A data transmission network has a plurality of modems to transmit and receive data and a nexus including at least two controllers to control the transmission of data betwen the modems. Each controller has input ports and output ports with each of the modems being connected to an input port and an output port means on each of the controllers to permit the passage of data between the modems and the controllers. Each of the controllers has one of its outputs connected to an input port of the other of the controllers so that data transmitted by one of the controllers will be transmitted to the input port of another of said controllers. Switches are provided between the controllers to prevent continuous circulation of data between the controllers.
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