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Intro to Computer Networks Spring 2020 EECS148/CS132 Homework 3: Solution Sketch Topic: Transport Layer and TCP University of California, IrvineCS 132HW3sol-2020-updated

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Prof. Athina Markopoulou Intro to Computer Networks Spring 2020 EECS148/CS132 Homework 3: Solution Sketch Topic: Transport Layer and TCP Posted on 5/10/2020 1. (50 Points) Reliability Protocols: Go-ba ... ck-N, Selective Repeat, TCP. Suppose that host A sends N = 8 packets to host B using one of the following protocols we learned in class (a) Go-Back-N (GBN) (b) Selective Repeat (SR) (c) TCP (considering only reliability, not congestion control). All protocols have (sender and/or receiver if applicable) window sizes equal to 5 packets and timeout value equal to 10 ms. The one-way propagation delay between host A and B, as well as from B to A, is 4ms, the transmission time of each data packet is 1ms, and the transmission time of each ACK packet is 0 ms. Suppose that Packet No. 5 is lost, the ACK generated when packet 2 is received is also lost, and no other packet is lost. The beginning of the space-time diagrams are provided below; the sequence numbers refer to packets. • Fill out the rest of the diagrams until all 8 packets are sent and acknowledged. Show all packets (transmissions, retransmissions and acknowledgments), their sequence numbers and the times they were sent/received. • For each scenario, write down the total time, i.e., when all 8 packets are successfully acknowledged to the sender A. • Note that we assume timer starts at the beginning of transmission [as discussed in book section 3.5.4, figure 3.33 and as we posted in discussion] while packet is being delivered to lower layers. The FSMs in fig 3.20 seem to convey contradictory hints as this might vary based on the implementation. (a) (15 Points) Go-Back-N. Answer: Total time = 43 ms, as per figure below. [Show More]

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