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WDS820S - WIRELESS DATA NETWORKS AND SYSTEMS - 2ND OPP - JAN 2020 |
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e
NAMIBIA UNIVERSITY
OF SCIENCE AND TECHNOLOGY
FACULTY OF COMPUTING AND INFORMATICS
DEPARTMENT OF COMPUTER SCIENCE
QUALIFICATION: BACHELOR OF COMPUTER SCIENCE HONOURS
QUALIFICATION CODE: O8BCSH
ACNODURSSEY:STWEIMRSELESS DATA NETWORKS
LEVEL: 8
COURSE CODE: WDS820S
DATE: JANUARY 2020
DURATION: 3 HOURS
SESSION: 2
MARKS: 80
SUPPLEMENTARY / SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S)
PROF GUY-ALAIN ZODI LUSILAO
MODERATOR:
MR. JULES ATUMBE BARUANI
INSTRUCTIONS
1. Answer ALL the questions.
2. Write clearly and neatly.
3. Number the answers clearly.
THIS QUESTION PAPER CONSISTS OF 6 PAGES (Including this front page)
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Part A QUESTION I (10 marks) —Multiple Choice 1 point for each problem
1. 802.11 falls into the category of:
(A) Pedestrian mobility and wireless (B) mobile and wired (C) fixed and wireless (D) vehicular
mobile and wireless
2. Which modulation scheme is used for 802.11 WLAN devices?
(A) DSSS (B) FHSS (C) OFDM (D) none of above
3. The antenna size for a 3G device which uses the 1800 MHz frequency band is
(A) 8.33 cm (B) 2.08 cm (C) 4.16 cm (D) none of above
4.The propagation effect that occurs when a radio wave hits an impenetrable object .
(A) blocking (B) diffraction (C) reflection (D) refraction
5. Which modulation is used in both 802.11b and 802.16?
(A) QPSK (B) QAM-16 (C) QAM-64 (D) none of the above
6. Which is not the advantage of cellular systems?
(A) higher capacity (B) robustness (C) less transmission power (D) none of the above
7. The maximum data rate over a 2 MHz channel whose signal to noise ratio is 10 dB.
(A) 2.16 Mbps (B) 3.33 Mbps (C) 6.66 Mbps (D) none of above
8. Which statement about Bluetooth is correct?
(A) It does not operate in the ISM band. (B) Two kinds of links (ACL and SCO) exist.
(C) Bluetooth 2.0 cannot offer the transfer rate up to 12 Mbps. (D) none of above
9. Which defines an extension of the 802.11 standard for QoS?
(A) 802.11 (B) 802.11d (C) 802.11e (D) 802.11h
10. Which statement is true?
(A) HSCSD is not Packet-switched. (B) GPRS offers data rates up to 171.2 Kbps.
(C) EDGE can achieve a higher transfer rate than GPRS. (D) none of above
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Part B (20 marks)- BASICS
QUESTION II [4 marks]
What are the two different types of destination addresses that can be assigned to a mobile node
while it is attached to a foreign network?
QUESTION III [4 marks]
What is the minimum bandwidth needed to achieve a data rate of 8 bits/sec if the signal is
transmitted using NRZ encoding? Explain your answer.
QUESTION IV [10marks]
Consider the following set of three links to a single base station in a cell. Each of their transmit
powers are indicated, as well as the received power at the tower.
1) Given that the tower wants to receive each signal at 20 mW, what would the TPC
algorithm dictate as the next transmit power of each mobile station? [6 marks]
2) What issue in 3G Cellular Network, the TPC algorithm attempts to address in balancing
the transmission power of mobile stations? [2 marks]
3) Why is TPC algorithm not widely adopted in 3G cellular network?[2 marks]
50 mW
100 mw
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QUESTION V [2 marks]
In the discussion of the handoff procedure based on relative signal strength with threshold, it
was pointed out that if the threshold is set quite low, the mobile unit may move far into the new
cell. This reduces the quality of the communication link and may result in a dropped call. Can you
suggest another drawback to this scheme?
Part C (30 marks)-CELLULAR AND MOBILE IP
QUESTION VI [16 marks]
Consider two different cellular systems that share the following characteristics. The frequency
bands are 825 to 845 MHz for mobile unit transmission and 870 to 890 MHz for base station
transmission. A duplex circuit consists of one 30-kHz channel in each direction. The systems are
distinguished by the reuse factor, which is 4 and 7 respectively.
a. Suppose that in each of the systems, the cluster of cells (4, 7) is duplicated 16 times. Find
the number of simultaneous communications that can be supported by each system. [4
marks]
b. Find the number of simultaneous communications that can be supported by a single cell
in each system. [4 marks]
c. What is the area covered, in cells, by each system? [4 marks]
d. Suppose the cell size is the same for both systems and a fixed area of 100 cells is covered
by each system. Find the number of simultaneous communications that can be supported
by each system.[ 4 marks]
QUESTION VII [4 marks]
In mobile IP indirect routing, when a mobile node that is away from its home network
communicates with a fixed correspondent node in the Internet, the packets in the two directions
traverse different paths — why?
QUESTION VIII [4 marks]
In a cellular network, When a mobile phone user is moving from one cell to another cell (call is
going on), the call is suddenly terminated, even though all the functionalities of the transmitters
and receivers are working properly. Explain why?
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QUESTION IX [6 marks]
LAN X
Internet
| LANZ
Considering the figure above.. Suppose that LAN Z is the home network for host E and that D
sends a block of data to E via IP.
a. Show the PDU structure, including the fields of the IP header and the lower-level headers
(MAC, LLC) with the contents of address fields indicated for the case in which E is on its home
network.[2 marks]
b. Repeat part a) for the case in which E is on a foreign network reachable via the Internet
through R3. Show formats for the MAC frame leaving D and the IP datagram leaving R3.
Assume that IP-to-IP encapsulation is used.[ 2 marks]
c. Repeat part b) for the IP datagram leaving R3, but now assume that minimal encapsulation
is used.[2 marks]
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PART D (10 marks)- WIRELESS LAN
QUESTION X [6 marks]
Consider the scenario shown below, in which node D sends an RTS to node C at t0. Node C
responds to the RTS with a CTS (which is heard by nodes B and C) in accordance with 802.11
protocol, and node D begins the transmission of its message at t2 in the meantime, node A sends
an RTS message to B at time t1.
el
Coes
C
t
RTs
cis
CTs
ome
a. Ifnode A were to begin transmitting to node B at some point after t3 would A’s transmission
be successfully received at B? [2 marks]
b. Ifnode A were to begin transmitting to node B at some point after t3 would A’s transmission
interfere with the ongoing transmission from D to-C?[2 marks]
c. Att3 can B respond to A’s RTS message with a CTS message? Why or why not?[2 marks]
QUESTION XI [4 marks]
We consider a WLAN in which the maximum propagation delay is 4 sec. The (4) WLAN operates
at a data rate of 10 Mbps. The data and ACK packets are of 400 and 20 bits, respectively. The
processing time for a data or ACK packet is 1 sec. If the probability p that a data packet or its ACK
can be corrupted during transmission is 0.01, find the data link protocol efficiency with the sliding
window protocol with window sizeW =8.
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Part E-(10 marks) Bluetooth
QUESTION XII [6 marks]
What is the maximum size of the data field for a 3-slot Bluetooth frame at basic rate?
Explain your answer
QUESTION XIII [4 marks]
List and describe four types of device specified in a piconet.
GOOD LUCK!