Lecture 1 Computer Networks Introduction.pptx

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1. The University of Faisalabad Computer Networks Week 1 Maryam Tanveer Lecturer (Department of Computer Science) [email protected]

2. Course Book Data Communication and Networking Fourth EDITION Behrouz A. Forouzan DeAnza College with Sophia Chung Fegan Text Book

3. Course Book Data and Computer Communication Eighth EDITION William Stallings Reference Book

4. Course Objective Build an understanding of the fundamental concepts of computer networking. To understand the physical phenomenon that can be used to transmit digital information Familiarize the student with the basic taxonomy and terminology of the computer networking area. To prepare students to know the characteristics and designs of types of computer networks and their applications.

5. What is Computer Networks?

6. Computer Networks Computer Network A Collection of computing devices that are connected in various ways in order to communicate and share resources Usually, the connections between computers in a network are made using physical wires or cables However, some connections are wireless, using radio waves or infrared signals

7. Computer Networks The generic term node or host refers to any device on a network Data transfer rate The speed with which data is moved from one place on a network to another Data transfer rate is a key issue in computer networks

8. Data Communication 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. The communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs). When we communicate, we are sharing information. This sharing can be local or remote.

9. Data Communication The effectiveness of a data communications system depends on four fundamental characteristics: Delivery : The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. Accuracy : The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. Timeliness : The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. Jitter : Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.

10. Data Communication Components of Data Communication A data communications system has five components

11. Data Communication Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 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. Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices.

12. Data Representation Information today comes in different forms such as text, numbers, images, audio, and video. Text In data communications, text is represented as a bit pattern, a sequence of bits (0s 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. Character sets – ASCII code and Unicode The ASCII code system (American Standard Code for Information Interchange) was set up in 1963 for use in communication systems and computer systems. A newer version of the code was published in 1986. The standard ASCII code character set consists of 7-bit codes (0 to 127 in denary or 00 to 7F in hexadecimal).

13. Part of the ASCII code table Extended ASCII code table

14. Data Representation 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 Bitmap images are made up of pixels (picture elements); an image is made up of a two-dimensional matrix of pixels. Pixels can take different shapes such as:

15. Data Representation Each pixel can be represented as a binary number, and so a bitmap image is stored in a computer as a series of binary numbers, so that: a black and white image only requires 1 bit per pixel – this means that each pixel can be one of two colors, corresponding to either 1 or 0 if each pixel is represented by 2 bits, then each pixel can be one of four colors (2 2 = 4), corresponding to 00, 01, 10, or 11 if each pixel is represented by 3 bits then each pixel can be one of eight colors (2 3 = 8), corresponding to 000, 001, 010, 011, 100, 101, 110, 111. The number of bits used to represent each colour is called the colour depth . Image resolution refers to the number of pixels that make up an image; for example, an image could contain 4096 × 3072 pixels (12 582 912 pixels in total).

16. Data Representation

17. Data Representation 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. Each sound wave has a frequency, wavelength and amplitude. The amplitude specifies the loudness of the sound.

18. Data Representation

19. Data Representation 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.

20. Data transmission / Data Flow Data transmission can be either over a short distance (for example, computer to printer) or over longer distances (for example, from one computer to another in a global network). Essentially, three factors need to be considered when transmitting data: the direction of data transmission (for example, can data transmit in one direction only, or in both directions) the method of transmission (for example, how many bits can be sent at the same time) how will data be synchronized (that is, how to make sure the received data is in the correct order). These factors are usually considered by a communication protocol.

21. Data transmission / Data Flow

22. Data transmission / Data Flow 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. 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. In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously

23. Data transmission / Data Flow

24. Data transmission / Data Flow Serial data transmission works well over long distances. However, the data is transmitted at a slower rate than parallel data transmission. Because only one channel/wire is used, data will arrive at its destination fully synchronized (i.e. in the correct order). An example of its use is when connecting a computer to a printer via a USB connection.

25. Data transmission / Data Flow Parallel data transmission works well over short distances. Over longer distances (for example, over 20metres), data can become skewed (that is, the data can arrive unsynchronized) and bits can arrive out of order. The longer the wire, the worse this can become. It is, however, a faster method of data transmission than serial. The internal circuits in a computer use parallel data transmission since the distance travelled between components is very short and high-speed transmission is essential.

26. Data transmission / Data Flow Comparison of serial and parallel data transmission methods

27. Networks

28. 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.

29. Networks Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. Performance Performance can be measured in many ways, including transit time and response time. Performance is often evaluated by two networking metrics: throughput and delay. Reliability Network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network's robustness in a catastrophe. Security Network security issues include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses.

30. Physical Structures 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. There are two possible types of connections: point-to-point and multipoint . Point-to-Point A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Multipoint A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared, either spatially or temporally.

31. Physical Structures Physical Topology The term physical topology refers to the way in which a network is laid out physically. Tw o or more devices connect to a link; two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. There are four basic topologies possible: mesh, star, bus, and ring.

