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).
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