& U O IGN Univ. n ndia I l l A

BCS-041

FUNDAMENTALS OF

COMPUTER NETWORKS

1

Fundamentals of Computer Networks BCS-041

For Bachelor of Computer Applications (BCA)

Useful For IGNOU, Rai Technology University, KSOU (Karnataka), NIILM University, Bihar University (Muzaffarpur), Nalanda University, Jamia Millia Islamia, Vardhman Mahaveer Open University (Kota), Uttarakhand Open University, Kurukshetra University, Himachal Pradesh University, Seva Sadan’s College of Education (Maharashtra), Lalit Narayan Mithila University, Andhra University, Pt. Sunderlal Sharma (Open) University (Bilaspur), Annamalai University, Bangalore University, Bharathiar University, Bharathidasan University, Centre for distance and open learning, Kakatiya University (Andhra Pradesh), KOU (Rajasthan), MPBOU (MP), MDU (Haryana), Punjab University, Tamilnadu Open University, Sri Padmavati Mahila Visvavidyalayam (Andhra Pradesh), Sri Venkateswara University (Andhra Pradesh), UCSDE (Kerala), University of Jammu, YCMOU, Rajasthan University, UPRTOU, Kalyani University, Banaras Hindu University (BHU) and all other Indian Universities.

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omputer networks connect nodes like computers, routers, and switches using cables, fiber optics, or wireless signals. These connections allow devices in a network to communicate and share information and resources. Networks follow protocols, which define how communications are sent and received. These protocols allow devices to communicate. Each device on a network uses an Internet Protocol or IP address, a string of numbers that uniquely identifies a device and allows other devices to recognize it. In this GPH book ‘Fundamentals of Computer Networks (BCS-41)’, we will deal with various concepts of communication and networking and its devices. Further, we will elaborate network transport, design and security. The book is written especially in question & answer format to provide students the instant gratification of a correct answer. In this book, we have tried to solve all possible questions from the exams’ point of view. Solutions of previous years’ question papers have also been included to help students to understand the unique examination structure. We hope that this book would not be only a favourite study material for the students but also can be a nice resource for teaching. An attempt has been carefully made to present this book more useful and meet the requirements and challenges of the course prescribed by Indian Universities. We wish you a successful and rewarding career ahead. Feedback in this regard is solicited. – GPH Panel of Experts

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The present book BCS-041 is targeted for examination purpose as well as enrichment. With the advent of technology and the Internet, there has been no dearth of information available to all; however, finding the relevant and qualitative information, which is focussed, is an uphill task. We at GullyBaba Publishing House Pvt. Ltd., have taken this step to provide quality material which can accentuate in-depth knowledge about the subject. GPH books are a pioneer in the effort of providing unique and quality material to its readers. With our books, you are sure to attain success by making use of this powerful study material. Provided book is just a reference book based on the syllabus of particular University/Board. For a profound information, see the textbooks recommended by the University/Board. Our site gullybaba.com is a vital resource for your examination. The publisher wishes to acknowledge the significant contribution of the Team Members and our experts in bringing out this publication and highly thankful to Almighty God, without His blessings, this endeavor wouldn’t have been successful. – Publisher

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Block-1

Concepts of Communication and Networking

Unit-1 Unit-2 Unit-3 Unit-4

Basics of Data Communication Modulation and Encoding Multiplexing and Switching Communication Mediums

Block-2

Networks and Devices

Unit-1 Unit-2 Unit-3 Unit-4

Network Classifications and Topologies OSI and TCP/IP Models Physical and Data Link Layer Internet Working Devices

Block-3

Network Transport and Application Layer

Unit-1 Unit-2 Unit-3 Unit-4

Network Layer Transport Layer Application Layer Network Applications

Block-4

Network Design & Security

Unit-1 Unit-3 Unit-2 Unit-4

Building A Simple Network Introduction to Wireless and Mobile Networks Introduction to Network Architectures Network Security

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Chapter-1

Concepts of Communication and Networking.............................1

Chapter-2

Networks and Devices.................………………………………59

Chapter-3

Network Transport and Application Layer...............................123

Chapter-4

Network Design & Security...........................................................207

