Bandwidth

[Jonathan Morton]

>> Also, if you plan to use an X terminal as a viewer, bear in mind that X
>> traffic consumes many times as much bandwidth as VNC traffic, and X
>> terminals tend to be slow anyway unless they are running directly on the
>> Linux/UNIX machine the X server is running on.  Personal experience there.
>
>I'm sorry but what do you mean by an X terminal as a viewer?  Do you mean a
>"dumb terminal" but with X capability?  Also you mentioned that X traffice
>consumes more bandwidth than VNC.  I had been thinking about running X-win
>pro, an X window server for Windows.  So by default would that mean VNC is
>faster?

Yes, a dumb X terminal, such as the NeoWare NCs we have here in Lancaster.

X window 'servers' for platforms other than *ix's tend to be slower, less
fully featured, and more prone to errors than native X servers.  VNC can
get around that problem by running the full X environment on the UNIX/Linux
machine and sending the graphics via VNC protocol.  VNC uses compression
methods to send graphics, wheras X usually doesn't.  X also relies on some
graphics processing that is done at the terminal end, which would make
486-class machines very slow - VNC doesn't have such high CPU requirements.

The excess bandwidth requirements of X mean that fewer connections could be
active simultaneously than on VNC - I would not like to be the person
running 6 X terminals from a 10baseT line, but I could easily contemplate
running a couple of dozen VNC sessions over the same link.  As I mentioned,
VNC can run fairly well across a modest modem, wheras X probably wouldn't.

What I really meant there was that running the UNIX version of vncviewer,
then viewing the X desktop on a 'dumb X terminal' would be particularly
wasteful - 64 bytes of VNC traffic may typically expand to a kilobyte
(estimated) of X traffic when put through the X environment.  This is
partly an artifact of the way the UNIX vncviewer decodes and displays the
Hextile encoding normally employed by VNC servers, and I've already made
note of this and pointed it out to the developers on this list (there are,
i think, more efficient ways of displaying hextile using X, but I don't
have UNIX programming experience to do it myself).

You would be much better off running the VNC viewer directly on your 486s,
and running Xvnc, WinVNC server or MacVNC server depending on the
controlled platform.  You can experiment to find the best configuration for
your needs, and to find out how many sessions you can run comfortably (what
is your definition of 'comfortable' anyway?).  Given that VNC should run
effectively even over a 14.4k modem link given a correctly configured
system (for example, use a flat plain non-dithered backdrop), you should
have no difficulty running a largish number of sessions on a 10baseT
network.

Hope this helps,

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi "at" cyberspace.org  (not for attachments)
uni-mail: j.d.morton "at" lancaster.ac.uk

The key to knowledge is not to rely on people to teach you it.
--------------------------------------------------------------
Contributing to the VNC Project - http://www.uk.research.att.com/vnc/
Ask me for Macintosh VNCserver v3.3.2 beta2.1
v3.3.2 beta 2.2 due out soon!



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