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1. MODULE 1: DATA COMMUNICATIONS Presented By MS. J. Swarnalakhshmi Assistant professor-I , CSE, Hits

2. CONTENTS Components Direction of Data flow N etworks Components and Categories T ypes of Connections Topologies Protocols and Standards ISO / OSI model Transmission Media Coaxial Cable – Fiber Optics – Line Coding – Modems.

3. What is Computer Network? A computer network is a set of devices connected through links. A node can be a computer, printer, or any other device capable of sending or receiving the data. The links connecting the nodes are known as communication channels. Computer Network uses distributed processing in which task is divided among several computers. Instead, a single computer handles an entire task, each separate computer handles a subset.

4. Computer Network Components Computer network components are the major parts that are needed to install the software. Some important network components are NIC, switch, cable, hub, router, and modem . Depending on the type of network that we need to install, some network components can also be removed. For example, the wireless network does not require a cable.

5. NIC A NIC (network interface controller) card, also known as a network adaptor or network interface card, is a circuit board that is installed on a computer to connect to the network. 

6. Switch

7. Hub A hub is a multi-port repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices.  In other words, the  collision domain  of all hosts connected through Hub remains one.  Also, they do not have the intelligence to find out the best path for data packets which leads to inefficiencies and wastage.

8. Router

9. Modem A modem in computer networks is an electronic device designed to facilitate the conversion of digital signals into analog signals and vice versa. Its primary purpose is to transmit data through various communication channels, including telephone lines, cable lines, or wireless networks. The modem possesses the ability to encode digital signals into an analog format for transmission over the communication channel. Upon reaching the receiving modem, the analog signal is decoded back into digital signals, which can be understood and processed by computers or other digital devices.

10. Modem

11. Network Components

12. DATA COMMUNICATIONS When we communicate, we are sharing information. This sharing can be local or remote. Local communication usually occurs face-to-face between individuals, while remote communication occurs over distance. The term telecommunication, which includes telephony, telegraphy, and television, means communication at a distance (tele is Greek for "far"). The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs). The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness, and jitter.

13. Four Fundamental Characteristics I. Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. 2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. 3. Timeliness. The system must deliver data on time. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. 4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 3D-ms. If some of the packets arrive with a 3D-ms delay and others with a 4D-ms delay, an uneven quality in the video is the result.

14. Components

15. A data communications system has five components 1. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2. Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. 3. Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5. Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

16. Data Representation Information today comes in different forms such as text, numbers, images, audio, and video.

17. Text In data communications, text is represented as a bit pattern, a sequence of bits ( Os or Is). Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the process of representing symbols is called coding. Today, the prevalent coding system is called Unicode, which uses 32 bits to represent a symbol or character used in any language in the world. The American Standard Code for Information Interchange (ASCII) , developed some decades ago in the United States, now constitutes the first 127 characters in Unicode and is also referred to as Basic Latin. Appendix A includes part of the Unicode.

18. Numbers Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the number is directly converted to a binary number to simplify mathematical operations. Images Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution.

19. Images For example, an image can be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better representation of the image (better resolution), but more memory is needed to store the image. After an image is divided into pixels, each pixel is assigned a bit pattern. The size and the value of the pattern depend on the image. For an image made of only black and white dots (e.g., a chessboard), a I-bit pattern is enough to represent a pixel. If an image is not made of pure white and pure black pixels, you can increase the size of the bit pattern to include a grayscale. For example, to show four levels of gray scale, you can use 2-bit patterns. A black pixel can be represented by 00, a dark gray pixel by 01, a light gray pixel by 10, and a white pixel by 11. There are several methods to represent color images. One method is called RGB, so called because each color is made of a combination of three primary colors: red, green, and blue. The intensity of each color is measured, and a bit pattern is assigned to it. Another method is called YCM, in which a color is made of a combination of three other primary colors: yellow, cyan, and magenta.

20. Audio Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal. Video Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion. Again we can change video to a digital or an analog signal.

21. Data Flow Communication between two devices can be simplex, half-duplex, or full-duplex

22. Simplex In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive (see Figure 1.2a). Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.

23. Half-Duplex In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa (see Figure 1.2b). The half-duplex mode is like a one-lane road with traffic allowed in both directions. When cars are traveling in one direction, cars going the other way must wait. In a half-duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time. Walkie-talkies and CB (citizen band) radios are both half-duplex systems. The half-duplex mode is used in cases where there is no need for communication in both directions at the same time; the entire capacity of the channel can be utilized for each direction.

24. Full-Duplex In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously (see Figure 1.2c). The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time. In full-duplex mode, signals going in one direction share the capacity of the link: with signals going in the other direction. This sharing can occur in two ways: Either the link must contain two physically separate transmission paths, one for sending and the other for receiving; or the capacity of the channel is divided between signals traveling in both directions. One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions.

