Frederick [5] states that in classes of any size, visual reinforcements are vital in order to focus attention and to clarify the context of verbal presentations. In a traditional classroom environment, this is performed by pointing with a finger or any object on the chalkboard or the overhead projector. In our system, visual reinforcement is provided through an overlay chalkboard.
The professor has access to this overlay chalkboard, activated by the pen or the keyboard, to draw or write text on the electronic transparency. Any input action performed by the professor in the electronic transparency area is transmitted only to the server computer. Hence, if a professor writes on the transparency with the pen, the strokes will appear on the classroom screen and not on the students' computer screens as shown in figure 9. Furthermore, when the professor moves the pen close to the computer screen, a cursor is displayed on the classroom screen and moves accordingly; it is used as a pointing device to focus students' attention.
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| Fig 9. The electronic chalkboard |
The Ethernet frame format employed by the professor's computer to send pen events is illustrated in figure 10, without the preamble and the FCS.
| Destination Address | Source Address | Frame Type | Function Code | X Coordinate | Y Coordinate | Status |
| Server's Address |
Professor's Address |
FACEh | Integer PenP=510 |
Integer | Integer | Integer |
The X and Y Coordinate fields contain the actual coordinates when the pen is pressed on the screen. The Status field contains zero when the pen does not touch the screen, contains one when the pen touches the screen and contains two when the barrel button located on the side of the pen is pushed. When the server receives this type of packet, it multiplies by two the pen coordinates as the electronic transparencies are not displayed in the upper left-hand corner of the screen, but utilizes the entire screen to display the transparencies.
Any other input device commands are transmitted to all computers by the professor's computer disregarding the cursor position, and keyboard keys are only transmitted to the server's computer if they are typed on the current electronic transparency. The Ethernet frame format employed to send these function commands is illustrated in figure 11, without the preamble and the FCS.
| Destination Address | Source Address | Frame Type | Function Code |
| FFFFFF | Professor's Address |
FACEh | Integer LæProf Function Command |
When such a packet is received by the server or student's computer, the command found in the Function Code field is given to LæProf internal procedures to duplicate the function activated on the professor's computer.
The data flow occurring during pointing and emphasizing is shown in figure 12.
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| Fig 12. Pointing and emphasizing data flow |
