COMPUTER NETWORKING PROTOCOLS EXAMINATION
2016/2017 ACADEMIC YEAR (FIRST SEMESTER)
THE UNIVERSITY OF DODOMA
COLLEGE OF INFORMATICS AND VIRTUAL EDUCATION
SCHOOL OF INFORMATICS
UNDERGRADUATE UNIVERSITY EXAMINATIONS
FIRST SEMESTER 2016/2017
IN 211: COMPUTER NETWORKING PROTOCOLS
Date: 20 February, 2017
Time Allocated: 3 Hours
Instructions:
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This question paper consists two Sections
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Attempt ALL questions from Section A and Any THREE Questions from Section B
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All University of Dodoma examination regulations apply.
SECTION A (40 Marks)
Question One
a) What is a protocol in internet world and briefly explain the key elements of a protocol. (3 Marks)
Answer (Click to show)
A protocol is a set of rules governing data communication. Key elements: Syntax, Semantics, Timing
b) Briefly describe the three types of UTP cable configuration and where they are used in a network. (6 Marks)
Answer (Click to show)
Straight-through: Switch to host
Crossover: Similar devices
Rollover: Console connection
c) Briefly explain how to distinguish a unicast physical address from a multicast physical address in a computer network. Then, identify the type of the following destination physical addresses (i) 4A:30:10:21:10:1A, (ii) FF:FF:FF:FF:FF and (iii) 47:20:1B:2E:08:EE. (4 Marks)
Answer (Click to show)
Unicast: Least significant bit of first byte is 0
Multicast: Least significant bit of first byte is 1
(i) Unicast, (ii) Broadcast, (iii) Unicast
d) Physical addresses in a network are transmitted in binary notation. Given the physical address in (c) part (iii) above, show how this address is transmitted in a network. Hint, just show the first two octets. (4 Marks)
Answer (Click to show)
01000111 00100000
e) Briefly discuss classful IPv4 addressing with their block ranges. (5 Marks)
Answer (Click to show)
Class A: 1-126, Class B: 128-191, Class C: 192-223, Class D: 224-239, Class E: 240-255
f) A classful address in a block is given as 73.21.50.25. Find the number of addresses in the block, the first address, and the last address. (4 Marks)
Answer (Click to show)
Number: 16,777,216
First: 73.0.0.0
Last: 73.255.255.255
g) Briefly discuss the three major differences between a router and a bridge. (2 Marks)
Answer (Click to show)
Router works at network layer, bridge at data link layer
Router uses IP addresses, bridge uses MAC addresses
Router connects different networks, bridge connects segments
h) TCP and UDP are protocols used in transport layer of TCP/IP protocol suit. Give at least two points to differentiate the two protocols? (2 Marks)
Answer (Click to show)
TCP is connection-oriented, UDP is connectionless
TCP provides reliability, UDP does not
Question Two
Assume that, Dar Es Salaam City Council is planning to install free internet cafes all over the city for public use. The City is having Hala, Kinondoni, Temeke and Kiganboni districts only. Suppose, the City is given a classful IP address block from 141.14.0:0 to 141.14.255.255 and you are asked to advise the City Council on how to share this resource equally between the four districts (Ilala, Kinondoni, Temeke and Kigamboni). Then,
a) How many host addresses will you allocate to each district? (2 Marks)
Answer (Click to show)
16,384 addresses per district
b) List the first and last host addresses of each district. (8 Marks)
Answer (Click to show)
Ilala: 141.14.0.1 - 141.14.63.254
Kinondoni: 141.14.64.1 - 141.14.127.254
Temeke: 141.14.128.1 - 141.14.191.254
Kigamboni: 141.14.192.1 - 141.14.255.254
SECTION B (60 Marks)
Question Three
a) Briefly discuss what a collision domain is and how to control it when a LAN performance is degraded. (5 Marks)
Answer (Click to show)
Collision domain: Network segment where collisions can occur
Control: Use switches to create separate collision domains
b) Briefly explain the CDMA/CD and CDMA/CA protocols and their differences in their applications. (5 Marks)
Answer (Click to show)
CSMA/CD: Used in wired Ethernet, detects collisions
CSMA/CA: Used in wireless, avoids collisions
c) Briefly describe algorithm flow charts of CDMA/CD and that of CDMA/CA protocols to show the work to support data communication in layer one devices. (10 Marks)
Answer (Click to show)
CSMA/CD: Listen→If busy→Wait/If free→Transmit→If collision→Backoff→Retry
CSMA/CA: Listen→If busy→Wait/If free→Send RTS→Wait CTS→Transmit
Question Four
a) Briefly describe the four addressing Systems as they are used in TCP/IP Protocol Suite. (10 Marks)
Answer (Click to show)
Physical addressing: MAC addresses
Logical addressing: IP addresses
Port addressing: Port numbers
Specific addressing: Application-specific
b) Describe and compare a TCP and UDP packets. (10 Marks)
Answer (Click to show)
TCP: Connection-oriented, reliable, sequencing, flow control
UDP: Connectionless, unreliable, faster, less overhead
Question Five
With their steps, briefly describe the Simplified router forwarding Modules,
a) With subnetting (10 Marks)
Answer (Click to show)
Extract destination IP→Apply subnet mask→Find matching subnet→Forward to next hop
b) Without subnetting (10 Marks)
Answer (Click to show)
Extract network ID→Find in routing table→Forward to interface
Question Six
a) Briefly describe the IEEE 802.3 Ethernet Frame format. (10 Marks)
Answer (Click to show)
Preamble→SFD→Destination MAC→Source MAC→Length/Type→Data→Padding→FCS
b) An Ethernet MAC sublayer receives 42 bytes of data from the LLC sublayer. Explain how the data can be encapsulated in Ethernet Frame format for transmission. (4 Marks)
Answer (Click to show)
Add 18 bytes header/FCS → Total 60 bytes → Pad to 64 bytes minimum
c) An Ethernet MAC sublayer receives 1510 bytes of data from the LLC layer. Briefly explain how many frames need to be sent? What is the size of the data in each frame? (6 Marks)
Answer (Click to show)
2 frames needed
First frame: 1500 bytes data
Second frame: 10 bytes data + padding
END OF EXAMINATION PAPER