| 摘要 |
The invention relates to an optical subscriber network transmission system and, in particular, means for smoothly enlarging the transmission capacity in such system. The invention shortens the time of service interruption during changeover of transmission line capacities by use of a spare optical transmission line. Installation of a low cost spare optical fiber line permits testing of transmission lines without service interruption. Successive changeovers are performed using the auxiliary fiber keeping service interruption to a minimum.
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