Teleprinter
The Telegraph is a telegraphic device for transmitting messages in writing by means of electrical signals. In English, the device teletypewriter means. ( In contrast, teletype is a trademark. ) Derived from this is the name for TTY serial interface driver in computer operating systems.
As a predecessor Morse equipment and developed by Siemens & Halske pointer telegraph may apply. The Telegraph related equipment are the Hellschreiber and the fax machine.
Input and output
A Telegraph resembles externally an electric typewriter, the keyboard that includes the sending unit and the printing unit, which houses the receiver to be operated in to the reading on your own site Written work independently but connected usually in series. More modern mechanical and electronic Telegraph also have facilities that signal to the receiver when the received character has been sent locally. The receiver then lifts one of the directions shown colored ( eg, red for the transmitted text).
The equipment of the Telegraph often include a paper tape reader and paper tape punch to transfer texts prepared by means of a punched tape with maximum speed and so to keep the connection time short or too can save text modules. Since the 1980s, electronic storage media are used.
A distinction chart recorder and strip chart recorder. Chart recorders enter the text like a typewriter on a continuous roll in the width of a standard letter (eg A4) from. Strip chart recorder, however, enter the text from on a typically 9.5 mm wide strip of paper. So the telegram service of the German Federal Post Office has used eg strip chart recorder.
Transmission method
Telegraph use a sequential digital asynchronous data transmission with start and stop bits, and usually use a 5 -bit code, the International Telegraph Alphabet No. 2 (short CCITT -2, ITA2 or Baudot - Murray code). This code limited the available character set to 32 characters ( 25 = 32). For the transmission of letters, digits and special characters of the code is split on two levels, which change with special characters for letter-number switching. As the two escape characters and carriage return and line feed at both levels are valid, is the maximum number of transferable numeral 56, some of which, however, are not used in ITA2.
Transfer is usually with 50 baud ( here equal to 50 bit / s); but there are also devices with 75 (see picture) and 100 baud transmission speed. The character format used consists of a start bit, 5 code bits and 1.5 stop bits. This allowed the telex network, due to the usual 50 baud, a transmission rate of 6.67 characters per second can be achieved. This corresponds to 400 strokes per minute, experienced writers with the ten-finger system could thus partly overwhelm the telegraph system, as they typed faster than could process the machine. Partly also the type lever entangled in a similar case as with the typewriter.
The speed of a mechanical teleprinter is controlled by a centrifugal governor on the motor, which is usually set with a tuning fork after Stroboskopprinzip.
The mechanical connection Telegraph done using a 40 mA current loop. The logical 1 (" rest " ) is represented by the closed loop, the logic 0 ( " character position ") by the broken circuit.
Later built remote electronic typewriters (eg HAL DS -3100 ASR) some have other interfaces such as RS232 or directly built-in modem.
From the rhythmic ticking noise when working a teleprinter, the phrase " a message runs over the ticker " her forwards.
Telex networks
1938 an official telex network in Hamburg was installed by Siemens & Halske. Telegraph are still places used by authorities.
Until 2007, there was in Germany Telex Telekom. However, telex terminals in Germany continue to move in by the company Swiss telex.
Bundeswehr
The Bundeswehr used until 1986 known as the Bundeswehr base network for military communications. It was a star -meshed network, which worked on guidance, node and Endvermittlungen and in case of failure of one of these components failing that, other switching paths in the network used ( reliability and availability were assured).
1986 this network was replaced by the AFDNBw (automated telex and data transmission network of the Federal Armed Forces), where still the old telex and key devices could be used.
As part of the cooperation agreement Hercules and the entire non-military IT Bundeswehr was, as one of many points contract renewed. This led inter alia to the fact that on 30 November 2006 off the entire AFDNBw and the new system MMHSBw (Military Message Handling System of the Federal Armed Forces) has been replaced.
This system provides among other things the extent a simplification of the message traffic is when the employee has to go through no expensive and more specialized training in a telex place. The new system is based on a modified MS Outlook client. This corresponds to a large extent to the normal e -mail program, MS- Outlook, but is extended to include some military specifications. So military priority levels can be (important in terms of maximum running time of a message from sender to receiver) and entered military classification levels, among others. In addition, encrypted by appropriate plug -ins military intelligence and by means of PKI (Personnel Key Infrastructure ) can also be signed.
Other networks
In addition to wired networks, telex ( Telex ) worldwide still exist numerous radio teletype networks that exchange messages via radio, for example, via shortwave. The designation of these services for this is radio teletype RTTY short.
The public telex network of the German Post and Deutsche Telekom was present as a separate network with its own exchanges in operation until the 1990s. The connections to exchange messages with the telex partners could be produced by a Wählzusatzgerätes based on their public telex number as a phone directly on an automatic dialer. This network was integrated into the international telex network.
Today, there are hardly any pure telex or telex networks and exchanges. Most telex networks will be integrated via gateways to other messaging or data networks and can be partly operated in these systems as an additional service.
Telegraph can also be fixedly connected to each other as peers in direct mode.
Telex networks in the GDR
In the GDR, several automatic telex networks Selbstwählbetrieb existed side by side:
- Public telex network of Deutsche Post for businesses
- S1- Network agencies and government departments
And other non- public networks of the NPA, the Ministry of the Interior ( mDI ), the Ministry of State Security and the Warsaw Pact.
According to the importance of a telex terminal and the exploitation of other telex network by network- foreign participants was directly and indirectly possible.
