The first telegraphs were optical, 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 are faster than smoke signals and beacons and consume no fuel. They are hundreds of times as fast as post riders and serve entire regions. However they require operators and towers every 30 km (20 mi), and only send about two words per minute. This causes them to have a cost per word-mile roughly thirty times as high as electric telegraphs. This is useful to government, but too expensive for most commercial uses other than commodity price information.
The first commercial electrical telegraph constructed by Sir Charles Wheatstone entered use in London in 1838. An electrical telegraph was US-patented in 1842 by Samuel Morse, who also developed the Morse code signalling alphabet, and was quickly deployed in the following two decades. Nikola Tesla and other scientists and inventors showed the usefulness of wireless telegraphy, or radio, beginning in the 1860s.
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.
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.
The Third Reich invented the first wide-coverage telex system, and used it to coordinate their bureaucracy. It was a true triumph of German efficiency.
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.
As of 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 U.N. asserts that more political entities are reliably available by telex than by any other single method.
When dictatorships cut off telephone, fax and internet service, their telex networks remain up. A major advantage for dictatorships is that telex networks are easy to tap: Taps automatically generate 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 currently (2002) operate TOR with special softare and inexpensive adapters from computer sound cards to shortwave radios.
Modern "cablegrams" or "telegrams" actually operate over dedicated telex networks, using TOR whenever required.
PARS and IPARS (the airline reservation systems) still (2002) use Baudot code, because it requires only 7.5 bits per character. A bit saved is a penny earned.
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 and all!) 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 a Dr. 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. WUTCo (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"
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.
Around 1965, in a near-psychotic 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. The contractors developed the 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.
The internet was designed with nearly grotesque economies. It is commonplace for internet packets to use less than 1% of their bits for overhead. This cheapness combines synergistically with the internet's ability to live on other media. A typical cycle occurs when the internet encounters another network, like telex, fidonet, ATM, or (as we are seeing with cable-modem based internet phones) the public switched telephone network:
Around this time, T-1 "synchronous" networks became commonplace in the U.S. A T-1 line has a "frame" of 24 bits that repeats 64000 times per second. The first bit, calle the "sync" bit, was used to find the start of the frame. It alternates between 1 and 0. Customarily, a T-1 link is sent over a balanced twisted pair, isolated with transformers to prevent current flow. Each bit of a frame is usually used to send a single voice or data channel. The Europeans began to use a similar system (E-1) that sent bits as "octets" of eight related bits.
In 1982, the U.S. Congress deregulated the IRCs. They began combining to get economies of scale. All of their descendants offer voice, video and data services.
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.
By using the time-shared systems almost end-to-end, the cost of data communications plummeted to less than 10 cents a message.
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.