+Data is broken into frames and each one is transmitted using the CSMA/CD algorithm until it arrives at the destination without colliding with any other packet. A station is either transmitting or receiving or idle at any instant. Newer equipment supports full-duplex, where a station can transmit acknowledgments without halting a receive. Full duplex requires a switch with support, rather than a hub. The bandwidth is from 10 Mbit/s (ethernet) to 100 Mbit/s (fast ethernet) to 1000 Mbit/s (gigabit ethernet.) Some time ago, a 10 Gbit/s ethernet standard was agreed upon, and it is now (2002) possible to buy commercial equipment for this. Somewhere . 

+Ethernet cables are classified as "XbaseY", e.g. 10Base5 , where X is the data rate in Mbps, "base" means "baseband" (as opposed to radio frequency) and Y was originally the maximum cable run from end to end (500m for 10Base5, nearly 200m for 10Base2, 100m for 10BaseT), but the introduction of Fibre and 1000BaseT, the T more seems to refer to Twisted Pair these days . The original cable was 10base5 ("full spec"), others are [10Base2] and [10BaseT] which is now (2002) dissappearing. [100BaseT] is the desktop standard, and [1000BaseT] is quite reasonable for servers.