Terminal device session management protocol

• US 5,165,020 A
• Filed: 10/11/1991
• Issued: 11/17/1992
• Est. Priority Date: 03/27/1987
• Status: Expired due to Fees

• Current Assignee: CIT Group Incorporated
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Leichter, Jerrold S., Porcher, Thomas C., Sudama, Ram
• Primary Examiner(s): Kriess, Kevin A.
• Application Number:
  US07/777,430
• Time in Patent Office: 403 Days
• Field of Search: 395/200, 395/650, 395/700
• US Class Current: 709/227
• CPC Class Codes: G06F 15/161 Computing infrastructure, e.g. computer clusters, blade chassis or hardware partitioning casings, cabinets, racks or drawers for data centers H05K5/00
• CPC Class Codes: H04L 69/00 Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass networks security protocols H04L9/40; wireless communication networks H04W

Abstract

The invention provides a new and improved system for transferring information between a host system and a terminal system. A digital data processing system includes a host computer system which runs processors and a terminal system which is connected to the application host computer system over a communication link. The terminal system includes one or more virtual terminals each of which allows an operator to enter information and allows output information to be displayed. The association between a terminal device and an application process is a session. Initially, a session is selected by means of a command transferred over the communications link. Thereafter, information, associated with the selected session, may be transferred over the communication link. This may continue until another session is selected. This transfer system minimizes the amount of control information which is required to identify the particular session with which data being transmitted over the communications link is associated. Once a session is selected, it remains selected until another session is selected, after which the data transmitted is associated with the newly selected session.

Claims

1. A terminal system for interconnection with a host computer system, said terminal system comprising:

at least one virtual terminal;

means for receiving from said host computer system control commands, each of said commands identifying a selected one of said virtual terminals;

means for receiving from said host computer system following each of said commands information for use by said virtual terminals and in response to the terminal identification contained in each of said commands directing to said selected virtual terminal all said information which is received from said host computer until a control command indicating the direction of information to another one of said virtual terminals is received.

2. A terminal system for interconnection with a host computer system, said terminal system comprising:

at least one virtual terminal;

means for receiving from said host first control commands, each of which establishes a session involving the transfer of information to a specified one of said virtual terminals;

means for receiving from said host computer system second control commands each of which identifies a previously established session;

means responsive to each of said second control commands, for transmitting to said host computer system a credit command, specifying the amount of information that said terminal system can receive without interruption; and

means for receiving from said host computer system information for use by said virtual terminals and in response to the identification of a session in said second control command directing to the virtual terminal specified for that session, all said information received after the second control command until another second control command is received identifying another one of said sessions.

3. A terminal system for interconnection with a host computer system having at least one application process, said terminal system comprising:

at least one virtual terminal;

means for receiving from said host computer system terminal control commands, each terminal control command identifying a session involving a specific one of said virtual terminals;

means for receiving from said host computer system information for use by said virtual terminals, and in response to each of said terminal control commands, directing to the virtual terminal involved in the session identified by that command all said information received until another terminal control command identifying another session is received;

means for transmitting to said host computer system host control commands, each of said host control commands identifying a session involving a specific one of said application processes, and

means for transmitting to said host computer system information for use by said application processes and for transmitting to said host system, after each host control command is transmitted, only information for use by the application process involved in the session identified by that command, without further identification of that process, until another host control command identifying another session is transmitted.

4. A terminal system, having at least one virtual terminal, for interconnection with a host system, having at least one application process, via a session management link to effect the transmission of information between a selected virtual terminal and a selected application process, said terminal system comprising:

means for receiving the information and terminal session management commands, transmitted from said host systems via said session management link, said terminal session management commands including terminal select session commands each of which identifies a session involving a specific one of said virtual terminals, and

means for responding to each of said terminal select session commands by directing to the virtual terminal involved in the session identified in that command all said information received after said command is received until another terminal_-- select session command identifying another session is received.

5. The terminal system defined in claim 4 further comprising:

means for transmitting to said host system via said session management link host session management commands, including host select session commands each of which selects a session involving a specific one of said application processes at said host system; and

means for transmitting to said host system after each transmitted host select session command only information for use by the application process involved in the session selected by said transmitted select session command, without further identification of that process, until another host select session command selecting another session is transmitted.

6. The terminal system defined in claim 5 further comprising means for transmitting a terminal session transmit credit command to said host system via said session management link, said terminal session transmit credit command defining a number of terminal transmit credits representative of the amount of information said terminal system can accept from said selected application process without interruption.

7. A terminal system, having at least one virtual terminal, for interconnection with a host system, having at least one application process, via a session management link to thereby effect the transmission of information between a selected virtual terminal and a selected application process, said terminal system comprising:

means for transmitting to said host system via said session management link host session management commands, including host select session commands each of which identifies a session in which a specific application processes at said host system receives information; and

means for transmitting to said host system after each transmitted host select session command information only for the application process specific to the session identified in that command, without further identification of said process, until another host select session command identifying another session is transmitted.

