Data Communication Concepts PDF

NWC1393 DATA COMMUNICATION CONCEPTS Topic 1: Introduction To Data Communications by Siti Fajar bt Jalal 1  OBJECTIVES At the end of this chapter, you should be able to: Define data communications and list down its components. Explain th...

NWC1393 DATA COMMUNICATION CONCEPTS Topic 1: Introduction To Data Communications by Siti Fajar bt Jalal 1  OBJECTIVES At the end of this chapter, you should be able to: Define data communications and list down its components. Explain the model of data communications systems. Network criteria: Performance, reliability, security. Line configurations and transmission mode. Explain the various network topologies. Explain the various network types: LAN, MAN, WAN. by Siti Fajar bt Jalal 2 DATA COMMUNICATIONS by Siti Fajar bt Jalal 3 DATA COMMUNICATIONS Data communications is the exchange of data between two devices via some form of transmission medium such as a wire cable. Communicating devices must be part of a communications hardware (physical equipment) system made up of a software (programs) combination of: by Siti Fajar bt Jalal 4  Data Communication : the exchange of data (0 and 1) between two devices via some form of transmission medium (wired/wireless). by Siti Fajar bt Jalal 5 Four fundamental characteristics 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. by Siti Fajar bt Jalal 6 Four fundamental characteristics (Cont.) 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. For example, let us assume that video packets are sent every 30 ms. If some of the packets arrive with a 30-ms delay and others with a 40-ms delay, the video will have an uneven quality. by Siti Fajar bt Jalal 7 PURPOSE OF DATA COMMUNICATION Data: refers to facts, In the context of computer concepts and instructions information systems, data presented in whatever form are represented by binary is agreed upon by the information units (or bits) in parties creating and using form of 0s and 1s. the data. by Siti Fajar bt Jalal 8 Message Information today comes in different forms such as text, numbers, images, audio, and video. by Siti Fajar bt Jalal 9 Message (Cont.) Text Numbers In data communications, text is Numbers are also represented by bit represented as a bit pattern, a patterns. However, a code such as sequence of bits (0s or 1s). Unicode is not used to represent Different sets of bit patterns have been numbers; a number is directly designed to represent text symbols. converted to a binary number to Each set is called a code, and the simplify mathematical operations (see process of representing symbols is Appendix B). coding. Today, the prevalent coding system is Unicode, which uses 32 bits to represent a symbol or character used in any language in the world.by Siti Fajar bt Jalal 10 Message (Cont.) Images Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small dot. The number of pixels depends on the resolution. For example, an image can be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better representation of the image (better resolution), but more memory is needed to store the image. by Siti Fajar bt Jalal 11 Message (Cont.) Audio Video Audio refers to the recording or Video refers to the recording or broadcasting of sound or music. broadcasting of a picture or movie. Audio is by nature different from text, Video can either be produced as a numbers, or images. It is continuous, continuous entity (e.g., by a TV not discrete. camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion. by Siti Fajar bt Jalal 12 Five components of a data communications system by Siti Fajar bt Jalal 13  Message. The message is the information (data) to be communicated. E.g.: text, numbers, pictures, audio, and video. Five Sender. The sender is the device that sends the data message. E.g.: computer, a telephone handset, a video camera, and so on. components of Receiver. The receiver is the device that receives the message. E.g.: a computer, a data workstation, telephone handset, television, and so on. Transmission medium. The transmission communicatio medium is the physical path by which a message travels from sender to receiver. E.g.: twisted-pair ns system wire, coaxial cable, fiber-optic cable, and radio waves. Protocol. A protocol is a set of rules that govern (Cont.) data communications. It represents agreement between the communicating devices. an Without a protocol, two devices may be connected but not able to communicate. E.g.: a person speaking French cannot be understood by a person who speaks only Japanese. by Siti Fajar bt Jalal 14 NETWORKS by Siti Fajar bt Jalal 15 NETWORKS A network is the interconnection of a set of devices capable of communication. A device can be: A host, such as a large computer, desktop, laptop, workstation, cellular phone, or security system. A connecting device such as a router that connects the network to other networks, a switch that connects devices together, or a modem (modulator-demodulator) that changes the form of data by Siti Fajar bt Jalal 16  To be considered effective and NETWORK efficient, a network must meet a number of criteria. The most CRITERIA important of these criteria are performances, reliability ad security. by Siti Fajar bt Jalal 17 PERFORMANCE Can be measured in many ways including transit time and response time. Transit time : the amount of time required for a message to travel from one device to another. Response time : the elapsed time between an inquiry and a response. The performance of network depends on: 1. Number of users A large number of concurrent users can slow response time in a network. by Siti Fajar bt Jalal 18 PERFORMANCE (Cont.) 2. Type of transmission medium The medium defines the speed at which data can travel through a connection (data rate). 