8 Computer Networks
8.1 INTRODUCTION The greatest breakthrough in technology and communication over the past 20 years has been the development and advancement of the computer network. From emailing a friend, to online bill payment, to downloading data from the internet, to e-commerce, networking has made our world much smaller and forever changed the way we communicate. Network provides salient features which have made our life easy and comfortable, be it sending an email, withdrawing money from an ATM machine, online railway or airline reservation, or sharing sent from a computer to get a printout from a printer attached to some other computer. All this involvesaudio and a network.video files. Apart from these, the most extensively-used feature is the Print command It is the network that connects various computers to each other and handles a large volume of data.
Fig. 8.1: A Computer Network
8.2 COMPUTER NETWORK—A BRIEF OVERVIEW Several devices connected to each other for reliable communication/transfer of data constitute a etc. A collection of interconnected computers is called a Computer Network. Two computers or devices network. A network can consist of a computer, a fax machine, a printer, a camera, a cell phone, other by following a protocol (set of rules). are said to be interconnected if they are capable of sharing and exchanging information with each CTM: A computer network is a collection of interconnected computers and other devices to share data and other resources (hardware and software resources). Computer Science with Python–XII 8.2 Networks have several advantages which are describedbelow: This leadsto better performance withhigh processing speed. the interconnectedall task, computers are responsiblefor assigned tothe task completing them. each other. Therefore, instead ofasingle computer beingresponsible forthe entire completing processing system inwhichis dividedtask a among severaldevices which are interconnected with overmachines? Yes, stand-alone networked systems are far better. Anetworkdistributeduses a Let usnow discuss why networks are essential.Are there any advantagesof networked computers 8.2.1 AdvantagesofComputerNetworks (d) (b) (a) (c)
storedcomputers. onmultiple In anetworksystem, computers all are connected to each ReliabilityReliabilityData: of of data, up means backing audio andvideodataat a low cost. image, text, receiving and sending in role important very a playing are networks mobile anmjd Internet cost. low a at data of quantity large a send can we networks, public Using Reduced CommunicationCost: Sharingresources also reduces communication cost. information. Thisincreases theirefficiencyandallows themto complete theirwork quickly. be seenby othermanagers andemployees. Thus,anetwork allows managersto easily update While working onanetwork, any change madeby onemanageronhis/her computer caneasily example communication between users.Itsaves timeand offers easy communicationmethods. Improved Communication: video files,antivirus software, applicationsoftware, printers andscanners, etc., canalsobeshared on acomputer network. shared byusers on thenetwork. multiple Other resources like hard disk,DVD drive, scanner, other system. Thisallowsof documentsby printing severalusers hence,theprinter and, is command isgiven ononecomputer, thedocumentisprinted by aprinter toattached some physical Youlocation. have must noticed inyour networked computerwhenthat labs print a and peripheraldata applications, devices connected to thenetwork,irrespective oftheir Resource Sharing:The primary useofanetworkis to share amongusers programs/ , in an organization, managers work at different locations to make financial reports. reports. financial make to locations different at work managers organization, an in , Fig. 8.2: Acomputer network reliable enables fast, andsecure The Network Diagram For example , sharingaudioand database, ., data can be copied and be can data i.e., etc. For For • • efficient andreliable. Thenetwork haspassedthrough several stageswhich are describedbelow: The network did not evolve inasingle day; rather, ittook decades to become more powerful, 8.3 EVOLUTIONOFNETWORK
(e) that links two ormore networks to make alarge network for sharingofinformation andmessages. ARPANET and NSFNET to make a more capable and broad network—the Internet. It is the internet activity.business Later, many private owntheir combined companies private networks with than ARPANET. Its main aim was to use network only for academic research and not for any private FederationScience (National NSFNET Network), networkcreatednew whichwas a more capable NSFNET (National Science Federation Network): messages andplaying long-distancegames, andsocializingwith peopleto share theirviews. connected a handfulof computers differentat universities and USDoD for sharing of and data that project a was It 1969. existencein into came and network first the was (DoD), Defence of Department US (ARPA)and Agency Projects ResearchAdvanced the by named and designed jointly was which ARPANET ARPANET, (AdvancedResearch Project Agency Network):
functional duplication ofdataandalmostnoredundancy. processing, isstoreddata retrieved and fromsingle a central Thus, therelocation. isno be shared andmadeavailableto eachandeveryorganization. userinan centralized With can that server) file (the node central a on stored be can Files Central StorageData: of and furtherprocessing withoutdisruption. be accessed can from anotherworkstationfor future use.This leads to smoothfunctioning gets corrupted and,thus,becomes unavailableon one computer, acopy of the samedata respective workstations (computers). If, dueto some reason (hardware crash, etc.), thedata other.Thus, theinformation or messagewhich isshared by eachdevice isstored ontheir ARPANET becomes 1969 computers linked 1,000 individual 1984 ARPANET has more than as hosts ARPANET +NSFNETPRIVATE = INTERNET NETWORKS connects NSF net connects becomes known becomes known to ARPANET and as theInternet Fig. 8.3: Evolution ofInternet 1986 NSF resumes status as research network network onthe terminates its 1995 NSFNet Internet and Inthemid-80’s,another federal agency, 1996 Internet2 is founded 550 millionhosts Today more than connect to the connect Internet 8.3
Computer Networks Computer Science with Python–XII 8.4 others. network access points andbackbones, we first need to understand how our computer connects to Before wethe basicunderlying learnabout structure e.g.,domain nameservers, oftheinternet, internet. the interactwith and use we how define protocolsthat and policies the of overseesformation the 1992, in established group non-profit a Society, Internet The ways. different in maintained and monitored not is it that mean not does internet However,the millions. owns nobody because just of tens to systems computer host four from grown has internet the 1969, in beginning its Since networks. singlewethat entity the very fact, In knowas internet. comes from name thisideaofinterconnected networks, These both bigand small. networks connect together in many different ways to form the greatestof the One internetthe thingsabout nobody isthat reallyglobalis a It of collection owns it. 8.4 HOWDOESINTERNETWORK • •
CTM: theinternet. Network ofnetworks makes of data. Interspaceof data. isthemostadvanced termavailable ofcommunication on theinternet today. files, video, audio and textual data in a 3-D environment. It facilitates online real-time exchange to communicate witheachother by sending and receivingof various data typessuchasdata Interspace: networks which are furtherconnected to abackbone network through gateways. computersemail, areconnected not directly to Instead, theinternet. they are connected todata, smaller files, sharing of purpose the for other each with connected are information andis known Millionsof domestic, business and government asinternet. networks Control Protocol-Internet Protocol, TCP/IP). It allows computers of different types to exchange compriseslargethat a networkand shares acommoncommunicationprotocol (Transmission WebWorldWide through ARPANET. evolvedconnected from arehas internetcomputers The Internet: n h 19’, nent wih s ntok f ewrs cm it existence.The into came networks, of network a is which internet, 1990’s, the In Interspace isasoftwareallows that users multipleinaclient-server environment Fig. 8.4(a): Working oftheInternet etc. Mostofthe Provider 3. 2. 1. Terminology8.4.1 Elementary ofNetworks packet issentto itsproper destination. (Internet Protocol) is responsible for handling the address of the destination computer so that the computer.IP destination The the at them reassembling and computer source message the on packets into the dividing for responsible is part Protocol) Control (Transmission TCP The TCP/IP. for protocol.communication. Asetofrulesiscalled Communicationprotocol used by internet is rules Howof set smoothly: functions it same Everythe uses internet the toconnectedcomputer The 1). before come packets are reassembled may intheorder oftheirnumberandmessageisrestored. (10 order random in packets the receives computer destination The computer.destination the to number,packetsgivenaresent these packetserial is a All 3. 2, 1, e.g., At the source computer the message to be sent is broken down into small parts called packets. Each interconnecting structure thatconnectsoneormore networks just like thetrunkofatree. Gateway: Gateway isadevice connectsdissimilarthat networks. Abackbone isacentral level networks connectingto eachotherthrough Network Access Points amazing thinghere istherethat is no overallcontrolling network. Instead, there are severalhigh- users to accessthecompany’s network,often throughor dedicatedphone number local a The line. regions. In each region, the company has a largeMost companies have communication theirowndedicated backbones connectingvarious and network become partoftheirnetwork. Theinternet issimplylarger anetwork ofnetworks. a to connect then may ISP The network. their of part becomes ISP,it the to companythe that contractedISP tointernethas connects an the using still connects it When with. For example home. our in one the even network, a of part is internet the to connected is that computer Every
helps inestablishing communication between theserver andtheclient. Network Interface Unit (NIU)(MAC Address): Anetwork interface unitis an interpreter that the network. Server: Acomputer facilitatesthat thesharing softwareof data, andhardware resources on are seekingto share resources. Nodes (Workstations): The term node refers to computers arethat attachedto anetwork and (ISP). At work, a computer may be part of a , we may useamodemnumbertoand dialalocal connectto an Fig. 8.4(b):POPandNAP (POP). The POP is a place for local for place a is POP The Point(POP). ofPresence Local Area Network orNAPs. (LAN),itmostlikelybut Internet Service
8.5
Computer Networks Computer Science with Python–XII 8.6 8.6 MODESOFDATA TRANSMISSION as follows: smooth functioning. To form a network, a lot of hardware devices are required which are described A networkcomprises severalcontributethat their functionalities with components along to its 8.5 COMPONENTSOFDATA COMMUNICATION 5. 4.
(a) methods which are to befollowed by thesendingandreceiving devices. Protocol: Asetofgovernsrules that data transmission. It represents the communication flows from senderto receiver. Acableorwire orradiowaves canbethemedium. Transmission Atransmission Medium: medium is a physical paththrough which the data or audio image, text, video. be may It communicated. be to information the is Message Message: Receiver: Adevice oracomputer thatreceives the data. AdeviceSender: oracomputer thatsendsthedata. must beunique. Domain Name:Itis a way to identify and locate the computers connected to It the internet. an IPAddress. called number identifying unique a has Network bar/IP TCP a on EveryIP Address:machine
• • • Analog orBroadband T
Telephone netw The signal Requir waves thatare of varying amplitudes. es modemfor transmitting dataover baseband medium. is a radio frequency signal or analog, orks usethistypeoftransmission. ransmission Fig. 8.5: Components ofaNetwork ., it can consist ofcontinuous electrical can it i.e., several among are used,namely: information or data of exchange reliable interconnected the nodes. For the delivery is of data with accuracy, networking various types of of switching techniques goal main The 8.7.2 SwitchingTechniques switched network ismadeupof aseriesofinterconnected nodescalledswitches. another.A to node a of port one from data of packets transfer to used are techniques switching star topology between pairs of devices, botharebut notrelevantfor a large network. Hence, various A networkis madeupofseveral interconnected nodes. There canbeapoint-to-point connectionor 8.7.1 NetworkSwitching connection/communication. formmessages, ofcalls, There are severalways from ofsendingdata onenode to anotherthrough network.can beinthe It 8.7 DIFFERENTWAYS OFSENDINGDATA ACROSSNETWORK (d) (b) (e) (c) 3. 2. 1.
