BCA_Sem IV_Computer Networks_Second Draft

BACHELOR OF COMPUTER APPLICATIONS SEMESTER–IV COMPUTER NETWORKS

CHANDIGARH UNIVERSITY Institute of Distance and Online Learning SLM Development Committee Prof. (Dr.) H.B. Raghvendra Vice- Chancellor, Chandigarh University, Gharuan, Punjab:Chairperson Prof. (Dr.) S.S. Sehgal Registrar Prof. (Dr.) B. Priestly Shan Dean of Academic Affairs Dr. Nitya Prakash Director – IDOL Dr. Gurpreet Singh Associate Director –IDOL Advisors& Members of CIQA –IDOL Prof. (Dr.) Bharat Bhushan, Director – IGNOU Prof. (Dr.) Majulika Srivastava, Director – CIQA, IGNOU Editorial Committee Prof. (Dr) Nilesh Arora Dr. Ashita Chadha University School of Business University Institute of Liberal Arts Dr. Inderpreet Kaur Prof. Manish University Institute of Teacher Training & University Institute of Tourism & Hotel Management Research Dr. Manisha Malhotra Dr. Nitin Pathak University Institute of Computing University School of Business © No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any formor by any means, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of the authors and the publisher. SLM SPECIALLY PREPARED FOR CU IDOL STUDENTS 2 CU IDOL SELF LEARNING MATERIAL (SLM)

First Published in 2021 All rights reserved. No Part of this book may be reproduced or transmitted, in any form or by any means, without permission in writing from Chandigarh University. Any person who does any unauthorized act in relation to this book may be liable to criminal prosecution and civil claims for damages. This book is meant for educational and learning purpose. The authors of the book has/have taken all reasonable care to ensure that the contents of the book do not violate any existing copyright or other intellectual property rights of any person in any manner whatsoever. In the event, Authors has/ have been unable to track any source and if any copyright has been inadvertently infringed, please notify the publisher in writing for corrective action. 3 CU IDOL SELF LEARNING MATERIAL (SLM)

CONTENT Unit – 1: Data Communications Concepts Part 1 ................................................................... 5 UNIT- 2: Data Communications Concepts Part 2 ................................................................ 28 UNIT – 3: Wired Transmissions Part 1............................................................................... 42 UNIT – 4: Wired Transmissions Part 2................................................................................ 55 UNIT – 5: Transmission Media Part 1................................................................................. 66 UNIT – 6: Transmission Media Part 2................................................................................. 79 UNIT – 7: Wireless Transmission Part 1 ............................................................................. 96 UNIT- 8: Wireless Transmission Part 2............................................................................. 107 UNIT – 9: Wireless Transmission Part 3 ........................................................................... 124 UNIT 10 – Network Reference Models Part 1 ................................................................... 136 UNIT – 11: Network Reference Models Part 2 .................................................................. 162 UNIT – 12: Data link Layer Design Issue Part 1................................................................ 172 UNIT – 13: Network Layer Design Issues ......................................................................... 192 UNIT – 14: Application Layer Part 1 ................................................................................ 218 UNIT – 15: Application Layer Part 2 ................................................................................ 245 4 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT – 1: DATA COMMUNCIATION CONCEPTS PART 1 STRUCTURE 1.0 Learning Objectives 1.1 Introduction 1.2 Digital and Analogue 1.2.1 Data – types 1.2.2 Signal – types 1.2.3 Characteristics of Digital and Analogue Signal 1.3 Parallel and Serial 1.4 Synchronous and Asynchronous 1.5 Summary 1.6 Keywords 1.7 Learning Activity 1.8 Unit End Questions 1.9 References 1.0 LEARNING OBJECTIVES After studying this unit, you will be able to:  Define digital data and analogue data and explain its characteristics.  Illustrate the different types of data and signal.  Explain parallel and serial data transmission.  Illustrate synchronous and asynchronous serial transmission. 1.1 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.Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. Data communication involved the following like communication networks, different communication services required, the kind of networks available, protocol 5 CU IDOL SELF LEARNING MATERIAL (SLM)

architectures, OSI models, TCP/IP protocol models etc. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process. In Local Area Networks, we are interested in \"connectivity\", connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources.The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in data communications. Figure 1.1: Source and destination system Source It is the generator of data that will pass on the destination using networks. Without any request source never passes the data to destination. So, if source is passing the data means any of the destinations is requesting for data using some query languages. Transmitter It is simply a device used to convert the data as per the destination requirement. For example a modem, converts the analogue (telephonic signals) signal to digital (computer signals) signals and alternatively digital to analogue also. TransmissionSystem To transmit the data on different connected systems we use different transmission systems. Data transmission using transmission system means the physical transfer of data over point- to-point or point-to-multipoint communication channels. Example of such channels are copper wires, optical fibres even wireless communication channels etc. Receiver This receives the signals from the transmission system and converts it into a form that is suitable to the destination device. For example, a modem accepts analogue signal from a transmission channel and transforms it into digital bit stream which is acceptable by computer system. 6 CU IDOL SELF LEARNING MATERIAL (SLM)

1.2 DIGITAL AND ANALOGUE To be transmitted, data must be transformed to electromagnetic signals. Data can be analogue or digital. Analogue data refers to information that is continuous. Example: - Sounds made by a human voice. Digital data refers to information that has discrete states. Digital data take on discrete values. For example, data are stored in computer memory in the form of zeros and one. Similarly signals can be of two types. 1. Analoguesignal - They have infinite values in a range. 2. Digital signal - They have limited number of defined values. Figure 1.2: Value vs timerepresentation of Analogue signal and digital signal Periodic and Non-Periodic Signals Signals which repeat itself after a fixed time period are called periodic signals. Periodic analogue signals can be classified as simple or composite. A simple periodic analogue signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analogue signal is composed of multiple sine waves.Signals which do not repeat itself after a fixed time period are called non-periodic signals. In data communications, we commonly use periodic analogue signals and non-periodic digital signals. Analogue Signal An analogue 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 1.2. A simple analogue signal is a sine wave that cannot be further decomposed into simpler signals. 7 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.3: Sine wave The sine wave is the most fundamental form of a periodic analogue signal. When we visualize it as a simple oscillating curve, its change over the course of a cycle is smooth and consistent, a continuous, rolling flow. Figure 1.2 shows a sine wave. Each cycle consists of a single arc above the time axis followed by a single arc below it. 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. A digital is a signal that has discrete values. The signal will have value that is not continuous. Level Information in a digital signal can be represented in the form of voltage levels. For example: - In the signal shown below, a ‘1’ is represented by a positive voltage and a ‘0‘is represented by a zero voltage or negative voltage. Figure 1.4: A digital signal with two levels It is to be noted that a signal can have more than two levels. Figure 1.4 shows a digital signal with four levels. 8 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.5: A digital signal with four levels In general, if a signal has L levels then, each level need log2L bits. Example Consider a digital signal with four levels, how many bits are required per level? Number of bits per level = Log2L = Log24 = 2 Hence, 2 bits are required per level for a signal with four levels. 1.2.1 Data- types At a practical level, the difference between analogue and digital is in how the information / data are measured. Analogue data attempts to be continuous and identify every nuance of what is being measured, while digital data uses sampling to encode what is being measured. Analogue Data Analogue data is data that is represented in a physical way. Where digital data is a set of individual symbols, analogue data is stored in physical media, whether that's the surface grooves on a vinyl record, the magnetic tape of a VCR cassette, or other non-digital media. One of the big ideas behind today's quickly developing tech world is that much of the world's natural phenomena can be translated into digital text, image, video, sound, etc. For example, physical movements of objects can be modelled in a spatial simulation, and real-time audio and video can be captured using a range of systems and devices. Analogue data may also be known as organic data or real-world data. Digital Data Digital data is information stored on a computer system as a series of 0's and 1's in a binary language. Information is stored on computer disks and drives as a magnetically charged switch which is in either a 0 or 1 state. A single 0 or 1 is also called a bit.Whenever you send an email, read a social media post, or take pictures with your digital camera, you are working with digital data. We all probably hear this term on a daily basis, but have you ever wondered what digital means? If you think it means any electronic information on a computer, you are 9 CU IDOL SELF LEARNING MATERIAL (SLM)

