QUIC vs TCP: Connections, Streams and Reliability
TCP supplies a reliable ordered byte stream. QUIC is a secure transport over UDP that supplies independently ordered streams within a connection.
By Protocol Explorer ·
Connection setup and security
TCP uses a three-way handshake to establish a connection. Applications can then negotiate TLS separately when encryption is needed. QUIC integrates a TLS handshake into its transport setup and encrypts much of its packet content. QUIC can support 0-RTT in suitable resumed connections; 0-RTT data has replay considerations and is not available for every connection.
Streams and packet loss
TCP exposes one ordered byte stream per connection. If earlier data is missing, later bytes in that stream wait for recovery. QUIC multiplexes streams within one connection: loss affecting one stream does not necessarily block delivery of unrelated stream data, although congestion control still applies to the connection.
Transport and addressing
TCP is an IP transport protocol. QUIC packets are carried in UDP datagrams and include connection identifiers that can help a connection survive some network path changes. Neither protocol makes applications immune to network loss or congestion.
HTTP examples
HTTP/2 is commonly used over TCP with TLS. HTTP/3 uses QUIC. These versions preserve HTTP semantics while changing framing and transport; application performance depends on network conditions, implementations and workload.
Explore further
TCP handshake guide · QUIC overview · HTTPS and TLS
The TCP interactive lesson is free. The QUIC overview is free; the full QUIC lesson is part of the one-time $4.99 Pro pass, which requires an account to purchase and restore.