Of course bits occupy line space. It's called
wavelength. And bits aren't signalled by
different voltages, in ethernet. They are
signalled by a voltage change, from -1 to +1
or +1 to -1. Try doing a web search on Manchester
encoding.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
whatshakin
Sent: Saturday, October 07, 2000 12:20 AM
To: [EMAIL PROTECTED]
Subject: Re: Ethernet Trivia
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.
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
>
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> > Kevin L. Kultgen
> > Sent: Thursday, October 05, 2000 10:12 AM
> > To: Tim O'Brien; [EMAIL PROTECTED]
> > Subject: Re: Ethernet Trivia
> >
> >
> > They would both start at the same time. The 100bT interface would be
> > placing bits on the wire faster than the 10bT interface and would
complete
> > placing bits on the wire in 1/10 the time. But those bits can't
actually
> > move any faster through the copper medium. The copper isn't more
> > conductive
> > (it's still Cat 5(e)) and the speed of light hasn't increased.
> > So the bits
> > that are placed on the wire will move through the wire at exactly the
same
> > rate. If the bits for 10bT consume 5 meters of cable megth before the
NIC
> > moves the the next bit then a bit for 100bT will be 1/2 meter (.5
meters)
> > before the next bit is placed on the wire. This is just an
> > example, I'm not
> > sure of the exact lengths of the bits on the wire, but the point
> > is that the
> > bits can't move any faster because the speed of electricity through
copper
> > is fixed. The difference is that the 100bT card is placing bits
> > on the wire
> > 10x faster than the 10bT card. And 1000bT (gigabit ethernet)
> > places bits on
> > the wire 100x faster than the 10bT card (or each bit would be .05
> > meters (5
> > centimeters), given the above example).
> >
> > So, on 100bT the end of the packet (the whole packet) would arrive
before
> > the 10bT would be done (in fact depending on the size of the packet 10bT
> > might still be sending the preamble or headers), but the start of the
> > packets (first bit of the preamble) would arrive at the same time.
> >
> > HTH,
> >
> > Thanx
> >
> > Kevin L. Kultgen
> >
> > Disclaimer: YMMV, the 5/.5/.05 meters are all fictional, I was told at
one
> > point how long a bit is on the wire but I forgot it. If I have anything
> > that needs clarification (or correction) then please feel free to
> > add it or
> > request it. This is helping me too, because I'm looking at taking the
> > CNX-Ethernet exam (http://www.mycnx2000.com, http://www.cnx2000.com).
>
> **NOTE: New CCNA/CCDA List has been formed. For more information go to
> http://www.groupstudy.com/list/Associates.html
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