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UNIVERSITY OF LONDON
GOLDSMITHS COLLEGE
B. Sc. Examination 2007 (Internal)
COMPUTING
IS53026A (CIS339)
Enterprise Networking
Duration: 2 hours 15 minutes
Date and time:
This paper is in two parts, Part A and Part B. There are a total of three questions in
each part. You should answer the one compulsory question from Part A and two
questions from Part B.
Full marks will be awarded for complete answers to a total of three questions, one
compulsory question from Part A and two from Part B. Each question carries 25 marks.
The marks for each part of a question are indicated at the end of the part in [ ] brackets.
There are 75 marks available on this paper.
No calculators should be used.
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PART A
Question 1
(a)
State, in your answer book, which two of the following statements are true and
which two are false and, if false, write out a correct version of the statement:
i.
ii.
iii.
iv.
Layer 2 switches will only separate broadcast domains if VLANs are being
operated.
A Full Mesh network design provides a more scalable solution than a
Hierarchical design for a company that is expanding geographically.
A brouter will firstly attempt to bridge a frame at layer 2, but if the layer 3
protocol is routable, it will route the packet at layer 3.
A big bang approach to network implementation is often the cheapest, unless
it goes badly wrong.
[3]
(b)
List the four main measurable criteria that can be used to evaluate whether a
design meets requirements.
[2]
(c)
Identify four major differences between LAN and WAN design.
(d)
A builder who has just completed a block of 50 flats, is finding that the flats
are difficult to sell. He has decided that he needs a unique selling point to
attract buyers and has decided that very high speed internet of at least 50
Mbit/s could be just what is needed. The telephone company has already
installed a 155 Mbit/s fibre to the telephone exchange. This has been installed
primarily for voice communications and to support broadband. It only has
eight 2 Mbit/s circuits currently enabled and of these two are configured to
support voice and the remainder to support broadband. The local cable TV
operator has also installed a fibre operating at 1.2 Gbit/s into the premises
primarily to carry cable TV from the head end to each flat, but has configured
622 Mbit/s downstream and 52 Mbit/s upstream to support broadband.
[4]
You are a consultant who has been asked to carry out a feasibility study to
evaluate a number of alternative solutions.
The design options you should consider are:
i.
ii.
iii.
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To run a Gigabit Ethernet LAN using optical fibre media around
the block, linked to router within the block that will communicate
via the cable TV company’s 622/45 Mbit/s data channels to the
company’s IP network.
To run an FDDI ring operating at 100 Mbit/s around the block,
linked to router within the block that will communicate via the
telephone company’s 155 Mbit/s data circuits to the company’s IP
network.
To install a 802.11g Wireless LAN operating at 54 Mbit/s
connected to a router within the block that will communicate via
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iv.
(e)
the telephone company’s three 2 Mbit/s data circuits to the
company’s IP network.
To install a VDSL multiplexer within the block offering 55 Mbit/s
downstream and 2.5 Mbit/s upstream to a VDSL modem in each
flat. The VDSL multiplexer is then connected via ATM permanent
virtual circuits on the 622/52 Mbit/s data channels to the Cable TV
company’s IP network.
List the advantages and/or disadvantages of all the above designs.
[4]
Identify any security issues with the designs.
[2]
State which of the above design options best suits the requirements.
[1]
A cinema chain has decided to investigate whether it could digitally distribute
its films in a high definition format from its head office to all its cinemas in
100 locations throughout the country. Each cinema will on average receive 5
films per week (to be screened in the following week), and each film will
typically be coded into a 12.096 GByte file (1 GByte = 109 Bytes). The data
communications protocols being used add a 20% overhead to the data. You
can assume that many of the cinemas will offer similar (but not identical)
programmes.
You are a consultant who has been asked to carry out a feasibility study to
evaluate a number of alternative solutions.
Your first task is to calculate what is the equivalent in Mbits/s of 5 films per
week.
[2]
The design options you should consider are:
i.
ii.
iii.
iv.
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A Gigabit Ethernet based on dark fibre leased from an insurgent
operator in a star topology and using the broadcast address.
An ATM network using switched virtual circuits operating at 155
Mbit/s between the head office and each of the cinemas.
A VSAT network providing a 1.2 Gbit/s broadcast from the head
office to the cinemas.
An SMDS service operating at 34 Mbit/s using with transmissions
from the head office using the broadcast address.
List the advantages and/or disadvantages of all the above designs.
[4]
Identify any security issues with the designs.
[2]
State which of the above design options best suits the requirements.
[1]
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PART B
Question 2
(a)
State, in your answer book, which two of the following statements are true and
which two are false and, if false, write out a correct version of the statement:
i.
ii.
iii.
iv.
10 Gbit/s Ethernets do not support the CSMA/CD access method as they are
always operate half duplex mode.
Token Ring networks, unlike Ethernets, are deterministic in the sense that they
can guarantee that a station will always be able to transmit a frame within a set
time.
