Data Communication and Network - Transmission Medium and Switching

Data Communication and Network - Transmission Medium and Switching

1. Transmission Medium and Switching Chapter-2 Mr. C. P. Divate Department of Computer Engineering

2. What is Topology? Topology defines the structure of the network of how all the components are interconnected to each other. There are two types of topology: physical and logical topology. Physical topology is the geometric representation of all the nodes in a network.

3. Bus Topology The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable. Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable. When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not.

4. Bus Topology The bus topology is mainly used in 802.3 ( ethernet ) and 802.4 standard networks. The configuration of a bus topology is quite simpler as compared to other topologies. The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations. The most common access method of the bus topologies is CSMA (Carrier Sense Multiple Access).

5. Bus Topology This network requires Coaxial cable as backbone cable and BNC connectors to join each node. Each node can be connected to backbone cable using T Type BNC connector.

6. Bus Topology This network requires Coaxial cable as backbone cable and BNC connectors to join each node. Each node can be connected to backbone cable using T Type BNC connector.

7. Bus Topology The network can expand with another bus network simple by joining using connectors. At the end of cable there is a necessity to connect cable terminator to avoid the data signal loss.

8. Bus Topology CSMA( Carrier Sense Multiple Access) : It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost.

9. Bus Topology CSMA( Carrier Sense Multiple Access) : It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost.

10. Bus Topology CSMA( Carrier Sense Multiple Access) : It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost.

11. Bus Topology There are two alternative ways of handling the problems that occur when two nodes send the messages simultaneously. CSMA CD:  CSMA CD ( Collision détection ) CSMA CA:   CSMA CA (Collision Avoidance)

12. Bus Topology CSMA/CD:  CSMA/CD ( Collision détection ): CSMA CD (Collision detection) is an access method used to detect the collision. Once the collision is detected, the sender will stop transmitting the data. Therefore, it works on "recovery after the collision".

13. Bus Topology CSMA CA: CSMA CA (Collision Avoidance): is an access method used to avoid the collision by checking whether the transmission media is busy or not. If busy, then the sender waits until the media becomes idle. This technique effectively reduces the possibility of the collision. It does not work on "recovery after the collision".

14. Bus Topology Advantages of Bus topology: Low-cost cable: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low. Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps. Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available. Limited failure: A failure in one node will not have any effect on other nodes. It is easy to set up, handle, and implement. It is best-suited for small networks. It costs very less.

15. Bus Topology Disadvantages of Bus topology: Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling. Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes. Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other. Reconfiguration difficult: Adding new devices to the network would slow down the network. Attenuation: F or long distance data flow attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal. Small network: It is applicable to design small LAN with limited Computers as node. Less secured: Each device on the network “sees” all the data being transmitted, thus posing a security risk . It is heavily dependent on the central bus. A fault in the bus leads to network failure . It is suitable for networks with low traffic. High traffic increases load on the bus, and the network efficiency drops . This network topology can perform well only for a limited number of nodes. When the number of devices connected to the bus increases, the efficiency decreases . The cable length is limited. This limits the number of network nodes that can be connected.

16. Ring Topology Ring topology is like a bus topology, but with connected ends. The node that receives the message from the previous computer will retransmit to the next node. It has no terminated ends, i.e., each node is connected to other node and having no termination point.

17. Ring Topology The data flows in one direction, i.e., it is unidirectional. The data flows in a single loop continuously known as an endless loop. The data in a ring topology flow in a clockwise direction.

18. Ring Topology The most common access method of the ring topology is token passing. Token passing: It is a network access method in which token is passed from one node to all other nodes network before accessing the media. Token: It is a test frame that circulates around the network. Failure of any host results in failure of the whole ring. Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring.

19. Ring Topology Working of Token passing A token moves around the network, and it is passed from computer to computer until it reaches the destination. The sender modifies the token by putting the address along with the data. The data is passed from one device to another device until the destination address matches. Once the token received by the destination device, then it sends the acknowledgment to the sender. In a ring topology, a token is used as a carrier.

20. Ring Topology Advantages of Ring topology: The data being transmitted between two nodes passes through all the intermediate nodes. A central server is not required for the management of this topology. The traffic is unidirectional and the data transmission is high-speed. In comparison to a bus, a ring is better at handling load. The adding or removing of network nodes is easy, as the process requires changing only two connections. The configuration makes it easy to identify faults in network nodes. In this topology, each node has the opportunity to transmit data. Thus, it is a very organized network topology. It is less costly than a star topology .

21. Ring Topology Advantages of Ring topology: Network Management: Faulty devices can be removed from the network without bringing the network down. Product availability: Many hardware and software tools for network operation and monitoring are available. Cost: Twisted pair cabling is inexpensive and easily available. Therefore, the installation cost is very low. Reliable: It is a more reliable network because the communication system is not dependent on the single host computer.

22. Ring Topology Disadvantages of Ring topology: Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes. Failure: The breakdown in one station leads to the failure of the overall network. Reconfiguration difficult: Adding new devices to the network would slow down the network. Delay: Communication delay is directly proportional to the number of nodes. Adding new devices increases the communication delay. Small network: It is applicable to design small LAN with limited Computers as node. Less Security: Data sent from one node to another has to pass through all the intermediate nodes. This makes the transmission slower in comparison to that in a star topology. The movement or changes made to network nodes affect the entire network’s performance. The transmission speed drops with an increase in the number of nodes. There is heavy dependency on the wire connecting the network nodes in the ring .

23. Star Topology Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer. Star topology is the most popular topology in network implementation. Hubs or Switches are mainly used as connection devices in a physical star topology.

24. Star Topology UTP cable and RJ-45 (Registered Jack-45 ) connectors are used to connect the computers. UTP cable CAT5 cable is required for making connection between computer and switch using RJ45 Connector. The central switch is required, to connect computers.

