ACCNET-A corporate computer network
Contents
1. 948 Wulf W A Russell D B Habermann A N BLISS A Lan guage for Systems Programming Comm of the ACM Vol 14 December 1971 pp 780 790 From the collection of the Computer History Museum www computerhistory org2. large time shared computers called Hosts so that a user can access and run a program on a distant computer through a terminal connected to his local computer It is set up as a message service where any computer can submit a message destined for another computer and be sure it will be delivered promptly and correctly A conversation between two computers has messages going back and forth similar to the types of messages between a user console and a computer on a time shared system Each Host is connected to the net work by a mini computer called an Interface Message Processor IMP A message is passed from a Host to its IMP then from IMP to IMP until it arrives at the IMP serving the distant Host who passes it to its Host Relia bility has been achieved by efficient error checking of each message and each message can be routed along two physically separate paths to protect against total line failures The ARPA network was designed to give an end to end transmission delay of less than half a second Design estimates were that the average traffic between each pair of Hosts on the network would be 5 to 2 kilobits per sec ond with a variation between 0 and 10 kilobits per second and the total traffic on the network would be between 200 and 800 kilobits per second for a 20 IMP network To handle this load the IMPs were interconnected by leased 50KB lines For the initial configuration of the ARPA network communication circuits cost 49 0
3. of magnitude when dissimilar machines are involved Using ASCII as the standard network code allows the interchange of files containing character data but does not address the prob lem of different representations of numerical data e g packed decimal short floating point long floating point etc Two alternatives present themselves either allow each machine to translate from the representation of every other machine to its own or use a standard network repre sentation and have each machine translate between its own and the network s The first is attractive when only a few different types of machines will be allowed on the network If there are N different types of machines then N N 1 translation routines might have to be written The second alternative requires more effort in developing the standard network representation but is really the only choice when the number of different types is larger than three or four Another problem is the large amount of translation that must take place It may not be desirable to place this CPU laden task on a time sharing machine for fear of degrading response time so the solution seems to lie in executing the translation within the IMPs If performing translation interferes with the ability of the IMP to per form communication an additional CPU can be attached to each in order to perform this task With hardware costs decreasing 50 percent every two or three years this seems an attractiv
4. systems may be achieved This will allow controlled access to records at the element level rather than at the file level EXISTING SITUATION The existing configuration of the DEC 10 installation provides a 300 to be extended to 1200 baud link to the 370 via a COMTEN 60 a mini computer based system which provides store and forward message switching capability for the corporate teletype network This link is adequate to support the immediate needs of a Sales Order Entry System but is totally inadequate for the general capability of making the computational power and the massive file storage of the 370 available to a user on the DEC 10 Five DATA 100 terminals provide remote batch service into the 370 for users at various locations including three plants and a research center Most of the other plants have medium scale computer systems to support their local data processing needs All make extensive use of process control mini computers and two have UNIVAC 494 systems which can handle both real time control and batch data processing Approximately 25 interactive CRTs scattered through out various sales offices across the country have recently been installed to upgrade our Sales Order Entry System Each terminal is connected to the DEC 10 on a dial up 300 baud line PROPOSED SOLUTION The most obvious solution to the problem of 370 DEC 10 communication would be to connect the DEC 10 to the 370 in a back to back fashion To provi
