With an Rx-only arrangement, special serial cables are used to connect the new server to the Rx line at the existing server’s connection. The new server contains the configuration for the relevant outstations, points, and so on, as well as the direct or PSTN channel that represents the connection. The channel has the eavesdropping feature enabled so that the new server can identify that the input (the data from the existing system’s Rx line) is unsolicited.
The Tx line of the new server’s connection to the existing system is disconnected. With this line disconnected, the new server cannot send data to the outstations, and therefore cannot affect the operation of the existing system.
