Lecture notes on Data communication and networking

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1 Unit 1. Introduction to data communications and networking 1 NETWORKING FUNDAMENTALS Unit Structure 1.0 Objectives 1.1 Introduction 1.2 Data & Information 1.3 Data Communication 1.3.1 Characteristics of Data Communication 1.3.2 Components of Data Communication 1.4 Data Representation 1.5 Data Flow 1.5.1. Simplex 1.52. Half Duplex 1.5.3. Full Duplex 1.6 Computer Network 1.6.1 Categories of a network 1.7 Protocol 1.7.1 Elements of a Protocol 1.8 Standards In Networking 1.8.1 Concept of Standard 1.8.2 Standard Organizations in field of Networking 1.9 Review Questions 1.10 References 1.0 OBJECTIVES:  Introduce the readers to data communication and its fundamentals  Define networks  Define protocols  Standards in networking 2 1.1 INTRODUCTION This chapter provides an introduction to Computer networks and covers fundamental topics like data, information to the definition of communication and computer networks. The main objective of data communication and networking is to enable seamless exchange of data between any two points in the world. This exchange of data takes place over a computer network. 1.2 DATA & INFORMATION Data refers to the raw facts that are collected while information refers to processed data that enables us to take decisions. Ex. 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. The word data refers to any information which is presented in a form that is agreed and accepted upon by is creators and users. 1.3 DATA COMMUNICATION Data Communication is a process of exchanging data or information In case of computer networks this exchange is done between two devices over a transmission medium. This process involves a communication system which is made up of hardware and software. The hardware part involves the sender and receiver devices and the intermediate devices through which the data passes. The software part involves certain rules which specify what is to be communicated, how it is to be communicated and when. It is also called as a Protocol. The following sections describes the fundamental characteristics that are important for the effective working of data communication process and is followed by the components that make up a data communications system. 1.3.1 Characteristics of Data Communication The effectiveness of any data communications system depends upon the following four fundamental characteristics: 3 1. Delivery: The data should be delivered to the correct destination and correct user. 2. Accuracy: The communication system should deliver the data accurately, without introducing any errors. The data may get corrupted during transmission affecting the accuracy of the delivered data. 3. Timeliness: Audio and Video data has to be delivered in a timely manner without any delay; such a data delivery is called real time transmission of data. 4. Jitter: It is the variation in the packet arrival time. Uneven Jitter may affect the timeliness of data being transmitted. 1.3.2 Components of Data Communication A Data Communication system has five components as shown in the diagram below: Fig. Components of a Data Communication System 1. Message Message is the information to be communicated by the sender to the receiver. 2. Sender The sender is any device that is capable of sending the data (message). 3. Receiver The receiver is a device that the sender wants to communicate the data (message). 4. Transmission Medium It is the path by which the message travels from sender to receiver. It can be wired or wireless and many subtypes in both. 4 5. Protocol It is an agreed upon set or rules used by the sender and receiver to communicate data. A protocol is a set of rules that governs data communication. A Protocol is a necessity in data communications without which the communicating entities are like two persons trying to talk to each other in a different language without know the other language. 1.4 DATA REPRESENTATION Data is collection of raw facts which is processed to deduce information. There may be different forms in which data may be represented. Some of the forms of data used in communications are as follows: 1. Text Text includes combination of alphabets in small case as well as upper case. It is stored as a pattern of bits. Prevalent encoding system : ASCII, Unicode 2. Numbers Numbers include combination of digits from 0 to 9. It is stored as a pattern of bits. Prevalent encoding system : ASCII, Unicode 3. Images ―An image is worth a thousand words‖ is a very famous saying. In computers images are digitally stored. A Pixel is the smallest element of an image. To put it in simple terms, a picture or image is a matrix of pixel elements. The pixels are represented in the form of bits. Depending upon the type of image (black