Some Theoretical Issues in Distributed Systems
In this 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 principles to distributed applications. These theoretical issues/principles 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, 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 in 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 in the project, 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 key role of web service in distributed computing.
Submission
You will need to address the above issues in a Microsoft Word document. You must submit your assignment via the online submission system from the unit Moodle site. Any hardcopy or email submission will not be accepted. After the marked assignments are returned, any late submissions will not be accepted. The Marking Criteria
Marking Criteria Available Marks
Question 1: UDP and TCP vs Thread per Request and Thread per Connection 8
1. UDP reliability and overhead 2
2. TCP reliability and overhead 2
3. Whether thread-per-request model is correctly described 1
4. Whether thread-per-connection model is correctly described 1
5. Whether communication protocols and thread models are sensibly related 2
Question 2: Document Signing and Verification 6
1. Whether correct terms are used 2
2. Whether the procedure is correctly described 4
Question 3: Priority-Based Central Server Algorithm 10
1. Whether request priority is applied in the algorithm 2
2. Whether the procedure of the algorithm is correctly described 2
3. Whether the safety feature is well justified 2
4. Whether the liveness feature is well justified 2
5. Whether the ordering feature is well justified 2
Question 4: SOAP Web Service 11
1. Whether the end point of web service is correctly described 2
2. Whether the naming convention is correctly described 2
3. Whether the lookup service is correctly described 2
4. Why the wsimport tool introduces a better way to create a web service client 2
5. The contrast of web service and normal client/server 3
Sub Total for Assignment 3 35
Late Penalty -1.75 (5% each calendar day, either full or part)
Plagiarism Penalty
Total for Assignment 3
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