The speed is only negotiated once when you plug in the cable or power up the device. The packet structure is the pretty much the same for 10 and 100. The type of encoding used on the wire is different, 10Mb is manchester encoded (2 voltage levels with some predistortion) and 100Mb is MLT3 encoded (3 voltage levels). But this is nothing you have to worry about the switch chip and phy chip take care of all of that. The switch chip is your transformer although a FIFO is probably a more accurate term. I packet is brought in , buffered, the preamble is rebuilt and it is routed via a lookup table to the correct port where it is sent out at the proper speed for that port. The bit width on 10Mb is 100nS and 100Mb is 8nS. (100Mb actually pushes 125Mb down the wire but it's 4B5B so for every 5 bit symbol only 4 are valid data.) If you are really interested in the nuts and bolts I think IEEE standard 802.3u covers 100Mb ethernet in nightmarish detail. Warning you will probably need a whole case of Bawls to make it through any IEEE standard on one sitting. I get the feeling I am not making this any clearer. -----Original Message----- From: Mike Bresnahan [mailto:mbresnah at visi.com] Sent: Monday, November 19, 2001 2:55 PM To: tclug-list at mn-linux.org Subject: RE: [TCLUG] Co-living 100mb and 10mb ethernet The machines are connected via a Netgear DS108 dual speed hub. I think I understand what you are saying except for one thing. Does the speed get negotiated for every packet? If so, isn't there a lot of overhead? If not, how does a packet from a machine connected at 100mb get switched/routed to a machine connected at 10mb? Does it go through a "transformer"? It might help my understanding if I knew what was different about 10mb and 100mb ethernet other than the maximum throughput. For example, does 100mb use a greater frequency bandwidth, does it send more pulses per unit time, or what? I measured the throughput using ftp from a 1.0Gz PIII to a 400Mhz K6-3 and to a 750Mhz PIII. Mike > -----Original Message----- > From: tclug-list-admin at mn-linux.org > [mailto:tclug-list-admin at mn-linux.org]On Behalf Of Troy.A Johnson > Sent: Monday, November 19, 2001 8:58 AM > To: tclug-list at mn-linux.org > Subject: Re: [TCLUG] Co-living 100mb and 10mb ethernet > > > Mike, > > Here are my (not necessarily correct) answers: > > >>> mbresnah at visi.com 11/18/01 04:15PM >>> > >Could someone explain to me in a nutshell how 10mb and 100mb co-exist > >happily on the same ethernet? > > Technically, as stated before, they cannot. If your local > network is connected by a HUB, they are all on the > same ETHERNET SEGMENT. If your local network > is connected by a SWITCH, the switch provides a > separate a ethernet segment for each connection and > connects those with a BACKPLANE (which runs at > least as fast as the fastest network segment). Steve > explained dual speed hubs, but basically they provide > two ethernet segments: one 10Mb, one 100Mb; via an > internal two port switch. > > >For example, I have 3PCs and a DSL modem on > >my local network. 1 PC and the modem have 10mb cards and 2 of > the PCs have > >100mb cards. When I transfer a file from one of the 100mb > machines it takes > >about 5 times less time than when I transfer to the 10mb machine, so it > >certainly appears that the network is capable of both speeds. > Evidently the > >10mb is able to detect and handle collisions with the 100mb and > vice versa. > >Perhaps it's because they both use the same carrier frequency; > if they use > >such a thing? Also, is a 5x speed difference what I should expect? Not > >10x? > > The speeds are differentiated by a factor of 10 only > for the theoretical maximum throughput for each > medium. It may be difficult for your PCs to push a > 100Mb connection close to it's max. It may be that > the 10Mb connection is full duplex (actually 20Mb > max) while the 100Mb connection is half duplex. > A factor of 5 is not an unusual speed difference, > but it may depend on the service used (those with > less overhead (like FTP) will probably be faster). > > >Take pity on me. I'm a software guy. > I do pity you, Mike, and I pity me too. ;-) > > Troy > > _______________________________________________ > Twin Cities Linux Users Group Mailing List - Minneapolis/St. > Paul, Minnesota > http://www.mn-linux.org > tclug-list at mn-linux.org > https://mailman.mn-linux.org/mailman/listinfo/tclug-list _______________________________________________ Twin Cities Linux Users Group Mailing List - Minneapolis/St. Paul, Minnesota http://www.mn-linux.org tclug-list at mn-linux.org https://mailman.mn-linux.org/mailman/listinfo/tclug-list