Download Data Communications and Enterprise Networking

UNIVERSITY OF LONDON
GOLDSMITHS COLLEGE
B. Sc. Examination 2005
COMPUTING AND INFORMATION SYSTEMS
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. Your answers to Part A and Part B should be written in separate answer
books.
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 calculators should be used.
IS52016A (CIS222)
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TURN OVER
PART A
Question 1
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
(b)
If a perfectly formed square waveform is to be received over a channel
without any distortion, the bandwidth of the channel would have to be infinite.
Propagation delays at each router result in Round Trip Times on the Internet
being proportional to the size of packets.
Most modern data link protocols owe their origins to HDLC and, as a result,
use an address field in their headers even over point-to-point links.
CRC-32 requires a 2 byte checksum field and can detect 100% of burst errors
of 32 bits or less.
[3]
State Shannon’s Law, defining each of the terms and giving the units in which
they are usually measured.
[3]
Use Shannon’s Law to demonstrate that a PSTN circuit with 3.4 kHz
bandwidth and a signal to noise ratio of 30dB will not be able to transmit a 34
kbit/s signal.
[4]
(c)
Write down the bits coded in the diagram below, assuming that they are coded
using Manchester encoding.
[4]
(d)
Describe the main differences between the Password Authentication Protocol
and the Challenge Handshake Authentication Protocol used by PPP.
[4]
(e)
Binary Coded Decimal is a code, which represents a decimal digit as a 4-bit
binary number. (E.g. 3 is encoded as 0011 and 9 as 1001).
Show how the BCD code for the decimal digit 5 could be further coded to
allow a single bit error to be corrected using an even Hamming Code.
[3]
A different even Hamming Coded BCD digit was received as 0010100. Show
how the error can be detected and corrected. What decimal digit was
originally encoded?
[4]
IS52016A (CIS222)
2005
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TURN OVER
Question 2
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
ICMP is a network layer protocol that is encapsulated in another network layer
protocol (IP) for which it provides testing and diagnostic functions.
IP Version 6 incorporates the Secure Sockets Layer for its security functions.
UDP uses the Internet checksum but it only protects the UDP header fields.
The TCP congestion control mechanism increases the variability of delay but
helps protect the whole Internet from congestion because the majority of the
traffic on the Internet uses TCP as its transport protocol.
[3]
(b)
A router receives a packet with an unknown IP address for a device on a LAN.
Describe how the router resolves the physical address and how it handles
another packet with the same IP address arriving immediately afterwards. [6]
(c)
Explain why classful addressing on the Internet has been abandoned and how
routers now determine which part of the IP address is the network ID and
which part is the host ID.
[5]
(d)
Show how the IP checksum calculation would be used to check the four bytes
of protocol information given below:
11001010
01010011
11010010
10100110
(e)
[8]
Describe how a client computer establishes a TCP connection to a server using
a three-way handshake.
[3]
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TURN OVER
Question 3
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
SMTP is used to retrieve emails from a server, but it does not allow just the
mail headers to be retrieved. To do this users should configure their mail
clients to use the IMAP protocol.
The Open Systems Interconnection Reference Model distinguishes between
the service provided by one layer to the layer above and the protocols that are
carried between the layer and its peer layer.
TFTP uses the Go Back N flow control mechanism.
Few people consciously use FTP these days, but it is often used by software
that uploads web pages.
[3]
(b)
Produce a table that shows the mapping between the layers of the ISO
reference model, the DoD (or TCP/IP) Reference Model and the hybrid
reference model.
[4]
(c)
Define the main structure of a Uniform Resource Locator (URL) and list three
possible values of the first field of the URL.
[4]
(d)
Describe the process by which a domain name is resolved into an IP address.
[6]
(e)
Use the Huffman Code defined in the table below to compress the word
“PORT”.
[3]
Using the same Huffman code, draw the Huffman Tree and use it to decode
the sequence of letters represented by 00101001100001000.
A
C
D
F
G
H
L
000
01000
01001
10100
10101
10110
1000
N
O
P
R
S
T
0101
011
10111
1001
001
11
[5]
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TURN OVER
PART B
Question 4
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
Ethernet supports data rates of 10 Mbit/s, 16 Mbit/s, 1 Gbit/s and 10 Gbit/s.
10Base-T uses two category 3 Unshielded Twisted Pair cables.
FDDI runs over a fibre optic ring at 100 Mbit/s and was designed for use in
backbone LANs.
IEEE 802.11 (otherwise known as Wi-Fi) uses the CSMA/CD access method.
[3]
(b)
Describe the main difference between Ethernet II and IEEE 802.3 and how
each de-multiplexes to the correct network layer protocol (giving the names of
any other data link protocols that need to be used and the order in which they
are encapsulated).
[5]
(c)
A type of Ethernet is described as 100Base-T4. What does each of the parts of
this designation describe.
[4]
(d)
What is the main difference between a hubbed and a switched Ethernet? How
else might the two types of Ethernet be described?
[5]
(e)
Describe why the Token Ring protocol is regarded by many as being superior
to the Ethernet protocol.
[4]
Explain why it did not succeed in the market place.
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[4]
TURN OVER
Question 5
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
SMDS uses the ITU-T’s E.164 telephone numbering scheme for its
addressing.
Basic Rate ISDN provides two 64 kbit/s B channels and a 16 kbit/s S channel
that is used for signalling and can also carry packet-switched data.
GSM mobile phones use a combination of frequency and time division
multiple access.
ATM is connectionless and switches fixed length packets known as cells. [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.
[5]
(c)
Distinguish between repeaters, bridges and routers with regard to whether or
not they separate collision domains and broadcast domains.
[3]
(d)
Outline the two types of de-centralised routing and the types of network they
are best suited to.
[6]
(e)
Use Dijkstra’s algorithm to calculate and mark the shortest route between A
and D in the network below, where the numbers represent distances between
the nodes:
[8]
B
9
C
4
8
2
A
3
1
D
5
6
F
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E
TURN OVER
Question 6
(a)
State, in your answer book, whether each of the following statements are true
or false and, if false, write out the correct statement:
i.
ii.
iii.
iv.
Bridges are difficult to install, as they require considerable manual
configuration.
Each local area network should be given its own sub-network address.
SNMP v2 is insecure as it uses community strings, which are plaintext
passwords.
The biggest threat to a company’s security comes from external hackers.
[3]
(b)
List the main numerical network performance and reliability criteria that
should be specified in a Requirements Document and indicate the units in
which they are normally measured.
[6]
(c)
List the advantages and disadvantages of a full-mesh WAN design.
(d)
What is meant by MTTR? What does it describe in the context of a circuit?
[2]
[3]
A private circuit has an availability of 99.6% and an MTBF of 332 hours.
What is the average duration of its circuit failures?
[6]
(e)
What are the characteristics of a virus? What steps can network managers
take to help prevent their networks from being affected by viruses.
[5]
IS52016A (CIS222)
2005
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END OF EXAMINATION