Message Swit Packet Switching Circuit Switching • • Synchronous orAsynchronous Transmission • • Parallel Communication • • Serial Communication Digital orBasebandTr
In as In When sender and r When bitsare sentoneaft When datais tr is a The signal No specialdevice f synchronous transmission. called is it data, actual the receiversends characterscontrolthe tothen sends and first communication. called parallel communication. Disadvantage—Slower thansynchronous mode. Advantage—Hardware required issimpleandcheap. bit respectively. Nosynchronization isrequired. Disadvantage—Costly andcomplex set-uprequired. Advantage—Faster thanasynchronous mode. ynchronous transmission,is preceded data succeeded and byand stopbit start a ching By using various types of switching techniques, we can establish the establish can we techniques, switching of types various using By etc. groupof discrete whichunits electrical istransmitted inrapid succession. ansmitted through wires multiple with each wire itis carrying each bit, or conversion ofsignalto betransmitted over basebandmedium. eceiver synchronize their checks before transmission, ansmission 10001------10001 er another inaseries a wire,along itisserial called i.e., thesender 8.7
Computer Networks Computer Science with Python–XII 8.8 address. address, it is received; otherwise it is passed on to the next node until it reaches the destination IP node the with matches packet the If address. IP destination for checks node intermediate each so order.During thetransfer ofpackets, eachpackethas to passthrough severalintermediate nodes, destination address. It is the TCP protocol which then arranges all received packets in a sequential follows different routes and, therefore, thepackets are delivered inarandom order the at As there is no direct connection establishedbetween thesender and thereceiver, eachpacket transmitted, inthesameway asapostmandelivers aletter to aspecificdestinationaddress. being foraddress) (IP address destination as well as addresssource a has packet Each operation. office post to similar is switching Packetbytes. 512 or bytes 128 usually size, fixed a of is packet packetIn dividedswitchingentireis technique,the fragmentsdata packets.into small called Each Packet Switching 4. 3. 2. 1. remains idle.Thefollowing actionstake placeduringcircuit switching: path the if even it use can user other no and dedicated remains link entire the technique, this In transfer ofdatatakes place. the sender and thereceiver. Thecircuitis establishedbetween thesetwobefore participants the In telephone system, thecommunicationmustbeestablished between the two participants, i.e., usuallytelephonea in networkwhere another isreceivingand call a onepersonismaking call. a This provides end-to-end connectionbetween two computers. Circuitswitching isestablished Circuit Switching the senderandreceiver thislink, madeduring be can andnoothercall even ifthelinkremains idle. CTM: of techniques usedare circuit switching, switching andmessage switching. packet CTM:
When thedatatransmission iscomplet signal. a receiving of acknowledgement the back sends it available, is node destination the If All intermediate nodesare identified.Thesenodesare alsocalledswitching nodes. receiver.the with connection the up set establishes to sender It the by sent is signal request A Hence, datatransmission begins. a physical connectionbetween thetwo participants. Circuit switching service. isaconnection-oriented Inthistechnique, there isadedicated linkbetween The technique ofsendingdata asSwitching across thenetwork isknown technique. The three types Receiver Fig. 8.6:Circuit Switching e, thecallcanbeterminated. Caller 7. 6. 5. 4. 3. 2. 1. 8.7.3 DifferencebetweenCircuitSwitchingandPacket forward and store called also is switching technique. it office, switching next the to sent then and buffer a in stored first is data the (receiver).As destination the to sent is data the until on goes process This office. its buffer. Itthenchecks theavailableand if link itis free, the datais relayed to anotherswitching storedin then is which first, office switching a to data the sends sender the switching, message In Message Switching between thesenderandreceiver. CTM: isoffixedpacket sizeswitching inpacket technology. CTM:
In circuitIn switching, thetelephone messageissentunbroken. Themessageisreceived inthe Packet switching ismore efficientbecausethecostof linkisshared by many users. Circuit-switched networks are used for andpacket-switchedphone calls networks handledata. the In circuit switching, ifthe path is overloaded,is thecallblocked and communicationis delayed. established, is connection the Once path. dedicated a requires switching Circuit Circuit switching is a fast technology ascompared to packet switching which is a slow switching packet whereasadvance, in bandwidth required the reserves switching circuit The then sequentially arranged. which are randomly sentfrom source and received in random order at destination,which is same order as itis originally Inpacket sent. switching, themessage is broken into packetssmall But inpacket switching, packets are allocated to different paths. sender to receiver, whereas inpacket switching, packets canuseany dynamic path. is entirelypath communication dedicated tois completelythe data until it transferred from mechanism oftransferring packets from senderto receiver. uses bandwidth asandwhen required by thepackets to betransmitted. Message switchingMessage is a store switching and forward technique where there connection is no direct Packet switching offers service. aconnectionless Data isfragmented into andeach smallpackets Mainframe Receiver Fig. 8.7:Packet Switching Caller 8.9
Computer Networks Computer Science with Python–XII 8.10 8.9 NETWORKDEVICES 6. 5. 4. 3. 2. 1. 8.8 DATA COMMUNICATION TERMINOLOGIES on LANs, Ethernets. especially CTM:
3. 1. 2. (kBps), megabits terabits persecond(mBps),gigabits persecond(gBps), persecond(tBps.) per secondbytesbits and secondhaveabbreviated been per second kilobits or baud, as(bps). by the time taken to transfer it inbitsper second (bps). The various measuring units are Both TransferData Rate: transferredof data amount is the It one direction in overdividedlink a sending andreceiving ofdatato data/information. andfrom thesender andreceiver. exchange to organizationsCommunication media is also known astransmission media. It plays an importantrole in two between up Communication mediaistheway oftransmittingfrom thesignal to oneplace another. set communication) of Communication/TransmissionMedia: Signals are theelectricorelectromagnetic encoding ofdataandare usedto transmit data. system. Whenthisdatais transmitted from onetoplace another, itis converted into signal. whichconvey1’s, computer and tothe are0’s meaning formstoredthat of special the some in entities are Data signals. and categories—data two into divided be can network computer a Data andSignals:Information is that stored withincomputer systems and transferred over Hz =1KiloHertz(KHz),103KHzMega Hertz(MHz). period of time (1 second) is termed as bandwidth. The measuring unit is hertz (Hz), where 103 Bandwidth: 1 bitpersecond. transmitted per second. 1 baud represents only 1 signal change per second and is equivalent to oftransferunit thedata rate. Technically,refers baud tonumber ofdiscrete a elements signal Baud: sender device to thereceiver device. Channel:
RJ-45 is a short term for Registered Jack-45.RJ-45 isashort isaneight-wire computers usedto connector connect It n tent ad a hscl drs o ec cmuiaig optr s mentioned. is computer communicating each Physical address isknown asMAC address. of address physical a card, Ethernet On interface card).is acard It allows that computers to communicate over a computer network. network. Ethernet card is also known as a network card, network adapter or NIC (network Ethernet Card:hardwareis a It devicehelps intheconnectionof nodesa thatwithin applications. They are usedprimarily for connectingLANs,particularly Ethernet. Jack) connectors aredevices theplug-in used innetworkingand telecommunications RJ-45Connector: RJ-45is astandard connector typeof for network (Registered RJ-45 cables.The and external modem. a intoand vicesignals versa. analog There are two typesofmodems, namely internal modem enables that device electronic an computer to transmitoverdata is telephonedeviceis a lines.It usedto convertsignals digital DEModulator) (Modulator MODEM A Modem: The number of changes in a signal per second signal isknown Thenumberofchangesina is themeasuring It as baud. A channel is a communication path throughpath communication is a Achannel whichis transmitted thedata from the The amount of data that can be passed along a communication channel in a givenin a channel communication a passed along be can that of data Theamount It is a means of communication or access(lines means ofcommunication is a It
CTM: Aswitch isadevice that transmits data to thecomputers inaLAN. CTM: Hubisadevice several usedto connect computers witheachother. 5. 4.
A hubcanbothsend as w the problemBut intelligentit isnotan is that with hub device. shares It bandwidthall with Hubs canbeeitheractiv attached to it. ontothe other allports, while switch keeps a record of the MAC addresses of the devices differencemain betweenand switch hub replicateshub isthat whatreceivesit ononeport from oneportofnetworkare refreshed deliveredand to theotherportofnetwork.The deviceis alsoamulti-port It with some but intelligence andsopacketsthe data received network. a acrosspackets forwards data and filters It network. a on devices or computers Switch:switch A (switchingnetworkis a hub) device which isusedto interconnect hub isaninexpensive way to connectmultiple nodes/devices to network. data andcausesunnecessarytraffic jams. nodes, as it does not remember devices/computers connected to it. Also, it cannot filter the devicesthe attached broadcasts and thedata, simply copiesthedatato allofthenodesconnected to thehub. the destinationaddresschanging without other portsofthehub all intheframe.Rather, it computers together with different ports.Whenthepacket reaches itis copied to one port, one portofthenetworkto another.hardwareis a hub A device usedtoseveral connect and unintelligentis multi-port Hub: It network device which simply transfers fromdata e orpassive. Hubscanusually support8,12or24RJ-45 ports. ell as receiveell information,only but oneatatime.However,task a Fig. 8.9:Switch Fig. 8.8:Hub ., sends framesi.e., thedata tothe connected all 8.11
Computer Networks Computer Science with Python–XII 8.12
CTM: Agateway isadevice dissimilar networks. that connects CTM: isadevice Abridge that linkstwo segments together network. oftheoriginal 6. 8. 7.
An important advantage of using a bridge is that it is a smarter hub as it can filternetworkcan it as smarter hub a is advantageit important that An is bridge a using of Gateway isadevice which establishes anintelligentconnection between area alocal traffic onthebasisofMAC addresses. address ofthedestinationandforwards thenewcopy only to thatport. enters a bridge, the bridge not only regenerates alsochecksthe signalbut the physical model. Bridges OSI relay frames between two originally separate segments.Whenaframe networknetworkbridge connectsmultiple layerlink the data segments at (layer 2)ofthe Bridge: Also, itis a two-port network device strengthensthat thesignalintensity andconnectstwo device receivesthat a signalbefore itbecomes too weak andregenerates the originalsignal. electronic an is repeater A transmission. long-distance for signals restores and amplifies As a signal travels a fixed distance, before attenuation of the signal, a repeater is used which Repeater: Arepeater is a device operatesthat only onthephysical layer of the OSImodel. network andexternal networks withcompletely different structures. make reliable communication,there mustbeadevice thathelpsincommunicating. are communicating with each other and each network has a different configuration. In order to Gateway: Agateway isadevice thatconnectsdissimilarnetworks. several Ininternet, networks A bridge is a devicebridge isa A works that physical onthe layer well as layer.link on data as A Fig. 8.10:Ethernet Bridge Fig. 8.11:Gateway
CTM: device from Arouter onemachineto that packets helps inforwarding another. isanetworking received inthesameway asitissent. CTM: 9.
Repeater isadevice that amplifiesasignalthat istransmitted across thenetwork sothat thesignalis Repeaters are also extensively used in broadcasting where they are termed as translators as termed are they where broadcasting in extensivelyused also are Repeaters network layer, which isthethird layer oftheOSImodel. machine tomachine by thedestination usingthe shortestRouters path. arethe usedat Router: Arouters is a networking device forwardsthat data packets from thesource or boosters. network; instead, itmakes thesignalstrong before itdegrades. the of functionality the change not repeaterdoes A metres. 100 than longer runs cable for required are repeaters configurations, Ethernet pair twisted most In networks. identical Fig. 8.12: Working ofaRepeater Fig. 8.13:Router 8.13
Computer Networks Computer Science with Python–XII 8.14 enabled headphones,wireless printers andTVremotes. video, and audio photos, technology implements PAN. digital PAN may emails, include wireless computer keyboard and including mouse, Bluetooth- files transfer to devices Bluetooth or Infrared. PANs are used to connect computers, laptops, mobiles and other IT-enabled wirelesssystemsconnectivityor likewiredUSB metresusing 10 to proximityup the of in devices PANs are small networks used to establish communication between a computer and other handheld 8.10.1 PersonalAreaNetwork(PAN) 4. 3. 2. 1. On thebasisofgeographical spread, networks may beclassifiedas: around theworld. A computer networkin aroom,be ona table, can city, building, country, across continents or network devices linked together. Thus, networks vary in size, complexity and geographical spread. A computer networkmay the numberofcomputersdependingupon or big besmall and other 8.10 TYPESOFNETWORKS CTM: The asPAN. network that to belongs oruser isknown asingleperson
10. WAN MAN LAN PAN
the PCI-Express card slotsonthemotherboard. fit to made cards Wi-Fi PCI-Express are computers desktop in used cards Wi-Fi common cards are widely usedinnotebook computers due to theirhighlynature. portable Themost as they allow theuser toanyconnection without setup wire. Wireless Fidelity(Wi-Fi) a user to establishaninternet connection.Wi-Ficards are known aswireless fidelity cards wirelessbuilt-in radio andantenna.A Wi-Ficard desktop isusedina computerenables that Card:Wi-Fi A Wi-Fi card is either an internal or external Local Area Network adapter with a Fig. 8.14:Personal Area Network (PAN) etc. The Bluetooth A good example of MAN is the interconnected offices of a Multinational Corporation (MNC) or (MNC) Corporation cable televisionMultinational networks available inthewhole city.a of offices interconnected the is MAN of example good A typically owned andoperated by asingle entitysuchasa government body or a large corporation. and unguided) aretypes All of communication media(guided used to setupaMAN. AMANis number ofLANsandindividuala computers. sharesalso It resources thecomputing users. among MAN islarger than aLAN and cancover a city anditssurrounding areas. AMANusually interconnects 8.10.3 MetropolitanAreaNetwork(MAN) Data transfer rate speedover aLocalArea Network canvary from 10mbpsto 1gbps. (Infrared, media modem, etc. wireless or etc.) cables, key purposeofaLAN is to share resources. LAN users sharecan programs, data, coaxial printer, disk, cables, (UTP media Radio waves). If aLAN is set upusingunguided media, itis known asWLAN (wireless LAN). The wired using up set space, aLAN is owned, controlled andmanagedby asingle person or organization. ALAN can be Occasionally,groupspan a LAN can a ofnearbyaddition to buildings.In operatingin alimited few a over spread area an cover metres to aradiuscan ofafew kilometres. It school. a as such building a or office home, a like area), LAN is aprivately owned computer network coveringgeographical asmall area physical (small 8.10.2 LocalAreaNetwork(LAN) LAN inCAMPUS Fig. 8.15:Local Area Network (LAN) 8.15