32. Physical Structures Mesh Topology In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects. Advantages It has dedicated links. It is robust. It ensures privacy and security Disadvantages It’s installation and reconnection are difficult The sheer bulk of the wiring Expensive hardware requirements (I/O ports and cable)

33. Physical Structures Star Topology In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub. The devices are not directly linked to one another. Advantages It i easy to install and reconfigure. less cabling required Robustness (If one link fails, only that link is affected) Disadvantages The dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.

34. Physical Structures Bus Topology The preceding examples all describe point-to-point connections. A bus topology, on the other hand, is multipoint. One long cable acts as a backbone to link all the devices in a network. Advantages Ease of installation. less length of cable cost-effective as compared to other network topology Disadvantages Difficult reconnection and fault isolation. Difficult to add new devices. Fault or break in the bus cable stops all transmission

35. Physical Structures Ring Topology In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Each device in the ring incorporates a repeater.

36. Physical Structures Ring Topology Advantages Ring topology facilitates easy installation and reconfiguration with devices linked to immediate neighbors, requiring only two connection changes for addition or deletion, while enabling efficient fault isolation through continuous signal circulation and alarm alerts for unresponsive devices. Disadvantages However, unidirectional traffic can be a disadvantage. In a simple ring, a break in the ring (such as a disabled station) can disable the entire network. This weakness can be solved by using a dual ring or a switch capable of closing off the break. Ring topology was prevalent when IBM introduced its local-area network Token Ring. Today, the need for higher-speed LANs has made this topology less popular.

37. Physical Structures Hybrid Topology A network can be hybrid. For example, we can have a main star topology with each branch connecting several stations in a bus topology

38. Categories of Networks Local Area Network A local area network (LAN) is usually privately owned and links the devices in a single office, building, or campus. Depending on the needs of an organization and the type of technology used, a LAN can be as simple as two PCs and a printer in someone's home office; or it can extend throughout a company and include audio and video peripherals. Currently, LAN size is limited to a few kilometers.

39. Categories of Networks Local Area Network LANs are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware (e.g., a printer), software (e.g., an application program), or data. LANs are distinguished from other types of networks by their transmission media and topology. In general, a given LAN will use only one type of transmission medium. The most common LAN topologies are bus, ring, and star. Early LANs had data rates in the 4 to 16 megabits per second (Mbps) range. Today, however, speeds are normally 100 or 1000 Mbps. Wireless LANs are the newest evolution in LAN technology.

40. Categories of Networks Wide Area Network A wide area network (WAN) provides long-distance transmission of data, image, audio, and video information over large geographic areas that may comprise a country, a continent, or even the whole world. A WAN can vary from a complex switched network connecting routers and multiple LANs to a simple point-to-point connection, such as a home computer using a leased line from a service provider for Internet access. A good example of a switched WAN is the asynchronous transfer mode (ATM) network, which is a network with fixed-size data unit packets called cells. Another example of WANs is the wireless WAN that is becoming more and more popular

41. Categories of Networks Wide Area Network

42. Categories of Networks Metropolitan Area Networks A metropolitan area network (MAN) is a network with a size between a LAN and a WAN. It normally covers the area inside a town or a city. It is designed for customers who need a high-speed connectivity, normally to the Internet, and have endpoints spread over a city or part of city. A good example of a MAN is the part of the telephone company network that can provide a high-speed DSL line to the customer. Another example is the cable TV network that originally was designed for cable TV, but today can also be used for high-speed data connection to the Internet.

43. Categories of Networks Interconnection of Networks: Internetwork

44. Categories of Networks Interconnection of Networks: Internetwork Today, it is very rare to see a LAN, a MAN, or a LAN in isolation; they are connected to one another. When two or more networks are connected, they become an internetwork, or internet. As an example, assume that an organization has two offices, one on the east coast and the other on the west coast. The established office on the west coast has a bus topology LAN; the newly opened office on the east coast has a star topology LAN. The president of the company lives somewhere in the middle and needs to have control over the company from her home. To create a backbone WAN for connecting these three entities (two LANs and the president's computer), a switched WAN (operated by a service provider such as a telecom company) has been leased. To connect the LANs to this switched WAN, however, three point-to-point WANs are required. These point-to-point WANs can be a high-speed DSL line offered by a telephone company or a cable modern line offered by a cable TV provider.

45. The INTERNET? The Internet is a structured, organized system.

46. Introduction of Internet Internet is composed of hundreds of thousands of interconnected networks . A network is a group of connected communicating devices such as computers and printers. An internet (note the lowercase letter i) is two or more networks that can communicate with each other. The most notable internet is called the Internet (uppercase letter I), a collaboration of more than hundreds of thousands of interconnected networks.

47. History of Internet ENIAC (Electronic Numerical Integrator and Computer) Feb. 14 1946

48. History of Internet Mid 1960s The Advanced Research Projects Agency (ARPA) in the Department of defense (DOD) was interested in finding a way to connect computers together. So that the researchers they funded could share their findings, thereby reducing costs and eliminating duplication of efforts. by 1969 By 1969, ARPANET was a reality. Four nodes, at the University of California at Los Angeles (UCLA) , the University of California at Santa Barbara (UCSB), Stanford Research Institute (SRI), and the University of Utah , were connected to form network.

