pipes / sockets is the mechanism but protocols is the means. what are some protocols and their elements worth knowing? I suspect folks will point at protocols

pipes / sockets is the mechanism but protocols is the means. what are some protocols and their elements worth knowing? I suspect folks will point at protocols that already exist and work great. But, ideally, we wouldn't start there. But instead, unpack them from the very basic (simplex, synchronous) to the advanced. For example, we have lists and trees as basic data structures to postgres as more advanced for managing data. At some point, you reach for the RDBMS but developers get plenty of mileage out of simpler solutions. Throughout our careers we've bumped into many protocols, I've not been able to digest, appreciate, and study their constituents. When should one mock up a quick protocol vs invest or extend an existing one? Design protocols is fascinating to me. Compared to things that I design on a regular basis, software or APIs, it seems different.