 2. versions will meet all the criteria of Table 1 and others which meet only criteria 1, 2 and 3. 2 Some 6 and Ethernet) 4 5 The X25 standard includes Network Layers of the OSI model and can support criteria 2 to 5 of Table 1. Multi master is not easily provided by X25, however a number manufacturers have developed products using X25 components enchancements to provide capabi1ity. Following a summary of present status among these standards, the paper discusses some areas which are not committees and some decisions which must be made. covered of the by the of trade-off with non-standard multi master PRESENT STATUS OF STANDARDS The functional requirements for an industrial data highway. Table 1 lists some of these requirements and reasons for their choice. IEC PROWAY Committee has defined AVAILABILITY PROWAY and 625-Serial are still in the definition stage and products meeting these standards are not expected in the market place until 1985 or later. 1. Multiple sharing passive connections from each station to the data highway. This ensures that loss of one station or loss of power in one part of the plant will interrupt communication other plant areas. master the stations with highway, IEEE definition and products for some of its subsets are now available in the market place. 802 is in the final stages of not among DEVELOPMENT FEATURES OF UPPER LAYER 2. Single wire, serial, multi-drop connection among This gives a simple path and economic benefits in cabling and Options include paths. stations. message The application of small DCCS projects will involve a single, local bus. case the functions of a network layer are not needed. Also for small systems the maximum frame length and task or session connections are usually installation time and absorbed into the application programs. system effectively has layer directly interfaced to the Layer. In such a connections. redundant fixed at 3. Variable length message frame with no restriction on the bits and bytes contained in a user's application message. The small its DCCS application Link 4. Operation of the communication system must be deterministic to support calculation of worst case access time and guaranteed response figures. For independent busses, Network and transport layers are needed to free the application from concern about message length, absolute addresses and connections. larger projects with multiple 5. Automatic acknowledge, within the communication for each message sent. This is a safety feature to support fast fault recovery, messages are not lost and keep them in sequence. For ease of system expansion from a small DCCS to a large Network DCCS the interface logic or state machines should be the same for each interface layer. If this goal is achieved, then low cost single bus applications can be built without the intermediate However, they can easily be expanded into larger networks by inserting the extra layers and changing the application address references from absolute to logical. sub-system, above the Network ensure layers (345). TABLE 1. GUIDELINES FOR GOOD INDUSTRIAL DCCS The PROWAY standards group is working to meet the Table 1 criteria by defining a standard for Layers 1 and 2 of the OSI model PASSIVE "T" CONNECTION OR STORE AND FORWARD 6. The industrial passive integrity community have requested "T" junctions to increase of their DCCS the installations.

29 Communication Among Distributed Computer Control Systems In some situations a DCCS requires links through the PTT for a remote sub-system or management computer. adaptations should interaction with PTT systems. PROWAY, Serial-625 and IEEE 802 each embody versions which meet this aim. this requirement will cause problems when optical data links are applied in industry. However, The use of X25 simplify such The technology of optical point-to-point data links is now well established and offers significant opportunity to eliminate such traditional problems as: electrical interference 1ightning effects ground loops spark hazard envi ronments REFERENCES AND NOTES 1. PROWAY is being developed by the International Commission Technical Committee 65C, Working Group 6. previously named drafts parts of circulated for national comment by TC65A. Electrotechnical This group was TC65A, WG6 and PROWAY in explosive were Passive "T" optical connections are not expected to be economic in the near future so other methods must be used to ensure link integrity when power fails at a station. Three consi dered:- Another working group TC65C WG1 is working on standards for message formats in industrial data highways. solutions can be i) Battery backup to sustain the active retransmission elements station. 2. International Commission Technical Committee 65C, Working Group 3. previously named defined a short serial, byte parallel data bus which has been published as an IEC standard number 625. now investigating a long distance, fully serial bus which will have maximum compatabi1ity This paper refers to the proposed serial extension as "625-Serial". Electrotechnical in each This group was TC66 WG3 and distance, bit ii) Optical switching relays which bypass the station active elements when power fails. This group is iii) Multiple point-to-point links giving a network solution for rerouting and bypassing a failed station. with 625. The choice among these will depend on a balance of first cost and installed maintenance cost. Future development of LSI components for Networking will probably favour the third solution. 