Automatically set up data link - using call signal to connect modem to line via switched telephone network

摘要

The date link is set up automatically via the switched telephone network by switching an modem to the line after disconnecting the telephone receiver on receipt of the call signal. Control signals are set back to the central unit via a control channel. A continuous signal is sent via the control channel from the central unti to the outstation after a connection has been established. The connection between modem and telephone line (initiated by the call signal) is maintained as long as breaks in this continuous signal do not exceed a given duration. Longer breaks cause the modem and line to separate.