| 摘要 |
PURPOSE:To prevent the deterioration of a transmission signal giving a test frame shorter than the minimum length of a specified communication frame to a ring transmission line so as to detect the transmission distortion an apply ing timing recovery relaying when the distortion is large. CONSTITUTION:A signal sent from the upstream is received (11) to nodes con nected in a ring, the frame length is indentified 13 and the test frame shorter than the minimum length of frame for communication is sent to a distortion identification circuit 14. When the distortion is smaller than the reference value, a switch 16 is turned to a contact (b) via a drive circuit 18 to apply timing non-recovery relaying. When the distortion is larger than the reference value, the switch 16 is turned to a contact (b) to apply timing recovery 15 for the relay. When the communication frame addressed to its own station is identified by a decoder 12, the frame is sent via a transmission controller CNT, a coder 20 and a contact (a) of a switch 17. When no reception signal exists, a test signal is generated 19 and sent 21 to the downstream. Thus, the deterioration of the transmission signal is prevented.
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