| 摘要 |
PROBLEM TO BE SOLVED: To provide a system that can enhance a space efficiency for a large- scale telephone exchange and ensure speeches even on the occurrence of double failures. SOLUTION: A plurality of private branch exchanges for a small scale building are distributed and installed in a large scale building or a large scale area such as a large-scale factory, a regional developed city and an airport. The two small-sized exchanges 1, 2 are designated as center nodes A, B and the other small-sized exchanges 3, 4 are designated as decentralized nodes A, B respectively. Each of the center nodes A, B accommodate external lines of a public network 5. Further, each of the center nodes A, B and the decentralized nodes A, B is connected to two other nodes or more respectively. Extension terminals 6 are connected to each node. Moreover, in this embodiment, a central supervisory section 7 is installed in the small-sized exchange 1. Since each node implements live/dead supervision with each other, each node can quickly find out a defect. A redundant configuration is adopted for each node to avoid an entire area from being fallen into service interruption even when one node is out of order.
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