Q.2 a) Suppose that 2 bits are used for the sequence number of a Go-back-N protocol. With the aid of a time-line diagram, explain why we cannot set the window size to 4 (6 marks) (b) Suppose the Go-back-N transport-layer protocol is adopted by a sender to send three packets to a receiver in an internetwork. The size of the sequence number field is 5 bits and the window size is set at 6The second packet is delayed as shown in Fig. Q2. i.Copy the time-line diagram as shown in Fig. Q2 to your answer book and complete it with all the packet/ACK transmissions, timer and windows at both ends. State your assumptions (9 marks) ii. Suppose that the system can detect error bits but not able to correct them. Calculate the line utilization of the system if the data rate, propagation time, packet size and bit error rate of the system are 30 Mbps, 10s, 128 bits and 2x10, respectively (6 marks) What is the maximum window size for this system? Calculate the line utilization of (4 marks) iii. the system if the maximum window size is now being used. Given: Utilization of the Go-Back-N protocol: U = min(U, , U2 ) W(1 p) T. where, U,- 1+2ap(1+2a)(-p+ pw) Sender Receiver StartenanPacket Packet 1 Packet 2 Timeout Q.2 a) Suppose that 2 bits are used for the sequence number of a Go-back-N protocol. With the aid of a time-line diagram, explain why we cannot set the window size to 4 (6 marks) (b) Suppose the Go-back-N transport-layer protocol is adopted by a sender to send three packets to a receiver in an internetwork. The size of the sequence number field is 5 bits and the window size is set at 6The second packet is delayed as shown in Fig. Q2. i.Copy the time-line diagram as shown in Fig. Q2 to your answer book and complete it with all the packet/ACK transmissions, timer and windows at both ends. State your assumptions (9 marks) ii. Suppose that the system can detect error bits but not able to correct them. Calculate the line utilization of the system if the data rate, propagation time, packet size and bit error rate of the system are 30 Mbps, 10s, 128 bits and 2x10, respectively (6 marks) What is the maximum window size for this system? Calculate the line utilization of (4 marks) iii. the system if the maximum window size is now being used. Given: Utilization of the Go-Back-N protocol: U = min(U, , U2 ) W(1 p) T. where, U,- 1+2ap(1+2a)(-p+ pw) Sender Receiver StartenanPacket Packet 1 Packet 2 Timeout