25. Star Topology Crimping Connections Straight Trough Connection. Cross Over Connection

26. Star Topology Cable connectivity between networking devices

27. Star Topology Operation of HUB and Switch Switch

28. Star Topology Operation of Router in network

29. Star Topology Operation of Router in network

30. Star Topology Cable connectivity between networking devices

31. Star Topology Simple operations: Due to its centralized nature, the topology offers simplicity of operation. Isolate path: It also achieves isolation of each device in the network. Easy Updates: Adding or removing network nodes is easy, and can be done without affecting the entire network. Easy fault Detect and correction: Due to the centralized nature, it is easy to detect faults in the network devices. More security: As the analysis of traffic is easy, the topology poses lesser security risk. Traffic control: Data packets do not have to pass through many nodes, like in the case of a ring network. Thus, with the use of a high-capacity central hub, traffic load can be handled at fairly decent speeds. Limited failure/ More Reliable: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network. Familiar technology: Star topology is a familiar technology as its tools are cost-effective. Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub. Cost effective: Star topology networks are cost-effective as it uses inexpensive UTP cable. High data speeds: It supports a bandwidth of approx. 100Mbps. Ethernet 100BaseT is one of the most popular Star topology networks. Advantages of Star Topology:

32. Star Topology A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other. Cable : Sometimes cable routing becomes difficult when a significant amount of routing is required. Disadvantages of Star Topology:

33. Tree topology Tree topology is a type of network topology in which the nodes are arranged in the design of a tree Tree topology combines the characteristics of bus topology and star topology. A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion. The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node. There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy . As the leaf nodes can add one or more nodes in the hierarchical chain, this topology provides high scalability.

34. Tree Topology Support for broadband transmission: Tree topology is mainly used to provide broadband transmission, i.e., signals are sent over long distances without being attenuated. Easily expandable: We can add the new device to the existing network. Therefore, we can say that tree topology is easily expandable. Easily manageable: In tree topology, the whole network is divided into segments known as star networks which can be easily managed and maintained. Error detection: Error detection and error correction are very easy in a tree topology. Limited failure: The breakdown in one station does not affect the entire network. Point-to-point wiring: It has point-to-point wiring for individual segments. Advantages of Tree Topology:

35. Tree Topology Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem. High cost: Devices required for broadband transmission are very costly. Failure: A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network. Reconfiguration difficult: If new devices are added, then it becomes difficult to reconfigure. Disadvantages of Tree Topology:

36. Mesh topology Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections. There are multiple paths from one computer to another computer. It does not contain the switch, hub or any central computer which acts as a central point of communication. Mesh topology can be formed by using the formula: Number of cables = (n*(n-1))/2 ; Where n is the number of nodes that represents the network.

37. Mesh topology in WAN / Internet The Internet is an example of the mesh topology. Mesh topology is mainly used for WAN implementations where communication failures are a critical concern. Mesh topology is mainly used for wireless networks .

38. Types of Mesh topology Mesh topology is divided into two categories: Fully connected mesh topology Partially connected mesh topology Full Mesh Topology: In a full mesh topology, each computer is connected to all the computers available in the network. Partial Mesh Topology: In a partial mesh topology, not all but certain computers are connected to those computers with which they communicate frequently.

39. Mesh Topology Reliable: The mesh topology networks are very reliable as if any link breakdown will not affect the communication between connected computers. Fast Communication: Communication is very fast between the nodes. Easier Reconfiguration: Adding new devices would not disrupt the communication between other devices . Less congestion: As there are several paths for communication so data can pass through any path in network. Less Cost: As wireless routers can establish mess topology, hence the cost of cable is reduced. Portable: Mesh topology network can be established at any location or site. Advantages of Mesh Topology:

40. Mesh Topology Cost : A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies. Management: Mesh topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected. Efficiency: In this topology, redundant connections are high that reduces the efficiency of the network . Administration: there is a need of network administration for monitoring and maintenance of mesh network. Security: network can be accessed by any person if not provide security like password. Complex: Owing to its complexity, the administration of a mesh network is difficult. Disadvantages of Mesh Topology:

41. Hybrid topology The combination of two or more different topologies in one network is known as Hybrid topology. A Hybrid topology is a connection between different links (coaxial cable, CAT, optical fiber, Wireless etc.) and nodes to transfer the data. When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology.

42. Hybrid Topology Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the network. Scalable: Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network. Flexible: This topology is very flexible as it can be designed according to the requirements of the organization. Effective: Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and weakness of the network is minimized. Advantages of Hybrid Topology:

43. Hybrid Topology Complex design: The major drawback of the Hybrid topology is the design of the Hybrid network. It is very difficult to design the architecture of the Hybrid network. Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other topologies. Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc . Management : Hybrid topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected. Administration: there is a need of network administration for monitoring and maintenance of mesh network. Security: network can be accessed by any person if not provide security like password. Disadvantages of Topology :

44. OSI Reference 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.

45. 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 . OSI Reference Model 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link Layer 1. Physical Layer

46. The OSI model is divided into two layers: upper layers and lower layers . Upper Layer: 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 combination just above lower layer. Lower 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. Characteristics of OSI Model: Upper layer Lower layer

47. 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 Functions of the OSI Layers in OSI Model:

48. 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. Physical layer Host-1 Host-2

49. Line Configuration: It defines the way how two or more devices can be connected physically (Wired/Wireless). 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 . Encoding: Digital to Analog / Light signal conversion at sender host for respective transmission medium Coaxial, Ethernet and Wi-Fi / Fiber Optic cable. Decoding: Analog / Light to Digital signal conversion at Receiver host for respective transmission medium Coaxial, Ethernet and Wi-Fi / Fiber Optic cable . Functions of a Physical layer:

50. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc . Components of a Physical layer: 1) Cables 1) Connectors Bayonet Neill– Concelman ) registered jack 1) Connectors Name SC- subscriber connector LC- Line Construction FC- Ferrule Connector or Fiber Channel ST- straight tip

51. Components of a Physical layer: Electromagnetic spectrum for type of signal on Transmission Medium on network

52. Components of a Physical layer: AS per requirement of speed of data transmission Network designer have to select type of cable for computer network

53. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc. Components of a Physical layer: 2 ) Network Interface Card ( NIC ) in HOST RJ45 Connector Port BNC Connector Port Fiber cable Connector Port Wi-Fi Connector Port

54. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc. Components of a Physical layer: 3) Repeater

55. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc. Components of a Physical layer: 4 ) HUB

56. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc. Components of a Physical layer: 5) Switch

57. Components of a Physical layer: 7 ) Bridge

58. Components of a Physical layer: 6 ) Bridge

59. Components of a Physical layer: 6 ) Router

60. Router Components of a Physical layer:

61. Components of a Physical layer: 6 ) Router works in Unicast an Multicast Mode

62. Components of a Physical layer: 7 ) Gateway

63. Examples of hardware in the physical layer are Cables, network adapters, ethernet , repeaters, networking hubs, switches, brides and routers etc. Components of a Physical layer: Repeater 1 ) Repeater / Hub 2 ) Switch 3) Router 4 ) Gateway

