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  • 1. LANLANLocal Area Network, LAN, in computer science,a group of computers and other devicesdispersed over a relatively limited area andconnected by .A communications link that enables any deviceto Interact with any other on the network.LANs commonly include microcomputers andshared (often expensive) resources such aslaser printers and large hard disks.
  • 2. MODERN LANMODERN LAN Most (modern) LANs can support a wide variety ofMost (modern) LANs can support a wide variety ofcomputers and other devices. Each devicecomputers and other devices. Each devicemust use the proper physical and data-linkmust use the proper physical and data-linkprotocols for the particular LAN, and all devicesprotocols for the particular LAN, and all devicesthat want to communicate with each other on thethat want to communicate with each other on theLAN must use the same upper-levelLAN must use the same upper-levelcommunications protocol.communications protocol. Although single LANs are geographically limitedAlthough single LANs are geographically limited(to a department or an office building, for example),(to a department or an office building, for example),separate LANs can be connected to form larger networks.separate LANs can be connected to form larger networks. Similar LANs are linked by bridgesSimilar LANs are linked by bridgeswhich act as transfer points between networks;which act as transfer points between networks;
  • 3. LAN MANAGERLAN MANAGERLAN Manager, in computer science, a local areanetwork technology developed by MicrosoftCorporation and distributed by Microsoft,IBM (as IBM LAN Server), and other originalequipment manufacturers (OEMs).LAN Manager connects computers runningthe MS-DOS; OS/2, and UNIX operating systemsand allows users to share files and systemresources such as hard disks and printers and torun distributed applications using a client-serverarchitecture.See also Client-Server Architecture; LAN;Network;
  • 4. ManagementManagementIt is a full-time job to keep a LAN operating as itIt is a full-time job to keep a LAN operating as itshould.should.Keeping a computer network that is distributedKeeping a computer network that is distributedacross the world running smoothly takes theacross the world running smoothly takes thechallenge of network management a step further.challenge of network management a step further.The essential concepts for managing distributedThe essential concepts for managing distributedand diverse networks have received a lot of attentionand diverse networks have received a lot of attentionlately.lately.There are now enough tools and standards forThere are now enough tools and standards forthis important aspect of computer networks to allowthis important aspect of computer networks to allowglobal networks to be supervised effectively.global networks to be supervised effectively.
  • 5. SecuritySecurityWith ever increasing amounts of importantWith ever increasing amounts of importantinformation being entrusted to ever more distributedinformation being entrusted to ever more distributedcomputers, computer security becomes ever morecomputers, computer security becomes ever moreimportant.important.In a highly distributed system it would be all too easyIn a highly distributed system it would be all too easyfor an informed superhighway man to accessfor an informed superhighway man to accessconfidential information without being seen.confidential information without being seen.The Data Encryption System (DES) standard forThe Data Encryption System (DES) standard forprotecting computer data, introduced in the late 1970s,protecting computer data, introduced in the late 1970s,has more recently been supplemented by “public key”has more recently been supplemented by “public key”systems that allow users to scramble and unscramblesystems that allow users to scramble and unscrambletheir messages easily without a third party intruding.their messages easily without a third party intruding.
  • 6. SECURITY AND MANAGEMENTSECURITY AND MANAGEMENTHaving fast computer networks built ofHaving fast computer networks built ofmachines that can talk to each other is notmachines that can talk to each other is notthe end of the story.the end of the story.The specters of the “informationThe specters of the “informationsuperhighwayman” and the “informationsuperhighwayman” and the “informationsuperroadworks” have yet to be dealt with.superroadworks” have yet to be dealt with.
