We have to design a special device....to implement a special protocol on top of ethernet. Rabbit 4k devices look like a good choice, but it comes with TCP/IP stack built in.
How easy it is in Rabbit 4K to get rid of the the TCP/IP stack from OS and take charge of packets arriving over ethernet.
I am aware of NE2000 compatibility. Please let me know whether it will be helpful and any other pointers will be of big help.