on the right track, but there is a bit more to it. Let's define digital data and take a look at how it is used in our daily lives. Digital data is a binary language. When you press a key on the keyboard, an electrical circuit is closed. The circuit acts like a switch and has only two possible options: open or closed. If you know Morse code, the idea is the same. A string of dashes and dots represents one letter or number. This is binary. There is no halfway or in-between. The status of the switch as open or closed is interpreted by the computer as a 0 or 1. Each digit is known as a bit.Computer disks and drives hold many switches to store this information as lines of 0's and 1's. A byteis composed of eight bits, and a kilobyte is 1,000 bytes; 1,000 kilobytes equals one megabyte. When information is put into a digital form, it is converted into sequences of 0's and 1's that can be interpreted by other computer systems. Digitizing information is the process of converting information into digital form and is necessary for a computer to be able to process and store information. 1.2.2 Signal - types Signals are classified into the following categories. They are 1. Continuous time and discrete time signals. 2. Deterministic and non-deterministic signals. 3. Even and odd signals. 4. Periodic and aperiodic signals. 5. Energy and power signals. 6. Real and imaginary signals. Continuous Time and Discrete Time Signals A signal is said to be continuous when it is defined for all instants of time. Figure 1.6: Continuous time signal A signal is said to be discrete when it is defined at only discrete instants of time. 10 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.7: Discrete time signal Deterministic and Non-deterministic Signals A signal is said to be deterministic if there is no uncertainty with respect to its value at any instant of time. Or, signals which can be defined exactly by a mathematical formula are known as deterministic signals. Figure 1.8: Deterministic signal A signal is said to be non-deterministic if there is uncertainty with respect to its value at some instants of time. Non-deterministic signals are random in nature hence they are called random signals. Random signals cannot be described by a mathematical equation. They are modelled in probabilistic terms. Figure 1.9: Non-deterministic signal 11 Even and Odd Signals A signal is said to be even when it satisfies the condition x (t) = x (-t). Example: t2, t4… cost etc. Let x (t) = t2 CU IDOL SELF LEARNING MATERIAL (SLM)

X (-t) = (-t) 2 = t2 = x (t) Therefore, t2 is even function Example As shown in the following diagram, rectangle function x (t) = x (-t) so it is also even function. Figure 1.10: Rectangle function Periodic and Aperiodic Signals A signal is said to be periodic if it satisfies the condition x (t) = x (t + T) or x (n) = x (n + N) Where, T = fundamental time period, 1/T = f = fundamental frequency. Figure 1.11: Periodic signal The above signal will repeat for every time interval T0hence it is periodic with period T0. Energy and Power Signals A signal is said to be energy signal when it has finite energy. A signal is said to be power signal when it has finite power. Note: A signal cannot be both, energy and power simultaneously. Also, a signal may be neither energy nor power signal. Power of energy signal = 0 12 Energy of power signal = ∞ CU IDOL SELF LEARNING MATERIAL (SLM)

Real and Imaginary Signals A signal is said to be real when it satisfies the condition x (t) = x*(t). A signal is said to be odd when it satisfies the condition x (t) = -x*(t). Example If x (t) = 3 then x*(t) =3*=3 here x (t) is a real signal. If x (t) = 3j then x*(t) =3j* = -3j = -x (t) hence x (t) is an odd signal. Note: For a real signal, imaginary part should be zero. Similarly for an imaginary signal, real part should be zero. 1.2.3 Characteristics of digital and Analogue Signal A sine wave is characterized by three parameters. They are 1. Peak amplitude 2. Frequency 3. Phase Characteristics of an Analogue Signal 1. Peak amplitude The amplitude of a signal is the absolute value of its intensity at time tothe peak amplitude of a signal is the absolute value of the highest intensity. The amplitude of a signal is proportional to the energy carried by the signal Figure 1.12: Amplitude of a sine wave 13 CU IDOL SELF LEARNING MATERIAL (SLM)

The peak amplitude of a signal is the absolute value of its highest intensity, proportional to the energy it carries. For electric signals, peak amplitude is normally measured in volts. Figure 1.5 shows two signals and their peak amplitudes. Example The power in your house can be represented by a sine wave with peak amplitude of 155 to 170 V. However, it is common knowledge that the voltage of the power in U.S. homes is 110 to 120 V. This discrepancy is due to the fact that these are root mean square (rms) values. The signal is squared and then the average amplitude is calculated. The peak value is equal to 2112 x rms value. Example The voltage of battery is a constant; this constant value can be considered a sine wave, as we will see later. For example, the peak value of an AA battery is normally 1.5 V. 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. Period refers to the amount of time, in seconds, a signal needs to complete 1 cycle. Frequency refers to the number of periods in I s. Note that period and frequency are just one characteristic defined in two ways. Period is the inverse of frequency, and frequency is the inverse of period, as the following formulas show. F= 1/ T or T = 1/ f. Frequency and period are the inverse of each other. Figure 1.13: Frequency and period of sine wave Period is formally expressed in seconds. Frequency is formally expressed in Hertz (Hz), which is cycle per second. Units of period and frequency are shown in Table 1.1. 14 CU IDOL SELF LEARNING MATERIAL (SLM)

Table 1.1: Units of period and frequency Example The power we use at home has a frequency of 60 Hz (50 Hz in Europe). The period of this sine wave can be determined as follows. T = 1 / f = 1 / 60 = 0.0166s = 16.6 ms This means that the period of the power for our lights at home is 0.0116 s, or 16.6 ms. Our eyes are not sensitive enough to distinguish these rapid changes in amplitude. 3. Phase Phase describes the position of the waveform with respect to time (specifically relative to time O). Figure 1.14: 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 1.14 shows the sine waves with same amplitude and frequency but different phases.The term phase describes the position of the waveform relative to time O. If we think of the wave as something that can be shifted 15 CU IDOL SELF LEARNING MATERIAL (SLM)

backward or forward along the time axis, phase describes the amount of that shift. It indicates the status of the first cycle. Phase describes the position of the waveform relative to time O. Phase is measured in degrees or radians. A phase shift of 360° corresponds to a shift of a complete period; a phase shift of 180° corresponds to a shift of one-half of a period; and a phase shift of 90° corresponds to a shift of one-quarter of a period. Relation between Frequency & Period Frequency and period are inverse of each other. It is indicated by the following formula. T = 1 / f, where f is the frequency and T is the time period. So, frequency f = 1 / T Example A wave has a frequency of 100 Hz. 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 4. Wavelength The wavelength of a signal refers to the relationship between frequency (and 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 OrWavelength =Propagation Speed X 1 a Frequency Wavelength is another characteristic of a signal traveling through a transmission medium. Wavelength binds the period or the frequency of a simple sine wave to the propagation speed of the medium. While the frequency of a signal is independent of the medium, the wavelength depends on both the frequency and the medium. Wavelength is a property of any type of signal. In data communications, we often use wavelength to describe the transmission of light in an optical fibre. The wavelength is the distance a simple signal can travel in one period.It is represented by the symbol, λ (pronounced as lambda). It is measured in micrometres. It varies from one medium to another. 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 1.15 show time and frequency domain plots of three sine waves. 16 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.15: 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. 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. Figure 1.16: Composite signal with three component signals 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 17 CU IDOL SELF LEARNING MATERIAL (SLM)

