Besides bsd socket, there are other apis, like winsock, TLI. Protocol implementation includes network layer (routing, address resolution, data link layer, physical layer and etc). BSD stack is a good implementation, however, it is NOT a standard. BSD socket api is a standard. There are many other stacks including interpeak, GHSNet2 and many other stack vendors.

I am also working on network stacks. There are far more for you to learn.