ENTERPRISE NETWORKING 11 MARCH 2012 MARKING SCHEME

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© NCC Education Ltd 2012





ENTERPRISE NETWORKING


11
th

MARCH 2012


MARKING SCHEME



This Marking Scheme has been prepared as a guide only to markers. This is not a set of
model answers, nor is the Marking Scheme exclusive, for there will frequently be
alternative responses whic
h will provide a valid answer. Unless a question specifies that
an answer be produced in a particular form, then an answer that is correct, factually or in
practical terms, must be given the available marks.


If there is doubt as to the correctness of an a
nswer the relevant NCC Education materials
and associated module textbook should be the first authority.





Throughout

the

question
s
,

please

credit

any

valid

alternative

point.



Notice to Markers


Where markers award half marks in any part of a question

they should
ensure that the
total

mark recorded for a task is rounded up to a whole
mark.
.
Enterprise Networking

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© NCC Education Ltd 2012


ANSWER ANY FOUR QUESTIONS



Question
1


a)

Name the FIVE (5) parts of the coaxial cable labelled A to E in the diagram
below.






Award 1 mark for each part up to a

maximum of 5 marks:


A.

Outer insulation and protection

B.

Inner insulation and protection

C.

Screen copper conductor

D.

Conductor insulation

E.

Central copper conductor

(5 marks)




b)

Briefly explain why coaxial cable was originally developed.


To enable the transmissio
n of radio frequency signals
.

(1 mark)



c)

Briefly describe the microwave signals that are used to transmit
telecommunications signals.


Award 1 mark for each part up to a maximum of 2 marks:




The wavelengths of the signals are very small



The frequencies o
f the signals are high, typically around 6GHz

(2 marks)



d)

State the main advantage of using microwave signals to transmit
telecommunications signals.


It removes the need for underground cabling and the disruption and cost
associated with installing such
cabling
.

(1 mark)

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© NCC Education Ltd 2012


e)

Explain the main disadvantage of transmitting signals via microwaves and
describe how the infrastructure of the transmitting system is created as a result of
this.


Award 1 mark for each part up to a maximum of 5 marks
.




Microwave radi
o signals can only transmit over short distances



Transmitting and receiving antennae must be in line of sight



Parabolic dishes used as antennae for directional control



Signals cannot pass through obstructions, e.g. buildings, ground, trees,
etc.



High build
ings and masts used to house antennae to lift them above
obstructions and increase transmission range
.

(5 marks)



f)

Explain how satellite telecommunications systems work.


Award 1 mark for each part up to a maximum of 4 marks
:



Satellites have been placed i
n geostationary orbit



The satellites are moving at the same speed as the earth and are
therefore stationary in relation to the ground



A radio signal can be transmitted directly from the Earth’s surface to an
orbiting satellite as there is a line
-
of
-
sight p
ath



The signal can be amplified and transmitted to another point on the
Earth’s surface with a line
-
of
-
sight path

(4 marks)



g)

State TWO (2) advantages to using satellites for telecommunications.


Award 1 mark for each part up to a maximum of 2 marks:



Allo
ws signal to be transmitted over long distances



Allows telecommunication in remote places with no land based network



Removes the need for undersea cabling

(2 marks)



h)

Describe fibre
-
optic cables and explain in detail how they are used to transmit
telecommu
nications signals.


Award 1 mark for each part up to a maximum of 5 marks:




Made of thin strands of silicone fibre



Transmission occurs at very high light wave frequencies



Allows for much greater transmission rates



Light waves are created by laser



Uses a m
ono
-
mode technique where a single stream of light travels
down each fibre

(5 marks)


Total: 25 Marks

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© NCC Education Ltd 2012


Question
2


a)

Describe the purpose of user authentication.


Award 1 mark for each part up to a maximum of 2 marks:




To determine the identity of a person o
r system connecting to a network



To determine if the user has permission to access the network

(2 marks)



b)

Describe how the user authentication process works.


Award 1 mark for each part up to a maximum of 2 marks
:




A challenge or series of challenges are

put to the user



The user responds and this must match the response expected by the
system

(2 marks)




c)

Describe in detail how an authentication process that requires a username and
password is used to authenticate a user and allocate permissions to that u
ser.



Award 1 mark for each part up to a maximum of 9 marks:



The system requests a username and password from the user



The user supplies both username and password



The system looks up the username in its database of authorised users



If the username does
not exist access is denied



If the username does exist the system checks the password it expects
for that username



If the password is incorrect access is denied



If the password exists the user is authenticated



The records holding the access rights associate
d with that user are
examined by the system



The user has access to network resources based upon those access
rights

(9

m
arks)




d)

Describe TWO (2) major drawbacks to using passwords as an authentication
method.


Award 1 mark for each part up to a maximum o
f 2 marks:



Many people use easily crackable passwords (names, common words,
etc.)



