| 摘要 |
PURPOSE:To complete the recovery by transmitting the re-transmission demand through a telephone line to which no error has occurred and making a transmitter which receives the re-transmission demand to send the re-transmission data block to the same telephone line by which the demad has been transmitted. CONSTITUTION:The data sent from a host device 15 is sent to a transmission part 16a of a transmitter 16, and then divided into blocks of certain size, distributed to a A line 19 and a B line 20, and transmitted after being modulated by a modem. The data transmitted is demodulated by the modem of transmitter 17, and the data block received by a reception part 171 is connected in the order of sequence number and sent out to a subordinate device 18. Suppose an error has occurred at a data block 22, then the reception part receives transmission number 3' right after transmission number 1', therefore is detects that the data block 22 is missing, then it reads a code A of the data block 22, indicates a transmission part 172 to send a re-transmission demand 24 for a data block 2' which has been sent through the A line 19 to the reception part 162 of the transmitter 16 through the B line 20 where no error has occurred.
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