(1) December 2017 (Solved)............................................................................................279 (2) June 2018 (Solved).......................................................................................................286 (3) December 2018 (Solved)............................................................................................289 (4) June 2019 (Solved).......................................................................................................291 (5) December 2019 (Solved)............................................................................................294

Concepts of Communication and Networking

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1

Concepts of Communication and Networking Introduction

T

he Internet has become one of the most important components of our life. We browse the Web, check e-mails, make VoIP phone calls, and have video conferences via computers. All of these applications are made possible by networking computers together, and this complex network of computers is usually referred to as the Internet. The most fundamental need to any communication system design is to cater to large number of users. But this requires a large number of resources and this requirement can be met if the resources are available, but this makes it cost ineffective. Therefore, the aim is always to use minimum number of resources and make their utilisation to their fullest potential. Networks always require us to accommodate multiple signals utilising a single piece of cabling to make it cost effective and reduce complexity. This need is seen throughout networking.

Fundamentals of Computer Networks [BCS-041]

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Q1. What is communication system? Also, explain its components and elements. Or Discuss the concept of communication system. Ans. Communication is the field of study concerned with the transmission of information through various means. It can also be defined as technology employed in transmitting messages. It can also be defined as the inter-transmitting the content of data (speech, signals, pulses, etc.) from one node to another. According to G.G. Brown, "Communication is transfer of information from one person to another, whether or not it elicits confidence. But the information transferred must be understandable to the receiver." According to Oxford Dictionary, "Communication system is the imparting or exchanging of information by speaking, writing, or using some other medium." Following is the block diagram of communication system: Information Source

Input Transducer

Sound picture speech data etc.

Transmitter

Channel

Receiver

Output Transducer

Information in original form

Information in electrical form Noise

Fig. 1.1: Block Diagram of Communication System Some communication systems around us are given as follows: • Telephone system is a kind of communication system which we use in day to day basis, it is a collection of individuals, telephone handsets for transforming voice into electrical signals), wires (communication medium), some controlling and call management devices, telephone exchange, etc. • Human communications operate through speech, signs, gestures, body language, etc. • A radio or television communication system is composed of several communications subsystems that give exterior communications capabilities. These are also known as public broadcasting systems, because they broadcast the messages/signals in the air and any one in the coverage area with a receiver can receive the signals. Such systems comprises of a large transmitting station for converting and transmitting the audio/video into the air, and on the other side if signals are

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public can be decoded and converted again into the same audio/video. Components of Communication System • Context: Every message (oral or written), begins with context. Context is a very broad field that consists different aspects. One aspect is country, culture and organisation. Another aspect of context is external stimulus. The sources of external stimulus includes; meeting, letter, memo, telephone call, fax, note, email and even a casual conversation. • Sender/Encoder: Encoder is the person who sends message. In oral communication the encoder is speaker, and in written communication writer is the encoder. • Message: Message is the information that is exchanged between sender and receiver. The central idea of the message must be clear. While writing the message, encoder should keep in mind all aspects of context and the receiver. • Medium: Medium is the channel through which encoder will communicate his message. The phone system, it is wire. Television and radio use air. • Receiver/Decoder: The person to whom the message is being sent is called 'receiver'/'decoder'. Receiver may be a listener or a reader depending on the choice of medium by sender to transmit the message. Elements of Communication System Following are the essential elements of communication system by Shannon: • Information Source: The communication system which we are using is act as the main communication source for data transmission between two machines. • Transmitter: The source generated electrical signals are then used by the transmitter after refining them and removes the noise and distortion there in it and makes signal in form that can be easily amplified, for the purpose of amplification in transmitter circuit we uses the digital modulator that converts sequence into electrical signals so that it can be easily transmitted over long distance. • Communication Channel: The physical medium which is used for the transmission of communication data signals from sender to receiver is referred as communication channel. • Receiver: The receiver machine work is to reproduce the message signal in electrical form from the noised and distorted signal.

Fundamentals of Computer Networks [BCS-041]

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•

Destination Machine: The last stage of the communication system is destination machine which converts these electrical signals into its original form for the data broadcasting so that it can be easily understand by the end user or receiver and then this same sort of communication process is used for the acknowledgment of signals to sender machine.

