Flow control is a mechanism to prevent the sender from overhelming the receiver. rwnd - receive window. Each ACK packet carries latest rwnd value for each side.
cwnd - congestion window. Sender-side limit on the amount of data the sender can have in flight before receiving an acknowledgment (ACK) from the client. cwnd is set up for each TCP connection. Maximum amount of data in flight is the minimum of the rwnd and cwnd.
- Time to reach the cwnd size of size N: Time = RTT(log(N/initial cwnd)) (RTT - round trip time)
Specifies algorithms for how to grow a window to minimize further packet loss once cwnd is reset.