Importance

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Abstract

In an exchange including: a call processing unit for processing a call occuring at any one of plural subscriber lines, a main line, or a private line; a switch unit for establishing the call route determined by the call processing unit; and a plurality of trunks for separately connecting to any one of these lines; wherein the exchange comprises: a single or plural decision units for determining whether an audio frequency signal or line signal which separately indicates a state of change of level of the call signal, is received or not, in the route formed by these lines; and a single or plural variable units separately provided between each of routes and a corresponding port of the switch, and performing the change of the level based on the state indicated by the audio frequency signal or line signal which gives a result of decision by the decision unit, for the level of the call signal transmitted toward the route in which the result of the decision is true.

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First Claim