TCP-FO lets you use recent proof of return routability to get 1 MSS of data in the SYN packet. It's akin (if you squint hard) to multiplexing multiple connecti

TCP-FO lets you use recent proof of return routability to get 1 MSS of data in the SYN packet. It's akin (if you squint hard) to multiplexing multiple connections onto one. So TCP-FO ought to have become useful, but mainly it's going to be useful in local networks, not on the big bad Internet. And TCP-FO does require more state on the server.