thats a pretty big subject , I would be thinking along these lines

the physical layer depends on :-
transfer rate is it megabytes/S or bits/S
transfer distance is it kilometers or millimeters
transfer cost [priority,interrrupts,reliability,latency]
is it a master slave or a multi master or peer to peer network
does the physical layer need collision sense , ack/nak ,crc
the protocol layer depends on :-
is it just master multi slave or will it need multi master or peer to peer comms
does it need ack/nak ,crc
is it a compelled sequence or asyncronous system
will the slaves be polled or do they need separate channel/s to signal master
when they have the need