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Path: utzoo!mnetor!seismo!mcvax!ukc!its63b!adam
From: adam@its63b.ed.ac.uk (ERCF02 Adam Hamilton)
Newsgroups: comp.dcom.lans
Subject: How busy can an Ethernet be?
Message-ID: <324@its63b.ed.ac.uk>
Date: Fri, 13-Mar-87 05:22:38 EST
Article-I.D.: its63b.324
Posted: Fri Mar 13 05:22:38 1987
Date-Received: Mon, 16-Mar-87 04:12:24 EST
Reply-To: adam@its63b.ed.ac.uk (ERCF02 Adam Hamilton)
Organization: I.T. School, Univ. of Edinburgh, U.K.
Lines: 25
Keywords: Ethernet, load, bandwidth, performance


	As the various Ethernets at Edinburgh University get busier, some
people start to worry that they are running out of capacity.  Occasionally
they ask me "when do we NEED to split up the load".  ( The usual suggestion
is bridges).  I have no feel for what proportion of the Ethernet bandwidth
can be used before performance suffers.
	Would someone out there like to offer me the benefit of their
experience.  I will certainly summarise e-mail responses but I suspect that
a direct posting by a net administrator who has been through this would be
better.
	Our monitor shows that typical day-time use is about 10% of the
maximum bandwidth over 1 minute periods with 1 second peaks of up to 50%.
This is our CS department, and they want to add another 15 or so Suns.
Another department (A.I. no surprise) shows even more use than this
with bursts of 10-15% (over 1 second).  The main heavy users seem to be
diskless Suns - a node and its server can use about 5% in bursts.
	My own view is that if the traffic made a 1-second paging time
change to a 2-second paging time that would be acceptable; if it made
other traffic substantially worse, that would not.  (Yes, I know this
is very woolly but I don't know any better.)
	OK, the question is HOW BUSY CAN AN ETHERNET BE before it NEEDS
to be split?
		Adam Hamilton

  !seismo!mcvax!ukc!ed.its63b!adam	I think

P.S.  Make that 30% steady average and up to 70% peaks.
Now I am worried :-!