3. Institute Electronic Engineers, Project 802. Draft documents were published for comment at the end of 1981. The drafts include many sub options some of which are very close to the Ethernet standard. of Electrical and Protocols ECONOMICS Table 2 gives an approximate estimate of the market for station couplers and logic i η DCCS applications. 4. The Ethernet, A Local Area Network: Data Link Layer and Physical Layer Specification. Jointly published by DEC, Intel and Xerox Corporations. Also referred to as the DIX Data Hi ghway. 5 Industrial Uses (e.g. PROWAY) 10 Units per year Laboratory and Light (e.g. Serial-625) 10 units per year. Office Automation (e.g. IEEE 802) very large PTT and CCITT (e.g. X25) very large. Industry 5. International Telephony Recommendation X25 covers physical, Data Link and Network functions. Telephone and Consultative Committee. 6. International Standardization "Reference Model for Open Systems Interconnection". Proposal 7598. Organization ISO for SC16 TC97 TABLE 2. MARKET ESTIMATE FOR DCCS STATIONS ISO Draft For economic reasons the development of PROWAY and Serial 625 standards consider adaptions of X25 or IEEE 802. This allows the economics of large scale productions. must

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 DISCUSSION Harri son : The only comment that I would make Ts" that, first of all, we are operating in real-time and in parallel in the sense that those two committees (IEEE- 802 and PROWAY) met basically at the same time. Graham (Wood) did have access to my paper but, I guess, really not about the same time he wrote his. Joudu: level of reliability of one undetected error for a thousand years? How can you prove the very high Wood: been a number of papers but what we are assuming is that the line noise is known. The noise is going to give us one residue faulty bit per 16° received at the link level. Once you have made that assumption, then for a given average message length and a given data rate it is simply a matter of statistics. We have been able to show that, with the CRC method that is available and with the bit stuffing situation, you can detect most of the bit faults that occur with the probability of eventually 3 χ 10" , that is one undetected fault in a thousand years. I am not sure if there has been a published paper, but there were a lot of papers presented and argued inside the PROWAY committee on that subject. It is very difficult. There have I'm not trying to defend IEEE-802, I'm trying to report on IEEE-802. I'd make the observation, however, that in his necessity to provide comparison charts in a very brief way Graham does advantages and disadvantages within the same chart in a way which is confusing. You cannot say that it is a disadvantage for CSMA/CD, but then in the same column put down the advantage of a token, because they are fundamentally non-comparable. You really need to take, go through and sort out the advantages and disadvantages of the ring token scheme which, in fact, does have immediate acknowledgement, as compared to the bus token scheme which does not yet have it as stated on your chart, compared to CSMA/CD which has no hope of ever getting it, for the present, and then also have a separate column for CSMA/CD. 802 has three standards. Now what? tend to mix Tavast: Would you comment on the choice of the HDLC frame for PROWAY. Wood: arguing was, the choice of IEEE-802 or HDLC. We had been analysing the HDLC frame for two or three years, evaluating all the error probabilities, and how we could extend it. So we felt we understood that frame reasonably well and we had satisfied ourselves that we could use it. If we are to start using the IEEE-802 frame, we'll have to do all the analyses again, if you like. There are still some questions about IEEE-802 applicability for some of the functions that PROWAY important. We have found ways of using the HDLC to satisfy all of those functions. So, with some question marks about parts of IEEE-802, our present position is to stay with HDLC. And of course there are plenty of LSI chips coming out that were aimed for HDLC. But we understand that the important bits that PROWAY wants to add on can be added as micro code on the chip. don't require inventing a new chip - which is a big economic problem. The economic situation that I was IEEE- Wood: that I was comparing PROWAY with the bus version of IEEE-802, not the ring, because PROWAY at the moment is aiming for a bus only, not a ring. I had assumed that we'd be comparing with the token version of IEEE-802. I had tried to make the assumption believes are Harrison: have shown the disadvantages of active taps, and truly, the only active tap is CSMA/CD. The other is the one we required to bend the cable and bring it in. But in a bus you really don't. tap. Well, that's true, but you also That's a passive So we Wood: that statement because I think you've also said the physical layer was identical across all versions. That is the first time I've heard Natiel1o: I'd also like to make a comment Tn that aspect. As a member of the 31