8. A terminal system, having at least one virtual terminal, for interconnection with a host system, having at least one application process, via a session management link to effect the transmission of information between a selected virtual terminal and a selected application process, said terminal system comprising:

means for receiving the information and terminal session management commands, transmitted from said host systems via said session management link, said terminal session management commands including

1) terminal open session commands each of which defines a session comprising an interconnection for transmitting information from a selected application process to a selected virtual terminal, and

2) terminal select session commands each of which identifies a previously defined session in which a virtual terminal is to receive information

means for storing identifications of the selected virtual terminals in association with identifications of the sessions to which they relate;

means responding to each of said terminal select session commands and the contents of said storage means for directing to the virtual terminal associated with the session identified by that command all information received after the receipt of that command until another terminal select session command identifying another of said sessions is received;

means for transmitting to said host system, host session management commands including

1) host open session commands each of which defines a session comprising an interconnection for transmitting information from a selected virtual terminal to a selected application process, and

2) host select session commands each of which identifies a previously defined session in which an application process is to receive information; and

means for transmitting to said host system after each transmitted host select session command only information for the application process associated with the session identified by that command, until another host select session command identifying another session is transmitted.

9. A terminal system for interconnection with a host computer system by a session management link, said terminal system having at least one virtual terminal and said host computer system having at least one application process, said terminal system comprising means for transmitting to said host computer system host open session commands each of which defines a session with a specific one of said application processes at said host computer system and host

select session commands each of which selects a previously defined session to be active, and means for transmitting to said host computer system following each of said transmitted host select session commands only information for the application process associated with the session selected by that command to be active until another host select session command selecting another one of said sessions is transmitted.

10. A terminal system for interconnecting with a host system by means of a session management link, said terminal system including a plurality of virtual terminals and said host system having at least one application process, said terminal system comprising

a) means for receiving from said host systemterminal session management commands, each of said terminal session management commands identifying a session in which a specific virtual terminal receives information from an application process, and

information for the specific virtual terminal at said terminal system without further identification of said identified virtual terminal, and

b) means directing all said information subsequent to a terminal session management command to the terminal specific to the session identified in that command at least until the completion of the transmission of information in the identified session.

11. The terminal system defined in claim 10 including means for

a) transmitting to said host system host session management commands including host select session commands each of which identifies a session involving an application process at said host system which is to receive information from a virtual terminal and

b) following each host session select command with the transmission to said host system of information only for the application process involved in the session identified in that command without further identification of that application process prior to the completion of said transmission of information.

12. A terminal system for interconnection with a host computer system by a session management link, said terminal system having a plurality of virtual terminals and said host computer system having at least one application process, said terminal system comprising:

means for receiving from said host computer system via said session management link (1) a plurality of terminal session management commands, each of said terminal session management commands identifying a session involving a specific one of said virtual terminals, and, (2) following each of said commands, information for use by the specific virtual terminal, without further identification of said virtual terminal and;

means for directing said information which is received subsequent to the reception of a terminal session management command to the specific virtual terminal until the completion of the transmission of said information.

13. The terminal system defined in claim 12 further comprising:

means for transmitting to said host computer system host session management commands each of which identifies a session involving a specific one of said application processes at said host computer system, and transmitting to said host system following each of said transmitted host session management commands information only for the application process involved in the session identified in that command until another host session management command identifying another session is transmitted.

14. The identified virtual terminal defined in claim 12 further comprising means for transmitting to said host computer system a credit command specifying the amount of information that said terminal system can receive without interruption.

15. The terminal system defined in claim 14 further comprising means for transmitting to said host computer system during reception of said information further credit commands specifying increases in the amount of information that said terminal virtual terminal can receive without interruption.

16. The terminal system defined in claim 13 further comprising:

a) means for receiving and storing a transmitted credit count representing the amount of information that said host computer system can receive without interruption,

b) means for incrementing said stored count in accordance with additional credit counts received from said host computer system,

c) means for decrementing said stored count in accordance with the amount of information transmitted to said host system, and

d) means for inhibiting transmission of information to said host system when said stored count equals zero.

17. A method for interconnecting a terminal system with a host computer system by a session management link, said terminal system having at least one virtual terminal and said host computer system having at least one application process, said method comprising the steps of:

receiving from said host computer system via said session management link a plurality of terminal session management commands, each of said terminal session management commands identifying a session in which a specific virtual terminal receives information from an application process, and information for specific virtual terminals without further identification of the specific virtual terminals, and;

directing said information which is received subsequent to the reception of a terminal session management command to the virtual terminal specific to the session identified in that command at least until completion of the reception of information in the identified session.

18. The method defined in claim 17 further comprising the steps of:

transmitting to said host computer system host session management commands including host select session commands each of which identifies a session involving an application process, at said host computer system, which is to receive information from a virtual terminal; and

following each host session select command with the transmission to said host system of information only for the application process involved in the session identified in that command without further identification of that application process prior to the completion of said transmission of information.