Computer Networks Computer Science with Python–XII 8.16 example ofaWAN Theinternet istheinternet. isthelargest WAN spanningtheentire planet. and unguided) aretypes of All communicationmedia (guided used to setupaWAN. The best known covering many continentsare examples ofWAN. offices, organizations’ international offices, government WANcover can area an a radius with hundreds spanning of kilometres. Anetworkof ATMs, banks, AWANhigh speedandlow cost. usescommoncarrierslike satellite systems, telephone lines,etc. networks suchasLANs,MANs, acrossWANscontinents. countriesand are generally usedto interconnectseveral other typesof WAN isatelecommunication network.This typeofnetwork spreads over a large geographicalarea 8.10.4 WideAreaNetwork(WAN) CTM: A WAN interconnects allthecomputers across theworld. Fig. Area 8.16:Metropolitan Network (MAN) They facilitate fast and efficient exchange of information at a at information of exchange efficient and fast facilitate They etc. Fig. 8.17: AreaWide Network (WAN) etc., spread over a country, continentor representation ofhow anetwork islaidout. more devices maketwoand link a ormore links formtopology. a is basicallyIt geometrical a Topology is a way of connecting devices with each other either physically or logically. Two or 8.11 NETWORKTOPOLOGIES 4. 3. 2. 1. televisioncable network.Thus, thebasicpointsofdifference between LANandWAN are asfollows: usually covers an entire city. It uses the LAN technology. The most common example of MAN is the toconfined is relativelyLAN A countries. or building, areas,a smaller office, an as such WANA geographicaldomains. their of basis extendsstatesover as geographical largearea,such a WANthe and on MAN categories LAN, into classified be networkscan computerhave weseen, As Comparing LANandWAN The following tablesummarizesthecharacteristics ofPANs, LANs,MANsandWANs. speed andlow error rates. Thus, wesay can in comparisonto that WANs, LANscoverlimited a areatheybut operatehigh with media used Technology/ used Network devices Error rate speed Transmission Networking cost Area covered CTM: Topology isaway several ofconnecting devices witheachotheronanetwork. emerged with technological advances. CTM:
Parameter As LANs ar involvedin distances short the of WANsbecause in that than lower is LANs in rate error The WANs while mbps 10 and (mbps) second per bit mega 1 of speeds between operate LANs upper The range. specific a to limited is connection LAN a in nodes the between distance The multiple organizations. such as anorganization. Onthe other hand, WANs are usually operated and controlled by LANs. Theerror rate inLANsisapproximately onethousand timeslessthanthatinWANs. to usetheopticalfibre technology. operate at speeds of less than 1 mbps. To achieve speeds of several hundred mbps, it is advisable are spread across thousandsofkilometres indifferent countriesorregions. limit is approximately 10 kilometres and the lower limit is one metre. On the other hand, WANs LAN and LAN WAN categories ofarea networks; andbest-known are thetwo primary theothershave e limited byentire distance,an LANisusually underthecontrolsingleof a entity, Infrared, Bluetooth WLAN, USBDongle Lowest High speed Negligible (up to10mradius) Small area PAN
Ethernet, Wi-Fi Repeater, Modem LAN/WLAN, Hub/Switch, Lowest High speed Inexpensive (up to10km) A buildingorcampus LAN
wave, Microwave Optical fibre,Radio- Router, Gateway Moderate Moderate speed Expensive radius) A city(upto100km MAN Microwave Satellite Router, Gateway Highest Low speed Very expensive or globe Entire country, continent WAN etc. AMAN 8.17
Computer Networks Computer Science with Python–XII 8.18 Advantages ofMesh Topology be 5(5–1)/2=10links. will there then one, other the with connected is each and fivearecomputersthere For if example, where nisthetotal numberofconnectingnodes. only between the two connected devices. A fully connected mesh network hasn(n–1)/2links, traffic carries link topology,the of type this In (workstation). node dedicated each between link meshIn topology,each computer isconnectedthe othercomputer. with Therepoint-to-point isa 8.11.1 MeshTopology Basically, there are five typesoftopologies andeachtopology hassomeadvantages anddisadvantages. Types ofTopologies Disadvantages ofMesh Topology (d) (b) (a) (e) (a) (c) Mesh TopologyMesh
Mesh t Point-to-point links make fault identification and fault isolation easy. Traffic can be routed to Expansion andmodificationintopology canbedonewithoutdisruptingothernodes. communicating Each the amountofcablingand thenumberofI/Oportsrequired. the precise locationofthefault andaidsinfindingitscausesolution. avoid links withsuspected problems. This facilityenables thenetwork managerto discover from gaining accessto messages. dedicated line, only the intended recipient Physicalsees it. boundaries prevent other users eliminating traffic problems. There is mesh topologyA does affectit not becomes unusable, one link If is robust. the entire system. opology is highly expensive to set up and involves high maintenance costs because of the advantageof privacy or security of data. Whenevery message travels alonga Star Topology Fig. 8.18:Classification of Network Topologies eie are is w dt truh t on eiae ln, hence link, dedicated own its through data own its carries device Fig. 8.19: Topology Mesh Typesof Topology Bus TopologyBus Ring TopologyRing
Tree Topology Advantages ofStar Topology currently operates inStarTopology. Most popularandwidely usedLANtechnology, Ethernet, data to thedestinationcomputer. that relays then which hub, the to sent first is data each can beaccomplished only by thecentralcontroller as computer and received by anothercomputer, thenthis one from sent be torequired is data the If hub. the from send and receiveindirectly; data passes thedatato and Unlike meshtopology, thedevices in startopology device usedto connectseveral computers together.) to acentralcontroller a hardwarehub is hub.(A called In startopology, eachdevicecommunicating is connected 8.11.2 StarTopology Disadvantages ofStar Topology CTM: When there isapoint-to-point linkbetween eachcomputer inanetwork, itforms meshtopology. (d) (d) (b) (b) (b) (a) (e) (a) (c) (c) (c) (f)
The perf Extra hardware isrequired for installationofcentral controller known ashub. Removalor additionofany topologynode instar takecan easily place affectingwithout the As thenodesare not an This meansthat is easyIt to detectfaults in thisnetwork computersall as are dependentonthecentralhub. number the reduces thus, which, topology mesh toFewercompared required areas wires Set-up and tree) asall nodesare directly connected to acentral hub. hub. Iftheserver isslow, itwillcausetheentire network to slow down. hub makes theentire network shutdown. entire performance ofthenetwork. performance ofothernodesinthenetwork. central hub. the central hub. of input/outputports. is tough. expensive. More cabling is required in star topology as compared to any other topology (ring, bus, (ring, topology other any to compared as topology star in required is cabling More nodes ofstartopologyAll are dependentoncentraltherefore,and, hub any problemin the The ratetransfer ofdata is fastpacketsthe data asall or messages are transferred through Installation andmaintenance ofnetw har The wr rqie t cnet ah ik IO ot ad al) a b prohibitively be can cable) and ports (I/O link each connect to required dware ormance oftheentire networkis directly dependentontheperformance of the maintenance of this topology is very difficult. Even administration of the network y problemwhich makes thenetworke tracedb can non-functioning to connected to eachother,any problemin onenode does hamperthe not ork iseasy andtakes lesstime. Fig.Star Topology 8.20: 8.19
Computer Networks Computer Science with Python–XII 8.20 signal passes throughnodes allintheentire network.is Whenthedatatransmitted from onenode fashion. Inringtopology, eachdevice isincorporated witharepeater to strengthenas a thesignal and onesuccessor istransmittednode. Signal only inonedirectionthe entire along ringinacircular network. It shows the line configuration in which each node is connected to one predecessor node ring topology,In each nodeisconnected toforming tworing a either sideofit, othernodeson 8.11.4. RingTopology Disadvantages ofBusTopology Advantages ofBusTopology example ofbustopology. common a is Ethernet line. a to connected nodes of number limited a be should thereTherefore, However, asthesignaltravels alongdistance,itbecomesweaker andweaker. cable. Thedataflows from oneendofthecableto theother. betweenand devicescable thelong areand taps theconnectors arethat punctured inside the main which acts asabackbone. Nodes are connected by dropA drop linesandtaps. lineis a connection configuration, multipoint a is topology Bus 8.11.3 BusTopology take place inbustopology.take CTM: (d) (d) (b) (b) (g) (e) (a) (a) (c) (c) (f)
There to whichisconnected isamaincable several workstations through taps. Collision ofdata can Collision of data can Collision ofdata Performance degradation occurswiththeincreased numberofnodes. The signalbecomesweak Fault isolation isdifficultto detect iftheentire network shutsdown. If there isaf Bus networ Nodes canbeconnected orr one time. When thenetwor Terminators are required atbothendsofthebackbone cable. It works well for smallnetworks. It requires lesscablelengththanastartopology. k iseasy to implementandcanbeextended upto acertainlimit. ault orbreak inthemaincable,entire network shutsdown. k isrequired inmore thanonebuilding,bus network cannotbeused. takebecause several place nodes transmit can todata eachotherat er ifnumberofnodesbecomeslarge. emoved easily from busnetwork. Fig. TopologyBus 8.21: i.e., several devices are connected to a mainlongcable Disadvantages ofRing Topology Advantages ofRing Topology Token Ring the destinednode. to itsrecipient node, then theintermediate node regenerates the signal andpasses the signalto successor and, node thus, forms aring. Data istransmitted onlyinonedirection. CTM: (d) (d) (b) (b) (e) (a) (e) (a) (c) (c) (f)
In ring topology,In ring eachworkstation withthepredecessor isconnected as well node aswiththe For proper communication between each node, it is required that each computer must be must computer each that required is it node, each between communication Forproper Transmission speedbecomesslower withanincrease inthenumber ofnodes. If there isaf It isrelati In thistopology The adding or removing of network nodes is easy as the process requires changing only two nodes two between passed is data the as topology ring in required not is server central A turned on. network shutsdown. connections. which thenpassthrough theentire network. If there isa The movement or changes madeto network nodes affect theentire network’s performance. The configuration mak The dataistransmitt isanexample ofringtopology. vely cheaperascompared to startopology. ault inasingle node,itcancausetheentire network to fail. faultor break tocable in a whichother nodes are all connected, theentire , eachnodetransmits thedatato itsnext nodeinaring. ed inonedirection only and,hence,thetransmission rate increases. es iteasy to identifyfaults innetwork nodes. Fig. 8.22: Ring TopologyRing 8.21
Computer Networks Computer Science with Python–XII 8.22 Advantages ofTree Topology longer distances. A passive hubsimply provides a connection between other all connectingnodes. activeAn hub. contains therepeater hub regenerates that when thesignal becomes weaker it with and someofthedevices are connected to thesecondarywhichhub, mayactive bean or passive hub treeIn topology, or some ofthedevicesall are connected to thecentralactivean called hub, hub, 8.11.5 Tree Topology Disadvantages ofTree Topology are witheachother. connected Tree aparent-child topology isjustlike relationship. CTM: (d) (b) (b) (a) (e) (a) (c) (c) (f)
In tree topology, the maincentral hubthrough whichalldevices to hubisconnected thesecondary Though As segments multiple are connected to acentralbus, thenetwork depends heavily onthe netw The Fault identification iseasy. The adv The tree topology isusefulincases where astaror be implementedbus cannot individually. central bus andonthecabletype. configuration isdifficultin comparisonto othertopologies. bus. Itsfailure affects theentire network. achieved. does notaffect therest ofthenetwork. individual starsegmentsinatree network. (root node). (star segment)functionsseparately,each unit connected andisalso node the main with wn t Owing star Each is mostsuitedIt innetworkinguniversitydepartmentsof a multiple orcorporation,where antages of centralizationantages arethat achievedstar topologya in are inherited by the it isthenumberof scalable, nodes that canbeadded depends on thecapacityof the is ie n cmlxt, aneac i nt ay n css r hg. Also, high. are costs and easy not is maintenance complexity, and size its o r cn e xadd y h adto o scnay oe. hs saaiiy is scalability Thus, nodes. secondary of addition the by expanded be can ork segment gets a dedicated link from the central bus. Thus, failing of one segment one of failing Thus, bus. central the from link dedicated a gets segment Fig. 8.23:Tree Topology and ifthedataissentwithoutwires, itiscalledunguidedmedia. wireswires. orwithout is sentacross Ifthedata networkthrough wires,guided media itiscalled transferred between twodevices, communicating knownCommunication mediaisalso as transmission media through whichis or signal data 8.12 COMMUNICATION MEDIA pair ofcomputers over anetwork. each between P-Plink a install to wayseveralis simplest ways.in The established be can P-Plink wires,theyoveror turns in occur can wiresame the by differentusing transmission techniques. A For better performance, thetransmit andreceive operations canoccur over separateor cables follows: Therefore, severalfactors are taken into consideration before selectingatopology which are as topology determines the typeof media and access methods wouldthat beused on thenetwork. The decision to selectaparticulartopology for a networkdoes nottakein isolationasthe place shows aP-P linkinanetwork. receiver.one onlyto transmitterdata transmitseach transmitterand onlyone from 8.23 data Fig. P-Pof receivetoand is send link overdata network.a P-P a In network, workstationeach receives A P-P link, also known as a dedicated link, is used to connect two nodes in a network. The function What isPoint-to-Point (P-P) Link CTM: Communication mediaisatransmission mediausedfor sendingdata orsignalacross thenetwork.
causes: system,network a encounteralso can failure. Anetworkfailure occur dueto can thefollowing Reliability: Flexibility: by reducing thedistancesbetween thenodes. wires) for data exchange between the network nodes. The network cost can also be minimized This can bedone by cost. the installation selectinganeconomicaltransmission medium (that is, Cost: Cost signifies that the network should be cost-effective. For this, it is required to minimize ones onthenetwork.new add or nodes existing the rearrange to means network a Reconfiguring reconfigure. to 2. 1.
