20105ee132B_1_hw4

20105ee132B_1_hw4 - UCLA Electrical Engineering Department...

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UCLA Electrical Engineering Department EE132B HW Set #4 Professor Izhak Rubin Problem 1 Consider an ARQ stop-and-wait communication session between to stations A and B. 1) If station A intends to transmit a single data frame, what is the average number of retransmissions required for the successful transport of data frames? (Hint: Let p denote the probability that the transmit frame is received with error. Express the average number of retransmissions in terms of p.) 2) If station A intends to transmit M data-frames (M 2), what is the probability that the number of retransmissions N R (M) is equal to 2? (Hint: Express the probability in terms of M and p.) Problem 2 Consider an ARQ stop-and-wait scheme which is similar to the scheme described in Problem 1 but a distinct feature: suppose that an acknowledgement can be lost during its transmissions with probability q. If an acknowledgement is lost, station A will retransmit the data-frame after time-out. Such retransmission process continues until station A receives an acknowledgement. 1) If station A intends to transmit a single data frame, what is the average number of retransmissions
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20105ee132B_1_hw4 - UCLA Electrical Engineering Department...

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