Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ucsd!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!cme-durer!wallace
From: wallace@cme-durer.ARPA (Evan Wallace)
Newsgroups: comp.dcom.lans
Subject: Re: 802.* a cornucopia ?
Summary: 802.? speed and applicability
Message-ID: <621@morticia.cme-durer.ARPA>
Date: 1 Sep 88 19:55:20 GMT
References: <10400002@osiris.cso.uiuc.edu> <4942@cos.com> <1698@spdcc.COM>
Organization: National Bureau of Standards, Gaithersburg, MD
Lines: 60

In article <1698@spdcc.COM>, eli@spdcc.COM (Steve Elias) writes:

> 	802.3 won't provide a deterministic network access time if
> 	it is under heavy load, as you say.  this is a key feature
> 	of 802.4, i think.  not so important for campus type 
> 	networks, but essential for factory & industrial networks.

Deterministic access time is not necessarily, essential.  We had a
horizontal milling workstation (or work cell) which operated quite well
over a V1 Ethernet.  We find that high throughput is an important
quality in a factory LAN.  We have embraced subnetting as a means to this
end, which can be implemented quite cheaply with Ethernet (Ethernet
in a box or thin Ethernet).  Thus I agree with Steve eliases later comments
that bridges and routers will become more important in the future.
Particularly as smaller users fight the monolithic LAN concepts
that certain large companies have pushed in the past.

In reference to 802.3 distance limitations for LANs spanning multiple 
buildings Steve Elias continues:

> 	a 802.3 to 802.4 bridge could be useful
> 	in this type of situation.  nowadays, people seem to be using
> 	remote bridges (nowhere near 10 M bits/sec), or microwave links
> 	and LANBridges (expensive?).  theoretically, there is no
> 	distance limitation for 802.4; miles of cable are expensive, though.
 
Another approach to this problem is to use broadband 802.3 to link
building sized baseband subnets.  Some vendors combine a filtering
bridge function with their broadband MAUs.  Functionally we have
an example of this configuration running at our site.

> 	...  what are the max bit rates of 802.4 and 802.5??  at least 
>	10 Mbps !?
> 	(i'll check on this, too.)

Bit rates for combined data & MAC overhead are:
	
	(old)802.4	broadband	5 Mbps
	802.4	broadband		10 Mbps
	802.4	carrierband		5 Mbps

	802.5	(available now)	4 Mbps
	802.5	(sometime)		16 Mbps
	
	
My copy of the 802.5 standard actually lists a 1Mbps rate (amazing).

Politics have certainly been involved in the development of the 802
standards, partially motivated by marketing concerns.  Some
examples of the results of this are an 802.3 standard incompatible
with Ethernet V2,  and the existance of the 802.5 standard.  But
politics in standards is not unique to IEEE,  it's just one of the
things that makes creating good standards so difficult.


Evan K. Wallace @ the National Institute for Standards and Technology
				  (formerly the NBS)

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