Distributed systems questions.

Briefly describe the worker pool multi - threaded server architecture

Give two types of security attacks on distributed systems

What are the main functions of DNS name service ?

Explain why it is possible in a wide area network (WAN) for messages to arrive in order different from which they were sent ?

One of the challenges of the design of distributed system is the issue of Transparencies . Explain what is meant by Transparency.

A web - based multiple choice examiniation system is to be implemented . The system should be able to handle a total of up to 1000 candidates. Candidates must first register

with the system and answer up to 50 questions, following  which the system will notify them of their percentage score. At most one registration per candidate is allowed. Candidates can amend their answers by simply re-sending a new answer for the same question. The system should implement the following operations.

Register, which inputs the candidate`s name and exam identifier, then generates a unique number for each candidate, if the candidate is found to have registered for this exam already , the system rejects the request to register.

Answer ,which inputs the question number and answer (1 up to 5)

Score , Which output the percentage score

• Is at least once invocation semantics acceptable for this system ? Justify your answer
• Assume the system has a single server connected to 50 terminals. The number of clients assessing the server simultaneously is normally below 10. with 50 at peak times . Suggest an appropriate multi - threaded server architecture for this system
• Assume the system is synchronous, describe how to achieve at least once invocation semantics over the UDP protocol in such a system.

What are the advantages of server - controlled recursive navigation compared to the non - recursive navigation ?

Distinguish between `Security Policy` and `Security Mechanism`

Describe any two purposes of Distributed File System

What is a Y2K problem ?