n white or color) each pixel would require different number of bits to represent the value of a pixel. The size of an image depends upon the number of pixels (also called resolution) and the bit pattern used to indicate the value of each pixel. Example: if an image is purely black and white (two color) each pixel can be represented by a value either 0 or 1, so an image made up of 10 x 10 pixel elements would require only 100 bits in memory to be stored. On the other hand an image that includes gray may require 2 bits to represent every pixel value (00 - black, 01 – dark gray, 10 5 – light gray, 11 –white). So the same 10 x 10 pixel image would now require 200 bits of memory to be stored. Commonly used Image formats : jpg, png, bmp, etc 4. Audio Data can also be in the form of sound which can be recorded and broadcasted. Example: What we hear on the radio is a source of data or information. Audio data is continuous, not discrete. 5. Video Video refers to broadcasting of data in form of picture or movie 1.5 DATA FLOW wo devices communicate with each other by sending and receiving data. The data can flow between the two devices in the following ways. 1. Simplex 2. Half Duplex 3. Full Duplex 1.5.1 Simplex Figure: Simplex mode of communication In Simplex, communication is unidirectional Only one of the devices sends the data and the other one only receives the data. Example: in the above diagram: a cpu send data while a monitor only receives data. 1.5.2 Half Duplex 6 Figure: Half Duplex Mode of Communication In half duplex both the stations can transmit as well as receive but not at the same time. When one device is sending other can only receive and vice- versa (as shown in figure above.) Example: A walkie-talkie. 1.5.3 Full Duplex Figure: Full Duplex Mode of Communication In Full duplex mode, both stations can transmit and receive at the same time. Example: mobile phones 1.6 COMPUTER NETWORK Computer Networks are used for data communications Definition: A computer network can be defined as a collection of nodes. A node can be any device capable of transmitting or receiving data. The communicating nodes have to be connected by communication links. A Compute network should ensure reliability of the data communication process, should c security of the data 7 performance by achieving higher throughput and smaller delay times 1.6.1 Categories of Network Networks are categorized on the basis of their size. The three basic categories of computer networks are: A. Local Area Networks (LAN) is usually limited to a few kilometers of area. It may be privately owned and could be a network inside an office on one of the floor of a building or a LAN could be a network consisting of the computers in a entire building. B. Wide Area Network (WAN) is made of all the networks in a (geographically) large area. The network in the entire state of Maharashtra could be a WAN C. Metropolitan Area Network (MAN) is of size between LAN & WAN. It is larger than LAN but smaller than WAN. It may comprise the entire network in a city like Mumbai. 1.7 PROTOCOL 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 must agree upon certain rules called protocol. A Protocol is defined as a set of rules that governs data communications. A protocol defines what is to be communicated, how it is to be communicated and when it is to be communicated. 1.7.1 Elements of a Protocol There are three key elements of a protocol: 8 A. Syntax It means the structure or format of the data. It is the arrangement of data in a particular order. B. Semantics It tells the meaning of each section of bits and indicates the interpretation of each section. It also tells what action/decision is to be taken based on the interpretation. C. Timing It tells the sender about the readiness of the receiver to receive the data It tells the sender at what rate the data should be sent to the receiver to avoid overwhelming the receiver. 1.7 STANDARDS IN NETWORKING Standards are necessary in networking to ensure interconnectivity and interoperability between various networking hardware and software components. Without standards we would have proprietary products creating isolated islands of users which cannot interconnect. 1.7.1 Concept of Standard Standards provide guidelines to product manufacturers and vendors to ensure national and international interconnectivity. Data communications standards are classified into two categories: 1. De facto Standard o These are the standards that have been traditionally used and mean by fact or by convention o These standards are not approved by any organized body but are adopted by widespread use. 2. De jure standard o It means by law or by regulation. o These standards are legislated and approved by an body that is officially recognized. 