| 摘要 |
PURPOSE:To secure a transmission line to transmit from the center side by providing plural communication channels that are divided in ones for transmission and others for in-coming signals under the command of a central control unit, and using a channel for transmission when a communication request is issued from said unit to a monitor. CONSTITUTION:The eight communication channels for one gate way (GWS) are divided into a group for transmission and another for in-coming signals by operating the MMU 25 of the central control unit 10. The channels in the former group are made transmission-dedicated lines for a transmission from the center side to remote sides, and the others for in-coming signals are made transmission-dedicated lines from the remote side to the center side, and they are not used for a communication in reverse direction respectively. The GWS 13 checks the channels for transmission, and there is a vacant channel, the opposite station is called through the vacant channel, if connected, the transmission is executed.
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