5. 00 per node per year and the network supports an average traffic of 17 kilobits From the collection of the Computer History Museum www computerhistory org 134 National Computer Conference 1973 per node Each IMP costs about 45 000 and the cost of the interface hardware is an additional 10 000 to 15 000 The IMPs are ruggedized and are expected to have a mean time between failures of at least 10 000 hours less than one failure per year They have no mass storage devices and thus provide no long term message storage or message accounting This results in lower cost less down time and greater throughput performance TYPES OF NETWORKS There are three major types of networks Centralized Distributed and Mixed A Centralized network is often called a Star network because the various machines are interconnected through a central unit A network of this type either requires that the capabilities of the central unit far surpass those of the peripheral units or it requires that the central unit does little more than switch the various messages between the other units The major disadvantage of a network of this type is the sensitivity of the network to failures in the central unit i e whenever the central unit fails no communication can occur The most common example of this type of network is one consisting of a single CPU linked to several remote batch terminals A Distributed network has no master unit R
6. 20 Conway Richard Maxwell William Morgan Howard Selective Security Capabilities in ASAP A File Management System Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Montvale N J pp 1181 1185 Crocker Stephen D Heafner John F Metcalfe Robert M Pos tel Jonathan B Function Oriented Protocols for the ARPA Computer Network Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Montvale N J pp 271 279 deMercado John Minimum Cost Reliable Computer Communi cation Networks Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 553 589 Dijkstra E W The Structure of the THE Multiprogramming System Comm of the ACM Vol 11 May 1968 Farber David Data Ring Oriented Computer Networks Com puter Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 79 93 Farben David J Networks An Introduction Datamation April 1972 pp 36 39 Frank Howard Kahn Robert E Kleinrock Leonard Computer Communication Network Design Experience with Theory and Practice Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Mont vale N J pp 255 270 Frank Howard Optimal Design of Computer Networks Com puter Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 167 183 Frank H Frisch I T Chou W Topological Considerations in the Design of the ARPA Computer Network Proc AFIPS 1970 SJCC Vol 36 AFIPS
7. ACCNET A corporate computer network by MICHAEL L COLEMAN Aluminum Company of America Pittsburgh Pennsylvania INTRODUCTION The installation of a Digital Equipment Corporation DEC 10 in close proximity to an existing IBM 370 165 initi ated an investigation into the techniques of supporting communication between the two machines The method chosen use a mini computer as an interface suggested the possibility of broadening the investigation into a study of computer networks the linking of several large com puter systems by means of interconnected mini comput ers This paper explains the concept of a network and gives examples of existing networks It discusses the justi fications for a corporate computer network outlines a proposed stage by stage development and analyzes and proposes solutions for several of the problems inherent in such a network These include software and hardware interfaces movement of files between dissimilar ma chines and file security WHAT IS A NETWORK A computer network is defined to be an intercon nected set of dependent or independent computer systems which communicate with each other in order to share certain resources such as programs or data and or for load sharing and reliability reasons In a university or a research environment the network might consist of interconnected time sharing computers with a design goal of providing efficient access to large CPUs by a user at a t
8. N A NETWORK The handling of files in a non homogeneous distributed network poses several complex problems These include control of access and transfer of information between dissimilar machines Control of access That any system supporting multiple simultaneous use of shared resources requires some sort of flexible easy to use method of controlling access to those resources seems obvious to everyone with the possible exception of the designers of IBM s OS 360 the main problem being how to provide the contrel at a reasonable cost Restricting ourselves just to file access control we see many potential methods with varying degrees of security and varying costs 13 14 31 43 Al provide control at the file level some at the record level and others at the element level By designing our system with a Structured Programming approach it should be possible to modify the method we choose upgrading or downgrading the protection until a cost benefit balance is reached Most designers of file access control systems have mentioned encryption of the data we shall be no differ ent Apparently finding the cost prohibitive they have failed to include this capability in their final product In the proposed network however translation between the data representations of dissimiliar machines will be per formed see below so the added cost of transforming from a scrambled to an unscrambled form will be small Eac
