The Datex-L network was a public switched network for the exclusive purpose of data transmission with circuit switching (L). The Datex-L network was increasingly replaced by ISDN in the 1990s and was discontinued at the end of 1996.
With circuit-switched connections, there is a fixed line between the data terminals for the duration of the connection. Compared with the telephone network, the main advantages were the shorter time required to set up the connection (max. 0.4 s) and the better transmission quality (bit error rate 10exp-6). Datex-L was specially designed for data communication and could be used for group 3 dial-up connections. Transmission speeds from 300 bit/s to 64 kbit/s (trial operation with 4 x 64 kbit/s) were offered in more than 5 user classes. The Datex-L service was discontinued in 1996.
The two interconnected data terminal equipment had to operate at the same transmission speed. Except for the user class 1 Datex-L300, in which the alphabet CCITT-No. 5 was prescribed, the connections were transparent for the transmission procedure. The following interfaces could be used to connect terminal equipment: X.20 and X.20bis for asynchronous connections, X.21 and X.21bis for synchronous connections and a multiplex interface X.22 for Datex-L64000.
Access to Datex-P was possible, as was access to a few foreign circuit-switched networks in Europe, USA and Japan.
Deutsche Telekom offered several user classes to the end user:
- Datex-L300: 300 bit/s asynchronous, access X.20(bis),
- Datex-L2400: 2,400 bit/s synchronous, access X.21(bis),
- Datex-L4800: 4,800 bit/s synchronous, access X.21(bis),
- Datex-L9600: 9,600 bit/s synchronous, access X.21(bis),
- Datex-L64000: 64,000 bps synchronous, X.21(bis), X.22,
- Datex-L4/64000: 4 x 64.000 bit/s.