This article is just another one which takes the complexities and puts them
into nice laymans terms so the budding networkers of the world can
understand them.
----- Original Message -----
From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
To: whatshakin <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Saturday, October 07, 2000 12:15 PM
Subject: Re: Ethernet Trivia
> At 10:20 PM 10/6/00, whatshakin wrote:
> >This makes it sound like there is actually something tangible being put
on
> >the wire. Bits are merely ones and zeros which are signaled by different
> >voltages etc in the line encoding.
> >
> >Bits do not occupy line space.
>
> Sure they do. Wasn't it Einstein that said time and distance are related?
> (Don't quote me on that.) Seriously, the discussion of how much space a
bit
> takes on the wire has been going on since Ethernet was invented. See
> Optimized Engineering's Technical Compendium for a discussion that brings
> up the space issue.
>
> http://www.optimized.com/COMPENDI/EN-Propa.htm
>
> And here's some more related trivia. Do you know why a 32-bit jam is sent
> when a station detects a collision? It's to increase the time and distance
> of the collision event. It's to avoid the case where the collision happens
> right next to you and you've stopped transmitting by the time the
collision
> event hits a repeater that could be 500 meters away.
>
> Why didn't they use a 16-bit jam? Because on thick coax Ethernet cable the
> signal travels at 231,000 kilometers per second. This means a bit occupies
> 23.1 meters on thick Ethernet. 16 x 23.1 wouldn't have been enough. 32 x
> 23.1 is 739 meters. An extension of 32 bits allows the sender to busy out
a
> maximum 500-meter segment. This explains both the jam size and the fact
> that a repeater extends a received fragment by at least 32 bits.
>
> I know this is a strange way of looking at things, but it is one way that
> engineers, including the inventors of Ethernet, looked at the Ethernet
> parameters.
>
> Priscilla
>
>
> >Measurements of how fast data can be moved over a wire are the time it
takes
> >for a signal at one end to be heard at the other. The amount of data
> >(signals) which can be moved across a wire is ascertained by the line
> >encoding method, and how many signals the encoding system can be made to
> >produce in a second. Minus the delay factors between point A and B of
> >course.
> >
> >I seem to recall reading some papers from folks at the US Berkley
computer
> >science dept a few years back that researched the various line encoding
> >techniques etc that were quite interesting. I cannot find them now that
I
> >need them though!!
> >
> >BTW, my calculations for the speed of light resulted in 299,793,100 m/s
> >
> >
> >----- Original Message -----
> >From: Leigh Anne Chisholm <[EMAIL PROTECTED]>
> >To: Kevin L. Kultgen <[EMAIL PROTECTED]>; Tim O'Brien
> ><[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
> >Sent: Friday, October 06, 2000 4:15 PM
> >Subject: RE: Ethernet Trivia
> >
> >
> > > Ahh Kevin, your post reminds me of some research I did when I was
putting
> >together my paper on LAN Switching for CertificationZone. I was looking
at
> >how to calculate the round-trip propagation delay for 10BaseT networks.
> >Here's a few technical numbers for you you (and possibly other Groupstudy
> >members) might find interesting.
> > >
> > > --- Beginning of Calculations ---
> > >
> > > Electrical signals travel in a copper wire travel (propagate) at
> >approximately two-thirds the speed of light. Remembering that the speed
of
> >10 Mbps Ethernet is 10,000,000 bits/second, we can determine the length
of
> >wire that one bit occupies, by using the following calculation:
> > >
> > > Speed of Light in a Vacuum = 300,000,000 meters/second
> > >
> > > Speed of Electricity in a Copper Cable = 200,000,000 meters/second
> > >
> > > 20,000,000 meters/second / 10,000,000 bits/second = 20 meters per
bit
> > >
> > > The minimum size Ethernet frame consisting of 64 bytes (512 bits)
occupies
> >10,240 meters of cable.
> > >
> > > --- End ---
> > >
> > >
> > > -- Leigh Anne
> > >
> > >
>
>
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
>
>
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