TCP Fast Open
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Y. Cheng, J. Chu, S. Radhakrishnan, A. Jain · 2014-12
Abstract
RFC 7413 defines TCP Fast Open (TFO), an extension that allows application data to be sent in the TCP SYN packet during connection establishment. TFO uses a server-issued cookie to authenticate returning clients, enabling data exchange to begin one round-trip earlier than the standard three-way handshake requires.
Why This RFC Matters
The TCP three-way handshake imposes a minimum one-round-trip overhead before any application data can be sent — a latency cost that accumulates across millions of short-lived connections on the web. TCP Fast Open, developed by Google and formalized in RFC 7413, eliminates this overhead for repeat connections by carrying data in the SYN packet. Google's experiments showed measurable page-load improvements, particularly for users on high-latency connections. TFO influenced the design of QUIC's 0-RTT connection establishment, demonstrating that the idea of sending data before a handshake completes is sound even if TFO itself saw limited deployment due to middlebox interference.