DOEACC Society 2006 DOEACC C Level C12 Distributed Systems ( ) - Question Paper

C12-R3: DISTRIBUTED SYSTEM
NOTE:
Time: three Hours Total Marks: 100
1.
a) provide an example of a URL. List the 3 main components of a URL, stating how their
boundaries are denoted and illustrating every 1 from your example. To what extent is a
URL location transparent?
b) How does a newly installed personal computer connected to an Ethernet discover the IP
addresses of local servers? How does it translate them to Ethernet addresses?
c) Java and other languages support exceptions, which are raised when an fault occurs. How
would you implement exceptions in RPCs and RMIs?
d) discuss what the kernel must give for a user-level implementation of threads, such as in
Java on Unix. Do page faults current a issue for user-level threads implementations?
Justify.
e) What is a digital signature? elaborate its uses in the security of a distributed system? provide a
method to create a digital signature.
f) define how a non-recoverable situation could arise if write locks are released after the
last operation of a transaction but before its commitment.
g) explain whether message passing or DSM (Distributed share memory) is preferable for
fault-tolerant applications.
(7x4)
2.
a) How do the client-server architecture of 1 or more major Internet applications involve the
partitioning and/or replication of data amongst servers? explain with the help of an
example.
b) presume the RRA (request-reply-acknowledge) protocol is in use. How long should servers
retain unacknowledged reply data? Should servers repeatedly send the reply in an attempt
to receive an acknowledgement?
c) Outline the design of a scheme that uses message retransmissions with IP multicast to
overcome the issue of dropped messages. Your scheme should take the subsequent points
into account:
i) there may be multiple senders;
ii) generally only a small proportion of messages are dropped;
iii) unlike the request-reply protocol, recipients may not necessarily send a message within
any particular time limit.
presume that messages that are not dropped arrive in sender ordering.
(6+6+6)
3.
a) Implement a simple client-server system using RPC. The server offers 1 procedure, next,
which takes an integer as input and returns its successor as output. Write a stub procedure
called next for use on the client side. Its job is to send the parameter to the server using
UDP and wait for the response, timing out if the response takes too long. The server
C12-R3 Page one of three January, 2006
1. ans ques. one and any 4 ques. from two to 7.
2. Parts of the identical ques. should be answered together and in the identical
sequence.
procedure should listen on a known port, accept requests, carry them out, and send back

Earning:   Approval pending.