Networks and Networks and CommunicationCommunication

Prepared By:Mazhar Javed AwanPrepared By:Mazhar Javed Awan

Networks Networks Is the series of computer systems that are linked Is the series of computer systems that are linked

together so that they are able to share computing power together so that they are able to share computing power or storage facilities.or storage facilities.

A network is connected with one another through A network is connected with one another through cables or telephone wires.cables or telephone wires.

The link way be between computers in the same The link way be between computers in the same building or between computers in different parts of the building or between computers in different parts of the country.country.

Network may be in form of Network may be in form of Terminal computer Terminal computer Server ComputerServer Computer

ExamplesExamples

Computer network can be used in offices or Computer network can be used in offices or computers Lab computers Lab

Internet is an example of network in which Internet is an example of network in which million of people are connected with phone million of people are connected with phone lineslines

Advantages of networking Advantages of networking

Information and resourceInformation and resource sharing by using printer or sharing by using printer or scannersscanners

Money savingMoney saving by using the same software by using the same software Easy communicationEasy communication with others using large network with others using large network

like internet.like internet. Internet Access SharingInternet Access Sharing by using one high speed by using one high speed

connection instead of many slower one.connection instead of many slower one. Avoid duplicate informationAvoid duplicate information by using to share same file by using to share same file Data Security and ManagementData Security and Management EntertainmentEntertainment through playing multi-player game through playing multi-player game Maintain and backupMaintain and backup data easily because these are data easily because these are

stored in centerstored in center

Disadvantages of networking Disadvantages of networking Hardware, software & SetupHardware, software & Setup Costs by designing and Costs by designing and

implementing the networkimplementing the network Hardware & Software ManagementHardware & Software Management Costs by hiring a network Costs by hiring a network

administratoradministrator Undesirable sharingUndesirable sharing by spreading viruses over networks by spreading viruses over networks Illegal or Undesirable BehaviorIllegal or Undesirable Behavior by downloading by downloading Data Security ConcernsData Security Concerns by unauthorized access through by unauthorized access through

hackers hackers Whole network becomes unusableWhole network becomes unusable if server breaks down if server breaks down

Types of computer networksTypes of computer networks

LAN ( LOCAL AREA NETWORK )LAN ( LOCAL AREA NETWORK ) WAN (WIDE AREA NETWROK )WAN (WIDE AREA NETWROK ) MAN ( MANIPULATION AREA MAN ( MANIPULATION AREA

NETWROK)NETWROK)

LAN LAN It covers small areaIt covers small area Most LANs are used to connect computer in a single building or group of Most LANs are used to connect computer in a single building or group of

buildingsbuildings LANs can be found in industrial plants , office buildings ,colleges or LANs can be found in industrial plants , office buildings ,colleges or

universitiesuniversities Capable of transmitting data at very fast rate Capable of transmitting data at very fast rate It is much faster than data transmission over a telephone lineIt is much faster than data transmission over a telephone line

LAN CHARACTERISTICSSize Transmission Technology Topology

 Restricted in Size

 Single Cable

10 to 100 Mbps

Low delay (ms)

Very few Errors

Megabits/Sec. (Unit)

 BUS (Ethernet) Ring (Token ring)  

Uses of LANUses of LAN Sharing of one copy by all usersSharing of one copy by all users System resources can be share System resources can be share

like printerlike printer Easy to manage data store Easy to manage data store Data is more secure from being Data is more secure from being

copied or destroyed copied or destroyed It may be in form of It may be in form of Peer-to-peer Network Peer-to-peer Network Client Server Network Client Server Network

WAN WAN It covers the large area It covers the large area WAN connects computer in different cities and countries WAN connects computer in different cities and countries Normally a WAN consists of two or more interconnected Normally a WAN consists of two or more interconnected

LANs LANs Connected through telephone lines or satellites Connected through telephone lines or satellites WAN is expensive than LAN WAN is expensive than LAN Speed depends on the speed provided by the companySpeed depends on the speed provided by the company Use in banks or in air ticketing system Use in banks or in air ticketing system

MANMAN

Is the communication network that covers a Is the communication network that covers a geographical area of the size of citygeographical area of the size of city

A MAN include one or more LANs but covers a A MAN include one or more LANs but covers a small geographical area than WANsmall geographical area than WAN

It act as a high speed network It act as a high speed network Mobile phone system often use MANMobile phone system often use MAN

Network Topologies Network Topologies The physical layout or the way in which network connections The physical layout or the way in which network connections

connection are made is called topology connection are made is called topology It refers especially to the locations of the computer and how It refers especially to the locations of the computer and how

the cable runs between them the cable runs between them It may be It may be Bus or Line Topology Bus or Line Topology Star TopologyStar Topology Ring Topology Ring Topology Tree TopologyTree Topology

