Question 1
1.1
Suppose that we are to transmit the following 10-bit message on the
Data Link layer: M = 1011001101. We wish to generate a Cyclic
Redundancy Code (CRC) using the following 6-bit generator G =
101101. Hence n = 10 and k = 5. Determine for this situation:
a) The required Frame Check Sequence (FCS)
[8 + 6 = 14
marks]
b) The actual transmitted frame T
1.2
An organisation is granted the block of addresses 130.56.0.0/16. The
administrator wants to create 1024 subnets.
1
a) Find the subnet mask required
1
b) Find the number of addresses in each subnet
2
c) Find the first and last addresses in subnet #1
2
d) Find the first and last addresses in subnet #1024
1.3
Briefly explain the procedure for checksum calculation and verification
in the IPv4 protocol. What part of an IPv4 packet is covered by the
checksum calculation? Why?
[2 + 1 + 1 = 4
marks]
1.4 Packet switching techniques require the packet payload to be prefixed
with a header. List three (3) essential items that must be included in
the packet header. Justify your choice of items.
[6 marks]
Total [14 + 6 + 4 + 6 = 30 marks]
Question 2
This question is concerned with Internet addressing concepts.
2.1 There are 5 different network classes for addressing in the
Internet (using IPv4). Compute the theoretical maximum
number of addressable hosts in all:
(a) Class A networks
2
(b) Class B networks
2
(c) Class C networks
2
2.2 The numbers computed in 2.1 above represent upper
bounds on the numbers of addressable hosts for these
classes of network:
(a) Briefly explain how this number is reduced through the
use of special reserved addresses.
(b) Provide an estimate of the number of actual available
host addresses for a given Class C network.
[2 + 4 = 6 marks]
2.3 What is meant by the term fragmentation in the context of the
Internet Protocol? Give an example of how it works.
[4 marks]
2.4
(a) What is the purpose of a subnet mask?
(b) Is the subnet mask 255.255.0.255 valid for a Class A
[2 + 2 = 4 marks]
address? Explain.
2.5 Briefly explain the difference between a switch and a router.
[4 marks]
2.6 Consider the following internet address: 136.27.32.104
a) Convert this address into Binary format.
b) Convert this address into Hex format.
c) What class does this internet address represent?
d) If we apply a subnet mask of FFFFFE00, obtain the
relevant network, subnet and host addresses for the
given internet address.
[1+1+1+3=6 marks]
Total [6 + 6 + 4 + 4 + 4 + 6 = 30 marks]
Question 3
3.1 Consider the TCP header shown above.
Provide a brief explanation of each field in this header.
[16 marks]
3.2 Briefly explain the principal differences between UDP and
TCP and the reasons for choosing between them for a given
internet application.
[4 + 4 = 8 marks]
3.3 Briefly describe the key differences between the Link State
Protocol OSPF and the protocol known as BGP4. Identify the
situations where each of these routing protocols would be
applied and reasons for selecting them for those situations.
[3 + 3 = 6 marks]
Total [16 + 8 + 6 = 30 marks]
Q4
Discuss the use masks in the manufacture of integrated circuits. Your answer should explain
what masks are, how they are used, and when masks are used.
[5 marks]
Two computers, X and Y, are being evaluated for use as weather prediction engines. They
will run a Fortran program called WETHA. Both computers, X and Y have 20 GHz clocks,
and three types of instruction, A, B, and C, which take 1, 2, and 3 clock cycles to execute
respectively. When WETHA is compiled on computer X, it will execute 5 x 1010 instructions
of type A, 1 x 1010 instructions of type B and 1 x 1010 instructions of type C. When WETHA
is compiled on computer Y, it will execute 1 x 1011 instructions of type A, 1 x 1010
instructions of type B and 1 x 1010 instructions of type C.
(A) Calculate the MIPS rating for computer X while executing the WETHA program,
[5 marks]
(B) Calculate the MIPS rating for computer Y while executing the WETHA program,
[5 marks]
(C) Calculate the execution time for WETHA on computer X
[5 marks]
(D) Calculate the execution time for WETHA on computer Y
[5 marks]
(E) Which computer would be preferable? Please state your reasons.
[5 marks]
Please include your working, and the equations you use. I don’t mind if you structure
your answers as some sort of table to avoid repetition, but please clearly indicate the
association between the answer and the individual components of the question.
Q5
(A) Describe the general purpose of the circuit shown in the diagram below, and how it
works.
[5 marks]
01100101
B
∑
∑
∑
∑
∑
∑
E
∑
∑
∑
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∑
∑
∑
∑
∑
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∑
∑
∑
∑
∑
∑
∑
∑
∑
∑
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D
∑
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∑
01100101
C
(B) – (F) Describe the specific function of each of the labelled sections of the circuit.
Note that the labels run from B to F, to match the section of this question.
[5 marks each]
[30 marks]
Q6
(A) What does it mean to describe the datapath of a computer architectures as gated, and
why are some computer architectures constructed this way?
[5 marks]
(B)
In a pipelined architecture, several sequential instructions are running simultaneously. How
are the control signals for these instructions amalgamated without causing ambiguities?
You may find it helpful to draw a diagram.
[5 marks]
(C) Is the architecture below a single-cycle architecture or a multicycle architecture? What
feature(s) of the design led you to that conclusion?
PC
memory
read
adddress
write
adddress
write
data
PC
Write
I or Mem
D Read
Mem
Write
memory data
register
instruction
register
IR
Write
Mem Reg
to Reg Dest
write data
read data1
write register
read register1
read register2 read data2
signextend
shift
left 2
A
4
B
1
0
zero
ALU
ALU
out
2
3
ALU ALU
SelB SelA
[5 marks]
(D)
Describe the problem that the sign-extend component is designed to handle, and
describe what it does.
[5 marks]
(E)
What type of circuit is the component labelled ALU SELB in the circuit diagram
above, and what is its purpose in the architecture? Why is one of its input values the number
4?
[5 marks]
(F)
The circuit has a control input called I or D. What does the device with this control
input do, and why is this action nmecessary?
[5 marks]