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. Figure 1.17: The time and frequency domains of a non-periodic composite analogue signal Characteristics of a Digital Signal The characteristics of a digital signal are described below. Bit Length or Bit Interval (Tb) It is the time required to send one bit. It is measured in seconds. Bit Rate It is the number of bits transmitted in one second. It is expressed as bits per second (bps). The relation between bit rate and bit interval can be as follows. Bit rate = (1 / Bit interval) 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‘ and ‘1‘ will have the same baud rate and bit rate & bit rate. The figure 1.10 shows three signal of period (T) 1 second i. Signal with a bit rate of 8 bits/ sec and baud rate of 8 baud/sec. ii. Signal with a bit rate of 16 bits/ sec and baud rate of 8 baud/sec. iii. Signal with a bit rate of 16 bits/ sec and baud rate of 4 baud/sec. 18 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.18: Three signals with different bit rates and baud rates 1.3PARALLEL AND SERIAL The transmission mode decides how data is transmitted between two computers. The binary data in the form of 1s and 0s can be sent in two different modes. They are parallel and serial. Data can be transmitted from Source to Destination in a number of ways. The different modes of data transmission are outlined as follows.  Parallel and Serial Communication  Asynchronous, Synchronous and Isochronous Communication Parallel Transmission Fundamentally, parallel I/O is quite easy to understand. A group of bits (typically a byte) is transferred from one device to another. A wire is used for each of the data bits. A common example of a parallel device is a printer connected to an LPT port of a PC. Traditionally parallel I/O has been regarded as being faster than serial I/O. This is easy to understand because several bits are transferred at a time. However it is possible for the individual bits to arrive at the receiving end at slightly different times, the data is ‘skewed’, consequently very high speed parallel devices can be complex and special attention must be paid to the cabling 19 CU IDOL SELF LEARNING MATERIAL (SLM)

etc. Recent high speed serial interfaces (USB and IEEE1394 or ‘Firewire’) have demonstrated that very high data transfers can be achieved quite simply and cheaply using serial I/O. Usually when two devices communicate (either serial or parallel) a system of handshaking is involved. Apart from the actual data connections there may be additional lines to support the handshaking. Let’s call these extra lines DAV (Data Available) and DACK (Data Acknowledge). Typically the device sending data will output its data and then assert DAV, telling the receiving device that new data is available, and then it waits for a response. The receiving device will recognise that data is available, receive it and then assert DACK. This tells the transmitting device that it can continue. The binary bits are organized into groups of fixed length. Both sender and receiver are connected in parallel with the equal number of data lines. Both computers distinguish between high order and low order data lines. The sender sends all the bits at once on all lines. Because the data lines are equal to the number of bits in a group or data frame, a complete group of bits (data frame) is sent in one go. Advantage of Parallel transmission is high speed and disadvantage is the cost of wires, as it is equal to the number of bits sent in parallel. Figure 1.19: Parallel transmission Serial Communications Instead of latching eight bits of parallel data, we could pass each bit in the byte to a single line, one at a time. Known as bit-serial interfacing, there are serial standards that cover this kind of transmission. Since microcomputers are parallel systems, we need to convert an eight bit byte of data to serial form before output, and from serial form to input. There are two ways to perform this conversion: by software, or with a UART (universal asynchronous receiver-transmitter).In serial transmission, bits are sent one after another in a queue manner. Serial transmission requires only one communication channel. 20 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.20: Serial transmission 1.4SYNCHRONOUS AND ASYNCHRONOUS Serial transmission can be either asynchronous or synchronous.In synchronization,  Sender & receiver need to synchronize  Different levels of sync i. Clock sync at the bit level. ii. Block sync at the block or message level (character/word level). Asynchronous Serial Transmission It is named so because there is no importance of timing. Data-bits have specific pattern and they help receiver recognize the start and end data bits. For example, a 0 is prefixed on every data byte and one or more 1s are added at the end. Two continuous data-frames (bytes) may have a gap between them. Figure 1.21 Asynchronous transmissions (a) Figure 1.22 Asynchronous transmissions (b) Bits are sent on a character-by-character basis. It is independent clocks at sender & receiver (but matching reasonably). In clock sync, the receiver resync’s its clock every character and in block sync, each character is “bracketed” by start & stop bits. Advantages  Asynchronous transmission is simple, inexpensive and is ideally suited for transmitting small frames at irregular intervals (e.g., Data entry from a keyboard).  As each individual character is complete in itself, if a character is corrupted during transmission, its successor and predecessor will not be affected. 21 CU IDOL SELF LEARNING MATERIAL (SLM)

Disadvantage  As start, stop and parity bits must be added to each character that is to be transmitted; this adds a high overhead to transmission. This wastes the bandwidth; as a result, asynchronous transmission is undesirable for transmitting large amounts of data.  Successful transmission inevitably depends on the recognition of the start bits, hence, as these bits can be easily missed or occasionally spurious, as start bits can be generated by line interference, the transmission may be unsuccessful.  Due to the effects of distortion the speed of asynchronous transmission is limited. Synchronous Serial Transmission Timing in synchronous transmission has importance as there is no mechanism followed to recognize start and end data bits. There is no pattern or prefix/suffix method. Data bits are sent in burst mode without maintaining gap between bytes (8-bits). Single burst of data bits may contain a number of bytes. Therefore, timing becomes very important.It is up to the receiver to recognize and separate bits into bytes. The advantage of synchronous transmission is high speed, and it has no overhead of extra header and footer bits as in asynchronous transmission.In synchronous transmission, sender & receiver have identical clocks.  Separate clock line to carry clock signal from sender.  “Self-clocking” transmission scheme i. Biphase encoding (e.g. Manchester) digital sig. ii. Using carrier signal Analogue sig.  Block sync i. – Special preamble & post-amble bit patterns used to indicate start/end of a block (frame). Figure 1.23 Synchronous format Advantages of Synchronous Communication  Synchronous transmission is more efficient because, only 4 additional bytes (for start and end frames) are required to transmit upto 64 k bits.  Synchronous transmission is not really prone to distortion; as a result, it can be used at high- speeds. Disadvantages of Synchronous Communication 22 CU IDOL SELF LEARNING MATERIAL (SLM)

 Synchronous transmission is expensive as complex circuitry is required and it is difficult to implement.  If an error occurs during transmission, rather than just a single character the whole block of data is lost.  The sender cannot transmit characters simply, as they occur, but has to store them until it has built up a block. Thus, this is not suitable where characters are generated at irregular intervals 1.5 SUMMARY  Data must be transformed to electromagnetic signals to be transmitted.Data can be analogue or digital. Analogue data are continuous and take continuous values. Digital data have discrete states and take discrete values.  Signals can be analogue or digital. Analogue signals can have an infinite number of values in a range; digital, signals can have only a limited number of values.In data communications, we commonly use periodic analogue signals and nonperiodic digital signals.  Frequency and period are the inverse of each other.Frequency is the rate of change with respect to time.Phase describes the position of the waveform relative to time O.A complete sine wave in the time domain can be represented by one single spike in the frequency domain.  A single-frequency sine wave is not useful in data communications; we need to send a composite signal, a signal made of many simple sine waves.  A group of bits (typically a byte) is transferred from one device to another. A wire is used for each of the data bits. A common example of a parallel device is a printer connected to an LPT port of a PC. Traditionally parallel I/O has been regarded as being faster than serial I/O. This is easy to understand because several bits are transferred at a time. However it is possible for the individual bits to arrive at the receiving end at slightly different times, the data is ‘skewed’, consequently very high speed parallel devices can be complex and special attention must be paid to the cabling etc.  Instead of latching eight bits of parallel data, we could pass each bit in the byte to a single line, one at a time. Known as bit-serial interfacing, there are serial standards that cover this kind of transmission. Since microcomputers are parallel systems, we need to convert an eight bit byte of data to serial form before output, and from serial form to input. 23 CU IDOL SELF LEARNING MATERIAL (SLM)

