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From: rbg@rbg.Sun.COM (Robert Garner)
Newsgroups: comp.arch
Subject: Re: Ethernet Factoid
Keywords: ethernet bandwidth perversion metcalfe
Message-ID: <134350@sun.Eng.Sun.COM>
Date: 12 Apr 90 02:58:58 GMT
References: <1718@aber-cs.UUCP>
Sender: news@sun.Eng.Sun.COM
Reply-To: rbg@rbg.Eng.Sun.COM (Robert Garner)
Organization: Sun Microsystems, Inc.  Mt. View, Ca.
Lines: 46

> In article <29801@amdcad.AMD.COM> phil@pepsi.AMD.COM (Phil Ngai) writes:
>  In article <76700190@p.cs.uiuc.edu> gillies@p.cs.uiuc.edu writes:
>
>  |He complained that DEC was unreasonable in demanding 10Mb/sec
>  |performance, when Xerox's 3Mb/sec performance would have been
>  |perfectly adequate.
>
> On this I thoroughly agree. The Xerox people were very clever guys, and
> they were "right".

I just picked up on this conversation.  I worked under Metcalfe in
Xerox's System Development Division (SDD) in 1978 on the first
10Mb/s Ethernet controller hardware, an evolution of Boggs' Alto
hardware.  Ron Crane, now also at 3Com, did the first analog
engineering analysis for the 10Mb Ethernet.

Long before DEC entered the scene, we were trying for 20Mb/s on
what was internally called the "XeroxWire."  One reason we
dropped back to 10Mb/s was the availability of a Fairchild CRC
chip that ran at 10 MHz!   Random STTL in the boards for the
Dolphin (D0) and Dandelion (Star) workstation comprised just
too many parts for the CRC.  (Keep in mind that the Dandelion's
Ethernet controller hardware was just 90 SSI chips--not bad for 1978.)

Anyways, based on electrical considerations--primarily the
attenuation of signals and the noise introduced by taps--
5 MHz would have been a better speed.  However, the idea
was that 10 MHz looked doable, so we went for it.
(The kludgery of the "put-your-transceiver-here marks" on the cable
came latter.)

On a different subject, since the whole world (or at least
Japan, Germany, and Fance) may be going to 64Kb/s ISDN in several
years, this could make 10Mb/s Ethernet look fast.

	- Robert Garner


p.s.  I assume everyone knows that the 3Mb-Ethernet was actually
2.94 Mb/s, which was half the Alto's clock rate, which was an integral
submultiple of the display's line rate...?

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