the transmission over a distance of alphameric messages—telegrams—and the transcription of such messages at the receiving station, accomplished by means of electrical signals transmitted by wire and/or by radio signals; a form of telecommunication.
The characteristic feature of telegraph communication is that the message is delivered to the addressee in the form of a printed or, more rarely, handwritten text. This feature and the speed of message transmission have facilitated the significant development of telegraph communication, particularly in administrative and business communications. In addition to transmitting telegrams, telegraph communication may also be used for transmitting records of negotiations, for transmitting numerical information, and for broadcasting news for newspapers and the radio and television media. Since the 1950’s and 1960’s, telegraph communication has also been used for data transmission.
Historical survey. The oldest form of telecommunication, telegraph communication began in the 1830’s. In ancient times, only nonelectrical methods of long-distance communication, or signaling, were used—light and sound; these were later supplemented by postal services. The drawbacks of these methods included low speed of information transmission, dependence on the time of day and weather, and the inability to observe secrecy in transmission. For these reasons, nonelectrical methods are now used very rarely.
The principles of telegraphy were formulated in Russia by P. L. Shilling, who designed the first practical electric telegraph equipment in 1832. Shilling’s system of telegraph communication was used in Great Britain beginning in 1837 and in Germany. In 1836 Shilling laid an experimental telegraph line around the Admiralty in St. Petersburg. The Winter Palace was linked by telegraph with the Main Headquarters in 1841 and with the Main Administration of Railroads and Public Buildings in 1842. In 1843 a 25-km line was laid between St. Petersburg and Tsarskoe Selo, a distance considered fairly long for that time. A whole series of successful designs for telegraph equipment for these lines was developed by B. S. Iakobi (M. H. Jacobi), who invented the electromagnetic register in 1839 and the letter-printing telegraph in 1850. In 1844 a telegraph communication line equipped with electromechanical equipment designed by S. F. B. Morse was put into service in the USA.
The development of telegraph communication in the second half of the 19th century was associated with the growth of industry and the network of railroads. In Russia, for example, approximately 27,000 km of telegraph lines and 160 telegraph stations were in operation in 1860; by 1870 these figures had risen to 91,000 km and 714 stations. The longest telegraph line in the world was opened in 1871 between Moscow and Vladivostok, a distance of approximately 12,000 km. International telegraph lines appeared in 1854. With the installation of submarine communications cables, intercontinental telegraph links were also established.
The major expense in establishing telegraph communication is incurred during the construction of telegraph lines. Research in the field was therefore directed toward increasing the efficiency of line use. In 1858 the Russian inventor Z. Ia. Slonimskii developed a method of simultaneous transmission in opposite directions of two pairs of telegraph messages over one wire. A version of this method, called the differential duplex system, is widely used in telegraph communication. In 1872, G. Baudot invented the multiplex telegraph apparatus, which simultaneously transmits two or more messages in one direction over a single wire. The principle of time-division multiplexing applied by Baudot remains one of the basic principles in modern telegraph communication. The Baudot telegraph was such a successful design that it continued to be used with only minor changes until the 1950’s.
In 1869 the Russian inventor G.I. Morozov developed a frequency-division multiplexer, which made it possible to transmit messages over a single line by means of AC signals of different frequency bands; the concept of frequency-division multiplexing had been proposed by the French inventor E. Laborde in 1860. The principle was later realized in voice-frequency telegraph systems, which made it possible to obtain a large number of economical telegraph channels. In 1880 the Russian inventor G. G. Ignat’ev proposed a method of simultaneous telegraphy and telephony over a single line.
The efficiency of use of telegraph lines increases with an increase in message transmission speed. Since the capabilities of the telegrapher have practical limitations, automatic transmission methods were developed; for example, messages were printed in advance on punched tape. The subsequent reading out and transmission of telegraph signals corresponding to the message on the punched tape requires less time, which increases the efficiency of use of a telegraph line or channel. In the period 1858–67, C. Wheatstone proposed designs for an autotransmitter—a device for automatic reading from punched tape—and a reperforator—a device for recording telegraph data on punched tape. In later years these were used not only to increase transmission speed, but also as memory devices in various telegraph data processing systems installed at telegraph stations.
Significant contributions to the development of telegraphy were also made by the Soviet scientists and inventors G. V. Dashkevich, A. F. Shorin, P. A. Azbukin, A. D. Ignat’ev, and L. I. Treml’.