9. Press Montvale N J pp 581 587 Frank Ronald A Commercial ARPA Concept Faces Many Roadblocks Computerworld November 1 1972 Fraser A G On the Interface Between Computers and Data Communications Systems Comm of the ACM Vol 15 July 1972 pp 566 573 Grobstein David L Uhlig Ronald P A Wholesale Retail Con cept for Computer Network Management Proc AFIPS 1972 FICC Vol 41 AFIPS Press Montvale N J pp 889 898 Hansen Morris H Insuring Confidentiality of Individual Records in Data Storage and Retrieval for Statistical Purposes Proc AFIPS 1971 FJCC Vol 39 AFIPS Press Montvale N J pp 579 385 Hansler E McAuliffe G K Wilkov R S Exact Calculation of Computer Network Reliability Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 49 54 Heart F E Kahn R B Ornstein S M Crowther W R Wal den D C The Interface Message Processor for the ARPA Computer Network Proc AFIPS 1970 SJCC Vol 37 AFIPS Press Montvale N J pp 551 1567 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 ACCNET A Corporate Computer Network 139 Hench R R Foster D F Toward an Inclusive Information Network Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Mont vale N J pp 1235 1241 Herzog Bert MERIT Computer Network Co
10. a stored on one machine from a program executing on another machine This avoids costly duplication of various files that would be used at various locations within the corporation Avoidance of software duplication Executing programs on a remote CPU with data sup plied from a local CPU may in many cases avoid costly software duplication on dissimilar machines For exam ple a sophisticated mathematical programming system is in existence for the IBM 370 With a network a user could conversationally create the input data on a DEC 10 and cause it to be executed on the 370 Without a net work the user would either have to use a more limited program travel to the 370 site or modify the system to run on his own computer Flexibility Without a network each computer center in the corpo ration is forced to re create all the software and data files it wishes to utilize In many cases this involves complete reprogramming of software or reformatting of the data files This duplication is extremely costly and has led to considerable pressure for the use of identical hardware From the collection of the Computer History Museum www computerhistory org ACCNET A Corporate Computer Network 135 and software systems within the corporation With a successful network this problem is drastically reduced by allowing more flexibility in the choice of components for the system Simplification of file backup In a network file backup can
11. ather the responsibility for communication is shared among the members a message may pass through several members of the network before reaching its final destination For reliability each unit in the network may be connected to at least two other units so that communication may con tinue on alternate paths if a line between two units is out Even if an entire unit is disabled unaffected members can continue to operate and as long as an operable link remains some communication can still occur The ARPA network is an example of a Distributed network A Mixed network is basically a distributed network with attached remote processors in most cases batch terminals providing network access to certain locations not needing the capability of an entire locally operated computer system These remote locations are then dependent on the availability of various central CPUs in order to communicate with other locations Within a network two types of message switching may occur circuit switching and packet switching Circuit switching is defined as a technique of establishing a complete path between two parties for as long as they wish to communicate and is comparable to the telephone network Packet switching is breaking the communication into small messages or packets attaching to each packet of information its source destination and identification and sending each of these packets off independently to find its way to the destination In circui
12. be achieved automati cally by causing the programs which update the file to create a duplicate record to be transmitted to a remote machine where they could be applied to a copy of the data base or stacked on a tape for batch update This would eliminate the tedious procedure of manually trans porting data from one machine to another the resulting inherent delay in the updates would be eliminated Reduction of communication costs The substitution of a high bandwidth channel between two separate locations for several low bandwidth channels can in certain cases reduce communication costs signifi cantly Ability to combine facilities With a network it is possible to combine the facilities found on different machines and achieve a system with more capability than the separate components have indi vidually For example we could have efficient human interaction on one machine combined with a computa tional ability of a second machine combined with the capability of a third machine to handle massive data bases Simplification of conversion Converting a site from its own computer to a remote batch terminal could be simplified by linking the com puter at the site into the network during the conversion Enhancement of file security By causing all references to files which are accessible from the network to go through a standard procedure advanced file security at a higher level than is currently provided by existing operating
