Priscilla Oppenheimer wrote:
> Does this help at all? Speed of light in twisted-pair cable is 177,000
> km/sec. So a bit occupies 177,000 divided by 10 million bits per second, or
> 17.7 meters, in 10 Mbps Ethernet.
>
> 177,000 divided by 100 million bits per second is 1.77 meters for 100 Mbps
> Ethernet. (I'm sure you figured that one out already.)
Some people questioned "the math" above, I'm guessing because it seems
to read that a bit travels 17.7 meters/sec in 10 Mb Ethernet. But
we missed the "physics" issues to keep things equivalent. By dividing
the 177,000 (or 200,000 as someone else suggested, or whatever) by
10M or 100M you do get a "bit length" on the media, but what was missed
was you must also divide the time (1 sec) as well by 10M or 100M.
This was alluded to in the "jam packet" discussion by Priscilla later
on the 16 vs 32 bit jam signal.
There were also some issues with thick ethernet (10Base5) where you
could only 'tap' a segment every 2 meters (as I recall) so that you
can detect a neighbor transmitting at/near the same time (the opposite
extreme of the endpoints). As far as I know this was practically
dropped with 10Base2 and totally dropped with 10BaseT.
There was also a mention of IFG (InterFrame Gap) which is also time
wise (and length-wise) related to bit/signal rate on the media.
Thus the complex blend of physical laws, timing, performance, and
other issues on the media.
Geeez, I hate layer 1 stuff :-)
Jeff Kell <[EMAIL PROTECTED]>
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