Organization of telegraph communication in the USSR. The following types of telegraph communication are distinguished according to the purpose and nature of the information transmitted: general public service, teletypewriter exchange service, official telegraph communication, and facsimile service.
General public telegraph communication is used for the transmission of telegrams, money orders, and notification in advance of telephone calls and the like arriving at communications agencies, such as city and rural communications departments and raion communications centers.
The teletypewriter exchange service enables subscribers to exchange printed messages and send messages without reply by means of telegraph equipment located in the subscribers’ offices. The system may also be connected to the general public telegraph network for the transmission and reception of telegrams. Communications agencies provide the technical servicing of subscribers’ units and offer temporary direct connections for message transmission for a set fee. Subscribers to this service include large enterprises, ministries and departments, and sales and supply organizations. A variant of teletypewriter exchange service—Telex—is used for international communication.
Official telegraph communication is established in sectors of the national economy where large amounts of printed matter must be transmitted, for example, in railroad transport, civil aviation, and the weather service. It may use the channels of the Ministry of Communications or the special lines and channels of a given department.
Facsimile service provides for the transmission of fixed images, that is, any illustrated, graphic, or written material, over a distance. Although this form of communication does not have all the characteristic features of telegraph communication, it is historically connected with telegraphy. Facsimile service is used for transmitting photographs, type pages of newspapers, and maps with plotted weather conditions.
Telegraph communication is classified as simplex or duplex, depending on the way transmissions are organized. Simplex telegraph communication between two telegraph stations or subscribers makes it possible to transmit messages in both directions alternately, and the same telegraph is used for both transmission and reception. In duplex communication, messages can be sent in both directions simultaneously; each station is equipped with two telegraphs, each of which is used for transmission and reception, or one telegraph with separate transmitting and receiving circuits.
Telegraph communication technology. Every alphameric text is discrete: regardless of the contents, it can be represented by a finite, relatively small set of characters—letters, digits, and punctuation marks. The components of telegraph communication systems, particularly telegraph equipment, are designed for the transmission of a specific, predetermined number of different combinations of elementary signals. For each combination, called a code combination, there is a single corresponding letter or digit. Telegraph communication uses binary signals, that is, signals that may have one of two possible values. This gives the signals maximum protection from the effects of interference in a line or channel and simplifies equipment design.
Various types of binary signals may be used to transmit code combinations. Figure 1 shows the wave forms of the most useful binary signals. Single- and double-polarity DC signals are used to transmit messages over relatively short distances, usually not exceeding 300–400 km, via cable and overhead lines. Trunk transmission usually uses telephone channels and AC binary signals, usually frequency-modulated. This system permits up to 44 independent telegraph communication channels in one telephone channel. Voice-frequency telegraphy is used for this purpose.
The basic principle of telegraph communication in the 1970’s is the principle of channel switching. In order to transmit a telegram from one telegraph station to another, a temporary direct connection is established and the telegraph signals are transmitted directly from the filing point to the point of destination. After completion of transmission, a clearing signal is sent, the connection is broken, and channels used in the connection are used for other connections. Subscribers’ terminal sets include telegraphs and ringing and clearing devices that have telephone-type dials. The switching equipment, which establishes connections between subscribers, is usually located at a junction office in an oblast or raion center, which also houses equipment for voice-frequency telegraph systems.
A telegraph network is composed of terminal offices with telegraphs, switching equipment, and telegraph communication channels for transmitting messages. Figure 2 shows a block diagram of the organization of all the components in a telegraph communication network designed according to the principle of channel switching. The diagram illustrates the connection of two terminal offices via junction offices A and B. Depending on the distance between terminal offices, the number of junction offices taking part in the completion of a connection varies from one to six.
In many cases, a telegraph network may not be equipped with switching devices; that is, it uses permanent channels connecting two communications agencies. In particular, fixed channels are primarily used in radiotelegraph communication and facsimile service.
The switching networks in modern telegraph communication are more economical than networks with permanent channels; they ensure greater flexibility and the possibility of connecting any given subscriber. Therefore, networks with automatic switching are the most widely used type, and they constitute one of the basic components of the Integrated Automatic Communications System.
