(a) (i) Open-loop congestion control approaches work by attempting to prevent congestion occurring on the network. One common open-loop approach is admission control. Explain how admission control works and give examples of two key traffic descriptors that might be used as part of the process. (ii) TCP uses a closed-loop congestion window to regulate traffic flow between senders and receivers. Assuming that the network is initially uncongested and that the default segment size is 1, explain the four phases of control the window may apply to the sender. (b) (i) A traffic shaping system based on a token bucket algorithm is being used to manage congestion in a packet-switched network. Explain how the token bucket algorithm is used to determine if traffic conforms to the agreed policy. (ii) The traffic shaping algorithm determines that packets are being delivered to the network from an end-user at a rate which doesn't conform to the traffic policy, suggest two actions that the system may take to maintain the performance of the network.