UDP is the New TCP
For 30 years, TCP (Transmission Control Protocol) ruled the web. It provided reliability, but at a cost. HTTP/3 changes the game by running over QUIC (a UDP-based protocol). This eliminates Head-of-Line blocking and drastically improves performance on unstable mobile networks.
The Head-of-Line Blocking Problem
In HTTP/2 (which uses TCP), if one packet gets lost, the entire connection waits. This is like a single slow car blocking a multi-lane highway. QUIC solves this by treating streams independently. If stream A drops a packet, stream B keeps moving.
Zero Round Trip Time (0-RTT)
One of the most magical features of QUIC is 0-RTT resumption. If a client has spoken to a server before, it can start sending data immediately without the lengthy 3-way handshake of TCP+TLS. This creates a perceived 'instant' connection for repeat visitors.
Implementing HTTP/3
Enabling HTTP/3 isn't just a code change; it's infrastructure. Nginx 1.25+ supports it, but you need to ensure your firewall allows UDP traffic on port 443 (previously, only TCP was needed). Cloudflare and AWS CloudFront now offer one-click HTTP/3 support.