Re: [Linux-decnet-user] naive LAT question regarding speed

[Mats M. <mat...@te...>]

On Sat, 20 Aug 2005 17:12:08 +0100
Patrick Caulfield <pa...@ty...> wrote:

> Zube wrote:
> > On Fri Aug 19 07:45:19 AM, Patrick Caulfield wrote:
> > 
> > 
> >>Could you tell me more about what you are doing? I know that
> >"reverse" >LAT is slower by about a factor of 1.8 or so but I've
> >never heard of >those sort of orders of magnitude. Normal terminal
> >access, in my >experience, is limited by the speed of the serial line
> >between the >terminal and the server.
> > 
> > 
> > Thanks for getting back to me.
> > 
> > The setup is a few dumb terminals (and a couple of scanners attached
> > to dumb terminals) hooked to a DecServer 200.  The logins on the
> > Debian Thinkpad machine automatically rlogin to another machine
> > where the programs are run, but I don't believe the problem is
> > between the Thinkpad and the remote machine.
> > 
> > For example, when I do:
> > 
> > c linux 
> > 
> > from the local prompt, I immediately get a login prompt.  But for a
> > three character account, say abc, typed immediately after the prompt
> > appears, the sequence appears this way:
> > 
> > ab <delay> c
> > 
> > Another example:  There is a program that is "downloaded" to a
> > scanner attached to a dumb terminal.  The code is displayed on the
> > screen as it is processed by the scanner.  When the DECStation was
> > in place, the code scrolled by at a regular, if unimpressive, clip;
> > now, it scrolls at the same unimpressive clip for a few lines and
> > then stops for several seconds, then continues for a few more lines
> > and stops, etc.  It all works, but the hangs make it tough to work
> > with.
> > 
> > Perhaps I will try to put Debian + the lat software on a different
> > machine. I've seen stranger things occur with Thinkpads; it was just
> > a very convenient choice.
> > 
> 
> Hmm, that sounds very odd. I use LAT regularly and have never seen
> that sort of slowdown and I run my connections at speeds faster than a
> DS200 can even dream of !
> 
> Check that the DS200 has the latest firmware installed, I did have
> some problems with old versions. Unfortunately my DS200 has now died
> and I can't remember the version I was using - I do still have the
> download image though :-)
> 
> It might also be worth checking that there isn't execssive packet loss
> - I suspect my code that copes with that may not be optimal. It would
> be interesting to see if similar problems occur on another Linux
> machine.

I have seen almost this kind of problems but using ordinary TCP/IP
between a few machines.

It turned out that I was using an old ethernet bridge to connect my
first tp-only ethernet interface to the bnc ethernet I was using at that
time, and when using fast enough ethernet cards in both ends (some tulip
21143 motherboard interface on the tp only machine, and 3c509 on the
other machine) the ethernet bridge didn't handle direction switching
fast enough, so the first packet arrived correctly but then either the
ack or the next packet (don't remember which or if both happened) didn't
get thorug correctly so there were a timeout delay each time i sent more
than a MTU of data. So, telnet and using ordinary commands worked fine
but for exampe ftp took ages. When transfering data between the machine
with tp interface and a machine with an older smc/wd8003 8-bit isa
interface everything worked fine, and all other directions of data
worked fine also. After replacing the old ethernet bridge with tp+bcn
transcievers and the crossed tp cable with a new tp+bnc hub all problems
disappeared.

Perhaps something similar happends. I don't have that much knowledge of
the LAT ptorocol, if LAT sends more than one packet + ack for each typed
character it could be this kind of problem.

I don't know if there is a way to delay every outgoing ethernet packet
in linux. If there is, try that.