4-16. Derek is disappointed in his high-speed Internet service. Although the Int

Question

4-16. Derek is disappointed in his high-speed Internet service. Although the Internet is seldom down, it kicks into slow mode quite often, which Derek considers to be a failure. He has tried three service providers with varying degrees of success. The number of failures in a typical eight-hour day and the average time to regain high-speed service are shown below. Derek must choose one of the following options. Calculate the system availability for each option. Which service would you recommend? Time to Regain ISP Number of Failures Service Xceptional 12 2 minutes Yourizon 4 4 minutes Zelltell 3 10 minutes

Explanation / Answer

The system availability can be calculated on the basis of it's Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR). The system availability = MTBF / (MTBF + MTTR)

In the given problem, the time to regain ISP number is the MTTR and the MTBF is caluclated as (8*60) / (Number of failures in 8 hrs). The system availability for each is calculated below. (The data is not in a proper tabular format so the values are taken based on my understanding. Change the values to the correct ones if required)

Based on the service availabilities, Yourizon is recommended since it has a high system availability

Number of failures in 8 hrs MTBF Time to regain ISP (MTTR) System Availability Xceptional 12 40 2 0.95 Yourizon 4 120 4 0.97 Zelltell 3 160 10 0.94

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