zlib compression on local LAN?

[Kelly F. Hickel]

Jonathan,
	Thanks for your response.  I'm following up because I should have
mentioned that both machines in this case are running windows 2000.

-Kelly

-----Original Message-----
From: Jonathan Morton [mailto:chromi "at" cyberspace.org]
Sent: Thursday, June 29, 2000 8:10 AM
To: vnc-list "at" uk.research.att.com
Subject: Re: zlib compression on local LAN?


>Hi All,
>	Does anybody have any opinion (HA!) as to using zlib compression on
>a local LAN?  I have two fast machines that are connected by a 100mbps
>switch on my desk.  I've noticed that when one is vnc'ing the other that
the
>server machine's screen updates slow noticeably.  Now, I understand that
>this is because I'm inserting a network operation into the video stream,
so,
>of course it's going to slow down.  My question is, Do you think the
>slowdown is primarily CPU bound (catching the update, hextile'ing it, etc)
>or is it network latency?  Since these are fast machines, I'd hope (but am
>to lazy to try right now!) that the CPU overhead of the zlib compression
>would impose a lesser load on screen updates than the network transmission
>does.

It's more likely to be the server being slowed by an inefficient VRAM->CPU
transfer rate, as is found in many PC-type graphics systems (CPU->VRAM
being much more heavily optimised).  Zlib normally introduces _more_
latency on fast LAN networks, due to the added CPU overhead compared to the
virtually non-existant network latency itself.

Also, try switching off Hextile and use RRE, CoRRE et al instead - Hextile
can sometimes be slow to decode, although it is very fast and efficient to
encode.

--------------------------------------------------------------
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.

Get VNC Server for Macintosh from http://chromatix.autistics.org/vnc/

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