The first is full compatibility at higher layer protocols,
such as exists with Foundation Fieldbus HSE,
MODBUS/TCP,
Ethernet/IP and P-Net on IP to name but a few.
This approach is especially prevalent in building automation fieldbusses.
Another approach is compatibility of data objects and models,
such as is the case with PROFINET.
This approach requires the use of proxy hardware to allow communication between the fieldbus media.
A lesser amount of compatibility is offered through the use of application layer profiles from existing protocols,
as is implemented in Ethernet Powerlink and EtherCAT.