Science Fair Project Encyclopedia
Telegraphy (from the Greek words tele = far away and grapho = write) is the long distance transmission of written messages without physical transport of letters, originally over wire. Radiotelegraphy or wireless telegraphy transmits messages using radio. This definition includes recent forms of data transmission such as fax, email, and computer networks in general. (A telegraph is a machine for transmitting and receiving messages over long distances, i.e. for telegraphy. The word telegraph alone generally refers to an electrical telegraph.)
- Telegraphy messages sent by telegraph operators using Morse code were known as telegrams or cablegrams, often shortened to a cable or a wire message. Later, telegrams sent by the Telex network, a switched network of teleprinters similar to the telephone network, were known as telex messages. Before long distance telephone services were readily available or affordable, telegram services were very popular. Telegrams were often used to confirm business dealings and, unlike e-mail, telegrams were commonly used to create binding legal documents for business dealings.
- Before fax machines came into general use, wire picture or wire photo was a newspaper picture that was sent from a remote location by a facsimile telegraph. This is why many fax machines have a photo option even today.
Optical telegraphs and smoke signals
The first telegraphs were optical telegraphs, including the use of smoke signals and beacons. These have existed since ancient times. A semaphore network invented by Claude Chappe operated in France from 1792 through 1846. It helped Napoleon enough that it was widely imitated in Europe and the U.S. The last (Swedish) commercial semaphore link left operation in 1880.
Semaphores were able to convey information more precisely than smoke signals and beacons and consumed no fuel. Messages could be sent at much greater speed than post riders and could serve entire regions. However, like beacons and smoke signals, they were dependent on good weather to work. They required operators and towers every 30 km (20 mi), and only send about two words per minute. This was useful to governments, but too expensive for most commercial uses other than commodity price information. Electric telegraphs were to reduce the cost of sending a message thirty-fold compared to semaphore.
The first commercial electrical telegraph was constructed by Sir Charles Wheatstone and Sir William Fothergill Cooke and entered use in London in 1837. An electrical telegraph was patented in the US in 1837 by Samuel Morse. He developed the Morse code signalling alphabet with his assistant, Alfred Vail. The Morse/Vail telegraph was quickly deployed in the following two decades. The first transatlantic telegraph cable was successfully completed on July 27 1866, allowing transatlantic telegraph communications for the first time.
In 1867, David Brooks (while working for the Central Pacific Railroad) was awarded (March 26) and U.S. Patent 69,622 (October 9) for his improvements to telegraph insulators. He was also awarded reissue number 2,717 on August 6 1867, for U.S. Patent 45,221, which was originally awarded to him on November 29 1864, for his insulator design. Brooks' patents allowed the Central Pacific to more easily communicate with construction crews building the First Transcontinental Railroad in America; the completion of the railroad was broadcast by telegraph on May 10 1869 with the telegrapher striking his key in unison with the strikes on the Golden Spike during the completion ceremony.
Nikola Tesla and other scientists and inventors showed the usefulness of wireless telegraphy, radiotelegraphy, or radio, beginning in the 1860s. Guglielmo Marconi sent and received his first radio signal in Italy in 1895. By 1899 he did it across the English Channel and in 1902 he radiotelegraphed the letter "S" across the Atlantic Ocean from England to Newfoundland.
Radiotelegraph proved effective in communication for rescue work when a sea disaster occurred. Effective communication was able to exist between ships and ship to shore.
A continuing goal in telegraphy has been to reduce the cost per message by reducing hand-work, or increasing the sending rate. There were many experiments with moving pointers, and various electrical encodings. However, most systems were too complicated and unreliable.
With the invention of the teletypewriter, telegraphic encoding became fully automated. Early teletypewriters used Baudot code, a 5-bit code. This yielded only thirty two codes, so it was over-defined into two "shifts," "letters" and "figures." An explicit, unshared shift code prefaced each set of letters and figures.
The airline industry still communicates with Teletype messages over the SITA or AFTN networks. For example, The British Airways operations computer system (FICO) as of 2004 still used teletype to communicate with other airline computer systems. The same goes for PARS (Programmable Airline Reservation System) and IPARS that used a similar shifted 6-bit Teletype code, because it requires only 8 bits per character, saving bandwidth and money. A teletype message is often much smaller than the equivalent EDIFACT or XML message.
