Software Terminal Switch for Teleconferencing

Simulating a crossbar switch in programming permits a number of terminals to be connected together so that the output from any application program is seen at all terminals and input may be made from any sequence of terminals, appearing to the application program as if from a single terminal. The figure shows the Software Terminal Switch For Teleconferencing (STSFT) crossbar matrix switch: Each terminal Tx is associated with a STSFT Logical Terminal Session Sy. The X indicates the logical connection between the terminals and the Logical Terminal Session. This connection is created, maintained and terminated by the STSFT. How STSFT works 1. STSFT is a subsystem which is imbedded in a larger system. The system (or front end) in which STSFT resides is responsible for managing all functions not included in the STSFT. These include (but are not limited to): I/O, time and other interrupts. Issuing STSFT requests for creation, maintenance and termination of STSFT sessions through the use of STSFT commands. Presenting the context, or interactive dialog, for systems using the STSFT. For example, the CVIEW Program Product uses a front end to present menus which retrieve information necessary to connect two users' terminals into a single STSFT session. 2. STSFT provides commands for: STSFT session creation with session attributes (e.g., terminal type for the Logical Terminal Session). Add terminals to a STSFT session. Delete terminals from a STSFT session. Modify a STSFT session parameter (e.g., terminal type for the Logical Terminal Session). Initiate a Logical Terminal Session for a defined STSFT session. Terminate a Logical Terminal Session for a defined STSFT session. STSFT session deletion - remove the association between the terminals and the Logical Terminal Sessions. Suspend and resume processing of interrupts from a specific or all active Logical Terminal Sessions. 3. The front end system can request the STSFT to process either of the following interrupt types: I/O requests: STSFT processes the terminal I/O request (i.e., issue a read command to the terminal). The results are presented to the application associated with the terminal by sending the data to the Logical Terminal Session system interface. Optionally, STSFT may update the output (e.g., screen or video display) of the other terminals in the session. The changes made by the terminal which cause the I/O request are copied onto the other terminals in the session. Application I/O requests: a.

Output from the application is written to all of the terminals in the session. b. A read request from the application causes STSFT to perform the read operation on the first terminal in the list of terminals associated with the session, and the result of the read is sent back to the application. Software Terminal Switch for Teleconferencing In the event that the terminals in a STSFT session are non-homogeneous (i.e., the terminals are not all 3277's, or all 3278's, etc.) STSFT provides a mapping of the device characteristics so the differences become transparent. For example, STSFT provides mappings so that 3277 and 3278 terminals may be in the same STSFT session even though the format of the data that is sent to and received from these terminal types is different. The cross-bar matrix allows multiple terminals to be attached to a single Logical Terminal Session. This permits two or more people to participate in interactive sessions for consulting, conferencing, teaching, demonstrations, computer operations, etc. No changes need be made to the application programs used in the interactive sessions. They still run as though there is only one terminal attached to the application. The software for STSFT is reusable for many different applications by replacing the front end of the system in which STSFT is used. By using the STSFT commands, terminals may enter or leave a STSFT session. This is done under the control of the front end which decides when to admit or remove a terminal from a session and issues appropriate commands to the STSFT cross-bar matrix switch. Because terminal I/O interrupts are handled by the front end, input from a terminal can be blocked so that the data from the terminal is not sent to STSFT. The application connected to the STSFT Logical Terminal Session, to which the terminal is connected, will not see the terminal input. This is particularly useful for some front ends where there is a desire to permit input from one or only a few of the terminals in a STSFT session. No changes need be made to the applications used in the inter active sessions established by STSFT. Also, no modifications are necessary to the operating system in which STSFT operates, provided that terminal I/O and Logical Terminal Session facilities are available. STSFT permits multiple simultaneous independent sessions. When half-duplex terminals are used, input from one terminal can be redisplayed on the other terminals in the session. STSFT does this, although it is optional. This "input redisplay" may be turned on or off at any time under the control of the front end. This mechanism permits the people at the other terminals in the STSFT session to see what was entered at the terminal which caused the interrupt. This is used particularly in demonstrations, consulting and other presentations where the input may be of interest to all parties in the session.