  • 7. Open SystemsOpen Systems This term covers the general aim of building computer systems so thatThis term covers the general aim of building computer systems so thatthey can readily be interconnected, and hence distributed. In practice,they can readily be interconnected, and hence distributed. In practice,open systems is all about unbundling all the complexities of aopen systems is all about unbundling all the complexities of acomputer system and using similar structure across different systems.computer system and using similar structure across different systems.And this entails a mixture of standards (which tell the manufacturersAnd this entails a mixture of standards (which tell the manufacturerswhat they should be doing) and consortia (groups of like-mindedwhat they should be doing) and consortia (groups of like-mindedpeople who help them to do it). The overall effect is that they can talkpeople who help them to do it). The overall effect is that they can talkto each other.to each other. The ultimate aim of all of the work in distributed systems is to allowThe ultimate aim of all of the work in distributed systems is to allowanyone to buy computers from a number of different manufacturers, toanyone to buy computers from a number of different manufacturers, tosite them wherever is convenient, to use broadband connections to linksite them wherever is convenient, to use broadband connections to linkthem, and to operate them as one cooperating machine that takes fullthem, and to operate them as one cooperating machine that takes fulladvantage of the fast links.advantage of the fast links.
  • 8. Object TechnologyObject TechnologyAnother way to build computer systemsAnother way to build computer systemsworks from the premise that they should beworks from the premise that they should bebuilt from well-defined parts—objects whichbuilt from well-defined parts—objects whichare encapsulated, defined, and implementedare encapsulated, defined, and implementedso that they can be independent agents.so that they can be independent agents.The adoption of objects as a means ofThe adoption of objects as a means ofbuilding computer systems has helped tobuilding computer systems has helped toallow interchangeability of parts.allow interchangeability of parts.
  • 9. Client ServerClient ServerInstead of building computer systems as monolithicInstead of building computer systems as monolithicsystems, there is now general agreement that they shouldsystems, there is now general agreement that they shouldbe constructed as client/server systems.be constructed as client/server systems.The client (a PC user) requests a service (such asThe client (a PC user) requests a service (such asprinting) and the server (a LAN-connected processor)printing) and the server (a LAN-connected processor)provides it.provides it.This consensus view on the structure of a computerThis consensus view on the structure of a computersystem means that there is a separation of functionssystem means that there is a separation of functionspreviously bundled together.previously bundled together.The implementation details that flow from a simpleThe implementation details that flow from a simpleconcept go a long way to enabling all computers to beconcept go a long way to enabling all computers to betreated uniformly.treated uniformly.
  • 10. The facilitiesThe facilitiesOn most LANs are very powerful. Most organizations do not wishOn most LANs are very powerful. Most organizations do not wishto have small isolated islands of computing facilities.to have small isolated islands of computing facilities.They usually want to extend facilities over a wider area so thatThey usually want to extend facilities over a wider area so thatgroups can work without having to be located.groups can work without having to be located.Routers and bridges are specialized devices that allow two orRouters and bridges are specialized devices that allow two ormore LANs to be connected. The bridge is the more basic devicemore LANs to be connected. The bridge is the more basic deviceand can only connect LANs of the same type.and can only connect LANs of the same type.The router is a more intelligent component that can interconnectThe router is a more intelligent component that can interconnectmany different types of computer network.many different types of computer network.
  • 11. LOCAL AREA NETWORKSLOCAL AREA NETWORKS1.One of the most dramatic events in computer networking 1.One of the most dramatic events in computer networking has been the introduction and rapid growth of the local has been the introduction and rapid growth of the local area network (LAN) as a way to standardize the system area network (LAN) as a way to standardize the system of linking computers used in office systems. of linking computers used in office systems.               As the name suggests, this is a means of connecting a As the name suggests, this is a means of connecting a number of computing elements together. At the simplest number of computing elements together. At the simplest level, a LAN provides no more than a shared medium  level, a LAN provides no more than a shared medium  along with a set of rules that govern the access to that along with a set of rules that govern the access to that medium.medium.              The most widely used LAN, Ethernet, uses a The most widely used LAN, Ethernet, uses a mechanism . This means that each connected device mechanism . This means that each connected device can only use the cable when it has established that no can only use the cable when it has established that no other device is using it. If there is contention directlother device is using it. If there is contention directl
  • 12. 2.In addition to providing shared access, modern LANs can 2.In addition to providing shared access, modern LANs can also give users a wide range of sophisticated facilities.also give users a wide range of sophisticated facilities.            Management software packages are available to control Management software packages are available to control the way in which devices are configured on the LAN, how the way in which devices are configured on the LAN, how users are administered, and how network resources are users are administered, and how network resources are controlled. controlled.             A widely adopted structure on local networks is to have a A widely adopted structure on local networks is to have a number of servers that are available to a (usually much number of servers that are available to a (usually much greater) number of clients. greater) number of clients.             The former, usually powerful computers, provide services The former, usually powerful computers, provide services such as print control, file sharing, and mail to the latter, such as print control, file sharing, and mail to the latter, which are usually personal computers.which are usually personal computers.