Information Source

Transmitter

Receiver

Signal Message

Received Signal

Destination

Message

Noise Source

Fig. 1.2: Shannon's diagram of a general communication system Here, the noise is considered as an error or undesired disturbance that occur during the transmission, from natural and sometimes manmade sources. Q2. Elucidate analog and digital communication. Give comparison between analog and digital communication. Ans. The name analog comes from the word “analogous”, meaning similar. Analog signal is a continuous signal whose amplitude can take any value in a continuous range. It can have infinite number of values. Analog communication is a communication method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. It could be the transfer of an analog source signal using an analog modulation method such as FM or AM, or no modulation at all. Analog transmission is still very popular, in particular for shorter distances, due to significantly lower costs and complex multiplexing and timing equipment is unnecessary, and in small "short-haul" systems that simply do not need multiplexed digital transmission.

Concepts of Communication and Networking Amplitude (in volts)

5 Amplitude (in volts)

Time (in milliseconds)

Time (in milliseconds) (a) Analog Signal

(b) Digital Signal

Fig. 1.3: Analog Signal Digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint transmission medium. Examples of such media are copper wires, optical fibers, wireless communication media, and storage media. The data is often represented as an electro-magnetic signal, such as an electrical voltage signal or an infra-red signal. Digital communication enables the data to be transmitted in an efficient manner through the use of digitally encoded information sent through data signals. These data signals are easily compressed and, as such, can be transmitted with accuracy and speed. Table 1.1: Comparison between Analog and Digital system Analog

Digital

• Signals are records waveforms as they are. Signal occupies the same order of spectrum as the analog data.

• Converts analog waveforms into set of numbers and records them. The numbers are converted into voltage stream for representation. In case of binary it is converted in 1's and 0's.

• In analog systems electronic circuits are used for transformation of signals.

• In this transformation is done using logic circuits.

• About Noise analog signals are more likely to get affected and results in reducing accuracy

• Digital signals are less affected, because noise response are analog in nature

• Analog signal is a continuous • Digital signals are discrete time signal which transmits signals generated by digital information as a response to modulation. changes in physical phenomenon. • Data transmission is not of high quality

• Data transmission has high quality.

• Analog devices are not very precise.

• Digital systems are very precise.

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Q3. Discuss about some modes of data communication used in computer networking. Or What is the role of parallel and serial transmission devices in computer networking? Explain. Or Write a short note on Synchronous and Asynchronous Transmission. [June-2019, Q.No.-5 (d)] Ans. Following are the data communication modes: (1) Serial and Parallel Transmission Serial transmission involves sending one data bit at a time. Fig. 1.4 shows how serial transmission occurs. It uses a pair of wire for communication of data in bit-serial form. Since communication within devices is parallel, it needs parallel-to-serial and serial-to-parallel conversion at both ends.

Sender

10110101

Receiver

Fig. 1.4: Serial mode of communication Parallel transmission involves grouping several bits, say n, together and sending all the n bits at a time. Fig. 1.5 shows how parallel transmission occurs for n = 8 . This can be accomplishes with the help of eight wires bundles together in the form of a cable with a connector at each end. Additional wires, such as request (req) and acknowledgement (ack) are required for asynchronous transmission. 8 bits 1 0 1 1 0 Receiver Sender 1 0 1 Req Ack Fig. 1.5: Parallel mode of communication with n=8 (2) Synchronous and Asynchronous Transmission Asynchronous transmission is used only when the rate at which characters generated is unknown or the transmission data rate is too low. For the transmission of a large block of data at relatively higher bit rates,

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synchronous transmission is used. In synchronous mode, the sending and receiving devices are synchronised with a common clock signal. This eliminates the need for the start and stop bits. The complete block of data is transmitted with fixed time interval between the bits. Before the start of transmission, clocks at both ends are to be synchronised. This is achieved by sending special character bytes called sync bytes or sync characters between the sender and the receiver. The sender informs the receiver about the start of a block. The receiver figures out the start of each character by knowing the coding scheme used. If the sender is idle or does not transmit any character, the receiver searches for the next group of sync characters. The devices are then resynchronised to receive the next block of characters. The block length varies from few bytes to many hundreds of bytes. The most commonly used protocol is the BISYNC or Bit Synchronous Protocol. Character Block Ck Sync Sync C1

Sender

C2

...

