Path: utzoo!utgpu!watserv1!watmath!att!att!iuvax!cica!ssw
From: ssw@cica.cica.indiana.edu (Steve Wallace)
Newsgroups: comp.dcom.lans
Subject: how far can you run ethernet over fiber
Message-ID: <7178@cica.cica.indiana.edu>
Date: 30 Oct 90 00:58:31 GMT
Organization: Center for Innov. Comp. Appl., Bloomington, IN
Lines: 25


How far can you run ethernet over fiber before the collision
detecting mechanism breaks down?  I came up the following which
seems too far:

     Min. frame size = 480 bits
     Time to transmit min. frame = frame size / transmission rate
                                 = 480 / 10,000,000 bits per sec.
                                 = .000048 sec.

     Distance light travels down the fiber during the
     transmission of min frame = .000048 * .8c
                  = .000048 * 240,000,000 meters/sec
                  = 11,520 meters

     11,520 meters is the round trip time.  This divided by 2
(the sender A must hear sender B transmitting) gives a ball park
figure (5,760 meters).  I'd give myself a fudge factor of 30
percent and end up with about 4,000 meters.  Is this close?


Thanks,

Steven Wallace
wallaces@ucs.indiana.edu