LAT drops info

[Matt Thomas]

> We are running a test application on a DECstation 5000 using the built-in
> Thinwire port and terminal servers for serial output.  Our test application
> involves writing data to 32 terminal server ports which have their serial
> ports looped directly to another 32 terminal server ports which are read
> into a file.  There is a process for each of the write tasks and a process
> for each of the read tasks for a total of 64 processing writing and reading
> as fast as possible.  Things begin to slow considerably on the DS5000 during
> the test.  The read processes put the correct number of bytes into the data
> files when running to the DECservers MOST OF THE TIME BUT NOT ALL OF THE
> TIME.

You really haven't given enough information to determine the problem.  How
do the programs set up the ports?  What speed are the ports set to?  etc.

Without that I can't begin to tell you where you're problem may lie though I
can probably guess.

> The read processes never put the correct number of bytes into the
> data files when running to the Xyplex servers (8-port cards in a rack).  This
> data loss seems to be load related because running fewer ports (32, 16, 8)
> provides NO data loss.  During the 64 port test to the DECserver 300, the
> DS5000 reports approx. 9000 frames received and 9000 frames transmitted over
> the course of 150 seconds or so using "lcp -c".  The same command run after
> a test of the 8-port cards in the Xyplex rack reports approximately 17,000
> frames.

I've never used Xyplex server so I can't say how good/bad their LAT
implementation is.  The frame count does seem excessive but that might be
just ineffeciency on their part with no protocol violations.  Note that if
Xyplex is less efficient than that means ULTRIX must process more LAT
messagess per character (than compared to a DECserver) which would result
in less overall throughput (and more data overruns).

> Is there a buffer associated with "lta" that may be getting overrun?  This
> seems to be implied by the Xyplex servers with lower port density using
> more frames and more data loss.  If there is a buffer that is getting
> overrun, what can be done about it?  What is a reasonable number of bytes
> and packets to expect LAT to handle correctly under Ultrix?

If flow-control is used then you should never run see data overruns.  If 
flow control is not being used then you will varying amounts of data overruns.
There are no ways to eliminate them.
-- 
Matt Thomas                     Internet:   thomas at wrl.dec.com
DECnet-ULTRIX Development       UUCP:       ...!decwrl!thomas
Digital Equipment Corporation   Disclaimer: This message reflects my own
Littleton, MA                               warped views, etc.