Discussion 32 layered structure, we see no problem to shift to that at a later date. following Lou's (Natiello) comment, we are quite happy to stay with 1 Mbit rate to get something quickly technology. We expect eventually to change the physical layer to optics which has other implications as well. get something published and something out, we are deliberately layers independent, so that they won't be affected if we do change the bottom layer. industrial community I emphasize that we badly need data communication standards for use in process control. necessarily want to developments of standards, but things which stay in the committee for ever and ever are not very useful to us. cases under time pressure. But We don't control stop or using existing We are in many If we want to making the higher Wood: think at least 50% of the people who are supplying industrial communications systems have to develop and systems. They don't intercommunicate, but many of them have used at least the HDLC frame chips which are available as the minimum building blocks of the present systems. We have found it easier to move up to larger, more integrated versions of an HDLC-related structure. Another point I could add is that I build their own Vohandu: 1 evel standard transmission coding tables in the higher (application) level standard? You are speaking on the lower protocols. What data formats, e.g. about use of ISO data protocols of your Wood: field as completely transparent. what I was getting at when I mentioned the IEC TC65A WG7 (now IEC TEC65C WG1), trying to agree standards for the application format which is the data content. will be considering the different data tables. There are some recommended formats used by the laboratory people. tried to say that for a floating point number you put your floating point this way and your mantissa goes this way. fairly arbitrary to make a decision, so we don't all invent our own different internal company standards protocol s. I think PROWAY is treating the data This is Narita: the very slow, sluggish, out-of-date speed of one megabit per second of PROWAY? you think it is enough for medium or large scale applications or is there any plan to raise the speed, say, to 5 or 10 Mbit/sec. What is your personal opinion of Do They I have Wood: we've industrial plants will be satisfied with the 1 Mbit rate. We are fairly happy as a committee that we can let the IEEE-802 and the IEEE-625 committees physical technology to run it with 10 Mbit and 20 Mbit. Because we are using a Yes, based on the data rates that evaluated, we feel that many It is pioneer the for higher level

Copyright © IFAC Distributed Computer Control Systems Tallinn, U.S.S.R. 1982 SESSION 3 Chair: L. Rosza DEVELOPMENT AND EVALUATION OF DISTRIBUTED SENSOR BASE MANAGEMENT SYSTEM QUANTITATIVE T. Muto, C. Imamichi, A. Inamoto and S. Kato Computer System Works of Mitsubishi Electric Corp., Kamakura, Japan Abstract. software package, designed to perform the control data aquisition and the control output data initiation, in place of application software. Furthermore, the distributed SBMS was newly developed to support distributed system architectures, upon success of the conventional SBMS. This distributed SBMS is assumed to be constituted on a distributed computer control system, where remote process input/output subsystems together with front-end-processors will be installed as local stations on the plant floor. The sensor-base-management-system (abbr. SBMS) is a standard In order to give the practical aspects of this distributed SBMS, the model system applied to a hot-strip-mill control system is outlined. tative evaluation studies on this distributed SBMS, focussing the interests on data communication cost, data processing cost and system performance loss are done with reference to the above-mentioned model. The objectives of these studies are to give the system designers adequate suggestions on where is the balancing point between a distributed and a non-distributed architecture, what is the optimal number of the local stations, and hope- fully more. The quanti- Keywords. computer applications; computer evaluation; mill. Data aquisition; data processing; large-scale system; steel industry; hot strip between two or more main computers and (2) To distribute the load of host computers to front-end-processors (abbr. FEP), are the major approaches. The former is the concept of multi-processing and the latter is the one of distribution. the discussion will be focussed on this distributed system architecture. INTRODUCTION two of In the field of industrial computer systems, some of the major trends in these years are that computer systems are getting larger in scale and more complex in configuration and that many of so-called large-scale systems have become common. This means that industria, computer systems are now being much more heavily relied and that the functions of computers are being widely expanded. to that, the control range of computer systems is now geographicly expanding and computer systems now control not limited to each of the local parts of the plants but totally control the plants. In this article, Meanwhile, the most important function of industrial computer systems is no other than to control the plants, and for this purpose, tremendous amount of data processing on process input/output is required. the data processing on process input/output has become much larger in scale and more complex in procedure, as the control algorithms become more advanced and more complicated. To develop these data processing software for each system exclusively