1.7.2 Standard Organizations in field of Networking 9 o Standards are created by standards creation committees, forums, and government regulatory agencies. o Examples of Standard Creation Committees : 1. International Organization for Standardization(ISO) 2. International Telecommunications Union – Telecommunications Standard (ITU-T) 3. American National Standards Institute (ANSI) 4. Institute of Electrical & Electronics Engineers (IEEE) 5. Electronic Industries Associates (EIA) o Examples of Forums 1. ATM Forum 2. MPLS Forum 3. Frame Relay Forum o Examples of Regulatory Agencies: 1. Federal Communications Committee (FCC) 1.8 REVIEW QUESTIONS 1. Differentiate between data & information. What are the different forms in which data can be represented? 2. What are the characteristics of data communication? 3. What are the components of a data communication system? 4. Define computer network and categorize. 5. Explain protocols in details 1.9 REFERENCES 1. Data Communication & Networking – Behrouz Forouzan           10 Unit 1 Introduction to data communications and networking 2 Signals Unit Structure 2.0 Objectives 2.1 Introduction 2.2 Data & Signals 2.2.1 Data –types 2.2.2 Signal – types 2.2.3 Periodic & Non Periodic Signals 2.3 Analog Signal 2.3.1 Characteristics of Analog Signal 2.3.1.1 Peak Amplitude 2.3.1.2 Frequency 2.3.1.3 Phase 2.3.2 Relation between Frequency & Period 2.3.3 Wavelength 2.3.4 Time & Frequency Domain Representation of a signal 2.3.5 Composite Signal 2.4 Digital Signal 2.4.1 Definition 2.4.2 Level 2.4.3 Bit lenght or Bit Interval 2.4.4 Bit Rate 2.4.5 Baud Rate 2.5 Types of Channel 2.5.1 Lowpass Channel 2.5.2 Bandpass Channel 2.6 Transmission of Digital signal 2.6.1 Baseband Transmission 2.6.2 Broadband Transmission 2.7 Review Questions 2.8 References 11 2.0 OBJECTIVES  Introduce the readers to fundamentals of data & signal  Types of data & signal  Characteristics and nature of analog & digital signal  Representation of signal  Transmission of digital signals 2.1 INTRODUCTION Computer networks are designed to transfer data from one point to another. During transit data is in the form of electromagnetic signals. Hence it is important to study data and signals before we move to further concepts in data communication. 2.2 DATA & SIGNALS To be transmitted, data must be transformed to electromagnetic signals. 2.2.1. Data can be Analog or Digital. 1. Analog data refers to information that is continuous; ex. sounds made by a human voice 2. Digital data refers to information that has discrete states. Digital data take on discrete values. 3. For example, data are stored in computer memory in the form of Os and 1s 2.2.2. Signals can be of two types: 1. Analog Signal: They have infinite values in a range. 2. Digital Signal: They have limited number of defined values Figure: a. Analog Signal b. Digital Signal 2.2.3. Periodic & Non Periodic Signals 12 Signals which repeat itself after a fixed time period are called Periodic Signals. Signals which do not repeat itself after a fixed time period are called Non-Periodic Signals. In data communications, we commonly use periodic analog signals and non-periodic digital signals. 2.3 ANALOG SIGNAL An analog signal has infinitely many levels of intensity over a period of time. As the wave moves from value A to value B, it passes through and includes an infinite number of values along its path as it can be seen in the figure below. A simple analog signal is a sine wave that cannot be further decomposed into simpler signals. Fig. Sine wave A sine wave is characterized by three parameters: 1. Peak Amplitude 2. Frequency 3. Phase 2.3.1 Characteristics of an Analog Signal 2.3.1.1 Peak Amplitude The amplitude of a signal is the absolute value of its intensity at time t The peak amplitude of a signal is the absolute value of the highest intensity. 13 The amplitude of a signal is proportional to the energy carried by the signal Fig. Amplitude of a sine wave 2.3.1.2. Frequency Frequency refers to the number of cycles completed by the wave in one second. Period refers to the time taken by the wave to complete one second. Fig: Frequency & Period of a sine wave 14 2.3.1.3. Phase Phase describes the position of the waveform with respect to time (specifically relative to time O). Fig: Phase of a sine wave Phase indicates the forward or backward shift of the waveform from the axis It is measured in degrees or radian The figure above shows the sine waves with same amplitude and frequency but different phases 2.3.2 Relation between Frequency & Period Frequency & Period are inverse of each other. It is indicated by the following formula: 15 Example1. A wave has a frequency of 100hz. Its period(T) is given by T = 1/ F = 1/ 100 = 0.01 sec Example2. A wave completes its one cycle in 0.25 seconds. Its frequency is given by F = 1 / T = 1 / 0.25 = 4 Hz 2.3.3 Wavelength The wavelength of a signal refers to the relationship between frequency (or period) and propagation speed of the wave through a medium. The wavelength is the distance a signal travels in one period. It is given by Wavelength = Propagation Speed X Period OR Wavelength =Propagation Speed X 1 a Frequency It is represented by the symbol : λ (pronounced as lamda) It is measured in micrometers It varies from one medium to another. 