heibe@forst.informatik.rwth-aachen.de (Bernd Heinrichs) (05/07/91)
Perhaps it is a nonsense idea. But I think in some environments it would make sense to run the already installed Ethernet configurations at higher speeds, e.g. at 100 Mbit/s. My question is: Is it physically possible to reach such data rates on 50-ohm or 75-ohm coaxial cables ? Of course the maximum cable length permitted must be shorter than 500 meters and the minimum packet length must be longer than 64 bytes. Perhaps some people can inform me about realization of such ideas. Bernd Heinrichs **************************** Aachen University of Technology Lehrstuhl fuer Informatik IV Ahornstr. 55 D-5100 Aachen, Germany Tel.: + 49 241 / 80-21410 Fax.: + 49 241 / 80-21429 email: heibe@informatik.rwth-aachen.de **************************** -- ______________________________________________ Bernd Heinrichs Lehrstuhl fuer Informatik IV RWTH Aachen D-5100 Aachen Germany
heibe@forst.informatik.rwth-aachen.de (Bernd Heinrichs) (05/07/91)
Perhaps this is not a realizable idea. But I think in some environments it would make sense to use the existing Ethernet installations running with higher data, e.g. up to 100 Mbit/s, instead of the expensive FDDI. My problem is, that I do not know, if it is physically possible to run 50- or 75-ohm coaxial cables at such high data rates. Of course the cable length must be shortened and the minimum packet length has to exceed 64 bytes. I would be very pleased when som people can tell me, such data rates are realizable or not. Bernd Heinrichs Technical University of Aachen email: heibe@informatik.rwth-aachen.de -- Bernd Heinrichs Lehrstuhl fuer Informatik IV RWTH Aachen D-5100 Aachen, Germany Tel. +241/80-21410 Fax: +241/80-21429 heibe@informatik.rwth-aachen.de
oberman@ptavv.llnl.gov (05/07/91)
In article <heibe.673604290@forst>, heibe@forst.informatik.rwth-aachen.de (Bernd Heinrichs) writes: > Perhaps this is not a realizable idea. But I think in some environments it > would make sense to use the existing Ethernet installations running with > higher data, e.g. up to 100 Mbit/s, instead of the expensive FDDI. > My problem is, that I do not know, if it is physically possible to run 50- > or 75-ohm coaxial cables at such high data rates. Of course the cable > length must be shortened and the minimum packet length has to exceed > 64 bytes. > > I would be very pleased when som people can tell me, such data rates are > realizable or not. The data rates are certainly realizable. Doing it and not violating FCC emmission specs is another matter. But I have heard from 3 different vendors who plan to announce copper based (coax and TP) token rings which are essentially FDDI on wire. One vendor referred to it as CDDI. Whether such a product will appear is uncertain, but the vendors were all big in the network arena and seemed very serious about it. I wouldn't be too stunned if someone made an announcement in the next few months and showed something at InterOp. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything. Especially anything gnu. P.S. Why did the original message get posted 3 times?
mart@csri.toronto.edu (Mart Molle) (05/07/91)
heibe@forst.informatik.rwth-aachen.de (Bernd Heinrichs) writes: >Perhaps this is not a realizable idea. But I think in some environments it >would make sense to use the existing Ethernet installations running with >higher data, e.g. up to 100 Mbit/s, instead of the expensive FDDI. >My problem is, that I do not know, if it is physically possible to run 50- >or 75-ohm coaxial cables at such high data rates. Of course the cable >length must be shortened and the minimum packet length has to exceed >64 bytes. >I would be very pleased when som people can tell me, such data rates are >realizable or not. Increasing the data rate by a factor of 10 in Ethernet is not going to work very well, because you cannot also make the signals travel 10 times as fast along the wires. The efficiency of CSMA/CD is a function of the ratio of *time* spent transmitting data to the propagation delay. Thus, increasing the data rate without shortening the network or forcing the minimum packet size to go up makes this ratio (and hence Ethernet efficiency) drop to unacceptable values. However, there are a number of proposals for "speeding up" Ethernet that end up doing what you want but via an approach that avoids the CSMA/CD bottleneck. Basically, the idea is to build the Etherent analog to a PBX: "low speed" (almost) dedicated lines (in this case 10Mbps Ethernet, instead of a 64Kbps digitised voice circuit) leading to a "switch port", with the internals of the switch using some proprietary very-high-speed internal architecture to move data between ports. The Kalpana EtherSwitch promises to do this using an internal 32x32 non-blocking buffered switch that supports store and forward with cut-through Real Soon Now, and SuperNet (nee Hubnet) has a product that uses a 100 Mbps collision arbitration rooted tree network to connect a bunch of "simulated" multiport transceivers (which looks like a DELNI, say, to the hosts but connects to the SuperNet backbone using the Hubnet protocol at 100Mbps). I guess one could say that these systems support "tunneling" of Ethernet frames between ports. There is also an issue of how to decide *where* to send a frame that originates from a given port, which was discussed in this forum recently.... These designs give a total bandwidth comparable to FDDI (or even higher), but limit the host-to-host bandwidth to Ethernet speeds. Mart L. Molle Computer Systems Research Institute University of Toronto Toronto Canada M5S 1A4 (416)978-4928
mikel@berlioz.nsc.com (Michael G. Lohmeyer) (05/08/91)
In article <heibe.673604290@forst> heibe@forst.informatik.rwth-aachen.de (Bernd Heinrichs) writes: >Perhaps this is not a realizable idea. But I think in some environments it >would make sense to use the existing Ethernet installations running with >higher data, e.g. up to 100 Mbit/s, instead of the expensive FDDI. >My problem is, that I do not know, if it is physically possible to run 50- >or 75-ohm coaxial cables at such high data rates. Of course the cable >length must be shortened and the minimum packet length has to exceed >64 bytes. > >I would be very pleased when som people can tell me, such data rates are >realizable or not. As was said in another posting in reply to the one above, the CSMA/CD protocols do not seem to lend well to 100 MBits/sec. I don't know enough about CSMA/CD to say one way or the other about that, but I do know that the current ethernet IC's do not operate up to 100MBits/sec even if you wanted them to. So in order to make ethernet go faster, it would take new chip designs to make it work. All the current ICs for ethernet are based on 10MBit/sec, and hence, are not designed to work very far outside that spec. Mike ------------- Mike Lohmeyer mikel@berlioz.nsc.com National Semiconductor Corporation (408) 721-8075