19. The method defined in claim 17 further comprising the step of transmitting to said host computer system a credit command specifying the amount of information that said identified virtual terminal can receive without interruption.

20. The method defined in claim 19 further comprising the step of transmitting to said host computer system during reception of said information further credit commands specifying increases in the amount of information that said identified virtual terminal can receive without interruption.

21. The method define in claim 18 further comprising the steps of:

a) receiving and storing a transmitted credit count representing the amount of information that said host computer system can receive without interruption,

b) incrementing said stored count in accordance with additional credit counts received from said host computer system,

c) decrementing said stored count in accordance with the amount of information transmitted to said host system, and

d) inhibiting transmission of information to said host system when said stored count equals zero.

22. A method for interconnecting a terminal system with a host computer system having at least one application process, said method comprising the steps of:

transmitting to said host computer system host session management commands, each of which identifies a session involving a specific one of said application processes; and

transmitting to said host computer system following each of said transmitted host session management commands information only for the application process involved in the session identified in that command until another host session management commands identifying another session is transmitted.

23. A method for interconnecting a terminal system, having at least one virtual terminal, with a host system, having at least one application process, via a session management link to effect the transmission of information between a selected virtual terminal and a selected application process, said method comprising the steps of

receiving information and terminal session management commands, transmitted from said host system via said session management link, said terminal session management commands including

terminal open session commands each of which defines a session comprising an interconnection for transmitting information from a selected application process to a selected virtual terminal, andterminal select session commands each of which identifies a session in which a virtual terminal is to receive information

storing identifications of the selected virtual terminals in association with identifications of the sessions to which they relate

responding to each of said terminal select session commands and the contents of said storage means for directing to the virtual terminal associated with the session identified by that command all information received after the receipt of that command until another terminal select session command identifying another of said sessions is received;

transmitting to said host system, host session management commands including

1) host open session commands each of which defines a session comprising an interconnection for transmitting information from a selected virtual terminal to a selected application process, and

2) host select session commands each of which identifies a previously defined session in which an application process is to receive information; and

transmitting to said host system after each transmitted host select session command only information for the application process associated with the session identified by that command, until another host select session command identifying another session is transmitted.

24. A method for interconnecting a terminal system with a host computer system by a session management link, said terminal system having at least one virtual terminal and said host computer system having at least one application process, said method comprising the steps of transmitting to said host computer system host session open session commands each of which defines a session with a specific one of said application processes at said host computer system and host system select session commands each of which selects a previously defined session to be active, and transmitting to said host computer system following each of said transmitted host select session commands only information for the application process associated with the session selected by than command to be active until another host select session command selecting another one of said sessions is transmitted.

25. A method for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said method comprising the steps of:

transmitting to the host system a first control command requesting the establishment of a session management link;

receiving from the host system a second control command indicating that the host system has at least one application process open;

responding to said received second control command from the host system, by transmitting to the host system a third control command requesting the re-establishment of the previous session management link, and;

receiving from the host system a fourth control command enabling the terminal command to re-establish the session management information so that subsequent information received from the host system is directed to the proper virtual terminal.

26. A method for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said method comprising the steps of:

receiving from the host system a first control command for initiating the re-establishment of the session management link and the session management information;

receiving from the host system a second control command identifying at least one virtual terminal corresponding to at least one open application process at the host system, and;

re-establishing the session management information, for the session management link, so that subsequent information received from the host system is directed to the proper virtual terminal.

27. A method for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said method comprising the steps of:

receiving from the host system a first control command requesting a session management link be established;

transmitting to the host system a second control command indicating the terminal system has at least one virtual terminal open, and;

transmitting to the host system a third control command indicating which application process corresponds to each open virtual terminal.

28. Apparatus for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said apparatus comprising:

means for transmitting to the host system a first control command requesting the establishment of a session management link;

means for receiving from the host system a second control command indicating that the host system has at least one application process open;

means for responding to said received second control command from the host system, by transmitting to the host system a third control command requesting the re-establishment of the previous session management link, and;

means for receiving from the host system a fourth control command enabling the terminal system to re-establish the session management information so that subsequent information received from the host system is directed to the proper virtual terminal.

29. Apparatus for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said apparatus comprising:

means for receiving from the host system a first control command for initiating the re-establishment of the session management link and the session management information;

means for receiving from the host system a second control command identifying at least one virtual terminal corresponding to at least one open application process at the host system, and;

means for re-establishing the session management information, for the session management link, so that subsequent information received from the host system is directed to the proper virtual terminal.

30. Apparatus for re-establishing a session management link between a host system and a terminal system when session management information required for the session management link is lost, the host system having at least one application process and the terminal system having at least one virtual terminal, said method comprising:

means for receiving from the host system a first control command requesting a session management link be established;

means for transmitting to the host system a second control command indicating the terminal system has at least one virtual terminal open, and;

means for transmitting to the host system a third control command indicating which application process corresponds to each open virtual terminal.