434hw1sol

434hw1sol - CSE 434 TTh 9:15 AM Homework #1 Sample Solution...

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CSE 434 – TTh 9:15 AM Homework #1 Sample Solution September 16, 2003 Please email Catherine ( [email protected] ) if you have questions about the sample solution. 1. (1.1) Imagine that you have trained your St. Bernard, Bernie, to carry a box of three 8mm tapes instead of a flask of brandy. (When your disk fills up, you consider that an emergency.) These tapes each contain 7 gigabytes. The dog can travel to your side, wherever you may be, at 18 km/hour. For what range of distances does Bernie have a higher data rate than a transmission line whose data rate (excluding overhead) is 150 Mbps? 1 gigabyte = 2 30 byte = 1 073 741 824 byte A data tape carries 7 GB. Since a dog can carry 3 tapes at a time, he can carry 3*7*(8*2 30 ) bits per load, at a rate of 18 km / hour (or 0.005 km / second). Let x be the distance Bernie travels. We need to determine for what range of distances Bernie have a data rate higher than 150 Mbps (or 150*10 6 bps), that is, ( 29 sec / 10 150 sec 005 . 0 2 8 7 3 6 30 bits xkm km bits × × × × × Solve to obtain x < 6.01km (1.5) A factor in the delay of a store-and-forward packet-switching system is how long it takes to store and forward a packet through a switch. If switching time is 10 microseconds, is this likely to be a major factor in the response of a client-server system where the client is in New York and the server is in California? Assume the propagation speed in copper and fiber to be 2/3 the speed of light in a vacuum ( 3 x 10 8 m/sec ). The distance between SJC airport (San Jose, CA) and JFK airport (New York, NY) is 2968.2 miles (or 4749.1 km). So the time for a signal from client to server (without switching) is ms s 95 09498 . 0 ) 300000000 * 3 2 /( 1000 * 1 . 4749 = = 10 microsecond : 95ms is approximately 1 : 10 4 , so the 10 microsecond switching time to store and forward packets is unlikely to have a significant effect on the response of the client- server system unless thousands of switches occur along the way. The more significant
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434hw1sol - CSE 434 TTh 9:15 AM Homework #1 Sample Solution...

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