When theentire netw When anindividual nodest of anindividual node. Flexibility signifies that the network must be flexible enough, Itrefers to thedegree of canbeplacedonanetwork.trust that Like any other ork fails. This is caused by amore serious faultstopsthat the working A Transmit Receive ops working. Fig. 8.24:APoint-to-Point Link i.e., from onesystem to anothersystem, through Transmit Receive B i.e., itshouldbeeasy 8.23
Computer Networks Computer Science with Python–XII 8.24 Twisted paircomesintwo varieties: Category 7twisted paircan supportstillhigher datarates. while metres 100 for mbps 200 as high as transmission data support can pair twisted 6 Category is known as crosstalk. Twisted pair can be specified as Category 1–5 and is abbreviated as Cat 1–5. in avoiding interference from thenearby similarpairs,which used for ground reference. The wires so twisted are helpful two these of Out thick. wires, onlywhilesignal one carries the actual theotheris mm 1 is wire Each wire. single a insulated copper wires which are twisted together to form common typeof conducted is media. Itmadeof two plastic simplestandthemost A twistedis theoldest, paircable 1. Twisted Pair Cable 8.12.1 GuidedMediaorWiredNetworkingTechnologies B. A. All communication/transmission mediacanbedivided into two categories: Types ofCommunication/Transmission Media (b)
(a) Unguided Media Unguided coaxial cableandfibre opticcable. These media usewires for transmittingVariousdata. wired connectionsare twisted pair wire, Media (WiredGuided Media): transmissions, cellularradio systems, infrared transmissions, etc. of electromagnetic waves, such as radio waves, terrestrial microwave transmissions, satellite as unguided media or non-physical mediaasthetransmission takes throughplace various types forcables transmission isknownof data as unguidedmedia.Wireless transmission is alsoknown
connected by RJ-45 connectors. arecables UTP areused. cables computernetworks, Cat-6 In and use. mostlyCat-5E Cat-5, Unshielded twistedUTP hasseven(UTP): pair categories,for each suitable specific a indifferent to noiseandcrosstalk. twistedShielded (STP): pair Pair Cable Twisted (Wireless Media): Guided Media Guided Coaxial Cable Fig. 8.25: Types of Communication Media Fibre Optic Guided media isalsoknown asphysical or conducted media. Cable STP cables A transmission media that does not require the use of use the require not does that media transmission A Communication Media are coveredfoil.metal in This makes them Radio wavesRadio Unguided Media Microwaves Fig. 8.26: Twisted Pair Cable Satellite Link in two primary physical types: high provide cables bandwidth rates of up to 450 mbps. Coaxial Coaxial cable also comes crosstalk. and noise against The wrappedcables. structure providesgood shield a it pair twisted of that than signals frequency higher carrying of capable are cables Coax jacket. plastic a in covered and insulated copperwires surrounded by abraided shield metal of consists It wire. coax a called generally is cable coaxial A 2. Coaxial Cable Disadvantages ofTwisted Pair Cable Advantages ofTwisted Pair Cable Advantages ofCoaxial Cable Guide. Coaxcablesare widely usedfor internet connectionsandcabletelevisions. cables, namely RG-59 (Cable TV), RG-58 (Thin Ethernet) and RG-11 Coax (Thick Ethernet). RG stands for Radio of categories three are There coaxialcable. (d) (d) (d) (b) (b) (b) (e) (a) (e) (a) (e) (a) (c) (c) (c)
Coaxial cable Coaxial It iswidely usedf Coaxial cable It cansupport19,200bpsupto 50f easilyIt pickswhichnoise signals up results inhigher error rates whenlength theline STP wire isphysically larger andmore expensive thantwisted pairwire. If aportionoftwisted paircableisdamaged,theentir a in wires or equipment nearby by caused interference electrical to susceptible less is It It issimpleto use. wires. baseband cableisused. ohm transmission,50 fordigital and used is broadbandcoaxial ohm transmission,75 data cable. exceeds 100metres. second canbeachieved for afew kilometres inmany cases. depends on thethicknessof the wire andthedistancetravelled,several but megabits per pair wires are used. telephone system.travelcan Signals several kilometres whenamplification without twisted broadband transmission. ox ar Coax It is useful f Being thininsize,itislikel STP ismore difficultto connectto aterminating block. These media It isinexpensi ue fr rnmtig eea canl simultaneously, channels several transmitting for used e or transmittingas wellanalog data acrossas digital the network. For analog can support greater cable lengths between network devices than twisted pair has excellent noise immunity because of thick coveringexcellentthick has of insulatedbecause the immunity outside noise can beused for anddigitaldatatransmission.both analog The bandwidth ve anddoesnotrequire skilledpersonnel. or cabletelevision andinternet connections. thin coaxialcable and y to break easily. eet onRS-232 port. thick e network isnotshut. Fig. 8.27: Twisted Pair Cable i.e., they arein helpful 8.25
Computer Networks Computer Science with Python–XII 8.26 Disadvantages ofFibre Optic Advantages ofFibre Optic width butmultimodefibre usesmultiplelight paths. Optical fibres may be single mode or multimode. Single mode optic fibre transmits only single light The light source usedinthisprocess islight emittingdiode(LED). cable. of length the along forth and back bouncing light the keep to reflection angle right the just angle,which helps inmoving thelight wave forward. The outer surface oftheglass wire provides similar a at wire the of walls outer the hits cable the inside pulse light the optic, fibre the enters signals travel into the fibre optic cable at one end and are received at the other end. When the light Light covering. insulated an in encased are and together bundled are fibres glass Several media. Fibre optictransmits light signalsratheris thenewestsignals. It electrical than form of guided 3. Fibre OpticCable Disadvantages ofCoaxial Cable (d) (d) (h) (b) (b) (b) (g) (g) (a) (e) (a) (a) (c) (c) (f) (f)
Thick coaxialcablesdonotbendeasily andthusar It isrelati Thick coaxialcablehasanextr As fibre opticismade of g A highl Fibre opticcablesare alsousedinresearch anddevelopment. A signalcanrunfor 50km withoutr It doesnotleaksignals,soitisimmuneto ea Lighter weight makes fibre easierto install. fibr Optical Fibre optictypically offers better bandwidth andcancarrymore information atonce. communication. hazards. It isrelati Fibre opticcablesare muchthinnerandlighter thanmetalwires. As thesignaltra It isexpensi As light tr y skilledlabourisrequired for itsinstallationandmaintenance. vely inexpensive ascompared to fibre opticcable. vely expensive ascompared to other guidedmedia. e wires are madeofglass, sothererisk offire islittle becauseofabsencespark avels in a straight line,two fibres are needed if we need bidirectional ve ascompared to twisted paircable. vels intheform there oflight, islessattenuation andsignaldegradation. lass, they can beeasily broken. Fig. 8.28:Fibre OpticCable a protective plasticcover thathelpskeep moisture away. equiring regeneration.
vesdropping. e difficultto install. Total internal occurs hereoccurs
Cladding Disadvantages ofMicrowave Transmission Advantages ofMicrowave Transmission receiving antenna. they mustbeproperly alignedwitheachother, otherwisenotbefocusedthe signalwill wellat the antennas are mounted on towers, buildings or hills to send and receive signalsthrough air. However, mission travelsas signal straighta in microwaveIn line. two communication, directionalparabolic Microwave signals are used to transmit datawithouttheuse of Itis cable. aline-of-sight trans- 1. Microwave 2. 1. Features ofUnguidedMedia: 8.12.2 UnguidedMediaorWirelessNetworkingTechnologies
(d) (b) (b) (a) (a) (c) (c) Transmission canbeeitherdirectional oromnidirectional. Transmission andreception are achieved by meansofanantenna. (b) (a)
Micro It isaninsecure modeofcommunication. Micro is acheaper It source ofcommunicationasitavoidsrepeaters. andmaintaining using cables antenna withareduced strength. The costofimplementingto can Signals Communication throug Dir • can berecei • signal spreads outinalldir Omnidirectional • transmitt • transmitting ant ectional wave propagation isaffected by weather conditionssuchasrain, thunderstorm, etc. wave system permits data transmission rate ofabout16gigabits persecond. be split and propagatedbe split indifferentdirections inairandreceived by thereceiver er andreceiver mustbealigned ved by many antennas enna putsoutfocused beam h microwave ismucheasier over difficultterrain. wers, antennas isrelatively high. ections Fig. 8.29:Microwave Direct PathDirect Secondary Secondary Path 8.27
Computer Networks Computer Science with Python–XII 8.28 there are transponders thatsendandreceive signalsfrom/to the earthstation. transmission takesfrom place satellite a tois knownit earth station, an as downlink. satellite,In When datais transmitted from anearthstationto asatellite, itis knownand when asuplink antenna to transmit andreceive datafrom satellites. satelliteIn applications. satelliteearth stationhasa an communication, dish, which functions asan video, andother email internet data, voice fax, transmitting as such providesIt various typesofservices medium. type of microwave transmission as microwave. Satellitespecial isa than 3 GHz, the transmission is known greater is frequency the When world. to transmitthroughoutsignals the line-of-sight transmission is that used Satellite transmission is also a kindof 3. Satellite Link Disadvantages ofRadio Waves Advantages ofRadio Waves and, hence,canpenetrate buildingseasily. Theysignals. are line-of-sight not transmission receiver use antennas to radiate andfetch radio message isreceived. Boththetransmitter and received by areceiver, are decoded and the and encodes them into sine waves which, when and receiver. Atransmitter sends radio waves communication. Aradio set-upuses transmitter allocated to private businesses for direct voice are which frequencies radio use waves Radio 2. RadioWaves (d) (b) (b) (a) (e) (a) (c) (f)
Radio wave communicationisaninsecure modeofcommunication. It offers easeofcommunication o It ischeaperthanlaying cablesandfibr Transmitter andreceiver antenna donotneedto bephysically aligned. They canbeusedindoorsoroutdoors. Radio wave propagation issusceptibleto weather effects like rain, thunderstorm, etc. Radio wave transmission offers mobility. They are omnidirectional andcantravel inany direction.
ver difficultterrain. es. Fig. 8.31: Fig. 8.30: Satellite Link Radio WavesRadio Disadvantages ofInfrared Transmission Advantages ofInfrared Transmission such asremote control ofaTVorAC, etc. control remote handheld a is transmissioninfrared of example good very A mbps. 16 to kbps 2.4 the walls of the room. It is an example of short range wireless network. Infrared speed varies from is transmitteddata throughpropagatecan airand intheopenspace;however,penetratecannot it The type of transmission that uses infrared light to send data is known asinfrared transmission. The 4. Infrared Disadvantages ofSatellite Link Advantages ofSatellite Link (d) (b) (b) (b) (b) (a) (a) (a) (a) (c) (c)
It canwor It isasecure mediumoftr Signals sentto thestationscanbeint It isvery e Earth station The area co It cannotpenetrat It isacheapmodeoftransmission. Low antenna gains result inovercrowding ofavailable bandwidth. Installation isextr No line-of-sight r Transmittor Reciever Housing k only for short distances. xpensive ascompared to othertransmission mediums. vered isquite large. which receives the signals can be at a fixed position or can be relatively mobile. estrictions suchasnatural mountains,tallbuildings,towers, etc. e walls andisaffected by distance,noiseandheat. emely complex. Shield Fig. 8.32:Infrared Transmission System Lens ansmitting data. errupted by external interference. Transmittor Reciever 8.29
Computer Networks Computer Science with Python–XII 8.30 technologies available are describedasfollows: two or moreare pointsthat notconnected by anelectricalconductor. The various wireless the of frequency radio the through carried electromagneticspectrum. Thus,wireless is thetransfer communication ofinformation between are video and voice data, as such Information air. Wireless technology is the process of sending information through invisible waves in the 5. Wireless Technology used wireless media—laserwaves andBluetooth. extensivelyand important other two discuss will we section, this In 6. OtherUnguided/Wireless Media (b) (b) (a) (a)
Transmissioninformationtoothof requiresBlue- using low-costa transceiver each in chip Wi-Fi (WirelessWi-Fi Fidelity): features suchasencryptionandverification to provide security. various with equipped is Bluetooth multipoint. or point-to-point either be can devices the between connection The standard. 802 IEEE the per as address 48-bit a has device Each mbps. 1 is transmissionavailable of is globally.whichtype this transferin data rateof The GHz, 2.45 of frequency the transferredat is Data connected. be to need that devices the of (WLAN). LAN Wireless of form the in connection wireless a establish to PDAs and laptops as such among eachother. Bluetooth technology is commonly used in various devicesportable that defines how different devices can beconnected virtually andtransfer information BluetoothTechnology: conditions. laser transmission is that itis badly affected by weather receivers for transmission. A disadvantageassociated with photosensitive and transmittersfaster.require much Lasers Similar toas buildings. microwave, alaserisunidirectionalbut transmission between pointslocatedshort distances,such at point-to-point provides It sight. of line direct requires that Technology:Laser between thetower andtheend-user. establish aconnection.Internet connectivity to end-user is provided by amicrowave link tobase station communicatethe user. with Instead ofwires, itusesamicrowaveto link as known tower a requires and connection internet broadband connectivity.uses Wi-Max internet and data voice, high-speed to access with users provides that technology 802.16 40 to 30 to up megabit-per-second rates and up to data 1 Gbit/s for provides fixed stations. Wi-Max It is based on wires. standard IEEE miles. without place 30 takes transmission to data up The accessibility internet broadband provides that system communication wireless a is (WorldwideWi-Max Wi-Max InteroperabilityMicrowavefor Access): haveuser must Wi-Fi, a broadband a wirelessconnection, a routerlaptopa and ordesktop. todoes becomesusceptible it not so that enabled hackers. For transmission throughof data use privacyuser must methods such asusingpasswords andmake theconnectionsecurity internetsecureda is not As it serviceusingcables. without mediaoftransmittingthe data, without wires. The users share the datawitheach other by connecting to the broadband Laser refers totransmission a medium Bluetooth refers totelecommunication a industry specification Wi-Fiis wireless fidelity where communicationtakes place Fig. 8.33: Bluetooth Technology 5. 4. 3. 2. 1. 8.13 NETWORKTERMINOLOGIES CTM: Protocol isasetofrules that governs thenetwork.
