More work may be needed on T/TCP congestion control. As a a compatible extension of TCP, T/TCP includes all the normal TCP congestion control machinery, which comes into play as transactions become larger. However, it was observed that TCP has no congestion control on SYN segments, and if there is heavy use of T/TCP for minimal transactions, the Internet will be filled with SYN segments. It may be necessary to include some rate-based control over transactions, in addition to the normal byte-based congestion control of TCP.
Initial Window Guess
"At the moment T/TCP sort of handwaves and says 'oh 4K sounds about safe to send into an unknown window'. On something like a low speed network thats not nice (eg AX.25). Something like 2*mtu might be safer since thats also the current policy for initial window. There was a lot of work done to make the initial congestion window two frames not one, and the mathematical end of the ietf did a lot of work to prove to the skeptics that they were right."
-- Alan Cox