HIGH-SPEED DATA TRANSMISSION SYSTEMS R. G. Matteson Stromberg-Carlson Rochester, New York. Division of General Dynamics Corporation

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1 97 Introduction HIGH-SPEED DATA TRANSMISSION SYSTEMS R. G. Matteson Stromberg-Carlson a Division of General Dynamics Corporation Rochester, New York For many years data and messages have been transmitted from point to point over slow speed data communication systems by telegraph. There is a rapidly growing increase in the use of centralized data processing equipment in large corporations however, making increasing demands upon existing data communication systems. Development has been carried out at Stromberg-Carlson during the past few years toward increasing the capabilities. of the standard telephone facility for the transmission of data at higher speeds and with greater reliability. It, is felt that this equipment will have widespread use in the business data field, the scientific field, the automatic control field, and for military data communication systems. Typical components required for the transmission of data ove~ tetephone lines at high speed include input/output equipment, buffer converters, modulatorldemodulators, and of course a transmission path. Stromberg-Carlson has developed a modulator/demodulator unit using a unique modulation principle specifically designed for minimizing the effects of the various types of distortion and interference associated with wireline systems. In addition, an installation has been completed for the Convair Division of General Dynamics Corporation which transmits data in the form of punched card information over a telephone line more than 200 miles long, and records the information on magnetic tape in a format compatable with IBM 704 programming. Applications Since the processing of data by digital computers is becoming common practice throughout many types of endeavors, the applications for the transmission of data at high speed over standard telephone facilities appears to be very wide spread. Some of these areas will be discussed in the following paragraphs. Many corporations are facing a decision today between large computers at a central location in the corporation or many small computers geographically separated at the various divisions. If a centralized computer facility is required for performing all the various operations and data processing for a corporation, the data must be transmitted from remote divisions of the corporation into the central data processing center. For a moderate size corporation this data can reach significant proportions and can only be transmitted by air mail or many slow speed data transmission systems operating in parallel at the present time. The availability of equipment to transmit data at higher speeds over telephone facilities which are normally available for telephone communications will assist in solving the data handling problem. For the co,rporation which decides to use individual smaller computers at each division, data transmission can still be of considerable benefit. For these corporations, high speed transmission of data can mean faster reporting between divisions and the possibility of using remote computers if thejocal computer becomes overloaded during peak operations. Many corporations are looking towards automatic data collection, data acquisition and transaction recording systems to accelerate the over-all data proce'ssing and reporting cycle. These systems will be used for such things as the compiling and accumulation of data concerning job moves, stockroom transactions, job change~, inspection results and attendance recording. This data may be recorded for several manual input units at an intermediate collection point. The data must then be transmitted from this intermediate collection point to a central collection agency

