Communication control method for ISDN, and data terminal adaptor apparatus for same

A method of controlling a communication system formed of a wide-area network and a plurality of data terminals respectively connectable to said wide-area network, wherein a data transfer by one of said data terminals via said wide-area network is controlled by operations comprising:

• establishing a first communication circuit between said data terminal and a terminal adapter apparatus, establishing a second communication circuit from said terminal adapter apparatus through said wide-area network and executing said data transfer via said terminal adapter apparatus and said wide-area network;
• detecting a cessation of said data transfer by using said terminal adapter apparatus to monitor said data transfer;
• detecting a condition in which said cessation of data transfer continues beyond a first time limit, and responding to said condition by breaking said second communication circuit while leaving said first communication circuit unchanged;
• and
• using said terminal adapter apparatus to detect whether said cessation of data transfer continues for a duration exceeding a second time limit which is longer than said first time limit, and responding to detection of continuation of said cessation in excess of said second time limit by breaking said first communication circuit.

A method of control of a communication system formed of a wide-area network and a plurality of data terminals respectively connectable to said wide-area network, for controlling data communication between a first and a second one of said data terminals via said wide-area network, comprising:

• establishing a communication circuit between said first and second data terminals through said wide-area network;
• setting a value for a time limit in accordance with a distance between said first ad second data terminals;
• monitoring a data transfer between said first and second data terminals via said communication circuit to detect an interruption of said data transfer;
• and
• breaking said communication circuit to fit is detected that said interruption persists for a duration exceeding said time limit.

A method of control of a communication system formed of a wide-area network and a plurality of data terminals respectively connectable to said wide-area network, for controlling data communication between a first and sa second one of said data terminals via said wide-area network, comprising:

• establishing a first communication circuit between a first terminal adapter apparatus and said first data terminal, a second communication circuit between said first terminal adapter apparatus and a second terminal adapter apparatus through said wide-area network, and a third communication circuit between said second terminal adapter apparatus and said second data terminal;
• detecting interruptions of data transfer between said first and second data terminals via said wide-area network, by using said terminal adapter apparatuses to monitor said data transfer;
• detecting a condition in which said data transfer is interrupted for a duration which exceeds a specific time limit and responding to said condition by breaking sad second communication circuit while leaving said first and third communication circuits unchanged;
• and
• using said terminal adapter apparatuses for detecting a subsequent resumption of said data transfer and responding to detection of said subsequent resumption by re-establishing said second communication circuit.

At terminal adapter apparatus adapted for connection between a data terminal and a wide-area network, comprising:

• first interface means controllable for transferring data between said data terminal and said terminal adapter apparatus under a condition in which a first communication circuit tis established between said data terminal nd said terminal adapter apparatus;
• second interface means controllable for transferring said data between said terminal adapter apparatus and said wide-area network under a condition in which a second communication circuit is established through said wide-area network from said terminal adapter apparatus;
• monitoring mean for monitoring a flow of said data;
• and
• control means responsive to detection by said monitoring means that said flow of data has been interrupted for a time exceeded a time limit,
• said control mean responsive to said detection by said monitoring mean by controlling said first and second interface means to break said second communication circuit while leaving said first communication circuit unchanged,
• said control means re-establishing said second communication circuit responsive to subsequent detection by said monitoring means that a flow of data from said data terminal has been resumed.

A terminal adapter apparatus adapted for connection between a data terminal and a wide-area network, comprising:

• first interface means controllable for transferring data between said data terminal and said terminal adapter apparatus under a condition in which a fist communication circuit is established between said data terminal and said terminal adapter apparatus;
• second interface means controllable for transferring data between said terminal adapter apparatus and said wide-area network under a condition in which a second communication circuit is established through said wide-area network from said terminal adapter apparatus;
• monitoring means for monitoring a flow of data through said first and second interface means;
• and
• control means responsive to detection by said monitoring means that said flow of data has been interrupted for a time exceeding a specific time limit,
• said control means responsive to said detection by said monitoring means by controlling said first and second interface means to break said second communication circuit while leaving said first communication circuit unchanged,
• said control means re-establishing said second communication circuit responsive to subsequent detection by said monitoring means that a flow of data from said data terminal has been resumed, unless a second time limit has been exceeded which is longer than said first time limit.