nAmiBIA UniVERSITY OF SCIEnCE AnD TECHnOLOGY

FACUL TV OF COMPUTING AND INFORMATICS

DEPARTMENT OF COMPUTER SCIENCE

QUALIFICATION: Bachelor of Computer Science

QUALIFICATION CODE: 07BACS LEVEL: 7

COURSE: Internet and WAN Telecommunication COURSE CODE: IWT711S

DATE: July 2016

DURATION: 2 hours

EXAMINER(S)

MODERATOR:

1. Answer all questions.

SESSION: 2

MARKS: 100

SUPPLEMENTARY EXAMINATION QUESTION PAPER

Mrs. Mercy Chitauro

Mr. Kudakwashe Madzima

THIS EXAMINATION PAPER CONSISTS OF 5 PAGES

(Excluding this front page)

INSTRUCTIONS

2. When writing take the following into account: The style should inform than impress, it should be formal, in third person, paragraphs set out according to ideas or issues and the paragraphs flowing in a logical order. Information provided should be brief and accurate.

3. Please, ensure that your writing is legible, neat and presentable. 4. When answering questions you should be led by the allocation of marks. Do not give too few or too

many facts in your answers. 5. Number your answers explicitly. 6. Clearly mark rough work as such or cross it out unambiguously in ink.

PERMISSIBLE MATERIALS

1. Calculators

1

1.

a. What is a differential encoding scheme? [1 mark]

b. Bipolar- Alternate Mark Inversion (AMI} and Pseudoternary are differential encoding schemes

where in bipolar - AMI one is represented by alternating positive and negative and in

pseudoternary zero is represented by alternating positive and negative. What is the problem

with both these schemes when there is long string of zeros for bipolar- AMI and long strings of

ones for pseudoternary? [2 marks]

c. What are the problems of biphase encoding schemes like Manchester and differential

Manchester in comparison to Non Return to Zero (NRZ) encoding schemes

d. State 3 ways/methods of evaluating or comparing various encoding schemes

[3 marks]

[3 marks]

e. Use the methods you stated in question 'ld' to compare the two encoding schemes A and B

given in table 1 in such a way that would show the preferred encoding scheme in a WAN digital

link with low bandwidth. [6 marks]

B A

1000Hz 2000Hz

Alternating current Direct current

Embedded clocking External clock required

Immune to noise Immune to noise

Signalling rate< data rate Signalling rate >data rate

Error detection No error detection

2. Given that a T1 TDM line is capable of 1.544 Mbps. How many of the following devices will be

accommodated by the Tlline if 2% of the Tlline capacity is reserved for synchronisation purposes.

3.

a.

i. 300-bps computer terminals

ii. 9600-bps computer ports

iii. 64-kbps PCM voice-frequency lines

b. Explain how the use of a statistical multiplexer would improve performance.

[5 marks]

[3 marks]

c. Explain the overhead incurred on frames when statistical multiplexing is used and why it is

necessary.

a. Explain cyclic redundancy check.

b. Explain the use of even parity error detection

c. What will be the even parity bit set by the transmitter for the following bytes

i. 11110000

ii. 10110110

[2 marks]

[3 marks]

[3 marks]

[3 marks]

2

iii. 11001010

d. If two communicating devices use single even parity check and the transmitter sends 10101010

and the receiver gets 11100010. Will the receiver detect the error? Why or why not?

[2 marks]

4. Internet Protocol (IP) provides a means for data transfer over networks. 1Pv4 provides fewer addresses

than are actually needed to connect all networked devices. 1Pv6 provides more addresses and thus it is

being adopted for use in networks.

a. What is the 1Pv6 address space?

b. Describe 1Pv41imitation besides the one of limited address space stated above.

c. Fill in the table below by stating what type of 1Pv6 address is given.

1Pv6 address Type

FE80::C001:1DFF:FEEO:O FF02::2 ::1 3001:0060:0000:0000:0000:0CB4: 1E24:981A/64 ::/128

[1 mark]

[4 marks]

[3 marks]

d. Given a MAC address of interface X as 0213:1978:5005. What will be the host part of the EUI-64

address generated for serial 0/0/0 interface?

e. What will be the fuii1Pv6 address for interface X using the scheme in 2a above?

f. What will be the link local address for interface X?

Figure 1 illustrates Bakers Fresh network diagram. Use the diagram to answer question 5.

