Subject: network performance
To: None <,>
From: David Carrel <>
List: current-users
Date: 07/13/1994 23:48:33
Can anyone explain why I am seeing different throughput rates on network
traffic depending on the direction.

I started out testing throughput on my slip link.  I am using ttcp (a tcp
test program).  When sending data TO my machine over a 28.8 modem with DTE
set to 38.4 (the max on the hp300), I see transfer rates of around
3.62KBytes/s (~=36Kbaud).  Pretty nice!  (Obviously I am getting good
compression in the modem.)  But when I tried reversing the direction
(sending FROM my NetBSD machine) my transfer rate dropped to .97KB/s (close
to one fourth).  I tried varying the packet lengths and the socket buffer
sizes (socket buffer sizes have an amazing affect on SunOS) but I saw no
appreciable effects under NetBSD.

I tried a similar test over my ethernet, and I noticed about a 10% drop
when sending versus receiving.

Over the slip link, things happen slowly enough that you can watch TCP "as
it happens" by watching the modem lights (you can count the ACKs).  When
sending from NetBSD, there are large periods where nothing is being sent.
It almost appears that TCP is backing too far off.  Seems like a tuning
problem, but I am not a TCP wiz.

My box is an hp375 running NetBSD 1.0-alpha.  (sources from 12 July 94)