Network and Delivery OptimizationLesson 5.1

How HTTP/2 and HTTP/3 improve web performance over HTTP/1.1

HTTP/1.1 limitations, head-of-line blocking, HTTP/2 multiplexing, HTTP/2 header compression (HPACK), HTTP/3 QUIC, 0-RTT connection, connection migration, server push deprecation

HTTP/2 and HTTP/3

HTTP/1.1 opens up to 6 TCP connections per origin. If you have 30 assets to load, they queue. Each connection requires its own TLS handshake. Headers repeat uncompressed on every request.

HTTP/2 solves this with multiplexing: unlimited parallel streams over a single TCP connection. Headers are compressed with HPACK. This makes the HTTP/1.1 optimization of bundling files to reduce connections counterproductive — HTTP/2 prefers many small files.

Check if your server supports HTTP/2:

curl -I --http2 https://example.com | grep HTTP

HTTP/3 replaces TCP with QUIC (UDP-based), solving TCP head-of-line blocking — a scenario where a single dropped packet stalls the entire connection. QUIC handles packet loss per-stream, so other streams continue unaffected.

HTTP/3 also provides 0-RTT connection resumption for repeat visitors — the TLS handshake is skipped on reconnect, reducing TTFB significantly on lossy mobile networks.

# Nginx config to enable HTTP/2
server {
  listen 443 ssl http2;
  ssl_certificate /etc/ssl/cert.pem;
  ssl_certificate_key /etc/ssl/key.pem;
}

# Enable HTTP/3 (QUIC) — requires Nginx 1.25+
server {
  listen 443 quic reuseport;
  listen 443 ssl;
  add_header Alt-Svc 'h3=":443"; ma=86400';
}