64. Physical characteristics of interfaces and medium : the purpose of the physical layer is to transport a raw bit stream from one machine to another . Various physical media can be used for the actual transmission. Each one has its own position in terms of bandwidth, delay, cost, and ease of installation and maintenance . Representation of bits : The physical layer data consists of a stream of bits (sequence of 0’s or 1’s) with no interpretation. To be transmitted, bits must be encoded into signals--electrical or optical. The physical layer defines the type of encoding (how 0’s and 1’s are changed to signals ). Data rate : The transmission rate-the number of bits sent each second-is also defined by the physical layer. In other words, the physical layer defines the duration of a bit, which is how long it takes for transmission over transmission medium . Functions of a Physical layer in details: Major duties of the physical layer are as follows :

65. Synchronization of bits : The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level. In other words, the sender and the receiver clocks must be synchronized . Line configuration : The physical layer is concerned with the connection of devices to the media. In a point-to-point configuration, two devices are connected through a dedicated link. In a multipoint configuration, a link is shared among several devices. Physical topology : The physical topology defines how devices are connected to make a network. Devices can be connected by using a mesh topology (every device is connected to every other device) A star topology (devices are connected through a central device) A ring topology (each device is connected to the next, forming a ring) A bus topology (every device is on a common link) A hybrid topology (this is a combination of two or more topologies ). Functions of a Physical layer in details:

66. T ra n sm i s sion mo d e : T he ph y s ical la y er al s o de f ines the direction o f transmission between two devices : Simplex Half-duplex Full-duplex. In s i m plex m o d e , o n l y one de v i c e c an s end and the other can o n l y r e ceive . T he simplex mode is a one-way communication. In the half-duplex mode, two devices can send and receive, but not at the same time. In a full-duplex (or simply duplex) mode, two devices can send and receive at the same time . Functions of a Physical layer in details:

67. Media is a general term used to describe the data path that forms the physical channel between sender and receiver. Transmission media can be twisted pair wire such as that used for telephone installation, wire media are referred to as Bounded Media and wireless media are sometimes referred to as Unbounded Media . Bandwidth , noise, radiation and attenuation are considered while using the different transmission media. Higher bandwidth transmission media supports higher data rates. Attenuation limits the usable distance that data can travel on the media. Noise is related to electrical signal noise that can cause distortion of the data signal and data errors.

68. 1 4 Radiation is the leakage of signal from the media caused by undesirable electrical characteristic of the transmission media. The transmission medium is the physical path between transmitter and receiver in a data transmission system. In transmission medium, communication is in the form of electromagnetic waves. The characteristics and quality of transmission are determined both by the characteristics of the medium and the characteristics of signal.

69. Design Factors: Bandwidth : The greater the bandwidth the higher the data rate can be achieved. Transmission Impairments : such as attenuation, limit the distance (repeater spacing) for guided media. Twisted pair generally suffer more impairment than co-axial cable. Interference Number of Receivers Guided or Unguided Media : D ep e n ding on t h e t y pe of a p p lic a t ion and geographical sit u a t ion s u i t a b l e guided or unguided media is chosen. For long distance point-to-point transmission guided media are suitable. For long distance broadcasting transmission unguided media are chosen .

70. TP is least expensive and most widely used. TP consists of two insulated copper wire arranged in regular spiral pattern. A wire pair act as a signal communication link. TP may used to transmit both analog and digital signals. For analog signal amplifiers are required about every 5 to 6 km. for digital signals, repeaters are required every 2 or 3 km . TP is most commonly used medium for in the telephone network. Compared to other commonly used transmission media, TP is limited in distance, bandwidth and data rate when two copper wire conduct electric signal in close proximity, a certain amount of electromagnetic inference occurs (EMI). This type of inference is called Cross Talk. Twisting the copper wire reduces cross talk. Twisted pair cable comes in two varieties. Unshielded twisted pair (UTP) cable. Shielded twisted pair (STP) cable.

71. 1 8 UTP is a set of twisted pairs of cable within a plastic sheet. UTP is ordinary telephone wire. This is the least expensive of all the transmission media commonly used for LAN, and is easy to work with and simple to install. UTP is subject to external electromagnetic inference. Category 3 and category 5 UTP are commonly used in computer networks . UTP can transfer data at 1 to 100 Mbps over a distance of 100 meters. The difference between cat3 and cat5 cable is the number of twists in the cable per unit distance cat5 is much more tightly twisted . TP cable contains eight separate wires with four pairs. Four of them are solid colors (Blue, Green, Orange and Brown), while the other four are striped with white.

72. Category 5 : Used in local network. It supports upto 100 Mbps data transmission speed . Category 4 : It support transmission speed of 16 Mbps and three twist per foot . Category 3 : It supports data transmission speed upto 10 Mbps. Atleast three twist per feet and used in telephone system . Category 2 : It supports data transmission speed upto 4 Mbps and suitable for voice data transmission . Category 1 : mostly used in telephone system. Cat1 is suitable for voice and low speed data communication. 1 8

73. 1 8

74. CHARACTERISTICS OF UTP : Transmission rate of 10-100 Mbps . UTP is less expensive than FOC and co-axial cable . Maximum cable segment of UTP is 100 meters. UTP cable is very flexible and easy to work. Most susceptible to electrical interference or cross talk. ADVANTAGES OF UTP : UTP is easy to terminate. Cost of installation is less. High installed base. DISADVANTAGES OF UTP : It is very noisy. It covers less distance. UTP suffers from interference.

75. APPLICATION OF TP CABLES : Twisted Pair can used for both analog and digital signals. Twisted Pair cable are used in telephone network. In LAN, TP wires mainly use for low cost, low performance application. STP offers a protective sheathing around the copper wire. STP provides better performance at lower data rates. They are not commonly used in networks. Installation of STP is easy. Special connectors are required for installation. Cost is moderately expensive. Distance is limited to 100 meters for 500 meters. STP suffers from outside interference but not as much UTP .

