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is, a system should have standardized procedures

Number of for only the smallest job units that can be formally

days to be Estimated monthly message volume

studied specified. These fixed subroutines can then be

Under 1000....

20 combined to form larger routines suitable for

1000 to 2000..

10 performing larger segments of the overall activity.

2000 to 5000..

5 At any point where two jobs are dissimilar, this


5000 to 10,000.... dissimilarity can be reflected not only in different

10,000 and over.....

2 flow diagrams but also in different formats, codes, sequencing procedures, indexing methods, displays, and so forth. To this extent, the system is neither

Ideally the working days to be studied should be tailor-made nor ready-made. It is not uneconomi

chosen at random, but if for any reason a series of cally designed so that every job is unique, nor is

consecutive days must be selected, care should be it standard but ill-fitting because dissimilar jobs

taken to avoid days immediately preceding or are forced into standardization. Rather, like a

following holidays. In addition, the count must be made-to-measure suit, the system is built around

made at each location from which information is small standardized parts, each designed to fit

sent and at which information is received." (Gentle, a small part of the overall job. The larger portions

1965, pp. 58-59.) of the system are not standardized as total units,

“Calculate the Total Transmission Time. The but are unique configurations of standardized

third step, after calculating the average number of smaller parts." (Bennett, 1964, p. 108).

characters per message, is to determine the average

daily total transmission time. At this point a trans3.22 Baran (1964) considers, for example,

mission speed must be assumed. This transmission

time can be calculated by dividing the average "four separate techniques that can be used singly

number of characters per message by the assumed or in combination to achieve, through automation,

speed of the system. If the average message has 'best' use of a seriously, degraded and overloaded

2,500 characters, for example, and the assumed communications plant, within within the framework

transmission speed is 10 characters per second, the of a rapidly changing organizational structure.

average transmission time per message will be 250 (p. v).

seconds. To this figure, however, must be added

some operating time for dialing the call, waiting for 3.23 “Calulation of the average daily volume the connection to be established and, in some cases, and the peak volume of information to be handled coordinating the forthcoming transaction with the in the system consists of four steps:

personnel at the receiving end. Operating time

should be calculated from a study of a sample of 1. Calculate the average daily volume of mes- calls, but if this is impracticable, the system sages presently flowing in the system.

designer may use 100 seconds as an overall average 2. Calculate the average number of characters

for the operating time on each dialed-up data in each message.

communications call.

“The amount of delay to be expected during the 3. Calculate the average daily total transmission busy hour depends upon the holding time of the time.

circuit at the receiving location and the total 4. Calculate the peak volumes.

number of minutes in the busy hour during which

information will be received. Data communication The communications designer must plan the

planners refer to a series of charts which indicate system to handle the peak traffic loads with accept

the expected delay in transmissions when holding able delay as well as the total traffic load.” (Gentle,

time, circuit use, and number of circuits in the 1965, p. 58.)

group are known factors. The number of incoming “Calculate Call Volume. The first step in cal

circuits affects the probability that a calling part

will receive a busy signal." (Gentle, 1965, pp. 63, 65). culating the volume of information that must be handled by the data communications system is

“The intervals at which messages are transto determine the number of messages (called

mitted. Are these intervals fixed or random? 'traffic') handled in an average day. This is done

What are the peak rates, and at what times of for traffic to and from every point in the system.

day will they occur?” (Reagan, 1966, p. 23). The volume is calculated by taking a sample

"To determine the proper size of a dial system of several days' traffic and actually counting required, it is necessary to study the company's the number of messages handled each day at busy hour, calculate the average message length, each location. The number of days to be included determine the total number of call seconds inin the study is based upon the estimated number volved, and then consult the hundred-call-second of messages that are handled in a month. An (CCS) tables developed for telephone trunk loading. estimate of the monthly volume should be made, On the CCS tables is a listing for the number of and the following table may be used as a guide trunk lines required for a given loading and grade of in determining the number of days to be studied. service desired. If you want only one lost (busy)

call in every hundred, the tables will show how many trunk lines are required. If you can tolerate 10 lost calls per hundred, the tables show that you can get by with fewer lines. In this manner, you choose the grade of service you require to handle your particular data communications problem.” (Birmingham, 1964, p. 37).

