How to login to NOUN Elearn Portal
You can now use you matric number to login as your username and password in a lowercase.
https://elearn.nouedu2.net/login/
Note that you are to change your passw...
NATIONAL OPEN UNIVERSITY OF NIGERIA
UNIVERSITY VILLAGE, PLOT 91, CASDASTRAL ZONE, NNAMDI AZIKIWE EXPRESS WAY, JABI, ABUJA.
FACULTY OF SCIENCES
JUNE/JULY 2013 EXAMINATION
COURSE CODE: CIT 303
COURSE TITLE: Principles of Communication Technology
TIME ALLOWED: 3hrs
INSTRUCTION: Attempt any five (5) questions
QUESTIONS:
1. With the aid of a diagram, identify and explain the 5 security services related to messages exchanged over a network. (17.5 marks)
2. a. List and briefly explain the 2 categories of cryptography algorithms (5 marks)
b. With a valid reason in each case, classify the ciphers used in each of the following as either monoalphabetic or not monoalphabetic (4.5 marks)
i. Plain text: DAVIDOBO Cipher text: BIUABCDC
ii. Plain text: WIZKID Cipher text: PRINCE
iii. Plain text: BANKYW Cipher text: BANKYW
c. The power of a signal is 100 W and the power of the noise is 1W. What are the values of SNR and SNRdB? (4 marks)
d. Briefly explain the term “decibel” and state its equation in terms of power. Include the meanings of variables used. (4 marks)
3. a. Encrypt the word “IGNORANCE” with the following ciphers:
i. Shift cipher with key=1 (1 mark)
ii. Shift cipher with key= 26 (2 marks)
iii. Shift cipher with key=0 (2 marks)
iv. Transposition cipher where plain text: 1 2 3 4 5 6 7 8 9 and cipher text: 4 3 1 5 2 6 7 9 8 (with no bogus character) (1.5 marks)
b. Decrypt the word “ANCEIGNOR” with the following ciphers:
i. Shift cipher with key=1 (1 mark)
ii. Shift cipher with key= 26 (2 marks)
iii. Shift cipher with key=0 (2 marks)
iv. Transposition cipher where plain text: 1 2 3 4 5 6 7 8 9 and cipher text: 4 3 1 5 2 6 7 9 8 (with no bogus character) (1.5 marks)
c. The amplification in a cable is usually defined in decibels per kilometer (dB/km). If the signal at the beginning of a cable with 2 dB/km has a power of 2 mW, what is the power of the signal at 5 km? (3 marks)
d. Briefly explain the term attenuation (1.5 marks)
4. a. Briefly explain the 3 modes of communication (with regards to the direction of communication). In each case, identify 2 examples of devices that utilize the mode of communication. (9 marks)
b. In one sentence, describe the OSI reference model (1 mark)
c. State the following:
i. 4 services/ functions provided by the OSI Physical Layer (2 marks)
ii. 4 services/ functions provided by the OSI Data Link Layer (2 marks)
iii. 4 services/ functions provided by the OSI Transport Layer (2 marks)
iv. 3 services/ functions provided by the OSI Session Layer (1.5 marks)
5. a. With the aid of a table ONLY, describe the five classes of IP addresses under the following columns:
i. IP Address Class
ii. Format
iii. Purpose
iv. Number of network/ host bits
v. Max number of hosts (10 marks)
b. Briefly explain each of the following terms:
i. Linear filter (2 marks)
ii. Stable filter (1 mark)
iii. Unstable filter (1 mark)
iv. Time-invariant filter (1 mark)
v. Adaptive filter (1 mark)
vi. Linearity (in the context of linear-time invariant (LTI) (1.5 marks)
6. a. Define the term “network topology”. (1 mark)
b. With the aid of diagrams, briefly explain the following network topologies:
i. Ring (3 marks)
ii. Mesh (3 marks)
iii. Tree (3 marks)
c. State and briefly explain 3 advantages and 3 disadvantages of using fiber optic cables in networking. (6 marks)
d. State 1 advantage and 2 disadvantages of STP cables in comparison to UTP cables. (1.5 marks)
7. a) Contrast between:
i) Analog Signal Processing
ii) Digital Signal Processing
b) Define:
(i) Multilayer Switch
(ii) Protocol Converter