2 98 (Figure 1). For a sizeable corporation, the amount of data transmitted into the central recording facility will be considerable. Transmission must therefore occupy a minimum of t~me in order to be, able to submit all da~a from each of the intermediate collection facilities, requiring high-speed transmission of data over standard wireline facilities. Some types of businesses such as banks and insurance companies have requirements for large data retrieval systems. In this case, a central file of information, upon receiving an inquiry from a remote station, will transmit the data requested in the inquiry. In this example, the amount of data transmitted during the inquiry is small, but the amount of data transmitted during the reply by the data file may be large indeed depending upon the particular application. In order to satisfy a number Qf independent inquiries in a reasonable amount of time, data will have to be transmitted at high speed over wireline facilities. For the solving of scientific problems, large scale computer facilities are required in order to handle the more complicated problems expected. For some of the large computer facilities required, it is economically impossible to duplicate a facility at remote corporation installations. In this case, remote facilities can use a large scale computer facility for the solution of scientific problems by transmitting the program and input data by high-speed data transmission systems to the central computer facility (Figure 2). The problem solution can then be transmitted back to the originating site. It is also occasionally possible to break down a large problem into subproblems which can be worked independently by separate computer facilities. In this case, various computers throughout a wide-spread corporation can be used for solving parts of the same problem by means of high-speed transmission of data over telephone facilities. The solutions to scientific problems transmitted over the high-speed data transmission system can be tabulated, reported or plotted by the use of direct on-line high-speed printing equipment. For applications where digital computers are useq in the automatic control of process or operating conditions, much data is transmitted between the operating system and the computer control system. In the case of process control computers, the requirement is for the transmission of measured values of the operating system, the transmission of control signals to change the operation of the system and the transmission of data to various indicators allowing manual supervision of the operation of the system. Operation of organizations such as gas and pipe lines, and railroads requires the transmission of operating data over long distances. This data can be economically transmitted at high-speed over the same wire-line facilities normally used for voice communication. Many requirements exist for the transmission of considerable amounts of data for military systems. Militarysystems such as the SAGE (semiautomatic ground environment) system for the detection, tracking and interception of enemy aircraft requires data to be transmitted between acquisition sites, control centers, and intercepter centers. With the military striving for higher speeds under tactical conditions, automatid displays and even the computer analysis of tactical situations provides a requirement for the transmission of digital data. Logistic Systems such as the Air Force COMLOGNET System will be used to transmit a tremendous amount of data concerning logistic information throughout the Air Force. EqUipment ReqUirements Any generalized Data Communication System can be broken down into input/ output components, buffer converter components, modulator/demodulator components, and the transmission path (Figure 3). The input/output equipment may consist of punched tape, punched card, or magnetic tape readers, manual input

99 ' keyboards, FLEXOWRITER, or electric typewriter equipment. The input/output equipment can also consist of the buffer storage portions of general purpose computer installations.

3 99 ' keyboards, FLEXOWRITER, or electric typewriter equipment. The input/output equipment can also consist of the buffer storage portions of general purpose computer installations. The buffer converter unit at the transmitting terminal of a data transmission system must accept the data from an input device, and transform this data into the proper format for application to the modulator unit. This may require parallel to serial conversion, temporary storage, and level changing. The buffer converter may also change the language of the data as in the case of card to tape transmission. Also, it may be required to add checking information to the transmitted signals. At the receiving terminal of the Data Transmission System the buffer converter must accept the data from the demodulation unit and convert it into the proper format for recording on the output device used. This operation may mean serial to parallel conversion, temporary storage, and the generation of additional format information such as inter-record and interfile gaps normally required for preparing magnetic tape for IBM computers. Error circuitry is required at the receiving terminal improving or at least indicating the reliability of data transmission. Errors can be detected by checking vertical and horizontal parity bits in the transmitted data, and indicating these to the operator at the receiving terminal. This gives a measure of transmission reliability but does nothing to correct the matter. In the event of an error circuitry can also be included to cause automatic retransmission of the previous block of data. Using this techniq~e, the final received and recorded data will be more reliable by several orders of magnitude than if automatic retransmission were not used. Another technique can be used which would correct certain types of errors in the transmitted data at the receiving terminal without requiring retransmission. By storing a complete block of data and checking horizontal and vertical parity signals, single bit errors in the transmitted message can be corrected automatically. Alternatively, if the information is destined for computer data processing, a program can be incorporated into the data processing routine to perform the same function, thereby simplifying the data transmission system. The telephone line which wi~l transmit voice information satisfactorily will not necessarily transmit data reliably; for example, impulse noise of very short duration may cause bits of information to be changed, added or deleted in the data being transmitted which could have serious consequences in the business data applications. Similarl y, a frequency translation will have serious effects on some types of data modulation techniques, but will hardly be apparent during voice transmission. Certain minimum requirements for line characteristics must be satisfied depending on the type of modulation/demodulation equipment used in the system. Equipment Description Data transmission equipment 'which has been developed at Stromberg-Carlson will be described as examples of the components mentioned in the preceeding sections. A tape transmission terminal suitable for tape to card, card to t~pe, and tape to tape systems is shown in Figure 4. A tape transport has been selected for low cost, reliable operation. The buffer converter is designed to accept data from the tape transport, convert it to a serial form, and provide control and synchronization signals to the receiving terminal. These and oth'er functions of the buffer converter are shown in Figure 5. The end of the file is automatically recognized by the buffer converter and the tape transport is turned off. In the event of an error recognized at the receiving terminal, the retransmission signal is recognized by the buffer converter and the data record in error will be retransmitted by reversing the tape transport and transmitting that record over again. The receiving portion of the buffer converter converts serial input data to parallel data for recording on the receiver tape transport. The data is synchronized to the incoming data by resetting the character bit counter with a start of record character. End of record gaps occurring on the transmitted tape will also be placed on the receiving tape. At the end of a file of data, the receiving tape transport will be stopped. A modulator/demodulator model SC- 301 is used to modulate the serial

