| 摘要 |
PURPOSE: Many lower devices of a data transmission system transmits the upper device and data through the leased line, and red. CONSTITUTION: A data transmission system includes a plurality of first type lower devices(204), and a plurality of second type lower devices(206). The first type lower devices are connected to a upper device through each one leased line, perform a data transmission through its own leased line, and include a wireless communication part. The second type lower devices include a wireless communication part, are radio-communicated with an adjacent first type lower device among many first type lower devices, and perform a data transmission through its own leased line. Thereby, the number of leased lines needed to a data transmission is considerably reduced.
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