1. Computer networks allow for the interconnection of independent computers to share information and resources. ARPANET, developed in 1967, was one of the first computer networks and connected four nodes through the use of IMPs (Interface Message Processors). 2. Computer networks provide advantages like central storage of data, sharing of information and resources, reliability, and reduced costs. However, they also present disadvantages such as requiring specific setups and introducing security and cost issues. 3. Common network topologies include bus, ring, and star configurations. A bus topology connects all nodes to a single cable or backbone but a failure of one node can shutdown the entire network. Ring topologies connect all nodes in a closed loop but also

1. Computer Networks
Introduction:
ComputerNetworkisacollectionof autonomouscomputersinterconnectedbyasingle
technology. Twoormore computersare saidto be interconnectedif theyare able toexchange
information. A computernetworkisasystemthatconnectsindependentcomputersinorderto
share information andresources.
Brief History of Network
 In 1967, ARPA (Advance ResearchProjectAgencybyDepartmentof Defence)
proposed the ideaof ARPANET– a small network of computers.
 By 1969, ARPANETbecame realitythatconnectfournodesatUniversityof California
at Los Angeles(UCLA),Universityof CaliforniaatSanta Barbara (UCSB),Stanford
ResearchInstitute (SRI) andUniversityof Utahvai IMPs ( Interface Message
Processor– a specializedcomputer).
 In 1973, VintCerf andBob Kahnpresented paperoutlinedthe protocol(
Transmission Control Protocol) toachieve end-to-enddelivery of packets.
Advantage of ComputerNetwork:
 Central Storage of Data
 Sharingof Information
 Sharingof Resources(Hardware&Software)
 Reliability
 Communication
 Reduced Cost
Disadvantage of ComputerNetwork:
 Computernetworks require aspecificsetup
 Lack of Security
 Costof network hardware andsoftware
Componentsof Data Communication:
 Message – it information tobe communicated
 Sender– The device whichsendthe message
 Receiver–The device whichreceivethe message
 Transmissionmedia–Itis physical pathbywhichmessage travel fromsenderto
receiver
 Protocol – It is setof rulesthatgovernsdatacommunication.Actuallyitis
agreementbetweenthe senderandreceiverregardingvariouscommunication
parameter.
Data Flow
 Simplex –Inthismode of communication, dataistransmittedin one direction only.
e.g. Keyboard, monitor. Itusesentirecapacity of channel tosendthe data.
 Half Duplex – Communicationisbi-directional butnotsame time.i.e.Walkie-Talkie.
It usesentire capacity of channel is utilizedforeach direction.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 53

2. MM : MM : MM : SS : SS : SS
 Full Duplex –Communicationsisbi-directional simultaneouslyi.e.bothsenderand
receivercanbe send data at same time.
NetworkTerminology
 Node- The device connected toanetwork.
 Client–The device thatrequestforaservice
 Server– The Device thatrender the services
 Client-Server- Inthismodel,the data are storedon powerful computerscalled
Server that can be accessedbya much simplercomputercalled Clientthatare
connected by a network.
 NetworkInterface CardorUnit (NetworkAdapterorLAN card) - It is hardware that
allows acomputer(or device) to connecttonetwork.
 MAC (MediaAccessControl) address –Each NICis assignedaunique 12 digit
hexadecimalnumber,knownaMAC address,isusedasnetworkaddressin
communication. The formatforthe MACaddress is
Manufacturer ID Card Id
 IP Address:Everydevice onnetworkhasunique identifiercalledIPaddress.It
consistsof 4 bytes(IPv4) decimal number(between0to 255) separatedby‘.’
(Period).
 Channel –It is communication paththroughwhichdataisactually transmitted.
 CommunicationMedia- Itisallowsdataorsignal to be communicatedacrossthe
devices. Itismeansof communication.
 Data – Information storedwithinthe computersysteminform of ‘0’ and‘1’
 Signal- Itiselectricor electromagneticencodingof datatobe transmitted.Itcanbe
categorized into:
o AnalogSignal – that hasinfinitelymanylevel of intensityoveraperiodof
time.
o Digital Signal –that can have only a limitednumberof definedvalues.
 Bit rate – It definesthe amountof datatransferred.Itisdefinedasnumberof bits
persecond (bps).[Bps – BytesperSecond]
 Baud – The numberof changes insignal persecond.
 Bandwidth – Itis difference betweenthe highestandthe lowestfrequencies
containedin the signal.
Mode of Transmission
 Analog or Broadband Transmission
 It usesanalogsignalstotransmitthe information
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 54

