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From: BILLW@MATHOM.CISCO.COM (William Westfield)
Newsgroups: sci.electronics
Subject: Re: LAN speed?????
Keywords: Ethernet, cable, transmission line.
Message-ID: <12581355675019@MATHOM.CISCO.COM>
Date: 13 Apr 90 01:30:51 GMT
References: <19603@boulder.Colorado.EDU> <7301@tekgvs.LABS.TEK.COM>
Sender: usenet@csl.sri.com
Organization: cisco Systems, Menlo Park, CA
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>[Personally I think LANS should be able to go lot faster than then
>the 10 megabit/sec. standard Ethernet---Anybody actually know?  I'm
>basing this guess on the fact that I'm able to receive 40 channles of
>real time videa over RG-59(just like RG-58 only different impedence) via
>local cable.   If each station requires about 6MHz of bandwidth alone,
>than ethernet should be no where near the limits of the RG-58 cable.

yes, ethernet speed is more limited by other factors (like everyone on
the cable haveing to hear the same packets and detect collisions reliably)
than by inherent limitations in the cable.  Similar cable used in broadband
networks has a total bandwidth much larger than 10 Mb, but the technology
is also much more complex (requiring repeaters, head ends, and other forms
of access control).  Things like "ultranet" run multiple 100Mbits over
coax, though not for the distances ethernet can travel over.


>The thru-put of ethernet is much lower than 10 megabits per second
>because of protocol and SW overhead.  An excellent system can run at 1
>megabit persecond.  Most workstations run at 100 to 300 kbits per second.

This is very obsolete information.  ANY workstation ought to be able to
get over 1 Mb these days, or be laughed at.  Good workstations get more
like 3 Mbps, and highly tuned implementations get better than 8 Mbps.
(yes, using real TCP, with checksumming, and even though there WERE
ethernet collisions during the data transfer.)

Even moderate speed PC/AT clones do better than 100 kbits most of the time.

Bill Westfield
cisco Systems.