Understand how HTTP/3 redefines packets, sessions, and security at both the transport and application layers to achieve unprecedented network performance.
The QUIC protocol defines its own packet format sitting on top of UDP datagrams. To work efficiently within the UDP space, QUIC implements its own handshake, reliability guarantees, and flow control.
Meanwhile, HTTP/3 uses QPACK (Quick Protocol Header Compression) to efficiently compress HTTP headers. This is more optimized than HTTP/2's HPACK and prevents head-of-line blocking.
QUIC introduces the concept of a Connection ID (CID). This randomly generated identifier is used to track sessions between clients and servers, rather than relying on traditional IP addresses and ports.
The use of CID is the key to achieving connection migration. Even if a user's IP address changes (e.g., switching networks), the session remains active via the CID, enabling seamless continuity.
QUIC integrates the TLS 1.3 handshake directly into its connection establishment process. Encryption is no longer an optional overlay but an inherent component of the protocol.
This integration eliminates the complexity of separate TCP + TLS handshakes and is the technical prerequisite for 0-RTT. All QUIC frames are authenticated and mostly encrypted, providing robust security.