25. Networks A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Distributed Processing Most networks use distributed processing, in which a task is divided among multiple computers. Instead of one single large machine being responsible for all aspects of a process, separate computers (usually a personal computer or workstation) handle a subset. Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security.

26. Network Criteria Performance: Measured using transit time and response time. Transit time: Amount of time required for a message to travel from one device to another. Response time: Elapsed time between an enquiry and a response. Performance depends on the number of users, Type of transmission medium, Capabilities of connected hardware, and Efficiency of software. Performance evaluated by two metrics: Throughput and Delay Reliability: Measured by frequency of failures, time it takes for a link to recover from failures. Security: Protecting data from unauthorized access, from damage and development, implementing policies and procedures for recovery.

27. N etwork attributes Type of Connection A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points. For communication to occur, two devices must be connected in some way to the same link at the same time. There are two possible types of connections: 1. point-to-point and 2. multipoint.

28. Physical Topology Geometric representation Of all the links and linking devices to one another. 4 basic topologies:

29. Mesh networks Every device has a dedicated point-to-point link to every other device. Number of physical links: n(n-1) For full-duplex links, n(n-1)/2 Every device on the network must have (n-1) I/O ports to be connected to n-1 stations.

30. Advantages & Disadvantages of Mesh networks Advantages: Each connection carries its own data load. (Eliminate traffic problems) Mesh topology is robust. Privacy and Security Point-to-point links make fault identification and fault isolation easy.(N/W manager can find precise fault location and aids in finding the cause and solution) . Disadvantages: Amount of cabling and no. of I/O ports used Installation and re-connection are difficult Sheer bulk of cabling can be greater than available space H/w required to connect each link can be very expensive Usually implemented in limited fashion Example: Connection of telephone regional offices.

31. Star topology Each device have a dedicated point-to-point link only to central controller(Hub). Devices are not directly linked to one another. Does not allow direct traffic between devices. Controller acts as exchange.

32. Advantages & Disadvantages of Star topology ADVANTAGES : Less expensive(1link & 1 I/O port) Easy to install and reconfigure Addition, moves, and deletion easy. Robust Easy fault identification and isolation DISADVANTAGES: If hub goes down whole system is dead. More cables required compared to Bus and Ring

33. Bus topology Multi-point connection Long cable acts as backbone to all connecting devices. Nodes are connected to bus cable by drop lines and Taps. Tap is connector that either splices into the main cable or punctures the sheathing of a cable to create contact with metallic core.

34. Advantages & Disadvantages of Bus topology ADVANTAGES : Ease of installation. Less cabling Redundancy is eliminated. DISADVANTAGES : Difficult reconnection and fault isolation Signal reflection at the taps cause degradation in quality. Adding new devices require modification or replacement of the backbone. Fault or break in the bus cable stops all transmission. Signal becomes weaker as it travels farther. Used in LAN

35. Ring topology Each device has a dedicated point-to-point connection with only 2 devices on either side. Each device incorporates a Repeater.

36. Advantages & Disadvantages of Ring topology ADVANTAGES: Easy to install and reconfigure Fault isolation is simplified. DISADVANTAGES: Media and traffic considerations( Max. ring length and no. of devices) Unidirectional traffic. A break in the ring can disable the entire network. Less popular due to the need for high-speed LANs.

37. Hybrid topology Combination of star and bus topology.

38. Categories of networks Determined by size of the network. LAN(Local Area Network)- area less than 2 miles WAN(Wide Area Network)-worldwide. In-between are normally referred to as MAN(Metropolitan area network)

39. Local area networks Privately owned. Links devices in a single office, building or campus. Can be single connection between 2 PCs and a printer or can be extended throughout a company. Size limited to few kilometers. Allow resources to be shared between personal computers and workstations. LAN also distinguished by their transmission media and topology Common are bus, ring and star. Data rates 4-16 Mbps. Now speeds are generally 100 or 1000Mbps. WLAN came later.

40. Local area networks

41. Wide area network Provides long-distance transmission of data, image,audio and video info over large geographic areas. Backbone that connect the internet- switched WAN. Dial-up line that connects home computer to internet.-Point-to-point WAN. Switched WAN connects end-systems to another LAN or WAN. Point-to-point connects home computer or small LAN to Internet Service Provider.

42. Wide area network

43. Metropolitan area network Size between Lan and WAN. Covers area inside town or city.

44. Internet-Interconnection of Networks

45. Protocols and standards Key elements: Syntax, Semantics and timing.

46. OSI Model OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI consists of seven layers, and each layer performs a particular network function. OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications. OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. Each layer is self-contained, so that task assigned to each layer can be performed independently.

