| 摘要 |
PURPOSE: To quickly recognize frequencies which can be used for communication. CONSTITUTION: When there is no incoming of a control channel and there is incoming from a public line 1.5, contents of a communication state storage part 2.4 are retrieved to discriminate whether the terminal of the destination is busy or not. If this terminal of the destination is busy, a busy signal is returned to the terminal of the transmission source of communication data, and it is returned to the standby state with the frequency of the control channel. If the terminal of the destination is not busy, the communication state storage part 2.4 is retrieved to designate a frequency which is not used at present, and prescribed data is transmitted to the terminal of the destination. |
