McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000

Data Communication & Networks

Muhammad Naveed Ahmad Qadri

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Lecture 1Introduction

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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS

Communication:Communication:•Sharing information.Sharing information.•Sharing can be local or remote.Sharing can be local or remote.•Local communication occurs face to face.Local communication occurs face to face.•Remote takes place over distance.Remote takes place over distance.Telecommunication:Telecommunication:•communication at a distance like telephony, telegraphy, communication at a distance like telephony, telegraphy, television (tele is Greek word for “far”)television (tele is Greek word for “far”)Data:Data:• Refers to information presented in whatever form is Refers to information presented in whatever form is agreed upon by the parties creating and using the data. agreed upon by the parties creating and using the data.

Data communications:Data communications: the exchange of data between two devices via some the exchange of data between two devices via some

form of transmission medium such as a wire cable.form of transmission medium such as a wire cable. Communication is the combination of Hardware Communication is the combination of Hardware

and software.and software. Effectiveness of data communication depends on Effectiveness of data communication depends on

four fundamental characteristics:four fundamental characteristics: Delivery: The system must deliver data to the correct Delivery: The system must deliver data to the correct

destination.destination. Accuracy: the system must deliver the data accurately.Accuracy: the system must deliver the data accurately. Timeliness: The system must deliver in timely manner.Timeliness: The system must deliver in timely manner. Jitter: refers to the variation of in the packet arrival Jitter: refers to the variation of in the packet arrival

time. Un-even delay in delivery of audio video packets.time. Un-even delay in delivery of audio video packets.1.4

1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS

Data communications Components:Data communications Components: Data communication has five components:Data communication has five components:

Message: Message: The message is the information (data) to be The message is the information (data) to be communicated. It may be text, picture, audio or video.communicated. It may be text, picture, audio or video.

Sender:Sender: The sender is the device that sends the data The sender is the device that sends the data message. e.g. computer, workstation, telephone etc.message. e.g. computer, workstation, telephone etc.

Receiver:Receiver: the receiver is the device that receives the the receiver is the device that receives the message. e.g. computer, workstation, telephone etc.message. e.g. computer, workstation, telephone etc.

Transmission Medium: Transmission Medium: physical path by which a physical path by which a message travels from sender to receiver. e.g. cables, message travels from sender to receiver. e.g. cables, radio waves.radio waves.

Protocol: Protocol: set of rules that govern data communication.set of rules that govern data communication.

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Components of Data CommunicationComponents of Data Communication

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Figure 1.1 Five components of data communication

Text:Text: Text is represented as a bit pattern (0s or 1s)Text is represented as a bit pattern (0s or 1s) Set of bit patterns have been designed for text symbols.Set of bit patterns have been designed for text symbols. Each set is called CODE.Each set is called CODE. The process of representing symbols is called CODINGThe process of representing symbols is called CODING

Numbers:Numbers: Also represented by bit patterns.Also represented by bit patterns. ASCII is not used to represent number, directly ASCII is not used to represent number, directly

converted to binary for simplification of operations.converted to binary for simplification of operations. Images:Images:

Also represented by bit pattern.Also represented by bit pattern.1.7

Data RepresentationData Representation

Image is composed of matrix of pixels (small dot).Image is composed of matrix of pixels (small dot). Image is divided into pixel, each pixel is assigned a bit Image is divided into pixel, each pixel is assigned a bit

pattern.pattern. Size and value of pattern depend on the image.Size and value of pattern depend on the image.

Audio:Audio: Recording or broadcasting of sound or music.Recording or broadcasting of sound or music. continuous signals.continuous signals.

Video:Video: Recording or broadcasting of a picture of movie.Recording or broadcasting of a picture of movie. Can be the combination of images,voice.Can be the combination of images,voice.

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Data RepresentationData Representation

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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

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1-2 NETWORKS1-2 NETWORKS

• A A NetworkNetwork is a set of devices (often referred to as is a set of devices (often referred to as nodesnodes) ) connected by communication connected by communication linkslinks. .