  • 13. 3.Ethernet and CSMA-CD are examples of LANs. 3.Ethernet and CSMA-CD are examples of LANs. There are many different layouts (such as bus, There are many different layouts (such as bus, star, ring) and a number of different access star, ring) and a number of different access protocols.protocols.  Despite this variety, all LANs share the feature that Despite this variety, all LANs share the feature that they are limited in range (typically they cover one they are limited in range (typically they cover one building) andbuilding) and  are fast enough to make the connecting network are fast enough to make the connecting network invisible to the devices that use itinvisible to the devices that use it
  • 14. TYPES OF LANTYPES OF LAN  LANs are linked by gateways, which both transfer data andLANs are linked by gateways, which both transfer data andconvert it according to the protocols used by the receivingconvert it according to the protocols used by the receivingnetwork.network.    The devices on a LAN are known as nodes, and the nodes areThe devices on a LAN are known as nodes, and the nodes areconnected by cabling through which messages are transmitted. connected by cabling through which messages are transmitted. Types of cables include twisted-pair wiring, coaxial cable, orTypes of cables include twisted-pair wiring, coaxial cable, orfibre-optic cable.  fibre-optic cable.            Nodes on a LAN can be wired together in any of three basic Nodes on a LAN can be wired together in any of three basic topologies, known as bus, ring, and star. topologies, known as bus, ring, and star.           As implied by their names, a bus network is more or lessAs implied by their names, a bus network is more or lesslinear, a ring, network forms a loop, and a star networklinear, a ring, network forms a loop, and a star networkradiates from a central hub.radiates from a central hub.          To avoid potential collisions when two or more nodesTo avoid potential collisions when two or more nodesattempt to transmit at the same time, LANs use either attempt to transmit at the same time, LANs use either contention and collision detection or token passing to regulatecontention and collision detection or token passing to regulatetraffic.traffic.
  • 15. MODEMS AND COMPUTER BUREAUXMODEMS AND COMPUTER BUREAUXAs recently as the 1970s, computers were expensive, fragile As recently as the 1970s, computers were expensive, fragile machines that had to be looked after by specialists and machines that had to be looked after by specialists and kept in a controlled environment. They could be used either kept in a controlled environment. They could be used either by plugging in a terminal directly or by using a phone line by plugging in a terminal directly or by using a phone line and modem to gain access from a distance.and modem to gain access from a distance.Computer networks during this period were not commercially Computer networks during this period were not commercially available. Even so, one of the most significant available. Even so, one of the most significant developments to shape the modern world of technology developments to shape the modern world of technology was initiated at this time: experimentation by the US was initiated at this time: experimentation by the US Defence Department in distributing computer resources to Defence Department in distributing computer resources to provide resilience against failure. provide resilience against failure. This work is now known as the Internet.This work is now known as the Internet.
