| 摘要 |
PURPOSE:To attain inexpensively the changeover of a digital communication line with ease of operation without hit by unifying a changeover system switching one of plural active lines to a spare line. CONSTITUTION:Each active line at the transmission side of the line has a pilot signal generating circuit 36, branching circuit 32a of a bipolar digital signal, and a branching circuit 32b of a bipolar pilot signal 33. Further, bipolar/unipolar converting circuits 34a, 34b, a synthesis circuit 35 synthesizing an output of the converting circuits into a series of the transmission signal, and a changeover switch 45 at the transmission terminal are provided. A receiving end logical circuit 40 to which a receiving signal is inputted, detecting a pilot pulse thereby counting errors and detecting alarm, a unipolar/bipolar converting circuit 41 and a receiving end changeover switch 43 changing over active and spare lines are provided to the line receiving side, and a voltage limit circuit 42 is inserted to the output. |