3. Hardware Types of hardware included in a network affect both the speed and capacity of transmission. 4. Software The software used to process data at the sender, receiver and intermediate nodes also affects network performance. Performance is often evaluated by two networking metrics: throughput and delay. by Siti Fajar bt Jalal 19  Can be measured by frequency of failure, the time it takes a link to recover from a failure and the network’s robustness in a catastrophe. i. Frequency of failure A network that fails often however is of little value to a user. ii. Recovery time of a network after a failure How long does it take to restore service? iii. Network's robustness in a catastrophe (disaster). Network must be protected from fire, earthquake or theft. RELIABILITY by Siti Fajar bt Jalal 20 SECURITY Protecting data from unauthorized access and viruses. i. Unauthorized access Sensitive data must be protected from unauthorized access. ii. Viruses A good network is protected from viruses by hardware and software designed specifically for that purpose. iii. damage and development And implementing policies and procedures for recovery from breaches and data losses. by Siti Fajar bt Jalal 21 LINE CHARACTERISTICS A link is a communications pathway that transfers data from one device to another. There are TWO line characteristic or line configurations; point-to-point and multi-drop point. by Siti Fajar bt Jalal 22 Types of connections: point- to-point and multipoint by Siti Fajar bt Jalal 23 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. E.g.: When you change television channels by infrared remote control, you are establishing a point-to-point line configuration between remote control and television. by Siti Fajar bt Jalal 24 Multipoint A multipoint (also called multidrop) connection is one in which more than two devices share a single link. The capacity of the channel is shared, either spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection. by Siti Fajar bt Jalal 25  PP 1.3.4 1.4.1 TYPES OF STANDARDS Figure 1.3:Types of Standards by Siti Fajar bt Jalal 26  PP 1.3.5 2 categories of data communication standards: i. De jure standard (by law) - standard that have been legislated by an officially recognized body. ii. De facto standard (by fact) - standard that have not been approved by an organized body but have been adopted as standards through widespread use. by Siti Fajar bt Jalal 27  Definition: Topology refers to the structure of a network including physical arrangement of devices. The term physical topology refers to the way in which a network is laid out physically. Two 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. NETWORK TOPOLOGIES by Siti Fajar bt Jalal 28 NETWORK TOPOLOGIES (Cont.) There are four basic topologies possible: mesh, Star Bus and ring. by Siti Fajar bt Jalal 29 Mesh Topology Definition: A network topology in which each 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. Number of links = n(n – 1)/2 (n: number of devices) Number of ports = n – 1 (n: number of devices) by Siti Fajar bt Jalal 30  Advantages: Disadvantages: Eliminate traffic problem: The Difficult in installation and use of dedicated links reconfiguration: every guarantees that each device must be connected to connection can carry its data every other device. load. Expensive hardware. Robust: If one link becomes unusable, it does not incapacitate the entire system. Privacy and security: Physical boundaries prevent other users from gaining access to message. by Siti Fajar bt Jalal 31 Star Topology Definition: A network topology in which all stations are attached to a central device (hub). Devices are not linked to each other. A star topology does not allow direct traffic between devices. The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device by Siti Fajar bt Jalal 32 Star Topology (Cont.) Advantages: Easy fault identification and isolation. Easy to install and reconfigure. Robustness Disadvantages: Each node must be linked to a central hub. More cabling is required. by Siti Fajar bt Jalal 33 Bus Topology Definition: A network topology in which all computers are attached to a shared medium (often a single cable). A bus topology, is multipoint. One long cable acts as a backbone to link all the devices in a network by Siti Fajar bt Jalal 34 Bus Topology (Cont.) Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. by Siti Fajar bt Jalal 35  Advantages: Ease of installation. Use less cabling. Disadvantages: Difficult reconfiguration and fault isolation – difficult to add new devices. A fault or break in the bus cable stops all transmission. Bus Topology (Cont.) by Siti Fajar bt Jalal 36 Ring Topology Definition: A network topology in which the devices are connected in a ring. 