| 摘要 |
A line switching apparatus is applied to a system which has a current system line and a spare system line, transmits identical ATM cell streams via the two lines, and adds protection switching cells to the ATM cell streams on a transmission side when line quality of the current system line deteriorates. The apparatus is adapted to switch a line to be used from the current system line to the spare system line in the system. The apparatus includes a first VPI converter, a multiplexer, a spare system line information read section, and a second VPI converter. The first VPI converter converts the VPI of the spare system line into a VPI different from the VPI of the current system line. The multiplexer detects a phase shift amount between the current and spare system lines on the basis of positions of the protection switching cells on the two lines, corrects the phase shift amount, and performs multiplexing processing of packing the cell stream on the spare system line, whose VPI has been converted, at empty cell positions of the cell stream on the current system line. The read section reads out the information of the spare system line from the multiplexed cell stream. The second VPI converter converts the readout cell stream on the spare system line into the initial VPI.
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