HTTP2 is not TCP on TCP (that's a very basic recipe for a complete disaster, the moment any congestion kicks in); it's mostly just multiplexing concurrent HTTP

HTTP2 is not TCP on TCP (that's a very basic recipe for a complete disaster, the moment any congestion kicks in); it's mostly just multiplexing concurrent HTTP requests over a single TCP connection. HTTP3 is using UDP for different reasons, although it effectively re-implements TCP from the application POV (it's still HTTP under the hood after all). Basically with plain old TCP your bandwidth is limited by latency, because every transmitted frame has to be acknowledged - sequentially. Some industries/applications (like transferring raw video files over the pond) have been using specialized, UDP-based transfer protocols for a while for this reason. You only need to re-transmit those frames you know didn't make it, in any order it suits you.