In reply to firstname.lastname@example.org:
layering is for protocols that have layers, like ethernet and PciE. The layering agents still hook up to a single driver. e.g. ill make a layering agent for ethernet. It will have UDP2IP agent, IP2Eth, Arp2Eth, etc. Finally, I'll plug it into a single physical layer agent, using the techniques from the paper. btw this technique is also discussed in the cookbook.
anyway. i hope it helps you.