Communication system using switching apparatus

摘要

In a telephone switching apparatus having an inter-office interface consisting of a plurality of communication circuits having different priorities and a control line for transfer of call control signals, a first circuit having the highest priority is hunted from the idle one of said communication circuits upon setting of a call and the communication is started. During the communication, if a second circuit having a higher priority than that of the first circuit becomes idle, by communicating a control signal to switch the circuit between the switching apparatuses, the busy circuit for the call is switched from the first circuit of a low priority to the second circuit of a high priority.