Consider a system in which N users (each with his/her own PC) connect to an Application Server (AS) that runs on its own processor ASP. On average, for each user request, the AS generates: 4 requests to a Database Server (DB) that runs on its own processor DBP, and 3 requests to a disk (Disk1) with an average disk service time of 0.03 sec per disk request. The CPU demand is as follows: for each user request, the AS demand is 0.125 seconds for a DB request the CPU demand is 0.4 sec. For every Database Server request DB generates: 1 request to Disk1 with an average service time of 0.04 sec per request. 0.5 requests to Disk2 with an average service time of 0.02 sec per request. -

a) Develop and design by hand a layered queueing network model and list its parameters. Please either draw it or use drawing software.

(b)Use the lqns tool to compute to determine the mean system throughput and mean system response time for 1, 2, 5, and 10 users. Use a think time of 2.5 sec. Tip: Use the tool lqngen to create an annotated model file which you can edit with a text editor, OR, use the Java lqn editor (available on the download site).

(c) Repeat step (b) with SPEX. Vary the number of users customers from 1 to 10 with a step size of 1. Plot the system response time, system throughput and utilization of the bottleneck task / processor.

(d)Which one is the bottleneck task / processor? Can you suggest a way to improve the system response time?

(e) Repeat step (c) after your suggested improvements are applied to the model and explain your results.