Date: Fri, 25 Feb 2000 11:08:24 -0800 (PST) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: wollman@khavrinen.lcs.mit.edu (Garrett Wollman) Cc: cwasser@v-wave.com (Chris Wasser), freebsd-current@FreeBSD.ORG Subject: Re: dc0 wierdness with Compex Freedomline Message-ID: <200002251908.LAA71093@gndrsh.dnsmgr.net> In-Reply-To: <200002251833.NAA31071@khavrinen.lcs.mit.edu> from Garrett Wollman at "Feb 25, 2000 01:33:16 pm"
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> <<On Fri, 25 Feb 2000 10:28:15 -0800 (PST), "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> said: > > >> I answered SPECIFICALLY about half-duplex. > > > The duplex does not in any way effect the maximal link layer transmission > > data rate. You seem to keep forgetting the maximal part... > > The maximum for full-duplex is utterly irrelevant, since the bounds on > performance for half-duplex Ethernet networks come from CSMA/CD. I will say it one last time, duplex falls out of the equations when you solve for ``maximal''. It has 0 meaning in the numbers used. Go read my analysis and tell me why I can't pump 12MB/sec on 100BaseTX, tell me that my 15 years of doing 97.5% of data clock on ethernet just doesn't happen. Then tell me why it can't happen, show me numbers and equations and I'll show you how you forget the keyword maximal and keep jumping over to something less than maximal as your not narrowing the scope of what it is your measureing/calculating. You keep throwing P(coll) in, P(coll) only occurs if your upper layer is causing P(coll) by doing things like ack packets. CSMA/CD does not define this. It defines the exact things I have used in the calculations to derive the number. There is no other number and no other formula to apply when solving for maximal. I can back up my numbers with lab data, 15 years of lab data. The only thing that effects maximal data transfer on a CSMA/CD network is IFG, MTU (not the upper layer MTU the layer 2 frame MTU) and layer 2 overhead bytes as clearly formulated in my post (preamble, Start of Frame, Source Address, Destination Address, type and CRC). The IFG is the multi-access window, if no one else accesses the media during the IFG (technically a violation of spec) one is free to start your next frame of transmission. If 2 nodes attempt to access the media at end of IFG you have P(coll), solving for maximal says that this never occurs to get maximal. THAT IS THE END OF THE STORY AS IT WORKS IN THE REAL WORLD DAY AFTER DAY IN 4 DESIGNS I HAVE DONE FOR PEOPLE. The only bloody ack that can cause a collission in our l3 design occurs after the whole of the data transfer, thus they don't effect our 1 way data transfer rate except by 64 bytes in Megabytes of data which shows up out in the 4th or 5th digit and is _NOT_ the maximal link layer data rate (the link layer is till doing 97.5% of data clock, the data is just going the other way :-)). -- Rod Grimes - KD7CAX @ CN85sl - (RWG25) rgrimes@gndrsh.dnsmgr.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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