UNIVERSITY EXAMINATIONS: 2018/2019
EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE IN
INFORMATION TECHNOLOGY /BACHELOR OF BUSINESS IN
INFORMATION TECHNOLOGY
BIT2303 BBIT308 DISTRIBUTED SYSTEMS
FULL TIME/PART TIME/DISTANCE LEARNING
DATE: DECEMBER, 2018 TIME: 2 HOURS
INSTRUCTIONS: Answer Question One & ANY OTHER TWO questions.
QUESTION 1: 30 MARKS (COMPULSORY)
a) Define the following terms 4 Marks
i. Distributed File System
ii. Middleware
b) With the help of well labeled diagrams illustrate your understanding of synchronous
communication and asynchronous communication 4 Marks
c) Draw the diagram of RPC Implementation model and illustrate how a message is passed
form the client to the server 8 Marks
d) There are two approaches to synchronizing the clocks so as to get a consistent view of time
in Distributed Systems. Mention and explain them 4 Marks
e) Discuss the six security requirements in any DS highlighting the attacks to each of the
requirements 6 Marks
f) Discuss the following forms of transparency 4 Marks
i. Failure transparency
ii. Scaling transparency.
QUESTION 2: 20 MARKS
a) There two forms of communication when processes are executing: original sharing and copy
sharing. Using well labeled diagrams differentiate the two. 5 Marks
b) Describe the Sun NFS 4 Marks
c) With the help of a diagram illustrate the basic file replication architectural model
5 Marks
d) Using simple diagrams, discuss differences between local procedure calls and remote
procedures calls. 4 Marks
e) Differentiate between a process and a program 2 Marks
QUESTION 3: 20 MARKS
a) Using a well labeled diagram illustrate how the Berkeley algorithm achieves external
synchronization from the UTC with Local Areas Networks (LANs). 6 Marks
b) Explain why Berkeley algorithm cannot work to achieve synchronization within Wide Area
Networks (WANs) 4 Marks
c) Discuss four advantages of Replication is Distributed Systems 4 Marks
d) In the context of IPC; define a “message”, illustrating its structure by the help of diagram.
6 Marks
QUESTION 4: 20 MARKS
a) Using appropriate diagrams describe three algorithms for achieving mutual exclusion.
6 Marks
b) Performance of a software system is one of the desirable characteristics of a distributed
system. Define the term reliability, describing two metrics of performance. 4 Marks
c) A fault causes an error and an error in turn causes failure of a system. Describe what a fault
is, giving two types of a fault. 4 Marks
d) Differentiate between the following terms in reference to Distributed Systems reliability
2 Marks
i. Fault avoidance
ii. Fault tolerance
e) Discuss two mechanisms of improving fault tolerance in Distributed Systems. 4 Marks
QUESTION 5: 20 MARKS
a) Using appropriate diagrams Differentiate between loosely coupled systems and tightly
coupled systems. 4 Marks
b) In order to provide concurrency transparency, the resource sharing mechanism of the DS
must have four properties. With appropriate examples and diagrams where possible, discuss
these properties. 4 Marks
d) Differentiate between Network Operating Systems (NOS) and Distributed Operating System
(DOS). 6 Marks
e) Describe the term dependability, explaining any three requirements for dependability in
Distributed Systems. 4 Marks
a) Define the following concept used in synchronization 2 Marks
i. Skew
ii. Clock drift