47. Characteristics of OSI Model:

48. Characteristics of OSI Model: The OSI model is divided into two layers: upper layers and lower layers. The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications. An upper layer refers to the layer just above another layer. The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.

49. 7 Layers of OSI Model There are the seven OSI layers. Each layer has different functions. A list of seven layers are given below: Physical Layer Data-Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer

50. 7 Layers of OSI Model

51. 1) Physical layer

52. 1) Physical layer The main functionality of the physical layer is to transmit the individual bits from one node to another node. It is the lowest layer of the OSI model. It establishes, maintains and deactivates the physical connection. It specifies the mechanical, electrical and procedural network interface specifications.

53. Functions of a Physical layer: Line Configuration:  It defines the way how two or more devices can be connected physically. Data Transmission :  It defines the transmission mode whether it is simplex, half-duplex or full-duplex mode between the two devices on the network. Topology :  It defines the way how network devices are arranged. Signals:  It determines the type of the signal used for transmitting the information.

54. 2) Data-Link Layer

55. Data-Link Layer This layer is responsible for the error-free transfer of data frames. It defines the format of the data on the network. It provides a reliable and efficient communication between two or more devices. It is mainly responsible for the unique identification of each device that resides on a local network.

56. Two sub-layers It contains two sub-layers: Logical Link Control Layer It is responsible for transferring the packets to the Network layer of the receiver that is receiving. It identifies the address of the network layer protocol from the header. It also provides flow control. Media Access Control Layer A Media access control layer is a link between the Logical Link Control layer and the network's physical layer. It is used for transferring the packets over the network.

57. Functions of the Data-link layer Framing:  The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address. Physical Addressing:  The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header. Flow Control:  Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed. Error Control:  Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occur, then the receiver sends the acknowledgment for the retransmission of the corrupted frames. Access Control:  When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time.

58. 3) Network Layer

59. Network Layer It is a layer 3 that manages device addressing, tracks the location of devices on the network. It determines the best path to move data from source to the destination based on the network conditions, the priority of service, and other factors. The Data link layer is responsible for routing and forwarding the packets. Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an internetwork. The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6.

60. Functions of Network Layer: Internetworking:  An internetworking is the main responsibility of the network layer. It provides a logical connection between different devices. Addressing :  A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet. Routing :  Routing is the major component of the network layer, and it determines the best optimal path out of the multiple paths from source to the destination. Packetizing:  A Network Layer receives the packets from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP).

61. 4) Transport Layer

62. Transport Layer The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no duplication of data. The main responsibility of the transport layer is to transfer the data completely. It receives the data from the upper layer and converts them into smaller units known as segments. This layer can be termed as an end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably.

63. The two protocols used in this layer are: Transmission Control Protocol It is a standard protocol that allows the systems to communicate over the internet. It establishes and maintains a connection between hosts. When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end. User Datagram Protocol User Datagram Protocol is a transport layer protocol. It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable.

64. Functions of Transport Layer: Service-point addressing:  Computers run several programs simultaneously due to this reason, the transmission of data from source to the destination not only from one computer to another computer but also from one process to another process. The transport layer adds the header that contains the address known as a service-point address or port address. The responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of the transport layer is to transmit the message to the correct process. Segmentation and reassembly:  When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers.

65. Functions of Transport Layer: Connection control:  Transport layer provides two services Connection-oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route. Flow control:  The transport layer also responsible for flow control but it is performed end-to-end rather than across a single link. Error control:  The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error.

66. 5) Session Layer

67. Session Layer It is a layer 3 in the OSI model. The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices. Functions of Session layer: Dialog control:  Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either half-duplex or full-duplex. Synchronization:  Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery.

68. 6) Presentation Layer

69. Presentation Layer A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems. It acts as a data translator for a network. This layer is a part of the operating system that converts the data from one presentation format to another format. The Presentation layer is also known as the syntax layer.

70. Functions of Presentation layer: Translation:  The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end. Encryption:  Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network. Compression:  Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video.

71. 7) Application Layer

72. Application Layer An application layer serves as a window for users and application processes to access network service. It handles issues such as network transparency, resource allocation, etc. An application layer is not an application, but it performs the application layer functions. This layer provides the network services to the end-users.

73. Functions of Application layer: File transfer, access, and management (FTAM):  An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. Mail services:  An application layer provides the facility for email forwarding and storage. Directory services: An application provides the distributed database sources and is used to provide that global information about various objects.

74. Figure: The interaction between layers in the OSI model

75. Figure: An exchange using the OSI model

76. Network – OSI models Layer Responsible For: 7.) Application Provides Services to User Apps 6.) Presentation Data Representation 5.) Session Communication Between Hosts 4.) Transport Flow Ctrl, Error Detection/Correction 3.) Network End to End Delivery, Logical Addr 2.) Data Link Media Access Ctrl, Physical Addr 1.) Physical Medium, Interfaces, Puts Bits on Med.

