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From: wsmith@cs.umn.edu (Warren Smith [Randy])
Newsgroups: comp.protocols.tcp-ip
Subject: Re: When is an ethernet full?
Message-ID: <1990May31.014041.13251@cs.umn.edu>
Date: 31 May 90 01:40:41 GMT
References: <1141@cica.cica.indiana.edu> <56724@bbn.BBN.COM>
Organization: University of Minnesota, Minneapolis - CSCI Dept.
Lines: 33

In article <56724@bbn.BBN.COM> craig@ws6.nnsc.nsf.net.BBN.COM (Craig Partridge) writes:
>> When is an ethernet full?  ....
>
>The best place I know of to start answering this question is Boggs,
>Mogul and Kent's article in Proc. of SIGCOMM '88 pp. 222-233.  The
>gist of that article is that you can drive the Ethernet all the way
>to its rated capacity assuming you are careful in the way you lay out
>your network, and all your systems have good Ethernet hardware.
>
....
>
>Craig

One thing to remember - while Boggs, Mogul and Kent's article shows that
the Ethernet will run right up to saturation (~95% depending on packet
size and number of stations), it does not fully address the matter of
delay.  Delay increases as your Ethernet becomes more heavily loaded.
BMK's measurement of delay does not include measurement of queueing
delays, and thus underestimates the real delays that will be seen by
many hosts (and users) on your network.

I have seen real Ethernets running more than 40% load (averaged over
1 hour!, bursts up in the 80-95% range).  Most of those nets aren't
around any more - they've been split to improve performance.  These
networks were (and are) growing, so they would have had to split at
some point anyway.   When you should split depends on what the needs
are for your network, and what the growth rate is.

-Randy
-- 
Randy Smith
wsmith@umn-cs.cs.umn.edu
...!rutgers!umn-cs!wsmith