Some Theoretical Issues in Distributed Systems - Tutoring 3

Tutoring 3

Question 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.