NATIONAL OPEN UNIVERSITY OF NIGERIA

UNIVERSITY VILLAGE, PLOT 91, CASDASTRAL ZONE, NNAMDI AZIKIWE EXPRESS WAY, JABI, ABUJA.
FACULTY OF SCIENCES
OCTOBER 2013 EXAMINATION

Course Code:                     CIT 303

Time Allowed:                   3hrs

Course Title:                       Principles of Communication Technology

Instruction:                         Attempt any five (5) questions

Question 1

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)

Question 2

a. With the aid of a table ONLY, describe the five classes of IP addresses under the following columns:                  

                v. IP Address Class

                vi. Format

                vii. Purpose

                viii. Number of network/ host bits

                ix. Max number of hosts                                                                                                                                               (10 marks)

b. Briefly explain each of the following terms:

                x. Linear filter                                                                                                                                                   (2 marks)

                xi. Stable filter                                                                                                                                                   (1 mark)

                xii. Unstable filter                                                                                                                                            (1 mark)

                xiii. Time-invariant filter                                                                                                                                                (1 mark)

                xiv. Adaptive filter                                                                                                                                           (1 mark)

                xv. Linearity (in the context of linear-time invariant (LTI)                                                                               (1.5 marks)

Question 3

                i) Outline four (4) basic Network Topologies.

                ii) List three guided Media.

Question 4

a. Encrypt the word “IGNORANCE” with the following ciphers:

                xvi. Shift cipher with key=1                                                                                                                          (1 mark)

                xvii. Shift cipher with key= 26                                                                                                                     (2 marks)

                xviii. Shift cipher with key=0                                                                                                                        (2 marks)

                xix. 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:

                xx. Shift cipher with key=1                                                                                                                           (1 mark)

                xxi. Shift cipher with key= 26                                                                                                                      (2 marks)

                xxii. Shift cipher with key=0                                                                                                                         (2 marks)

                xxiii. 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)

Question 5

                Contrast between:

                i) Analog Signal Processing

                ii) Digital Signal Processing

Question 6

a. Define the term “network topology”.                                                                                                                                (1 mark)

b. With the aid of diagrams, briefly explain the following network topologies:

                xxiv. Ring                                                                                                                                                             (3 marks)

                xxv. Mesh                                                                                                                                                           (3 marks)

                xxvi. 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)

Question 7

a) What is Data Communications?

b) Define Protocols.

c) The effectiveness of a data communications system depends on four fundamental characteristics.