“Whenever it is necessary to have a large number of stations communicate among a large number of potential addresses, it is a practical necessity to use some form of switching. There is always a very wide variety of potential groupings and possible network configurations. The shape and complexity of the resulting network is very much dependent upon the economies one wishes to make in circuit groupings. The choice of these groupings in turn depends upon the statistics of the expected traffic. If the traffic statistics are known very accurately, large savings in cost of selection of routes and assignment of channels can be realized." (Baran, 1964, p. 15).

“Complex data communications systems that terminate many lines in a central facility usually use either a multi-line communications controller in conjunction with general-purpose computer or a specialized, stored-program communications processor. These units are capable of buffering and controlling simultaneous input/output transmissions on many different lines. Again, a wide variety of equipment is now available to perform these functions. The available devices differ in the number and speed of lines they can terminate and in their potential for performing auxiliary or independent data processing. Examples include the three multi-line communications controllers available for use with the general-purpose IBM System/360 computers and the Collins Data Central system, a computer system designed especially for message switching applications." (Reagan, 1966, p. 26).

“Data rate alone, however, does not provide a complete measure of network loading; devices have a short duty cycle, such as one computer sending the contents of its core to a remote computer. While such devices place a heavy peak demand for service, they are highly intermittent. On the other hand, a pulse-coded telephone call places a lower peak demand load, but ties up network capacity for a longer period and results in heavier average loading. Therefore, we should include an expected message-duration or holding-time factor in the network-load weighting table." (Baran, 1964, p. 30).

“It is necessary to have some idea of the types of messages that the system will be handling so that estimates of transmission rate requirements can be made. This calculation is intimately tied in with the distribution of terminals from the central computer system. It may be economically justifiable, even a necessity, to multiplex several of the terminals

together onto one high-speed line.” (Stephenson, 1968, p. 55).

"It is vital to have some knowledge of the average mix of message types and message lengths in the system.” (Stephenson, 1968, p. 55).

“The results obtained from the numerical solution of a model give a precise and comprehensive description of the statistical effects of high traffic. The value of such precise and extensive data for computer systems may not be obvious, especially since ‘worst case' examples and physical reasoning can establish much of the qualitative behavior of the system. The two prominent facts which warrant such analysis are the large scale of most multiconsole systems, and the critical nature of machine response in their conception. Because multi-console systems are of such large scale, it can be worthwhile economically to thoroughly evaluate proposed designs, seeking to achieve maximum capacity. Such design evaluation requires a rather accurate knowledge of the traffic in the various parts of the system. Because much of the effectiveness of a multi-console system can be rapidly dissipated by poor response characteristics, an accurate statistical description of response is also needed. The existence of a capability for rapidly solving general queueing models makes this approach a much needed alternative to Monte Carlo simulations or experiments in traffic studies." (Fife and Rosenberg, 1964, pp. H1-6).

3.24 "The unequal and intermittent loading of net-type channels in present communications results in inefficient utilization of radio frequencies. If channels were made available to other users during periods of idleness, more communications could be handled within a given frequency band. A solution to the problem of frequency congestion can be found in giving each user access to a group of channels through a system which selects an idle channel for each call and releases the channel as soon as the call is terminated. Such a system may be called a random access system, since an idle channel is selected at random from the group each time a user wishes to place a call. After a channel is selected, a means is needed to direct the call to the intended group or individual without disturbing users to whom the call is not directed. This process is called discrete addressing and is applied in the form of tone signalling to many systems in use today. The combination of the terms Random Access Discrete Address describes a class of communication systems employing these principles and is frequently referred to by the acronym, 'RADA'." (Horne et al., 1967, pp. 115–116).

“Adaptive channel communication systems provide efficient bandwidth utilization by allowing time sharing of a small number of channels by a large group of users with low duty rates. Unlike fixed frequency netted systems, where a call to a nonbusy subscriber cannot be made if his assigned frequency is in use by another of the net members,



3.26 “If empirical data were available in the information field we could use an input-output matrix. On the input side the various international and national information services should be included. Many of these services act also as users of the input from other services, and they process it for their own purpose. Thus the output side will also contain most of the same services. The content of the matrix should be information just as economic matrix will contain employment, goods or services. The economist expresses his flows in dollar values, since money is the conventional substitute. A convention measuring the information flow of documents has to be developed.” (Tell, 1966,


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p. 119).

the adaptive system will allow completion of all calls provided the number of simultaneous calls is less than or equal to the number of system channels. The adaptive system is thus similar to the telephone system where each user has a private line, but the number of trunks connecting the lines is less than the number of lines.” (Horne et al., 1967, p. 120). 3.25 “In the distributed network routing scheme

if the preferred path is busy, the in-transit Message Block is not stored, but rather sent out over a less efficient, but non-busy link. This rapid passing around of messages without delay, even if a secondary route must be chosen, is called a 'hot-potato' routing doctrine. .