The development of telegraph communication technology is proceeding toward the further automation of transmission, reception, and processing and the improvement of telegraphs and multiplexing and switching equipment. The use of computers for processing telegrams in telegraph communication centers is extremely promising. The first models of electronic telegraphs, having higher performance characteristics than conventional electromechanical telegraphs, have already been developed and produced. The multiplexing equipment in voice-frequency telegraph systems uses methods of transmission and modulation that permit a larger number of noiseproof telegraph channels.
Technical and performance indexes. All the quantitative indexes of telegraph communication as a sector of the national economy are based to some degree on the information value of the processed telegrams. These indexes are classified as technical and performance indexes. The former include telegraph transmission speed, transmission fidelity, and the failure coefficient.
Telegraph transmission speed is measured by the number of elementary signals transmitted per sec. The number of characters transmitted per min is computed from the formula W = V60/n, where V is the transmission speed in bauds and n is the number of elementary signals per character. The number of words transmitted per hr is determined from the formula
where m is the average word length (equal to 5 characters). Qteo is a theoretical, calculated quantity. The quantities V, W, and Q,teo for transmission by international code no. 2 are given in Table 1. The table also shows the performance standard Qper, which differs from the theoretical Qteo by the amount of time lost by the operator in auxiliary operations during the transmission and reception of telegrams; Qper also takes the operator’s skill into account.
|Table 1. Technical indexes of telegraph communication|
|V (bauds)||W (characters per min)||Q (words per hr)|
Transmission fidelity is the ratio of the number of characters received with errors during one measurement to the total number of characters transmitted. The International Telegraph and Telephone Consultative Committee (CCITT) recommends a standard error coefficient of 3 × 10–5, which represents an average of no more than three errors per 100,000 transmitted characters. Because of the great distances involved, in the USSR another standard of 10–4 (no more than one error per 10,000 transmitted characters) is used for a telegraph line 2,500 km long.
The failure coefficient indicates how often an operator receives a “busy” signal in establishing a connection for telegram transmission in a switching network. Such a signal is received when the terminal office called or the switching devices at intermediate telegraph centers are busy. The failure coefficient is standardized for the 1-hr period of heaviest traffic and is expressed as the percent ratio of the number of failures in a connection to the total number of calls. The standard failure coefficient is 17 percent for communication via six intermediate centers.
The indexes of telegraph communication include volume of traffic, transmission quality, the passage time for a telegram, and the labor productivity of telegraph workers. The volume of traffic is measured by the number of telegrams arriving at a communication agency for transmission and delivery, the number of messages sent over a teletypewriter exchange network, and the number of telegraph channels leased to the organizations of official networks. Transmission quality is characterized by the accuracy of correspondence between the text of a telegram delivered to the addressee and the original text as written by the sender.
The passage time for telegrams may be regulated along the entire path from the sender to the receiver or only along individual links in the telegraph network. Telegrams that are delayed during processing beyond a fixed control period are also taken into account. Labor productivity is defined as the average number of incoming telegrams per telegraph communications worker per month or year. This index may be also expressed in monetary units for the cost of telegram transmission.
In the USSR the basic norms relating to the organization, planning, and operation of telegraph communication equipment are given in the Telegraph Regulations, put into effect by the Ministry of Communications in 1969. The regulations determine the order of reception, processing, transcription, and delivery of telegrams, the priority of transmissions, personnel duties, and types of services. A separate section in the regulations is devoted to the technical indexes and standards of telegraph communication, which are mandatory throughout the USSR.
International telegraph communication is regulated by documents of the International Telecommunication Union and by agreements between the communications administrations of individual countries. The Recommendations of the International Telegraph and Telephone Consultative Committee (CCITT) establish standards and regulations governing telegraph communication devices and equipment, such as code type, telegraph transmission speed, and service signals. The CCITT Recommendations are primarily intended to provide for joint operation of individual telegraph networks and equipment during the exchange of international telegrams.
Telegraph communication abroad. The structure of telegraph communication in developed capitalist countries is basically the same as in the USSR. Some countries, such as Switzerland, the Federal Republic of Germany, and the USA, are establishing fully automated telegraph networks with equipment that makes use of computer devices. A distinctive feature of telegraph communication in these countries is the large volume of international telegrams handled; these telegrams are transmitted by means of the international switching network Telex. Member countries of the Council for Mutual Economic Assistance (COMECON) use the GENTEX international telegraph network; GENTEX telegraph centers are located in the capitals of these countries.
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