Bus or Line Topology Bus or Line Topology All computers or network nodes are connected to a common communication All computers or network nodes are connected to a common communication

medium medium In a local network this medium is often a central wire called busIn a local network this medium is often a central wire called bus WorkingWorking If a computer wants to send data to the other computer in the network ,it sends If a computer wants to send data to the other computer in the network ,it sends

the data via the busthe data via the bus The data and address move from one computer to other and checks the address The data and address move from one computer to other and checks the address

if it matches then it goes to other computerif it matches then it goes to other computer

Server

WorkstationWorkstation Workstation

Workstation Laser printer

AdvantagesAdvantages Simple easy and suitable for small network Simple easy and suitable for small network Least amount of cable is requiredLeast amount of cable is required Easy to extend a bus Easy to extend a bus

Disadvantages Disadvantages Heavy network traffic can slow a network Heavy network traffic can slow a network A cable breaks or loose connector will disconnect the entire A cable breaks or loose connector will disconnect the entire

network network No of computer increase then speed of network will be slow No of computer increase then speed of network will be slow

Star Topology Star Topology Is one in which all the cables run Is one in which all the cables run

from the computers to a central from the computers to a central location location

Connected with the device called Connected with the device called hub hub

Used in client server network Used in client server network

WorkingWorking If two computers want to share If two computers want to share

data the sender computer sends data the sender computer sends data to the hub and hub sends it to data to the hub and hub sends it to the receiving computerthe receiving computer

Server

Workstation

Workstation Workstation

Workstation

Laser printer

Advantages Advantages

Hub can accommodate multiple cable typesHub can accommodate multiple cable types Easy to modify Easy to modify Finding faults becomes easyFinding faults becomes easy Single computer failure cannot break the network Single computer failure cannot break the network DisadvantagesDisadvantages If central hubs fails the entire network fails If central hubs fails the entire network fails It is more expensive because all network cables must It is more expensive because all network cables must

be pulled to a central pointbe pulled to a central point

Ring Topology Ring Topology

Each computer is connected to the Each computer is connected to the next computer with the last one next computer with the last one connected to the first connected to the first

Data flow around the circle from Data flow around the circle from device to device in one direction only device to device in one direction only

Working Working Each computer retransmits what it Each computer retransmits what it

receives from the previous computer receives from the previous computer The message flow in one direction The message flow in one direction

Advantages Advantages

There is no signal loss problem There is no signal loss problem Every computer has a equal access to the token Every computer has a equal access to the token

Disadvantages Disadvantages Failure of one computer on ring effect the whole Failure of one computer on ring effect the whole

networknetwork Difficult to troubleshoot Difficult to troubleshoot Adding or removing computers disrupts the network Adding or removing computers disrupts the network

Hierarchical networksHierarchical networks

In some networks one or more computers In some networks one or more computers are more powerful than the others.are more powerful than the others.

These networks are called hierarchical These networks are called hierarchical networks.networks.

These more powerful computers usually These more powerful computers usually look after specific functions on the network look after specific functions on the network and are called servers (e.g. file servers, and are called servers (e.g. file servers, printer servers).printer servers).

File servers manage all the files stored on File servers manage all the files stored on the network, including program and data the network, including program and data files.files.

File servers are also used to store program File servers are also used to store program and data files.and data files.

Printer servers manage all the printing Printer servers manage all the printing requests on the network.requests on the network.

Network software and Network software and hardwarehardware

Networks require specific software and hardware Networks require specific software and hardware in order to work including:in order to work including: A network operating system.A network operating system. Network cabling (e.g. metal or fibre optic cables) and Network cabling (e.g. metal or fibre optic cables) and

connectors connectors oror wireless media (e.g. radio, microwave, or wireless media (e.g. radio, microwave, or infra-red).infra-red).

Network cards.Network cards. The quality of the software and hardware used The quality of the software and hardware used

will determine the speed at which data is will determine the speed at which data is transferred (i.e. the data transfer speed).transferred (i.e. the data transfer speed).

The data transfer speed is the speed at which The data transfer speed is the speed at which data is transferred from the server to a data is transferred from the server to a workstation/terminal.workstation/terminal.

Download time is the time this data transfer Download time is the time this data transfer takes.takes.

Communications links Communications links Twisted pair (copper cable):Twisted pair (copper cable): Two wires twisted together.Two wires twisted together.

Makes them less susceptible to acting like an antenna and picking up radio Makes them less susceptible to acting like an antenna and picking up radio frequency information frequency information

Telephone company uses twisted-pair copper wires to link telephones.Telephone company uses twisted-pair copper wires to link telephones.

