QUIC (QUIC)
A transport protocol built on UDP that replaces TCP for HTTP/3. Provides built-in encryption, eliminates head-of-line blocking, enables connection migration, and reduces handshake latency.
Full Explanation
QUIC was developed by Google and standardized as RFC 9000. Think of it as TCP + TLS + HTTP/2 improvements, all rolled into one protocol running over UDP. It solves real problems that TCP can't fix without breaking backward compatibility.
The big wins for CDN traffic: independent stream multiplexing (packet loss on one stream doesn't block others), built-in TLS 1.3 (1-RTT handshake, 0-RTT resumption), and connection migration (switch from WiFi to cellular without dropping the connection). That last one is huge for mobile users.
QUIC also improves congestion control. Because it runs in userspace (not the kernel), CDN providers can iterate on congestion algorithms faster than waiting for OS kernel updates. This means better performance on varying network conditions.
Examples
# Check if a site supports QUIC/HTTP/3
$ curl -sI https://example.com | grep -i alt-svc
alt-svc: h3=":443"; ma=86400
# Force HTTP/3 with curl
$ curl --http3-only -I https://example.com
HTTP/3 200
# Nginx: enable QUIC
server {
listen 443 quic reuseport;
listen 443 ssl;
http3 on;
ssl_early_data on; # Enable 0-RTT
add_header Alt-Svc 'h3=":443"; ma=86400';
}
# Verify with Chrome DevTools
# Network tab > Protocol column shows "h3"Video Explanation
Frequently Asked Questions
A transport protocol built on UDP that replaces TCP for HTTP/3. Provides built-in encryption, eliminates head-of-line blocking, enables connection migration, and reduces handshake latency.
# Check if a site supports QUIC/HTTP/3
$ curl -sI https://example.com | grep -i alt-svc
alt-svc: h3=":443"; ma=86400
# Force HTTP/3 with curl
$ curl --http3-only -I https://example.com
HTTP/3 200
# Nginx: enable QUIC
server {
listen 443 quic reuseport;
listen 443 ssl;
http3 on;
ssl_early_data on; # Enable 0-RTT
add_header Alt-Svc 'h3=":443"; ma=86400';
}
# Verify with Chrome DevTools
# Network tab > Protocol column shows "h3"Related CDN concepts include:
- HTTP/3 — The latest HTTP version, built on QUIC instead of TCP. Eliminates TCP head-of-line blocking, enables …
- TLS (Transport Layer Security) (TLS) — The encryption protocol that secures HTTPS connections. TLS encrypts data in transit between client and …