I have a question, why is it that when opening two sockets on Windows and connecting them through TCP, there is about a 40% difference in transfer rate when sending from socket A to B, compared to sending from B to A?
That's not expected. Are you using loopback sockets or are these sockets on different endpoints? Is this unidirectional or bidirectional traffic, i.e. are you doing both transfers from A to B and B to A simultaneously?
I see the issue both on the same computer, so loopback, as well as on two computers on the same LAN. I tested with unidirectional traffic. Pretty easy to test for yourself. The problem appears to be with the TCP protocol implementation. For UDP transmission speed is the same both ways.