A standard timing system developed for telecommunications. The "space" state was defined as the powered state of the wire. In this way, it was immediately apparent when the line itself failed. The characters were sent by first sending a "start bit" that pulled the line to the unpowered "mark state". The start bit triggered a wheeled commutator run by a motor with a precise speed (later, digital electronics). The commutator distributed the bits from the line to a series of relays that would "capture" the bits. A "stop bit" was then sent at the powered "space state" to assure that the commutator would have time to stop, and be ready for the next character. The stop bit triggered the printing mechanism. Often, two stop bits were sent to give the mechanism time to finish and stop vibrating.
By 1935 message routing was the last great barrier to full automation. Large telegraphy providers began to develop systems that used telephone-like rotary dialing to connect teletypes. These machines were called "telex". Telex machines first performed rotary-telephone-style pulse dialing, and then sent baudot code. This "type A" telex routing functionally automated message routing.
At the then-blinding rate of 45.5 bits per second, up to 25 telex channels could share a single long-distance telephone channel, making telex the least expensive method of performing reliable long-distance communication.
In 1970 Cuba and Pakistan were still running 45.5 baud type A telex. Telex is still widely used in third-world bureaucracies, probably because of its low costs. The UN asserts that more political entities are reliably available by telex than by any other single method.
Many dictatorships that cut off telephone, fax and internet services, leave existing telex networks in place. This enables bureaucratic departments to communicate with each other, but also allows for easy communication control on the part of the dictatorship, since any wiretap automatically generates complete transcripts.
Around 1960[?], some nations began to use the "figures" baudot codes to perform "Type B" telex routing.
Telex grew around the world very rapidly. Long before automatic telephony was available, most countries, even in central Africa and Asia, had at least a few high-frequency (shortwave) telex links. Often these radio links were the first established by government postal and telegraph services (PTTs). The most common radio standard, CCITT R.44 had error-corrected retransmitting time-division multiplexing of radio channels. Most impoverished PTTs operated their telex-on-radio (TOR) channels non-stop, to get the maximum value from them.
The cost of telex on radio (TOR) equipment has continued to fall. Many amateur radio operators operate TOR with special software and inexpensive adapters from computer sound cards to shortwave radios.
Modern "cablegrams" or "telegrams" actually operate over dedicated telex networks, using TOR whenever required.
In Germany alone, more than 400,000 telex lines remain in daily operation. Over most of the world, more than three million telex lines remain in use.
Almost in parallel with Germany's telex system, Bell Labs in the 1930s decided to go telex one better, and began developing a similar service (with pulse dialing among other features) called "Teletype Wide-area eXchange" (TWX).
TWX originally ran 75 bits per second, sending Baudot code and dial selection. However, Bell developed a second generation of "four row" modems called the "Bell 101 dataset", which is the direct ancestor of the Bell 103 that launched computer time-sharing. The 101 was revolutionary because it ran on ordinary subscriber lines that could (at the office) be routed to special exchanges called "wide-area data service". Because it was using the public switched telephone network, TWX had special area codes: 510, 610, 710, 810 and 910, some of which remain in use.
The "four row" TWX service had "control characters" that let the machine behave like office typewriters. These provided paragraph indentation, form feeds, and other services that were never available with Baudot codes. However, the TWX code only used 93 of 128 characters.
The Teletype corporation was founded by Dr. E. E. Kleinschmidt. It had the cheapest teletypewriters that could be adapted to the TWX code. Bell purchased the corporation to assure its supply of "model 33" TWX teletypewriters.
The model 33 was the cheapest teletypewriter available for use with computers. Computer people of course wanted a full set of characters. Teletype provided them.
ASCII was born from TWX code. It was formalized as CCITT international alphabet 5. Careful study will show that ASCII traces many character codes back to Baudot, which in turn traces some characters back to manual telegraphy.
