Possible to modify VNC for screen-broadcast teaching? (drifting off topic)

[Wayne Throop]

::: There is a real need for software that can handle these functions. 
::: Currently the only good solutions are expensive hardware systems
::: (running US$20,000 - $30,000 for a 25-workstation lab). 

:: Are you including the 25 workstations in that price

: That does not include the workstations! The price is based on the
: going rate for systems like "TechCommander" that are complete
: solutions (including installation and profit margin, so there's a good
: chunk of the money).  These systems also control the client computer's
: keyboard and mouse, so there is some additional hardware at each
: workstation and a master control/touchscreen device at the
: instructor's podium to control the beast, and of course the cost of
: wiring the room.  They allow instructor to all students, instructor to
: individual students, student to instructor, and student to student
: viewing (and keyboard/mouse control). 

I see; what I experienced was nowhere near such a complete solution,
and hence was probably far less expensive as I suspected it might be.

: VNC (or NetOp School) could never be a complete replacement, but the
: price difference makes it far more than worthwhile to live with the
: drawbacks of a software solution. 

But I'm still puzzled here... are you saying that a software-only
solution on standard hardware and LAN could never compete with
custom hardware and such?  That doesn't seem reasonable; I don't
see anything in your list that an extended VNC servers and viewers
couldn't do.  Could you explain this bit a little more?

Mind you, I can certainly see why VNC now, and VNC with trivial mods,
doesn't compete on anything near equal terms; but why "NEVER compete"?

(I'm probably misinterpreting what you mean...)

: Thanks for the suggestions, but please also excuse my ignorance. 
: Other than for a thread here concerning capturing VNC sessions (which
: I've been ignoring), I've never heard of rfbproxy.  Can you point me
: to some more info? 

Well, you're right; rfbproxy hasn't made its way into the web pages
or the default release yet.  You'd have to do a search of the
archived mailing list, and contact somebody for the source.

If you want to stick with off-the-shelf stuff from the VNC release,
you can make a fan-out buffer out of a vncviewer plus a vncserver process,
under unix.  It's a horrible waste of codespace compared to rfbproxy,
since between the vncviewer and vncserver things get translated to
X protocol and back to rfb protocol, and this is horribly inefficient,
not to mention that most of the X protocol will never be invoked so
most of the code in the vncserver remains idle.  But it should work,
with just a bit of scripting.

By "a vncviewer plus a vncserver process", I mean something like this
(only specifying relevant arguments; some other stuff would probably
need to be filled in):

      Xvnc :1 & sleep 10
      vncviewer -display :1 -shared -viewonly -fullscreen teacherconsole:0

Starting several of these against teacherconsole would be the only clients
the teacher's server would need to handle; then each of the Xvnc desktops
could serve several student clients, hence, you could serve several times
as many student clients as would crash the teacher's server, and quite
possibly get the updates out to student screens faster (depending on
the horsepower available on the box running the above buffering
processes).

In theory.  And it's worth remembering the motto of the Acme Corporation
(supplier of fine gadgetry to coyotes for over a half-century)

        "Acme Corporation.  Products that work.  In theory."

I've tried it out for small cases (two clients to the teacher,
two students to a buffer) as proof of concept.  Haven't measured 
how it scales.  YMMV.


Wayne Throop   throopw "at" sheol.org
               http://sheol.org/throopw
---------------------------------------------------------------------
To unsubscribe, send a message with the line: unsubscribe vnc-list
to majordomo "at" uk.research.att.com
See also: http://www.uk.research.att.com/vnc/intouch.html
---------------------------------------------------------------------