 Asynchronous serial transmission is named so because there is no importance of timing. Data-bits have specific pattern and they help receiver recognize the start and end data bits. For example, a 0 is prefixed on every data byte and one or more 1s are added at the end.  Timing in synchronous transmission has importance as there is no mechanism followed to recognize start and end data bits. There is no pattern or prefix/suffix method. Data bits are sent in burst mode without maintaining gap between bytes (8- bits). Single burst of data bits may contain a number of bytes. Therefore, timing becomes very important. It is up to the receiver to recognize and separate bits into bytes. 1.6 KEYWORDS  Analogue Data - Analogue data is data that is represented in a physical way. Where digital data is a set of individual symbols, analogue data is stored in physical media, whether that's the surface grooves on a vinyl record, the magnetic tape of a VCR cassette, or other non-digital media.  DigitalData - Digital data is data that represents other forms of data using specific machine language systems that can be interpreted by various technologies. ... One of the biggest strengths of digital data is that all sorts of very complex analogue input can be represented with the binary system.  Frequency - Frequency is the number of occurrences of a repeating event per unit of time. Frequency is measured in hertz (Hz) which is equal to one event per second. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency.  Periodic Signal - A periodic signal is one that repeats the sequence of values exactly after a fixed length of time, known as the period. Examples of periodic signals include the sinusoidal signals and periodically repeated non-sinusoidal signals, such as the rectangular pulse sequences used in radar.  Sine Wave - A sine wave or sinusoid is a mathematical curve that describes a smooth periodic oscillation. A sine wave is a continuous wave. It is named after the function sine, of which it is the graph. 1.7 LEARNING ACTIVITY 1. Illustrate and confirm whether the AC voltage in our home is sinusoidal in nature. ___________________________________________________________________________ ___________________________________________________________________________ 24 CU IDOL SELF LEARNING MATERIAL (SLM)

2. The normal AC supply voltage to our home is 240 V. Prove the frequency of ac voltage is 50Hz. ___________________________________________________________________________ __________________________________________________________________________ 1.8 UNIT END QUESTIONS 25 A. Descriptive Questions Short Questions: 1. Define analogue and digital signals. 2. Explain composite analogue signals. 3. Express a period of 100 ms in microseconds. 4. Define serial data communication. 5. What is synchronous transmission? Long Questions: 1. Explain time and frequency domain representation of signals. 2. Explain the characteristics of an analogue signal. 3. Explain the characteristics of a digital signal 4. Describe the parallel data communication. 5. Explain asynchronous transmission with diagram. Write its advantage and disadvantage. B. Multiple Choice Questions 1. What are telegraph signals? a. Digital signals b. Analogue signals c. Impulse signals d. Pulse train 2. Which is the type of information used in digital data? a. Continuous b. Discrete c. Bits d. Bytes CU IDOL SELF LEARNING MATERIAL (SLM)

3. What is termed for the completion of one full pattern in a signal? a. Period b. Cycle c. Frame d. Segment 4. What is the term that refers to infinite number of values in the range? a. Peak b. Analogue signal c. Digital signal d. Data encryption slots 5. The period of a signal is 100 ms. What is its frequency in kilohertz? a. 1/10 b. 1/100 c. 1/1000 d. 1/10000 Answers 1-a, 2-b, 3-b, 4-b, 5-b 1.9 REFERENCES References  Behrouz, A, Forouzan & Coombs, Ann, Catherine & Chung, Sophia. (2001).Data Communication & Networking. Second edition. Mcgraw Hill.  Tanenbaum, A. (1989), Computer Networks, Second Edition, NJ. Prentice Hall, Englewood Cliffs.  Viniotis Y. and Onvural R. (editors) (1993) Asynchronous Transfer Mode, Networks, Plenum, New York, NY. Textbooks  Van, Duuren, J. Schoute, F & Kastelein, P. (1992) Telecommunication.  Networks and Services, Addison-Wesley, Reading, MA.  White, G. (1992) Internetworking and Addressing, McGraw-Hill, NY. 26 CU IDOL SELF LEARNING MATERIAL (SLM)

Websites  https://www.c-sharpcorner.com/uploadfile/abhikumarvatsa/basics-of-data- communication-part-1/  https://www.techopedia.com/definition/24871/analogue  https://www.monolithicpower.com/en/analogue-vs-digital-signal  https://en.wikipedia.org/wiki/Digital_signal  https://www.tutorialspoint.com/data_communication_computer_network/digital_trans mission.htm 27 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT- 2: DATA COMMUNICATIONS CONCEPTS PART 2 STRUCTURE 2.0 Learning Objectives 2.1 Introduction 2.2 Simplex 2.3 Half-duplex 2.4 Full duplex 2.5 Multiplexing 2.6 Summary 2.7 Keywords 2.8 Learning Activity 2.9 Unit End Questions 2.10 References 2.0 LEARNING OBJECTIVES After studying this unit, you will be able to:  Define simplex data tranmission.  Illustrate the importance of half duplex transmission.  Explain the features of full duplex transmission.  Describe the concept of multiplexing. 2.1 INTRODUCTION Communication from a source to a destination, that is, from one computer to another or from one device to another, involves the transfer of information from the sender to the receiver. The transfer of data from one machine to another machine such that, the sender and the receiver both interpret the data correctly is known as Data Communication. All communication between devices requires that the devices agree on the format of the data. The set of rules defining a format is known as a protocol. At the very least, a communications protocol must define the following:  Transmission media used. 28 CU IDOL SELF LEARNING MATERIAL (SLM)

 Rate of transmission (in baud or bps).  Whether transmission is to be synchronous or asynchronous.  Whether data is to be transmitted in half-duplex or full-duplex mode. Data can be transmitted from source to destination in a number of ways. The different modes of data transmission are outlined as follows.  Parallel and serial communication.  Asynchronous, synchronous and isochronous communication.  Simplex, half duplex and full duplex communication. Also the classification of data transmission is based on which question of, communication can send data and at what point of time. The three basic ways in which this can be done areSimplex, Half duplex, Full duplex, sometimes called duplex. In real life, we have links with limited bandwidths. The wise use of these bandwidths has been, and will be, one of the main challenges of electronic communications. However, the meaning of wise may depend on the application. Sometimes we need to combine several low- bandwidth channels to make use of one channel with a larger bandwidth. Sometimes we need to expand the bandwidth of a channel to achieve goals such as privacy and antijamming. Here we explore these two broad categories of bandwidth utilization: multiplexing and spreading. In multiplexing, our goal is efficiency; we combine several channels into one. In spreading, our goals are privacy and anti-jamming; we expand the bandwidth of a channel to insert redundancy, which is necessary to achieve these goals. Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic. We can accommodate this increase by continuing to add individual links each time a new channel is needed; or we can install higher-bandwidth links and use each to carry multiple signals. Today's technology includes high-bandwidth media such as optical fibre and terrestrial and satellite microwaves. Each has a bandwidth far in excess of that needed for the average transmission signal. If the bandwidth of a link is greater than the bandwidth needs of the devices connected to it, the bandwidth is wasted. An efficient system maximizes the utilization of all resources; bandwidth is one of the most precious resources we have in data communications. 2.2 SIMPLEX The simplest signal flow technique is the simplex configuration. In simplex transmission, one of the communicating devices can only send data, whereas the other can only receive it. Here, 29 CU IDOL SELF LEARNING MATERIAL (SLM)

