CIT 303 MARCH/APRIL 2016 EXAMINATION

NATIONAL OPEN UNIVERSITY OF NIGERIA

14-16 AHMADU BELLO WAY, VICTORIA ISLAND LAGOS

MARCH/APRIL 2016 EXAMINATION

SCHOOL OF SCIENCE AND TECHNOLOGY

COURSE CPDE: CIT 303

COURSE TITLE: PRINCIPLES OF COMMUNICATION

TIME ALLOWED: 3 HOURS

COURSE CREDIT UNIT: 3

INSTRUCTION: ATTEMPT ANY FIVE QUESTIONS. EACH QUESTION CARRIES 14 MARKS

Question 1

a. outline the layers of Open System Interconnection Reference Model (OSI model), in the right order.

b. write briefly on the physical layer.

c. cryptography algorithms (ciphers) can be divided into two groups

Question 2

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

i. IP Address Class

ii. Format

iii. Purpose

iv. Number of network/host bits

v. max number of hosts.

b. Briefly explain each of the following terms:

i. Linear filter

ii. Stable filter

iii. Unstable filter

vi. time-invariant filter.

v. adaptive filter

vi. Linearity (in the context of linear-time invariant (LTI))

Question 3a. Encrypt the word “IGNORANCE" with the following ciphers:

  i.            Shift cipher with key=1

         ii.            Shift cipher with key=26

           iii.            Shift cipher with key=0

               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)

b. decrypt the word “ANCEIGNOR” with the following ciphers:

                                                        i.            Shift cipher with key=1

                                                         ii.            Shift cipher with key=26

                                                   iii.            Shift cipher with key=0

                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)

The amplification in a cable is usually defined in decibels per kilometer (dfl/km). If the signal at the beginning of a cable with 2 dfl/km has a power of 2 mW, what is the power of the signal at 5 km?

Briefly explain the term attenuation.

Question 4

a. what us data communications

b. define protocols

c. The effectiveness of a data communications system depends on four fundamental characteristics. List and define these characteristics.

Question 5

Contrast between

a. analog signal processing and digital signal processing

b. OSI presentation layer and OSI application layer

c. symmetric-key and asymmetric-key

Question 6

a. define the term “network topology”

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

                     i.            Ring

                        ii.            Mesh

                      iii.            Tree

c. state and briefly explain 3 advantages if using fiber optic cables in networking.

d. state 1 advantage and 2 disadvantages of STP cables in comparison to UTP cables.


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