There are multipleprotocols definedfor computer networks, which are asfollows: this explain to example an take us Let how. and communicated is what specifies Protocol where fhandflare thehighest andlowest frequencies. two computers; inotherwords, ahardware connectionbetween two computers. Thus, theprotocolof communication oraconnectionbetweena channel up help insetting will protocol. the out carry and implement torequired be might two the of combination a even or using English as their common language. Similarly, in case of computers, the hardware, software the of because language other difference. However,each with they can exchange communicate their ideas and communicate with to each other able be not may Punjab from person a and InIndia,differentconcept. peoplespeakdifferentNow, languages. aperson from Tamil Nadu Types ofProtocols For example to exchange thosemessages. is aformal description of messageformatstwo andtherulesthat ormorefollow machinesmust communication is to proceed. Protocol means a set of rules that governs a network. A protocol Protocol: Aprotocol isanagreement betweenparties onhow thecommunicating Sol. the is what Hz, 50 is frequency bandwidth ofasignal? lowest and Hz 80 is frequency highest the If For example, transmission a on allowed media. frequencies lowest and highest the between difference the is It Bandwidth: Bits persecond: Itisthemeasuringunitofspeedatwhich datatransfer takes place. measurement for theinformation-carrying capacityofacommunicationchannel. Baud: transferred from thesenderto thereceiver. Data Channel: (d) (b) (g) (a) (e) (c) (f)
B =30Hz. B =80–50 B =fh–fl
TELNET (Remot POP3 (Post OfficePr SMTP (SimpleMailTr PPP (Point-t FTP (FileTr IP (Internet Pr TCP (Transmission Control Protocol) The number of changes in asignalper second is called abaud.Itis the unitof , usinglibrary books. The bandwidth measures the information-carrying capacity of a lineor a network. A channel is a communication medium throughis acommunication Achannel whichor messageis data ansfer Protocol) o-Point Protocol) otocol) e Login) otocol) ansfer Protocol) B =fh–fl 8.31
Computer Networks Computer Science with Python–XII 8.32
information sharing. CTM: (d) (b) (a) (c) File transfer protocol isusedto transfer system filesfrom server to requesting node, primarily for
IP (Internet Protocol) acknowledgementretransmission with is used to guarantee reliabilityof packet transfers. positive as known technique a reliable, not thus, and, networks many over transferred bytes received beidenticalwithbyteswill sent andinthecorrect order.all Sincepackets are that guarantees that service delivery stream reliable a is order.TCP sequential a in deliveredrandomly. Now, receiverthe TCPat packetsarrangesand all them collects side are they instead, order; sequential other.a each deliveredin aretopackets not data The TCP works with the Internet Protocol (IP), which defines how computers send packets of with packets only but TCPdeals protocolenables two IP hosts The to networks.establish TCP/IPa connection in and protocols exchange main streams the of data. of one is TCP TCP/IP (Transmission Control Protocol/Internet Protocol) h cmuiain ae pae hog hg sed oe. P i ue t connect to used is PPP modem. speed ISP. high of through server place the takes to communication PC Home The the connect to used is It compression. and encryption connection between two nodes. It canprovide connection transmissionauthentication, PPP is PPP (Point-to-Point Protocol) All theseproblems are solved by FTP. conventions,naming twoor systems may have different ways torepresent text data. and two systems may have different directory structures, two systems may have different file- sharing While upload afileto aserver (e.g.,uploadingaweb pagefileto aserver). is FTP • FTP usestheinternet’s T • To tr • To shieldauserfr • Indirect orimplicituseofr • Tr objectives ofFTPare: is FTP FTP (FileTransfer Protocol) will move to thedestinedaddress only by following theshortest route. computer. IP stores destination addresses in the form of IP addresses so that the packets destination the at order sequential a in assembled then arewhich destination, tosource movedrandomlyarefrompackets The number). IP (the address destination bytefour a on based packetforwards each IP headers. packet the in mentioned addresses IP the on is responsible for delivering packets from the source host to the destinationhost based is IP ansmitting andsharingoffiles(computer programs and/ordata). the primary protocol present in the internet layer of the internet protocol suite. It suite. protocol internet the of layer internet the in present protocol primary the the most commonly used data link protocol. It is a protocol used to establish a direct ansfer datareliably andefficiently. the simplest and most secure way to exchange files over the internet. The main The internet. the over files exchange to way secure most and simplest the most commonly used to download a file from a server using the internet or to or internet the using server a from file a download to used commonly most files from one system to another, we may encounter several problems— several encounter may another,we to system one from files om variations infilestorage systems amongdifferent hosts. CP/IP protocols to enabledatatransfer. emote computers.
(e) (f)
The various f • Open abro • Enter theloginandpass • Dial thenumberpro • Double clickonthedial-upicon. The follo internet to thecomputer. the by assigned drivers PPP install to needs user PPP,the through communicating For yourrequests, forward internettothe server,it forwardthen and responses toyou.back whenthat so connection PPP you anysend provider’sthe request, serverrespondcan to telephonelines to dial-up Internet theinternet. service provider may provide youa with users isimpossible twoby inbox same the to access simultaneous that means which access its during inbox protocolblocks POP3 network.overtext the plain circulatein email, passwords,the like using theuser authentication name andpassword; however, itis not secure becausethe manages thus protocol POP3 The account. email their passwordfor and username valid a enter must user server,a POP from mail a get To commands. text different radically using operate which and allocated respectivelyare 110 and 109 ports which POP3—to and protocol—POP2 this of versions main two server.are TherePOP the to commands lik Just are saved onthecomputer’s hard disk. connection isnolongerneeded to readA user themail.canreademails offline allasthese internet an downloaded, are messages the once that is advantage The protocol. POP of downloadmessages tocomputers. thelocal The user canreceive messages with thehelp POP The POP3 (Post Office Protocol 3) IMAP). or SMTP usesTCP portnumber25for standard communication. POP (usually messages incoming processes that server another and server SMTP both of addresses require clients email Thus, used. is protocol) office (post POP protocol another messages, receiving For host. another to messages send to TCP uses createnot messages: rather,forwardinghelps in it messagesbetweenservers. client It does SMTP messages. incoming not and messages outgoing only handles It computers. the As SMTP (SimpleMailTransfer Protocol) • It alsodefineshow tw • PPP supportsmultipleprot • PPP pro • Terminating thislinkaft • Configuring thislink. • Maintaining thisestablishedlink. • Establishing thelinkbetween tw name suggests, SMTP is used for sending email messages to other networks or networks other to messages email sending for used is SMTP suggests, name wt te MP rtcl te O pooo (O2 n PP) ed text sends POP3) and (POP2 protocol POP the protocol, SMTP the with e wing steps are required to connectto theinternet: (Post Office Protocol 3) is a simple and standard method to access mailboxand access to standard method and simple a Protocolis (PostOffice 3) vides error detection. eatures ofPPPare: wser like Internet Explorer or NetscapeNavigator. vided to you by theISP. o devices canauthenticate eachother. er thetransfer. word. ocols. o devices. 8.33
Computer Networks Computer Science with Python–XII 8.34 It is achannelaccess It method used by various radio communicationtechnologies. allowsIt the severalwhere transmitters send can information simultaneouslyaccess, oversingle a communication channel. multiple of example an is CDMA Access. Multiple Division Code for stands CDMA 8.14.2 CDMA(CodeDivision MultipleAccess) changing thehandset. along thephone book. This allows the user to use the phone book andother information even after generally knowncard. asSIM Itis a detachablesmartcard contains thesubscriber’s that information (SIM), Module Identity Subscriber the is GSM of feature key The rates. data of mbps 120 to kbps 64 carry to ability an has It (SMS). service message short as such alternativescalls cost making to low- and quality voice better with consumers provides It system. phone mobile (2G) generation other. GSMprovidesas well signalling digital facilitycall as digital and isso considered as asecond facilitytheyso that canusetheir mobile phonesoverall theworld to communicate witheach stands forGSM System Global forprovidescommunication. It Mobile its subscribersroamingwith 8.14.1 GSM(GlobalSystemforMobileCommunication) 8.14 WIRELESS/MOBILECOMMUNICATION quality, SMS, etc., through digitalsignals. CTM: (g) GSM isawireless communication mediumthat provides theuserwithroaming facility, voice good
(iii) (iv) Working ofTelnet on thatcomputer. whateverwith privileges they may have beengranted to thespecificanddata application user regular a as in logs user TELNET,a With system. remote the to/from files sharing log onto another user system andperform various functions such as accessing files or its originaluser.being Auserwhoin to islogging theirownsystem access toget also can Telnetis aremote helps auser that to login on to log anotheruser’s terminal without TELNET (Remote Login) prompt. t The usercan (ii) (v) (i)
the user’sscreen. and passesthemto aterminal server. TELNET server. from thekeyboard feed by theuser and passes one character atime,toat the system. client then establishes a TCP connection with the TELNET server on the destination client) by typing The terminal The server onthedestinationmachineacceptschar Once theconnectionhasbeenestablished,clientpr TELNET The A user is logged in to the local system and invokes a TELNET program (the TELNET erminate thetelnetsession byLOGOFF typing orLOGOUTon thesystem client is started on the local machine (if it isn’t already running). The running). alreadyisn’t it (if machine local the on started is client server givestoback outputs theTELNETserverdisplays and themon telnet
CDMA is adigitalcellular technology technique that usesspreadwhere spectrum theentire bandwidth GPRS provides data highspeed transfer. Auserisallowed to download videostreaming, audiofiles, Networ Multimedia MessagingService(MMS). Sending andrecei Internet applicationsfor smartdevices through Wireless ApplicationProtocol (WAP). Internet access. king facilityking one personseveral withor persons group, ina ving text messages. i.e., videoconferencing. 8.35
Computer Networks Computer Science with Python–XII 8.36 8.15 MOBILETELECOMMUNICATION TECHNOLOGIES—1G,2G,3G&4G to theextra distancetravelled. alternative paths on itsway to the receiver. These paths may causedelays in thereceived signal due electromagnetic waves are propagated through air,travelling asignal from atransmitter may take the receivingof at the signal end decreases even ifthere are noobstaclesinthe way. Second, as the telecommunication by deployingofmultichanneltransceivers. amultiplicity CTM:
3G technology has introduced more efficient ways of carrying data, making it possible to haveto possible it making data, wayscarrying efficient moreintroducedof has technology 3G with rates data higher much provides and 2000 year the in introduced was technology 3G that 1990’s early the in launched was that system cellular digital first the is technology 2G 1980’s. the in introduced was 1G phones. mobile first the in used was technology 1G For example faster web services, live fast downloading, chat, videoconferencing, etc., over mobile phones. speed from 144kbps to 2mbps. 3G Technology Salient features of2Gtechnology: mobiles, startingwithSMS. provides hightransmission data rate 2G format. also introduced indigital services data for 2G Technology Salient features of1Gtechnology: voice callsandnotfor transmitting text messages.For example for used was network 1G signals. radio analog through place took data voice Transmissionof 1G Technology • • • • • • • • • • • • •
Wireless isasystem loop inlocal that issimilarto telephone system whichprovides wireless Digital tr It allow It doesnotsupporttransf Support transf Transmission ofdatasuchastext messagesindigital format. Impro Higher datarates upto 64 kbps. Good qualityofsound. It doesnotpro It doesnotsupporttransmission oft Voice qualityisnotvery good. It usesanalogsignals. It provides datarates upto 2.4kbps. ved securitymechanism. s multipleusersperradio channelwitheachusertalkingoneatatime. , CDMA2000/EV-DO,WCDMA/HSPA+,TD-SCDMA. ansmissions enable compressed voice and multiplexing multiple users per channel. er ofpicture messagesandMMS. vide security. For example er ofcomplex datasuchasvideos. , D-AMPS, GSM/GPRS, CDMAOne. ext messages. , NMT, C-Nets,AMPS,TACS. The improved processor technology hasalsomademodern mobiledevices more power-efficient. to churn out best graphic pictures, have 3-D capability, Virtual Reality and 4K recording capability. devices the enabled has Unit) Processing (Graphics GPU with processors mobile equip to ability now.The GHz 3.0–3.5 touched also has speed earlier.processing The 32-bit against as 64-bit are we now have quad core, hexa core and even octa core processors. Most processors available today and core, dual the came then core, singlewas it First cores.manyavailable in now areProcessors desktop computers. powerful,they somuchthat cancompete with Today’sprocessors smartphonesandmobile are very Processors system, anddocertaintasks. mobile. runapplications a or laptop provide the necessary resources tooperating startan desktop, a it be system, operating an run to required are Processors 8.16 MOBILEPROCESSORS
Unlike previous generations of mobile technology, 4G mobile technology uses ultra-high Salient features of4Gtechnology: Integrated wireless solution;Customized personalservices). referredalso to “MAGIC”as Anytime/anywhere;multimedia; (Mobile support; mobility Global is 4G of feature anywhere” “anytime, The 3G. than speed faster much a at transmission data and anywhere”voice“anytime, and video streaming quality high access, internetprovides 4G 4G mobiletechnology isusedfor internet access on computers anditistotallyalso, mbps– wireless. technology, mobile 100 of generations between previous Unlike typicallymarket. mobile the speed, rules 4G Now, data 1gbps. faster much with services internet broadband 4G Technology Salient features of3Gtechnology: • • • • • • • • • • • •
The “anytime,referredanywhere”multimedia) The also “MAGIC” (Mobile is as tofeature4G of anytime/anywhere. and datatransmission atamuchfaster speedthan3G. It provides more datacapacityfor richercontent andmore connections. It deliv voiceanywhere” “anytime, and video streaming quality high access, internet provides 4G It isusedfor int Splits channelinto timeint High bandwidth isrequired. It allow It provides broadband internet services. A usercanseeliv It allow Live fast downloading, chat, videoconferencing, etc., are alsopossibleover mobilephones. It hasintroduced mor ers faster andbetter mobilebroadband experiences. s theuserto sendandreceive large emailmessages. s theuserto play 3Dgames. ernet accessoncomputers alsoandistotally wireless. e streaming onsmartphones. e efficientways ofcarryingdatawithfaster web services. ervals enablingasingle userto getalltheresources atonce. 8.37
Computer Networks Computer Science with Python–XII 8.38 • • • • Some oftheprocessors intheseriesare A4,A5,A5X,A6,A6X,A7,A8,A8X,A9,A9XandA10. iPad, iPad Touch andAppleTV. iPhone, in used be to processors for designed is series A Apple version was builtby TSMC. 16nm A9 the while Samsung, by built was processor 14nm A9 that suit its design and performance expectations. For instance, mainly SamsungandTSMC,forcustom-built making processors into contracts with processor-manufacturing companies, does manufactureApple not microprocessors. Instead,enters it 8.16.2 AppleMobileProcessors which isthelatest version. S821, or S820 either is market phone high-end medium-to the in processor Qualcomm common and S800. S800 series has already released S800, S801, S805, S808, S600, S810, S400, S820 and S200, S821. S4, The most S3, S2, ofseries—S1, number a with out come has Snapdragon 2005, Since GHz 1 first the introduced it after market processor processors when theaverage speedofmostsmartphoneswas only 512MHz. the in name big a became Snapdragon modems LTE(4G). and processors mobile marketing for responsible etc. isnow Qualcomm known for itsSnapdragonbrand which is satellitereality, phones,virtual wireless charging,communications, to semiconductor designing fordevices, mobile trackingdevices, CDMA the introduced they technology.is activelyQualcomm when involved in technology related brand known a became first TechnologiesQualcomm US-based company. isa Qualcomm 8.16.1 QualcommSnapdragon processors. Intelprocessorsmobile areand someothergiants the market. ruling Letusdiscuss these mobile Today, there are many processors availablein themarket. QUALCOMM,processors,mobile Apple
