Importance

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Abstract

In a protection switching system for N working transmission systems and a spare transmission system, first to Nth protection switches (11-1.about.11-n) am provided corresponding respectively to the N working transmission systems (21-1.about.21-n). Each protection switch includes a forward/backward impedance matching circuit (30, 31) and first, second and third pairs of terminals (c, d; h, i; g, j), the first pair terminals (c, b) of each protection switch (11) being connected to the corresponding working transmission system. The second pair terminals (h, i) of each of the first to (N-1)th protection switches are connected respectively to the third pair terminals (g, J) of the second to Nth protection switches, the second pair terminals (h, 1) of the first protection switch being connected to the spare transmission system (20), and the third Fair terminals (g, j) of the Nth protection switch being connected together. In each protection switch, a first two-way connection (22, 23) is established between the forward/backward impedance matching circuit and the first pair terminals (c, d) and a second two-way connection (24, 25) between the second pair terminals (h, i) and the third pair terminals (g, i) when the corresponding working system is working properly. When the corresponding working system is not working properly, the first two-way connection (22, 23) and the second two-way connection (24, 25) are cleared and a third two-way connection (22a, 23a) is established between the forward/backward matching circuits and the third pair terminals (g, j).

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First Claim