76. RJ45 is a type of connector commonly used for Ethernet networking. It looks similar to a telephone jack, but is slightly wider. Since Ethernet cables have an RJ45 connector on each end, Ethernet cables are sometimes also called RJ45 cables. The "RJ" in RJ45 stands for "registered jack," since it is a standardized networking interface. Each RJ45 connector has eight pins, which means an RJ45 cable contains eight separate wires. Four of them are solid colors (Blue, Green, Orange and Brown), while the other four are striped with white. Connector for Twisted Pair Cable RJ45

77. Crimping of Twisted Pair Cable RJ45 Click to see the video Click to see how to Crimp Twisted Pair Cable with RJ45 connector RJ45 cables can be wired in two different ways. One version is called T-568A and the other is T-568B. These wiring standards are listed below:

78. It is made up of two conductors that shares the common axis. It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. Coaxial cable is used to transmit both analog and digital signals . Data transfer rate of coaxial cable is in between TP and FOC. It is relatively inexpensive. The cost for thin coaxial cable is less than STP. Thick coaxial cable must be grounded and terminated. A typical data rate for today’s coaxial network is 10 Mbps, although potential is higher. It suffers from attenuation.

79. Coaxial cable is classified by size (RG) and by the cable resistance to direct or alternative electric currents. RG means Rating Government. 50 ohm, RG-8 and RG-11 for thick Ethernet. 50 ohm, RG-58 used for thin Ethernet. 75 ohm, RG-59 used for cable TV. 93 ohm, RG-62 used for ARC net

80. CHARACTERISTICS OF CO-AXIAL CABLE : 10 Mbps is transmission rate . Ma x i m um ca b l e l e ng t h f or th i nn e t i s 185 m e t e r s a nd th ick n e t i s 500 meters. Flexible and easy to work with thinnet for small distance . Ethernet designation to 10 base 2 (thinnet) or 10 base 5 ( thicknet ). Less expensive than FOC but more expensive than TP. Good resistance to electrical interference . APPLICATION OF CO-AXIAL CABLE : In analog and digital transmission. In telephone networks. In Ethernet LANs. In cable TV network.

81. ADVANTAGES OF CO-AXIAL CABLE : Coaxial cable used for both data transmission i.e. analog and digital data transmission. It has higher bandwidth. Easy to handle and relatively inexpensive as compared to FOC. It uses for longer distance at higher data rates. Excellent noise immunity. DISADVANTAGES OF CO-AXIAL CABLE : Distance is limited. Number of nodes connection is limited. Proper connectors and termination is must.

82. Coaxial cable connectors are used to connect cables to other devices. High-quality connectors offer reliable, long-lasting connections . There are two distinct connector styles; male and female. Male connectors have a protruding metal pin in the center, whereas female connectors have a receptacle to receive that pin. Within digital, video, audio, RF, and microwave industries, there are several varieties of coaxial cable connector types. Type of Connectors for Coaxial cable Following are the types of Coaxial Cables, BNC Bayonet Neil- Concelman (BNC)- Originally designed for military use. The coaxial connector used for quick connect/disconnect in RF equipment and test instruments like radio, television, and video signal. are best suited for frequencies below 4GHz,

83. Type of Connectors for Coaxial cable TNC Threaded Neil- Concelman ( T NC )- It is the threaded version of a BNC connector. It performs better microwave frequencies than BNC connectors. TNC Connectors are weatherproof, miniature units that operate up to 12 GHz and are commonly used in cellular phone and RF/antenna connections to resolve leakage and stability issues

84. Striping of Coaxial Cable RJ45 Click to see the video Click to see how to striping coaxial Cable with BNC connector

85. Fiber optic cable is a cable that uses light signals for communication. Fiber optic is a cable that holds the optical fibers coated in plastic that are used to send the data by pulses of light. Fiber optics provide faster data transmission than copper wires. It is a light pipe which is used to carry a light beam from one place to another place. Light is an electromagnetic signal and can be modulated by information. since the frequency of light is extremely high hence it can be achieved with excellent reliability. The modulated light travel along the fiber and at the far end, are converted to an electrical signal by means of a photo electric cell. Thus the original input signal is recovered at the far end .

86. Basic elements of Fiber optic cable: Core : The optical fiber consists of a narrow strand of glass or plastic known as a core. A core is a light transmission area of the fiber. The more the area of the core, the more light will be transmitted into the fiber. Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding is to provide the lower refractive index at the core interface as to cause the reflection within the core so that the light waves are transmitted through the fiber. Jacket(Buffer): The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fiber strength, absorb shock and extra fiber protection.

87. FOC transmits light signal rather than electrical signals. Each fiber has a inner core of glass or plastic that conducts light. the inner core is surrounded by cladding, a layer of glass that reflects the light back into core. A cable may contain a single fiber, but often fibers are bundled together in the centre of the cable. FOC may be multimode or signal mode. Multimode fibers use multiple light paths whereas signal mode fibers allow a single light path and are typically used with laser signaling. It is more expansive and greater bandwidth.

88. Plastic Core and Plastic Cladding G lass Cor e w ith P lastic C ladd i n g ( o ften called P C S fib e r , p l a stic - c l a d silica) Glass Core and Glass Cladding. Plastic fibers have several advantages over glass fibers. Plastic fibers are more flexible and , consequently, more rugged than glass. They are easy to install, can better withstand stress, are less expensive, and weight approximately 60% less than glass. The disadvantages of plastic fibers is their high attenuation characteristics; they do not propagate light as efficiently as glass. Plastic fibers are limited to relatively short runs, such as within a single building or a building complex. Plastic Core and Plastic Cladding

89. Fibers with glass cores exhibit low attenuation characteristics. PCS fibers are slightly better than SCS fibers. PCS fibers are less affected by radiation and are therefore more attractive to military applications. PCS- Class Core and Plastic Cladding

90. SCS fiber have the best propagation characteristics and they are easier to terminate than PCS fibers. SCS cables are the least rugged, and they are more susceptible to increase in attenuation when exposed to radiation. The selection of fiber for a given application is a function of specific system requirements. They are always trade-offs based on the economics and logistics of a particular application. Glass Core and Glass Cladding.

91. Transmission rate of 100 G bps . Not affected by the electrical interference. Most expensive cable. FOC support cable length of 10 km or more. It supports voice, video and data. It provides most secure media. Commonly used as backbones between buildings and token ring networks. Not very flexible, difficult to work.