may be too much burden to application software. management-system (abbr. SBMS), a standard software package, has been developed in order to remove such burden from application software. So, the major functions of the SBMS are data aquisition of process input data, initiation of process control output data, filing of historical or time-serial In addition Recently, To fit to those needs or trends, the power of industrial computers has been drastically and continuously up-graded with respect to CPU processing capability, capacity of mass storage, speed of I/O channels and so on. However, it has been proved that power-up of individual computers alone may not cater for all the requirements on system scale, but that the final solution may be placed on system structure. (1) To share CPU tasks The sensor-base- 33

34 T. Muto, C. Imamichi, A. Inamoto and S. Kato process data and the other functions concerning process data handling. The details concerning this SBMS will appear in section 2. Users' scheme ' ^ I System engineer User programs / Ν π ^—π As mentioned before, distributed system architectures have becoLie extremely common in industrial computer system fields,so that this SBMS together should have the distributed architecture. The distributed SBMS, described in this paper, has been newly developed to respond to these requirements, of which design concepts are: (1) Despite that physically the system may be distributed, the users of SBMS need not be conscious of the distributed architecture ; (2) The data processing load on host computers should be distributed to FEPs ; (3) The system should have the support facilities for multi-computer system architectures. The detailed descriptions on this distributed SBMS will be given in section 3. 1 TU Ν / " ο ." ™ * L f ü L ] j = } SBMS Λ — Μ Process I/O hardware t î · · · Process î Fig. 1. System configuration of the sensor base system 3) To control and to process all of process input/output data systematically; 4) To standardize data-processing, such as limit checking, digital filtering and the other error checkings. In other words, if the SBS is introduced, application programmers need not know about complex hardware addressing of process input/ output mechanism, nor about scanning and filing procedures, concerning time-serial process data. Also, in case of hardware interface change, the modification will be made on the SBS only and no maintenance will be necessary on application programs. As for the practical applications of this SBMS. the model will be presented, where the distributed SBMS is applied to a h o t strip mill, line control system of the steel mill plants. In section 4, the system configuration, system scale and utilization aspects of this SBMS at the hot strip mill application model will be given. The quantitative evaluation studies on this SBMS, the major framework of this paper, will be tried and presented in section 5 on the model of the hot strip mill application. The advantages of distributed system architectures have been qualitatively reported in the variety of articles and papers, but not quantitatively. However, the quantitative evaluation data concerning the trade-off between distributed architecture and conventional architecture would be so much helpful to the system designers, when the decision whether distributed or not should be made at the system design stage. At quantitative evaluation paper the attentions will be concentrated on the three items, say (1) data communication cost; (2) data processing cost; and (3) system performance loss. The special formula and premises on each of three items, will be introduced, to offer the numerical results. The SBS, of which basic configuration is illustrated in Fig.l, is composed of process input/output hardware, physical image files, logical image files, an SBMS, data-base scheme files and users' access-subroutines. The general descriptions on each of these main components of the SBS are given below. Sensor-base-management-system (SBMS). The SBMS, the principal part of the SBS, is composed of data processing and system management programs. The logical image files and physical image files of the SBS are all under control of this SBMS. studies in this Physical-image-file (PIF), The hardware image of the process input-output system is maintained and updated periodically in this PIF, Logical-image-file (LIF). At the data aquisition procedure, the SBMS processes and arrange the physical data in PIFs and saves the processed logical data in the LIFs. At the output procedure, the process is vice-versa. THE SENSOR BASE MANAGEMENT SYSTEM System Configuration The sensor base system (abbr. SBS) is a kind of control data base system, to be constituted on a process input/output hardware system. The main objectives of the SBS are : 1) To offer user programs (application programs) logical access-methods on process input/output hardware system; 2) To keep off user programs from complex procedures on historical data processing (high-speed data scanning or long-term data storing); Sensor-base-scheme-file (SBSF). The processing procedures or the schemes concerning the SBMS are stored on these SBSFs, which include logical-to-physical-conversion (LTPC) procedures , physical-to-logical-conversion (PTLC) procedures, and process data speci- fications. The SBMS performs its data processing jobs, with reference to these SBSFs.

