In future photonic networks (which will do relativistic cut-through directly in a photonic crossbar without converting photons to electrons and back) the fiber is not just a transport channel but also a photonic buffer (e.g. at 10 GBit/s Ethernet a short reach fiber already buffers a standard 1500 MTU). Of course photonic gates are expensive, individual delays do add up so even with slow light buffers or optical delay loops taken into consideration current TCP/IP header layout has not been optimized for leading edge containing most significant switching/routing information, or even local-knowledge routing (with no global routes). It's too bad IPv6 was not radical enough, so today's legacy protocols have to be tunneled through the networks of the future. I presume this future is some 20-30 years away still.