"With such a doctrine, only enough storage at each node need be provided to permit retransmitting messages if an acknowledgement of correct receipt is not received from the adjacent station within a prescribed time interval. Message storage capacity is modest. ..

“A dynamically-updated routing table stored at each node indicates the best route for each Message Block to take to reach its directed end terminal station . . . When two messages seek the same preferred line, a random choice is used to select which message is sent out over the best path ... Simulation has shown that this use of secondary paths in lieu of storage is a surprisingly effective doctrine, enabling transmission of about 30–50 per cent of the peak theoretical capacity possible in a store-and-forward system having infinite storage and infinite delays.” (Baran, 1964, pp. 9, 12).

3.27 “Based upon information taken in these {Lockheed] studies, it is quite clear that long term information exchange requirements will include wide band data and image transmission and that data entry points may ultimately involve more than 10,000 terminals throughout the nation.” (Johnson, 1967, p. 7).

“The issues of communication in the sense of the electrical transmission of data have come to the forefront during 1966. Most computer-system implementers and users are encountering the problems of communication engineering for the first time. Many have found disquieting the fact that the element of system cost arising from the necessary datacommunication support of large, multiaccess systems is surprisingly large- often of the same order as that of the central computer facility." (Mills, 1967,

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p. 244).

4. Input-Output, Terminal Design, and Character Sets

4.1 “The display-computer interface is a gen- networking via the IMP.” (System Development eralized requirement of all displays and provides Corp., 1968, p. 1-13). computer buffering for the display system. In addi- 4.3 “A method must be devised to develop the tion, some systems may require logic level and/or storage adress of a record from a key in the record word length changes from computer to display. itself. This is usually referred to as a randomizing These operations are also performed by the inter- formula. What is implied is an arithmetical operation face.” (Mahan, 1968, p. 9).

on a key in the record to develop from this key an 4.2 Plans for implementation of an experimental actual storage address for the record. Study is network for the Advanced Research Planning required to ascertain which technique or formula Agency (ARPA) have been reported as follows: provides a good file utilization, with the least number "The ARPA contractors' network is in the of common addresses for different keys to keep overplanning stage. As one of the nodes of this network, flow records down." (DeParis, 1965, pp. 30-31). SDC would receive a small computer (of the PDP-8 “The logical address of a data item defines the class) as an interface message processor (IMP). All relative position of the item within the structure of other nodes in the network would likewise have a the data base. The logical address is coded so that a similar IMP. The IMP would be two-faced: one view. unique code may be created for each item in the facing the local contractor's time-sharing system; data base. The logical code is a numerical reprethe other facing other node IMPs. In this fashion, sentation of the nodes in the multi-list tree structure network protocol would be standardized at the of the data base, and is called the Item Position IMP, while still maintaining the flexibility of per- Code." (Barnum, 1965, p. 50). mitting dissimilar local time-sharing systems to be “The technique of hash addressing by randomizincluded as nodes. An IMP will support up to two ing the input word was used to generate an address local time-sharing systems, thereby permitting local for the dictionary look-up. This method results in


376-411 0 - 70 - 5


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the address of the first element of a chain of words in “[A] CRT display console ... [should meet storage, each of which yielded the same random at least three on-line capability criteria. First, address. An examination of the chain would pro- it is directly tieable to a data processing system. ceed in sequence until the word was found or until Second, it has ability to initiate messages the last element of the chain was compared.' control signals from a data entry keyboard or (Baker and Triest, 1966, p. 3–13).

