Teletex » History » Version 5
laforge, 02/04/2023 05:29 PM
1 | 1 | laforge | h1. Teletex |
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2 | 2 | laforge | |
3 | 3 | laforge | Teletex is a mostly-forgotten technology somewhere between [[Telex]] and [[Telefax]]: |
4 | * like Telex, it transmitted data as characters |
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5 | ** however, Teletex supports a more complete alphabet with lowercase characters and special characters (Telex: Only 5-bit uppercase) |
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6 | * like Telefax, it transmitted formatted entire pages/documents |
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7 | ** however, Teletex transmits the text characters and their formatting (Telefax: A raster-pixel-image). |
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9 | Teletex was invented aroud 1981. German operation was from 1981 through 1993. |
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11 | h2. Terminal Devices |
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13 | Early/Simple Teletex devices are typically built from pre-existing daisy-wheel typewriters with single-line memory/editing/display capability. Those typewriters were extended with additional communications hardware and software in order to receive and/or transmit in Teletex format. |
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15 | Later, more complex Teletex devices were text/word processing systems, either dedicated or in the form of personal computers. Those were then likewise extended with a Teletex communications hardware + software. |
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17 | 2 | laforge | {{child_pages()}} |
18 | 3 | laforge | |
19 | h2. Network |
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21 | Teletex is designed to use a [[CSPDN__Datex-L|CSPDN]] (circuit-switched public data network). The Teletex user equipment interfaces to the network via a 2400 bps synchronous [[X21|X.21]] interface. |
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23 | 4 | laforge | ITU specifications also specify operation of Teletex over PSPDN, PSTN or ISDN networks, but it is not known if any of this was ever deployed anywhere. |
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25 | h2. Communications protocol (stack) |
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27 | * X.21 is used as physical layer (synchronous 2400 bps) |
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28 | * X.21 is used for CSPDN signaling, i.e. for dialing the call |
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29 | * once the transparente bit-synchronous 2400bps channel is established via X.21, the following protocols are spoken (from bottom to top): |
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30 | ** X.75 SLP in HDLC framing with parameters as per T.70 section 3.3.2.2 |
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31 | ** T.62 session layer |
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32 | ** T.62 document layer |
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34 | 3 | laforge | h2. Relevant Specifications |
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36 | 1 | laforge | * ITU-T F.200 (Teletex service) |
37 | * ITU-T T.61 (Teletex character set) |
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38 | 5 | laforge | * ITU-T T.62 (Session and Document layer) |
39 | * ITU-T T.70 (Transport layer profile) |
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40 | * ITU-T X.75 (Transport layer) |
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41 | 3 | laforge | * ITU-T X.21 (interface) |