Telephone exchange system and switching connection method improved in efficiency for long-distance calling

摘要

A telephone exchange system comprises out-of-town exchanges and local exchanges, the local exchange keeping a communication channel established between a telephone and an out-of-town exchange without breaking the communication channel until satisfying a predetermined condition even if the telephone is on the hook when the connection has been established between the out-of-town exchange and the telephone having made a call, the out-of-town exchange keeping a communication channel established between a local exchange or an out-of-town exchange and the other out-of- town exchange or itself without breaking the communication channel until satisfying a predetermined condition even if the telephone is on the hook when the connection has been established between the local exchange or the out-of-town exchange that is a calling source and the out-of-town exchange or the local exchange that is a calling destination.