switches for transmission to the computer. Finally “Every word encountered in the scan of an input it has ability to receive digital messages or control text, i.e., during the actual operation of ELIZA, is signals.” (Frank, 1965, p. 50). randomized by the same hashing algorithm as was “Desire to display data rapidly ... places originally applied to the incoming keywords, hence a premium on the efficiency of the graphical yields an integer which points to the only possible language used at the display level.” (Dertouzos, list structure which could potentially contain that 1967, p. 203). word as a keyword.” (Weizenbaum, 1966, p. 38). “The CAFE system permits definition of, or

4.4 “The concept of on-line information control selection from, a library of pictorial elements implies the ability of such users of the system to (static and dynamic), formation of complex pictures change the performance of the system to meet their from simpler ones, and parameter control of their own changing needs or wishes. With adequate con- individual display characteristics as well as their trol, they can experiment with the display of alter- synchronization into a sequence of composite native data formats or configurations, with alternative displays. Once a pictorial element is defined sequences of data retrieval, with alternative by the user-editor, it is readily available by reference formulae for summarizing, processing, or analyzing to a name supplied at the time of its definition." data." (Bennett et al., 1965, p. 436). “Other sugges

(Nolan and Yarbrough, 1968, p. C103). tions indicate the need to reconcile data formats of “High-level methods for expressing scope considerable variety.” (Brown et al., 1967, p. 54). output and console input operations have pro

4.5 "Special provisions (perhaps in the software) duced a great deal of display programming activity. may be required to prevent overlap of symbology,

The obvious advantages over assembly coding as might result from adjacent aircraft tracks. of clarity, brevity, and fewer mistakes are a strong (Israel, 1967, p. 208).

incentive for users. The compiler-compiler system 4.6 “Time-shared computers need an accurate,

on TX-2 has made relatively easy the impleversatile clock to schedule programs, subroutines mentation and evolution of an extended highor problems, and to synchronize the computers with level language based on ALGOL. The language, a desired time base. Large computer systems

called LEAP (Language for Expressing Associausually have their own built-in clock, but smaller tive Procedures) has associative data structuring units used in a time-sharing mode must be modified operations, reserved procedure forms for display by the addition of an external clock.” (Electronics or input manipulation, and real time variables 38, No. 23, 194 (1965).

such as the clock time and tablet stylus coordinates. 4.7 The question of color on output is reflected

Direct means for invoking the symbol recognizer's first in the more conventional documentation or services even incorporated. A 'Recognize' library situation. Thus it is to be noted that "the statement gets a symbol from the tablet just as use of color in printing is of increasing importance", a 'Read' statement gets a symbol from the console but that there are questions of whether copies in

keyboard. Writing interactive programs which use color, such as the color film versions of valuable the display is straightforward, and experimentation manuscripts supplied by the Bodleian Library or

and modification can be rapid. the French Bibliothèque Nationale (Günther, 1962,

"Having LEAP available as a programming p. 8), can be preserved over extended periods of

tool has facilitated the evolutionary development time. (Applebaum, 1965, p. 493).

of application programs for graphical program

ming, data analysis, logic diagram input, and 4.8 “The term “graphical communication' pre

integrated circuit mask layout. The largest effort supposes a graphical language in which pictorial

has been on circuit mask programs. A circuit information is transmitted between the designer and

designer controls the mask layout program with the computer." (Lang et al., 1965, p. 1).

freehand figures sketched on the Sylvania tablet. 4.9 "M. Stafford of Westboro, Mass.. The computer recognizes his rough marks as discussed the ways in which graphic communica- commands to create, move, group, and delete tions systems are currently used, with emphasis various integrated circuit components. Once a on their interface between computers and infor- circuit design is complete, output tapes for each mation storage centers. Some examples of their of the mask levels required can be punched for use, he noted, are to send signature samples ,

later use by a precision patterns making machine. and information on accounts between a main Individual variations among designers in drawing bank and its branches, to send weather maps style are accommodated easily by the trainable and technical drawings across the country, and to recognizer.” (Sutherland et al., 1969, p. 632). send pages of newspaper copy between cities.” “First of all, this language must be concise and (LC Info. Bull. 25, App., 288 (1966).)

easily learned. It should permit the user to specify


p. 606).

