Refer to RFC 1122 and RFC 2581 for more information on TCP congestion window.
128 to 1,073,741,824
This is the maximum value a TCP cwnd can grow to. Note that even if an application uses setsockopt(3SOCKET) to change the window size to a value higher than tcp_cwnd_max, the actual window used can never grow beyond tcp_cwnd_max. Thus, tcp_max_buf should be greater than tcp_cwnd_max in general.