CMP-2540 Computer Communication &Networks Solved Past Paper 2018

University of Sargodha

MSc.IT 2nd Term Exam 2018.

Subject I.T Paper: Computer Communication &Network (CMP-2540)

Time Allowed: 2.30 Hours                                                                 Maximum Marks: 80


Note: Objective part is compulsory. Attempt any four questions from subjective part.


Objective Part     (Compulsory)


Q.01: write short answer of the following in 2-3 lines on your answer sheet.

1.      What are the differences between amplitude shift keying and frequency shift keying?


ASK: In ASK, the amplitude of carrier signal is varied to represent binary 1 or 0, whereas both frequency and phase remain constant. This signal is very susceptible to Noise. Speed of transmission during ASK is limited by the physical characteristics of transmission medium.

FSK: In ASK, the frequency of carrier signal is varied to represent binary 1 or 0, whereas both amplitude and phase remain constant. This signal is not susceptible to Noise.

2.      Why are protocols needed?


Protocol is a set of rules that govern communication and applied to transfer data from sender to receiver efficiently. Protocols specify format and method of transmission and help to synchronize sender with receiver. 

3.      What are differences between half duplex and full duplex transmissions?


 Half Duplex

Full Duplex

Communication is two-directional but, one sided at a time.

Communication is two directional and done simultaneously.

A sender can send as well as receive the data but one at a time.

A sender can send as well as receive the data simultaneously.

The half-duplex mode is a  slower method of transmission.

Full duplex has better performance as it doubles the utilization of bandwidth.

Example: Walkie-Talkies.

Example: Telephone.

4.      What types of addresses are used in each of the following layers?

a)      Application Layer    b) Network     c) Transport


a)      Application Layer use application level address.

b)     Network Layer use Port address.

c)      Transport layer use logical address.

5.      If there is a single path between the source host and destination host, do we need a router between the two hosts?


No, we don’t need a router when there is a single path between sender and receiver because a router is required to choose best route between multiple paths between source and destination.

6.      Distinguish between baseband transmission and broadband transmission?


Baseband: Baseband is a communication technique in which data is transferred in form of digital signals over transmission media. In this technique data is transmitted in form of digital signals directly. Only one signal can be transmitted in this technique at one time

Broadband: Broadband is a technique which is used to transmit large amount of data over long distance. In this technique FDM (Frequency Division Multiplexing) is used. FDM modulates each signal onto a different frequency and send them using same transmission line. It divides transmission channel in multiple smaller channels and sends separate signals over these channels. Therefore, broadband provides faster communication than baseband.

7.      Define scrambling and give its purpose.


In digital-to-digital conversion, modifying part of the rules in a line coding scheme to create bit synchronization is called scrambling. It does not increase the number of bits and does provide synchronization by substituting long zero-level pulses with a combination of other levels.

8.      Define digital to analog conversion.


Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data. Any of the three characteristics can be altered in this way, giving us at least three mechanisms for modulating digital data into an analog signal:

      1.      Amplitude shift keying (ASK)

      2.      Frequency shift keying (FSK)

      3.      Phase shift keying (PSK)

  In addition, there is a fourth (and better) mechanism that combines changing both the amplitude and phase, called quadrature amplitude modulation (QAM).

9.      Describe the goal of multiplexing?


Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Its goal is to provide efficient utilization of channel bandwidth.

10.  What are two types of line configurations?


1.      Point to Point configuration: Only a pair of communication devices shares the complete channel capacity of the link.

2.      Multipoint Line Configuration: multiple communicating devices share the channel capacity and take turn to communicate.

11.  How does sky propagation differs form line of sight propagation?

ANSWER: In sky

In sky propagation, higher-frequency radio waves radiate upward into the ionosphere(the layer of atmosphere where particles exist as ions) where they are reflected back to earth. This type of transmission allows for greater distances with lower output power.

In line-or-sight propagation, very high-frequency signals are transmitted in straight lines directly from antenna to antenna. Antennas must be directional, facing each other.

12.  What is refraction?


Refraction is the bending of a wave when it enters a medium where its speed is different. Refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium

13.  What is difference between third and fourth generation cellular wireless networks?



3G Technology

4G Technology

Maximum upload rate of 3G technology is 5 Mbps.

While the maximum upload rate of 4G technology is 500 Mbps.

Maximum download rate of 3G technology is 21 Mbps.

While the maximum download rate of 4G technology is 1 Gbps.

It uses packet switching technique.

While it uses packet switching technique as well as message switching technique.

The frequency range of 3G technology is from 1.8 GHz to 2.5 GHz.

While it’s frequency range is from 2 GHz to 8 GHz.

It lenient horizontally.

While it lenient horizontally as well as vertically.

It is wide area cell based network architecture.

While it is the integration of Wireless LAN as well as Wide Area cell based network architecture.

There is turbo codes are used for error correction in 3G technology.

4G technology uses concatenated codes for error correction.

14.  Is this a valid IP Address?


No, it is an invalid address because value of any class in IPV4 address can’t exceed from 255 where in this address 3rd class value is 256.

15.  What is meant by high speed Ethernet?


Fast Ethernet is one of the versions of the Ethernet standard that enables the transmission of data over 100 megabits per second on local area networks (LAN). It was launched in 1995 and was the fastest network connection of its time.

Fast Ethernet is also known as 100 Base X or 100 Mbps Ethernet, and is defined by the IEEE 802.3u protocol.

16.  What is flow control? Where it is implemented in OSI Model?


Flow control is a mechanism to make sure that source does not overwhelm destination by sending data faster than it can be handled and processed

It is implemented in:

       1.      Data Link Layer

       2.       Transport Layer