Retronetworking

h1. Teletex

Teletex is a mostly-forgotten technology somewhere between [[Telex]] and [[Telefax]]:

* like Telex, it transmitted data as characters

** however, Teletex supports a more complete alphabet with lowercase characters and special characters (Telex: Only 5-bit uppercase)

* like Telefax, it transmitted formatted entire pages/documents

** however, Teletex transmits the text characters and their formatting (Telefax: A raster-pixel-image).

Teletex was invented aroud 1981. German operation was from 1981 through 1993.

h2. Terminal Devices

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.

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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h2. Network

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.

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.

h2. Communications protocol (stack)

* X.21 is used as physical layer (synchronous 2400 bps)

* X.21 is used for CSPDN signaling, i.e. for dialing the call

* once the transparente bit-synchronous 2400bps channel is established via X.21, the following protocols are spoken (from bottom to top):

** X.75 SLP in HDLC framing with parameters as per T.70 section 3.3.2.2

** T.62 session layer

** T.62 document layer

h2. Relevant Specifications

* ITU-T F.200 (Teletex service)

* ITU-T T.61 (Teletex character set)

* ITU-T T.62 (Session and Document layer)

* ITU-T T.70 (Transport layer profile)

* ITU-T X.75 (Transport layer)

* ITU-T X.21 (interface)

h2. Literature

* Kapitel 9 von Eckart Giese, Klaus Görgen, Dr. Elfriede Hinsch, Günter Schulze, Dr. Klaus Truöl: Dienste und Protokolle in Kommunikationssystemen; 1985, Springer, Berlin/Heidelberg

* Rolf Rüggeberg: Telefax und Teletex in nachrichten elektronik + telematik (net), Heft 12, Dezember 1982, S. 526-529

* Peter Mogdans, Burkard Berning: Teletex - Ein neuer Fernmeldedienst der Bundespost; 1983, Unterrichtsblätter Jg. 36/1983 Nr. 9 S. 355-364

* Frithjof Kroemer: 50 Jahre Telex in Deutschland; Unterrichtsblätter Jg. 37/1984 Nr. 3 S. 88-114

* Franz Müller: Teletex-Dienst und Teletex-Endeinrichtungen; Unterrichtsblätter Jg. 40/1987 Nr. 6 S. 191-202

* Richtlinie FTZ 111 1 R 293 1, Rahmenwerte für Teletex-Endgeräte, Deutsche

Bundespost

* Schenke, K.: Textkommunikationsdienste für das Büro, Bundesministerium für das

Post- und Fernmeldewesen

* Müller, F.: Teletex - Technik der Endeinrichtungen, Sonderdruck aus fernmelde-

praxis, Heft 22 u. 23/1985

* Hans Dieter Hellige: "GENESE UND NIEDERGANG VON TELETEX: LEHREN AUS EINER GESCHEITERTEN REVOLUTION DER BÜROKOMMUNIKATION":https://www.uni-bremen.de/fileadmin/user_upload/sites/artec/Publikationen/Mitglieder/Hellige_1994_Teletex_Genese_und_Niedergang.pdf ; Gekürzt erschienen in: H. Kubicek, G. Müller, E. Raubold, A. Roßnagel (Hrsg.), Jahrbuch Telekommunikation und Gesellschaft Bd. 2, Heidelberg 1994, S. 22-35