  • 16. COMPUTER NETWORKCOMPUTER NETWORK Computer Networks, the widespread sharing of information among Computer Networks, the widespread sharing of information among groups of computers and their users, a central part of the information groups of computers and their users, a central part of the information age. The popular adoption of the personal computer (PC) and the local age. The popular adoption of the personal computer (PC) and the local area network (LAN) during the 1980s has led to the capacity to access area network (LAN) during the 1980s has led to the capacity to access information on a distant database; download an application from information on a distant database; download an application from overseas; send a message to a friend in a different country; and share overseas; send a message to a friend in a different country; and share files with a colleague—all from a personal computer.files with a colleague—all from a personal computer. The networks that allow all this to be done so easily are sophisticated The networks that allow all this to be done so easily are sophisticated and complex entities. They rely for their effectiveness on many and complex entities. They rely for their effectiveness on many cooperating components. The design and deployment of the worldwide cooperating components. The design and deployment of the worldwide computer network can be viewed as one of the great technological computer network can be viewed as one of the great technological wonders of recent decades.wonders of recent decades.
  • 17. Token Ring NetworkToken Ring Network Token Ring NetworkToken Ring Network, in computer science, a local , in computer science, a local area network formed in a ring (closed loop) topology area network formed in a ring (closed loop) topology that uses token passing as a means of regulating that uses token passing as a means of regulating traffic on the line.traffic on the line.   On a token ring network, a token governing the right On a token ring network, a token governing the right to transmit is passed from one station to the next in a to transmit is passed from one station to the next in a physical circle. If a station has information to transmit, physical circle. If a station has information to transmit, it “seizes” the token, marks it as being in use, and it “seizes” the token, marks it as being in use, and inserts the information. The “busy” token, plus inserts the information. The “busy” token, plus message, is then passed around the circle, copied message, is then passed around the circle, copied when it arrives at its destination, and eventually when it arrives at its destination, and eventually returned to the sender.returned to the sender.   The sender removes the attached message and then The sender removes the attached message and then passes the freed token to the next station in line.passes the freed token to the next station in line.   Token ring networks are defined in the IEEE 802.5 Token ring networks are defined in the IEEE 802.5 standards. standards. See alsoSee also LANLAN; ; Star NetworkStar Networks.s.
  • 18. World Wide WebWorld Wide Web1.World Wide Web, library of resources available to 1.World Wide Web, library of resources available to computer users through the global Internet. It computer users through the global Internet. It enables users to view a wide variety of enables users to view a wide variety of information, including magazine archives, public information, including magazine archives, public and college library resources, and current world and college library resources, and current world and business news. and business news. 2.World Wide Web (WWW) resources are organized 2.World Wide Web (WWW) resources are organized so that users can easily move from one resource so that users can easily move from one resource to another. The connections to different source to another. The connections to different source computers, or servers.computers, or servers.
  • 19. 3.WWW pages are formatted using Hypertext 3.WWW pages are formatted using Hypertext Markup Language (HTML), and WWW Markup Language (HTML), and WWW communication among computers uses the communication among computers uses the Hypertext Transfer Protocol (HTTP), or Wireless Hypertext Transfer Protocol (HTTP), or Wireless Access Protocol (WAP) for mobile phones. This Access Protocol (WAP) for mobile phones. This communication is usually through the Internet via communication is usually through the Internet via Transmission Control Protocol (TCP) connections, Transmission Control Protocol (TCP) connections, but almost any kind of connection can be used.but almost any kind of connection can be used.
  • 20.  4.The WWW was developed in 1989 by Timothy 4.The WWW was developed in 1989 by Timothy Berners-Lee, a British computer scientist at the Berners-Lee, a British computer scientist at the CERN research facility near Geneva, Switzerland, CERN research facility near Geneva, Switzerland, to allow information-sharing among internationally to allow information-sharing among internationally dispersed teams of high-energy physics dispersed teams of high-energy physics researchers. It subsequently became a platform researchers. It subsequently became a platform for related software development, and the for related software development, and the numbers of linked computersnumbers of linked computers
  • 21.   TelegraphTelegraph              Telegraph system of communication Telegraph system of communication employing electrical apparatus to transmit employing electrical apparatus to transmit and receive signals in accordance with a and receive signals in accordance with a code of electrical pulses.                   code of electrical pulses.                                   Originally the term Originally the term telegraphytelegraphy referred to  referred to any form of communication over long any form of communication over long distances in which messages were distances in which messages were transmitted by signs or sounds.transmitted by signs or sounds.
