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# sol-Bonus - Question 1(5 5 5 = 15 points Consider sending a...

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Question 1 (5 + 5 + 5 = 15 points) Consider sending a large file of F bits from Host A to Host B. There are two links (and one router) between A and B, and the links are uncongested (that is, no queuing delays). Host A segments the file into segments of S bits each and adds 40 bits of header to each segments, forming frames of L = 40 + S bits. Each Link has a transmission rate of N bps. There is no propagation delay. Router R always processes a frame of size L after it receives it for L/2N seconds. Host A --------------- R --------------- Host B (i) When does the first frame arrive at Host B after Host A starts sending the frame at time T? T + L/N + L/2N + L/N = T + L/2N + 2L/N (ii) Assume that the router R can send, receive and process simultaneously and A sends frames continuously (one after another), when will the second frame arrive at Host B? T + L/N + L/N + L/2N + L/N = T + L/2N + 3L/N (iii) When will the file transfer be completed? If F is divisible by S then T + L/2N + ((F/S) + 1) L/N Else if F is not divisible by S then T + L/2N + (( F/S ) + 2) L/N Question 2 (10+10 = 20 points) Consider the following message sent by A to B (a) A → B: E K [M] (b) A → B: E KUb [M] A and B shares the secret key K.

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