| 摘要 |
PROBLEM TO BE SOLVED: To provide a private branch exchange that can select the least expensive path and the least cost carrier which are within the range which does not sacrifice speech quality. SOLUTION: A CPU 3 of the private branch exchange 1 calculates and compares respective speech charges when a leased line 7 and carriers a, b of a public network 8 are use, ranks them in the order of offered cheaper cost, and checks idle/occupied lines according to the order of cheaper cost. When an idle line is used for an internet phone call, the CPU 3 requests transmission of a packet transmission time and traffic information required for the internet phone call. The CPU 3 receiving them compares the obtained transmission time and the traffic information with preset threshold data to discriminate speech quality of the internet phone call and transmits the call to a subscriber terminal 11, according to the discrimination result.
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