5. Distributed Systems
1. What aspects of a distributed system
would you select for a system running on a totally reliable network? [4]
2. Present an algorithm for
reconstructing a logical ring after a process in the ring fails. [7]
aans :-- the ring algorithm assumes that the links netween processes are
unidirectional and that ech process sends th its messages to the neighte on the
right. The main data structure used by the algorithm is the active list. List that contains the priority numbers of
all active process in the system when the algorithm ends; eeach process
maintains its own active list. The algorithm works as follows :--
1)
if process p I detects a
failure, it creates a new active list that is initially empty. It then sends a message
elect(i) to its neighbor on the right and adds the numbers I to its active
list.
2) If p I recive a messages elect
d)
Under what circumstances is a token ring network
more effective than an Ethernet network? [4]
Ans :--
3.
Compare a stateless file server
with a stateful file server in a distributed system.
4. What are the various methods of
concurrency control? Which of these may lead to deadlock and why? [6]
5 Why
is disabling interrupts a pessimistic approach to ensure concurrency
control? [6]
6 In what ways is using a name server
better than using static host tables? What are the problems and complications
associated with name servers? What methods could be used to decrease the amount
of traffic name servers generates to satisfy transaction requests? [6]
7 To
build a robust distributed system, you must know what kind of failure can
occur.
i) List possible types of failures in a
distributed system.
ii) Specify
which items in your list also are applicable to a centralized system. [6]
8 Enforcing
mutual exclusion with respect to a set of Re-Usable resources does not
guarantee elimination of Starvation. Justify or refute this claim by an
Example. [4]
9 What are the advantages of a
distributed System over a conventional system? Highlight all the salient
points. [4]
b) Compare
the methods of caching vis-à-vis Remote services in a distributed system. [5]
10 What are the advantages of distributing
execution of entire process or a part of it at different sites in a distributed
operating system? [4]
11.
Define a
Distributed File System. Explain location transparency and location
independence. Consider a user on ‘site A’ that wants to access data one ‘site
B’. How the situation is handled by Network Operating System and
Distributed Operating System?
Ans :-- . Consider a user on ‘site A’ that
wants to access data one ‘site B’ . the system can be transfer the data
by one of two basic methods. One approach to data migration is to transfer the
entire file to site A. From that point
on, all access to the file is local. When theuser no longer needs access to the
file, a copy of the file is sent back to site B. even if only a modest change
has been made to a large file, all thedata must be transferred. This mechanism
can be through of as an automated FTP system. This approach was used in the
Andrew file system.
The other
approach is to tranfer to site A only those portion of the file that are
actually necessary for the immediate task. If another portions is required
later,another tranfer will take place. When the user no longer wants to access the file,any part of it that
has been modified must be sent back to
site B. [8]
12. Ina distributed system employing caching
mechanism, a client machine is faced with the problem of deciding whether
locally cached copy of the data is consistent with master copy. Which two
approaches are used to verify the validity of cached data?
[8]
13. What are the key design issues that must
be dealt with in building a distributed operating system? [2]
14
What are the
advantages and disadvantages of distributed system over centralized system? [6]
Ans :-- a distributed system is a collection of loosely
coupled procesors interconnecte by a communication network. The processors in a
distributed system may vary in size and function. They may include small microprocessors, workstations,minicomputers.
A distributed system is acollection of processors that donot share memory or a
clock. Instead each processor has its own local memory. Adventage :--
1)
rsource sharing
2)
computation speedup
3)
reliablilty
4)
remote file transfer :--if a user at
one site wants to access a file located on another computer then the file must
becopied explicity from the computer at yale to the computer
5)
data migration:--suppose a user on site Awants
to access data that reside at site B.The system can transfer the data by one of
two basic methods. One approach to data migration is to transfer the entire
file to site.
disadventage
:--
1) memory
–intensive program, such as RDBMS and expert system ,are particularly
vulnerable to networking because of memory requirment.
2) Some
type of security system mustbe
a)
Explain transparency design issue in a Distributed
operating system.
b)
Some control on the part of the user is lost.
c)
Distributed operating system adds another level of
complexity to the computer opertion.
d)
The financial cost of the local rea networking is
still high.
[6]
Ans :-- a distributed system is a collection of processors
that donot share memory or a clock. Instead,each processor has its own local memory. The processor
communication with one another variours communiation networks,such as high
level speed buses or telephone lines. A distributed system is a collection of
loosely coupled processors interconecte by a communication network. CORBA (OMG) is a distributed system
architecures.
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