  • 22. THE MORSE TELEGRAPHTHE MORSE TELEGRAPH The first electrical instruments for telegraphicThe first electrical instruments for telegraphictransmission were invented in the United States bytransmission were invented in the United States bythe American inventor Samuel F. B. Morse in 1837the American inventor Samuel F. B. Morse in 1837and in Britain the same year by the British physicistand in Britain the same year by the British physicistSir Charles Wheatstone in collaboration with theSir Charles Wheatstone in collaboration with theBritish engineer Sir William F. Cooke.British engineer Sir William F. Cooke. The simple code that became known as Morse codeThe simple code that became known as Morse codetransmitted messages by electric pulses passing overtransmitted messages by electric pulses passing overa single wire. Morses apparatus, which sent the firsta single wire. Morses apparatus, which sent the firstpublic telegram in 1844, resembled a simple electricpublic telegram in 1844, resembled a simple electricswitch.switch. It allowed current to pass for a prescribed length ofIt allowed current to pass for a prescribed length oftime and then shut it off, all at the pressure of atime and then shut it off, all at the pressure of afinger. The original Morse receiver had anfinger. The original Morse receiver had anelectromagnetically controlled pencil that madeelectromagnetically controlled pencil that mademarks on paper tape moving over a clockwork-marks on paper tape moving over a clockwork-operated cylinder.operated cylinder.
  • 23. Type MODERN TELEGRAPH SERVICESType MODERN TELEGRAPH SERVICES1.TELEX-1.TELEX-In 1958 a system of direct-dial teleprinter exchange, calledIn 1958 a system of direct-dial teleprinter exchange, calledTelex, was introduced, and within ten years it had more thanTelex, was introduced, and within ten years it had more than25,000 subscribers.25,000 subscribers.The Telex system enabled subscribers to send messagesThe Telex system enabled subscribers to send messagesand data directly to other subscribers in North America and,and data directly to other subscribers in North America and,through the facilities of international carriers, in many otherthrough the facilities of international carriers, in many otherparts of the world.parts of the world.In some areas Telex subscribers could also sendIn some areas Telex subscribers could also sendmessages to non-subscribers by dialing specialmessages to non-subscribers by dialing specialcommunications centre that delivered the messages ascommunications centre that delivered the messages astelegrams.telegrams.
  • 24. 2. Facsimile Reproduction2. Facsimile ReproductionFacsimile telegraph systems, which send and receiveFacsimile telegraph systems, which send and receiveimages and text, have been rendered largelyimages and text, have been rendered largelyobsolete by fax (facsimile transmission).obsolete by fax (facsimile transmission).
  • 25. AUTOMATIC TELEGRAPH SYSTEMSAUTOMATIC TELEGRAPH SYSTEMS 1 In teleprinting, the message is received in1 In teleprinting, the message is received inthe form of typed words on a paper form. Inthe form of typed words on a paper form. Inthis system each letter of the alphabet isthis system each letter of the alphabet isrepresented by one of 31 combinations of fiverepresented by one of 31 combinations of fiveequal-interval electronic impulses, with theequal-interval electronic impulses, with thesequence of used and unused intervalssequence of used and unused intervalsdetermining the letter. The start-stop printingdetermining the letter. The start-stop printingcode uses seven pulses for each character,code uses seven pulses for each character,the first pulse indicating the beginning and thethe first pulse indicating the beginning and theseventh pulse the end of the letter.seventh pulse the end of the letter....