Coaxial cableCoaxial cable Also two wires: Also two wires:

One of the wires is woven of fine strands of copper forming a tube. One of the wires is woven of fine strands of copper forming a tube. The wire mesh surrounds a solid copper wire that runs down the center. The wire mesh surrounds a solid copper wire that runs down the center. Space between has a non-conducting material.Space between has a non-conducting material. Makes them more impervious to outside noise.Makes them more impervious to outside noise.

Fiber-optic cableFiber-optic cable

Light is electromagnetic.Light is electromagnetic. Can transmit more Can transmit more

information down a information down a single strand. single strand.

It can send a wider set of It can send a wider set of frequencies.frequencies.

Each cable can send Each cable can send several thousand phone several thousand phone conversations or conversations or computer computer communications.communications.

InfraredInfrared

Commonly used in TV Commonly used in TV and VCR remote controls.and VCR remote controls.

Use infrared frequencies Use infrared frequencies of electromagnetic of electromagnetic radiation that behave radiation that behave much like visible light.much like visible light.

Must be in the line of Must be in the line of sight.sight.

Often used to connect Often used to connect keyboards, mice, keyboards, mice, and printers. and printers.

MicrowaveMicrowave

Often used to communicate Often used to communicate with distant locations.with distant locations.

Must be line of sight.Must be line of sight. Satellite communications use Satellite communications use

microwaves.microwaves.

Radio frequencyRadio frequency

•Uses radio frequencies.•Function even though line of sight is interrupted.

•Not commonly used because of the possible interference from other sources of electromagnetic radiation such as old electric drills and furnace motors.

Network securityNetwork security

Keeping networks secure is very Keeping networks secure is very important.important.

This is usually done by giving all This is usually done by giving all users a:users a: User ID – a unique name or number that User ID – a unique name or number that

identifies each individual network user identifies each individual network user and allocates each user’s file access.and allocates each user’s file access.

Password – a string of letters and/or Password – a string of letters and/or numbers that is only known by each numbers that is only known by each individual user.individual user.

Modem Modem To do this the computer must be equipped with a To do this the computer must be equipped with a

modemmodem ((MoModulator – dulator – DemDemodulator).odulator).

The modem converts digital signals into analogue The modem converts digital signals into analogue signals that can be sent along telephone lines.signals that can be sent along telephone lines.

It can also convert analogue signals it receives It can also convert analogue signals it receives back into digital signals the computer can use.back into digital signals the computer can use.

MODEM

Digital signal

‘1’

‘0’

One Tone representsBinary ‘1’

A different TonerepresentsBinary ‘0’

Telephone line

Dial up Connection Dial up Connection

•Dial up ties up your telephone line and so it cannot be used for anything else.•It takes a while for the computer to set up a connection i.e many seconds.•Internet Service Providers may charge you by the minute and so a slow link means you pay more.

Disadvantages

Integrated Services Digital NetworkIntegrated Services Digital Network

You do not need a modem but instead need a device called an ISDN terminal adapter.You do not need a modem but instead need a device called an ISDN terminal adapter. In this network sending voice, video and computer data and user can receive telephone In this network sending voice, video and computer data and user can receive telephone

calls using the one line.calls using the one line. Conduct videoconferencing easily.Conduct videoconferencing easily. Designed to replace public telecom systemDesigned to replace public telecom system Wide variety of servicesWide variety of services Entirely digital domainEntirely digital domain First generation ( narrowband ISDN )First generation ( narrowband ISDN )

64 kbps channel is the basic unit64 kbps channel is the basic unit Circuit-switching orientationCircuit-switching orientation Contributed to frame relayContributed to frame relay

Second generation ( broadband ISDN )Second generation ( broadband ISDN ) 100s of mbps100s of mbps Packet-switching orientationPacket-switching orientation Contributed to ATM ( cell relay )Contributed to ATM ( cell relay )

Disadvantages Disadvantages

Your main telephone socket has to be changed to an ISDN box Your main telephone socket has to be changed to an ISDN box by an engineer.by an engineer.

Your computer has to be fitted with an ISDN modem which is Your computer has to be fitted with an ISDN modem which is more expensive than a standard modem.more expensive than a standard modem.

It is more expensive than Dial-up on a monthly basis.It is more expensive than Dial-up on a monthly basis. Should you move house, you have to pay for your telephone Should you move house, you have to pay for your telephone

line to be converted back again to a normal line.line to be converted back again to a normal line.

Message SendingMessage Sending

Sending data down a communication line is Sending data down a communication line is not just a question of sending the streams of not just a question of sending the streams of bits that represent each character.bits that represent each character.

