TCP's fundamental problems
HTTP/2 improved application-layer efficiency, but TCP still has deep problems:
1. Slow setup: TCP (1 RTT) + TLS (1-2 RTT) = 2-3 RTTs before sending data
2. HOL blocking: one lost TCP segment blocks ALL HTTP/2 streams
3. No migration: IP change (WiFi → 4G) kills the TCP connection
4. OS bottleneck: TCP is in the kernel — updating TCP behavior requires OS updates
QUIC solves all four at once.