Arbitrary selecting of a terminal to be called in key telephone systems

A key telephone system including a key service unit connected to communication network and a plurality of data terminals connected to said key service unit, said key telephone system comprising:

• an interface conversion unit effecting a conversion between a user interface of said communication network and a communication interface of each of said data terminals;
• wherein said interface conversion unit answers an incoming call from said communication network;
• said interface conversion unit being connected to said key service unit;
• wherein said key service unit includes:
• a communication network interface unit connected to said user interface of said communication network;
• a plurality of first data interface units respectively connected to said data communication interfaces of said plurality of data terminals;
• a user interface unit connected to an interface for said communication network of said interface conversion unit, for affording an identical interface to said user interface of said communication network;
• a second data interface unit connected to an interface for said data terminal of said interface conversion unit, for affording an identical interface to said communication interface of said data terminal;
• a switching unit for selectively forming a data communication path among said communication network interface unit, said plurality of first data interface units, said user interface unit, and said second data interface unit;
• and
• a microcomputer, connected to said communication network interface unit, said plurality of first data interface units, said user interface unit, said second data interface unit, and said switching unit, for controlling said communication network interface unit, said plurality of first data interface units, said user interface unit, said second data interface unit, and said switching unit;
• wherein said microcomputer includes:
• means for controlling said switching unit for establishing a first data communication path between said communication network interface unit and said second data interface unit so as to supply succeeding communication data from said communication network to said interface conversion unit, when an incoming call reaches said communication network interface unit from said communication network;
• means for receiving an extension number data contained in said succeeding communication data from said interface conversion unit through said second data interface, when said succeeding communication data is inputted to said interface conversion unit, thereby controlling a single said first data interface unit corresponding to a single said data terminal designated by said extension number data so as to send an incoming call command to said designated signal data terminal;
• and
• means for establishing a second data communication path between said single first data interface unit and said second data interface unit, when said designated single data terminal answers said call command, thereby establishing a data communication link between said designated single data terminal and said communication network through said interface conversion unit after a data communication between said interface conversion unit and said communication network is established.