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Question 7 (1) Explain what the congestion control in computer networks is, and how it differs [15%) from the flow control. Which layers are responsible for the flow control and congestion control? (11) Explain what are the Explicit Congestion Notification (ECM) and Congestion [10%] Window Reduced (CWR), and how they work (iii) Draw schematically the dependence of the congestion window W. (in kilobytes) [50%] on the transmission time 1 (in the RTT units) for congested internet assuming the following scenario: At t = 33RTT the first three duplicate ACKs have been received by the sender host before the RTO. After this another three duplicate ACKs were received at t = 67RTT, and then at t=75RTT the first RTO of the sender's acknowledgement clock has occurred. Between t = 75 RTT and t=85 RTT the network operates without disruptions. You need to draw the dependence for a time interval between t=0 and t=85 RTT and explain in detail each stage of the congestion window evolution. Assume that at t=0 the first packet loss took place due to the RTO and the initial window size is set to W. - MSS - 1 kilobyte. The slow-start threshold for a fully open congestion window is SST, = 64 kilobytes. (iv) Consider that in the case from part (iii) at t=85 RTT the receiver reports to the [25%) sender that its sliding window is W, = 30 kilobytes, and W, is kept at this value in the following transmissions. Find how long it will take (beginning from t=85 RTT) before the full window will be sent. Your answer should be in units of RIT