Network load

[W. Brian Blevins]

Jonathan,

> Date: Tue, 28 Mar 2000 11:27:35 -0600
> From: "Jonathan A. Leonard" <jonathan "at" planet-neptune.com>
> Subject: Network load
> 
>         Hello, I am very new to VNC and am wondering if there are any general
> statistics about network load.  My sniffer is down for the moment- do
> any of the docs cover this issue on the site?

I'm not aware of any documentation on this.  However, consider
for a moment that the specific amount of data transferred
depends to a large extent on the following factors:

  - screen resolution on the server and depth requested by viewer
  - applications in use on the server (gimp/Photoshop very demanding)
  - desktop background (solid colors encode/compress best)
  - user behavior (exposing windows causes traffic)

For this reason, analyzing the network load in one environment
will not be very applicable to another environment.

By using the Hextile encoding, you can get reasonable
compression of the screen data with very low CPU utilization.
Typically, the compression ratio runs from 10-20 to 1.  So,
a single, complete update of an 8bit 800x600 rectangle/screen
might require approximately, 800 * 600 / 15 = 32,000 bytes
on the network.  Of course, this depends greatly on the actual
complexity of the screen data being encoded and transmitted.
Scanned images often compress at less than 5 to 1 and solid
background colors often compress at better than 100 to 1.

If network traffic is critical in your environment, you can use
standard lossless compression mechanisms (like zlib in SSH or as
an internal modification) to trade extra CPU utilization on the
server/viewer for less traffic on the network.  My work with
zlib encoding indicates roughly twice the compression ratio
provided by hextile which means about half the network traffic.
Of course, the compression algorithm itself takes time to run
and will actually degrade performance as seen by the user on
faster networks.

> 
>         Thanks,
> 
>                 Jonathan
> 

-- 
Brian 
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