35 Evaluation of Distributed Sensor Base Management System From the view-points of file size, scanning period and number of logical points in normal application, the above-mentioned three subsystems are compared to be arranged in tabular form, as in TABLE 1. The functional configuration of this SBMS has been designed and developed, so that this SBMS would be applied in the wide range of industrial computer system application field. Here, some quantative comparison work will be done on these three subsystems of the SBS. In Fig.2, the required response time or scanning period of the process data as the X-coordinate axis, while the system scale evaluated by the number of logical points is taken as the Y-coordinate axis. normal application range of each subsystem is evaluated to be shown as an enclosed area in XY-plane of Fig.2. Scheme-file-maintenance-utility (SFMU). utility program allows the SBS users to do maintenance works on the scheme files, such as registration, elimination and modification. The problem-oriented-language (POL) is provided for this utility program. This T-access-subroutines (UAS). Users routines are provided for interface the user programs and the SBMS. These sub- between Process-simulator (PS). This is a CRT (Cathode-ray-tube) based support facility associated with the SBMS, which supports system test, simulation and monitoring. further descriptions are coming in the succeeding subsection. is taken The The Functional Description From the view-points of functional configuration, the SBMS could be divided into following three subsystems. O.üls STQS Logical process I/O subsystem (LPIO). subsystem will furnish not physical but logical access methods on the process I/O hardware system. This subsystem performs basic, functions of the SBMS and supports instantaneous process data handling. Interface with hardware system, engineering unit conversion, malfunction checking and logical conversions are included in this subsystem. This 0.1s •S ω LPIO number of logical points Short-term-quick-scanning (STQS). will initiate high-frequency but short term process data scanning, when it gets an event from the process. The time-serial process data, corresponding to each of the process events, are offered to the user program. user program can retrieve these short-term time-serial data, by specifying an event number Process Simulation & Monitoring as a key, from the logical files of the SBS. The SBMS Fig.2. Application range of three subsystems. The In the industrial computer system application field, the support function, associated with the SBMS is one of the most important points for qualification, when application of the SBMS is actually studied or planned. associated support functions, the SBMS furnishes the functions on system test and maintenance, of which man-machine interfaces are totally CRT-based. functional descriptions on these support functions are given immediately after. Long-term-slow-scanning (LTSS). periodically aquires the specified process data and does some data-processing such as digital filtering, averaging and getting maximum & minimum. The acquiredand processed data are to be stored on the large-scale disk memory files, for long term use. The user program can demand the retrieval of these time- serial process data to the SBMS by specifying a set of time and logical point number as a key. The SBMS As The detailed TABLE 1 Comparison of SBMS Three Subsystems LTSS STQS LPIO Subsystem Scanning period or response time 1.0 s ^ 60.0 s 20 ms ^ 200 ms 100 ms ^ 1.0 s number of logical 50 pts. ι* 300 pts. 30 pts. ^ 200 pts. 100 pts. ^ 2500 pts. points time - serial (long term) time - serial (short term) instantaneous data processing * \ > 1 M words ^ 10 Κ words ^ 2.5 Κ words file size 1 week ^ 1 month 50 s ^ 100 s instantaneous file holding period

T. Muto, C. Imamichi, A. Inamoto and S. Kato 36 physical image files, logical image files, scheme files and users' access subroutines, and has almost identical structure as the host station sensor-base system has. In normal situation, very limited scale of process I/O hardware (limited to interface within the host computer room) is provided in the host station. Process simulation. SBS is isolated from the process I/O hardware system, so that the input process data can be fed by a CRT key-board manually and the output process data from the user programs can be monitored by a CRT viewer, but not put to the process. To facilitate this process simulation function, the SBMS has two alternative modes, on-line mode and off-line mode ( = simulation mode). In simulation mode, the The fundamental sensor-base system is "Distribution of process I/O hardware and data processing CPU load". However, this DSBS ensures to its users "Transparency" as a distributed system. "Transparency" is described more in detail. philosophy of this distributed Process I/O signal test. signal testing could be done by means of a CRT keyboard, while the system is connected with the plant. Process input/output This Transparency tribution. "Distributed system architecture". words, although the process I/O hardware is distributed and localized, from the view points of DSBS users who have interface with process I/O only by the access subroutines, the total system seems to be one unique centralized system. about process I/O hardware dis- The users need not be conscious of Process monitoring. ating in on-line mode, the status of the process and the control output signal of the users' control programs could be monitored on a CRT viewer. While the system is oper- In other THE DISTRIBUTED SENSOR BASE MANAGEMENT SYSTEM Transparency about location of user programs. Regardless of the location of the user program, the