Using the data in WSData.XLS workbook, compute the basic statistics for the file size for the set of all files downloaded (PDF and ZIP) taken together. Compute the coefficient of variation of the file size. Compare the results obtained with the separate statistics for PDF and ZIP files shown in this chapter.
Use the results in the previous problem and construct a single class model (i.e., single file type). Calculate new service demands. Solve the new model and plot its throughput and average download times. Assess the "error" made by assuming this single class model when the actual system is multiclass. What is an appropriate SLA for this single class model?
Use the data in the WSData.XLS workbook and compute the 25th percentile and the 75th percentile of the PDF and ZIP file sizes. Draw a Box and Whisker plot for each data set.
Compute a 90% confidence interval for the size of PDF and ZIP files. Compare these intervals with the 95% confidence intervals shown in this chapter.
Show that when the throughput X0(n) saturates, the response time grows linearly with the number of customers n. (Hint: use Little's Law.)
Explain why the balanced configuration of Section 6.5 is better for ZIP files but worse for PDF files when compared with the original configuration.
Consider the three security options of Section 6.6. How much faster should the CPU be in order to support 164 concurrent downloads with same SLAs for each of the security options? (Hint: use the ClosedQN-Secure.XLS workbook.)
Reconsider the experimental comparison of the two servers in Section 6.7. At what confidence level would the new and the original Web servers be considered not to be significantly different?