13. calls on the HASP Submit Receive function on level 5 User waits a brief period until he gets an OK from the terminal signifying that the program has been submitted He is then free to either perform other actions or to sign off of the net work At some later time the user receives an output ready message on his terminal User can now examine his output file e Level 5 On level 5 is found the HASP Submit Receive function HSR and functions to perform network access control file access control and remote pro gram control Let us examine the actions of the HSR function applied to our example The HSR function obtains the name of the HASP READER process of the specified Host It then calls on a level 4 function to pass the input file to that process When the level 4 func tion which controls process to process communi cation is completed it will return a value corre sponding to the job number that HASP has assigned The HSR function sends an OK to the user It then obtains the name of the HASP WRITER process on the specified Host and calls on a level 4 to pass the job number and to specify the output file to the HASP WRITER Control returns when the output file is complete The HSR function then sends an OUTPUT READY message to the user Level 4 On level 4 is found the functions which control the file descriptors file access and process to process communication Examining the actions of th
14. de an upward flexibility however it is proposed that rather than con necting the machines in that way they will be connected using a mini computer as an interface By designing the system which controls their interaction with a network approach additional communication links may be obtained with a relatively small software investment For example if in the future our research center obtains a large computer that they wish to incorporate into the communications process of the other two an additional mini computer would be placed there and connected via a communication line to the other This approach has several advantages First by going through a mini computer each of the two interfaces can be very carefully debugged in isolation and thus not affect the other machine Second once an IBM interface to the mini computer is designed one can connect any IBM machine into the network without rewriting any of the other interfaces We would not have to write an IBM to UNIVAC interface an IBM to CDC interface an IBM to Honeywell interface etc Third the only change neces sary in the existing portion of the network as the network expands would be to inform the mini computers of the presence of the other machines System description In order to effectively describe a system as potentially complex as this one we shall make use of techniques being developed under the classification of Structured Programming 37 4 5538 The system
15. e proc ess to process communication function PPC applied to our example we find The PPC function converts the name of the process into a well known port number and then establishes a logical link to the desired process It then formulates a message containing the information to be passed and uses a level 3 func tion to transmit the message It then receives a message in reply which con tains the job number in one case and the output in another It passes this up to level 5 after destroying the links Level 3 Level 3 contains among others the function which transfers a message from one Host to another To do this it Takes the message breaks it into pages and calls a level 2 function to transmit each page When the last page has been transmitted it waits for an acknowledgment If the acknowledgment indicates that a reply is being sent it receives each page of the reply and passes up to level 4 Level 2 On level 2 is handled the passing of pages The steps are The page is transferred from the Host to its IMP The page is then translated into the standard network representation and broken into packets From the collection of the Computer History Museum www computerhistory org ACCNET A Corporate Computer Network 137 A level 1 function is called to transmit each packet e Level 1 At level 1 is handled the details of transmitting a packet from IMP to IMP This includes retra
16. e solution INTERFACES IMP Host interface The ARPA network is optimized toward supporting terminal interaction A commercial network must be optimized toward maximizing throughput of lengthy data files which produces large peak loads requiring high bandwidth channels between each Host and its IMP In order to allow an IMP to communicate with its Host with a minimum of CPU intervention by either party data must be transferred directly between the memory of the IMP and the memory of the Host This can be achieved by connecting to an equivalent of the memory bus of the DEC 10 or multiplexor channel of the 370 With this type of interconnection it will be necessary to configure the software so that each member of the communicating partnership appears to the other member as if it were a peripheral device of some sort presumably a high speed tape drive Communication therefore would take place by one member issuing a READ while the other member simultaneously issues a WRITE IMP IMP interface The IMPs will be linked by standard synchronous communication interfaces Initial plans call for 40 8KB full duplex leased lines but 19 2KB lines could also be used A Cyclical Redundancy Check will provide detec tion of errors and cause the offending packet to be retransmitted Software interfaces One of the main reasons for using mini computers between the Hosts is to insure that the number of inter face programs which must be w