People write down complex passwords and keep them next to a
workstation



Passwords should regularly be changed to maintain security



People let other people have their password


(2 marks)




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e)

Explain how biometric authentication methods are more secure than passwords.


Award 1 mark for each part up to a maximum of 3 marks:



Passwords let the system know that the user knows the password but it
may not be the actual person



Biomet
ric methods use a part of the body such as fingerprint or eye and
it is extremely likely that the real user is present



It is very difficult to fake or guess a biometric record
.


(3 marks)



f)

Briefly describe
SIX

(
6
)
specific

ways in which a firewall can pr
otect a network.


Award 1 mark for each part up to a maximum of 6 marks:



Prevent an unauthorised user from accessing the network from outside
the firewall



Selectively allowing access to specific areas of the network



Selectively filtering incoming e
-
mail
messages



Performing virus checks on attachments to incoming e
-
mail messages



Preventing users from accessing specific external websites



Preventing the transfer of files into the network
.

(
6

marks)



g)

Explain what a personal firewall is
.


A firewall that p
olices a single computer by policing traffic through its
external interface
.


(
1

mark
)



Total: 25 Marks

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Question
3



a)

State THREE (3) limitations of using
Bluetooth

to connect devices on a network
.



Award 1 mark for each part up to a maximum of 3 marks:
.




Short operating range



Limited data throughput



Reliance on a crowded spectrum band (2.4 GHz)

(
3

marks)



b)

Describe in detail a
piconet
.


Award 1 mark for each part up to a maximum of 3 marks
.



An ad
-
hoc, short
-
range, wireless network used for Bluetoot
h



It consists of 2 or more devices on the same physical channel



They are synchronised by a common clock and hopping sequence

(3 marks)




c)

Describe
the role of a master in a
piconet
.


Award 1 mark for each part up to a maximum of 3 marks
.



A single Bluetoo
th device acts as the master



The common clock used by the piconet is identical to the clock of the
master



The hopping sequence is derived from the master’s clock and address


(
3 marks)




d)

Describe how a Bluetooth device operates in a scatternet.


Award 1
mark for each part up to a maximum of 3 marks:



The device is a member of several piconets at the same time on a time
-
division multiplexing basis



It does not have any routing capabilities



It can only be the master of one piconet

(3 marks)



e)

Describe the THR
EE (3) classes of Bluetooth device.



Award 1 mark for each part up to a maximum of 3 marks:




Class 3 radios have a range up to 1 metre



Class 2 radios are commonly used in mobile devices and have a range of
10 metres



Class 1 radios are primarily for indus
trial use and have a range of 100
metres

(3 marks)

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f)

Define a
mobile communications network
.


Award 2 marks for a complete answer and 1 mark for a partial answer:

A communications network that allows communication to take place whilst
some or all of the us
ers of the network are moving relative to each other
.



(2 marks)




g)

Describe FOUR (4) characteristic features of
Private Mobile Radio

(
PMR
).


Award 1 mark for each part up to a maximum of 4 marks:




Provides local radio communication on a single channel
(e.g. taxi firm)



Communications are half
-
duplex and require strict operating procedures
(e.g. the use of “over” at the end of a message)



Requires a licence from the relevant government department



Bandwidth and channel availability is limited

(4 marks)



h)

De
scribe THREE (3) disadvantages inherent in Private Mobile Radio.


Award 1 mark for each valid point up to a maximum of 3 marks:
.



Lack of privacy as all communication takes place on a single channel
and anyone with a suitable receiver can listen to the br
oadcasts



Communications are limited to a small radius resulting in a mobile unit
losing the ability to communicate when it is out of range



The channel may become congested at peak times making it difficult to
access

(3 marks)



i)

State the prime application
of Public Trunked Mobile Radio (PTMR).


Fleet vehicle communications

(1 mark)



Total: 25 Marks

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Question
4



a)

Briefly describe the principles underpinning telecommunications traffic theory
.



Award 1 mark for each part up to a maximum of 3 marks:




It i
s possible to create a network that connects half of the population to
the other half of the population simultaneously



It is extremely unlikely that such a situation will occur



The key is to determine the maximum percentage of customers that will
require s
imultaneous connection

(3 marks)



b)

State the aims of telecommunications traffic theory
.



Award 1 mark for each part up to a maximum of 3 marks




To minimise the number of circuits provided



Whilst maximising the number amount of traffic carried



And provid
ing an acceptable grade of service

(3 marks)



c)

Briefly describe how the aims of telecommunications traffic theory are achieved
.



Award 1 mark for each part up to a maximum of 2 marks:





By setting a figure for the percentage of maximum traffic that will
be
connected



But this should be at a level that does not frustrate callers who cannot
connect

(2 marks)




d)

Explain why the distribution of telephone traffic is no longer of importance in
network dimensioning
.



Award 1 mark for each part up to a maximum o
f 4 marks:
.



