The Assignment 3 Specification and Marking Criteria

Some Theoretical Issues in Distributed Systems

In the assignment, you are to address some theoretical issues in the area of distributed systems or distributed computing. You will need to demonstrate your understanding of these theoretical issues or competence to apply these theoretical issues. These theoretical issues have been introduced by this unit through the textbook, weekly lectures or tutorials/labs. You will need to review these learning materials to address the following questions and prepare to do personal research if necessary.

Please note: copying from the unit learning materials or internet resources cannot show your understanding of the following issues, but may incur plagiarism or loss of marks. Thus you will need to address the following issues in your own word with proper citation and reference.

Question 1

1. Contrast UDP and TCP protocols in terms of reliability and overheads. Provide some examples of internet application to justify for what internet applications UDP or TCP is more appropriate.

2. Contrast multi-thread models: thread-per-request and thread-per-connection.

3. Assume you will need to design and implement a server to respond to UDP or TCP requests, justify which multi-thread model you will use to program such a server to respond to UDP or TCP.

Question 2

Compose an example to describe the procedure to digitally sign a document and verify the originality of the signed document.

Question 3

Design a central server algorithm for mutual exclusion based on the REQUEST PRIORITY. Based on your design, discuss the safety, liveness and ordering features of the algorithm.

Note: no marks will be given if the request priority is not considered in your algorithm. Detailed answers are required to justify your understanding.

You will need to review the generic central server algorithm, which is detailed on Week 8 lecture and Chapter 15 of the textbook

Question 4

Address the following questions that are specific to the sample web service applications of Week 11 tutorial.

1. What is an end point? To access the end point from a web browser, what will be returned?

2. RPC style web service uses a convention to register target name space and service name, what is it? Note: you will need to refer to the WSDL document of Task 1 of Week 11 tutorial to address this question.

3. Refer to the HelloWorldClient.java, describe how to look up a web service and what is returned by the lookup

4. Task 2 or Week 11 tutorial introduces another way to create the HelloWorldClient with the aid of wsimport tool. Compare the HelloWorldClient in Task 1 and Task 2 to address why using wsimport tool is a better way to create the client of a web service.

5. Based on the practical programming tasks of web service of Week 11, address the main difference between web service and normal (or generic) client/server and the main role of web service.