49. History of Internet September, 1971

50. History of Internet 1972: Birth of the internet Vint cerf and bob kahn , both of whom were part of the core ARPANET group, collaboration on what they called the internetting project. They want to link different networks together so that a host on one network could communicate with host on a second, different network. They developed Gateway to connect different Network. They develop TCP(Transmission Control Protocol). Which splits into TCP and IP and then called TCP/IP.

51. The Internet Today The Internet today is not a simple hierarchical structure. It is made up of many wide- and local-area networks joined by connecting devices and switching stations.

52. PROTOCOLS AND STANDARDS Synonymous with rule Agreed-upon rules

53. Protocols In computer networks, communication occurs between entities in different systems. An entity is anything capable of sending or receiving information. A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key elements of a protocol are syntax, semantics, and timing. Syntax The term syntax refers to the structure or format of the data, meaning the order in which they are presented. For example, a simple protocol might expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of the receiver, and the rest of the stream to be the message itself.

54. Protocols Semantics The word semantics refers to the meaning of each section of bits. How is a particular pattern to be interpreted, and what action is to be taken based on that interpretation? For example, does an address identify the route to be taken or the final destination of the message? Timing The term timing refers to two characteristics: when data should be sent and how fast they can be sent. For example, if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and some data will be lost.

55. Standards Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes. Data communication standards fall into two categories: de facto (meaning "by fact" or "by convention") and de jure (meaning "by law" or "by regulation"). De facto Standards that have not been approved by an organized body but have been adopted as standards through widespread use are de facto standards. De jure Those standards that have been legislated by an officially recognized body are de jure standards.

56. Internet Standards An Internet standard is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is a formalized regulation that must be followed. An Internet draft is a working document (a work in progress) with no official status and a 6-month lifetime. Upon recommendation from the Internet authorities, a draft may be published as a Request for Comment (RFC). Each RFC is edited, assigned a number, and made available to all interested parties. RFCs go through maturity levels and are categorized according to their requirement level.

57. Internet Standards

58. Internet Standards

59. Transmission Medium A transmission medium can be broadly defined as anything that can carry information from a source to a destination.

60. Transmission Medium A transmission medium is the way in which data is transmitted from one place to another. It provide a pathway over which the message can travel from sender-to-receiver. Each of the message can be sent in the form of data by converting then into binary digits. These binary digits are then encoded into a signal that can be transmitted over the appropriate medium.

61. Types of Transmission Medium

62. Guided Media Guided Transmission media are the cables that are tangible or have physical existence. Bounded Transmission means having connectivity between a source and destination using cables or wires. The signals have to travel through this this channel i.e. physical media.

63. Guided Media Twisted-Pair Cable: A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference.

64. Guided Media Types of Twisted-Pair Cable: Unshielded twisted-pair (UTP) Shielded twisted-pair (STP) The most common twisted-pair cable used in communications is referred to as unshielded twisted-pair (UTP). STP cable has a metal foil or braided mesh covering that encases each pair of insulated conductors. Although metal casing improves the quality of cable by preventing the penetration of noise or crosstalk, it is bulkier and more expensive.

65. Guided Media Coaxial Cable Coaxial cable (or coax) has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two. The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit. This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover.

66. Guided Media Coaxial Cable Coaxial cable carries signals of higher frequency ranges than twisted pair cable.

67. Guided Media Coaxial Cable Applications Coaxial cable was widely used in analog telephone networks, digital telephone networks. Cable TV networks also use coaxial cables. Another common application of coaxial cable is in traditional Ethernet LANs

68. Guided Media Fiber-optic cable A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance suddenly enters another substance(of a different density), the ray changes direction. Optical fibers use reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic.

69. Guided Media Fiber-optic cable Advantages Higher bandwidth. Less signal attenuation. Immunity to electromagnetic interference. Resistance to corrosive materials. Light weight. Greater immunity to tapping. Disadvantages Installation and maintenance More expensive than other guided media.

70. Unguided Media Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Radio Waves Microwaves Infrared

71. Unguided Media

72. Unguided Media

73. Unguided Media Radio Waves Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves. Radio waves are omni directional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna sends waves that can be received by any receiving antenna. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signals using the same frequency or band. Omni directional Antenna: Radio waves use omnidirectional antennas that send out signals in all directions.

74. Unguided Media Radio Waves The Omni directional characteristics of radio waves make them useful for multicasting, in which there is one sender but many receivers. AM and FM radio, television, maritime radio, cordless phones, and paging are examples of multicasting.

75. Unguided Media Microwaves Electromagnetic waves having frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. The sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas. Applications: Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

76. Unguided Media Microwaves Unidirectional Antenna Microwaves need unidirectional antennas that send out signals in one direction. Two types of antennas are used for microwave communications: the parabolic dish and the horn.

77. Unguided Media Infrared waves Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm), can be used for short-range communication. Infrared waves, having high frequencies, cannot penetrate walls. Infrared signals useless for long-range communication. We cannot use infrared waves outside a building because the sun's rays contain infrared waves that can interfere with the communication. Applications: Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.