Copyright © Romilly Bowden 1999.
The Fieldbus Foundation is now proposing High Speed Ethernet ("HSE") instead of the earlier H2 specification, for applications needing a faster communication link than the 31.25 kbps H1 protocol.
HSE runs at 100 Mbps, and is based on existing industrial ethernet specifications.
Note, however, HSE's severe distance limitation. I'm not sure about this, but unless someone has changed the rules, it looks to me as though the maximum network diameter is about 200m, compared with up to nearly 2 km (or 10 km with repeaters) for the low-speed H1 specification. Switching hubs, operating as "store and forward" devices (which examine message addresses and re-transmit only relevant messages), can extend this by connecting multiple networks into a single system, but this inherently introduces transmission delays.
For an excellent background on the theory of ethernet, take a look at the article "Looking deeper into ethernet" by George Thomas in IN+OC Online (September 1999).
By the way, notice the unfortunate possibility of confusion in the UK, where HSE is also well known as an abbreviation for the Health and Safety Executive!