Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!ut-emx!!spurgeon
From: spurgeon@.uucp (Charles E. Spurgeon)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet collisions
Keywords: LANalyzer Ethernet
Message-ID: <41178@ut-emx.uucp>
Date: 11 Dec 90 17:03:48 GMT
References: <467@pirates.UUCP> <2184@cybaswan.UUCP>
Sender: news@ut-emx.uucp
Reply-To: spurgeon@atget.cc.utexas.edu.UUCP (Charles E. Spurgeon)
Organization: UTexas Computation Center, Austin, Texas
Lines: 64

In article <2184@cybaswan.UUCP> iiitih@cybaswan.UUCP (Ivan Izikowitz) writes:
>If you don't think you have a faulty card, then you probably have a 
>heavily loaded network. Just take a look at any of the published
>performance curves for the 802.3 protocol - throughput is severely
>degraded once the offered load exceeds a certain value (I think about
>40% of channel capacity?)
>

I think that the 40% figure you refer to comes from simulations of
"Ethernet" that don't happen to reflect the real Ethernet protocol all
that well.  Ethernet traffic tends to be bursty, and one second
samples of traffic showing 40% utilization would be nothing to get
worried about.  Even a constant load of 40% on an Ethernet (a
situation that is unusual) would still not be all that big a deal.

For the empirical evidence as to Ethernet's ability to move data, see
the SIGCOMM paper presented a couple of years back.  Here's the access
info from the Network Manager's Reading List:

      The following technical report from the Digital  Equip-
      ment   Corporation's  Western  Research  Lab  documents
      empirical evidence showing that the 10 megabit Ethernet
      system is capable of transmitting large amounts of data
      in a reliable fashion.  The report is also  useful  for
      its  analysis of what makes a good Ethernet implementa-
      tion.  Included is a brief set of  guidelines  for  the
      network  manager who wants their Ethernet system to run
      as well as possible.

      o    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