Distributed Information Systems

1DT066 Distributed Information Systems Homework 2 1) This is a g eneral question on distributed systems. a) With examples describe Access, Location and Migration transparency in a distributed system. b) With…

1DT066 Distributed Information Systems
Homework 2
1)
This is a g
eneral
question
on distributed systems.
a)
With examples describe Access, Location and Migration transparency in a
distributed system.
b)
With example
s describe what Middleware is.
c)
With examples
de
s
cribe the client server model?
d)
What is redundancy and why is it used in a distributed system.
2)
This is a question on remote procedure call.
a)
What are Client and Server Stubs and how are they used in re
mote
procedure calls?
b)
When passing data values betwe
en d
ifferent machines with dif
ferent
operating systems what proble
ms have to be solved?
c)
When calling a remote procedure or method where a reference parameter
is passed, what problems have to be solved and how are they solved?
3)
Consider the events of proces
ses P1, P2 and P3 in the following figure:
L(e): denotes the Lamport timestamp of event e.
V(e): denotes the Vector timestamp of event e.
a)
Write down the Lamport timestamps
in the above figure
.
b)
Write down the Vector timestamps
in the above figure
.
c)
C
an the order of Lamport timestamps infer the order of events? In other
words, if L(e) < L(e’), can we infer that e
à?
e’ in Lamport timestamps?
d)
Similarly, if V(e) < V(e’), can we infer that e
à?
e’ in Vector timestamps?
4)
Consider a server provides the
R
ead
and
W
rite
operations for its clients to a
number of objects
M1, M2, … , Mn
:
Read(i)
returns the value of object
Mi
.
Write(i, Num)
assigns
Num
to object
Mi
.
There are two transactions A and B defined as follows:
A:
x=Read(j); y=Read(i); Write(j,4),
Write(i,3);
B:
x=Read(k); Write(i,5); y=Read(j); Write(k,6).
Give three serially equivalent interleavings of the transactions A and B.
5)
a)
What duties does the ‘link layer’ have in an standard network stack?
Describe at least 3 points.
b)
When consid
ering Medium Access Control, describe an advantage and a
disad
vantage
of “Channel Partitioning” approaches compared to “Random
Access” approaches.
c)
With

Random Access

approaches, i
f nodes listen to the medium to
ensure it is free before transmitting data, how can collisions still occur?
6)
a) A
computer program wants to load a file from the hard disk into memory.
Describe at least 4 steps that occur during this process.
b) The file has been loaded to memory.
At some point in its operation, the
program wants to have the first byte from
the file in its CPU
. Describe at least
4 operations that will be performed before the byte can be
manipulated
in the
CPU.
7) a)
What is the difference between two

phase locking and two

phase
commit? How
does two

phase locking prevent inconsistent analysi
s?
b)
Which transactional property is enforced by distributed commit
protocols? Explain briefly.
Please submit your personal answers electronically to
liam.mcnamara@gmail.com
b
y 15:00 Dec 9
th

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