Ck Sync

Kth Character Synchronisation Character

Receiver

Fig. 1.6: Synchronous Transmission Asynchronous mode is also known as start-stop mode. This mode is used when data to be transmitted is generated at random intervals. For example, when a user communicates with a computer using a keyboard, the time interval between two successive keystrokes is random. This means that the signal on the transmission line will be in idle state for a long time interval between characters. With this type of communication, the receiver must be able to resynchronise at the start of each new character received. To accomplish this, each transmitted character or byte is encapsulated between an additional start bit and one or more stop bits. This mode is mainly used for the transmission of characters between a keyboard and a computer. Asynchronous transmission can also be used for the transmission of a block of characters or bytes between two computers. The time interval between successive characters is a variable entity.

Fundamentals of Computer Networks [BCS-041]

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St Character Sp Sender

Receiver

St

Start Bit

Sp

Stop Bit

Fig. 1.7: Asynchronous Transmission (3) Simple, Half-Duplex, Full-Duplex Communication The data transmission mode on the channel, can be classified into three ways simplex, half-duplex and full-duplex which are tabulated below: Table 1.2 Simplex In simplex transmission, the communication is unidirectional. Its transmission is like a one-way street.

Example: Key boards and Monitors, the keyboard can only introduce input; the monitor can only accept output.

Half-duplex In half-duplex transmission, each station can both transmit and receive, but not at the same time. Its transmission is like a one-lane road with twodirectional traffic. Example: Walkie-talkie and CB radio

Full-duplex In full-duplex transmission, both stations can transmit and receive simultaneously. Its transmission is like a two-way street with traffic flowing in both direction at the same time. Example; Data transmission over Telephone lines.

Q4. What are the different problems in computer communication? Ans. We encounter some challenges when protocols are implemented for computer communication due to the infrastructure and machines used in computer may not be compatible and aligned with one another. The concept of internetworking though, highly desirable, is not easily achievable. For example, one network could represent a binary 0 by -5 volts, another by +5 volts. Similarly, one could use a packet size of 128 bytes, whereas other could use 256 byte packets. The method of acknowledgement or error detection could be different. There could be many such differences. The incompatibility issues are handled at two levels: • Hardware Issues: An additional component called router is used to connect physically distinct networks at the hardware level. A router connects to the network in the same way as any other computer. Any computer connected to the network has a Network Interface Card (NIC), which has the address (network id+ host id), hard coded into it. A router is a device with more

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than one NICs. Router can connect incompatible networks as it has the necessary hardware (NIC) and protocols. • Software Issues: The routers must agree about the way information would be transmitted to the destination computer on a different network, since the information is likely to travel through different routers, there must be a predefined standard to which routers must confirm. Packet formats and addressing mechanism used by the networks may differ. One approach could be to perform conversion and reconversion corresponding to different networks. But this approach is difficult and cumbersome. Therefore, the Internet communication follows one protocol suite, the TCP/IP. The basic idea is that it defines a packet size, routing algorithms, error control, flow control methods universally. To club all these features in a single piece of software would be unwise; it would make it very bulky. Thus, all these features are logically sub-grouped and then the sub-groups are further grouped into groups called layers. Each layer has an interface with the adjacent layers, and performs specific functions. Q5. Describe the OSI reference model and explain the function of each layer. Or Write a short note on 'OSI Model'. [June-2018, Q.No.-5 (c)] Ans. The OSI model is an abstract description for layered communications and computer network protocol design open system means that it can communicate with any other system that follows the specified standards, formats and semantics. Protocols give the rules that specify how the different parties may communicate. In its most form, it divides network architecture into seven layers which from top to bottom are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model. A layer is a collection of conceptually similar functions that provide services to the layer above it and receives service from the layer below it. On each layer an instance provides services to the instances at the layer above and requests service from the layer below. For example, a layer that provides error free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that make up the contents of the path. Any two instances at one layer are connected by a horizontal protocol connection on that layer. The following are the layers of OSI model:

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