4 100 train of data in a form for reliable transmission on telephone facilities at 2400 bits per second. The SC-30l converts the input binary information to a trinary form which then amplitude-modulates a subcarrier signal.' Advantages of using a trinary, rather than binary. baseband signal in~lude the following~ 2 (a) (b) (c) Elimination of low frequency components, reducing noise bandwith and easing requirements for transmission circuit characteristics. Constant average power level in transmitted signal. Permits use of bistable detector, rejecting noise impulses of one polarity. At the receiving terminal, the signal is demodulated and regenerated to form the original binary information. A free-running multivibrator is synchronized to the incoming data to provide a clock signal at the synchronous rate of data transmission. A photograph of th~ SC-301 in a separate cabinet is SROwn in Figure 6. A telephone handset is sunplied on the front panel of the data communication terminal for intercommunication capability. This enables the operators to coordinate the transmission of data at the beginning and the end of the transmission. A self-test capability allows the operators to check out the transmission link before the start of transmission. Amplitude and time delay equalizers are also provided with the terminal as required to compensate for characteristics of. the telephone facility. A card data transmission terminal is shown in Figure 7. This unit can be used to transmit data between itself and another card terminal, a tape terminal, or a computer input terminal. This terminal has been designed to read punched cards at the rate of 100 cards per minute. The terminal is similar to the tape transmission terminal described above except for the addition of a card buffer module. The card buffer will store all of the data on one card as received on a row by row basis. The buffer will then feed the data character by character into the buffer converter, which then performs functions similar to that performed by the tape terminal buffer converter. The third type of data transmission terminal developed at Stromberg-Carlson is for transmitting data from computer to computer. This type terminal is shown in Figure 8 and is exactly the same as the card transmission terminal except that the card reader and the card buffer are not required. The buffer converter accepts data from the buffer storage unit of a computer exactly as it would from the card buffer unit. At the receiving terminal, the data is provided to the buffer storage unit of the receiving computer. Since the tape, card, and computer data transmission terminals all have standard outputs, they can be used interchangeably with each other to form tape to tape, card to card, card to tape, computer to computer, tape to computer, etc. systems. A card to tape system has been installed at the Convair Division of General Dynamics Corporation to transmit data over a 200 mile telephone line between Pomona, California and San Diego, California. This system enables Convair personnel in Pomona to utilize an IBM 7043Camputer facility located in San Diego.. In addition, an SC-3000 high speed communications printer can be used directly on line at the receiving terminal to print out data. A new type of tape transport is being developed for use in specific applications for data transmission and data collection systems. This tape transpor~ will operate in two modes, a stepping, asynchronous mode or a continuous, synchronous mode. In the stepping mode, the transport can be used with a FLEXOWR1TER, manual keyboard, slow speed punched card device or other equipment operating asynchronously. In this mode the unit can be used to record or reproduce data character by character for data recording, collection, and acquisition applications. In the continuous mode, the transport can be used as a substitute for the tape transport discussed previously in connection with the tape transmission terminal. The transport can therefore be used to store data asynchronously and accumulate it over a period of time. The unit can then be rewound and used to supply the data at high speeds into a data transmission system. In this application a telephone facility can be used for voice communications most of the time, since data can be transmitted at high speed during a small portion of