Developments
Through the use of electronics and software, the expensive maintenance and adjustment of the mechanical components of a teleprinter and the telex network are largely omitted.
The classical mechanical teletype has been replaced by a telex e- mail gateway or a PC with printer and special hardware for connection to the existing telex connection or a radio station today often.
So not own telex trunk is required for the PC software WinTelex32 dial by Swisscom. Connection to the telex exchange is done via the public telephone network. WinTelex32 TCP / IP in turn provides over the public Internet connects to the telex exchange, wherein the normal telex number remains. The authentication of the device is made using X.509 certificates ( with 512 - bit keys ), the communication over the Internet using a 128 -bit key is saved.
Nevertheless, faxes, mailbox systems and the Internet have in the late 1990s virtually replaced as the main communication method for texts and data in the telex.
Advantages of the telex
In contrast to the Morse code the message can be processed automatically when receiving immediately or later read as plain text and when required. Furthermore, the automatic encryption and decryption of coded telex by appropriate devices with punched tape is possible.
The news channels used do not need to be constantly monitored manually to incoming messages. Thus, also the remote write operation performed largely automatically when needed and a preset message to be sent automatically at a specified time using paper tape reader. Hence, a high efficiency can be achieved in the utilization of the communication channel.
The Telegraph can be connected directly via a special modem to an existing V.31 interface for data transfer. Also, automatic monitoring stations or remote control devices can be easily connected to an existing telex connection and send data and commands as " telex ".
The biggest advantages of the telex are still the simple and safe method of automatic word processing and data transmission over any transmission media such as radio and data networks, as well as Wechselstromtelegrafie over existing telephone lines.
Today, the telex service is often channeled through existing data connections via converter or converter as a guest, or through gateways to other networks or radio.
Wechselstromtelegrafie
Using the so-called Wechselstromtelegrafie (WT) can be prepared by the multiple use of an existing telephone channel more remote write channels can be operated simultaneously and independently of each other. It is customary to frequency modulation of the individual telex channels in these processes. The carrier frequencies are modulated with the message content, and transmitted together on a line and separately demodulated again at the end. A telephone channel can thus hold up to 24 telex channels with a Telegrafiergeschwindigkeit of up to 50 baud. At higher Telegrafiergeschwindigkeiten are correspondingly less Telegrafiekanäle due to the limited bandwidth of the carrier channel is possible.
In limiting the bandwidth of a telephone channel, and the Telegrafiergeschwindigkeit simultaneous independent operation is possible from both modes on a voice channel with the MWT Wechselstromtelegrafiegerät NVA 1/2.
Gateway systems for telex
The gateway systems for Telegraph e- mail often allow the exchange of data from plain text messages in both directions.
In these systems, for example, can be assigned to any telex connection in the gateway simply their own e - mail address. The messages themselves are implemented in the gateway as a system -mail message and can be received via mailbox systems, or directly over the Internet as an e -mail by the recipients.
When you receive an e- mail in text format, the e- mail gateway accepts the text message and translates them as telex.
The addressing and automatic forwarding (routing ) to the desired message recipient via certain conditions laid down by the gateway telex addresses and address rules when sending the message to the telex or by the remote station.
Often, the address of the gateway includes in addition to the recipient 's still the telex address. Based on this, the direct automatic assignment and forwarding ( routing) of the message to multiple desired telex receiver through the gateway automatically possible.
Radio teletype for sea weather
The best known application of radio telex in shipping are the sea-weather forecasts, which are even today still shipped via radio regularly to the ships' crews. This service is also provided by the German Weather Service.
Telex in amateur radio
In amateur radio were ( and still are today partly ) discarded teletype machines of conventional design and use used. Strip chart recorder were and are popular because of these devices, a loss of the command " carriage return " no effect on the readability of the message has ( lines can not be overwritten). Amateur radio operators around the world use a transfer rate of 45.45 baud (as opposed to professional services with 50/75/100 baud ) in which sound frequencies are " keyed " depending on the character polarity ( frequency shift keying ). These frequencies can then be AFSK using appropriate methods ( eg SSB) send out.
Today, computers are used for telex traffic mainly staff who produce the required sound signals via a modem and the sound card of the computer and evaluate the reception. The necessary programs often control the operating modes of fax, LIGHT and Morse code.
The successor service Teletex
→ Main article: Teletex
In the Federal Republic of Germany in the early 1980s an attempt was made ( not to be confused with teletext as a generalization of teletext ) introduce the Teletex service as attractive successor to the telex service.
In today's practice, the e-mail has largely replaced this technique.
Telegraph and computer
Telegraph in principle as serial working, digital input and output devices dar. Consequently, they were widely used as computer peripherals - the one with its pressure part as an output device, on the other hand, in addition to the keyboard as a terminal for direct control of a computer. Traces of this usage can be found to this day, such as the control characters carriage return (CR ) and Line Feed (LF). At some universities were still up in the 1970s teletype for creating program tape and print the results produced on a strip holes in use.
As in the 1970s emerged the first microcomputer, there were initially few offers affordable printer. In many companies or in universities instead stood Telegraph, which could be connected via suitable interfaces as a printer. The data was exchanged via the punched tape or over an existing COM interface such as RS -232 and using a special connecting device. All this was true of early home computers (before about 1980 ), where you began used relatively inexpensive especially available Telegraph.
Also telegraph models with improved 7-bit ASCII code were used instead of the usual in normal telex operation 5 -bit code very early on.
The serial data transfer when telex is up to the present time unchanged in use (see for example TTY ).