17. erence 1969 pp 431 441 Sevcik K C Atwood J W Grushcow M S Holt R C Horn ing J J Tsichritzis D Project SUE as a Learning Experience Proc AFIPS 1972 FICC Vol 41 AFIPS Press Montvale N J pp 331 338 Stefferud Einar Management s Role in Networking Datama tion April 1972 pp 40 42 Thomas Robert H Henderson D Austin McROSS A Multi Computer Programming System Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Montvale N J pp 281 293 From the collection of the Computer History Museum www computerhistory org 140 National Computer Conference 1973 52 Tobias M J Booth Grayce M The Future of Remote Informa tion Processing Systems Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 1025 1035 Walden David C A System for Interprocess Communication in a Resource Sharing Computer Network Comm of the ACM Vol 15 April 1972 pp 221 230 Weis Allan H Distributed Network Activity at IBM Computer Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 1 25 54 Williams Leland H A Functioning Computer Network for 55 Higher Education in North Carolina Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 899 904 Wulf William A Systems for Systems Implementors Some Experience From BLISS Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 943
18. erminal In a commercial environment a network would consist primarily of interconnected batch processing machines with a goal of efficiently processing a large number of programs on a production basis One example of the use of a network in a commercial environment would be preparing a program deck on one computer transmitting it to another computer for processing and transmitting the results back to the first computer for output on a printer OTHER NETWORKS Functioning networks have been in existence for several years 6 These include CYBERNET a large commer cial network consisting of interconnected Control Data 133 Corporation machines the Distributed Computer Sys tem DCS at the University of California at Irvine the Michigan Educational Research Information Triad Inc MERIT a joint venture between Michigan State Uni versity Wayne State University and the University of Michigan the OCTOPUS System at the Lawrence Berkeley Laboratory the Triangle Universities Compu tation Center TUCC Network a joint undertaking of the Duke North Carolina State and North Carolina Universities ad the TSS Network consisting of inter connected IBM 360 67s 5 But perhaps the most sophisticated network in existence today is the one cre ated by the Advanced Research Projects Agency ARPA referred to as the ARPA network 0 22 28 38 34 40 42 44 46 The ARPA network is designed to interconnect a number of various
19. h file access control system is based on a method which associates with each user file pair a set of descrip tors listing the rights or privileges granted to that user for that file e g Read Access Write Access Transfer of Read Access to another user Conceptualized as entries in a matrix these descriptors are almost never stored as From the collection of the Computer History Museum www computerhistory org 138 National Computer Conference 1973 such due to its sparceness Rather they are stored as lists either attached to each element of a list of users or attached to each element of a list of files Assuming that we have a system for controlling file access one design question for a distributed network is where to store the file access descriptors For example let us look at a network with three machines A B and C and a file F located at A but created by a user at B To be accessible from the other machines the file must be known by them and therefore each machine must have a file descriptor stating that file F is located at A If we also distribute the file access descriptors an unauthorized user at C could gain access to the file by obtaining control of his machine and modifying the file access descriptors Hence each file access descriptor should be stored at the same location as the file it protects Transfer of information The complexity of transferring information between two machines is increased by an order