The problemThe problem is that each computer is that each computer manufacturer has its own standards for manufacturer has its own standards for encoding data.encoding data.

ProtocolsProtocols Used for communications between entities in a systemUsed for communications between entities in a system An agreed-upon format or set of rules for transmitting data An agreed-upon format or set of rules for transmitting data

between two devices. between two devices. Must speak the same languageMust speak the same language EntitiesEntities

User applicationsUser applications E-mail facilitiesE-mail facilities TerminalsTerminals

SystemsSystems ComputerComputer TerminalTerminal Remote sensorRemote sensor

Key Elements of a ProtocolKey Elements of a Protocol

SyntaxSyntax Data formatsData formats Signal levelsSignal levels

SemanticsSemantics Control informationControl information Error handlingError handling

TimingTiming Speed matchingSpeed matching SequencingSequencing

HandshakingHandshaking

Handshaking is the exchange of signals between devices to establish their Handshaking is the exchange of signals between devices to establish their readiness to send or receive data. readiness to send or receive data.

E.g. Between Computer and PrinterE.g. Between Computer and Printer It is one method of ensuring that both the sender and receiver are ready It is one method of ensuring that both the sender and receiver are ready

before transmission begins. before transmission begins. The conversation between the two devices is along the lines of following The conversation between the two devices is along the lines of following Device 1Device 1 Device 2Device 2 Are you ready to receive data Yes go aheadAre you ready to receive data Yes go ahead Sends data Sends data Message received thanks Message received thanks

File CompressionFile Compression

File compression is the process of condensing File compression is the process of condensing repetitive information. repetitive information.

It is used when sending a data through It is used when sending a data through telecommunications link.telecommunications link.

Since the smaller the file, the cheaper the file Since the smaller the file, the cheaper the file transfer will be.transfer will be.

File compression may be performed by File compression may be performed by software before the data is sent or by the software before the data is sent or by the modem itself as the data is being sent.modem itself as the data is being sent.

Access Speed Access Speed

The speed with which you can surf the web or view The speed with which you can surf the web or view data over a wide area network depends on a couple of data over a wide area network depends on a couple of factors.factors.

The speed of your modem will determine how fast The speed of your modem will determine how fast the pulses are sent and the speed of the receiver’s the pulses are sent and the speed of the receiver’s modem will determine the speed with which they can modem will determine the speed with which they can arrive.arrive.

The speed of the slowest modem will determine the The speed of the slowest modem will determine the speed of the over link.speed of the over link.

Different types of cables also influence the speed.Different types of cables also influence the speed.

BandwidthBandwidth Bandwidth is a measure of how much data can be carried Bandwidth is a measure of how much data can be carried

at one time, measured in Megabits per second (Mbps).at one time, measured in Megabits per second (Mbps). The bandwidth is determined by the transmission media The bandwidth is determined by the transmission media

(cabling) and the protection around it to lessen (cabling) and the protection around it to lessen interference.interference.

BandwidthBandwidth: : DigitalDigital Number of bits per second (bps) that can be sent over Number of bits per second (bps) that can be sent over

a link.a link. The wider the bandwidth, the more diverse kinds of The wider the bandwidth, the more diverse kinds of

information can be sent.information can be sent. Simplest is voice, most sophisticated is moving Simplest is voice, most sophisticated is moving

videos.videos. BandwidthBandwidth: : AnalogAnalog

The difference between the highest and lowest The difference between the highest and lowest frequencies that can be sent over an analog link (like frequencies that can be sent over an analog link (like phone lines).phone lines).

Measurement is given in hertz (Hz).Measurement is given in hertz (Hz). For bothFor both:: The wider the bandwidth, the more information The wider the bandwidth, the more information

can flow over the channel.can flow over the channel.

Cost of installationCost of installation

Terminal costs Terminal costs Servers costsServers costs Cabling costs Cabling costs Network cards Network cards Software Software Back up devices Back up devices The cost of modem or ISDN The cost of modem or ISDN Cost of ISP Cost of ISP Telephone or other communication charges.Telephone or other communication charges.

Electronic data interchange (EDI)Electronic data interchange (EDI)

EDI is the electronic transmission of business data, EDI is the electronic transmission of business data, such as purchase orders and invoices from one firm such as purchase orders and invoices from one firm to another. to another.

Speed and reliability are major advantages of EDI.Speed and reliability are major advantages of EDI. Data such as O level result are now commonly Data such as O level result are now commonly

transmitted direct to schools and colleges rather then transmitted direct to schools and colleges rather then being sent by mail.being sent by mail.