• A node can be a computer, printer, or any other device.A node can be a computer, printer, or any other device.• Most networks use distributed processing, in which a Most networks use distributed processing, in which a

task is divided among multiple computers.task is divided among multiple computers.• A network must be able to meet a certain number of A network must be able to meet a certain number of

criteria. The most important of these are:criteria. The most important of these are:• Performance:Performance: (transit time and response time) (transit time and response time)• Reliability:Reliability: Accuracy of delivery of the packet. Accuracy of delivery of the packet.• Security: Security: protecting data from unauthorized access, protecting data from unauthorized access,

from damage & development and implementing from damage & development and implementing policies for recovery from breaches.policies for recovery from breaches.

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1-2.2 PHYSICAL STRUCTURE1-2.2 PHYSICAL STRUCTURE

• A A NetworkNetwork is two or more devices connected through is two or more devices connected through link.link.

• A A LinkLink is a communication pathway that transfer data. is a communication pathway that transfer data.• A Link is a line drawn between two points.A Link is a line drawn between two points.• Both devices must connected in some way to same link at Both devices must connected in some way to same link at

same time.same time.• Two possible types:Two possible types:• Point-to-Point:Point-to-Point: provides a dedicated link between provides a dedicated link between

two devices e.g. remote control and television.two devices e.g. remote control and television.• MultipointMultipoint: it is a connection in which more than two : it is a connection in which more than two

specific devices share a single link.specific devices share a single link.

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Figure 1.3 Types of connections: point-to-point and multipoint

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Figure 1.4 Categories of topology

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MESH TOPOLOGYMESH TOPOLOGY

• Every device has dedicated point-to-point link.Every device has dedicated point-to-point link.• We need n(n-1) physical links.We need n(n-1) physical links.• In duplex mode we need n(n-1)/2 links.In duplex mode we need n(n-1)/2 links.• Each connection can carry its own data load.Each connection can carry its own data load.• If one link becomes unusable, it does not down whole If one link becomes unusable, it does not down whole

system.system.• There is the advantage of privacy and security.There is the advantage of privacy and security.• Point-to-point links make fault identification easy.Point-to-point links make fault identification easy.• Maximum amount of cabling and the number of I/O Maximum amount of cabling and the number of I/O

ports required.ports required.

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Figure 1.5 A fully connected mesh topology (five devices)

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STAR TOPOLOGYSTAR TOPOLOGY

• Every device has dedicated point-to-point link only to a Every device has dedicated point-to-point link only to a central controller, called hub or switch.central controller, called hub or switch.

• Star topology does not allow direct traffic b/w devices.Star topology does not allow direct traffic b/w devices.• Central controller acts an exchange.Central controller acts an exchange.• If one link becomes unusable, it does not down whole If one link becomes unusable, it does not down whole

system.system.• Point-to-point links make fault identification easy.Point-to-point links make fault identification easy.• Amount of cabling and the number of I/O ports required.Amount of cabling and the number of I/O ports required.• This topology is used in LAN.This topology is used in LAN.• Dependency of the whole topology on one single point.Dependency of the whole topology on one single point.

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Figure 1.6 A star topology connecting four stations

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BUS TOPOLOGYBUS TOPOLOGY

• Bus topology is Bus topology is Multipoint.Multipoint.• Long Long BackboneBackbone cable to link all the devices in a network cable to link all the devices in a network• Nodes are connected to cable through drop lines & taps.Nodes are connected to cable through drop lines & taps.• Drop line is a connection running b/w the devices & Drop line is a connection running b/w the devices &

cable.cable.• Tap is a connector that splices into the main cable.Tap is a connector that splices into the main cable.• A signal travels along the backbone.A signal travels along the backbone.• Easy installation.Easy installation.• Use less cabling than star and mesh.Use less cabling than star and mesh.• Adding new devices may therefore require modification Adding new devices may therefore require modification

or replacement of the backbone.or replacement of the backbone.• Fault or break in the bust cable stops all transmission.Fault or break in the bust cable stops all transmission.

