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Comp 464: Distributed Systems 2009/2010 Academic Year Question Paper
Comp 464: Distributed Systems 2009/2010 Academic Year
Course:Bachelor Of Computer Science
Institution: Kabarak University question papers
Exam Year:2010
INSTRUCTIONS:
Answer question ONE Compulsory and any other TWO.
Question One: [30 Marks]
a) Explain the major characteristics of Distributed systems. [4 Marks]
b) Describe the problems of concurrency in distributed computing. [5 Marks]
c) Describe the basic operations of remote procedure calls. [5 Marks]
d) Describe the bully election algorithm. [5 Marks]
e) Differentiate the following terminologies.
i. Shared secret key and Public/ Private key pairs. [2 Marks]
ii. Symmetric cryptosystem and asymmetric cryptosystem [2 Marks]
f) State and explain the main error detection techniques. [4 Marks]
g) If there is an error in a message, how is it detected and rectified? [3 Marks]
Question Two: [20 Marks]
a) Define the following terms:
i. Distributed system. [1 Mark]
ii. Synchronization. [1 Mark]
iii. A packet. [1 Mark]
iv. A component. [1 Mark]
v. Concurrency [1 Mark]
b) Contrast between TCP and UDP. Under what circumstances would you choose one over
the other? [6 Marks]
c) Describe the network evaluation criteria when designing a distributed network system.
[4 Marks]
d) An open distributed system allows new resource sharing to be added and accessed by a
variety of client programs. Discuss in the context of this example, to what extent the needs
of openness differ from those of heterogeneity. [5 Marks]
Question Three: [20 Marks]
a) List and explain three techniques that will provide the cryptographic basis for secure
access control. [3 Marks]
b) Distributed systems design is obviously a challenging endeavor. How do we do it
when we are not allowed to assume anything, and there are so many complexities?
[4 Marks]
c) Explain any four major benefits of distributed systems. [4 Marks]
d) Describe the cryptographic technique for securing distributed systems and
applications. [4 Marks]
e) Whenever a RPC system is designed, there arise several classes of failures. What are
they? Explain. [5 Marks]
Question Four: [20 Marks]
a) A server manages data items, and allows read and write operations. Give three serializable
schedules of the following transactions [4 Marks]
i. T: R(j),R(i),W(j,44),W(i,33)
ii. U: R(k),W(i,55),R(i),W(k,66)
b) Describe some of the ways in which conventional email is vulnerable to eavesdropping,
masquerading, tampering, replay and denial of service. [4 Marks]
c) Suggest methods by which email could be protected against each of these forms of attack.
[4 Marks]
d) Define an inconsistent retrieval. What pattern of operational conflicts may lead to an inconsistent
retrieval [4 Marks]
e) A process group using CBcast has three members, 0,1,2. Process 0 sends two messages with vector
timestamps (6,9,10) and (7,10,11). Process 1 sends two messages with vector timestamps (5,9,10)
and (5,10,10). Process 3 sends two messages with vector timestamps (6,9,11) and (6,9,12). Show a
possible ordering of the transmission and delivery events at these processes. [4 marks]
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