| 摘要 |
PURPOSE:To prevent transfer efficiency from being lowered by increasing check points or the quantity of retransmitting data by setting a transmission length corresponding to the state of line quality. CONSTITUTION:A transmission length setting means 6 calculates an error ratis by dividing the counted value of a fault counting area with the counted value of a communication quantity counting area in a storage part 7 and when the time fault ratis is higher than the preceding fault ratis, the value of the preceding transmission length area is reduced and set to a transmission length area. When the fault ratis is lower, the value of the preceding transmission length area is increased and set to the transmission length area. In this case, however, the upper and lower limit values of the transmission length are set in advance so as to settle the value in that range. Thus, the transfer efficiency can be prevented from being lowered by increasing the check points because of shortening the transmission length too much in comparison with the line quality or by increasing the quantity of retransferred data because of extending the transmission length excessively.
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