Full-duplex video communication system

• US 5,119,319 A
• Filed: 12/14/1989
• Issued: 06/02/1992
• Est. Priority Date: 12/14/1989
• Status: Expired due to Term

• Current Assignee: Options UnLtd Research Corporation
• Original Assignee: Options UnLtd Research Corporation
• Inventors: Tanenbaum, Richard
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Ramirez, Ellis B.
• Application Number:
  US07/450,641
• Time in Patent Office: 901 Days
• Field of Search: 364/514, 364/226.2, 364/239, 364/518, 364/521, 340/717, 340/825.08
• US Class Current: 709/205
• CPC Class Codes: G06F 3/1454 involving copying of the display data of a local workstation or window to a remote workstation or window so that an actual copy of the data is displayed simultaneously on two or more displays, e.g. teledisplay
• CPC Class Codes: G06F 40/166 Editing, e.g. inserting or deleting
• CPC Class Codes: H04M 11/085 using a television receiver, e.g. viewdata system

Abstract

Each terminal in a full-duplex communication system comprises a computer-controlled display screen such as a CRT, at least one input means such as a keyboard, a mouse or a light pen and bidirectional communication means through which the terminals are interconnected. Each communication means comprises a receiver for receiving display information received at the terminal from the remote terminal(s) and a transmitter for transmitting information to the remote terminal(s) where it is displayed. In accordance with the invention, each terminal also comprises control means which periodically read sits input means and communications means and uses the information contained therein to control the content of its display. Further, the control means at each terminal also provides to its transmitter instructions which are transmitted to the remote terminal to change the display at the remote terminal so that all the displays are the same. As a result of this arrangement, changes in the display that are made at the same time by the user at the local terminal and by the user at the remote terminal are entered on the display screens at both terminals at substantially the same time so far as is discernable by the users. As a result, not only can each user interact with the display but it is also possible for each user to interact with the other users through the display without having to wait for one user to complete his entry of information as in the prior art. As a result, truly interactive communication is possible through the display.

Claims

1. A communication system for creating substantially identical simultaneously interactive displays at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a functionally similar second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

2. The communication system of claim 1 wherein the means at each terminal for continuously receiving display instructions from an input means and a communication buffer comprises means for polling said input means and communication buffer.

3. The communication system of claim 1 wherein display instructions are communicated from one terminal to another using message packets.

4. The communication system of claim 1 wherein display instructions are communicated from one terminal to another using message packets and the system further comprises:

means at each terminal for assigning a number to each message packet transmitted to another terminal,

means for storing the message packets transmitted from a terminal,

means for checking for errors in the message packets received at a terminal,

means for requesting that a message packet be sent again from a transmitting terminal if the error checking means at a receiving terminal detects an error in a received message packet, and

means for retrieving a stored message packet upon receipt of a request for retransmission and for transmitting said packet again.

5. The communication system of claim 4 wherein the message packet includes at least three copies of the message packet number and the system further comprises means at each terminal for reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

6. The communication system of claim 4 further comprising at least one additional terminal similar to the first and second terminals and communicating with said first and second terminals via said communication line wherein the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the system further comprises means at each terminal for reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

7. The communication system of claim 1 wherein the first terminal and the second terminal are controlled by functionally similar programs each of which is executing asynchronously at a different one of the terminals.

8. A communication system for creating substantially identical simultaneously interactive displays at two locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, and a first means for transmitting information via the full-duplex communication line,

a functionally similar second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions on said first display means upon receipt thereof,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions on said second display means upon receipt thereof,

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means, and

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being functionally similar,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

9. The communication system of claim 8 wherein display instructions are communicated from one terminal to another using message packets.

10. The communication system of claim 8 wherein display instructions are communicated from one terminal to another using message packets and the system further comprises:

means at each terminal for assigning a number to each message packet transmitted to another terminal,

means for storing the message packets transmitted from a terminal,

means for checking for errors in the message packets received at a terminal,

means for requesting that a message packet be sent again from a transmitting terminal if the error checking means at a receiving terminal detects an error in a received message packet, and

means for retrieving a stored message packet upon receipt of a request for retransmission and for transmitting said packet again.

11. The communication system of claim 9 wherein the message packet includes at least three copies of the message packet number and the system further comprises means at each terminal for reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

12. The communication system of claim 11 further comprising at least one additional terminal similar to the first and second terminals and communicating with said first and second terminals via said communication line wherein the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the system further comprises means at each terminal for reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

13. The system of claim 8 wherein the display instructions transmitted from one terminal to another specify a change in the information to be displayed by a display means and a location of said change in the information displayed.

14. The system of claim 8 wherein the stored programs under which the first and second terminals operate are the same.

15. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a functionally similar second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

a method of creating substantially identical simultaneously interactive displays at the two locations comprising the steps of;

continuously receiving display instructions at said first terminal from said first input means and said first communication buffer and implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

continuously receiving display instructions at said second terminal from said second input means and said second communication buffer and implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

16. The method of claim 15 wherein the step of continuously receiving display instructions from an input means and a communication buffer comprises the step of polling said input means and communication buffer.

