Building a Standalone Softmodem Enabled PABX

Inspired by the article ‘Build your own PABX and Modem Emulator’ by HereBeDragons, this project aims to build on top of that work and create an Asterisk (v18) PABX on a Raspberry Pi with two local extensions and two external connections to the Telstar Viewdata system. The idea is that I can connect a Prestel or Minitel terminal or an 1980s computer with modem, to the Telstar viewdata system.

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The TELSTAR Viewdata System

The TELSTAR videotex system provides a viewdata/videotext platform similar to those that were prevalent during the 1980s such as Prestel.

The aim of the system is to provide a Viewdata experience for anyone who is interested in how things ‘used to be’. Services in the past typically provided access via the public switched telephone network (PSTN) connection and this is indeed how Telstar works, however, Telstar also makes use of a simple internet connection for modern internet modems.

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Telstar Viewdata Client

To experience Telstar properly it needs to be accessed by a microcomputer or Viewdata Terminal from the 1980s. However, for a simple way to get started, the Telstar Viewdata Client can be used.

The Telstar Viewdata client is available for Mac, Linux and Windows and has no dependencies, It allows access to viewdata systems through either a direct TCP/IP connection or via a Modem connected to a local serial port.

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Using Minitel Terminals with Telstar

a Minitel Terminal, switches in a final translation layer at the point of rendering a frame. This translation layer converts Prestel type frames (CEPT3) to Minitel type frames (CEPT2), it should be a simple process but alas, it is not.

Telstar is a CEPT3 Prestel like system and cannot host CEPT2 type Minitel frames, it simply converts CEPT3 frames to CEPT2 frames on the fly at the point of rendering.

If for some reason Telstar fails to automatically detect the Minitel Terminal a single press of the Connection button (two presses will disconnect) should sort things out.

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