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Aucbvax.6477 fa.works utcsrgv!utzoo!decvax!ucbvax!works Sun Mar 14 23:57:58 1982 Re: Ethernet Doomed? >From mo@Lbl-Unix Tue Mar 9 05:41:43 1982

"Rumors of my recent demise have been greatly over-exagerated." -Mark Twain

The market survey which pronounced the death of Ethernet is not completely accurate and grossly oversold, but could you think of a better scam to sell zillions of your document?

All the same, the comments by Xerox about broadband are equally ill-informed. I have spent quite a while comparing the two schemes and have come to the following conclusions.

1) Broadband does require a bit more initial planning because you are wiring the world once and for all. But contrary to Xerox, the design process isn't that complex, and if designed properly, doesn't require the constant diddling Xerox implies. Admittedly the required modem is complex, but for a good RF designer, not that much more complex than an Ethernet transceiver and occupies the same place in the architecture. Production economies and special chips will get the modem cost down, just like for Ethernets.

2) For a given piece of Coax, broadband systems get 5-10 times the bandwidth out of the cable. Broadband systems multiplex in two domains: time in each channel, and frequency within the cable. This allows data, voice, video, and whatnot all on the same cable. I know it is possible to put voice and maybe even video on Ethernet, but you can get a lot more with 5 logical networks within the same cable! Most of the modem designs are frequency-agile, so there are lots of optimizations possible for either high-bandwidth applications, or private subnets, again, all in the same cable.

3) On the other hand, Ethernet is CSMA/CD, while most wideband systems are either pure CSMA, or CSMA/hopefully-CD. You have to look closely and think hard to understand the real behavior of the wideband systems, and the suppliers haven't been to helpful giving away fine details to make these distinctions.

4) The other problem with Ethernet is its DC coupling. While it will work fine in an electrically-quiet office, there are some very real problems with electrical noise, ground loops, sheild currents, and other similar evils. Some are just nusiances, but others can be deadly, if accidently applied to a human. When wiring a large building, you won't run an Ethernet through the building core with the power feeds and elevator circuits. Here at LBL, we have power transients which would certainly kill an Ethernet going further than one building, and possibly even within a single building.

Ethernet and Broadband aren't natural enemies; they are in fact more similar than different. Same basic algorithms, different encoding on the medium. I forsee large building or campuses with wideband backbones interconnecting small baseband subnets. I think Ethernet will be viable in that many people are building things to plug into it, but Broadband does have advantages for large building or campuses. The two will co-exist quite usefully. At least one vendor, Ungermann-Bass, intends to make sure of it.

-Mike

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