17. The method of claim 15 wherein display instructions are communicated from one terminal to another using message packets.

18. The method of claim 15 wherein display instructions are communicated from one terminal to another using message packets and the method further comprises the steps of:

assigning at each terminal a number to each message packet transmitted to another terminal,

storing the message packets transmitted from a terminal,

checking for errors in the message packets received at a terminal,

requesting that a message packet be sent again from a transmitting terminal if an error checking means at a receiving terminal detects an error in a received message packet,

retrieving a stored message packet upon receipt of a request for retransmission, and

transmitting said packet again.

19. The method of claim 18 wherein the message packet includes at least three copies of the message packet number and the method further comprises the steps of reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

20. The method of claim 19 wherein at least one additional terminal similar to the first and second terminals communicates with said first and second terminals via said communication line and the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the method further comprises the steps of reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

21. The method of claim 15 wherein the first terminal and the second terminal are controlled by functionally similar programs each of which is executing asynchronously at a different one of the terminals.

22. A communication system for creating substantially identical simultaneously interactive displays at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and said means for continuously receiving display instructions comprising a means for polling said first input means and said first communication buffer,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and said second means for continuously receiving display instructions comprising a means for polling said second input means and said second communication buffer, and

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

23. A communication system which utilizes message packets for creating substantially identical simultaneously interactive displays at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said first terminal for communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

means at said second terminal for communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

26. The communication system of claim 23 further comprising at least one additional terminal similar to the first and second terminals and communicating with said first and second terminals via said communication line wherein the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the system further comprises means at each terminal for reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

24. A communication system which utilizes message packets for creating substantially identical simultaneously interactive displays at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting message packets to a second location via the communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting message packets to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said first terminal for communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said second terminal for communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

means at each terminal for assigning a number to each message packet transmitted to another terminal,

means for storing the message packets transmitted from a terminal,

means for checking for errors in the message packets received at a terminal,

means for requesting that a message packet be sent again from a transmitting terminal if the error checking means at a receiving terminal detects an error in a received message packet, and

means for retrieving a stored message packet upon receipt of a request for retransmission and for transmitting said packet again,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

25. The communication system of claim 24 wherein the message packet includes at least there copies of the message packet number and the system further comprises means at each terminal for reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

27. A communication system for creating substantially identical simultaneously interactive displays at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed, and

functionally similar programs controlling said first and second terminals, each of which programs is executing asyncronously at a different one of the terminals,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

28. A communication system for creating substantially identical simultaneously interactive displays at two locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, a first means for generating display instructions formed of message packets, and a first means for transmitting information via the full-duplex communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, a second means for generating display instructions formed of message packets, and a second means for transmitting information via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions on said first display means upon receipt thereof,

means at said first terminal for communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions on said second display means upon receipt thereof,

means at said second terminal for communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means, and

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being functionally similar,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

31. The communication system of claim 28 further comprising at least one additional terminal similar to the first and second terminals and communicating with said first and second terminals via said communication line wherein the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the system further comprises means at each terminal for reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

29. A communication system for creating substantially identical simultaneously interactive displays at two locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, a first means for generating display instructions formed of message packets, and a first means for transmitting message packets via the full-duplex communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, a second means for generating display instructions formed of message packets, a second means for generating display instructions formed of message packets, and a second means for transmitting message packets via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions on said first display means upon receipt thereof,

means at said first terminal for communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions on said second display means upon receipt thereof,

means at said second terminal for communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means,

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being functionally similar,

means at each terminal for assigning a number to each message packet transmitted to another terminal,

means for storing the message packets transmitted from a terminal,

means for checking for errors in the message packets received at a terminal,

means for requesting that a message packet be sent again from a transmitting terminal if the error checking means at a receiving terminal detects an error in a received message packet, and

means for retrieving a stored message packet upon receipt of a request for retransmission and for transmitting said packet again,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

30. The communication system of claim 29 wherein the message packet includes at least three copies of the message packet number and the system further comprises means at each terminal for reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

32. A communication system for creating substantially identical simultaneously interactive displays at two locations comprising:

first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, and a first means for transmitting information via the full-duplex communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means, and

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being functionally similar,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

33. A communication system for creating substantially identical simultaneously interactive displays at two locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, and a first means for transmitting information via the full-duplex communication line,

a second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions on said first display means upon receipt thereof,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions on said second display means upon receipt thereof,

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means, and

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being the same,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

34. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line, and

a second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

a method of creating substantially identical simultaneously interactive displays at the two locations comprising the steps of;

polling said first input means and said first communication buffer to continuously receive display instructions therefrom and implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

polling said second input means and said second communication buffer to continuously receive display instructions therefrom and implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

35. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line, and

a second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

a method of creating substantially identical simultaneously interactive displays at the two locations comprising the steps of;

continuously receiving display instructions at said first terminal from said first input means and said first communication buffer and implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

continuously receiving display instructions at said second terminal from said second input means and said second communication buffer and implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

38. The method of claim 35 wherein at least one additional terminal similar to the first and second terminals communicates with said first and second terminals via said communication line and the message packet also includes at least three copies of an identification of the terminal from which the packet is transmitted and the method further comprises the steps of reading each copy of the terminal identification and determining if one value of the terminal identification appears a majority of times.

36. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting message packets to a second location via the communication line, and

a second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting message packets to said first location via said communication line,

a method of creating substantially identical simultaneously interactive displays at the two locations comprising the steps of;

continuously receiving display instructions at said first terminal from said first input means and said first communication buffer and implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating in message packets display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

continuously receiving display instructions at said second terminal from said second input means and said second communication buffer and implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating in message packets display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

assigning at each terminal a number to each message packet transmitted to another terminal,

storing the message packets transmitted from a terminal,

checking for errors in the message packets received at a terminal,

requesting that a message packet be sent again from a transmitting terminal if an error checking means at a receiving terminal detects an error in a received message packet,

retrieving a stored message packet upon receipt of a request for retransmission, and

transmitting said packet again,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

37. The method of claim 36 wherein the message packet includes at least three copies of the message packet number and the method further comprises the steps of reading each copy of the message packet number and determining if one value of the message packet number appears a majority of times.

39. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line, and

a second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

a method of creating substantially identical simultaneously interactive displays at the two locations comprising the steps of;

continuously receiving display instructions at said first terminal from said first input means and said first communication buffer and implementing such instructions on said first display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed,

communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information displayed,

continuously receiving display instructions at said second terminal from said second input means and said second communication buffer and implementing such instructions on said second display means upon receipt thereof, said instructions specifying a change in the information to be displayed by said display means and a location of said change in the information displayed, and

communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information displayed,

wherein said first and second terminals are controlled by functionally similar programs each of which is executing asyncronously at a different one of the terminals,

whereby the same display is generated and updated substantially simultaneously at each of said first and second terminals.

40. A communication system for operating at a plurality of locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a functionally similar second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

means at said first terminal for continuously receiving display instructions from said first input means and said first communication buffer and for implementing such instructions upon receipt thereof, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information to be displayed,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information to be displayed,

means at said second terminal for continuously receiving display instructions from said second input means and said second communication buffer and for implementing such instructions upon receipt thereof, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information to be displayed, and

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information to be displayed,

whereby the same information is generated and updated substantially simultaneously at each of said first and second terminals.

41. A communication system for operating at two locations comprising:

a first terminal at a first of said locations comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a full-duplex communication line, and a first means for transmitting information via the full-duplex communication line,

a functionally similar second terminal at a second of said locations comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information via said communication line,

means at said first terminal for repeatedly polling said first input means and said first communication buffer for display instructions and for implementing such instructions upon receipt thereof,

means at said first terminal for communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line,

means at said second terminal for repeatedly polling said second input means and said second communication buffer for display instructions and for implementing such instructions upon receipt thereof,

means at said second terminal for communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line,

a central processor at said first terminal operating under a stored program and controlling said first display means, said first input means, said first communications buffer, said first transmitting means, said polling means, and said communicating means,

a central processor at said second terminal operating under a stored program and controlling said second display means, said second input means, said second communications buffer, said second transmitting means, said polling means, and said communicating means, said stored programs under which the first and second terminals operate being functionally similar,

whereby the same information is generated and updated substantially simultaneously at each of said first and second terminals.

42. In a communication system comprising:

a first terminal at a first location comprising a first interactive display means, a first local input means for input of information to be displayed by said first display means, a first communications buffer for receiving information from a communication line, and a first means for transmitting information to a second location via the communication line,

a functionally similar second terminal at a second location comprising a second interactive display means, a second local input means for input of information to be displayed by said second display means, a second communications buffer for receiving information from said communication line, and a second means for transmitting information to said first location via said communication line,

a method of generating substantially identical information at the two locations comprising the steps of;

continuously receiving display instructions at said first terminal from said first input means and said first communication buffer and implementing such instructions upon receipt thereof, said instructions specifying a change in the information to be displayed, and a location of said change in the information to be displayed,

communicating display instructions entered at said first input means to the communications buffer of the second terminal via the communication line, said instructions being communicated upon receipt from said first input means, said instructions specifying a change in the information to be displayed by the second display means and a location of said change in the information to be displayed,

continuously receiving display instructions at said second terminal from said second input means and said second communication buffer and implementing such instructions upon receipt thereof, said instructions specifying a change in the information to be displayed and a location of said change in the information to be displayed, and

communicating display instructions entered at said second input means to the communications buffer of the first terminal via the communication line, said instructions being communicated upon receipt from said second input means, said instructions specifying a change in the information to be displayed by the first display means and a location of said change in the information to be displayed,

whereby the same information is generated and updated substantially simultaneously at each of said first and second terminals.