The current version, Apple S2, is a dual core processor with built-in GPS used in Apple WatchApple in used GPS built-in with processorcore dual a is S2, Apple version,current The released tilldate isApple T1. version only The Pro. MacBook in TouchIDsensors in used be to designed is Appleseries T Apple W1,isusedinwireless headphonesandAirPods. Apple Wseries Series 2.Theprocessor ismanufactured by Samsung under acontract withApple. the seriesare AppleS1,S1Pand S2. Apple Sseriesis designed for processors to be used in AppleWatch. Some of the processors in by 50%.Thisprocessor ismanufactured by TSMC. core PowerVR GPU. A10 is twice as fast as its predecessor A9 and improves graphic processing hexa a and speed 2.4GHz at running of capable processor FinFET nm 16 on built core quad a Apple A10Fusion isusedinheadphones for wireless audio connectivity. The current series, is the latest processor which is used in iPhone 7 and iPhone 7 Plus. A10 is A10 Plus. 7 iPhone and 7 iPhone in used is whichprocessor latest the is mostly popularwithChinese manufacturers. Xiaomi, Meizu, areMediaTek usedinsmartphones andtablets. processors are The latest processors from MediaTek, (4 core), hexa core (6core) anddeca core (10core). core quad core), (2 core dual as such cores of variety a They in come speed. GHz 3 to up supports processor MediaTek latest The architecture. ARM 64-bit on built areMediaTek processors chips for mobile devices, HDTVs andotherelectronic devices. MediaTek is a Taiwanese semiconductor company providing 8.16.5 MediaTek The Tegra processors mainly usedinsmartphonesandtabletsare Tegra 4,Tegra 4i andTegra K1. is currently usedinNvidiaSHIELDAndroid TV. technology.nm processor 20 The on built are chips The capabilities. video 4K and cores GPU 256 Tegra X1 is currently the most advanced Tegra chip in the market. The processor is Quad Core with Tegra X1. TegraK1, Tegra4i, Tegra4, Tegra3, Tegra1, marketed already Tegra processors are built on 64-bit ARM architecture. Tegra has the brand Tegra. as transmitting fax, voice data, tablets and mobile devices under devices.and mobile Nvidia develops chips for smartphones, such specializes processingin making unitsfor graphics, gamingunits Nvidia Corporation is a US-basedtechnology company which 8.16.4 NvidiaTegra as compared to theearlier versions. be scaled up to 3.2 GHz. Intel Core M processors offer 40% boost in CPU and graphics performance forideal batterylong life. areThese coredual processors whichGHz 1.5 about of speed can a with mobile devices and 2-in-1 convertibles. The processor consumes 4.5 watts or less power, making it also released Intel Core Multra low-voltagemicroprocessors designed for ultra-thin notebooks, Intel Ghz. 2.4 to up scaled be can that GHz 1.6 to up of speeds with size nm 14 in processorscore quad 64-bit are chips These series. X7 and IntelAtomX5 Atomin currentlyareprocessorsused only Windows, they now supportallmajormobileoperating systems. mobile devices.all Though Atom processors supportedin thebeginning consumption, bringingitdown to less than 5watts, which is ideal for The latest versions of Intel processors have reduced the power consumes but moreARM than power compared toarchitecture. ARM architectureX86 processorsIntelon are morebased powerful whichis for manufactured chips 64-bit smartphones andtablets. and 32-bit low-cost and consuming microprocessors. Atom is thebrandgivenname for thelowpower- and PC with synonymous company multinational American an is Intel 8.16.3 IntelAtomandCoreMProcessors Helio X20andX25 , 8.39
Computer Networks Computer Science with Python–XII 8.40 • • • • common emailprotocols are: Some recipients. more or one to sender a from messages digital exchanging of method a is Email 8.17 ELECTRONICMAIL(EMAIL) built on14nmtechnology. Exynos8Octa8890 are chips The resolution. UHD 4K and gaming 3D for support with GHz 2.3 of speed a at running of capable is processor The GPU. Mali with architecture The processor is equipped with Octa Core on 64-bit ARM Exynos. from processor latest the is 8890 Octa 8 Exynos Exynos 7Octa7580,7870. processors7420, areseries Exynos the Dual, in 7 Exynos processors architecture.based onARM Someofthe makes which Electronics Samsung of brand a is Exynos 8.16.7 SamsungExynos 16 nmFinFETtechnology. Theprocessor isquadcore capableofattainingaspeed2.4GHz. 960 Kirin Honor 8,Huawei mate 8andHuawei MediaPad M3. Kirin 930, 950 and Kirin 960. Some of the devices with Kirin Kirin 950 are 920, Kirin 910, Kirin 650, Kirin 620, Kirin K3V2E, K3V2, K3V1, are HiSilicon by released processors the of Some circuit designerinChina. architecture.based onARM is thelargest It domestic integrated technology. Thecompany, owned by Huawei, creates chips HiSilicon is a Chinese company specializing in semiconductor 8.16.6 HiSilicon respectively. Bothare decacore with2dualcore andasingle dualcore builtinsidetheprocessor. processors nm 20 and nm 10 use stable, company’s the from latest the X27, Helio and X30 Helio of theothermanufacturers thatuseMediaTek processors intheirtablets. LeEco Le, Yu, etc., use them in smartphones. Acer, Asus, Lenovo, Amazon Fire HD, QMobile are some
resources and thensendsthematerial to us. browse for information without knowing where the material is located. It letsussearch a listof GOPHER: internet. TransferMail Simple Protocol (SMTP): Aprotocol used for sending email messages on the from remote servers. Post Office Protocol Version 3 (POP3): Aprotocol used by emailclientsto retrieve messages internet. Internet MessageAccess Protocol (IMAP): Aprotocol for receivingmessages emailon the is the latest model to be released in the series. It is built on 64-bit ARM architectureARM 64-bit on on built is It series. the releasedin be to model latest the is Anothertool oftheinternet isGopher, amenu-basedprogramus toenables that isusedinSamsungGalaxyS6andedge. on aBBSto chatamongstthemselves. The IRC protocol was developed over four years since it was first implemented as a means for users help usdownload anIRC clientonourPC. chatting and file sharing, such as Talk City. IRC networks such as the Undernet provide servers and with eachother. Itprovides one-to-one communication aswell asgroup communicationfor client server and the server forwards this request to another client to enable them to communicate with IRC chat server to transfer messages to other clients. In fact, the IRC client sends request to IRC model whereIRCinstall the clients program client their systemon they sothat communicatecan server client uses It messages. text share to users allows that protocollayer application an is IRC 8.19.1 IRC(InternetRelayChat) videoconferencing protocols are H.323 andSIP(SessionInitiationProtocol). protocols.protocol Themostcommonchat isIRC (Internet Relay Chat)while themostcommon gained popularity.this section,weIn videoconferencingand some commonchat about talk shall With thearrival communicationformatsof internet, suchaschatandvideoconferencing, etc., have 8.19 PROTOCOLSFORCHAT AND VIDEOCONFERENCING The mostpopularsoftware usedfor videoconferencing is: location, soitsaves timeandmoney. meetings or conferences tothe need beheldwithoutforto theparticipants all travel to asingle allows it because business of field the in popular especially is technologysimultaneously. this So, Basically,system thisisa allows that ustomeetings ortrainings conduct indifferentplaces microphone, avideoscreen andasoundsystem. of users whovideoconferencein a is participating typicallyhave must computer, a camera,a a group or user Each location. each at people multiple includes often it and communication on-one communication between three or more users who are in atleasttwo locations, rather than one- users anywhere intheworld asifthey were inthesameroom. This term usually refers to Videoconferencing is a communications technology thatintegrates video and audio to connect 8.18 VIDEOCONFERENCING 2. 1. Some othernetworking-related terms are: server, thisrequest which thenforwards to anotherclient to communicate witheachother. CTM:
(b) (a) (c) computers andusers. Domain Host Configuration Protocol automatically(DHCP): It assignsinternet addresses to understood by humans(suchasdomain names)andviceversa. SystemName Domain (DNS):
IRC is used forIRC chatting by sendingandreceiving messages. text The sender sends request to IRC Skype TCP Cam Ekiga It translates network address (such as IP addresses) into terms 8.41
Computer Networks Computer Science with Python–XII 8.42 • • • • mechanisms: of variety a in applied be can It Ethernet. over TCP/IP on like systems delivery placed packet “best-effort” be to constraints management traffic and prioritization real-time allows technology QoS (QoS). Service of forwarding/transfer.Quality and teardownis set-up, H.323 of featurekey A call supports H.323 applications. entertainment and areas—consumer,business of variety wide a in applied be can it facilities, communication various protocolsprovides H.323 and As services. standards these all the for specifies It network. packet-based over communication video data audio, as and such services multimedia for communication provides that protocol a is H.323 1. H.323Protocol forVoIP 2. 1. The various protocols usedfor VoIP are: implementation. VPN, Unified Messaging, Wireless Connectivity,using SS7,IPPABX INApplications andsoftswitch applications, centre call services, class (1-800), number free toll (TCCS), CCS transparent Phone, IP email, to voice fax, to fax fax, to email email, to fax PC, to phone phone, to PC phone, to Phone providedServices by VoIP are: 3. 2. 1. There are 3maincausesfortheevolution ofthevoice-over IPmarket: costs. data communications to be run over a single network, which can significantly reduce infrastructure technology where each packet follows best route to reach its destination. VoIP allows both voice and Area Networks (LAN). As the data is transmitted in the form of packets,Local VoIPand intranetsuses packet switchinginternet, the IP,like uses that network data any on achieved be can VoIP So, ( traffic voice carry to users enables implementation (VoIP) Voice-over-IP network. cross (IP) Protocol Internet by relayed then are used. The voice calls are first digitized, compressed and then fragmented into small packets, which VoIP stands for Voice over Internet Protocol. For transferring of voice, voice over internet protocol is 8.20 PROTOCOLFORV
It uses high speed broadband useshighspeed internet connection. It CTM:
Audio, videoanddata Audio andvideo Audio anddata Audio only Session InitiationProt H.323 Merging ofdata/voice infrastructures Add-on servicesandunifiedmessaging Low-cost phonecalls VoIP isaprotocol that isusedfor transmitting voice data andmultimediadata over internet protocol. oIP ocol (SIP) , telephone calls and faxes) over an IP network. IP an over faxes) and calls telephone For example, Damage caused by Viruses: Viruses are broadly classifiedinto three types: easily most spread withemailattachments. are Viruses macros. program application and files areas, system system, operating functioning of a computer. Viruses anycan attack partof a computer’s software such as bootblock, These programs are spread from onecomputer system to anotherwhich interrupts thenormal Viruses are small programs that are written intentionally to damage the data and files on a system. 1. Viruses 8.22 Types ofThreatsandPrevention password authentication,digitalsignature, challengehandshake authenticationprotocol, etc. strategiesarechoices and available workthat blocksbuilding as networkof security. include These cyberattacks.other To prevent networkthe from practices,unethical and/or malicious these various is usedfor thispurpose, thelesser isthesecurity ofdata,either interms ofvirusesorhackingand Network isusedfor sharing,messagingandcollaboration ofdata.However, more andmore network 8.21 NETWORKSECURITYCONCEPTS personal mobility. support which services redirection and mapping name transparentlysupports SIP games. online streaming multimedia distribution, instant messaging and information, file transfer, fax over IP and include applications SIP Other time. a at person one than more with communicate can user a that modifies and terminates VoIP telephone calls. It provides videoconferencing service to the users, so specifically, a signalling protocol) originally developed(more in 1996. protocolIt uses IP protocolcommunication that establishes, a is SIP Protocol. Initiation Session is SIP of form expanded The 2. SIPProtocol forVoIP Characteristics ofViruses: (d) (d) (b) (b) (b) (e) (a) (e) (a) (a) (c) (c) (c)
They can format specific tracks onthedisks orformat theentire disks. They can destroy system programs and files. They corruptfileallocationtablewhich results incorruptingtheentire filesystem. Dialog box Computer r Speed ofacomputer s in reinstallation ofasystem. Macro Viruses: They infect datafilesandcorruptthedata. Boot Sector Viruses: File Infector Viruses: They can cause destruction of specific executable files and alteration in data files resultingfiles executablealteration specific data and of in files destruction cause Theycan Replication offilesoccurs that decreases spaceinhard disk. Various applicationsofcomputer donotfunction properly. Computer s es, menusandothererror messagewindows are distorted. estarts automatically after every few minutes. ystem frequently hangsup. Virusesthatinstallthemselves inbootsectors ofhard drive. ystem becomesslower thannormal. Virusesthatattachthemselves to aprogram file. 8.43
Computer Networks Computer Science with Python–XII 8.44 The various typesofWorms are: Characteristics ofWorm: more damage. connections. The characteristics of viruses and worms are more or less awormsame, but causes A worm is a self-replicating programruns thatindependently andtravels across network 2. Worms Prevention from Viruses: Damage caused by Worms: without humanintervention, andhasmaliciouscontent. CTM: allocation table. CTM: (d) (d) (b) (b) (b) (b) (a) (a) (a) (a) (c) (c) (c)
A virus isamaliciousprogram that damagesdata andfilesofasystemcan also and thefile corrupt A worm isacomputer program self-replicate whichcan andpropagate over thenetwork, withor Frequent update your computer system. Use antivirus softw A worm may corruptthefilesonhostcomputer. It spreads acr It replicates itself. safeguard your system. send spamonalarge scale. this way to andhadtheability stealpersonal information, credit including card details,and and repeats the process. In 2004, a worm called “Phatbot” infected millions of computers in folder, theworm gets downloaded ontheir system also. Inthisway, theworm copies itself unassuming name.Whenanother user on thenetwork downloads files from the shared when theuser downloadsany file,thewormcopy will itselfinto ashared folder an with requireddownloadedfilesby user.the awarenot is user A wormthis about therefore, and, File SharingNetwork Worms: the particularprogram are affected by it. wormsemail as the recipient needs toThe the messagelink.users accept and clickof or instant-message program to send links to infected websites. These are not aseffective as Internet Worms: by sendingmailsto infected website. Instant Messaging Worms: to any infected website. Email Worms: Worms runindependently. Unlike virus,w Always scanpendrives andothersecondary storagemedia inorder to detect viruses and It may aff ect communicationbetween thehostandother systems. oss networks through email,instantmessagingorjunkmails. orm doesnotrequire hostanditisself-contained. Worms spread through any emailwhich contains anyor fileattachmentlink Theinfected wormof theuser’slist chat-roomuse thecontact will profile are to permanently remove viruses. Worms spread throughmessaging across instant the network These types of worms are downloaded along withthe are thensentto the web server for later use. Cookie is basically apieceis of that storeddata by the which them for pages web prepares and users identifies cookie a website, any browses user the When cookie. browser or cookie internet cookie, web cookie, HTTP an as known also is cookie A 8.23 COOKIES Spams canbeavoided by usingemailfiltering, spamtraps, etc. text uses message serviceofmobilephone. that spamming of form a is spam phone Mobile etc. schemes, quick rich get products, variouspampering theuserwith discountschemes, or commercialadvertising, often for dubious same messagetotosent be user which a hemayotherwise receive. not Generally,formthe is in it of the of copies many with internet the floods it form, non-malicious In space. disk entire the eat to order in person unidentified or unauthorized an by sent is which mail unwantedbulk an is Spam 4. Spams as itrunsahiddencode. that caused by viruses. Sometimes the user is unaware about a Trojan because of its masking effect to similar Trojansis by caused damage Trojans.The spread also Wormscan computers. between information and disks of exchange and attachments email through spread generally are Trojans There are several typesofTrojan Horse: and candamagethesystem completely. which programs, executable arewhenmeans that user runsany a or plays application games, they workapplication behind that Trojans destructive. are they but themselves replicate not do background.systemTrojanscomputerUnlikethe viruses, a destroy in informationalteron can or gamesuch asa spreadsheetor a the systemdamage can that whenIt runningtheseapplications. A Trojan horse is a kind of virus that looks safe but has hidden effects. It is a hidden code in a 3. Trojan Horse program applications. CTM: Spam refers junk mailthat to eats electronic uptheentire computer’s space. CTM: (d) (d) (b) (e) (a) (e) (c) (c) (f)
Trojan horseisahiddencode that safe looks whilerunning butithassomehidden effects Denial-of-service attackTr FTP Tr Destructiv Remote accessTrojan horse A worm consumestoo muchsystem memory(ornetworkbandwidth), web causing servers, mayIt disabletheantivirus software whichit to enable will onthehost, causemore damage. network servers andindividual computers to stop responding. Proxy Trojans Data sendingTr Bulk emailchainingcanbecreat ojans e Trojans ojans ojans ed withanintention to guessemailpasswords.