identical access methods (subroutine) are offered from the DSBS. System Configuration In the previous section, the general descriptions of the conventional or centralized SBS, have been presented. newly developed distributed sensor base system architecture. (DSBS) with distributed SBMS will be described.local process I/O hardware is shared between The general system configuration of the DSBS is the user programs on more than two host illustrated in Fig.3, which corresponds to Fig.l of the conventional SBS. In case of the pletely implemented by the SBMS DSBS, the total process I/O hardware system is localized and distributed among the local stations as local process I/O. The each of the local stations, which will be installed on the plant floor, closer to the controlled equipment, is composed of a front-end-processor stations and the SBMS in host stations are (FEP) as intelligence and a data communication designed to have organic coupling in this device, in addition to a local process I/O In this section, the Transparency about multi-computer system Even if one resource of the corn- stations, the resource management is co No burden M u- ~ will be imposed to the user programs, concerning resource sharing of process data. In order to realize the above-mentioned transparency, the local SBMS in local DSBS. To be more concrete, this organic subsystem. constituted on each of FEPs, as illustrated in measures, with high speed and high per- Fig.3, is composed of a local management system formance. The local sensor base system, coupling requires the data communication Normally, in this case, dataway system seems to be the most suitable I for the data communication measure, and this DSBS is to be based on the dataway ' system. Fig. 3. System configuration of the distributed sensor base system

37 Evaluation of Distributed Sensor Base Management Systems process data are ready. in a host station can access those data in the local LIF by the access subroutine. data flow concerning this STQS tributed system is illustrated in Fig.5. The user program Functional Description The Described in this subsection is how the main three subsystems of the SBMS are implemented in the newly developed distributed SBMS. in the dis- Logical process input/output (LPIO). of all, as for logical input function, the physical image of each local process input is made-up at each local station. The logical process input image after processing by the local SBMS is transfered to each host station, to build-up an identical copy of the logical input image made-up in the local station. At the host station, the logical image from each local station is put together, to be built-up as a total system image. logical input mechanism is shown in Fig.4(a). First This Next, as for logical process output, the logical image is first built-up at each host station, the copy of which is transfered to the local stations. At the local station, the copies of logical output image from the host stations are merged and resource-control concerning process outpout is managed at that time by the. local SBMS. local logical image is converted into the physical image, which is given to the process output hardware. The above mechanism is illustrated in Fig. 4(b). The functions concerning on-line and off-line (simulation) mode are the same as in the original SBMS and the process simulation and monitoring support are the same as well. And after that, the Fig. 5. Data flow of short term quick scan Long-term-slow-scanning (LTSS). scale logical files associated with this LTSS are reserved on the host computer disk memory, since these file could not be reserved on FEP memory. As shown by the data flow of Fig.6, the host computer SBMS processes the logical input data transmitted over from local station SBMS and builds up the long term data files, with reference to the scheme file SBSF in the host computer. So, this LTSS is designed to be constituted over the distributed LPIO system. The large- Short-term-quick-scanning (STQS). case, the most parts of data processing job are done in the local station. The time- serial data acquired by the local SBMS are saved in LIFs on the local memory for a certain period. Every time when the short- time scanning is terminated and the data are ready in the local file, an event signal is transmitted from the local station to host stations, to inform that the corresponding In this Fig. 4. Data flow of logical process I/O subsystem

T. Muto, C. Imamichi, A. Inamoto and S. Kato 38 (1) Hot strip mill plant is a complex and large-scale plant and needs large-scale computer control system; (2) It is relatively easy to decompose the overall control system into several subsystems ; (3) Physical range of a plant is so wide (normally 500m to 1,000m). The distributed computer control systems have been introduced to the hot-strip mill from the early development stage of the distributed computer system, in advance to the other plants application. System Configuration The distributed computer control system configuration shown in Fig.7 is a respresentative system configuration on hot strip mill application, where the distributed sensor-base system could be applied. total mill line is thought to be divided into five zones, for each of which an intelligent local station with FEP is to be installed. On the other hand, in the host station, two sets of main computers are to be applied, one of which is for mill line control and the other is for furnace area control. These two main computers are loosely coupled, to form a loosely-coupled multi-computer system. Fig.6. Data flow of long term scan In this case, the APPLICATION In order to make the discussions and descriptions on the distributed