B.E. (Information Technology) DISTRIBUTED SYSTEMS (Sem. – II) (2008 Pattern)
Time :3 Hours] [Max. Marks :100
Instructions to the candidates:-
1) Answer question 1 or 2, 3 or 4 and 5 or 6 from Section -1 and question 7 or 8, 9 or 10 and 11 or 12 from Section – II.
2) Answers to the two sections should be written in separate answer sheet.
3) Neat diagrams must be drawn wherever necessary.
4) Pigures to the right indicate full marks.
5) Assume suitable data, if necessary.
SECTION – I
QI) a) Following are the classical set of assumptions made by developers in distributed systems. 
i) The network is reliable.
ii) Latency is zero.
iii) Bandwidth is infinite.
iv) The network is secure.
Discuss why these assumptions maybe wrong. Justify these assumptions may not always true while designing the real distributed systems.
b) List the main software components that may fail when a client process invokes a method in a server object. Suggest how the components can be made to tolerate one another’s failures? 
Q2) a) What is marshaling? List out the different approaches of external data representation and discuss each approach in detail. 
b) The Internet enables users to access services and run application over a heterogeneous collection of computers and networks. How to apply heterogeneity for networks, computer hardware, operating systems and programming languages in distributed systems. 
Q3) a) Write a C function for adding two integers and call it using RPC and identify the contents generated by stub. 
b) Explain the purpose of following with respect to RMI. 
ii) Reflection and
iii) Registry in RMI
c) State and explain the Invocation models supported in CORBA. 
Q4) a) List and explain the steps involved in doing remote computation through RPC. 
b) Compare static and dynamic remote method invocation with the help of suitable example. 
c) Explain Message Queuing model with suitable example. 
Q5) a) Discuss following with an examples : 
i) Logical Clock
ii) Physical Clock and
iii) Clock Skew
b) Write Lamport’s time stamp algorithm in pseudo C and explain it with suitable example. 
Q6) a) Write Bully algorithm for electing a coordinator in pseudo C and explain it with suitable example. 
b) List and compare various algorithms used to achieve Mutual exclusion in a Distributed Systems with respect to. 
i) Messages per entry/exit ii) Delay before entry
i) Time complexity iv) Problems
SECTION – II
Q7) a) List and explain the forms of transparency which have been partially or wholly addressed by current distributed file systems. 
b) Describe basic NFS architecture for Unix system with the help of neat diagram. 
c) What is naming service X.500? 
Q8) a) How does the Coda file system used for replication strategy? 
b) What are different requirements and pitfalls in the design of distributed file system? Explain any four requirements. 
c) How does mounting of a remote file system take place in NFS? Describe the functionality of an auto-mounter in NFS. 
Q9) a) Consider the following set of concurrently executing processes PI P2 P3
x=l; y=l; z=1;
print (y, z); print (x, z); print (x, y);
Is 001110 a legal output for a sequentially consistent memory? Explain your answer. 
b) Explain following consistency models with suitable examples :
i) Causal ii) FIFO 
c) Describe object replication and scaling technique in distributed shared memory systems. 
QI0) a) How does granularity affect DSM system performance? 
b) Explain following consistency models with suitable examples : 
i) Strict ii) Entry
c) What kind of consistency would you use to implement an electronic stock market? Justify your answer. 
QII) a) Describe at-least-once and at-most once semantics in detail. For each of the following applications do you think at-least-once semantics or at-most once semantics is best? Discuss. 
i) Reading and writing files from a file server.
ii) Compiling a program.
b) What is recovery line? Draw and explain domino effect in detail. 
QI 2) a) In a fault tolerant distributed system how check-pointing is used. Describe following check-pointing : 
i) Independent check-pointing
ii) Coordinated check-pointing
b) Consider a Web browser that returns an outdated cached page instead of a more recent one that had been updated at the server. Is this a failure, and if so, what kind of failure? 
Draw and explain triple modular redundancy.