communication is only in one direction (unidirectional) where one party is the transmitter and the other is the receiver as shown in the Figure 3. Examples of simplex communication are the simple radio, and Public broadcast television where, you can receive data from stations but can’t transmit data back. The television station sends out electromagnetic signals. The station does not expect and does not monitor for a return signal from the television set. This type of channel design is easy and inexpensive to set up. 2.3 HALF-DUPLEX Half duplex refers to two-way communication where, only one party can transmit data at a time. Unlike, the Simplex mode here, both devices can transmit data though, not at the same time, that is half duplex provides Simplex communication in both directions in a single channel as shown in figure 2.2. When one device is sending data, the other device must only receive it and vice versa. Thus, both sides take turns at sending data. This requires a definite turn-around time during which, the device changes from the receiving mode to the transmitting mode. Due to this delay, half duplex communication is slower than simplex communication. However, it is more convenient than simplex communication as both the devices can send and receive data. Figure 2.2: Half duplex connection Note: The difference between simplex and half-duplex. Half-duplex refers to two-way communication where, only one party can transmit data at a time. Simplex refers to one-way communication where, one party is the transmitter and the other is the receiver. For example, a walkie-talkie is a half-duplex device because only one party can talk at a time. Most modems contain a switch that lets you select between half-duplex and full-duplex modes. The correct choice depends on which program you are using to transmit data through the modem. 2.4 FULL DUPLEX Full duplex refers to the transmission of data in two directions simultaneously. Here, both the devices are capable of sending as well as receiving data at the same time as shown in figure 2.3 that simultaneously bi-directional communication is possible, as a result, this configuration requires full and independent transmitting and receiving capabilities at both 30 CU IDOL SELF LEARNING MATERIAL (SLM)

ends of the communication channel. Sharing the same channel and moving signals in both directions increases the channel throughput without increasing its bandwidth. For example, a telephone is a full-duplex device because both parties can talk to each other simultaneously. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time. Figure 2.3: Full duplex connection Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on which communications program you are running. 2.5 MULTIPLEXING To make efficient use of high-speed telecommunications lines, some form of multiplexing is used. Multiplexing allows several transmission sources to share a larger transmission capacity. Most individual data communicating devices typically require modest data rate, but the media usually has much higher bandwidth. Two communicating stations do not utilize the full capacity of a data link. The higher the data rate, the most cost effective is the transmission facility. When the bandwidth of a medium is greater than individual signals to be transmitted through the channel, a medium can be shared by more than one channel of signals by using Multiplexing. For efficiency, the channel capacity can be shared among a number of communicating stations. Most common use of multiplexing is in long-haul communication using coaxial cable, microwave and optical fibre. Basic Concept A device known as Multiplexer (MUX) combines ‘n’ channels for transmission through a single medium or link. At the other end a De-multiplexer (DEMUX) is used to separate out the ‘n’ channels. Figure 2.4: Multiplexing 31 CU IDOL SELF LEARNING MATERIAL (SLM)

Types of Multiplexing  Frequency Division Multiplexing (FDM)  Wavelength Division Multiplexing (WDM)  Time Division Multiplexing (TDM) i. Synchronous ii. Asynchronous  Inverse TDM Figure 2.5: Classification of Multiplex Frequency Division Multiplexing (FDM) FDM can be used with analogue signals. A number of signals are carried simultaneously on the same medium by allocating to each signal a different frequency band. FDM is possible when the useful bandwidth of the transmission medium exceeds the required bandwidth of signals to be transmitted. A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency and the carrier frequencies are sufficiently separated that the bandwidths of the signals do not significantly overlap. 32 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.6: FDM multiplexing process Figure 2.7: FDM de-multiplexing process Guard Band A Guard-Band is a narrow frequency range that separates two ranges of wider frequency. This ensures that simultaneously used communication channels do not experience interference or cross-talk, which would result in decreased quality for both transmissions. Figure 2.8 represents frequency range in guard band. 33 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.8 Guard band Applications of Frequency Division Multiplexing (FDM) It includes  Transmission of AM/FM Radio broadcasting  TV broadcasting  Cable television A very common application of FDM is AM and FM radio broadcasting. Radio uses the air as the transmission medium. A special band from 530 to 1700 kHz is assigned to AM radio. All radio stations need to share this band. As discussed in Chapter 5, each AM station needs 10 kHz of bandwidth. Each station uses a different carrier frequency, which means it is shifting its signal and multiplexing. The signal that goes to the air is a combination of signals. A receiver receives all these signals, but filters (by tuning) only the one which is desired. Without multiplexing, only one AM station could broadcast to the common link, the air. However, we need to know that there is physical multiplexer or demultiplexer here. Multiplexing is done at the data link layer. The situation is similar in FM broadcasting. However, FM has a wider band of 88 to 108 MHz because each station needs a bandwidth of 200 kHz. Another common use of FDM is in television broadcasting. Each TV channel has its own bandwidth of 6 MHz The first generation of cellular telephones (still in operation) also uses FDM. Eachuser is assigned two 30-kHz channels, one for sending voice and the other for receiving.The voice signal, which has a bandwidth of 3 kHz (from 300 to 3300 Hz), is modulated byusing FM. Remember that an FM signal has a bandwidth 10 times that of the modulatingsignal, which means each channel has 30 kHz (10 x 3) of bandwidth. Therefore, each useris given, by the base station, a 60-kHz bandwidth in a range available at the time of the call. Wavelength Division Multiplexing Optical fibre medium provides enormous bandwidth. WDM is the most viable technology that overcomes the huge opto-electronic bandwidth mismatch. WDM optical fibre network comprises optical wavelength switches/routers interconnected by point-to-point fibre links. End users may communicate with each other through all-optical (WDM) channels known as Light-paths, which may span over more than one fibre links. Figure 2.9 shows the wavelength division multiplexing. 34 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.9: Wavelength Division multiplexing Time Division Multiplexing Possible when the bandwidth of the medium exceeds the data rate of digital signals to be transmitted. Multiple digital signals can be carried on a single transmission path by interleaving portions of each signal in time. Interleaving can be at the bit level or in blocks of bytes. The incoming data from each source are briefly buffered.  Each buffer is typically one bit or one character in length.  The buffers are scanned sequentially to form a composite data stream.  The scan operation is sufficiently rapid so that each buffer is emptied before more data can arrive. The main two classifications of time division multiplexing are synchronous TDM and asynchronous TDM. Synchronous TDM Composite data rate must be at least equal to the sum of the individual data rate. The composite signal can be transmitted directly or through a modem. 35 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.10: Synchronous TDM Frame Synchronization In this scheme, typically, one control bit is added to each TDM frame. An identifiable pattern of bits, from frame to frame, is used as a “control channel.” Thus, to synchronize, a receiver compares the incoming bits of one frame position to the expected pattern. If the pattern does not match, successive bit positions are searched until the pattern persists over multiple frames. Once frame synchronization is established, the receiver continues to monitor the framing bit channel. If the pattern breaks down, the receiver must again enter a framing search mode. Pulse Staffing If each source has a separate clock, any variation among clocks could cause loss of synchronization. With pulse stuffing, the outgoing data rate of the multiplexer, excluding framing bits, is higher than the sum of the maximum instantaneous incoming rates. The extra capacity is used by stuffing extra dummy bits or pulses into each incoming signal until its rate is raised to that of a locally generated clock signal. The stuffed pulses are inserted at fixed locations in the multiplexer frame format so that they may be identified and removed at the de-multiplexer. Limitations of Synchronous TDM In synchronous TDM, many of the time slots in a frame may be wasted. The problem is overcome in Statistical / Asynchronous / Intelligent TDM. In Statistical TDM, time slots are allocated dynamically on demand. It takes the advantage of the fact that not all the attached devices may be transmitting all of the time. Asynchronous TDM As with a synchronous TDM, the statistical multiplexer has a number of I/O lines on one side and a higher-speed multiplexed line on the other. Each I/O line has a buffer associated with it. In the case of the statistical multiplexer, there are ‘n’ I/O lines, but only k, where k< n, time slots available on the TDM frame. For input, the function of the multiplexer is to scan the input buffers, collecting data until a frame is filled, and then send the frame. On output, the multiplexer receives a frame and distributes the slots of data to the appropriate output buffers. Since data arrive from and are distributed to I/O lines unpredictably, address information is required to assure proper delivery. This leads to more overhead per slot. Relative addressing can be used to reduce overhead. 36 CU IDOL SELF LEARNING MATERIAL (SLM)

