Congestion control refers to techniques and mechanisms that can either prevent congestion, before it happens, or remove congestion, after it has happened. In general, we can divide congestion control mechanisms into two broad categories: open-loop congestion control (prevention) and closed-loop congestion control (removal). Match congestion control mechanism to its category. Open Loop Retransmission policy Drag answer here Closed Loop Window policy Drag answer here Admission policy Drag answer here Back pressure Drag answer here