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| Authored by: JamesK on Saturday, May 25 2013 @ 03:35 PM EDT |
The limit was not 15 or 30 feet, it was about 500 metres for 10base5 and 200 M
for 10base2. Twisted pair 10baseT is good for 100 M These are the distances
that are designed as maximum, but in practice you could go a bit beyond them.
The other distance limitation, that had nothing to do with cable type, was the
collision distance. Because Ethernet was originally half duplex, sharing a
cable or hub, it was possible to have collisions. So, the designers said that a
valid collision must take place within 512 bit times or 64 bytes. This limits
copper cables to a length of 0.5 x 51.2 mS x velocity factor (about 65% - 70%)
or roughly 5 Km. Of course, that distance is far greater than can be carried
over copper without repeaters. The 0.5 factor is to allow for return trip
time.
With switches, collisions are no longer a factor and fibre can carry
multi-gigabit Ethernet hundreds of kilometres without any repeaters.
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