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From: eli@spdcc.COM (Steve Elias)
Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip
Subject: experience using commercial cable TV as a MAN.
Message-ID: <164@ursa-major.SPDCC.COM>
Date: 9 Oct 89 21:55:22 GMT
References: <160@ursa-major.SPDCC.COM>
Reply-To: eli@ursa-major.spdcc.COM (Steve Elias)
Lines: 46
Organization:


 dyer@ursa-major.spdcc.COM (Steve Dyer) writes:
>Has anyone ever investigated using a couple of channels from a town's
>cable TV system as the basis of a metropolitan-area network? 

	look no further, Steve!  the cities of Springfield, Mass and
	St. Paul, Minnesota have linked their respective ethernets
	over their local cable systems -- the result for each is a 
	full speed ethernet that spans many buildings, many miles apart.  

	a large company local to the Boston area is also looking
	into linking their building ethernets this way.

>like this *might* work with broadband modems and the right link-level hardware.
>For connection to a regional network also located in the same town
>(e.g., NEARnet), it might be preferable to lots of relatively low speed
>leased lines.

	indeed.  we at Chipcom are exploring the possibilities of attaching
	to NEARnet via broadband cable technology (yes, folks: 802.4!).
	our Marathon bridge is a very zippy .3 to .4 learning bridge.
	i'd call it a transparent bridge, but after BOFing at Interop,
	let's just call it a translucent bridge.  the bridge runs at
	nearly 9000 packets per second at short distance, and drops
	to about 4000 pps at ten miles....  naturally, latency increases
	with long distance as well.  (you knew that!)

	naturally, there are some gotchas with this technology.  the local
	cable system has to be fairly high quality stuff.  some cable 
	companies are fairly lax about attenuations and other nifty RF stuff;
	such conditions would cause many physical layer 802.4 errors.

>I'd appreciate hearing from people who know a little bit more about
>the issues and whether or not this is completely unrealistic.

	it's being done already.  the major reason Chipcom has not hooked
	to internet or NEARnet via broadband is that we will be moving
	to Southboro next year...

	(by the way, i work for Chipcom and worked on the Marathon bridge
	 software and systems for most of the last 18 months.  ok?)

-- 
 ... Steve Elias (eli@spdcc.com);6178906844;6179325598; {}
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