the various features of a drawing in the natural duced, but also the associations which may exist order in which they occur to him and in a continuous between parts of the picture. A display routine stream rather than in segmented form in separate within the executive threads its way through this statements. For publication purposes, it must give ring structure transmitting the data if finds in the the user direct and ultimate control of every line structure to the display generator." (Forgie, 1965, drawn if he so desires. Yet, where applicable, the user should be able to cause a particular version of 4.11 “A three dimensional windowing subsystem a whole superstructure to be generated by the sys- is available for the AGT [Adage Graphics Terminal] tem merely by specifying a few simple options. in which upper and lower bounds can be placed Toward this end, the language should include the (in digital registers) on x, y, and z. The vector facility to construct higher level statements from the generator then blanks whenever the beam goes basic language statements. It is envisioned that a beyond one of the bounds, and it also tells the set of such 'user defined' statements could be de- program which bound was exceeded. This device veloped by an experienced programmer for a par- finds use in a number of applications including ticular application. Once defined, such statements uncluttering pictures, testing the dimensions and could then be used by non-programmers without intersections of solids, and splitting the CRT screen knowledge of their genesis. Preferably, the language up into rectangles allocated to different pictures, should meet the needs of users of widely varying which can then move beyond the 'edge' without computer experience. At one end of the scale it encroaching upon its neighbor's display space.' should appeal to a user essentially untrained in (Hagan et al., 1968, p. 753). computer programming for the simple transcription 4.12 “Early graphics systems, such as the GM of drawings from a rough draft. At the other end of DAC system and Sketchpad, were little better than the scale it should satisfy a user desiring to generate automated drafting boards. This statement is not pictures controlled by algorithm at execution time. intended in any way to belittle their efforts, but Drawing on a conditional basis is particularly attrac- merely to underline the fact that there was very tive for applications such as circuit drawings and little that could be done with a picture once it had the production of musical scores. Finally, the im- been generated. Certain of Sutherland's illustrations plementation of this language should readily accom- are quite startling in their apparent sophistication, modate minor changes in syntax dictated by user but generally return to the use of constraints (which experience. In addition, it should be designed to run were satisfied using least squares fit, which is an easily on a variety of computers, and hopefully on a energy constraint in engineering). In endeavoring variety of terminal CRT systems, such as the to ascribe meaning to pictures, later investigators Stromberg Carlson 4060 or the RCA Videocomp.” were forced to use data structures in a more (Frank, 1968, p. 179).

sophisticated manner, and it became obvious that "For the past five years, hardware has existed associations should be much more complex than the that allows a computer user to enter drawn, printed original ring structures, etc. The CORAL language, or written information directly into a computer as APL, and AL, the language described by Feldman, easily as writing with pencil on paper. The missing are all outgrowths of the need to ascribe extra assoelement that would make such devices viable ciations and meanings to a picture. Many are now entities in computer systems has been the appro- working on this problem but information in technical priate software support. At SDC, we are developing literature is relatively sparse. To illustrate the the necessary programs to allow a user scientist to techniques being developed at the University of hand-print, on-line, two-dimensional

two-dimensional structures Michigan, and to show the power of the associative required in the statement and solution of his prob- language, a detailed example will now be given." lem. These programs include an on-line, real-time (Sibley et al., 1968, p. 553). character recognition program that is independent of 4.13 Some other examples of experimental both position and size of the input; editing programs capabilities in this area are as follows: "GRIN that can deal with two-dimensional entities (as [(GRaphical INput) language) is particularly suitopposed to linear strings); and contextual parsing able for use in problems requiring the extensive programs that re-structure the recognized, edited real-time manipulation of graphical information at input for subsequent processing. This work is being the console. It takes full advantage of the incredone within the constraints of the SDC Q-32 Time- mental display structure of the scope . . . Thus, Sharing System

if a display part is composed only of a sequence “The editing facilities are simple and straight- of incremental words, its position on the display forward, requiring a minimum of effort on the part scope can easily be changed by changing only the of the user while providing repositioning, erasure, initial absolute entry point. Also if a part is reprereplacement and insertion for such diverse notations sented only incrementally, it can be called up using as mathematics and organic chemical structures.” the display part subroutine linkage at many places (Bernstein and Williams, 1968, p. C84).

on the scope face. The part has to exist in storage 4.10 "The display information is stored in a only once, however." (Ninke, 1965, p. 845). ring-type list structure, which reflects not only the "The GRIN-2 (GRaphical INteraction) language order in which parts of the display are to be pro- is a high-level graphical programming language that

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