Instead of a projected video image of the Mosaic documents, the computer screen of each machine in the room displayed the demonstration in real time. The software used to accomplish this was XMX, a unix-based computer conferencing program developed at Brown which is freely available . XMX allows any program which uses the X Window System to display itself on many workstations simultaneously.
Though a local operator was employed to run the demonstration at Brown, the presenter could have controlled it remotely, adding gestural communication using the mouse for the presentation. Tests established that this would work, but it was judged too risky to try in front of an audience, given the vagaries of the Internet, and because remote control added some significant delays.
Therefore we found it important to transfer large image, sound, or video files as well as data or programs to the presentation site before the actual presentation takes place, say, the night before. This takes into account the situation in underdeveloped countries with slow mail (otherwise transparencies could be sent by Next Day Mail) and unreliable telephone systems. Even on a relatively fast link like the one that was used between the conference site at Brown University and the University of Illinois at Urbana-Champaign it would not have been feasible to access the visuals in realtime across the network.
When we did experiments with XMX that would also allow the operator to present
the visuals
interactively by simultaneous display on the screens at the conference site
and at the remote site of the presenter. We found that there was a considerable
difference in the delay for displaying even a moderately sized visual depending
on wether it is also viewed by the presenter across the network, or if we have
a local operator who displays the visuals on site while the presenter displays
the same files at the same time (but not simultaneously) on his/her
workstation or PC,
loaded from a local medium. For the images that we tested the difference was
for a display across the network. During a
is tolerable and can be filled
with spoken text, but more than
delay seems to disrupt the presentation.
The situation is much easier, of course, when the presentation does not require
the display of large files but only formatted text and line drawings in PostScript.