8.45
Computer Networks Computer Science with Python–XII 8.46 3. 2. 1. A firewall canusevarious methodsforfiltering theinformation suchas: Netscreen 25,etc. firewall, NetGear firewall, CISCO are firewalls of examplesVarious rules. of set a on based traffic network a is firewall A security system, another. either hardware- orsoftware-based, controls that to incomingandoutgoing network computer one from virus of spread the preventing in helps it firewall, software of terms in and network, the protectsrouter, it as such firewallhardware of form the hardwareIn a application. as and softwaresolution a as both system.Firewallexists the The access. protect to computer a or user network the to internet the unauthorized from coming information the filtersfirewall from network private the protects that software a is firewall A 8.24 FIREWALL 4. 3. 2. 1. be ofthefollowing types: The information which is stored by awebsite isknown asstate information. The information can 5. 4. 3. 2. 1. Working ofCookies the cookiesfolder isstored inc:\windows\cookies. website ontheuser’s hard disk.Theinformation isstored intheformvalue ofname pair. Generally, any website. CTM:
What isthefrequency ofaparticularvisit How many are repeat visitors? How many are newvisitors? How many visitors have visited thesite? The server cr is supplied, If nocookiesdata The IPaddress isusedt The browser contacts the DNS server to convert the domain name into IP address. The browser The userenters thenameofw firewall. by blocked is name domain or address IP particular that from data the then data, unwanted IP addressis comingfrom blocking:Ifthedata a networkor websitecontains some that effectively hidesthetruenetwork addresses. and network the the leaving toand entering messages sent all intercepts serverserver. proxyproxy then The and firewall in received first is information the rather, request; the makes Proxy service: users, butitisdifficultto configure. Inaddition, itissusceptibleto IPspoofing. to transparent and effectivefairly is filtering Packet rules. user-defined on based it rejects or of form the packets, is in filtered. incoming Packet or filter outgoinglooks at is each whichpacket entering data, or the leaving the filtering, network packet and In accepts filtering: Packet website for thefirsttime. looks for thecookiesonhard disk. Cookies areCookies the messageswhich are stored by the website on a user’s hard disk whenever they visit eates anIDofapersonwhich isthenstored by cookiesonthe hard disk. h ifrain hc i rqetd s o drcl sn t te esn who person the to sent directly not is requested is which information The o contactthecorresponding server alongwithcookiesdata. then thewebsite comesto knowthe userisvisiting that ebsite onthebrowser. or? cyber laws. privateunauthorized personorgetting an information, etc.,have prevented been by implementing and fine. A large number of cyber-criminal activities such as hacking passwords or accessing files by in which various cyber crimes have beendeclaredoffences aspenal imprisonment with punishable (Amendment) Act, 2008, is known as the cyber law. It has a separate Chapter XI entitled “Offences” physical world to humanactivity 2000, as amended by InIndia, theITAct, ontheinternet. theIT computer-related activities. In essence, cyber law is anattempt to apply laws designed for the The lawgovernsthat thecyber spaceis knownas cyber law.is thelawIt which various dealswith 8.26 CYBERLAW or incidentalthereto.” therewithconnected mattersfor and 1934 Act, India of ReserveBank the and 1891 Act, Evidence Books Bankers’ the 1872, Act, Evidence Indian the Code, Penal Indian the amend to further and agencies Government the with documents of filing electronic facilitate to information, of storage commerce‘,which involve theuseofalternatives data to paper-basedmethods and of communication electronic of means by out interchange carried andothermeansofelectroniccommonly communication, referred to as’electronic transactions for recognition legal provide to Act “An IT Act 2000hasbeendefinedas: Indian Parliament (No.21of2000)notifiedonOctober 17,2000. The 8.25 INDIA’S ITACT 6. 5. 4. 3. 2. 1. 7. 6. 5. 4. Firewall protects theuserfrom thefollowing: person. CTM:
Spam orjunkmails Viruses andmacros Email bombs SMTP sessionhijacking Application backdoors Remote loginby otherswho are notauthorizedto gain accessto thesystem services useport80andport21. Generally,FTP block. and HTTP particular a block to used be can firewall The Portblocking: further checking. without hosts the between flow can packets made, been has connection the Once established. Circuit-level Gateway: Telnet servers. Thisisvery effective butcanimposeperformance degradation. ApplicationGateway: It applies security mechanisms to specific applications, such as FTP and a to service protocol particular a disallow particular userorgroup ofusers. to set be can firewall The Protocol blocking: Information TechnologyInformation Act2000 Firewall isasystem that isdesignedto thenetwork protect from illegaluseby anunauthorized t ple scrt mcaim we a C o UP oncin is connection UDP or TCP a when mechanisms security applies It (also known(also as ITA-2000 or theITAct Act) isan of the
8.47
Computer Networks Computer Science with Python–XII 8.48 types ofcyber crimesandthemostcommononesare explained below: When any crime is committed over itis referred the internet, to as cyber crime. There are many 8.27 CYBERCRIMES protect individual usersandorganizations from unauthorizedintrudersinto thesystem. tovery important become exponentialrate, has an it growingat been has internet of usage the As 3. 1. 6. 8. 7. 5. 4. 2.
person may notbeaware ofhiscomputer beingaccessedfrom aremote location. hacking, acriminaluses a variety of software so as to enter a person’s computer and that whichhacking, many organizations useto checktheirinternet securityprotection. In access to theircomputer system illegally isknownThis as hacking.isdifferent from ethical Hacking: electronically andthenmisusedby afraudulent personororganization. funds which may beintercepted anddiverted. Validcredit cardbe hacked numberscan Electronic Funds Transfer Fraud: products atcheaperrates. They alsopromise thecustomers heavy discountsandfreebies. quality poor sell that sites fraudulent some are There common. increasingly becoming is fraudulentsales pitches, deceptiveinvestmentsolicitations orbogus charitable overtures technology to fraudulentendeavours much greater. hasbecomethat The useoftelephone for andInvestmentSales Fraud: Withtheincrease in e-commerce,of theapplicationdigital soliciting. and abuse child preventing and reducing of hope the with children by frequented rooms purpose of child pornography. The FBI has been spending a lotof time monitoring chat that sexually exploit underage children. The criminals solicit minors via chat rooms for the Pornography:Child Inthiscyber crime, defaulters create, distribute or access materials system. steal sensitive information or data that can cause damage to existing software in a computer software are that used to disruptproper functioning ofthenetwork. The software is used to Software:Malicious These are internet-based software orprograms knownas pirated major financiallossfor thevictimandeven spoilthevictim’s credit history. information to gainmoney orto buy thingsonlineinthevictim’sresultcan namethat in person’s creditaccount, card, bank socialsecurity card, debitcard andother sensitive transactionsservices. andbanking In this cyber crime, a criminalaccesses a data about cash for internet the using people with problem major a become has This Identity Theft: stalking to make theirvictim’s life miserable. cyber isnothaving stalking thedesired they effect, with cyberalong begin offlinestalking and instead ofresorting tothey offlinestalking, usetheinternet toIf they stalk. noticethat unwanted abusive online messages and emails. Typically, these stalkers know their victims CyberStalking: Cyber is akindofonlineharassment stalking where thevictimgets (FBI). and many of these websites are now beingtargeted by theFederalBureau of Investigation violating copyright. There are even peer-sharing websites which encourage software piracy Theft: Theft occurs when a person downloads music,movies, games andsoftware by Gainingknowledgesomeone’s aboutprivate andsensitive information by getting Acyber crimeoccurs when theretransfer isa of There are various methodsto protect network threats. Theseprotection methodsare asfollows: Prevention from Threats Security Geographicalthe Indicationsof Goods(Registration &Protection) Rules, 2002,respectively.and 1999 Act, Protection) & (Registration Goods of Indications Geographical the and 2001, geographical and designs Trademarksthe and Rules,Design and 2000 Rules, CopyrightsAct, Design Indian 1957, 2002, Act, copyrights, trademarks, patents, 1999 Trademarks Act, 2003, Rules, Patent and 1970 Act, Patents the likebygoverned are indications India in issues IPR-related areas ofacountry. of itsresultapplication and encourage fair trading which helps indeveloping socialandeconomic rights to theowner property. ofthat These rights alsopromote creativity anddissemination and funded Safeguardingit. intellectual property from illegal use can be done by giving some exclusive of intellectual property is the person who has developed the product or the organization which has industrial design rights, trademarks, trade dress and, in some jurisdictions, trade secrets. The owner refers to creations of the mind. Intellectualproperty rights may beprotected by patents, copyrights, literature andartisticworkcreated by aperson.Intellectual property(IP) isalegal term that music, as such property intangible to right the is which rightsproperty intellectualfor stands IPR 8.28 IPRISSUES CTM: Cyber ofinternet andthe lawaspects definesallthelegaland regulatory WorldWide Web. 11. 10. 9. 1.
• • • • to auser to become an authorized user of the system. Authorization checks canalso be a person access to a network for legal use. It is an actof giving authorityor legal identity Authorization: be ofthefollowing types: do notallowthe attacker to modify or access information onthecomputer.can ADoSattack computer are denied access or use of the resources ofcomputer. that Generally, DoS attacks Attacks: (DoS) Service Denial of byattack is an ADoSattack which legitimate users of a consequences through theuseofacomputer network, Assault by Threat: Itrefers to threatening aperson or his family members with dire person’s account. hacking into theirandsending email accountmailsusingvulgarto language anunknown involvesDefamation: It cyber a crimetheintentwith of lowering thedignityofsomeone by
legitimate useriseitherdestroyed orchangedto someunsubtleform. Denial ofAccess to Information: excessive traffic. An example of this type of attack is flooding a computer with junk mail. range from cutting wires and jamming radio communications to flooding networks with Denial ofAccess to Communications: applications installedonthesystem orany datastored onthesystem. Denial ofAccess toSystems: Refers to theunavailabilityof thesystem, the all including prevent theuser(ororganization) from usingapplicationsto perform any task. by application an or unavailable.either unusable it making This is usually doneto Denial of Access to Applications: Authorization meansIntrusion Detection. Authorization meansto grant Refers toin which anattack information sought by a Refers todenies that auser from anattack accessing Refers tocan that acommontype ofattack i.e., email,videosorphones. 8.49
Computer Networks Computer Science with Python–XII 8.50
6. 3. 9. 8. 7. 5. 4. 2.