Performance of Asynchronous TDM In ATM, the data rate at the output is less than the data rate at the input. However, in peak periods the input may exceed capacity. Buffers of suitable size may be included to overcome this problem. Let ‘n’ = number of inputs, ‘r’ = data rate of each source, ‘M’ = effective capacity of the output, ‘α’=mean fraction of time each input is transmitting, 0 < α < 1. Then, a measure of compression is C = M/ (nr), bounded by α < C < 1. Inverse Multiplexing An inverse multiplexer (IMUX) is a device performing the opposite function of a multiplexer (MUX). Instead of allowing one or more low-speed analogue or digital input signals (or data streams) to be selected, combined and transmitted at a higher speed on a single shared medium i.e. multiplexing, an inverse multiplexer breaks the combined and related higher speed analogue or digital signals into several concurrent lower-speed related signals or data streams. Thus, using multiple slower lines, the data stream can be more evenly distributed across all lines. The difference between de-multiplexing (DEMUX) and inverse multiplexing is that the output streams of de-multiplexing are unrelated but the output streams of inverse multiplexing are related. Just as multiplexers are combined with de-multiplexers to create bi- directional data flow, inverse multiplexers may be combined with an inverse DEMUX (i.e. the reverse of an inverse multiplexer). 2.6 SUMMARY  Bandwidth utilization is the use of available bandwidth to achieve specific goals. Efficiency can be achieved by using multiplexing; privacy and antijamming can be achieved by using spreading.Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. In a multiplexed system, n lines share the bandwidth of one link. The word link refers to the physical path. The word channel refers to the portion of a link that carries a transmission.  There are three basic multiplexing techniques: frequency-division multiplexing, wavelength-division multiplexing, and time-division multiplexing. The first two are techniques designed for analogue signals, the third, for digital signals Frequency- division multiplexing (FDM) is an analogue technique that can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted.  Wavelength-division multiplexing (WDM) is designed to use the high bandwidth capability of fibre-optic cable. WDM is an analogue multiplexing technique to 37 CU IDOL SELF LEARNING MATERIAL (SLM)

combine optical signals. Time-division multiplexing (TDM) is a digital process that allows several connections to share the high bandwidth of a link. TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one. We can divide TDM into two different schemes: synchronous or statistical. In synchronous TDM, each input connection has an allotment in the output even if it is not sending data. In statistical TDM, slots are dynamically allocated to improve bandwidth efficiency.  In spread spectrum (SS), we combine signals from different sources to fit into a larger bandwidth. Spread spectrum is designed to be used in wireless applications in which stations must be able to share the medium without interception by an eavesdropper and without being subject to jamming from a malicious intruder. The frequency hopping spread spectrum (FHSS) technique uses M different carrier frequencies that are modulated by the source signal. At one moment, the signal.  In a multiplexed system, n lines share the bandwidth of one link. In this the lines on the left direct their transmission streams to a multiplexer (MUX), which combines them into a single stream (many-to-one). At the receiving end, that stream is fed into a de-multiplexer (DEMUX), which separates the stream back into its component transmissions (one-to-many) and directs them to their corresponding lines. In the figure, the word link refers to the physical path. The word channel refers to the portion of a link that carries a transmission between a given pair of lines. One link can have many (n) channels.There are three basic multiplexing techniques: frequency- division multiplexing,wavelength-division multiplexing, and time-division multiplexing. The first two are techniques designed for analogue signals, the third, for digital signals.  Frequency-division multiplexing (FDM) is an analogue technique that can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted. In FOM, signals generated by each sending device modulate different carrier frequencies. These modulated signals are then combined into a single composite signal that can be transported by the link. Carrier frequencies are separated by sufficient bandwidth to accommodate the modulated signal. These bandwidth ranges are the channels through which the various signals travel. Channels can be separated by strips of unused bandwidth-guard bands-to prevent signals from overlapping. In addition, carrier frequencies must not interfere with the original data frequencies. 2.7 KEYWORDS 38 CU IDOL SELF LEARNING MATERIAL (SLM)

 Frequency-Division Multiplexing (FDM) - It is an analogue technique that can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted.  Wavelength-Division Multiplexing (WDM) - It is designed to use the high bandwidth capability of fibre-optic cable. WDM is an analogue multiplexing technique to combine optical signals.  Time-Division Multiplexing (TDM) – It is a digital process that allows several connections to share the high bandwidth of a link. TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one.  Multiplexing - Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. In a multiplexed system, n lines share the bandwidth of one link. The word link refers to the physical path.  Bandwidth Utilization - Bandwidth utilization is the use of available bandwidth to achieve specific goals. Efficiency can be achieved by using multiplexing; privacy and anti-jamming can be achieved by using spreading. 2.8 LEARNING ACTIVITY 1. Assume that a voice channel occupies a bandwidth of 4 kHz. We need to combine three voice channels into a link with a bandwidth of 12 kHz, from 20 to 32 kHz. Show the configuration, using the frequency domain. Assume there are no guard bands. ___________________________________________________________________________ ___________________________________________________________________________ 2. Five channels, each with a 10a-kHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 kHz between the channels to prevent interference? ___________________________________________________________________________ ___________________________________________________________________________ 2.9 UNIT END QUESTIONS A. Descriptive Questions 39 Short Questions: 1. Define simplex mode of data transmission. 2. Explain half duplex mode of data transmission. 3. What do you mean by guard band? CU IDOL SELF LEARNING MATERIAL (SLM)

