[FreeNX-kNX] NX in higher latency environment

[Mario Becroft]

ford prefect <fpmailinglists at googlemail.com> writes:

> Using a WAN emulator (WanEm) with DSL Settings (Speed: 1024/256 kb/s, Latency:
> 300ms, Packet Loss: 0,1%) it was quite bad, using NX in comparison to Citrix.
> When moving windows arond, there is a quite noteble delay which makes it hard
> to drop windows where you want it. Also writing and clicking around seems to be
> handled worse then in Citrix. Using connection delay's < 180ms there are not
> really notable differences between Citrix and NX. >180ms, Citrix seems to be
> more usable for me.

Nx essentially eliminates client-server round trips, which are normally
a major problem with X11 on high-latency links, and heavily compresses
and caches data. From what I have seen it is very effective as far as it
goes.

I haven't used Citrix much but I am not sure what else it could do to
improve performance in high latency conditions. I know it has a feature
called speedscreen where it can paint characters locally in response to
keypresses. This doesn't sound all that useful to me in practice, since
if you are touch typing then you normally don't care about a 300ms delay
in reading the characters on-screen. Still, it could give the impression
of being faster. That said, I think this feature is available only on
the Windows version of Citrix anyway.

You mentioned moving windows. Obviously this will require a round-trip
to the server (assuming the window manager is running on the remote
system). Unless Citrix is highly integrated with the remote window
manager and able to do something ultra clever, like moving the window
around locally, I don't see how it could be any better in this
situation.

Or could it be that in the Citrix configuration, your window manager is
running locally? This would account for a huge difference in the
responsiveness of moving windows, but if you tried doing something that
interacts with the application, like, say, popping up a menu or opening
a new window, this would incur the full link latency. If so, then
running nx in the same configuration should achieve similar results.

Perhaps you could do some more testing to pin down exactly what is
faster in Citrix?

I would have thought that with latency in the region of 300 ms, any
highly interactive application is going to get clumsy to use. I don't
think there is much you can do about that, sadly, without an approach
completely different to that of any current windowing system (or
discovering an as-yet unknown law of physics).

Our users report that nx is quite good over a link with 250 ms rtt, but
I reckon that is pushing it. Obviously, it depends on what you are
doing. Reading a few web pages and doing some word processing will be
less critical than, say, doing CAD work.

-- 
Mario Becroft <mb at gem.win.co.nz>