Re: TCP-IP/ETHERNET QUESTION


Bill Nowicki (nowicki@Sun.COM)
Fri, 21 Nov 86 15:17:27 PST


        I am in the process of establishing a TCP/IP network that will
        run on Broadband ethernet.

In a way, "Broadband ethernet" is an oxymoron. Ethernet is
baseband. There are several companies that build systems that are
compatible with Ethernet transciever specs, but use broadband
signalling instead of baseband signalling. Although this is an analog
issue that is mysterious to software types like me, the fact
that you modulate and demodulate should not help collision problems, so
you have the usual Ethernet length restrictions. Of course you can
exceed the length restrictions, with possible collision problems.

        The prototype installation will consist of 4 mainframe
        computers (VAX 780) and 8 or 16 users using IBM-PC clones.

Your definition of "mainframe" is interesting, since the workstation on
my desk is twice as fast, and is the middle of our line. At any
rate, we have many Ethernets with up to about 100 Sun-3 machines. It is
interesting that bandwidth is not the first limitation. The main
reason you don't want more than about 100 machines is that one faulty
machine can bring the whole network down. The probability that someone
shorts the cable, or starts to continuously broadcast, or at least has
bad collision detection circuitry, becomes pretty close to one with
over 100 nodes.

Of course this might be because Ethernet networks just evolve, while
broadband networks are usually "planned". We make each floor of each
building its own Ethernet, with additional Ethernets for labs. You can
make a Sun into a gateway just by sliding in another Ethernet
controller. It also helps to use transceiver multiplexor boxes such as
the ones made by TCL, to reduce the number of actual taps, (less likely
to short the cable). So you probably can put 400 PCs onto a single net,
but do you want to?

        -- Bill Nowicki
           Sun Microsystems



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