Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!uunet!mcsun!hp4nl!tuegate.tue.nl!eba!wjw From: wjw@eb.ele.tue.nl (Willem Jan Withagen) Newsgroups: comp.sys.apollo Subject: Re: "Ethernet or Apollo Token Ring?" Keywords: Ethernet performance. Message-ID: <506@eba.eb.ele.tue.nl> Date: 9 Apr 90 09:05:28 GMT References: <499c0c96.12c9a@digital.sps.mot.com> <21091@joshua.athertn.Atherton.COM> Sender: wjw@eba.eb.ele.tue.nl (Willem Jan Withagen) Organization: Technical University Eindhoven, The Netherlands Lines: 39 In article <21091@joshua.athertn.Atherton.COM> joshua@Atherton.COM (Flame Bait) writes: >chen@digital.sps.mot.com (Jinfu Chen) writes: >> Also in ethernet environment you can't never get over 50% of the >> spec'ed speed due to the collsion. > >Wrong answer. The right answer is that the maximum real world throughput >is at least 8.9 Mbits over the wire and over 1Mbyte task-to-task, or over >85% of spec. Interesting details: > 2 processes talking to each other. > Two 20MHz 68020 machines > Running 4BSD UNIX (I assume 4.3). > The test was done in Sept. 88 > Using an AMD LANCE chip with a receive buffer of 10 packets or more. > I wonder wether this is the right correction. One of the key remarks in this is 'collision'. Now collisions do not happen on an ethernet with only two communicating processes. As soon as more processes want to communicate at the same time, their packages start to collide and are resent ( even more than once ). And this fact is specifically ignored in the above test. Hence, the 8.9Mbits spec tells you taht an 10Mbit ethernet without collisions does not even get close to an 10Mbit performance. Using Jinfu Chen estimate gives this ~4.5Mbits real troughput on a wire with more than 2 communicating processes. Well at least this is the story, as I tell it during my classes. If things have altered this significantly then I must have been sleeping. And will now be awakend by the flames of the net. Greetings Willem Jan Withagen Eindhoven University of Technology DomainName: wjw@eb.ele.tue.nl BITNET: ELEBWJ@HEITUE5.BITNET room EH 10.10 Digital Systems Group P.O. 513 Tel: +31-40-473401 5600 MB Eindhoven The Netherlands