I'IHITIIBIFI UFIIVERSITY

OF SCIENCE PII'ID TECHNOLOGY

FACULTY OF COMPUTING AND INFORMATICS

DEPARTMENT OF COMPUTER SCIENCE

QUALIFICATION: BACHELOR OF COMPUTER SCIENCE

QUALIFICATION CODE: 07 BACS LEVEL: 6

COURSE: DISTRIBUTED SYSTEMS COURSE CODE: DTS6205

DATE: NOVEMBER 2017 SESSION: THEORY

DURATION: 2 HOURS MARKS: 80

FIRST OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER: MR. ATTLEE.M. GAMUNDANI

MODERATOR: PROF. JOSE. QUENUM

THIS QUESTION PAPER CONSISTS OF 2 PAGES

(Excluding this front page)

INSTRUCTIONS

Answer ALL questions.

Write clearly and neatly.

P‘P‘PWN!‘Begin each question on a new page.

Number the answers clearly as per the question paper numbering.

Marks/Scores per question paper are given in H.

NUST examination rules and regulations apply.

Question 1

(a) Highlight and explain any two reasons why openness of a computer system is a major

characteristic of distributed system design? [4 marks]

(b) Outline any two purposes of inter-process communication in a distributed system.

[4 marks]

(c) When searching for files in an unstructured peer—to-peer system, it may help to restrict the

search to nodes that have similar files as yours. Explain how gossiping can help to find those

nodes. [6 marks]

(d) Scalability in a distributed system can be achieved by applying different techniques. Explain

any three such techniques citing examples for each. [5 marks]

Question 2

(a) Outline at least any three steps, which are followed in developing RMl applications.

[6 marks]

(b) How can you implement group communication for the orientation system of first year

students at NUST? [6 marks]

(c) How does a distributed system guarantee four intertwined ACID properties of a transaction?

[8 marks]

Question 3

(a) Given the communication between Alice, Bob and Carol for messages:— M1, M2, M3 and M4.

Name and apply with justification a suitable algorithm that ensures the time stamps shown

in figure 1, respect causality. [7 marks]

B°bCarol

15

M2

13

M3 30

28

43

Figure 1: Time stamps

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(b) Middleware assumes so many styles in its implementation. Identify any three (3) and give

an example for each. [3 marks]

(c) Why is it not always a good idea to aim at implementing the highest degree of transparency

possible? [6 marks]

(d) Why do you think mutual exclusion is important in distributed system design? [4 marks]

Question 4

(a) Describe the ways in which the request-reply protocol masks the heterogeneity of operating

systems and of computer networks. [6 marks]

(b) Give any two trends driving the growth of distributed systems. [2 marks]

(c) Suppose you are connecting from your personal laptop to the webserver of NUST, to

retrieve the exam timetable page. Explain how the three protocols IP, TCP and HTTP interact

so that you can view the page you requested. [6 marks]

(d) Many distributed systems are needlessly complex caused by mistakes that required

patching later on. What could be some of the causes of such a scenario? [6 marks]

*****END OF EXAMINATION PAPER*****

Page 3