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Note for Computer Communication Network - CCN By JAYAPRASAD KM

  • Computer Communication Network - CCN
  • Note
  • Visvesvaraya Technological University Regional Center - VTU
  • Electronics and Communication Engineering
  • 6 Topics
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Jayaprasad Km
Jayaprasad Km
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MODULE 1 NOTES 15EC64 CONTENTS 1 2 3 INTRODUCTION 1.1 Data Communications 1.1.1 Components 1.1.2 Representations 1.1.3 Data Flow 1.2 Networks 1.2.1 Network Criteria 1.2.2 Physical Structures 1.3 Network types 1.3.1 LAN 1.3.2 WAN 1.3.3 Switching 1.3.4 Internet NETWORK MODELS 2.1 Protocol Layering 2.1.1 Scenarios 2.1.2 Principles of Protocol Layering 2.1.3 Logical Connections 2.2 TCP/IP Protocol Suite 2.2.1 Layered Architecture 2.2.2 Layers in the TCP/IP Protocol Suite 2.2.3 Description of each layer 2.2.4 Encapsulation and Decapsulation 2.2.5 Addressing 2.2.6 Multiplexing and Demultiplexing 2.3 The OSI Model 2.3.1 OSI versus TCP/IP DATA LINK LAYER 3.1 Introduction to Data Link Layer 3.1.1. Nodes and Links 3.1.2 Services 3.1.3 Two Categories of Links 3.1.4 Two Sublayers 3.2 Link Layer Addressing 3.2.1 Three types of addresses 3.2.2 Address Resolution Protocol (ARP) 3.2.3 An Example of Communication 3.3 Data Link Control(DLC) Services 3.3.1 Framing 3.3.2 Flow and Error Control 3.4 Data Link Layer Protocols 3.4.1 Simple Protocol 3.4.2 Stop-and-Wait Protocol 3.4.3 Piggy Backing COMPUTER COMMUNICATION NETWORKS 2 2 3 4 5 7 7 8 14 14 15 17 20 22 22 22 25 26 26 27 29 30 34 36 36 37 38 40 40 41 42 45 45 45 48 49 53 57 57 61 63 64 66 69 Page 1

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MODULE 1 NOTES 15EC64 PART 1 INTRODUCTION Data communications and networking have changed the way we do business and the way we live. Business decisions have to be made ever more quickly, and the decision makers require immediate access to accurate information. Why wait a week for that report from Europe to arrive by mail when it could appear almost instantaneously through computer networks? Businesses today rely on computer networks and internet- works. Data communication and networking have found their way not only through business and personal communication; they have found many applications in political and social issues. People have found how to communicate with other people in the world to express their social and political opinions and problems. Communities in the world are not isolated anymore. But before we ask how quickly we can get hooked up, we need to know how networks operate, what types of technologies are available, and which design best fills which set of needs 1.1 DATA COMMUNICATIONS The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs). The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness, and jitter. 1. Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. 2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. COMPUTER COMMUNICATION NETWORKS Page 2

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MODULE 1 NOTES 15EC64 3. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. 4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and others with 40 ms delay, an uneven quality in the video is the result. 1.1.1 Components A data communications system has five components (see Figure 1.1) Figure 1.1 Five components of data communication 1. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2. Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. 3. Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5. Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese COMPUTER COMMUNICATION NETWORKS Page 3

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MODULE 1 NOTES 15EC64 1.1.2 Data Representation Information today comes in different forms such as text, numbers, images, audio, and video. Text In data communications, text is represented as a bit pattern, a sequence of bits (0s or1s). Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the process of representing symbols is called coding. Today, the prevalent coding system is called Unicode, which uses 32 bits to represent a symbol or character used in any language in the world. The American Standard Code for Information Interchange (ASCII), developed some decades ago in the United States, now constitutes the first 127 characters in Unicode and is also referred to as Basic Latin. Numbers Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the number is directly converted to a binary number to simplify mathematical operations. Appendix B discusses several different numbering systems. Images Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution. For example, an image can be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better representation of the image (better resolution), but more memory is needed to store the image. After an image is divided into pixels, each pixel is assigned a bit pattern. The size and the value of the pattern depend on the image. For an image made of only black- and-white dots (e.g., a chessboard), a 1-bit pattern is enough to represent a pixel. If an image is not made of pure white and pure black pixels, we can increase the size of the bit pattern to include gray scale. For example, to show four levels of gray scale, we can use 2-bit patterns. A black pixel can be represented by 00, a dark gray pixel by 01, a light gray pixel by 10, and a white pixel by 11. There are several methods to represent color images. One method is called RGB, so called because each color is made of a combination of three primary colors: red, green, and COMPUTER COMMUNICATION NETWORKS Page 4

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