[plug] X over a Modem

[Nick Bannon]

On Wed, Jun 21, 2000 at 03:12:04PM +0800, Brad Campbell wrote:
> Allright, I know this is old hat to all you linux (UNIX) guru's
> but I have to say how impressed I am at getting my first remote
> X session running lastnight.
[...]

Congratulations! Now you can appreciate how much faster a command
line is! ::-)

Yes, it works, but modems are slow devices: low bandwidth _and_ the
real killer - high latency (~150ms). X assumes that it's "fast" to
send messages between the client and the server all the time, which
is why it works well over an ethernet (~1ms), almost passably over
64k ISDN (~10ms) and painfully slowly over a modem.

What can you do to improve things?

 1. Tune the X protocol to be lighter across the network. Matt
mentioned the Low Bandwidth X proxy, and the LBX extension to X
is probably already in your X server (type "xdpyinfo" to get a list
of extensions and other intersting display information). Peter
mentioned DXPC which does a similar job.

 2. Data compression. Your modem probably does this with V42bis, and
SSH can do it. It's not as "clever" as LBX or DXPC, and it can only
make the latency worse, but it can help a lot. SSH has other bonuses -
it can let your X connections get tunnelled, compressed and encrypted
back to you and _increase_ convenience. On a slow machine or a fast
network it can slow things down, though. Something like ;

bash-2.03$ hostname
roj
bash-2.03$ echo $DISPLAY
:0
bash-2.03$ ssh -C -X spark.plug.linux.org.au
nick at spark.plug.linux.org.au's password: 
[...]
nick at spark:~$ echo $DISPLAY
spark:10.0
nick at spark:~$ xauth list
spark.tld:10  MIT-MAGIC-COOKIE-1  b69ddcfbbd8019a06d28c0b9d625db09
spark/unix:10  MIT-MAGIC-COOKIE-1  b69ddcfbbd8019a06d28c0b9d625db09

If I were to run an xterm on spark, it'd connect to the new "display"
spark:10.0, which SSH is tunnelling back to my box. SSH has already
set up the authentication for that connection.

 3. VNC (like PC Anywhere, or RSM, or some others) - basically sends
(parts of) screenshots backwards and forth. "this area changed, here's
what it looks like now", "the mouse was clicked here". This is better
over a high latency link, but X is usually better over an ethernet.

 4. Use SSH (or telnet/rlogin). You might not be able to use Netscape,
but you can use lynx. Might not be able to use GNOME, but you can
still copy and paste. <grin>

Nick.

-- 
  Nick Bannon  | "I made this letter longer than usual because
nick at it.net.au | I lack the time to make it shorter." - Pascal