Path: utzoo!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!ut-emx!atget.cc.utexas.edu!spurgeon
From: spurgeon@atget.cc.utexas.edu (Charles Spurgeon)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet performance degradation?
Keywords: PC, NFS, Novell, Netware, DOS
Message-ID: <45323@ut-emx.uucp>
Date: 8 Mar 91 14:38:37 GMT
References: <1991Mar7.220351.9761@uhura1.uucp> <1991Mar7.221028.9883@uhura1.uucp>
Sender: news@ut-emx.uucp
Reply-To: spurgeon@atget.cc.utexas.edu (Charles Spurgeon)
Distribution: usa
Lines: 56

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).

There have been a number of papers written about performance on various
simulations of "Ethernet like" networks.  These simulations seem to be 
the ones cited when people are describing "hard limits"  in the Ethernet
protocol.  For some empirical tests of Ethernet performance that show 
what the real Ethernet protocol can deliver, check out the DEC Technical
Report listed below:

	   Measured Capacity of an Ethernet: Myths and  Real-
           ity
           David R. Boggs, Jeffrey C. Mogul,  Christopher  A.
           Kent.
           Proceedings of the SIGCOMM '88 Symposium  on  Com-
           munications   Architectures   and  Protocols,  ACM
           SIGCOMM, Stanford, CA., August 1988, 31 pps.

      From the Abstract:

      "Ethernet, a 10 Mbit/sec CSMA/CD network, is one of the
      most  successful LAN technologies.  Considerable confu-
      sion exists as to the actual capacity of  an  Ethernet,
      especially  since  some of the theoretical studies have
      examined operating regimes that are not  characteristic
      of actual networks.  Based on measurements of an actual
      implementation, we show that for a wide class of appli-
      cations,  Ethernet  is  capable of carrying its nominal
      bandwidth  of  useful  traffic,   and   allocates   the
      bandwidth fairly."

      This paper is also  available  over  the  Internet  via
      electronic  mail  from the DEC Western Research archive
      server.  Send a message to the following  address  with
      the  word "help" in the Subject line of the message for
      detailed   instructions.    The   address    is    WRL-
      Techreports@decwrl.dec.com.

      You may also request a copy of the report  through  the
      U.S. postal system by writing to:

           Technical Report Distribution
           DEC Western Research Laboratory, UCO-4
           100 Hamilton Avenue
           Palo Alto, California 94301