92. Wide Bandwidth Low Losses Immune to Cross Talk Interference Immune Lightweight Small Size More Strength Security Long Distance Transmission Environment Immune Safe and Easy Installation Reliable Accuracy

93. High Initial Cost : The initial installation or setting up cost is very high compared to all other systems . Maintenance and Repairing Cost : The maintenance and repairing of fiber optics systems is not only difficult but expensive also. Clicking for video to attach Fiber cable to connectors Terminate The Fiber optical cable to connector

94. Types of Fiber Optical Cable Connectors SC- subscriber connector ST- straight tip LC- Line Construction FC- Ferrule Connector or Fiber Channel The main difference between APC and UPC connectors is the fiber endface . APC connectors feature a fiber endface that is polished at an eight-degree angle; UPC connectors are polished with no angle.

95. An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as  wireless transmission . In unguided media, air is the media through which the electromagnetic energy can flow easily. Unguided transmission is broadly classified into three categories : 1 ) Radio waves 2) Microwaves 3) Infrared

96. Radio waves are the electromagnetic waves that are transmitted in all the directions of free space. Radio waves are omnidirectional, i.e., the signals are propagated in all the directions. The range in frequencies of radio waves is from 10 Khz to 1 Ghz . In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by the sending antenna can be received by any receiving antenna. An example of the radio wave is FM radio . Radio waves includes following types : Short wave. Very High Frequency (VHF) television and FM radio. Ultra High Frequency (UHF) radio and television. Various kind of antennas can be used to broadcast radio signals. The power of the radio frequency signal is determined by the antenna and transreceiver (a device that transmit and receive a signal over a medium such a copper, radio waves, or fiber optic cables).

97. Radio waves are easy to generate. They can travel long distances. They can penetrate building easily so they are widely used for communication both indoor and outdoors. Radio waves are omni directional. The properties of radio waves are frequency dependent. At low frequencies , radio waves pass through obstacles well, but the power falls off sharply with distance from the source. At high frequencies, radio waves are subject to interference from motors and other electrical equipment. Low frequency and medium frequency range cannot be used for data transfer because of their very small bandwidth.

98. A Radio wave is useful for multicasting when there is one sender and many receivers. An FM radio, television, cordless phones are examples of a radio wave . Applications Of Radio waves: Radio transmission is mainly used for wide area networks and mobile cellular phones. Radio waves cover a large area, and they can penetrate the walls. Radio transmission provides a higher transmission rate. Advantages Of Radio transmission :

99. Microwaves are of two types: Terrestrial microwave Satellite microwave communication. Microwaves

100. Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from one ground-based microwave transmission antenna to another. Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz. Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves sent by the sending antenna are narrowly focused. In this case, antennas are mounted on the towers to send a beam to another antenna which is km away. It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct sight of each other. Terrestrial Microwave Transmission

101. Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz. Bandwidth: It supports the bandwidth from 1 to 10 Mbps. Short distance: It is inexpensive for short distance. Long distance: It is expensive as it requires a higher tower for a longer distance. Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and antenna size. Characteristics of Microwave:

102. Design of Microwave Communication

103. Design of Microwave Communication

104. Microwave transmission is cheaper than using cables. It is free from land acquisition as it does not require any land for the installation of cables. Microwave transmission provides an easy communication in terrains as the installation of cable in terrain is quite a difficult task. Communication over oceans can be achieved by using microwave transmission. Advantages Of Microwave:

105. Disadvantages Of Microwave: Eavesdropping: An eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna. Out of phase signal: A signal can be moved out of phase by using microwave transmission. Susceptible to weather condition: A microwave transmission is susceptible to weather condition. This means that any environmental change such as rain, wind can distort the signal. Bandwidth limited: Allocation of bandwidth is limited in the case of microwave transmission.

106. Mobile telephone network uses microwave communication. Wireless LAN. Point-to-point communication between stations. Line –of sight communication.

107. Satellite Microwave Communication A satellite is a physical object that revolves around the earth at a known height. Satellite communication is more reliable nowadays as it offers more flexibility than cable and fiber optic systems. We can communicate with any point on the globe by using satellite communication. How Does Satellite work? The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified signal is retransmitted to another earth station.

108. Advantages Of Satellite Microwave Communication: The coverage area of a satellite microwave is more than the terrestrial microwave. The transmission cost of the satellite is independent of the distance from the centre of the coverage area. Satellite communication is used in mobile and wireless communication applications. It is easy to install. It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile communication, etc.

109. Disadvantages Of Satellite Microwave Communication : Satellite designing and development requires more time and higher cost. The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit. The life of the satellite is about 12-15 years. Due to this reason, another launch of the satellite has to be planned before it becomes non-functional.

110. An infrared transmission is a wireless technology used for communication over short ranges. The frequency of the infrared in the range from 300 GHz to 400 THz. It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer, VCR and stereos all use infrared communication and cell phone resides in the same closed area. They do not pass through solid objects . An infrared system in one room of a building will not interfere with a similar system in adjacent rooms . Infrared light is suitable for indoor wireless.

111. It supports high bandwidth, and hence the data rate will be very high. Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one room cannot be interrupted by the nearby rooms. An infrared communication provides better security with minimum interference. Infrared communication is unreliable outside the building because the sun rays will interfere with the infrared waves. Characteristics Of Infrared:

112. T he da t a l i nk l a y e r i s r e s ponsib l e f or m oving frames from one hop (node) to the next. 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.

113. T he da t a l i nk l a y e r i s r e s ponsib l e f or m oving frames from one hop (node) to the next. The Data Link Layer protocols are Ethernet, token ring, FDDI and PPP. An important characteristic of a Data Link Layer is that datagram can be handled by different link layer protocols on different links in a path. For example, the datagram is handled by Ethernet on the first link, PPP on the second link.

114. It contains two sub-layers: 1) 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. 2) 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.

115. It contains two sub-layers: 1) Logical Link Control Layer 2) Media Access Control Layer

116. ▶ Following services are provided by the Data Link Layer: Functions of the Data-link layer

117. Framing . Functions of the Data-link layer

118. Framing . Functions of the Data-link layer The data link layer divides the stream of bits received from the network layer into manageable data units called frames. T he D LL breaks t he st r e am into discrete f ra m es and co m putes the checksum for each frames . At the destination the checksum is recomputed . At breaking of bit stream by inserting spaces or time gaps is called framing . Since it is difficult and risky to count on timing and mark the start and end of each frame, various simple method used for framing are , Character count Starting and ending character, with character stuffing. Starting and ending flags, with bit stuffing.