5 101 the day. A block diagram of the tape transport is shown in Figure 9. Conclusion The applications for data communication systems have been discussed. Equipment requirements have been discussed and examples of equipment meeting. those requirements which have been developed by Stromberg-Carlson have been described. A special tape transport has been described which has been developed to meet a particular requirement in data transmission systems, where it is desired to accumulate data at a slow asynchronous rate and deliver it at a rapid, synchronout rate so as to obtain full time usage of a telephone facility. The general approach being taken at Stromberg-Carlson in the development of card to tape, tape to tape, and card to card systems 1s to arrive at a complete line of components which can be interconnected in flexible fashion to meet a variety of requirements for specific data transmission applications. References: J. L. Wheeler, "High-Speed Digital Data Transmission", IRE Fourth National Aero-Com Symposium, Rome, N.Y., October 22, J. L. Wheeler, "Preparation, Transmission and Distribution of InformatiDn in an Automatic Data Communition System Utilizing Telephone Facilities", A:I:EE Empire District No.1, 1959 Spring Meeting, Syracuse, N. Y., April 29, F. DaVid, C. J. Zarcone, R.L. Wolfr, "Card-to-Magnetic-Tape Data System", AlEE Conference Paper CP60-917, 1960 Summer General Meeting, June 21, J. L. Wheeler, "Telephone Line Input to an rem 704 Computer", IRE Sixth Annual Communications Symposium, Utica, N. Y., October 4, 1960.

6 102 WORK STATION A WORK STATION B STOCKROOM A INTERMEDIATE COLLECTION POINT COMPUTER FACILITY INSPECTION STATION A TIMECLOCK DATA COLLECTING SYSTEM Fig. 1. Data Collecting System

7 TEST SITE A TEST SITE B COMPUTER INSTALLATION ENGINEERING LABORATORY TEST SITE C SCIENTIFIC DATA Fig. 2. Scientific Data r-.;> 0 ~w

8 Ir= INPUT / OUTPUT... _... DEVICE ~... DATA TRANSMISSION TERMINAL CONVERTER BUFFER MODULATOR / "'''' r-... J DEMODUL~.., t-:) t-' 0 ~~ : ----: 1'f\~NSt.A\SS\ON p~1'\'\ J c DATA TRANSMISSION TERMINAL -I L M DE JULATOR / JDULATOR... ~..... BUFFER- CONVERTER INPUT / OUTPUT DEVICE.:J GENERALIZED DATA COMMUNICATION SYSTEM Fig. 3. Generalized Data Communication System

9 105 Fig. 4. Tape Transmission Terminal

106 Buffer-Converter Functions Transmitting Parallel/Serial Conversion Generate SOR & EOR Characters Synchronize Data Transmission Rate and Tape Transport Detect End of File Cause Data Record to be

10 106 Buffer-Converter Functions Transmitting Parallel/Serial Conversion Generate SOR & EOR Characters Synchronize Data Transmission Rate and Tape Transport Detect End of File Cause Data Record to be Retransmitted Upon Receiptof Error Signal from Receiver Provides Intercom Capability Receiving Serial/Parallel Conversion Check Lateral & Longitudina~ Parity Generate Retransmission Signal in Event of Errors Synchronize characters to incoming Data Generate EOR Gap Detect End of File Provides Intercom Capability Fig. S. Buffer-Converter Functions Fig. 6. SC-301 Binary Data Transceiver

11 lo7 Fig. 7. Card Transmission Terminal

12 108 Fig. 8. Computer Transmission Terminal'

13 DATA BUFFER ~.. TAPE ~~ CONTINUOUS DRIVE CONTINUOUS DRIVE MODE ~~ CLOCK " AUTOMATIC... SPEED CONTROL.,.... DATA... BUFFER ~ TAPE ~~ STEP-DRIVE MODE STEP COM MAND... STEPPING.. DRIVE Fig. 9. Tape Transport Block Diagram

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