20. her machine At this stage strict security controls would be integrated into the system The additional hardware required for this stage would include an additional CPU with 8K of memory and adaptors to interconnect the two CPUs The approximate purchase cost would be 9 000 12 000 with a monthly maintenance cost of approximately 75 e Stage 3 This stage would expand the network to include computers at other locations Additional hardware at the original site would include one synchronous communication controller for each outgoing line at a cost of 2 000 2 500 with a maintenance cost of 25 and appropriate modems Total cost for the original site assuming two outgoing lines would be between 36 000 and 49 500 excluding disk rental modems and communication lines e Stage 4 This stage could be developed in parallel with stage 3 It would add the capability for a user on a termi nal attached to one machine to submit and interact with a program executing on the other machine No additional hardware would be required Stage 5 This stage consists of the design and implementa tion of automatic back up procedures Most of the preliminary analysis can be done in parallel with stages 2 4 These procedures would automatically create duplicate transactions of updates to critical files and have them routed to an alternate site to be applied to the back up data base No additional hardware is required HANDLING OF FILES I
21. mputer Networks R Rustin Ed Prentice Hall Engiewood Ciiffs N J 1972 pp 45 48 Hoffman Lance J The Formulary Model for Flexible Privacy and Access Controls Proc AFIPS 1971 FJCC Vol 39 AFIPS Press Montvale N J pp 587 601 Hootman Joseph T The Computer Network as a Marketplace Datamation April 1972 pp 43 46 Kahn Robert Terminal Access to the ARPA Computer Net work Computer Networks R Rustin Ed Prentice Hall Engle wood Cliffs N J 972 pp 147 166 Kleinrock Leonard Analytic and Simulation Methods in Com puter Network Design Proc AFIPS 1970 SJCC Vol 36 AFIPS Press Montvale N J pp 569 579 Kleinrock Leonard Survey of Analytical Methods in Queueing Networks Computer Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 185 205 Lichtenberger W Ed Tentative Specifications for a Network of Time Shared Computers Document No M 7 ARPA September 9 1966 Liskov B H A Design Methodology for Reliable Software Sys tems Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 191 199 Luther W J Conceptual Bases of CYBERNET Computer Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 111 146 McKay Douglas B Karp Donald P IBM Computer Network 440 Computer Networks R Rustin Ed Prentice Hall Engle wood Cliffs N J 1972 pp 27 43 McQuillan J M Cro
22. n Edward K Sr Network Computer Modeling Proc ACM Annual Conference 1972 pp 254 264 From the collection of the Computer History Museum www computerhistory org J Q0 s 10 11 12 13 14 16 17 18 19 20 21 22 23 24 20 26 28 Bhushan Abhay The File Transfer Protocol ARPA Network Information Center Document No 10596 July 8 1972 Bhushan Abhay Comments on the File Transfer Protocol ARPA Network Information Center Document No 11357 August 18 1972 Carr C Stephen Crocker Stephen D Cerf Vinton G Host Host Communication Protocol in the ARPA Network Proc AFIPS 1970 SJCC Vol 36 AFIPS Press Montvale N J pp 589 597 Carroll John M Martin Robert McHardy Lorine Moravec Hans Multi Dimensional Security Program for a Generalized Information Retrieval System Proc AFIPS 1971 FJCC Vol 39 AFIPS Press Montvale N J pp 571 577 Casey R G Allocation of Copies of a File in an Information Network Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Mont vale N J pp 617 625 Cocanower Alfred MERIT Computer Network Software Con siderations Computer Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 65 77 Conway R W Maxwell W L Morgan H L On the Imple mentation o1 Security Measures in Information Systems Comm of the ACM Vol 15 April 1972 pp 211 2
23. nsmis sion in case of errors Stages of development In order to allow the concept of a corporate computer network to be evaluated at minimum expense it is desira ble to break the development into discrete stages each stage building on the hardware and software of the pre vious stage to add additional capability Stage 1 This first stage would connect the DEC 10 to the local IBM 370 165 by using a single mini computer It would allow a user on the DEC 10 to conversation ally build a program on a terminal and submit it to the 370 to be run under HASP His output would be printed either at the 370 at the DEC 10 or at his terminal This stage would also support the transfer of files consisting solely of character data to be trans ferred from one machine to the other The mini computer hardware required for the stage would include one CPU with 16 24K of mem ory power monitor and restart autoload and tele type two interfaces one to the 370 and one to the DEC 10 a real time clock and a cabinet The approximate purchase price would be 25 000 to 35 000 with a monthly maintenance cost of ap proximately 300 In addition a disk and controller should be rented for program development This cost is approximately 500 per month and would be car ried for the remaining stages e Stage 2 The second stage would remove the restriction on file transfer and allow files consisting of any type of data to be accessed from the ot
