UNIVERSITY OF LONDON
GOLDSMITHS COLLEGE
B. Sc. Examination 2010 (Internal)
COMPUTING AND INFORMATION SYSTEMS
INFORMATION TECHNOLOGY
IS52016A (CIS222)
Data Communications and Enterprise Networking
Duration: 3 hours
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 two questions from Part A and two questions from
Part B.
Full marks will be awarded for complete answers to a total of four questions, two 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 100 marks available on this paper.
No calculator may be used.
THIS PAPER MUST NOT BE REMOVED FROM THE EXAMINATION
ROOM
IS52016A (CIS222)
2010
1
TURN OVER
PART A
Question 1
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
(b)
An ADSL local loop is terminated on a Digital Subscriber Line Access
Multiplexer at the local telephone exchange.
The variability in network delays on the Internet is primarily caused by
queuing delays at routers.
HDLC is a byte-oriented connection-oriented protocol that uses byte stuffing
for data transparency.
Ethernet frames have a maximum length of 1000 bytes.
[3]
Write down the Nyquist’s Theorem equation, explaining each of the terms and
giving the units in which they are usually measured.
[3]
Use this equation to calculate the capacity provided by a channel with a
bandwidth of 500 MHz when 4 signaling levels are used.
(c)
[4]
Write down the 8 bits coded in the diagram below, assuming that they are
coded using Manchester encoding.
[4]
(d)
Explain, by describing the access method used, why the Ethernet protocol
cannot guarantee transmission of a frame within a specified time and cannot
even guarantee that a frame will be transmitted.
[4]
(e)
International Telegraph Alphabet Number 2 (ITA2) is a 5-bit code used by
teleprinters. Show how the ITA2 character 00101 can be further coded using
an even Hamming Code to support single bit error correction.
[3]
Another even Hamming coded ITA2 character was received with one bit
corrupted and the bits received were 110100111. Show how the error can be
detected and then corrected. What was the 5-bit character code that was
encoded originally?
[4]
IS52016A (CIS222)
2010
2
TURN OVER
Question 2
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
IGMP must always be implemented whenever IP is implemented and is used
to report errors and to diagnose IP problems.
If the M bit is set in the IP header of a datagram, it indicates that the datagram
is the last fragment of a larger datagram.
The checksum in the UDP header also checks some of the fields in the IP
header.
Every TCP connection on the Internet is uniquely identified by a combination
of source and destination IP addresses and port numbers.
[3]
(b)
Describe how IP version 4 uses the TTL field to prevent routing loops.
(c)
Describe how a TCP connection is established using a three-way handshake
with reference to the acknowledgement numbers signaled in the TCP headers.
[3]
(d)
Describe what happens when a ping command is issued to the operating
system of a PC.
(e)
[5]
[6]
A company has been allocated an IP network address 194.212.64.0/19.
How many valid host addresses can the company allocate?
What is the network mask for this network?
What is the broadcast address for this network?
What is the first valid host address and the last valid host address that the
company can use?
[8]
IS52016A (CIS222)
2010
3
TURN OVER
Question 3
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
(b)
POP3 is a mail protocol that is used to transfer an email message from a client
to a mail server.
The interface between the application layer and the transport layer is
implemented as a socket in Unix.
The Domain Name System normally uses UDP as its transport layer.
HTTP is a presentation layer protocol that defines how web pages are
displayed.
[3]
In your answer book draw a table that shows how the layers of the OSI
reference model map to those of the DoD model and the hybrid model.
[6]
(c)
Explain why application designers might choose to use an unreliable transport
service.
[4]
(d)
Describe the structure of the Uniform Resource Locator used by HTTP with
reference to an example.
[4]
(e)
A Huffman code has been defined to store and transmit the moves made in
chess matches using descriptive notation, compressed with the codes defined
in the following table:
1
2
3
4
5
6
7
8
0001
0010
0011
0100
0101
0110
0111
0000
K
Q
P
B
N
R
“space”
100
101
11000
11001
11010
11011
111000
111001
“new line”
x
ch
e.p.
(
)
O
mate
111010
111011
111100
111101
1111100
1111101
1111110
1111111
How would the move Q-KB5xPch be coded?
