The protocols in the TCP/IP protocol suite are designed in a layered fashion where each protocol performs a specific function and the interactions between the protocol layers are strictly defined. While the layered approach is a good way to design protocols, it is not always the best way to implement them. For the lwIP implementation, we have chosen a fully modular approach where each protocol implementation is kept fairly separate from the others. In the smaller uIP implementation, the protocol implementations are tightly coupled in order to save code space.
