CS5233 Assignment 1 (11/12 Semester 2)

You are not to start the assignment until you have formed your group. When you have formed your group, email gtan@comp.nus.edu.sg with your names and matric numbers, and you will be given a group number.

Assignment Deadline: noon, 16^th February 2012.

Select either A or B:

(A) Simulation and Analysis of a Travel Agency

Background and Problem

A travel agency has decided to open its first office in Singapore. The travel agency has no experience in such openings and hence it has decided to engage you for advice on the office operation. Before deciding on the size of the office, the number of employees, terminals, etc, the agency would like to simulate the operational flow of the office. Since the business is very competitive it is very important that the customers are happy with the service to be provided by the agency. The company would like to provide good service yet work as cost-efficiently as possible.

Your assignment

Your task will be to create a model of the office and simulate its operation. Some questions of interest are:

• What will the average waiting time of the customers be if there is a single customer service desk (or terminal)?
• What percentage of customers will wait longer than 5 minutes if there is a single terminal?
• How many terminals would be needed to guarantee that 90% or more of the customers will wait less than 4 minutes for service?

Assume that both the inter-arrival and the service times are exponentially distributed with mean l₁ and l₂ respectively.

(a) Initially, you may assume that there are 10 customer arrivals per hour on average and each customer needs 8 minutes service on average.

(b) You should run other experiments with various values for l₁ and l₂ and summarize your findings in a table.

(B) Simulation and Analysis of a Telephony system

Background and Problem

In telephony systems different models are used to evaluate the quality of service (QoS). Consider a model consisting of two nodes connected to each other by a number of communication channels. Typically, a node represents a city and channels are the available telephone lines. A telephone call may originate in any of the two nodes at any time. If there is a free channel available the originating call is established and one of the free channels is allocated to the call. The channel allocation lasts throughout the whole telephone conversation and no other call may use that channel until the conversation is terminated. If all channels are occupied the originating call is blocked. The caller has to hang up and try again later. In some older models the channels can operate in one direction only. In such systems, a predefined number of channels are used in one direction and the rest of the channels are used to initiate calls in the other direction. In the newer systems, all channels can operate in both directions.

Your assignment

A system like the one described above is used by two cities, X and Y. The system is about to be upgraded from an older type where the channels are unidirectional to a newer type where the channels are bi-directional. The system designers want to create a simulation model of the new system to predict its performance. The following data has been collected from the current system:

• Times between attempted calls from X to Y are exponentially distributed with a mean of 10 seconds
• Times between attempted calls from Y to X are exponentially distributed with a mean of 12 seconds
• Length of conversations are exponentially distributed with a mean of 4 minutes

The designers wish to address the following questions:

• How many channels would be needed in the old system to achieve a QoS guarantee of maximum 5% blocked calls, if there were equal number of channels in each direction?
• How could the old system be configured to reduce the number of blocked calls further if it is allowed to assign different number of channels to each direction?
• For the new system, how many channels are needed to provide the same QoS guarantee of maximum 5% blocked calls? How are the channels utilized in this case?

Approach

You may use a high-level programming language to implement your simulator, or you can also use the simulation package Arena. You can download and install the Arena educational version from here. Type STUDENT when prompted for the serial number. A guided tour of arena can be found in the book “Simulation with Arena”, by Kelton, Sadowski and Sturrock, McGrawHill.

Documentation

You are expected to write a report (a maximum of 8 pages is allowed for your report) for this assignment describing your experiments, results obtained, and your conclusion. Additional pages will incur penalty.

Please submit your report to me at COM2, #03-50 by the deadline. Please also email me a softcopy of your report (gtan@comp.nus.edu.sg). Remember to include your group number and details in your report. Omission of required information will also incur penalty.