what's the relation between cwnd (Congestion Window ) and unacknowledged packets ?

Question

Plz explain this :

The amount of unacknowledged data at a sender must not exceed the minimum of cwnd (congestion window ) and rwnd ( receiver side window )

$LastByteSent - LastByteAcked<= min\{cwnd , rwnd \}$

What's the role of cwnd here ?

Unacknowledged data is already outstanding in the network so what's the relation between cwnd and unacknowledged packets here ?

Answer 1

The unacknowledged data at the sender side must be less than or equal to the minimum of cwnd and rwnd.If it does not follow this condition then in that case buffer overflow might be there.As we have seen in TCP when an advertisement window comes from receiver side  to sender side then sender can not send more than that much amount as of advertisement window throughout .Hence we always follow this condition otherwise possibility of buffer overflow.