  • 26. 2 . system of communication employing2 . system of communication employingelectrical apparatus to transmit and receiveelectrical apparatus to transmit and receivesignals in accordance with a code ofsignals in accordance with a code ofelectrical pulses. Originally the termelectrical pulses. Originally the termtelegraphytelegraphy referred to any form ofreferred to any form ofcommunication over long distancescommunication over long distancesin which messages were transmitted by signsin which messages were transmitted by signsor soundsor sounds
  • 27. WAP Mobile PhoneWAP Mobile Phone Internet services became available to mobileInternet services became available to mobilephone users in the United Kingdom in 2000phone users in the United Kingdom in 2000with the introduction of WAP (Wirelesswith the introduction of WAP (WirelessAccess Protocol) enabled handsets.Access Protocol) enabled handsets. dpa Deutsche Presse-AgentuGmbH/Marcusdpa Deutsche Presse-AgentuGmbH/MarcusKrügerKrüger
  • 28. Types of cablesTypes of cables The devices on a LAN are known as nodes,The devices on a LAN are known as nodes,and the nodes are connected by cabling throughand the nodes are connected by cabling throughwhich messages are transmitted.which messages are transmitted.Types of cablesTypes of cables include twisted-pair wiring, coaxial cable, or fibre-opticinclude twisted-pair wiring, coaxial cable, or fibre-opticcable. Nodes on a LAN can be wired together in any ofcable. Nodes on a LAN can be wired together in any ofthree basic topologies, known as bus, ring, and star.three basic topologies, known as bus, ring, and star. As implied by their names, a bus network is moreAs implied by their names, a bus network is moreor less linear, a ring network forms a loop, andor less linear, a ring network forms a loop, anda star network radiates from a central hub.a star network radiates from a central hub. To avoid potential collisions when two or more nodesTo avoid potential collisions when two or more nodesattempt to transmit at the same time, LANs use eitherattempt to transmit at the same time, LANs use eithercontention and collision detection orcontention and collision detection ortoken passing to regulate traffic.token passing to regulate traffic.
  • 29. Childrens TelevisionChildrens Television◊ historical development of broadcasting aimed at young viewers.historical development of broadcasting aimed at young viewers.◊ Children’s television in the United Kingdom owes much to the publicChildren’s television in the United Kingdom owes much to the publicservice ideals of the BBC, where John Reith, as the first director-service ideals of the BBC, where John Reith, as the first director-general, made a commitment to provide programmes for children ongeneral, made a commitment to provide programmes for children onthe new “wireless”:the new “wireless”:◊ ““It is not to be like school.It is not to be like school.◊ They’ve been at school all day. You will need to devise something toThey’ve been at school all day. You will need to devise something toentertain and inform children and, if possible, to delight them.entertain and inform children and, if possible, to delight them.◊ Children’s programmes must become a wonderment.” The daily radioChildren’s programmes must become a wonderment.” The daily radioprogrammeprogramme Children’s HourChildren’s Hour became a popular tradition in manybecame a popular tradition in manyhouseholds at teatime as it provided a carefully planned mixture ofhouseholds at teatime as it provided a carefully planned mixture ofinformation and entertainment.information and entertainment.◊ When television became available throughout the United KingdomWhen television became available throughout the United Kingdomafter World War II it was a natural progression to build on this legacy.after World War II it was a natural progression to build on this legacy.◊ The new visual medium attracted even the youngest children to stringThe new visual medium attracted even the youngest children to stringpuppets, such aspuppets, such as Muffin the MuleMuffin the Mule andand Andy PandyAndy Pandy, and many other, and many otherprogrammes became firm favouritesprogrammes became firm favourites
  • 30. ClientClient//Server ArchitectureServer Architecture IIn computer science, an arrangement used on local area networksn computer science, an arrangement used on local area networksthat makes use of “distributed intelligence” to treat both the serverthat makes use of “distributed intelligence” to treat both the server the individual workstations as intelligent, programmable devices,the individual workstations as intelligent, programmable devices,thus exploiting the full computing power of each.thus exploiting the full computing power of each. This is done by splitting the processing of an application betweenThis is done by splitting the processing of an application betweentwo distinct components: a “front-end” client and a “back-end”two distinct components: a “front-end” client and a “back-end”server.server. The client component, itself a complete, stand-alone personalThe client component, itself a complete, stand-alone personalcomputer (versus the “dumb” terminal found in older architecturescomputer (versus the “dumb” terminal found in older architecturessuch as the time-sharing used on a mainframe) offers the user itssuch as the time-sharing used on a mainframe) offers the user itsfull range of power and features for running applications.full range of power and features for running applications. The server component, which can be another personal computer,The server component, which can be another personal computer,minicomputer, or a mainframe, enhances the client component byminicomputer, or a mainframe, enhances the client component byproviding the traditional strengths offered by minicomputers andproviding the traditional strengths offered by minicomputers andmainframes in a time-sharing environment:mainframes in a time-sharing environment: data management, information sharing between clients, anddata management, information sharing between clients, andsophisticated network administration and security features.sophisticated network administration and security features.
