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From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Re: Thinwire vs. Thickwire (Why 30 nodes only on thin?)
Message-ID: <2480004@hprnd.HP.COM>
Date: 13 Oct 89 19:14:14 GMT
References: <2525@aecom.yu.edu>
Organization: HP Roseville Networks Division
Lines: 33

> / hprnd:comp.protocols.tcp-ip / glen@aecom.yu.edu (Glen M. Marianko) /  6:01 pm  Oct  7, 1989 /
> In article <8909291306.AA06775@jvnca.csc.org>, aggarwal@JVNCA.CSC.ORG (Vikas Aggarwal none) writes:
> > 
> > Just to collect one's views on Thinwire ethernet vs Thickwire ethernet,
> > I am listing what I know about the topic:
> > 
> > THINWIRE
> > ...
> > 	Max segment length - 185 meters (30 nodes per segment)
> 
> This posting reminded me of a question I had about thin ethernet and
> the 30 nodes per segment limit.  Why is this?  I thought on thin
> ethernet you can have a node every .5 meters (vs. thick which is
> marked for much more).  If so, then 185/.5=370 according to my
> calculator with the weak battery :-).  So why couldn't I have more
> than 30 workstations?    Tell ya, the only place I ever saw this in
> print was in a DEC catalog.  Maybe this is a DEC restriction?
> -- 
It comes from the IEEE 802.3 10BASE2 standard. It is actually 30 MAUs
per segment that is important, not how many stations are attached to 
those MAUs.  It is due to the effect of the MAU (leakage current,
loading, etc.) and the effect of the connectors used to attach the MAU
on the media.  The spacing requirement is to ensure you don't have a bunch
of MAUs clustered right together as that can lead to a larger reflection.
MAUs can be closer together on thin than on thick for two reasons: 1) the
attenuation of thin is higher (part of the reason it only goes 185 m);
and 2) the number of MAUs is smaller on thin 30 vs. 100.

> -- Glen M. Marianko  Manager, LAN Services  Glasgal Communications, Inc.
>    151 Veterans Drive  Northvale, New Jersey 07647  201-768-8082
>    glen@aecom.yu.edu - {uunet}!aecom!glen (Courtesy of AECOM & unaffiliated)
> ----------
Pat Thaler