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Ch01 introduction

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  • 1.*Lecture 1

    Introduction.

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    1-1 DATA COMMUNICATIONS

    Communication:Sharing information.Sharing can be local or remote.Local communication occurs face to face.Remote takes place over distance.

    Telecommunication:communication at a distance like telephony, telegraphy, television (tele is Greek word for far)

    Data: Refers to information presented in whatever form is agreed upon by the parties creating and using the data.

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  • Data communications: the exchange of data between two devices via some form of transmission medium such as a wire cable.Communication is the combination of Hardware and software.Effectiveness of data communication depends on four fundamental characteristics:Delivery: The system must deliver data to the correct destination.Accuracy: the system must deliver the data accurately.Timeliness: The system must deliver in timely manner.Jitter: refers to the variation of in the packet arrival time. Un-even delay in delivery of audio video packets.

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    1-1 DATA COMMUNICATIONS

  • Data communications Components: Data communication has five components:Message: The message is the information (data) to be communicated. It may be text, picture, audio or video.Sender: The sender is the device that sends the data message. e.g. computer, workstation, telephone etc.Receiver: the receiver is the device that receives the message. e.g. computer, workstation, telephone etc. Transmission Medium: physical path by which a message travels from sender to receiver. e.g. cables, radio waves.Protocol: set of rules that govern data communication.

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    Components of Data Communication

  • 1.*Figure 1.1 Five components of data communication

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  • Text:Text is represented as a bit pattern (0s or 1s)Set of bit patterns have been designed for text symbols.Each set is called CODE.The process of representing symbols is called CODINGNumbers:Also represented by bit patterns.ASCII is not used to represent number, directly converted to binary for simplification of operations.Images:Also represented by bit pattern.

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    Data Representation

  • Image is composed of matrix of pixels (small dot).Image is divided into pixel, each pixel is assigned a bit pattern.Size and value of pattern depend on the image.Audio:Recording or broadcasting of sound or music.continuous signals.Video:Recording or broadcasting of a picture of movie.Can be the combination of images,voice.

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    Data Representation

  • 1.*Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

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    1-2 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.Most networks use distributed processing, in which a task is divided among multiple computers.A network must be able to meet a certain number of criteria. The most important of these are:Performance: (transit time and response time)Reliability: Accuracy of delivery of the packet.Security: protecting data from unauthorized access, from damage & development and implementing policies for recovery from breaches.

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    1-2.2 PHYSICAL STRUCTURE

    A Network is two or more devices connected through link.A Link is a communication pathway that transfer data.A Link is a line drawn between two points.Both devices must connected in some way to same link at same time.Two possible types:Point-to-Point: provides a dedicated link between two devices e.g. remote control and television.Multipoint: it is a connection in which more than two specific devices share a single link.

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  • 1.*Figure 1.3 Types of connections: point-to-point and multipoint

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  • 1.*Figure 1.4 Categories of topology

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    MESH TOPOLOGY

    Every device has dedicated point-to-point link.We need n(n-1) physical links.In duplex mode we need n(n-1)/2 links.Each connection can carry its own data load.If one link becomes unusable, it does not down whole system.There is the advantage of privacy and security.Point-to-point links make fault identification easy.Maximum amount of cabling and the number of I/O ports required.

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  • 1.*Figure 1.5 A fully connected mesh topology (five devices)

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    STAR TOPOLOGY

    Every device has dedicated point-to-point link only to a central controller, called hub or switch.Star topology does not allow direct traffic b/w devices.Central controller acts an exchange.If one link becomes unusable, it does not down whole system.Point-to-point links make fault identification easy.Amount of cabling and the number of I/O ports required.This topology is used in LAN.Dependency of the whole topology on one single point.

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  • 1.*Figure 1.6 A star topology connecting four stations

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    BUS TOPOLOGY

    Bus topology is Multipoint.Long Backbone cable to link all the devices in a networkNodes are connected to cable through drop lines & taps.Drop line is a connection running b/w the devices & cable.Tap is a connector that splices into the main cable.A signal travels along the backbone.Easy installation.Use less cabling than star and mesh.Adding new devices may therefore require modification or replacement of the backbone.Fault or break in the bust cable stops all transmission.

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  • 1.*Figure 1.7 A bus topology connecting three stations

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    RING TOPOLOGY

    Dedicated point to point connection.Signal pass along the ring in one direction from device to device until it reaches the destination.Each device incorporates a repeater.Ring is relatively easy to install and reconfigure.To add or delete a device requires changing only two connections.In a ring, signal is circulating at all times.If one device does not receive a signal within a specified period, it can issue an alarm.The alarm alerts the network operator to the problem and its location.Unidirectional traffic.

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  • 1.*Figure 1.8 A ring topology connecting six stations

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    HYBRID TOPOLOGY

    A network can be hybrid.It can be made up of several topologies like star, bus.We have main star topology.Each branch is connected with several stations in bus topology.

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  • 1.*Figure 1.9 A hybrid topology: a star backbone with three bus networks

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    1.3 NETWORK TYPES

    LOCAL AREA NETWORK(LAN)Usually privately owned and connects some hosts in a single office, building or campus.Each host in LAN has an identifier, an address.A packet sent by a host to another carries both addressI past all host in network were connected through a common cable.Packet sent by one was received by all.Intended recipient kept the packet, other drops.Today LAN uses the smart connecting switch.

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  • 1.*Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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    1.3 NETWORK TYPES

    WIDE AREA NETWORK(WAN)LAN is limited in size, WAN has wider geographical area.LAN interconnects hosts;WAN interconnects devices like switches, routers or modems.Point-to-Point WAN:It is network that connects two communicating devices through a transmission media(cable or air) like dial up modems.Switched WAN:Switched WAN is a combination of several point-to-point WANs that are connected by switches.

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  • 1.*Figure 1.11 WANs: a switched WAN and a point-to-point WAN

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  • 1.*Figure 1.12 A heterogeneous network made of four WANs and two LANs

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    1.3 NETWORK TYPES

    METROPOLITAN AREA NETWORK(MAN)Network with a size between LAN and WAN.Normally covers the area within town and city.It is designed for the customer who needs high speed connectivity.Good example is a part of telephone company network that can provide high speed of DSL line to customers.Another example is Cable TV network.

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    1-3 THE INTERNET

    The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use.

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  • 1.*Figure 1.13 Hierarchical organization of the Internet

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    1-4 PROTOCOLS AND STANDARDS

    Communication occurs b/w the entities of different systems.For the communication they must agree on the protocol.Protocols are the set of rules that governs the communication to occur.Syntax:Structure and format of the data, means order in which the data will be presented. Like 1st 8 bits sender last 8 bit receiver address rest is message.Semantics:Meaning of each section of bit. How a particular pattern be interpreted.Timing:When the data should be sent and how fast that can be sent.

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