119. 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 . If the frame is intended for a system outside the sender's network, the receiver address is the address of the device that connects the network to the next one Functions of the Data-link layer

120. Flow control 1) Rate Based Flow Control: If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer imposes a flow control mechanism to avoid overwhelming the receiver. 2) Feedback based flow control: Flow control mechanism is incorporated which includes a feedback mechanism requesting transmitter a retransmission of incorrect message block . Functions of the Data-link layer

121. 1) Stop and Wait Flow control Functions of the Data-link layer The primitives of stop and wait protocol are: Sender side Rule 1: Sender sends one data packet at a time. Rule 2: Sender sends the next packet only when it receives the acknowledgment of the previous packet. Therefore , the idea of stop and wait protocol in the sender's side is very simple, i.e., send one packet at a time, and do not send another packet before receiving the acknowledgment . Receiver side Rule 1: Receive and then consume the data packet. Rule 2: When the data packet is consumed, receiver sends the acknowledgment to the sender. Therefore , the idea of stop and wait protocol in the receiver's side is also very simple, i.e., consume the packet, and once the packet is consumed, the acknowledgment is sent. This is known as a flow control mechanism.

122. 1 ) Disadvantages of Stop and Wait protocol Functions of the Data-link layer 1. Problems occur due to lost data 2. Problems occur due to lost acknowledgment

123. 1 ) Disadvantages of Stop and Wait protocol Functions of the Data-link layer 3 . Problem due to the delayed data or acknowledgment Delay in ACK The most common retransmission technique is known as Automatic Repeat Request. Retransmission of data in three cases : Damaged frames Lost frames Lost acknowledgements.

124. Sliding Window Flow control Functions of the Data-link layer The sliding window is a technique for sending multiple frames at a time. It controls the data packets between the two devices where reliable and gradual delivery of data frames is needed. In this technique, each frame has sent from the sequence number. The sequence numbers are used to find the missing data in the receiver end. The purpose of the sliding window technique is to avoid duplicate data, so it uses the sequence number.

125. Types of Sliding Window Flow control Functions of the Data-link layer Go-Back-N ARQ Selective Repeat ARQ Go-Back-N ARQ

126. Types of Sliding Window Flow control Functions of the Data-link layer Go-Back-N ARQ Selective Repeat ARQ Selective Repeat ARQ

127. Error Detection: Functions of the Data-link layer When data is transmitted from one device to another device, the system does not guarantee whether the data received by the device is identical to the data transmitted by another device. An Error is a situation when the message received at the receiver end is not identical to the message transmitted . Due to error the data Integrity features lost in data communication. Data integrity refers to the accuracy and consistency (validity) of data over its lifecycle.  Errors can be introduced by signal attenuation and noise . It also uses a mechanism to recognize duplicate frames . Data Link Layer protocol provides a mechanism to detect one or more errors. This is achieved by adding error detection bits in the frame and then receiving node can perform an error check . The data link layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames.

128. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Errors can be classified into two categories: Single-Bit Error Burst Error

129. Error Detection: Functions of the Data-link layer Types Of Errors Error 1) Single-Bit Error : The only one bit of a given data unit is changed from 1 to 0 or from 0 to 1 . In the following figure, the message which is sent is corrupted as single-bit, i.e., 0 bit is changed to 1 . Single-Bit Error does not appear more likely in Serial Data Transmission . For example, Sender sends the data at 10 Mbps, this means that the bit lasts only for 1 ?s and for a single-bit error to occurred, a noise must be more than 1 ? s. Single-Bit Error mainly occurs in Parallel Data Transmission. For example, if eight wires are used to send the eight bits of a byte, if one of the wire is noisy, then single-bit is corrupted per byte.

130. Error Detection: Functions of the Data-link layer Types Of Errors Error 2) Burst Error: The two or more bits are changed from 0 to 1 or from 1 to 0 is known as Burst Error. The Burst Error is determined from the first corrupted bit to the last corrupted bit.. The duration of noise in Burst Error is more than the duration of noise in Single-Bit. Burst Errors are most likely to occurr in Serial Data Transmission. The number of affected bits depends on the duration of the noise and data rate.

131. Error Detection: Functions of the Data-link layer Error Detecting Techniques : The most popular Error Detecting Techniques are : Single parity check / Vertical Redundancy Check (VRC) Two-dimensional parity check / Longitudinal Redundancy Check (LRC) Checksum Cyclic redundancy check

132. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 1) Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC ) It is also known as Vertical Redundancy Check (VRC) or Parity Check

133. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 1) Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC ) If even number of bits are changed during transmission the Vertical Redundancy Check (VRC) or Parity Check

134. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Examples of Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC )

135. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 1) Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC ) Advantages : Parity bit/ VRC can detect all single bit error. The major disadvantage of using this method for error detection is that it is not able to detect burst error if the number of bits changed is even, i.e. 2, 4, 6, 8, …….etc. Disadvantages : It can also detect burst errors but only in those cases where number of bits changed is odd, i.e. 1, 3, 5, 7, …….etc.

136. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 2) Two-Dimensional Parity Check / Longitudinal Redundancy Check (LRC ) : At Sender / Transmitter End

137. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 2) Two-Dimensional Parity Check / Longitudinal Redundancy Check (LRC ) : At Receiver End

138. Error Detection: Functions of the Data-link layer Performance can be improved by using Two-Dimensional Parity / Longitudinal Redundancy Check which organizes the data in the form of a table. In Two-Dimensional Parity check / Longitudinal Redundancy Check, a block of bits is divided into rows . Parity check bits are computed for each column, which is equivalent to the single-parity check for that column. In order to detect an error, a redundant bits(Parity bits / LRC) are added to the whole data block and this block is transmitted to receiver. The receiver uses this redundant row to detect error. At the receiving end, the column-wise parity bits /LRC are again computed the received data. T he incoming parity bits are compared with the computed parity bits from at receiver. After checking the data for errors, receiver accepts the data and discards the redundant row of bits . Types Of Errors Error Detection Techniques 2) Two-Dimensional Parity Check / Longitudinal Redundancy Check (LRC ) :

139. Error Detection: Functions of the Data-link layer Advantage : LRC is used to detect burst errors . Disadvantage : The main problem with LRC is that, it is not able to detect error if even no of bits in a data unit same columns are changed /damaged. Types Of Errors Error Detection Techniques 2) Two-Dimensional Parity Check / Longitudinal Redundancy Check (LRC ) : Example : If data 110011 010101 is changed to 010010110100.

140. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Examples of Single-Bit Error Detection: Parity Check

141. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Drawback of Two-Dimensional Parity Check If two bits in one data unit are corrupted and two bits exactly the same position in another data unit are also corrupted, then 2D Parity checker will not be able to detect the error. This technique cannot be used to detect the 4-bit errors or more in some cases.

142. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 3) Checksum Error Detection A Checksum is an error detection technique based on the concept of redundancy .

143. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Checksum A Checksum is an error detection technique based on the concept of redundancy. It is divided into two parts : Checksum Generator ii. Checksum Checker

144. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Checksum Error Detection Algorithm at Sender and Receiver Checksum Generator The Sender follows the given steps: The block unit is divided into k sections, and each of n bits. All the k sections are added together by using one's complement to get the sum. The sum is complemented and it becomes the checksum field. The original data and checksum field are sent across the network. Checksum Checker The Receiver follows the given steps: The block unit is divided into k sections and each of n bits. All the k sections are added together by using one's complement algorithm to get the sum. The sum is complemented. If the result of the sum is zero, then the data is accepted otherwise the data is discarded.

145. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Find Error by check sum method for following data

146. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection CRC is a redundancy error technique used to determine the burst error in data transmission in computer network.

147. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection CRC is a redundancy error technique used to determine the error in data transmission in computer network. Cyclic Redundancy Check (CRC) is an error detection method. It is based on binary division . CRC Generator- CRC generator is an algebraic polynomial represented as a bit pattern. Consider the CRC generator is x 7  + x 6  + x 4  + x 3  + x + 1. Bit pattern is obtained from the CRC generator using the following rule- The power of each term gives the position of the bit and the coefficient gives the value of the bit . The corresponding binary pattern is obtained as-

148. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques Cyclic Redundancy Check Algorithm at Sender and Receiver At Sender Side Sender has a generator G(x) polynomial. Sender appends (n-1) zero bits to the data . Where n= no of bits in generator Dividend appends the data with generator G(x) using modulo 2 division (arithmetic). Remainder of (n-1) bits will be CRC. At Receiver Side Receiver has same generator G(x). Receiver divides received data (data + CRC) with generator. If remainder is zero, data is correctly received. Else, there is error.

149. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection A Cyclic redundancy is an error detection technique based on the concept of Appended data bits(i.e.000…), Divisor and cyclic redundancy check (CRC) .

150. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection Examples to solve: Problem-01: A bit stream 1101011011 is transmitted using the standard CRC method. The generator polynomial is x 4 +x+1. What is the actual bit string transmitted ? Solution- The generator polynomial G(x) = x 4  + x + 1 is encoded as 10011. Clearly , the generator polynomial consists of 5 bits. So , a string of 4 zeroes is appended to the bit stream to be transmitted. The resulting bit stream is 11010110110000. Now , the binary division is performed as-

151. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection From here, CRC = 1110. Now , The code word to be transmitted is obtained by replacing the last 4 zeroes of 1101011011 0000  with the CRC. Thus, the code word transmitted to the receiver = 1101011011 1110 .

152. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection Problem-02: A bit stream 10011101 is transmitted using the standard CRC method. The generator polynomial is x 3 +1. What is the actual bit string transmitted? Suppose the third bit from the left is inverted during transmission. How will receiver detect this error? Solution- Part-01: The generator polynomial G(x) = x 3  + 1 is encoded as 1001. Clearly, the generator polynomial consists of 4 bits. So, a string of 3 zeroes is appended to the bit stream to be transmitted. The resulting bit stream is 10011101 000 . Now , the binary division is performed as-

153. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection From here, CRC = 100. Now, The code word to be transmitted is obtained by replacing the last 3 zeroes of 10011101 000  with the CRC. Thus, the code word transmitted to the receiver = 10011101 100 .

154. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection Problem-02: A bit stream 10011101 is transmitted using the standard CRC method. The generator polynomial is x 3 +1. What is the actual bit string transmitted? Suppose the third bit from the left is inverted during transmission. How will receiver detect this error? Solution- The code word transmitted to the receiver = 10011101100. Part-02: According to the question, Third bit from the left gets inverted during transmission. So, the bit stream received by the receiver = 10 1 11101100 . Now, Receiver receives the bit stream = 10111101100. Receiver performs the binary division with the same generator polynomial as-

155. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection From here, The remainder obtained on division is a non-zero value. This indicates to the receiver that an error occurred in the data during the transmission. Therefore, receiver rejects the data and asks the sender for retransmission.

156. Error Detection: Functions of the Data-link layer Types Of Errors Error Detection Techniques 4) Cyclic redundancy check Error Detection Properties Of CRC Generator- The algebraic polynomial chosen as a CRC generator should have at least the following properties- Rule-01: It should not be divisible by x. This condition guarantees that all the burst errors of length equal to the length of polynomial are detected. Rule-02: It should be divisible by x+1. This condition guarantees that all the burst errors affecting an odd number of bits are detected .

157. Error Correction . Functions of the Data-link layer Error Correction codes are used to detect and correct the errors when data is transmitted from the sender to the receiver. Error Correction can be handled in two ways : Backward error correction / Error Control:  Once the error is discovered, the receiver requests the sender to retransmit the entire data unit. Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors.

