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X.21bis is a practice-oriented intermediate standard with which data terminals designed for asynchronous data transmission via modems in analoguetelephone networks can be operated via digital networks with packet or circuit switching.

This X.21bis interface variant is used to connect synchronously operating data terminal equipment (DTE) with a V.24 interface to public networks.

Overview of the X.21 and X.21bis

Overview of the X.21 and X.21bis

interfaces X.21bis will gradually be phased out in favor of X. 21 as old terminals are replaced by X.21 terminals and also as more digital connections are installed. ITU designations with the suffix "bis" are second generation. This designation is an older German term for "second".

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Englisch: X.21bis
Updated at: 25.03.2013
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