The Frame Relay protocol is a connectionless protocol that supports error
detection but there is no error correction.
A product is a problem child if it has a low market share and low growth. [3]
(b)
Carry out a brief SWOT analysis of BT in the UK fixed network operator
market. You are expected to write no more than a couple of sentences about
two points under each of the four headings.
[8]
(c)
A type of Ethernet is described as 100Base-T2. What does each part of this
designation describe?
[2]
(d)
What are the main differences between a hubbed and a switched Ethernet?
How else might the two types of Ethernet be described?
[6]
(e)
Complete the blank cells of the table below in your answer book. It is part of
a subnetwork addressing scheme for an IP network with the network address
147.36.116.0/25, supporting up to 4 subnetworks of up to 126 hosts, up to 7
subnetworks of up to 62 hosts and up to 16 point-to-point WAN circuits. The
boundaries between the network part of the address and the subnetwork part of
the address and between the subnetwork part of the address and the host part
of the address are shown as vertical bars (|).
[6]
Subnetwork
3rd Byte
4th Byte
LAN A
LAN B
LAN C
LAN D
LAN E
LAN F
LAN G
LAN H
LAN I
LAN J
LAN K
Cct 1
…
011101|00
011101|00
011101|01
011101|01
0|XXXXXXX
1|XXXXXXX
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0111011|0
0111011|0
0111011|0
0111011|1
0111011|1
0111011|1
0111011|1
…
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10|XXXXXX
11|XXXXXX
00|XXXXXX
01|XXXXXX
10|XXXXXX
Subnetwork
Address
First Host
Address
Last Host
Address
147.36.116.128/25
147.36.117.0/25
147.36.117.128/25
147.36.116.129
147.36.117.1
147.36.117.129
147.36.118.1
147.36.118.65
147.36.118.129
147.36.118.193
147.36.119.1
147.36.119.65
147.36.119.129
147.36.119.193
…
147.36.116.254
147.36.117.126
147.36.117.254
147.36.118.62
147.36.118.126
147.36.118.190
147.36.118.252
147.36.119.62
147.36.119.126
147.36.119.190
147.36.118.194
…
147.36.118.64/26
147.36.118.128/26
147.36.118.192/26
147.36.119.64/26
147.36.119.128/26
…
…
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Question 3
(a)
State, in your answer book, which two of the following statements are true and
which two are false and, if false, write out a correct version of the statement:
i.
ii.
iii.
iv.
iMode provides always on Internet access from a mobile phone using TCP/IP.
SONET in N. America and SDH in the rest of the world are compatible at all
speeds greater than or equal to 155 Mbit/s.
Multi Protocol Label Switching provides some connection-oriented features
that allow IP networks to offer quality of service.
The Home Location Register stores the current Base Station System for each
phone within a Mobile Switching Centre’s area.
[3]
(b)
Describe how adaptive playout delay can be used to smooth out variations in
delay when playing real-time audio or video.
[5]
(c)
Describe why the Token Ring protocol is regarded by many as being superior
to the Ethernet protocol.
[3]
(d)
(e)
Explain why it did not succeed in the market place.
[2]
Describe with the aid of diagrams, how an FDDI ring can recover from a
circuit failure.
[5]
Use Dijkstra’s algorithm to calculate and mark the shortest route between A
and E in the diagram below (showing all the labels produced by executing the
algorithm), where the numbers represent distances between the nodes.
[7]
A
10
4
H
2
B
8
9
12
7
G
C
11
1
13
F
D
A
6
5
14
E
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Question 4
(a)
State, in your answer book, which two of the following statements are true and
which two are false and, if false, write out a correct version of the statement:
i.
ii.
iii.
iv.
Administrative Distance is a measure of the trustworthiness of information
from routing protocols .
Network Address Translation is used to redirect network layer traffic to a
different IP address.
Session Initiation Protocol is an ISO protocol that is used to establish and
control sessions for audio, video and data conferencing.
The Total Cost of Ownership of Personal Computers can easily be more than
10 times the purchase price of a PC over 3 years.
[3]
(b)
What are the main reasons that caused network operators to replace their
Plesiochronous Digital Hierarchy transmission networks with Synchronous
Digital Hierarchy transmission networks.
[6]
(c)
Describe the threats associated with denial of service attacks, worms and
external hackers. Outline the measures that network managers can take to deal
with them.
[6]
(d)
Describe briefly the main purpose of a disaster recovery plan?
[2]
(e)
What is meant by percentage availability, how is it related to MTBF and
MTTR?
[2]
A LAN has two identical routers with availabilities of 99.9% directly attached,
which are each connected via separately routed circuits each with an
availability of 99.8% to another pair of identical routers with an availability of
99.9% on a different LAN. Write down an expression for the overall
unavailability of the communications service that is provided between the two
LANs and hence calculate the overall availability of the communications
service between the two LANs?
[6]
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END OF EXAMINATION