Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!caen!hellgate.utah.edu!basset.utah.edu!haas
From: haas%basset.utah.edu@cs.utah.edu (Walt Haas)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet performance degradation?
Keywords: PC, NFS, Novell, Netware, DOS
Message-ID: <1991Mar11.131724.10459@hellgate.utah.edu>
Date: 11 Mar 91 20:17:24 GMT
References: <1991Mar7.220351.9761@uhura1.uucp> <1991Mar7.221028.9883@uhura1.uucp> <45323@ut-emx.uucp> <1991Mar11.133033.25283@jarvis.csri.toronto.edu>
Organization: University of Utah CS Dept
Lines: 31

In article <1991Mar11.133033.25283@jarvis.csri.toronto.edu> mart@csri.toronto.edu (Mart Molle) writes:
>spurgeon@atget.cc.utexas.edu (Charles Spurgeon) writes:
>
>>In article <1991Mar7.221028.9883@uhura1.uucp>, bryan@uhura1.uucp (Bryan
>>Curnutt) writes:
>>|>I've also heard (though I don't know how true it is) that Ethernet
>>|>network performance degrades drastically if too many nodes are added
>>|>to the network, and that the number of nodes to do this is relatively
>>|>small.  Is there any truth to this?
>
>>Every Ethernet, indeed every LAN no matter what the technology used, has
>>a different equipment mix and load profile, so your mileage will vary.  On
>>the other hand, there are no special limits to host population/traffic on an
>>Ethernet other than those listed in the spec (for example, 100 transceivers 
>>per thick Ethernet segment, 30 connections per thin Ethernet segment,
>>1024 addressable stations per Ethernet system linked with repeaters).
>
>It is not as simple as you suggest.  There is indeed very strong evidence
>to show that network performance can degrade drastically when the number
>of active hosts reaches a threshold that is significantly below 1024.

A realistic limit for an Ethernet is probably on the order of 200 hosts,
at least in our environment.  We limit router legs to 100 to 200 hosts, and
usually run into loading issues before we get to that number.

I know of sites that have built larger bridged Ethernets, and the broadcast
traffic became unmanageable.  One such site is now introducing routers into
the net to manage broadcasts etc.  In view of this experience the exponential
backoff issue seems pretty academic.

-- Walt Haas    haas@ski.utah.edu