Possible to modify VNC for screen-broadcast teaching?

[Dries Feys]

This is allready implemented, with the vnc listener deamon.  The only thing 
I encounter, is that vnc may start up several clients if he gets several 
triggers from the 'master' computer.


-----Original Message-----
From:	David Griffiths [SMTP:dgriff "at" direct.ca]
Sent:	Thursday, June 01, 2000 1:18 AM
To:	vnc-list "at" uk.research.att.com
Subject:	Possible to modify VNC for screen-broadcast teaching?

Just wondering if anyone had any ideas on modifying VNC to act as a screen
broadcaster for teaching applications.  For example, here's the situation
I'm in:

I have 25 workstations in a lab (running NT 4), and an instructor's 
position
at the front of the room.  Currently we're using a dated old video 
projector
which has low resolution, and isn't particularly easy to see from the back
of the room.  For applications like teaching photoshop where small icons 
and
such must be utilized, it's a real pain.

Ideally, what I'd love to see (or pay for - hint hint ;P):
----------------------------------------------------------
A type of VNC which could be set to broadcast from one machine (in this
case, the instructor's machine), to a set IP range (or list of IP
addresses).  Meanwhile, clients are running a modified viewer routine in 
the
background, which is listening for an "activate" packet.

The instructor hits their "send" hotkey, which transmits an "activate
packet" which is hashed with the correct password to all of the machines in
the range/block.

When the packet is received by a client, the client program takes control 
of
the student's machine (which is to say, like a screen saver, disables all
keyboard/mouse input), and shows whatever image the instructor's server is
broadcasting.  When the instructor finishes, they release the clients (with
their hotkey), and the students get their individual machines back.

Some considerations I see in this are:

- Instructor's image sent to all computers at a high resolution, making it
easy to see small details which are difficult to observe on an overhead.

- Instructor and student machines basically run modified versions of VNC,
and as such, cross-platform development for teaching on UNIX, Mac, Windows
should be easy to implement.

- Client machines are (optionally) locked on whatever the instructor is
teaching at the time, preventing task switching, and mouse/keyboard inputs,
so students can't be checking email, playing games, chatting, etc when a
class is in session.  Ideally, two share modes could be implemented - one
which completely locks out student access while the share is on, and the
second which allows task switching and student input so they can follow
along while being taught.

- To get student's undivided attention, share a blank-screen to all of the
client computers ;P

- Clients should have a configurable address (or range) that they will
accept server connections from so in the event that the server is
compromised by students, only a set number of clients would be effected.

- Hashing an activation code with a password when sent to clients, should
help prevent troublemakers from sharing screens from their own machine and
disrupting other students.

- After a configurable network timeout (30 sec for example) without a
broadcast packet, clients should time-out and return control of the 
computer
to the student (incase the server crashes, for instance).

Any thoughts, comments, offers of coding? ;P

I had this thought after seeing Norton Ghost run in "broadcast ghost" mode,
to reduce network usage.  Seems very effective.

Dave.
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