3.  The data can be sentsimultaneously usingvarious frequencies.
 It isa unidirectionalmethodof datatransmission.
 Multiple signalscanbe transmittedusingmultiple frequencies usingonlyone
channel
 Signal range islong.
 Example- Usedtotransmitcable TV topremises
 Digital or basebandTransmission
 It usesdigital signal (square wave) totransmitthe information.
 It isbi-directional transmission.
 Entire bandwidth isforsingle signal transmission.
 Shortdistance signal travelling
 EthernetisusingBasebandsforLAN
 Parallel Communication
 SeriesCommunication
 Synchronous Transmission
 Asynchronous Transmission
SwitchingTechnique
 A switchednetworkconsistsof aseriesof interlinkednodescalledswitchescapableof
creatingtemporaryconnectionsbetween twoormore likeddevices.
 There are three basicswitchingtechnique
 Circuit–Switching
 PacketSwitching
 Message Switching
CircuitSwitchingvs Packet Switching
NetworkDevices
 Modem
 It standsformodulatoranddemodulator
 It a computerhardware device thatconvertsdatafrom a digital formatintoa format
suitable forananalog.
 A modemtransmitsdataby modulatingone ormore carrierwave signalstoencode
digital information,whilethe receiverdemodulatesthe signal torecreate the original
digital information.
 Repeater
 Repeatersare networkdevicesthatamplifyorregenerateanincomingsignal before
retransmittingit.
 It operate atphysical layerof the OSI model.
 The repeaterallows totransferthe data throughlarge area distance
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 55

4.  Hub
 It isa multiportdevicethatallowsmultiple computerstocommunicate witheachother
overa network.
 It isa non-intelligentnetwork device thatsends message toall ports( i.e. Broadcast)
 Types of Hub
 Active Hub –
 It strengthen the signal mayboostnoisetoo.
 It needelectricity.
 Passive Hub –
 It repeat/copy signals.
 It doesnotneed electricity
 Switch
 NetworkSwitchorswitchisalsoa networkmultiportdevice thatallow multiple
computertoconnecttogether.
 Networkswitchinspectsthe packet,determine source anddestinationaddressand
route the packetaccordingly.
 It operates atData LinkLayer (layer2) of OSI model.
 Bridge
 It connectsmultiplenetworksegmentshavingsame protocol
 It worksat Data LinkLayer (Layer2).
 Bridge doesnotsimply broadcasttrafficfromone network.
 Bridges use bridge table tosendframesacrossnetwork segments.
 It alsoimproves the overallnetwork performance.
 Router
 Gateway
 RJ45
 Ethernet Card
 Wi-Fi card
Type of Network
 PAN
 It standsforPersonal AreaNetwork.
 It isa computernetworkformed around aperson.
 It generally consistsof acomputer, mobile, orpersonal digital assistant.
 Appliances use forPAN:cordless mice,keyboards, andBluetoothsystems.
 PAN includes mobiledevices, tablet, andlaptop.
 LAN
 It isa groupof computerandperipheral deviceswhichare connectedinalimitedarea
such as room,building&campus.
 HigherData Speed.
 LowerError Rate.
 LANsare ina narrowergeographicscope (upto1Km).
 It isa private network.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 56

5.  MAN
 A MetropolitanArea Networkor MAN is consistingof acomputernetworkthatspan
across a city.
 It mostlycovers townsand citiesinamaximum50 km range.
 The dual businMAN networkprovidessupporttotransmitdatainboth directions
concurrently.
 Moderate Data Rate.
 Moderate Error Rate.
 WAN
 It connectdevice across globe.
 It usespublicnetwork
 Internet
 BSNL
 VSNL
NetworkMedia
TwistedPair Cable
 A twistedpaircable comprisesof twoseparate insulatedcopperwires,whichare twisted
togetherandrun inparallel.
 A STP (ShieldedTwistedPair)cable hasafine wire meshsurroundingthe wiresto
protectthe transmission
 UTP (Unshielded TwistedPair) cable doesnothasa fine wire mess.
 It isalsoknown as Cat# cable where # denote number.e.g. Cat6
 Connector: RJ 45
TwistedPair Cable – Advantages
 It isthe leastexpensivemediumof transmission forshortdistances.
 It isrelativelyeasy toimplementandterminate.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 57

