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NAPIER UNIVERSITY
DEPARTMENT OF ELECTRICAL & ELECTRONIC ENGINEERING
Level IV
SESSION 1997/98
Duration: 3 hours
DATA AND COMPUTER COMMUNICATIONS
MODULE NO: EE42006
There are SIX questions in this paper
Attempt FOUR questions.
There are four pages in this paper.
Examiner:
Dr. W.Buchanan.
Dept Ref:
WB42006.56d
Attempt FOUR Questions
1.
(a)
Discuss the format of an IEEE 802.3 frame. Also estimate
the minimum and maximum times to transmit an IEEE
802.3 frame.
(b)
(8)
Explain, with the use of diagrams, how 100BASE-4T and
4VG-AnyLAN can transmit 100Mbps over Cat-3 cable.
Also explain the concept of DC wander and show how
100BASE-4T avoids this.
(c)
(11)
Estimate, stating all assumptions, the time taken for a pulse
on an 10BASE2-based system to propagate from one end
of a 500m cable to the other. From this also estimate the
maximum number of pulses that can be transmitted before
a node knows that there has been a collision on a 500m
segment.
(6)
Total Marks [25]
2.
(a)
Explain the methods that FDDI uses to overcome the
problems of ring-based networks.
(b)
(5)
Outline the format of the IEEE 802.5 Token Ring frame and
identify the purpose and size of each of the fields.
(c)
(10)
Explain the usage of 4B/5B coding in FDDI and show how
this is used to differentiate the start and end of an FDDI
frame.
(d)
(5)
A ring system is 60 km in circumference and it uses a glass
fibre. Stating all assumptions made, estimate the time that a
frame takes to travel completely round the ring.
(5)
Total Marks [25]
3.
(a)
Discuss the ISO 7-layered model and show how different
network types, such as Ethernet, Token Ring and FDDI, fit
with networking protocols, such as SPX/IPX, TCP/IP, and
NetBEUI. Give some examples of practical networks and
the protocols that they use.
(b)
(9)
Explain the main differences between routes, bridges and
repeaters. Also give an example of a commonly used
routing protocol.
(c)
(4)
For the network given in Figure Q3.1. Determine the
number of possible routes that can be taken when routing
between node A and node F (without ever going through
the same node twice).
(d)
(6)
The unit time delays for the network in Figure Q3.1 are
given for each of the links. Determine the shortest and
longest path unit delays.
(6)
2
B
E
2
3
A
1
3
F
1
4
C
D
1
Figure Q3.1
Total Marks [25]
4.
(a)
Explain how TCP uses ports and sockets to transmit data
between two TCP/IP hosts.
(b)
(6)
The TCP protocol is described as a connection-oriented,
reliable protocol, whereas the IP is described as a
connectionless, unreliable protocol. Discuss, with reference
to the TCP and IP headers, these descriptions.
(c)
(7)
If a TCP/IP network has a subnet mask of 255.255.240.0,
determine the maximum number of hosts that can be
connected to the subnet.
(d)
(4)
Discuss how the Department of EEE (Electrical and
Electronic Engineering) at Napier University connects to
EaStMAN (Edinburgh and Stirling MAN), and how this
connects to the global Internet.
(8)
Total Marks [25]
5.
(a)
(i)
Explain, using an example, how ATM routes cells
through a network.
(ii)
(6)
Explain, using examples, how ATM uses Virtual
Path and Virtual Circuit switches.
(10)
(iii) An ATM cell has a 12-bit VPI field. Determine the
number of unique addresses that this can have.
(b)
(3)
If 256 bits of data are sent and the probability of a single
bit being in error is 0.1%, determine the probability that
there is no errors in the data and the probability that there
will be errors.
(6)
Total Marks [25]
6.
(a)
Explain the main Firewall methods used to provide security
in Intranets.
(6)
(b)
Explain the usage of intermediate systems in Intranets.
(6)
(c)
Determine the encoded message which has a CRC
generator polynomial of x 4 + x 3 + 1 and data input of
110001100. Prove that there will be no error when the
encoded message is received.
(d)
(8)
Determine how many double and triple bit errors that can
occur in an 8-bit data byte.
(5)
Total Marks [25]
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