| 摘要 |
In a closed-loop data transmission system, the terminals 1-6 of the system each send round the loop a message formed by service data and a random bit stream. Each such message is sent in a time position in a time division cycle individual to that terminal. When such a message reaches a terminal with a data message to be sent to the originating terminal that data message is encoded into the random bit stream: the now-encoded message continues round the loop in the same direction until it reaches the originating terminal where it is received and decoded. To improve system security, in addition to the links which interconnect adjacent terminals in the loop there are so-called leap-frog links each of which extends from one terminal to the next but one terminal in the loop. The invention is described in its application to a system in which the links are optical fibre cables, but the invention is also applicable where the links are of the metallic wire type. <IMAGE>
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