Communication system for converting ISDN signaling protocol between local and public network having first group of mandatory elements and second group of non-mandatory elements

A station terminal arranged to communicate ISDN D channel control information in a Q.931 control protocol message over a communication facility to a control unit, said terminal comprising

• means for receiving information over said facility from said control unit, said information being received in a local protocol message format having a first group of information elements including
• a first group of control information elements containing mandatory elements of said Q.931 protocol messages for controlling a call setup at station terminal and
• a second group of control information elements derived from a third group of information elements selected from one or more sets of information elements including 1) a first set of non-mandatory Q.931 protocol message information elements, and, 2) a second set of local information elements obtained from a data memory accessible by said control unit and
• means for controlling user interactions with said terminal, via said user-interface device, using said second group of control information elements.

A control unit for use in a communication system including at least one station terminal connected over a communication facility to said control unit, said control unit also connected to an external communication channel, said control unit comprising

• means for receiving ISDN D channel call control information in a Q.931 control protocol message over said external communication channel,
• means for converting a received Q.931 control protocol message which controls call connections over said first channel using said D channel information, into a local protocol message for controlling communications with said at least one station terminal over said facility on a per second channel basis, said local protocol message controlling said at least one station terminal, said local protocol message including
• a first group of information elements containing mandatory Q.931 protocol message information elements for establishing a call connection between said control unit and said at least one station terminal and
• a second group of information elements derived from a third group of information elements selected from one or more sets of information elements including 1) a first set of non-mandatory Q.931 protocol message information elements, and 2) a second set of local information elements obtained from a data memory accessible by said control unit and
• means for sending said local protocol message over said facility to said at least one station terminal.

A method of operating a communication system arranged to receive ISDN D channel information in a Q.931 protocol message over a first communication channel, said system including a control unit connected to said first channel and connected over a communication facility, including one or more second communication channels, to at least one station terminal, said method comprising the steps of

• at said control unit
• converting a received Q.931 protocol message which controls call connections over said first channel using said D channel information, into a local protocol message,
• controlling communication with said at least one station terminal, over said facility on a per second channel basis, said local protocol message controlling said at least one station terminal, said local protocol message including
• a first group of information elements containing mandatory Q.931 protocol message information elements and
• a second group of information elements derived from a third group of information elements selected from one or more sets of information elements including 1) a first set of non-mandatory Q.931 protocol message information elements and 2) a second set of local information elements obtained from a data memory accessible by said control unit, and at said at least one station terminal
• controlling a calling state of at least one second channel of said at least one station terminal.

A method of operating a station terminal arranged to communicate ISDN D channel control information in a Q.931 control protocol message over a communication facility to a control unit, said method comprising the steps of

• receiving information over said facility from said control unit, said information being received in a local protocol message format having a first group of information elements including
• a first group of control information elements containing mandatory elements of said Q.931 protocol messages for controlling a call setup at said station terminal and
• a second group of control information elements derived from a third group of information elements selected from one or more sets of information elements including 1) a first set of non-mandatory Q.931 protocol message information elements, and, 2) a second set of local information elements obtained from a data memory accessible by said control unit and
• controlling user interactions with said terminal, via said user-interface device, using said second group of control information elements.

A method of operating a control unit for use in a communication system including at least one station terminal connected over a communication facility to said control unit, said control unit also connected to an external communication channel, said method comprising the steps of

• receiving ISDN D channel call control information in a Q.931 control protocol message over said external communication channel,
• converting a received Q.931 control protocol message which controls call connections over said first channel using said D channel information, into a local protocol message for controlling communications with said at least one station terminal over said facility on a per second channel basis, said local protocol message controlling said at least one station terminal, said local protocol message including
• a first group of information elements containing mandatory Q.931 protocol message information elements for controlling a call setup at said at least one station terminal and
• a second group of information elements derived from a third group of information elements selected from one or more sets of information elements including 1) a first set of non-mandatory Q.931 protocol message information elements, and, 2) a second set of local information elements obtained from a data memory accessible by said control unit and
• sending said local protocol message over said channel to said at least one station terminal.

A communication system arranged to receive ISDN D channel information in a Q.931 protocol message over a first communication channel, said system including a control unit connected to said first channel and connected over a communication facility, including one or more second communication channels, to at least one station terminal, said system further including

• at said control unit
• means for converting a received Q.931 protocol message, which controls call connections over said first channel using said D channel information, into a local protocol message for controlling communications with said at least one station terminal over said facility, on a per second channel basis, said local protocol message controlling said at least one station terminal, said local protocol message including
• a first group of information elements containing mandatory Q.931 protocol message information elements and
• a second group of information elements derived from 1) non-mandatory Q.931 protocol message information elements and 2) local information elements obtained from a data memory accessible by said control unit and
• at said at least one station terminal
• means for receiving said local protocol message and for controlling a calling state of at least one second channel of said at least one station terminal.

A method of operating a communication system arranged to receive ISDN D channel information in a Q.931 protocol message over a first communication channel, said system including a control unit connected to said first channel and connected over a communication facility, including one or more second communication channels, to at least one station terminal, said method including the steps of

• at said control unit
• converting a received Q.931 protocol message, which controls call connections over said first channel using said D channel information, into a local protocol message,
• controlling communications with said at least one station terminal over said facility, on a per second channel basis, said local protocol message controlling said at least one station terminal, said local protocol message including
• a first group of information elements containing mandatory Q.931 protocol message information elements and
• a second group of information elements derived from 1) non-mandatory Q.931 protocol message information elements and 2) local information elements obtained from a data memory accessible by said control unit and
• at said at least one station terminal
• receiving said local protocol message and for controlling a calling state of at least one second channel of said at least one station terminal.