DIS.SYS OU -08

Faculty of informatics
M.C.A  II Year II Semester (main )ExaminatioN
DISTRIBUTED SYSTEMS
UNIT-I
1. (a) Explain the role of middleware in a distributed system.
(b) What is the difference between a vertical distribution and a horizontal?
(c) Sketch the design of a multi threaded server that supports multiple protocols .using, sockets as its transport level interface to the underlying operating system.
2. 


(a) Explain what is meant by transparency and give examples of different types of transparency.
(b) What is an open distributed system and what benefits does open ness provide ?
(c) Discuss the various approaches to code migration. Also mention the alternatives for code migration.
UNIT-II
3. (a) What are the basic approaches for locating mobile entities ?
(b) What is the goal of an election algorithm ? Explain election algorithm
based on the use of a ring.
4. (a) Compare garbage collection that requires the support of reference
counting with that of trace based methods.
(b) Explain any one algorithm for achieving distributed mutual exclusion 


UNIT-III
5. (a) Why is replication useful ? How does replication relate to scalability ? 3
(b) Can linearizability be implemented for physically distributed data stores ?
(c) For each of the following applications, do you think at-least-once semantics or at most once semantics is best ? Discuss.

(1) Reading and writing files from a file server.
(2) Compiling a program.
(3) Remote banking. 
(d) In two-phase commit protocol, why can blocking never be completely
eliminated, even when the participants elect a new coordinator ?
6. (a) Explain the different consistency models for distributed shared
memory.
(b) Briefly explain the motion of incremental snapshot.
UNIT-IV
7. (a) What was the design goal of CORBA ? Give an overview of CORBA
system.
(b) In NFS, attributes are cachedlisThg write-through cache coherence policy. Is it necessary to forward all attributes changes immediately ? 
8. (a) Compare DCOM and Globe.
(b) In NFS, what kind of security measures can be taken to prevent a malicious client from reclaiming a lock it never was granted when a server enters its grace period ?
(c) Explain how coda solves read-write conflicts on a file that is shared between multiple readers and only a single write.
UNIT - V
9. (a) Explain why the write-invalidate protocol is suitable to maintain
coherence if several updates occur between reads or when a
program exhibits per-node locality of reference.
(b) Classify the load distribution algorithms.
(c) Explain the sender initiated algorithm for load distribution.

10. (a) Contribute your comments on granularity and page replacement
issues in the design of distributed shared memory systems. 
(b) Explain briefly about adaptive algorithms for load distribution. ,