6.  It isflexible andlightweight.
 It iseasy to setup and install.
 Lesssusceptibletoelectrical interference causedbynearby equipmentorusesof wires.
TwistedPair Cable – Disadvantages
 Attenuation isvery high.
 It offerspoornoise immunityas the resultsignal distortion istoomuchmore.
 STP calledshielded twistedpaircable ismore difficulttoconnecttoa terminatingblock.
 Susceptibletonoise andinterference.
Co-axial Cable
 Coaxial cablinghasa single copperconductoratits center, anda plasticlayerthatprovides
insulation betweenthe centerconductoranda braided metal shield.
 Connector:BNC(BayonetNeill-Concelman)
Co-axial Cable Advantage


 The cost of a coaxial cable isless.
 Highlyresistant tophysical damage.
 Highly resistanttoEMI.
 Great channel capacity.
 The transmission rate ishigh.
 It islesssusceptible tonoise interference compare totwistedpair.
 It iseasy to wire andeasyto expand toflexibility.
 It supporthighbandwidth signaltransmissioncompare totwisted pair.
 It requiresfewerrepeaterthantwistedpair.
Co-axial Cable – Disadvantage:
 It isexpensive to install.
 Costmaintenance isalsohigh.
 Inflexible construction.
 Unsupported bynewernetworkingstandards.
 It isbulky.
 It has a more security problem.
 It doesnotsupporthigh-speed transmission.
 It mustbe grounded to preventinterference.
 In case of failure inone cable,the entirenetwork willbe down byusingthiswire.
Optical Fibre
 An optical fiberisaflexible,transparentfibermade bydrawingglassorplasticto a diameter
slightlythickerthan thatof a humanhair.
58
Page No-
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION

7.  It useslightfordatatransmission usingtotal internal reflection.
Optical Fibre- Advantages
 Higherbandwidth
 Lesssignal attenuation
 Immune tocross-talk
 Optical fiberhave longlifemore than100 or above years
 Grater immune totapping
 Resistance tocorrosive material
 Long distance transmission ispossible
 Immunity toelectromagneticinterference
Optical Fibre-Disadvantage
 Unidirectionalpropagation
 Highinitial cost
 Optical fibermore tensile stressthancoppercables
 Installation andmaintenance
 Fiberjoiningprocessisverycostly andrequireskilledmenpower
 Difficulttosplice (join)
 Difficulttofinderror
UnguidedMediaor WirelessMedia
 NoPhysical mediaisused
 LessSecure
 Relatively lowspeed
 Can be usedforlongerdistance
 Bestsuitedfordifficultterrain
 There isno needtoacquire landrights
Radio Wave
 Frequency –3KHz – 1GHz
 Omni-Directional
 Penetrate obstacle
 Antennaof senderand receivershouldnotbe aligned
Infrared
 300GHz to 400THz
 Line of sight- antennaof senderand receivermustbe aligned
 Shortdistance communication
 It cannotpenetrate obstacle –bestsuitedforindoor
 Secure
 Supporthighdata rate
 TV Remote
Microwave
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 59

8.  1GHz to 300 GHz
 Line of sight- antennaof senderandreceiver mustbe aligned
 Cannotpenetrate obstacles
 Rainor otherdisturbance cause issue withMicrowave
 Types of microwave propagation
 Terrestrial Microwave propagation
 SatelliteMicrowave propagation
Bluetooth
 It alsousesradiowaves
 2.4 GHz
 Range 10mtr
 Shortdistance
Topology
 Physical andLogical arrangementof nodesin the network iscalledNetwork Topology.
 The Key Elements tobe considered tochoose correcttopology foryournetwork
 Length of the Cable Needed– longerthe cable, more workisrequired forsetup
 Cable Type- Dependingonrequirement of bandwidth
 Cost- Installation CostandComplexity
 Scalability– Ease of expansion
 Robustness– Ability torecoverfromerror
Typesof Topology
 Bus
 Ring
 Star
 Tree
 Mess
 Hybrid
Bus Topology
 In BusTopology all the nodesare connected tosingle cable orbackbone
 Both the end have terminators.
Advantage – Bus Topology
 It iseasy to connecta device tothe network.
 It require lesscable length.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 60

