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

b

y 15:00 Dec 9

th