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Figure 1.7 A bus topology connecting three stations

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RING TOPOLOGYRING TOPOLOGY

• Dedicated point to point connection.Dedicated point to point connection.• Signal pass along the ring in one direction from device Signal pass along the ring in one direction from device

to device until it reaches the destination.to device until it reaches the destination.• Each device incorporates a repeater.Each device incorporates a repeater.• Ring is relatively easy to install and reconfigure.Ring is relatively easy to install and reconfigure.• To add or delete a device requires changing only two To add or delete a device requires changing only two

connections.connections.• In a ring, signal is circulating at all times.In a ring, signal is circulating at all times.• If one device does not receive a signal within a specified If one device does not receive a signal within a specified

period, it can issue an alarm.period, it can issue an alarm.• The alarm alerts the network operator to the problem The alarm alerts the network operator to the problem

and its location.and its location.• Unidirectional traffic.Unidirectional traffic.

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Figure 1.8 A ring topology connecting six stations

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HYBRID TOPOLOGYHYBRID TOPOLOGY

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

topology.topology.

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Figure 1.9 A hybrid topology: a star backbone with three bus networks

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1.3 NETWORK TYPES1.3 NETWORK TYPES

• LOCAL AREA NETWORK(LAN)LOCAL AREA NETWORK(LAN)• Usually privately owned and connects some hosts in a Usually privately owned and connects some hosts in a

single office, building or campus.single office, building or campus.• Each host in LAN has an identifier, an address.Each host in LAN has an identifier, an address.• A packet sent by a host to another carries both addressA packet sent by a host to another carries both address• I past all host in network were connected through a I past all host in network were connected through a

common cable.common cable.• Packet sent by one was received by all.Packet sent by one was received by all.• Intended recipient kept the packet, other drops.Intended recipient kept the packet, other drops.• Today LAN uses the smart connecting switch.Today LAN uses the smart connecting switch.

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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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1.3 NETWORK TYPES1.3 NETWORK TYPES

WIDE AREA NETWORK(WAN)WIDE AREA NETWORK(WAN)• LAN is limited in size, WAN has wider geographical LAN is limited in size, WAN has wider geographical

area.area.• LAN interconnects hosts;WAN interconnects devices LAN interconnects hosts;WAN interconnects devices

like switches, routers or modems.like switches, routers or modems.• Point-to-Point WAN:Point-to-Point WAN:• It is network that connects two communicating It is network that connects two communicating

devices through a transmission media(cable or air) devices through a transmission media(cable or air) like dial up modems.like dial up modems.

• Switched WAN:Switched WAN:• Switched WAN is a combination of several point-to-Switched WAN is a combination of several point-to-

point WANs that are connected by switches.point WANs that are connected by switches.

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Figure 1.11 WANs: a switched WAN and a point-to-point WAN

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Figure 1.12 A heterogeneous network made of four WANs and two LANs

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1.3 NETWORK TYPES1.3 NETWORK TYPES

METROPOLITAN AREA NETWORK(MAN)METROPOLITAN AREA NETWORK(MAN)• Network with a size between LAN and WAN.Network with a size between LAN and WAN.• Normally covers the area within town and city.Normally covers the area within town and city.• It is designed for the customer who needs high It is designed for the customer who needs high

speed connectivity.speed connectivity.• Good example is a part of telephone company Good example is a part of telephone company

network that can provide high speed of DSL line to network that can provide high speed of DSL line to customers.customers.

• Another example is Cable TV network.Another example is Cable TV network.

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1-3 THE INTERNET1-3 THE INTERNET

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

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Figure 1.13 Hierarchical organization of the Internet

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1-4 PROTOCOLS AND STANDARDS1-4 PROTOCOLS AND STANDARDS

• Communication occurs b/w the entities of different systems.Communication occurs b/w the entities of different systems.• For the communication they must agree on the protocol.For the communication they must agree on the protocol.• Protocols are the set of rules that governs the Protocols are the set of rules that governs the

communication to occur.communication to occur.• Syntax:Syntax:• Structure and format of the data, means order in which Structure and format of the data, means order in which

the data will be presented. Like 1the data will be presented. Like 1stst 8 bits sender last 8 bit 8 bits sender last 8 bit receiver address rest is message.receiver address rest is message.

• Semantics:Semantics:• Meaning of each section of bit. How a particular pattern Meaning of each section of bit. How a particular pattern

be interpreted.be interpreted.• Timing:Timing:• When the data should be sent and how fast that can be When the data should be sent and how fast that can be

sent.sent.