9.  Low setupcost
 There isno needof Hub/Switch.
 It can be extended easily.
Disadvantage – Bus Topology
 Failure of one node canshutdown entire network
 There isa limitoncentral cable lengthand numberof nodesthatcan be connected.
 Difficulttofindandcorrecterrors
 Terminatorisrequired.
 Maintenance costs can gethigherwithtime.
 Notsuitable forBignetwork.
 Low Security due tobroadcastingof data.
Ring Topology
� In RingTopologyall the nodesare connected toeach-othertoforma loop.
� Each workstation isconnected totwoothercomponents oneitherside
� It communicateswith thesetwoadjacentneighbors.
� Data is sentandreceived usingToken.
Advantage – Ring Topology
 It iseasy to connecta device tothe network.
 It require lesscable length.
 Low setupcost
 There isno needof Hub/Switch
 Minimumcollision
 Suitable forOptical Fibre Network
Disadvantage – Ring Topology
 Failure of one node canshutdown entire network
 There isa limitoncentral cable lengthand numberof nodesthatcan be connected.
 Difficulttofind andcorrecterrors.
 Maintenance costs can gethigherwithtime.
 Notsuitable forBignetwork.
 Low Security due tobroadcastingof data.
 Unidirectional
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 61

10. Star Topology
 In StarTopology all the nodes are connected toa central device calledHub/Switch.
 All communication is controlled bythe central Device(Hub/Switch)
Advantages–Star Topology
 Reliable
 Robust
 Failure of node does notaffectthe workingof the network.
 Faultdetection andisolation iseasy.
 Maintenance of the networkis easy.
 It doesn’tcreate bottleneckswhere datacollisions occur.
Disadvantages – Star Topology
 Require more cable length
 Central Device dependency
 More costly
 Performance dependonHub/Switch
Tree Topology
 In Tree Topology, the devicesare arrangedinatree fashion similartothe branches of a tree.
 It multilayerarchitecture.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 62

11. Advantages- Tree Topology
 It isa combination of busand star topology
 It provides highscalability, asleaf nodes canaddmore nodesin the hierarchical chain.
 Othernodesin a networkare not affected,if one of theirnodesgetdamaged
 It provides easy maintenanceandfaultidentification.
 Point-to-pointwiringforindividualsegments.
Disadvantages -Tree Topology
 Large cablingisrequired ascompared tostar and bus topology.
 On the failure of ahub, the entire network fails.
 Tree network isvery difficulttoconfigure thanothernetwork topologies.
Protocol
 It issetof rulesorstandardthat governs communication.
Typesof Protocol
 TCP/IP
 FTP
 HTTP/HTTPS
 IMAP
 POP3
 SMTP
 PPP
 TELNET
 VoIP
TCP/IP – TransmissionControl Protocol/ InternetProtocol
 It isa protocol suite consistof twoprotocols TransmissionControl Protocol and Internet
Protocol.
 TCP ensures reliabletransmission ordelivery of packets onthe network.
 TCP isstate full protocol.
 IP isresponsible foraddressingof node onthe network
HTTP (HyperText TransferProtocol)
 It isis anapplication-layerprotocol fortransmittinghypermediadocuments, suchasHTML.
 It isdesigned forcommunication betweenClient(WebBrowser)andWebServer.
 It usesportnumber80.
 It isstateless protocol.
HTTPS (Secure HyperText TransferProtocol)
 It isis an extensionof HTTPprotocol for transmittinghypermediadocuments,suchasHTML
securely overanetwork.
KENDRIYA VIDYALAYA SANGATHANRANCHI REGION Page No- 63

12.  It encryptsdatato be sentusingTLS (TransportLayerSecurity)/SSL(Secure
SocketsLayer).
 The defaultportis443.
FTP (File TransmissionProtocol)
 It isusedforthe transferof computerfilesamonghostsoverTCP/IP (internet).
 It allowsaccess to directoriesorfoldersonremote computers.
 It usesclient-serverarchitecture.
 It isstatefull protocol
 The defaultportis21
Telnet(TErminaL NETWork)
 It isan application protocol thatallowsauserto communicate witharemote
device.
 It usesportno 23
SMTP (Simple MainTransferProtocol)
 It isused to sendmail frommail clienttomail serveroverinternet.
 It can senda single messagetoone ormore recipients.
 Sendingmessage can includetext, voice, videoorgraphics.
 It isconnection OrientedProtocol.
POP3 (PostOffice Protocol)
 It provides mechanismforretrievingemailsfromaremote serverforamail
recipient.
 POP3 downloadsthe email fromaservertoa single computer,then
deletesthe emailfromthe server.
 DefaultportforPOP3 110 and secure port995
IMAP(InternetMessage AccessProtocol)
 It isalsoused to retrieve mail frommailservertoclientoverinternet(TCP/IP).
 It allowsaccesstomail fromdifferent device.
 E-mail clientestablishesaconnectionwiththe servereverytime
youlog inand maintainedforthe whole session.
 Email will notautomaticallygetsdeleted.
 DefaultPortis– 143 and Secure portis 993.