| 摘要 |
PROBLEM TO BE SOLVED: To avoid a useless wait time by opening an external line when infrared ray communication is interrupted in an extension phone call linked by the infrared ray communication. SOLUTION: A master set 1 contains plural external lines 2, 3 and plural extension telephone sets 4-8, and wireless communication employing infrared rays is adopted for the master set 1 and the extension telephone sets 4-8. While any of the extension telephone sets 4-8 making an external line speech with an opposite party, if the infrared ray communication between the master set 1 and the extension telephone sets 4-8 is interrupted due to any cause, a signal detection circuit in an extension I/F 15 detects it. When the interruption is not restored within a prescribed time as a result of time count by a timer 14, the detection circuit allows an external line I/F 16 to open the external line. |
