There is not much to grok really. It's just that there's plenty of low level transmission protocols like Ethernet, PPP or CDP, there's plenty of even lower level physical media types like copper or fiber or pigeons. Then there's a lot of higher level things that rely on IP: TCP/UDP, ATP, SPX and so on, and then the entire universe built upon them. But in the middle there is just IP (v4 or v6) and that's it.