2.3.4. Time Domain and Frequency domain representation of signals A sine wave can be represented either in the time domain or frequency domain. The time-domain plot shows changes in signal amplitude with respect to time. It indicates time and amplitude relation of a signal. The frequency-domain plot shows signal frequency and peak amplitude. The figure below show time and frequency domain plots of three sine waves. 16 Fig: Time domain and frequency domain plots of three sine waves A complete sine wave in the time domain can be represented by one single spike in the frequency domain 2.3.5. Composite Signal A composite signal is a combination of two or more simple sine waves with different frequency, phase and amplitude. If the composite signal is periodic, the decomposition gives a series of signals with discrete frequencies; if the composite signal is non-periodic, the decomposition gives a combination of sine waves with continuous frequencies. Fig: A Composite signal with three component signals 17 For data communication a simple sine wave is not useful, what is used is a composite signal which is a combination of many simple sine waves. According to French Mathematician, Jean Baptist, any composite signal is a combination of simple sine waves with different amplitudes and frequencies and phases. Composite signals can be periodic or non periodic. A periodic composite signal can be decomposed into a series of signals with discrete frequencies. A non-periodic signal when decomposed gives a combination of sine waves with continuous frequencies. Fig The time and frequency domains of a non-periodic composite analog signal 2.4 Digital Signal Information can also be explained in the form of a digital signal. A digital signal can be explained with the help of following points: 2.4.1 Definition:- A digital is a signal that has discrete values. The signal will have value that is not continuous. 2.4.2 LEVEL Information in a digital signal can be represented in the form of voltage levels. Ex. In the signal shown below, a ‗1‘ is represented by a positive voltage and a ‗0‘ is represented by a Zero voltage. 18 Fig: A digital signal with Two levels. „1‟ represented by a positive voltage and „0‟ represented by a negative voltage A Signal can have more than two levels 11 10 01 00 00 01 10 10 LEVEL 4 LEVEL 3 LEVEL 2 LEVEL 1 Fig: A digital signal with four levels In general, if a signal has L levels then, each level need Log L bits 2 Example: Consider a digital Signal with four levels, how many bits are required per level? Answer: Number of bits per level = Log L 2 = Log 4 2 = 2 Hence, 2 bits are required per level for a signal with four levels. 2.4.3 BIT LENGTH or Bit Interval (T b) It is the time required to send one bit. It is measured in seconds. 19 2.4.4 BIT RATE It is the number of bits transmitted in one second. It is expressed as bits per second (bps). Relation between bit rate and bit interval can be as follows Bit rate = 1 / Bit interval 2.4.5 Baud Rate It is the rate of Signal Speed, i.e the rate at which the signal changes. A digital signal with two levels ‗0‘ & ‗1‘ will have the same baud rate and bit rate & bit rate. The diagram below shows three signal of period (T) 1 second a) Signal with a bit rate of 8 bits/ sec and baud rate of 8 baud/sec b) Signal with a bit rate of 16 bits/ sec and baud rate of 8 baud/sec c) Signal with a bit rate of 16 bits/ sec and baud rate of 4 baud/sec Fig: Three signals with different bit rates and baud rates 20 2.5 TYPES OF CHANNELS: Each composite signal has a lowest possible(minimum) frequency and a highest possible (maximum) frequency. From the point of view of transmission, there are two types of channels: 2.5.1 Low pass Channel This channel has the lowest frequency as ‗0‘ and highest frequency as some non-zero frequency ‗f1‘. This channel can pass all the frequencies in the range 0 to f1. 2.5.2 Band pass channel This channel has the lowest frequency as some non-zero frequency ‗f1‘ and highest frequency as some non-zero frequency ‗f2‘. This channel can pass all the frequencies in the range f1 to f2. Fig: Lowpass Channel & Bandpass Channel 2.6 Transmission of Digital signal Digital signal can be transmitted in the following two ways: 2.6.1 Baseband Transmission The signal is transmitted without making any change to it (ie. Without modulation)

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