Kumar Data Communication and Computer Networks

Networking
1. Auflage 2021
ISBN: 978-3-7487-7635-2
Verlag: BookRix
Format: EPUB
Kopierschutz: 0 - No protection

E-Book, Englisch, 92 Seiten

The text book is written in simple and easily understandable language.This book can be used as a self-study guide for compter science students.I made (Dr.Prakash Kumar)sincere attempts to analyse every important topic completely and put before the reader of this book in the best presentable form.This book is uniquely different from many other books in a number of ways. Some of the unique features of the book are as under: - Beginner to advanced apporoach to the subject. - Simple and easy understandable language. - Include examples to illustrate concept. - Systematic and sequential arrangement of different topics. - It can be used for one semester or one quarter course. - Eminently suitable for self study. - Detailed study of important topics such as Communication system, OSI Model, Ethernet LAN ,Network security and Cryptography.

Autoren/Hrsg.

Kumar, Prakash

Kumar, Dr.Prakash

Leseproben

Chapter 1 : DATA COMMUNICATIONS
    1   DATA COMMUNICATIONS ---------------------------------------------------------------------------------------------------------------------------------   OVERVIEW     The term communication means sending or receiving information. When we communicate, we share information or data. A communication system can be defined as the collection of hardware and software that facilitates intersystem exchange of information between different devices.   1.1 DATA & INFORMATION   The word data refers to any information which is presented in a form that is agreed and accepted upon by its creators and users.   Data refers to the raw facts that are collected while information refers to processed data that enables us to take decisions.   When result of a particular test is declared it contains data of all students, when you find the marks you have scored you have the information that lets you know whether you have passed or failed.     1.2 Data Communication   It is the exchange of data between two devices using some form of transmission media or medium. It includes the transfer of data or information and the method of preservation of data during the transfer process. Data is transferred from one place to another in the form of signals.   In Data Communications, data generally are defined as information that is stored in digital form. Information is defined as the knowledge or intelligence. Data communications can be summarized as the transmission, reception, and processing of digital information. Communication or transmission channels  refer to the direction of signal flow between two linked devices.   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.   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. Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. 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. 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 30ms. If some of the packets arrive with 30ms delay and others with 40ms delay, an uneven quality in the video is the result.     1.2.1 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 (Os or Is). 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 I-bit pattern is enough to represent a pixel. If an image is not made of pure white and pure black pixels, you can increase the size of the bit pattern to include gray scale. For example, to show four levels of gray scale, you 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 blue. The intensity of each color is measured, and a bit pattern is assigned to it. Another method is called YCM, in which a color is made of a combination of three other primary colors: yellow, cyan,and magenta.   Audio: Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal.   Video: Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a combination of images,each a discrete entity, arranged to convey the idea of motion. Again we can change video to a digital or an analog signal.       1.2.2 Data Flow     Communication between two devices can be simplex, half-duplex, or full-duplex.   Simplex   In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.   Half-Duplex   In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. The half-duplex mode is like a one-lane road with traffic allowed in both directions. When cars are traveling       in one direction, cars going the other way must wait.   In a half-duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time.Walkie-talkies and CB(citizens band) radios are both half-duplex systems.     Full Duplex   In full-duplex mode, both stations can transmit and receive simultaneously. The full-duplex mode is like a two way street with traffic flowing in both directions at the same time. One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time.     1.3 PROTOCOL   In computer networks, communication occurs between entities in different systems. An entity is anything capable of sending or receiving information. However, two entities cannot simply send bit streams to each other and expect to be understood. For communication to occur, the entities must agree on a protocol. A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated.   i.e,   A Protocol is one of the components of a data communications system. Without protocol communication cannot occur. The sending device cannot just send the data and expect the receiving device to receive and further interpret it correctly. When the sender sends a message it may consist of text, number, images, etc. which are converted into bits and grouped into blocks to be transmitted and often certain additional information called control information is also added to help the receiver interpret the data. For successful communication to occur, the sender and receiver...