Bell's original consent agreement limited it to international dial telephony. Western Union Telegraph Company had given up its international telegraphic operation in a 1939 bid to monopolize U.S. telegraphy by taking over ITT's PTT business. The result was deemphasis on telex in the U.S. and a cat's cradle of small U.S. international telex and telegraphy companies. These were known by regulatory agencies as "International Record Carriers"
- Western Union Telegraph Company developed a spinoff called "Cable System." Cable system later became Western Union International.
- ITT's "World Communications" was amalgamated from many smaller companies: "Federal Telegraph," "All American Cables and Radio," "Globe Wireless," and a common carrier division of Mackay Marine.
- RCA communications had specialised in crossing the Pacific. It later joined with Western Union International to become MCI.
- Before World War I, Tropical Radiotelegraph put radio telegraphs on ships for its owner, The United Fruit Company, in order to deliver bananas to the best-paying markets. Communications expanded to UFC's plantations, and were eventually provided to local governments. TRT Telecommunications (as it is now known) eventually became the national PTT of many small Central American nations.
- The French Telegraph Cable Company (owned by French investors) had always been in the U.S. It laid cable from the U.S. to France. It was formed by "Monsieur Puyer-Quartier". This is how it got its telegraphic routing ID "PQ".
- Firestone Rubber developed its own IRC, the "Trans-Liberia Radiotelegraph Company". It operated shortwave from Akron OH to the rubber plantations in Liberia. TL is still based in Akron.
Bell telex users had to select which IRC to use, and then append the necessary routing digits. The IRCs converted between TWX and Western Union Telegraph Co. standards.
Arrival of the Internet
As the PSTN became a digital network, T-carrier "synchronous" networks became commonplace in the U.S. A T-1 line has a "frame" of 193 bits that repeats 8000 times per second. The first bit, called the "sync" bit, alternates between 1 and 0 to identify the start of the frames. The rest of the frame provides 8 bits for each of 24 separate voice or data channels. Customarily, a T-1 link is sent over a balanced twisted pair, isolated with transformers to prevent current flow. Europeans adopted a similar system (E-1) of 32 channels (with one channel for frame synchronisation).
Around 1965, in a radical break with existing standards, DARPA commissioned a study of decentralized switching systems, hoping to find something more advanced than TOR that could still hope to survive a nuclear war. Some of the ideas developed in this study provided inspiration for some of the ideas the development of the ARPANET packet switching research network, which later grew to become the public Internet.
The Internet was a radical break in three ways. First, it was designed to operate over any media. Second, routing was decentralized. Third, large messages were broken into fixed size packets, and then reassembled at the destination. All previous networks had used controlled media, centralized routers and dedicated connections. As the Internet grew, it used progressively faster digital carrier links, using the digital systems which had been developed for the PSTN.
E-mail starts to displace telegraphy
E-mail was first invented for Multics in the late 1960s. At first, E-mail was only possible between different accounts on the same computer. UUCP allowed different computers to be connected to allow E-mails to be relayed from computer to computer. With the growth of the Internet, E-mail began to be possible between any two computers with access to the Internet.
Various private networks (UUNET, the Well, GENIE , DECNET) had E-mail from the 1970s, but subscriptions were quite expensive for an individual, $25 to $50 a month, just for E-mail. Internet use was then limited to government, academia and other government contractors until the net was opened to commercial use in the 1980s.
In 1992, computer access via modem combined with cheap computers, and graphic point & click interfaces to give a radical alternative to conventional telex systems: personal e-mail.
Individual e-mail accounts were not widely available until local ISPs were in place, although demand grew rapidly, as e-mail was seen as the Internet's killer app. The broad user base created by the demand for e-mail smoothed the way for the rapid acceptance of the World Wide Web in the mid-1990s.
Telegraphy as a legacy system
International Telex remains available via e-mail ports. It is one's e-mail address with numeric or alpha prefixes specifying one's IRC and account.
Telex has always had a feature called "answerback", that asks a remote machine to send its address. If using telex via e-mail, this address is what a remote telex user will want in order to contact an e-mail user.
- optical telegraph
- electrical telegraph
- Morse code
- Samuel Morse
- telegraph code
- Daily Telegraph the London newspaper.
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