77. Examples Layer Example 7.) Application HTTP, FTP, SMTP 6.) Presentation ASCII, JPEG, PGP 5.) Session BOOTP, NetBIOS, DHCP, DNS 4.) Transport TCP, UDP, SPX 3.) Network IP, IPX, ICMP 2.) Data Link Ethernet, Token Ring, Frame Relay 1.) Physical Bits, Interfaces, Hubs

78. Transmission media 6 February 2024 78

79. Transmission Media Guided Medium Twisted-Pair cable (metallic) Co-axial cable (metallic) Fiber-optic cable(light) Unguided Medium (Wireless) Radio Waves Microwaves Infrared 6 February 2024 79

80. Transmission Media 6 February 2024 80

81. Transmission Media 6 February 2024 81 Categories: 7 types Connectors: RJ45(registered jack) Performance: Attenuation Vs Frequency and distance Application: Used in telephone lines

82. Co-axial Cable(coax) Categories: 6 February 2024 82

83. Carries signal of higher frequency ranges. It has a central core conductor of solid or stranded wire enclosed in insulating sheath. BNC Connector( Bayone Neill Concelman ) 6 February 2024 83

84. Coaxial Cable - Transmission Characteristics superior frequency characteristics to TP performance limited by attenuation & noise analog signals amplifiers every few km closer if higher frequency up to 500MHz digital signals repeater every 1km closer for higher data rates

85. Co-axial cable connectors Bayone -Neill- Concelman (BNC) connectors 6 February 2024 85

86. Fiber-optic cable Made of glass or plastic and transmits signals in the form of light. Bending of light ray 6 February 2024 86

87. Angle of Incidence- The angle the ray makes with the line perpendicular to the interface between the two substances. Angle of incidence < critical angle, ray refracts and moves closer to the surface Angle of incidence= critical angle, light bends along the interface. Angle> critical angle, ray reflects and travels again the denser surface. Optical fiber uses reflection to guide light through a channel. 6 February 2024 87

88. A glass or plastic core is surrounded by a cladding of less dense glass or plastic. The difference in density should be such that beam of light is reflected off instead of being refracted. 6 February 2024 88

89. PROPAGATION MODES: Multimode -Multiple beam from a light source move through the core in different paths. Step index: Density of core remain constant from center to edges. Beam of light move through a constant density in a straight line There is abrupt change in density at the interface. 6 February 2024 89

90. Graded-index: Varying densities. Index of refraction is related to densities. Density is the highest at the center and lowest towards the edges. Single-mode: Uses step-index. Highly focused source of light that limits beam to a small range of angles, all close to horizontal. Small diameter, substantially lower density. 6 February 2024 90

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92. Fiber sizes 6 February 2024 92

93. Ratio of diameter of the core to the diameter of the cladding. CABLE CONNECTORS: Subscriber-channel connector(SC)-used in cable TV. Uses push/pull locking system. Straight-tip connector(ST)-connecting cable to network devices.uses Bayonate locking system. MT-RJ Connector 6 February 2024 93

94. Optical Fiber - Transmission Characteristics uses total internal reflection to transmit light effectively acts as wave guide for 10 14 to 10 15 Hz can use several different light sources Light Emitting Diode (LED) cheaper, wider operating temp range, lasts longer Injection Laser Diode (ILD) more efficient, has greater data rate relation of wavelength, type & data rate

95. applications Self Study.. 6 February 2024 95

96. advantages Higher Bandwidth Less signal Attenuation Immunity to Electromagnetic Interference Resistance to Corrosive Materials Light weight Greater Immunity to Tapping. 6 February 2024 96

97. disadvantages Installation and Maintenance Cost Unidirectional light propagation 6 February 2024 97

98. Digital-to-digital conversion We can represent digital data by using digital signals. The conversion involves 3 techniques. Line coding Block coding Scrambling 6 February 2024 98

99. Line coding Line Coding is a process of converting digital data to digital signals.(Sequence of bits to digital signals) Digital data are encoded into digital signals at the sender; Digital data are recreated by decoding the digital signal at the receiver. 6 February 2024 99

100. characteristics Signal element Versus Data Element: Signal element is the shortest unit of digital signal; Data element is the smallest entity that can represent a piece of information. Signal element carries data element(what we can send); Data elements are what we need to send. Data elements- carried; Signal elements are carriers. R-No. of data elements carried by each signal element. 6 February 2024 100

101. characteristics 6 February 2024 101

102. Data rate Versus Signal rate: 6 February 2024 102

103. BANDWIDTH:Bandwidth is proportional to the signal rate. 6 February 2024 103

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106. Line coding schemes 6 February 2024 106