Question

Suppose in TCP the congestion window and size is 1500 and the receiver window size is 3000. The sender can send only 1000 bytes which has not been acknowledge. How many more bytes it can send?

Answer 1

Window size = Minimum ( Congestion window, Receiver Window)

                       = Min(1500, 3000) = 1500 

Since the sender has already sent out  1000 B which have not been acknowledged, it can still send 1500-1000 =  500 more bytes