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# s6 - Cmpen/EE 362 Asst 6 Solution Spring 2009 Problem 1 A...

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Cmpen/EE 362 Asst. 6 Solution Spring 2009 Problem 1 . A two-way link has a data rate of 40 kb/s while transmitting data in either direction, and a propagation delay of 20 milliseconds in each direction. A is sending frames of L bits to B using stop-and- wait ARQ. A 160-bit acknowledgment frame is returned by B immediately after B receives a full frame of data. from A. Define efficiency as the percentage of time that A is sending a frame of data. This ignores the additional inefficiency due to overhead in A's frames a) Draw a space-time diagram of the communication process. b) What range of values of L gives an efficiency of at least 50% ? ACK f Solution. a) T = 160/40000 = 4 milliseconds. T = L/40000. b) We see from the diagram that A will be sending 50% of the time if f f f T + 20 + 4 + 20 = 2 T ; T = 44 milliseconds . f T = L/40000 = 44*10 ; L = 1760. Thus L \$ 1760. -3

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Problem 2. Make the assumption transmission is over a single link, so frames can’t “jump” over each other in time. a) Consider a go-back protocol with 3-bit sequence numbers and a window range of 7
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s6 - Cmpen/EE 362 Asst 6 Solution Spring 2009 Problem 1 A...

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