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, which regenerates the bits and passes them along by Siti Fajar bt Jalal 37 Ring Topology (Cont.) Advantages: Easy to install and reconfigure. Easy fault identification and isolation. Disadvantages: Unidirectional traffic. A break in the ring can disable the entire network. by Siti Fajar bt Jalal 38 HYBRID TOPOLOGY Definition: A network topology which is composed of more than one basic topology. by Siti Fajar bt Jalal 39 EXERCISE 1 Draw a hybrid topology with a star backbone connecting with 2 ring networks. by Siti Fajar bt Jalal 40 EXERCISE 2 Draw a hybrid topology with a bus backbone connecting with 3 star networks. by Siti Fajar bt Jalal 41 EXERCISE 3 Draw a hybrid topology with a ring backbone connecting with 2 bus networks and for every bus network connecting with 2 star networks. by Siti Fajar bt Jalal 42 TRANSMISSION MODE by Siti Fajar bt Jalal 43  Definition: Transmission mode refers TRANSMISSION to the direction of information flow MODE between two devices. There are three types of transmission modes: simplex, half duplex and full FULL-DUPLEX SIMPLEX HALF-DUPLEX duplex. (DUPLEX) Transmission mode by Siti Fajar bt Jalal 44  Definition: A transmission mode in which communication is one way. Unidirectional as on a one-way street. Only one of the two stations on a link can transmit; the other can only receive. E.g.: keyboards and traditional monitors. The keyboard can only introduce input; the monitor can only accept output. Simplex mode by Siti Fajar bt Jalal 45 Half-duplex mode Definition: A transmission mode in which 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. E.g.: walkie-talkie and citizen band (CB) radio. by Siti Fajar bt Jalal 46 Full-duplex mode Definition: A transmission mode in which communication can be two way simultaneously. Both stations can transmit and receive simultaneously. Like a two-way street with traffic flowing in both directions at the same time. E.g.: telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. by Siti Fajar bt Jalal 47 NETWORK TYPES: LAN, MAN by Siti Fajar bt Jalal 48 Local Area Network (LAN) Definition : LAN is a network connecting devices in a relatively small area such as building. It usually privately owned and connects some hosts in a single office, building, or campus. LAN are distinguished from others type of networks by its transmission media and topology. In general, a given LAN will use only one type of transmission medium. The most common topologies are bus, ring and star. by Siti Fajar bt Jalal 49 Local Area Network (LAN) (Cont.) LANs today are connected to each other and to WANs (discussed next) to create communication at a wider level. by Siti Fajar bt Jalal 50 Wide Area Network (WAN) Definition : A network connecting devices within very large areas such as states, countries and the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network. Complicated. by Siti Fajar bt Jalal 51  PP 2.3.8 Figure 1.10 : Wide Area Network (WAN) by Siti Fajar bt Jalal 52 1. Point-to- Point WAN A point-to-point WAN is a network that connects two communicating devices through a transmission medium (cable or air). by Siti Fajar bt Jalal 53 2. Switched WAN A switched WAN is a network with more than two ends. It is used in the backbone of a global communications network today. by Siti Fajar bt Jalal 54  LAN WAN limited in size: has a wider spanning an office, a geographical building, or a campus; span, spanning a town, a state, a country interconnects hosts interconnects connecting devices such as switches, routers, or modems normally privately normally created and owned by the run by organization that uses communication it companies and leased by an organization that uses it by Siti Fajar bt Jalal 55 Internetwork When two or more networks are connected, they make an internetwork, or internet. by Siti Fajar bt Jalal 56 Internetwork (Cont.) As an example, assume that an organization has two offices, one on the east coast and the other on the west coast. Each office has a LAN that allows all employees in the office to communicate with each other. To make the communication between employees at different offices possible, the management leases a point-to-point dedicated WAN from a service provider, such as a telephone company, and connects the two LANs. Now the company has an internetwork, or a private internet (with lowercase i). Communication between offices is now possible. by Siti Fajar bt Jalal 57 The Internet Today by Siti Fajar bt Jalal 58 EXERCISE 4 SECTION A: (TRUE/FALSE) 1. A LAN is a data communication system covering an area the size of a town or city. (TRUE/FALSE) 2. Networks are judged by their performance, reliability and compatibility. (TRUE/FALSE) 3. Full duplex is transmission mode in which communication can be two way but not at the same time.(TRUE/FALSE) 4. In a point-to-point line configuration, three or more devices share a link. (TRUE/FALSE) by Siti Fajar bt Jalal 59 Conclusion? by Siti Fajar bt Jalal 60