QUESTION 4 [TOTAL MARKS: 25] Q 4(a) [13 Marks] Suppose a client and a Web server directly connected by one link of rate R Suppose the client wants to retrieve an object whose size is exactly equal to 15S, where S is the maximum segment size (MSS). Denote the round-trip time between client and server as RTT (assumed to be constant). Ignoring the protocol headers, determine the time to retrieve the object (including TCP connection establishment) when 4S/R> S/R RTT > 2SIR. You may assume there is no loss and that the threshhold value is large. Be sure to EXPLAIN your answer. Q 4(b) Consider the plot of TCP window size as a function of transmission round given in Figure 4(b). Assume TCP is the protocol experiencing the behaviour in this figure 12 Marks] i) Identify the intervals of time in which slow start is operating. (4 marks) i) What is the value of the threshold after the 6th transmission and what event caused the change? (4 marks) ii) What is the value of the threshold after the 13h transmission and what event caused the change? (4 marks) 14 12 10- 0 0 1 2 3 45 6 7 8 9 10 11 12 13 14 15 Transmission Round Figure 4(b)