File accesspermissionisgrant Three typesoffileaccesspermissionsthatare granted to auser: resources baseduponasecret word entered by theuser. a system mustbepassword protected. A password protected system allows access to Password Protection: To protect thesystem or network from anunauthorized person, involves digitalsignature, fingerprints,retinal patterns, etc., to establishidentity. System:Biometric Biometric system formsthe mostsecure levelof authorization.It Secrecy: Hidingsomerelevant information from anunauthorizedpersoniscalledsecrecy. data. Privacy: The data which is accessible only to anauthorized person is known asprivate intruder orapersonisdifficultandneedscomplex protocols basedoncryptography. or sensitiveor information data is known Verifying authentication. as identityofan the Authentication: To determine the identityofaperson before grantingaccess to private worms orTrojan horse. implemented toprogram a or process to makefree data entering ofrisk,suchas ofviruses, and managersoftheorganization. Agoodsecuritypolicymustbe: shouldclearlyThe policy communicateto thesecuritygoals the users,administrators all its employeesof therulesthat need to followto accessinformationthe organization. about Proper Policy:Security Anorganization’s security policy is a formal statement consisting rules andothercriteria. of set a upon based domains security differentbetweentraffic computer out) and (in wall proxyor deny, decrypt, permit, to encrypt, configured devices of set or device softwareor unauthorized access while permittingauthorizedisaprogrammercommunication. It block to designed is that network or system computer a of part a is firewall A Firewall: which user orgroup accountshave what typeofaccessto thefile. describes that attribute list control access an has file Each authorization. their to modify a file, etc. Different types of permissions can be given to a specific person according Permission:File (b) (b) (a) (a) (c) (c)
Others: Refers to allotherusers. Group: Refers to thegroup ofuserswhich isworking withthefileowner. RefersOwner: to theuserwho hascreated thefile. Execute: Allows auserto execute afile. Write: Allows auserto editandwrite onafile. Read: Allows auserto viewandread afile. able to adjust itself according to the changing configurations of computer networks. able to definetheareas ofresponsibility for auser, anadministrator oramanager. enforced withadequate securitytools. A user can give access to a person to read a file, write to a file, open a file, ed to three typesofusers:
3. 2. 1. These elementsare specifiedby thefollowing respective tags: Any ingeneral, HTMLdocument, containsatleastthree elements—HTML,HEAD, andBODY. file withextension either NOTEPADas NOTEPAD2such editoror textany save using a and written be can document HTML known astagsfor formatting thedocumentandto specifythehyperlinks. language, specification hyperlink and layout document a is HTML displays. link that to related document the link, specified a on clicks person etc.also helpsincreating It hyperlinks sovariousthat documents can belinked together. Whena is HTML screen. the on supports that multimediadocuments a languageandconsists of audio, video, graphics, pictures, links and pictures text, display to how browser the tells language This used tois that language HTML isa create webwhichpages aredisplayed then by webbrowsers. 8.30.2 HyperText MarkupLanguage(HTML) called aweb server. is server WWW a and browser web a called is client WWW A responses. sends and request that processes server the and request a sends client a wherearchitecture client-server upon based is providesWorldwellThe graphics,as linksfiles. as todocumentsvideo otherand audio WebWide Text(Hyper HTML called that language markupLanguage) Markup a formattedarein documents and other multimedia componentsaswellas web navigation features consisting of hyperlinks. The videos images, text, contain may pages Web documents. hypertext interlinked through internet is WWW aninformation service can beused that for sending and receiving information over the 8.30.1 WWW(World WideWeb) follows: Internet offers several important and extensively used features or services which are described as 8.30 INTRODUCTIONTOWEBSERVICES mistaken for any security-related cyber crime. Due to themassattention given tohat hackers black by themedia,whole hackingterm is often etc., anditisnotlimited to eitherofthem. hacking, brain hacking, phone as such also, formssecurity. other many in existsHowever hacking Computer hacking is the most popular form of hacking nowadays, especially in the field of computer accepted hackingasalifestyle andphilosophy oftheirchoiceiscalledahacker. the creator’sperson whopurpose. A original consistently engagesactivities inhacking has and is thepracticeHacking of modifying thefeatures ofasystem inorder tooutside goal accomplisha 8.29 HACKING pages and is linked to theinternet.pages andislinked CTM:
.. .. .. WWW isasetofprograms andprotocols that allows theuserto create anddisplay multimediaweb .HTM or.HTML , a language that uses variousthat language i.e., a coded elements 8.51Computer Networks Computer Science with Python–XII 8.52 W3C recommendation specifiesboththelexical grammar andtherequirements for parsing. The standard. open free a is It (W3C). WebWorldConsortium Wide the by recommended is XML separate style sheetknown ascascadingstyle sheetisused. MarkupXML was language. designed to carryandnottodata displayFor data. formattinga data, createtocustom allowsusers that general-purposespecification a is It tag. correspondingclosing user for their own purpose. Unlike HTML, in XML,tagsare case-sensitivemust have andeachtag a rather,predefined; not are the tags bycreatedare the they differentXML, ways. representedin In create to user the allows that their own to tags storein astructured data However, format. Language these structured formats canbe Markup text-based a is Language Markup Extensible 8.30.3 ExtensibleMarkupLanguage(XML) Now, execute thisfileusingany web browser anditwilldisplay apageasbelow: The structure ofHTMLdocumentisasfollows: tags. Tags are coded called elements. CTM: HTML is a Markup language that enables users HTMLto is a Markup create web pages and format them using predefined
It isusedfor displa responses sends and server,it the processesserverto request the sends (client) browser The It isanobject-oriented pr simultaneously executed are commands several that means this protocol; stateless a is It to theclient. without knowing thecommandwhich isalready executing before anothercommand. XML is a Markup Language forXML is a Markup creating documents format. in a structured Users can create their own
Computer Networks Computer Science with Python–XII 8.54 IP address. IP address is short for Internet Protocol (IP) address. An IP address is an identifier foridentifier an addressis forProtocolIP Internetaddress. short An address address.(IP) is IP IP haveshould addressunique a TCP/IP a toon it identify network. addressunique This knownis as device each that important becomes it Therefore, network. TCP/IP the of example an is internet Protocol/Internet Protocol or TCP/IP. A network using TCP/IP is known as a TCP/IP network. The communication over networks. However, themostcommon one is the Transmission Control each other. These sets ofrules are knownas protocols. Severaltypes ofprotocols are usedfor The computers connected to anetwork alsoneed to follow some rules to communicate with 8.30.7 IPAddress specified the html documentonthewebsite ofCBSE. of name the specifies ‘academics.html’ located. is source the where name domain the or address‘www.cbse.nic.in’ IP hypertextand transferprotocol,forthe indicatesstands ‘http’ for example, URL standsfor uniform resource locatorwebsiteparticular a in locating helps that web ora page, 8.30.6 URL Country SpecificDomainNames Generic DomainNames The top-level domainsare categorized into following domainnames: cbse isthesub-domainofnic. nic isthesub-domainofin in istheprimarydomainname In thedomainname For example, 2. 1. A domainnameconsistsofthefollowing parts. CTM: URLstandsfor uniform resource locator that stores theaddress ofaweb page.
Sub-domain name(s). Top-level domainnameorprimaryname,and ·com -commercial business .us -United Stat .jp- Japan .pk- Pakistan .nz- NewZealand .ch- China ·ca- Canada ·au -Austr .in -India ·org -Organizations (non-profit) ·net -Networ ·mil -Military ·gov -Government agencies ·edu -Educational institutions is a URL for a specific website. In this URL, this In website. specific a for URL a is http://www.cbse.nic.in/academics.html alia cbse.nic.in: k organizations es ofAmerica hyperlinks. through possible is page web another to page web one Traversalfromform. graphical or textual A webelectronicis an page designed displays document/page using HTML.It information in 8.30.9 Web Page protocol. HTTP through accessed Examples of various websites are: cbse.nic.in,google.com, amazon.in,etc. are that hyperlinks several of consist documents HTML The protocol. HTTP through internet transferredthe overis information the and HTML using written page where thelinksall related to other documents are displayed. The web pagesof a website are assets that are hosted on one or several web servers. The first page of a website is known as home A website isacollectionofvarious web pages,images,videos, audios or other kinds ofdigital 8.30.8 Website 3. 2. 1. You canfindouttheIPaddress ofyour computer by performing thefollowing steps: connection isusedonthatcomputer. internet whose (ISP) Provider Service Internet the by assigned is computer a of address IP The The preceding IPaddress initsbinaryform is:11000000.10101000.00000001.00001010 following isanexample ofIPaddress inthedecimalform: 192.168.1.10 internally.The form binary into numbers these converts computer the processed, is address an IP When form. decimal the in are address IP an in numbers the examples, above the in seen As addresses are: 192.168.1.2,10.324.1.3and109.134.2.2. written as four numbers separated by periods. Each number can be 0 to 255. Some examples of IP address numeric 32-bit a is address IP of format The destination. the of address IP the on based messages route protocol TCP/IP the using Networks network. TCP/IP a on device or computer a CTM: Awebsite ofseveral isacollection web pageswhichare related to eachotherthrough hyperlinks.
(as shown intheoutputwindow given below). Type Type cmdinthe Open the Click the ipconfig and press Enter. The output appears, displaying the IP address of your computer Start Run dialogbox. button. Apop-upmenucontainingvarious optionsappears. Run dialogbox andpress Enter. Thecommandprompt (cmd)window opens. 8.55
Computer Networks Computer Science with Python–XII 8.56 languages. webis theonly hostingcompaniesinIndia.It hostingcompany which provides support inregional likeapplications webhostingsitesindia.co.in email. is oneofthetop domainnameregistration and users. A clientcanalsousecontrolfor panel scripts installing as wellas other modules and service to their organizationor for some information uploading which may bevaluablefor theinternet interfacean or control forpanel the web managing server soasto addnewsevents and related display information for theirorganization intheform ofweb pages.Thehostmayprovide also use byas welltheir clients as provide internet connectivity.The websites which are constructed companies are known These companies aswebprovide host. space onaweb server they own for their own websites which are accessible to the internet users via World Wide Web. Such Web hosting is a service which is provided by companies to its clientsto allow themto construct 8.30.12 Web Hosting internet information server, etc. webSome popular servers are: Apachewebserver, Netscape enterprise webserver, Microsoft hosted onseveral linked ormirrored web servers. be may website single a or websites, multiple support may server web single A it. for requested that browser the to back sends and required, if information, generates and documents the finds request, a for waits serverWeb internet. the to connected computer a on runs that program servera is web A pages. web requested the displays and request the to responds server server,a a to request any sending is client web a when and pages web stores that server a is server web A 8.30.11 Web Server are: MozillaFirefox, Opera, AOL, Webkit, Iceweasel, etc. user to navigate through theWorld WideWeb anddisplay webweb pages.Somepopular browsers It is asoftwarehelps inaccessing thatweb Ithelpsthe pagesand,thus,is also calledweb client. 8.30.10 Web Browser A web pagecanbeclassifiedinto two types: CTM: Web that isprovided hostingisaservice by thecompany to usersto create web-based applications. CTM: stores Aweb web server documents andresponds to therequests madeby web browsers. CTM: Aweb browser isa WWW client that navigates through the WWW anddisplays web pages.
.php, .asp,or.jspasextension. toscripting languages displaycontent changing on theweb generallypage Such a page. has Dynamic webinteractiveAn page: webdynamicis a page web dynamicA page. web uses page it isknown asastaticweb page.Astaticweb pagegenerally has.htmor.htmlasextension. webStatic page:Aweb pagewhich displays samekindof information whenever a user visits WEB Fig. andReceiving Request 8.34:Sending Sends requestSends WEB (a) Client-Side Web Languages Scripting through theweb scripts written inWeb ScriptingLanguage. automated and interpreted are server web a by executed are which tasks The requirement. the written codes for a script may beused by theserver side or may beused by theclientside as per The page. web executed,displaysthe when which, programminglanguage a is Script scripts. web communication between web browser and web server happens throughprograms small called Website Scriptingis used for creatingweb pagestothem ontheweb publish interactively. The 8.30.14 Web Scripting 3. 2. 1. The DNRprocess takes placeinthebackground, andcanbeexplained inthefollowing steps: IP addresses ofdomainnames. the finds computer your which by process the givento name the is DNR (DNR). Resolution Name tomatchingfindits address.IP Howaddress? this find does it answerThe byis: Domain the using to remember than the IP address. When you use the URL to access a website, your computer needs addresses.However,IP of easier much is it because website,URL particular youits a use access to You already knowcommunication between that computers on anetwork takes place withthehelp 8.30.13 DomainNameResolution(DNR) This isdoneinthefollowing manner: different have Unix configurations. and Linux, 7, Windows XP, Windows, as such systems, operating Different The domain name is resolved according to the configuration of the operating system you are using. scripting engine.scripting CTM: CTM: Aweb browser isa WWW client that navigates through the WWW anddisplays web pages.
Client-side scripting enables the usert Client-side scriptingenables has that browser Web the to it sends system operating the address, IP the obtaining After The Web browser issues acommandto theoperatingsystem of your computer to generate the Enter thedomainnameofwebsite thatyou want to accessintheWeb browser. online games, downloading datafrom theserver, etc. enabled that can interpret the script code. Examples of client-side scripting where it is used are The browser. web the by client-side scriptingis browsertherefore, dependent and, the browser executedscripting- be must and interpreted then and end client the at downloaded requested it. given domainnameandreturns itto theoperating system. and IP addresses that are registered on the internet. The DNS server finds the IP address of the on anetwork.The DNS server adirectorymaintains the domainnames of all alist containing IP the find to address ofthegivenfile domainname. this checks first system operating the Therefore, names. domain some of IP address ofthegiven domainname. If the IP address is not found in the HOSTS file, the operating system connects to the DNS server Generally, the operating system maintains a HOSTS file, which contains a list of the IP addresses A script isalistofcommandsA script inaweb embedded pagewhichare executed program by or acertain o interactweb with The client-side scriptsarepages. 8.57
Computer Networks Computer Science with Python–XII 8.58
1. 3. 2. 1. 2. Some PopularSome Client-Side Languagesare: Scripting
3.