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From TCP to UDP, head-of-line blocking, 0-RTT, connection migration and deployment tips
Every web page load depends on protocols that move data between browsers and servers. HTTP/3, standardised by the Internet Engineering Task Force as RFC 9114 in June 2022, is the latest major version of HTTP. It runs over QUIC, a transport protocol standardised as RFC 9000 in May 2021, which grew out of work started at Google in the early 2010s. Major browsers, CDNs and large websites already support it.
| Version | Year | Transport | Key feature |
|---|---|---|---|
| HTTP/1.1 | 1997 | TCP | Persistent connections |
| HTTP/2 | 2015 | TCP | Multiplexing many requests on one connection |
| HTTP/3 | 2022 | QUIC over UDP | Faster setup, independent streams, connection migration |
HTTP/2 allowed many requests to share one TCP connection, but TCP delivers data strictly in order. If a single packet is lost, all streams wait until it is retransmitted. This is transport-level head-of-line blocking, and it hurts most on lossy mobile networks.
Setting up a secure TCP connection also requires separate handshakes for TCP and TLS, adding round trips before data flows.
QUIC runs over UDP, which does not enforce ordering, and implements its own reliability, congestion control and ordering per stream.
A lost packet affects only the stream it belongs to. Other resources, such as images and scripts, keep loading.
QUIC integrates TLS 1.3 directly, combining transport and encryption setup, typically in one round trip. For returning visitors, 0-RTT resumption can send data immediately.
TCP connections are tied to IP addresses and ports. When your phone switches from Wi-Fi to mobile data, TCP connections break. QUIC uses connection IDs, so connections can survive network changes, which is useful for users on the move.
Encryption is mandatory in QUIC, and more of the protocol's metadata is encrypted, improving privacy.
Gains are often modest on fast, stable connections and larger on poor ones, which makes HTTP/3 particularly relevant for mobile-heavy markets such as India.
Servers advertise HTTP/3 support through:
Alt-Svc: h3=":443"; ma=86400All major browsers support HTTP/3, and a substantial share of websites, roughly a third by various measurements, have enabled it, largely through CDNs.
Not always. The biggest improvements appear on poor or changing networks. On fast wired connections, differences may be small.
Not directly, but faster, more reliable page delivery supports better user experience and Core Web Vitals.
Usually no. It is enabled at the server or CDN level.
HTTP/3 and QUIC modernise how the web moves data, with faster connections, resilience to packet loss and seamless network switching. For most sites, enabling it through a CDN is a low-effort performance upgrade, especially for mobile users.