158. Error Correction . Functions of the Data-link layer Backward error correction / Error Control:  Once the error is discovered, the receiver requests the sender to retransmit the entire data unit . Categories of Error Control:

159. Error Correction . Functions of the Data-link layer Backward error correction / Error Control:   Categories of Error Control: i ) Stop-and-wait ARQ Stop-and-wait ARQ is a technique used to retransmit the data in case of damaged or lost frames. This technique works on the principle that the sender will not transmit the next frame until it receives the acknowledgement of the last transmitted frame. Two possibilities of the retransmission: Damaged Frame – (case of Error correction) Lost Frame - (case of flow control)

160. Error Correction . : Backward error correction / Error Control:  Functions of the Data-link layer Four features are required for the retransmission: The sending device keeps a copy of the last transmitted frame until the acknowledgement is received. Keeping the copy allows the sender to retransmit the data if the frame is not received correctly. Both the data frames and the ACK frames are numbered alternately 0 and 1 so that they can be identified individually. Suppose data 1 frame acknowledges the data 0 frame means that the data 0 frame has been arrived correctly and expects to receive data 1 frame. If an error occurs in the last transmitted frame, then the receiver sends the NAK frame which is not numbered. On receiving the NAK frame, sender retransmits the data. It works with the timer. If the acknowledgement is not received within the allotted time, then the sender assumes that the frame is lost during the transmission, so it will retransmit the frame. Stop-and-wait ARQ

161. Error Correction . Functions of the Data-link layer Backward error correction / Error Control:  Once the error is discovered, the receiver requests the sender to retransmit the entire data unit . Categories of Error Control: ii ) Sliding Window ARQ Sliding Window ARQ is a technique used for continuous transmission error control . Two protocols used in sliding window ARQ: Go-Back-n ARQ Selective-Reject ARQ

162. Error Correction . : Backward error correction / Error Control:  Functions of the Data-link layer Three Features used for retransmission : In this case, the sender keeps the copies of all the transmitted frames until they have been acknowledged. Suppose the frames from 0 through 4 have been transmitted, and the last acknowledgement was for frame 2, the sender has to keep the copies of frames 3 and 4 until they receive correctly. The receiver can send either NAK or ACK depending on the conditions. The NAK frame tells the sender that the data have been received damaged. Since the sliding window is a continuous transmission mechanism, both ACK and NAK must be numbered for the identification of a frame. The ACK frame consists of a number that represents the next frame which the receiver expects to receive. The NAK frame consists of a number that represents the damaged frame. The sliding window ARQ is equipped with the timer to handle the lost acknowledgements. Suppose then n-1 frames have been sent before receiving any acknowledgement. The sender waits for the acknowledgement, so it starts the timer and waits before sending any more. If the allotted time runs out, the sender retransmits one or all the frames depending upon the protocol used. Sliding Window ARQ

163. Error Correction . Functions of the Data-link layer Categories of Error Control- Sliding Window ARQ- : i ) Go-Back-n ARQ : In Go-Back-N ARQ protocol, if one frame is lost or damaged, then it retransmits all the frames after which it does not receive the positive ACK. Three possibilities can occur for retransmission : Damaged Frame (Case of Error Correction) Lost Data Frame (case of flow control) Lost Acknowledgement (case of flow control )

164. Error Correction . Functions of the Data-link layer Categories of Error Control : Sliding Window ARQ- ii ) Selective-Reject ARQ : Selective-Reject ARQ technique is more efficient than Go-Back-n ARQ . In this technique, only those frames are retransmitted for which negative acknowledgement (NAK) has been received. The receiver storage buffer keeps all the damaged frames on hold until the frame in error is correctly received. The receiver must have an appropriate logic for reinserting the frames in a correct order. The sender must consist of a searching mechanism that selects only the requested frame for retransmission.

165. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error correction Hamming code is a error-correction codes that can be used to  detect and correct the errors  that can occur when the data is moved or stored from the sender to the receiver. It is  technique developed by R.W. Hamming for error correction . Redundant bits – Redundant bits are extra binary bits that are generated and added to the information-carrying bits of data transfer to ensure that no bits were lost during the data transfer. The number of redundant bits can be calculated using the following formula : 2 r ≥ m + r + 1 where, r = redundant bit, m = data bit e.g. Suppose the number of data bits is 7, then the number of redundant bits can be calculated using: 2 4 ≥ 7 + 4 + 1 i.e. 16 ≥ 12 Thus, the number of redundant bits= 4

166. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction a) Determining the position of redundant bits – These redundancy bits are placed at the positions which correspond to the power of 2. As in the above example: The number of data bits = 7 The number of redundant bits = 4 The total number of bits = 11 The redundant bits are placed at positions corresponding to power of 2=> 1, 2, 4, and 8

167. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction b) Determining and place the Data bits positions– Suppose the data to be transmitted is 1011001, the bits will be placed as follows:

168. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction d ) Determining the Redundant bits positions(R1) Using Even Parity– R1 bit is calculated using parity check at all the bits positions whose binary representation includes a 1 in the least significant position. R1 : bits 1, 3, 5, 7, 9, 11 R1, 1, 0, 1, 1,1 R1=0

169. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction d ) Determining the Redundant bits positions(R2) Using Even Parity– R2, 1, 0, 1, 0,1 R2 bit is calculated using parity check at all the bits positions whose binary representation includes a 1 in the second position from the least significant bit. R2 : bits 2,3,6,7,10,11 R1=0 R2=1

170. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction d ) Determining the Redundant bits positions(R4) Using Even Parity– R4, , 0, 1 R1=0 R2=1 R4=1 R4 bit is calculated using parity check at all the bits positions whose binary representation includes a 1 in the third position from the least significant bit. R4 : bits 4, 5, 6, 7

171. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction d ) Determining the Redundant bits positions(R8) Using Even Parity– R8, 1, 0, 1 R1=0 R2=1 R4=1 R8=0 R8 bit is calculated using parity check at all the bits positions whose binary representation includes a 1 in the fourth position from the least significant bit. R8 : bit 8,9,10,11

172. Error Correction . Functions of the Data-link layer 2) Forward error correction:  In this case, the receiver uses the error-correcting code which automatically corrects the errors. Hamming Code Error Correction d ) Determining the Redundant bits positions(R8) Using Even Parity– Thus, the data transferred is: R1=0 R2=1 R4=0 R8=0

173. Error Correction: Forward error correction Functions of the Data-link layer Hamming Code Error Correction 6) Error Detection by Hamming Code– Suppose in the above example the 6th bit is changed from 0 to 1 during data transmission, then it gives new parity values in the binary number:

174. Error Correction: Forward error correction Functions of the Data-link layer Hamming Code Error Correction 7) Error Corrections By Hamming Code– Here, The bits give the binary number as 0110 whose decimal representation is 6 . Thus , the bit 6 contains an error. To correct the error the 6th bit is changed from 1 to 0. Let the Received Bit Frame is  Find the Redundant Bits using Even Parity at Receiving End Recovered Data at Receiving End is

175. Half-Duplex & Full-Duplex Communication: Functions of the Data-link layer

176. Half-Duplex & Full-Duplex Communication: Functions of the Data-link layer