4. What are the different classifications of multiplexers? 5. Write a short on multiplexing? Long Questions: 1. Give reasons as to why full duplex is more challenging then simplex and half duplex transmission. 2. Explain full duplex mode with suitable diagram. 3. Explain the concept of multiplexing using suitable diagram. 4. Explain frequency division multiplexing with a diagram. 5. Explain the various application of FDM. B. Multiple Choice Questions 1. What is termed for sharing of a medium and its link by two or more devices? a. Multiplexing b. Fully duplexing c. Microplexing d. Duplexing 2. Which multiplexing technique is used to transit digital signals? a. FDM b. TDM c. WDM d. FDM and WDM 3. Which is correct about multiplexing? It provides a. Efficiency b. Privacy c. Anti-jamming d. Both efficiency and privacy 4. Identify the mode in which communication is unidirectional? 40 a. Simplex b. Half duplex CU IDOL SELF LEARNING MATERIAL (SLM)

c. Full duplex d. Hybrid 5. Identify the transmission mode in which both stations can transmit and receive at the same time? a. Simplex b. Half duplex c. Full duplex d. None of these Answers 1-a, 2-b, 3-d, 4-a, 5-c 2.10.REFERENCES References  Behrouz, A, Forouzan & Coombs, Ann, Catherine & Chung, Sophia. (2001). Data Communication & Networking. Second edition. Mcgraw Hill.  Tanenbaum, S, Andrew & Wetherall, J, David. (2012). Computer Networks. Fifth edition. Pearson Education.  Hildebrant, Michael, Benjamin. (1950). Distortion in audio systems. Cornell University. Textbooks  W. Stallings, (2010), Data and Computer Communications.  NPTL lecture on Data Communication, by Prof. A. K. Pal, IIT Kharagpur.  B. A. Forouzan, (2013), Data Communication and Networking. Website  www.cisco.com/go/ipv6  http://www.cisco.com/en/US/technologies/tk648/tk872/technologies_white_paper090 0aecd80260042.pdf  http://www.cisco.com/en/US/products/ps6350/prod_command_reference_list.html 41 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT – 3: WIRED TRANSMISSIONS PART 1 STRUCTURE 3.0 Learning Objectives 3.1 Introduction 3.2Telephone Lines 3.3 Leased Lines 3.4 Switch Line 3.5 Summary 3.6 Keywords 3.7 Learning Activity 3.8 Unit End Questions 3.9 References 3.0 LEARNING OBJECTIVES After studying this unit, you will be able to:  Illustrate the basic wired transmission system.  Explain the over-all idea about telephone networks.  Illustrate the different components of telephone networks.  Describe about leased lines of wired transmission.  Illustrate the aspects of switch line in wired transmission. 3.1 INTRODUCTION The term “Data Communication” comprises two words: Data and Communication. Data can be any text, image, audio, video, and multimedia files. Communication is an act of sending or receiving data. Thus, data communication refers to the exchange of data between two or more networked or connected devices. These devices must be capable of sending and receiving data over a communication medium. Examples of such devices include personal computers, mobile phones, laptops, etc. The four different types of devices — computer, printer, server and switch are connected to form the network. These devices are connected through a media to the network, which carry information from one end to other end. Whenever we talk about communication between two computing devices using a network, five most important aspects come to our mind. These are sender, receiver, communication 42 CU IDOL SELF LEARNING MATERIAL (SLM)

mediumthe message to be communicated, and certain rules called protocols to be followed during communication. The communication media is also called transmission media. A sender is a computer or any such device which is capable of sending data over a network. It can be a computer, mobile phone, smart watch, walkie-talkie, video recording device, etc. A receiver is a computer or any such device which is capable of receiving data from the network. It can be any computer, printer, laptop, mobile phone, television, etc. In computer communication, the sender and receiver are known as nodes in a network. Message is the data or information that needs to be exchanged between the sender and the receiver. Messages can be in the form of text, number, image, audio, video, multimedia, etc. Communication media is the path through which the message travels between source and destination. It is also called medium or link which is either wired or wireless. For example, a television cable, telephone cable, Ethernet cable, satellite link, microwaves, etc. Telephone networks were originally created to provide voice communication. The needto communicate digital data resulted in the invention of the dial-up modem. With theadvent of the Internet came the need for high-speed downloading and uploading; themodem was just too slow. The telephone companies added a new technology, the digitalsubscriber line (DSL). Although dial-up modems still exist in many places all over theworld, DSL provides much faster access to the Internet through the telephone network.In this chapter, we first discuss the basic structure of the telephone network. We then seehow dial-up modems and DSL technology use these networks to access the Internet.Cable networks were originally created to provide access to TV programs for thosesubscribers who had no reception because of natural obstructions such as mountains.Later the cable network became popular with people who just wanted a better signal. Inaddition, cable networks enabled access to remote broadcasting stations via microwaveconnections. Cable TV also found a good market in Internet access provision usingsome of the channels originally designed for video. After discussing the basic structureof cable networks, we discuss how cable modems can provide a high-speed connectionto the Internet. 3.2 TELEPHONE LINES Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analogue system using analogue signals to transmit voice. With the advent of the computer era, the network, in the 1980s, began to carry data in addition to voice. During the last decade, the telephone network has undergone many technical changes. The network is now digital as well as analogue. Major Components The telephone network, as shown in figure 3.1, is made of three major components: local loops, trunks, and switching offices. The telephone network has several levels of switching offices such as end offices, tandem offices, and regional offices. 43 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.1: A telephone system Local Loops One component of the telephone network is the local loop, a twisted-pair cable that connects the subscriber telephone to the nearest end office or local central office. The local loop, when used for voice, has a bandwidth of 4000 Hz (4 kHz). It is interesting to examine the telephone number associated with each local loop. The first three digits of a local telephone number define the office, and the next four digits define the local loop number. Trunks Trunks are transmission media that handle the communication between offices. A trunk normally handles hundreds or thousands of connections through multiplexing. Transmission is usually through optical fibres or satellite links. Switching Offices To avoid having a permanent physical link between any two subscribers, the telephone company has switches located in a switching office. A switch connects several local loops or trunks and allows a connection between different subscribers. LATAs After the divestiture of 1984, the United States was divided into more than 200 local-access transport areas (LATAs). The number of LATAs has increased since then. A LATA can be a small or large metropolitan area. A small state may have one single LATA; a large state may have several LATAs. A LATA boundary may overlap the boundary of a state; part of a LATA can be in one state, part in another state. Intra-LATA Services The services offered by the common carriers (telephone companies) inside a LATA arecalled intra-LATA services. The carrier that handles these services is called a localexchange carrier (LEC). Before the Telecommunications Act of 1996 (see Appendix E),intra-LATA services were granted to one single carrier. This was a monopoly. After 1996,more than one carrier 44 CU IDOL SELF LEARNING MATERIAL (SLM)

could provide services inside a LATA. The carrier that provided servicesbefore 1996 owns the cabling system (local loops) and is called the incumbent localexchange carrier (ILEC). The new carriers that can provide services are calledcompetitive local exchange carriers (CLECs). To avoid the costs of new cabling, itwas agreed that the ILECs would continue to provide the main services, and the CLECswould provide other services such as mobile telephone service, toll calls inside a LATA,and so on. Figure 3.2 shows a LATA and switching offices. Figure 3.2: Switching offices in LATA Communication inside a LATA is handled by end switches and tandem switches. A call that can be completed by using only end offices is considered toll-free. A call that has to go through a tandem office (intra-LATA toll office) is charged. Inter-LATA Services The services between LATAs are handled by interexchange carriers (IXCs). These carriers, sometimes called long-distance companies, provide communication services between two customers in different LATAs. After the act of 1996, these services can be provided by any carrier, including those involved in intra-LATA services. The field is wide open. Carriers providing inter-LATA services include AT&T, MCI, WorldCom, Sprint, and Verizon. The IXCs are long-distance carriers that provide general data communications services including telephone service. A telephone call going through an IXC is normally digitized, with the carriers using several types of networks to provide service. Points of Presence As discussed, intra-LATA services can be provided by several LECs (one ILEC and possibly more than one CLEC). We also said that inter-LATA services can be provided by several IXCs. How do these carriers interact with one another? The answer is, via a switching office called a point of presence (POP). Each IXC that wants to provide interLATA services in a LATA must have a POP in that LATA. The LECs that provide services inside the LATA must provide connections so that every subscriber can have access to all POPs. Figure 3.3 illustrates the concept. 45 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.3: Point of presence (POPs) A subscriber who needs to make a connection with another subscriber is connectedfirst to an end switch and then, either directly or through a tandem switch, to a POP. Thecall now goes from the POP of an IXC (the one the subscriber has chosen) in the sourceLATA to the POP of the same IXC in the destination LATA. The call is passed throughthe toll office of the IXC and is carried through the network provided by the IXC. Signalling The telephone network, at its beginning, used a circuit-switched network with dedicatedlinks (multiplexing had not yet been invented) to transfer voice communication. A circuit-switched network needs the setup and teardown phases toestablish and terminate paths between the two communicating parties. In the beginning,this task was performed by human operators. The operator room was a center to whichall subscribers were connected. A subscriber who wished to talk to another subscriberpicked up the receiver (off-hook) and rang the operator. The operator, after listening tothe caller and getting the identifier of the called party, connected the two by using a wirewith two plugs inserted into the corresponding two jacks. A dedicated circuit was createdin this way. One of the parties, after the conversation ended, informed the operator todisconnect the circuit. This type of signalling is called in-band signalling because the samecircuit can be used for both signalling and voice communication.Later, the signalling system became automatic. Rotary telephones were invented thatsent a digital signal defining each digit in a multidigit telephone number. The switches inthe telephone companies used the digital signals to create a connection between the callerand the called parties. Both in-band and out-of-band signalling were used. In in- bandsignalling, the 4-kHz voice channel was also used to provide signalling. In out-of- 46 CU IDOL SELF LEARNING MATERIAL (SLM)