system more concrete, here in this section, the practical aspects of the distributed SBMS will be offered by introducing a model system applied to a hot strip mill control system. A hot strip mill has been proved to be one of the most respresentative application fields of the distributed sensor base system, so that the model system may give the relevant image of the distributed SBMS. sensor base In this system configuration, not only process input/output hardware, but also peripheral devices are distributed. this paper most attention trated on the sensor base system. However, in will be concen- Hot Strip Mill Computer System The general hardware specification of the processors and data-ways involved in this system configuration is outlined in TABLE 2, where the hardware equipment of Mitsubishi Electric Corp. happen to be applied. A hot strip mill very naturally requires a distributed computer control system, according to the following reasons : CRT: Cathode ray tube OTW: Output typewriter FEP: Front-end-processor VAS: Voice annaunciator LP : Line printer STW: System FDD: Froppy-disk-drive DAD: Dual access disk FDD Fig.7. The representative hot strip mill computer control system

39 Evaluation of Distributed Sensor Base Management Systems Distributed Sensor Base System TABLE 2 Hardware Specification The system scale of the distributed sensor base system applied to the host strip mill computer control system will be shown. of all, regarding physical scale, the number of process input/output hardware points and distance from the host station to local station are shown in TABLE 3, where distance is not direct distance but cable length. As for the distance data, the following two cases are taken into account. host station is assumed to be installed inside the plant floor, while in CASE-2, the host station is to be installed in the plant- office detached to the plant floor. General Specification Component First MELCOM 350 - 50 (A2500) add time memory cycle time = 0.65 Ms/64 b i t s maximum memory size = 1 M words number of instructions = 0.2 ym Host computer computer In CASE-1, the = 250 MELCOM 350 - 50 (A2100) add time memory cycle time = 0.60 ps/16 bits maximum memory size = 192 Κ words number of instructions = 1.2 ys Local Local computer Next, from Logical point scale will be shown as the numbers of logical points, at every local station. as to LPIO, HSQS & LTSS subsystems are listed up and tabulated in TABLE 4, indexing a station. The data in these tables will be utilized as basic data at the quantitative evaluations of the distributed SBMS in the next section. of view, the system = 164 These numbers MDWS - 30S transmission Data way system rate = 15 M bps maximum no. of stations = 256 In addition to those quantitative figures concerning the distributed SBMS, to show how each of three subsystem, i,e. LPIO, STQS and LTSS actually fulfills its functions, the practical aspects of these subsystems at the hot strip mill control system application are arranged in tabular form as in TABLE 5. TABLE 3 Physical Scale of SBMS Distance from host station (m) CASE-1 Number of PI/0 points points Number of PI/0 Local station identifier identifier Local station No. No. CASE-2 Finishing mill EVALUATION STUDIES 100 20 2000 1 Quantitative Evaluation Roughing mill 350 250 600 2 Concerning the system model for evaluation analysis, the DSBS applied for a hot strip mill computer control system, which has been outlined beforehand in the previous section, will be adopted. Further, in order to make evaluation results visual and understandable, the following expression techniques will be applied. As one of the parameters of evaluation on each case, system scale will be chosen. This means that the cross-point or the conflict point between the distributed architecture and the conventional architecture may be obtained, by increasing system scale. Here,on increasing the system scale as an index, it is temporarily assumed that the number of the local station should be increased sequentially starting from local station No.l to local station No.5. increasing sequence assumed here is just the temporary sequence and so that sequence itself is trivial. Coiler & conveyor 300 200 700 3 450 350 750 4 Furnace Furnace entry side 600 500 900 5 TABLE 4 Logical Scale of SBMS Local station identifier identifier Local station Number of logical points No. No. LTSS STQS LPIO The Finishing mill 40 100 700 1 Roughing mill 20 50 100 2 Besides, the system scale as an index will be appropriately arranged and normalized to con- venience of every evaluation case, so that the curves of the conventional architectures may be linear or quadratic. Coiler & conveyor 20 30 250 3 200 10 400 4 Furnace Furnace entry side 0 10 250 5

T. Muto, C. Imamichi, A. Inamoto and S. Kato 40 TABLE 5 Practical Aspect of SBMS CDW + n * CF E P , (2) CDW η C FEP: cost of FEP hardware cost; total data communication cost , where Use dataway system initial cost ; number of local stations ; Subsystem ο ο Operator's desk interface, Interface with electric drive system, Interface with sensors specially tracking sensors, Miscellaneous process I/O. Cd LPIO ο ο ο Data aquisition for mill control model calculation, Data aquisition for learning control or feed forward control. Data aquisition for precise quality control. ο STQS ο ο Data aquisition for furnace combustion control and energy saving control, Data aquisition for long term quality control and long term learning of models. LTSS ο Fig.8(a). Evaluation of data communication cost in CASE-1 Process Data Communication Cost As far as the hot strip mill computer control system is concerned, the data communication cost on the process input/output interface, say mostly the