Most traffic carried on telephone networks is for other network services
such as the Internet



The data transmission on the network for these services is much greater
than voice transmission



Modern networks have much greater capacity than in t
he past and the
ability to connect all users is no longer an issue



The current priorities are call set
-
up delays and managing overloads
rather than an inability to connect

(
4

marks)


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e)

Use a diagram to model the results of user repeat call attempts during
overload in
a network. State what each part of your model represents.



Award 1 mark for a suitable diagram with correct flow, e.g
.






Award 1 mark for each correctly labeled element of the diagram:



Carried traffic



Blocked traffic



Abandoned attempts



Rep
eated attempts



C = arrival time of new calls



B = blocking probability



R = re
-
attempt rate

(8 marks)



f)

Describe in detail the role that cost and resilience play in network planning
.



Award 1 mark for each part up to a maximum of 5 marks





It is not cost
-
e
ffective to have a dedicated link between every node but
some redundancy via additional links is desirable



Additional links can be brought into play if a link fails thus improving
reliability



There is a balance to be had between the cost of the extra links

and the
importance of the traffic



Physical threats and the physical paths followed by the links will also
influence the decision



Load sharing between main and back
-
up links can be organised to
improve network performance but this must be carefully managed

(5 marks)



Total: 25 Marks

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Question
5



a)

Each computer (host) connected to the Internet has a unique IP address.
Describe the form of this address and explain what it is used for.


Award 1 mark for each valid point up to a maximum of 4 marks:
.



Addresses

have the form of a dotted quad a.b.c.d



Where a, b, c, d are 8
-
bit numbers between 0 and 255



These addresses are attached to packets



Allowing the target address to be determined

(4 marks)



b)

Describe how subnet addressing works.


Allocate 1 mark for each
valid point up to a maximum of 4 marks





A part of the HOSTID section of the address is used to indicate which
network is intended



These subnets are meaningless to any router outside the business



Internal routers can use this to route packets to the releva
nt subnetwork



A subnet mask is used to show which part of the address is used for the
host

(4 marks)




c)

Describe the role each of the following bodies plays in the development of the
Internet.



i.

The Internet Society (ISOC)



Award 1 mark for each point up
to a maximum of 2 marks




A professional organisation concerned with the political and social
development of the Internet



It oversees the resolution of technical issues that arrive as a result
of use of the Internet


(2

marks)


ii.

The Internet Engineering Stee
ring Group (IESG)



A technical management group responsible for the administration of
Internet Standards
.


(1 mark)

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iii.

The Internet Engineering Task Force (IETF)


Award 1 mark for each point up to a maximum of 3 marks



An informal grouping of people who c
ontribute directly to the
development of the Internet at a technical level



It makes recommendations to the IESG regarding the standardisation
of communications protocols.



It facilitates the transfer of new technologies from the Internet
Research Task force

(IRTF)


(3

mark
s
)




d)

Describe in detail the responsibilities of the Internet Corporation for Assigned
Names and Numbers (ICANN).


Award 1 mark for each valid point up to a maximum of 6 marks



Responsible for coordinating and managing the Domain Name Syst
em
(DNS)



Ensures that every address is unique and that all users can find all
addresses



It does this by distributing unique addresses and domain names and
ensuring that they map onto each other



Also responsible for accrediting domain name registrars



This m
eans to identify and set minimum standards for registration
functions



And recognise entities meeting those standards and enter into
accreditation agreements

(
6

marks)



e)

Describe the token passing process in the IEEE 802.5 standard for the Token

Ring topol
ogy
.


Award 1 mark for each valid point up to a maximum of 3 marks



A special pattern of bits (called a token) passes around the ring in one
direction which prevents collisions



A node can only transmit data when it has the token



Resources can be placed at a
ny point on the ring as data will reach them



(3 marks)



f)

Describe the inherent problems of a ring topology.


Award 1 mark for each valid point up to a maximum of 2 marks
.



They are dependent on all nodes and cable segments working



If a device is to be a
dded the ring must be broken and remade

(2 marks)


Total: 25 Marks

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LEARNING OUTCOME/QUESTION MATRIX FOR EN
Examination

March 2012


LO

Chapter/Page
Reference

Topic

Question
number

LO1

Ch 2, p15
-
17

Network link media

Q1


Ch15, p276
-
277

Authentication

Q2a),

b), c),
d), e)


Ch15, p281
-
282

Firewall

Q2f), g)


Ch11, p180
-
181

Form of IP address

Q5a)


Ch11, p181
-
182

Subnet address

Q5b)


Ch11, p194
-
195

Internet administration

Q5c), d)

LO2

Ch10, p171
-
164

Bluetooth

Q3a). b). c).
d), e)


Ch6, p84
-
85

Mobile Radio

Q3f), g), h),
i)


Ch14, p252

Token Ring

Q5e), f)

LO5

Ch5, p68
-
77

Traffic Theory

Q4a), b), c),
d), e)


Ch16, p290

Cost & resilience in
network planning

Q4f)