24. ritten only grows linearly with the number of different types of Hosts The effort in writing subsequent versions of the IMP Host interface can be minimized by at least two methods 1 Put as much of the system software as possible into the IMPs Make use of sophisticated architecture e g multi processor mini computers read only memory to obtain the power required 2 For that portion of the system which resides in the Host write the software using a standard high level language e g FORTRAN for as much of the code as possible REFERENCES 1 Anderson Robert et al Status Report on Proposed Data Recon figuration Services ARPA Network Information Center Docu ment No 6715 April 28 1971 2 Aupperle Eric MERIT Computer Network Hardware Consider ations Computer Networks R Rustin Ed Prentice Hall Englewood Cliffs N J 1972 pp 49 63 3 Bell G Cady R McFarland H Delagi B O Laughlin J Noonan R A New Architecture for Mini Computers The DEC PDP 11 Proc AFIPS 1970 SJCC Vol 36 AFIPS Press Mont vale N J pp 657 675 4 Bell G Habermann A N McCredie J Rutledge R Wulf W Computer Networks Computer IEEE Computer Group Sep tember October 1970 pp 13 23 5 Bjorner Dines Finite State Automation Definition of Data Communication Line Control Procedures Prec AFIPS 1970 FICC Vol 37 AFIPS Press Montvale N J pp 477 491 6 Bowdo
25. t switching all conflict and allocation of resources must be resolved before the circuit can be established thereby permitting the traffic to flow with no conflict In packet switching there is no dedication of resources and conflict resolution occurs during the actual flow This may result in some what uneven delavs being encountered by the traffic WHY A NETWORK By examining the general characteristics of a network in the light of a corporate environment specific capabili ties which provide justification for the establishment of a corporate computer network can be itemized These are load balancing avoidance of data duplication avoidance of software duplication increased flexibility simplification of file backup reduction of communication costs ability to combine facilities simplification of conversion to remote batch terminal enhancement of file security Load balancing If a network has several similar machines among its members load balancing may be achieved by running a particular program on the machine with the lightest load This is especially useful for program testing e g a COBOL compilation could be done on any IBM machine in the network and achieve identical results Additionally if duplicate copies of production software were main tained programs could be run on various machines of the network depending on observed loads Avoidance of data duplication In a network it is possible to access dat
26. will be broken down into various levels of abstraction each level being unaware of the existence of those above it but being able to use the functions of lower levels to perform tasks and supply information When a system is specified in terms From the collection of the Computer History Museum www computerhistory org 136 National Computer Conference 1973 of levels a clear idea of the operation of the system may be obtained by examining each level starting from the top and continuing down until further detail becomes unimportant for the purposes of the specification Let us now examine the first few levels of a portion of the proposed system The top most level is level 6 under that is level 5 and so on We shall look at what occurs in the case of a user at a terminal on the DEC 10 submitting a program to a distant IBM 370 under HASP e Level 6 On level 6 is found user and program processes All interaction with the user or with a program written by the user occurs on this level In fact after this level is completely specified the User Manual for the system can be written In our example an examina tion of what is happening would show the following steps User creates the input file and a file for the output User logs onto the network specifying his ID number User types SUBMIT command specifying the input file the output file and the Host on which the program is to be run This submit command
27. wther W R Cosell B P Walden D C Heart F E Improvements in the Design and Performance of the ARPA Network Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Montvale N J pp 741 754 Mendicino Samuel F OCTOPUS The Lawrence Radiation Laboratory Network Computer Networks R Rustin Ed Pren tice Hall Englewood Cliffs N J 1972 pp 95 110 Metcalfe Robert M Strategies for Operating Systems in Com puter Networks Proc ACM Annual Conference 1972 pp 278 281 Needham R M Protection Systems and Protection Implemen tations Proc AFIPS 1972 FJCC Vol 41 AFIPS Press Mont vale N J pp 571 578 Ornstein S M Heart F E Crowther W R Rising H K Russell S B Michel A The Terminal IMP for the ARPA Computer Network Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Montvale N J pp 243 254 Roberts Lawrence G Extensions of Packet Communication Technology to a Hand Held Personal Terminal Proc AFIPS 1972 SJCC Vol 40 AFIPS Press Montvale N J pp 295 298 Roberts Lawrence G Wessler Barry D Computer Network Development to Achieve Resource Sharing Proc AFIPS 1970 SJCC Vol 36 AFIPS Press Montvale N J pp 543 549 Rutledge Ronald M Vareha Albin L Varian Lee C Weis Ailan H Seroussi Saiomon F Meyer James W Jaffe Joan F Angell Mary Anne K An Interactive Network of Time Sharing Computers Proc ACM Annual Conf
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