Question

Half-duplex and full duplex operation issues?

Half Duplex, Full Duplex, Ethernet, fast ethernet, Gigabit ethernet, UTP, 10Mbps, 100Mbps, 1Gbps

Although I have studied some information on half-duplex and full-duplex operation I am not entirely sure how the following figures work out, any help would be appreciated.

For this scenario lets assume UTP cable is being used: So far in my studies, the information provided to me states that the following cable configurations/statistics are correct.

10 Mbps half-duplex operation = 2 of 8 wires used.
100 Mbps half-duplex operation = 4 of 8 wires used.
1 Gbps full-duplex operation = 8 of 8 wires used.

Now I know that going from half-to-full-duplex allows a theoretical 2x line bandwidth increase, but I do not understand how going from 2 wires in ethernet use to 4 wires in fast ethernet use, increases the speed ten-fold, while maintaining half-duplex operation?

Not only that but the increase from fast ethernet to gigabit ethernet is also ten-fold, yet it has been upscaled to full-duplex, does this mean all 8 wires being used at half-duplex gives 512Mbps? If yes then why is the increase not as great as the previous, and if not then please explain.

I am sure I am probably missing something small yet fundamental into how these speeds are calculated, but I just dont see how you get a ten-fold increase by doubling the wires in use for one scenario and then a different increase in the next?

Thanks in advance, Sean.

Hi,

The increase in speed is only partially by the wires. Half to full duplex gives you a theoritical doubl;ing of speed but not always in reality. You can use 10 MBPs at full duplex, but only with a switch and not a hub.
The speed increase from 10 to 100 is entirely by better technology and faster data flow down the same wires. Better frequencies and the like. The speed increase in 100 to gig is also an increase in technology and is a lot more to do with the cards then the cables since 100 and GB can use the same cables in full duplex.
Concentrating on the wires is diverting your attention from the real issue, the technology and how the cards have changed.