I wounder what the longest chain of protocols you can construct is? We all know HTTP over TCP over IP over Ethernet. But, Ethernet can travel over USB and you can have more USB ports as a PCIE card and a PCIE card can be run over thunderbolt, so you could have HTTP over IP over Ethernet over USB over PCIE over Thunderbolt. Can you do longer? Is their a database of protocols that could used to authoritatively answer this question? Are cycles possible?

On second thought, with egpu enclosures could you do thunderbolt over pcie over thunderbolt over pcie over thunderbolt, etc. It will have to remain a mystery because I have no interest digging though some arcane standard only accessible to those who have made a blood sacrifice to the IEEE gods.