bandsignalling, a portion of the voice channel bandwidth was used for signalling; the voicebandwidth and the signalling bandwidth were separate.As telephone networks evolved into a complex network, the functionality of the signalling system increased. The signalling system was required to perform other tasks such as  Providing dial tone, ring tone, and busy tone  Transferring telephone numbers between offices  Maintaining and monitoring the call  Keeping billing information  Maintaining and monitoring the status of the telephone network equipment  Providing other functions such as caller ID, voice mail, and so on These complex tasks resulted in the provision of a separate network for signalling. This means that a telephone network today can be thought of as two networks: a signalling network and a data transfer network.However, we need to emphasize a point here. Although the two networks are separate,this does not mean that there are separate physical links everywhere; the two networksmay use separate channels of the same link in parts of the system. Data Transfer Network The data transfer network that can carry multimedia information today is, for the mostpart, a circuit-switched network, although it can also be a packet-switched network. Thisnetwork follows the same type of protocols and model. Signalling Network The signalling network, which is our main concern in this section, is a packet- switchednetwork involving the layers similar to those in the OSI model or Internet model. The nature of signalling makes it more suited to a packet-switchingnetwork with different layers. For example, the information needed to convey a telephoneaddress can easily be encapsulated in a packet with all the error control and addressinginformation. Figure 3.4 shows a simplified situation of a telephone network in which thetwo networks are separated. 47 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.4: Data transfer and signalling networks The user telephone or computer is connected to the signal points (SPs). The linkbetween the telephone set and SP is common for the two networks. The signalling networkuses nodes called signal transport ports (STPs) that receive and forward signalling messages. The signalling network also includes a service control point (SCP) that controlsthe whole operation of the network. Other systems such as a database center maybe included to provide stored information about the entire signalling network. Signalling System Seven (SS7) The protocol that is used in the signalling network is called Signalling System Seven (SS7).It is very similar to the five-layer Internet model we saw in Chapter 2, but the layers havedifferent names, as shown in the following figure. Figure 3.5 Layers in SS7 48 CU IDOL SELF LEARNING MATERIAL (SLM)

3.3 LEASED LINES Any fixedthat is permanent, point to point data communications link, which is leased from a telco or similar organisation. The leased line involves cables, such as twisted pair, coax or fibre optic, and may involve all sorts of other hardware such as (pupin) coils, transformers, amplifiers and regenerators. A permanent telephone connection between two pointsset up by a telecommunications common carrier. Not a dedicated cable, a leased line is actually a reserved circuit between two points. Leased lines can span short or long distances. They maintain a single open circuit at all times, as opposed to traditional telephone services that reuse the same lines for many different conversations through a process called “switching.” Leased lines most commonly are rented by businesses to connect branch offices, because these lines guarantee bandwidth for network traffic. So-called T1 leased lines are common and offer the same data rate as symmetric DSL (1.544 Mbps). Individuals can theoretically also rent leased lines for high-speed Internet access, but their high cost (often more than $1000 USD per month) deters most. Fractional T1 lines, starting at 128 Kbps, reduce this cost somewhat and can be found in some apartment buildings and hotels.Virtual Private Networks (VPNs) are an alternative technology to leased lines. 3.4 SWITCH LINE A switched line allows a physical transmission path to be established and dedicated to a single connection between two points of a network for the duration that the connection lasts. However, the switched network does not have dedicated links between the points or users, and therefore requires extra switching hardware. The switching equipment provides a temporary communication path between the two user terminals, giving the two users exclusive use of the link. The communication path provided by the switched line may vary each time a connection is established between two users.Switched lines are commonly used for ordinary voice telephone systems where the telephone company reserves the established physical path between a caller and the called number. The reservation lasts throughout the call and no one else can use the associated physical lines during this time. A switching device such as a private branch network (PBX) is often used within an organization to provide users with the ability to share a number of external phone lines directly from their extensions. The PBX allows users to access and share a few external lines, and hence eliminates the need to assign each user an individual line.Advantages of a switched line are  Low cost, especially if there is low usage or traffic between terminals.  Provides means to access and connect multiple distant machines. 49 CU IDOL SELF LEARNING MATERIAL (SLM)

 Flexibility since many machines offering different services can be accessed.  Once a breakdown occurs on a connection to a facility, the user or machine can redial and obtain an alternative route to the facility. 3.5 SUMMARY  Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analogue system using analogue signals to transmit voice. With the advent of the computer era, the network, in the 1980s, began to carry data in addition to voice. During the last decade, the telephone network has undergone many technical changes. The network is now digital as well as analogue.  The services offered by the common carriers (telephone companies) inside a LATA are called intra-LATA services. The carrier that handles these services is called a local exchange carrier (LEC). Before the Telecommunications Act of 1996 (see Appendix E), intra-LATA services were granted to one single carrier. This was a monopoly. After 1996, more than one carrier could provide services inside a LATA. The carrier that provided services before 1996 owns the cabling system (local loops) and is called the incumbent local exchange carrier (ILEC). The new carriers that can provide services are called competitive local exchange carriers (CLECs).  Intra-LATA services can be provided by several LECs (one ILEC and possibly more than one CLEC). We also said that inter-LATA services can be provided by several IXCs. How do these carriers interact with one another? The answer is, via a switching office called a point of presence (POP). Each IXC that wants to provide interLATA services in a LATA must have a POP in that LATA.  In the beginning, this task was performed by human operators. The operator room was a center to which all subscribers were connected. A subscriber who wished to talk to another subscriber picked up the receiver (off-hook) and rang the operator. The operator, after listening to the caller and getting the identifier of the called party, connected the two by using a wire with two plugs inserted into the corresponding two jacks. A dedicated circuit was created in this way. One of the parties, after the conversation ended, informed the operator to disconnect the circuit. This type of signalling is called in-band signalling because the same circuit can be used for both signalling and voice communication. Later, the signalling system became automatic. Rotary telephones were invented that sent a digital signal defining each digit in a multi digit telephone number.  The nature of signalling makes it more suited to a packet-switching network with different layers. For example, the information needed to convey a telephone address 50 CU IDOL SELF LEARNING MATERIAL (SLM)