DHCP POO.. N.AM:S

VLAN 30: STAFF ',tAN 40' SALES

g ""01# Pf4

Fo0,1)1 I

Se O.,t'A'\ (:_§ :~ J"' ~ Mlf1 12.11.~~jp~,l. - ~.'i!'.!fJ/,,5/6

2911~ ISP ~Mftl ~~ ""~

sil-11 . 10. 1/30 ;;-!~ f;Qtci6 .70.254/21 FaO/: Fa0/'2 G .f:!',¥"' ~ O,IJ/1 'f lliiCtV •

Fa0/1 Fo0/1 ~ G ~O,Il/ l 12.1l. ID .6/30 281l 2960·24TI 172. 16.50.2/30 2811 ~ O,ll/1 BRANCH2 52

,.~ HQ m . I6 .50.S/JO

F.oy"' Dla 200 sea ~;..;;::, Fa0/1

,uJr X, vu3{.¥; 1n.16.30.0/ l 4 172. 16 . .;().0/24

172.16.50.1/30

Se: rver· PT DNS

IJtNj 100 192.l6B.lOO .Oi2~

Figure 1: Bakers Fresh network

192.168.100.3S/l 4

2811 BRANCHL

[3 marks]

[1 mark]

[1 mark]

FaOrlQ ... PC-PT PCJ

m . I6.70.S/24

3

5. You are given that the ISP network is connected through Multi-Protocol Label Switching (MPLS). You are

also told that the ISP router is the first router in the MPLS network

a. What type of MPLS router is the ISP router? What is this type of MPLS router responsible for in

the MPLS network? [3 marks]

b. State and explain the use of any other two types of MPLS routers. [4 marks]

c. Describe two reasons why MPLS networks are popular. [2 marks]

d. If the ISP is implementing traffic engineering. Which Label distribution protocol is being used by

the ISP? [1 mark]

e. Name any other label distribution protocol you know

f . In which OSIIayer is MPLS?

g. Is MPLS circuit switched or packet switched?

6. Use Figure 2 to answer question 6.

IPSec tunnel between HQ and BRNKH2

Fig 2: ADSL and VPN

[1 mark]

[1 mark]

[1 mark]

a. State two valid ADSL modulation techniques that can be used between HQ and BRANCH1

[2 marks]

b. Assume DMT ADSL is used between HQ and BRANCH1. Two consecutive channels are operating

using the frequency 72.5 KHz and 77.5 KHz.

i. What is the size of each DMT channel?

ii. What are the frequencies of these two channels?

[1 mark]

[2 marks]

c. What is the actual size of each DMT channel used in real ADSL networks? [1 mark]

d. DSL access multiplexer (DSLAM) is used to accept all of the ADSL connections and combines or

multiplexes them into one link. Assume DSLAM is getting 15 different signals? How many

frequencies does the DSLAM output to make one link? [2 marks]

e. Which multiplexing technique does the DSLAM use to achieve the result in '6d' above?

[1 mark] f. What are guard bands used for in DSL? [1 mark]

4

r •

g. ADSL signals coexist with voice signals in the same physical medium. A DSL splitter is used to

separate voice and data signals. A signal of 6Hz will represent what type of ADSL signal?

[1 mark]

7. Use Figure 2 to answer question 7.

8.

A site-to-site VPN exists between HQ and BRANCH2. The tunnel is using IPSec to establish the VPN. The

VPN is used to enable communication between VLAN 15 and 25 and BRANCH2 LAN. BRANCH2 LAN is

using the network address 192.168.35.0/24. VLAN 15 and 25 use the networks 192.168.15.0/24 and

192.168.25.0 respectively. The tunnel is terminated at HQ serial 0/0/0 interface and BRANCH2 serial

0/1/0 interface.

a. Which network/swill be allowed through the tunnel through serial 0/0/0 interface on HQ

router? [1 mark]

b. Which IP address is used to identify IPSec peer for BRANCH2? [1 mark]

c. Given that the tunnel uses AES encryption. For the 1Pv4 packet sourced from VLAN25 state or

describe the following; the source IP address, destination IP address, IPSec information, and the

data at the following points:

i. HQ serial 0/0/0

ii. ISP serial 0/1/0

[6 marks]

[2 marks]

d. Which process is used at serial 0/0/0 of router HQ in order to send information through the

IPSec tunnel? [1 mark]

e. Which type of VPN will be used on BRANCH1 router to enable a network administrator working

from home to access the network? [1 mark]

f. Which four security measures must each VPN achieve?

g. What can be said about the AES key between HQ and BRANCH2 routers?

a. Define the terms data integrity and system integrity.

[2 marks]

[1 mark]

[4 marks]

b. Integrity is part of CIA security triad. Which two other concepts are required to have almost

complete security? [2 marks]

c. Explain how the following counter security threats

i. Firewall

ii. IPSec

d. Describe what a virus is.

[2 marks]

[3 marks]

[1 mark]

5