"John Stumbles" wrote in message
...
On Sun, 18 May 2008 15:56:20 +0000, Andrew Gabriel wrote:

And [twisted pair] ethernet works exactly the same way -- there's
an isolating transformer at both ends of the cable (rated to 4kV
each IIRC).

Really? I thought 10 and 100BASE-T used basically RS422 Tx/Rx and 1000BASE
upward more or less followed suit with more fancy signalling. Squeezing
the higher rates through transformers whilst still being
backward-compatible with the lower rates is a feat that boggles my little
mind!

Nope, there is an isolating pulse transformer at each end of each signal and
and isolating DC-DC convertor in the PSU for each Ethernet TP interface (if
it is done correctly). The transformer usually looks like a DIL pack but a
bit higher than normal.

There are a few variants of 100M too some which use two pairs and some that
use four pairs, don't mix them as they wont work.
The four pair variant (100base4) was supposed to be for older cat 3 cable
runs AIUI but IME people just plug it in and if it doesn't work they run a
new cat5 anyway.

1000M uses the four pairs IIRC.


--
John Stumbles

Testiculate [v.t]
To wave one's arms around while talking ********.