hardwiring cost, may occupy approximately 10 to 30% of the total system cost, so that the reduction of hardwiring cost may be the serious problem for the system designer. If the distributed system architecture will be adopted, the amount of the hardwiring and consequently total wiring cost may be reduced, while the cost of both a dataway hardware system and local stations containing FEPs may be increased. In order to evaluate these data communication cost, some of the formu- lation techniques are required. paper, two cost functions are introduced, one for the cabling cost estimation in the conventional architecture and the other for data communication hardware in the distributed architecture. Those cost functions are detailed below. Here, in this Fig.8(b), Evaluation of data communication cost in CASE-2 Hardwiring cost. of process I/O system could be approximated and be formulated as : Cost function of hardwiring In the TABLE 3, the basic data concerning data communication cost were shown in two cases, CASE-1 that the host station is installed within the plant-floor, maybe next to the finishing mill pulpit and CASE-2 that the host station is inside the plant-office detached to the plant floor. The results of the data communication cost evaluation, are shown in Fig.8 (a) and Fig.8 (b) for CASE-1 and CASE-2 respectively. Σ (a*Pi + 3*Li*Pi). i=l (1) where Cw : total hardwiring cost ; Pi : number of process I/O points; Li a,3: parameters; i : local station index. : length from host station; In CASE-1, the conflict point between a distributed and a conventional system seems to be at the point of three or four local stations, saying in system scale. A distributed system may get more advantage in CASE-2, where the , conflict point maty be a couple of local stations. In other words, it is supposed that the hardwiring cost may be proportional both to the number of process I/O points and to the number of process I/O points multiplied by cable length Data communication hardware. data communication hardware could be formulated as : Cost function of

41 Evaluation of Distributed Sensor Base Management Systems Data Processing Cost The evaluation measure on this CPU load distribution is how the total system cost of data processing is reduced by distributing system duty of host computers among FEPs. As for the data processing cost, the unit processing cost at FEPs should be set much low, compared with the unit cost at host computers, of which hardware cost could be naturally high. On the other hand, the data processing cost for data communication between stations should be taken into account at the distributed architecture. The following premises should be made for the data processing cost evaluation. Fig.9. Cost coefficient vs. response time Premise-1. The data-processing cost for a particular job at each station is proportional to the average CPU duty ratio (%) occupied by that job. (number of local station) System scale at LPIO subsystem 3 1 V~ 5 ' ι 1 1 2 1 • r Premise-2. The data-processing cost is also related to the required response time (or turn-around time). On those jobs which require quick service of CPU, high processing cost may be imposed. This relation between CPU cost and response time may naturally differ, depending on whether a host station or a local station. The processing cost vs. response time curves at each station shown in Fig.9 are thought to be practical. Premise-3. The data processing cost at each station is proportional to the processing hardware system cost of that particular station, where the processing hardware system includes a CPU, a main memory unit and a set of disk-memory-drives. System scale at STQS subsystem (number of local station) Premise-4. The data processing cost related to the SBMS contains the processing cost of (1) Interface with the process I/O hardware system; (2) Engineering unit conversion; (3) Logical to physical or physical to logical conversion; (4) Error checking; and (5) Image data communication between stations, if necessary. Fig.10. Evaluation of data processing cost on LPIO & STQS of which the definitions are : Definition. associated with the fault of a particular hardware subsystem should be assessed as the sum of the hardware cost of all the hardware subsystems of which performance or functions are lost due to that fault. The ESPL should be defined as this system performance loss multiplied by the down-time ratio (down-time ratio = 1.0 - availability) of that hardware subsystem. The system performance loss, Under the above-listed premises, the actual numerical calculations are done on the hot strip mill system application, of which results are presented both in Fig. 10 for the LPIO subsystem and the STQS subsystem. Reviewing these figures, it may be concluded that the distributed system architecture may favor to the conventional architecture, supposed that the system may include three or four local stations or more. The following premises are required. Premise-1. station is well balanced as in the following formula : The hardware cost of a host System Performance Loss On evaluating the system reliability of the sensor-base system, it seems that to offer the expected amount of system performance loss may be more practical, rather than just to give the reliability data of the total hardware system and/or the individual hardware components. According to this philosophy the concept of the expected system performance loss(abbr. ESPL) will be introduced, CHOST(j) =C*H0ST(j)+ Σ CF EP(i,j) , i=l 3 = 1 , 2 (3) cH 0 S T ( j ) : cost of a host station(j) at the conventional architecture; cH 0 S T ( j ) : cost of a host station(j) at where Λ

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