Draw the Huffman Tree in your answer book and hence use it to decode the move
coded by:
11000111000100110110000111110010111111011111111
[8]
IS52016A (CIS222)
2010
4
TURN OVER
PART B
Question 4
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
Amazon.com is an example of a Global Distribution System.
The protocol used by Token Rings is technically superior to the protocol used
by Ethernet as Token Ring supports higher speeds.
Virtual LANs can be defined by physical ports or by datalink, network or
transport addresses.
The distribution function in IEEE 802.11 wireless networks is normally
provided by an IEEE 802.3 LAN.
[3]
(b)
Describe the life cycle of a typical network product.
(c)
Describe how a VSAT network can operate with a small satellite dish. What
is the main disadvantage of using such a network?
[6]
(d)
A type of Ethernet is described as 10GBase-T. What does each of the parts of
this designation describe?
[3]
(e)
Use the Spanning Tree Protocol to determine which bridge ports should be
blocked in the following LAN topology. Draw this diagram in your answer
book. Show which bridge is elected as the root bridge by means of a thick
lined box and show the path costs from each bridge port to the root bridge.
Mark all the root ports with an R and all the designated ports with a D and all
the blocked ports with an X. Draw the spanning tree with thick lines on the
diagram.
[7]
IS52016A (CIS222)
[6]
1000Base-T
Cost = 4
Priority 1
Address 3
10Base-T
Cost = 100
Priority 2
Address 5
Priority 2
Address 1
Priority 1
Address 2
10Base-T
Cost = 100
Priority 1
Address 4
100Base-T2
Cost = 19
2010
5
TURN OVER
Question 5
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
A plesiochronous data link operates synchronously with occasional losses of
synchronisation, known as frame slips.
Primary Rate ISDN supports a 64 kbit/s signalling channel known as the S
channel.
3G mobile phone networks still make use of telephone switches for voice
communications.
ATM is a connection-oriented protocol that transmits variable length packets
known as cells.
[3]
(b)
Identify three main intelligent network databases required by a mobile phone
network and what sort of information each of them stores.
[3]
(c)
Identify five main differences between transparent bridges and source route
bridges.
[5]
(d)
Outline six main requirements for a good routing protocol.
(e)
Draw the network diagram below in your answer book and use Dijkstra’s
algorithm to calculate the shortest route between A and E, where the numbers
represent distances between the nodes. On your diagram, show the node
labels you have used at each step of the algorithm and mark the shortest path
with a thick line.
[6]
B
10
C
7
[6]
D
5
11
A
2
1
E
6
9
4
H
12
G
8
F
In your answer book, draw up a routing table which shows the next hop and
the shortest distance from node A to each of the other nodes on the network.
[2]
IS52016A (CIS222)
2010
6
TURN OVER
Question 6
(a)
State, in your answer book, whether each of the following statements is true or
false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
A Brouter will attempt to route a packet and if the network layer protocol is
not routable, it will bridge the frame.
When address space is limited, it is allowable to use all 0s and all 1s in the
subnetwork part of the address.
SNMP traps are used by network devices to report events to Intrusion
Detection Systems.
Availability can be calculated by dividing the Mean Time Between Failures by
the Mean Time to Repair.
[3]
(b)
Briefly describe the three cyclical steps used in building block network design.
[3]
(c)
Distinguish between security threats, vulnerabilities and attacks and provide
examples of each.
[6]
(d)
What is Electronic Software Delivery and what are the main advantages of
using it, to network managers?
[6]
(e)
A company has been allocated the Class C IP address 196.33.7.0. It has two
LANs which require up to 62 IP addresses and three LANs that require up to
30 IP addresses and up to 8 private circuits that require 2 IP addresses. The
table below defines a variable length subnetwork addressing scheme for this
company with most of the entries missing. Copy the table into your answer
book and complete the missing entries in the table.
Subnetwork
4th Byte
LAN A
LAN B
LAN C
LAN D
LAN E
Cct 1
Cct 2
Cct 3
Cct 4
Cct 5
Cct 6
Cct 7
Cct 8
00|XXXXXX
Subnetwork Address
First Host
Address
Last Host
Address
100|XXXXX
111000|XX
[7]
IS52016A (CIS222)
2010
7
END OF EXAMINATION