Earlier data

QUIC offers both 0-RTT and 1-RTT handshakes that reduce the time it takes tonegotiate and setup a new connection. Compare with the 3-way handshake of TCP.

In addition to that, QUIC offers “early data” support from the get go which isdone to allow more data and it is used more easily than TCP Fast Open.

With the stream concept, another logical connection to the same host can bedone at once without having to wait for the existing one to end first.

TCP Fast Open is problematic

TCP Fast Open was published as RFC 7413in December 2014 and that specification describes how applications can passdata to the server to be delivered already in the first TCP SYN packet.

Actual support for this feature in the wild has taken time and is riddled withproblems even today in 2018. The TCP stack implementors have had issues and sohave applications trying to take advantage of this feature - both in knowingin which OS version to try to activate it but also in figuring out how togracefully back down and deal when problems arise. Several networks have beenidentified to interfere with TFO traffic and they have thus actively ruinedsuch TCP handshakes.