  • 31. The advantage of the client/serverThe advantage of the client/serverarchitecturearchitecture The advantage of the client/server architectureThe advantage of the client/server architectureover older architectures is that the client andover older architectures is that the client andserver machines work together to accomplish theserver machines work together to accomplish theprocessing of the application being used.processing of the application being used. Not only does this increase the processingNot only does this increase the processingpower available, but it also uses that power morepower available, but it also uses that power moreefficiently.efficiently. The client portion of the application is typicallyThe client portion of the application is typicallyoptimized for user interaction, whereas the serveroptimized for user interaction, whereas the serverportion provides the centralized, multi-userportion provides the centralized, multi-userfunctionality.functionality.
  • 32. Application Program InterfaceApplication Program Interface IIn computer science, a set of routines that ann computer science, a set of routines that an applicationapplication program usesprogram usesto request and carry out lower-level services performed by ato request and carry out lower-level services performed by acomputerscomputers operating systemoperating system.. An application program carries out two types of tasks: those related toAn application program carries out two types of tasks: those related towork being performed, such as accepting text or numbers input to awork being performed, such as accepting text or numbers input to adocument or spreadsheet, and those related to maintenance chores,document or spreadsheet, and those related to maintenance chores,such as managing files and displaying information on the screen.such as managing files and displaying information on the screen. These maintenance chores are performed by the computers operatingThese maintenance chores are performed by the computers operatingsystemsystem.. On local area networks, an API, such as IBMs NetBIOS, providesOn local area networks, an API, such as IBMs NetBIOS, providesapplications with a uniform means of requesting services from theapplications with a uniform means of requesting services from thelower levels of the network.lower levels of the network.
  • 33. TelecommunicationsTelecommunications Dumb TerminalDumb Terminal, in computer science, a, in computer science, aterminal that does not contain anterminal that does not contain aninternalinternal microprocessormicroprocessor. Dumb. Dumbterminals are typically capable ofterminals are typically capable ofdisplaying only characters and numbersdisplaying only characters and numbersand responding to simple control codes.and responding to simple control codes.See alsoSee also LANLAN;; Smart TerminalSmart Terminal;;
  • 34. UES OF WIRELESS LANUES OF WIRELESS LAN The reasons why electricity is universallyThe reasons why electricity is universallyemployed as a medium of energy transferemployed as a medium of energy transferand use are thatand use are that: (: (11)) It can be efficientlyIt can be efficientlytransported fromtransported from generatorsgenerators to the point ofto the point ofuse in the consumers premises through ause in the consumers premises through asimplesimple--toto--install network of wiresinstall network of wires. (. (22)) It can beIt can beconverted at high efficiency into heat,converted at high efficiency into heat,mechanical, and chemical energymechanical, and chemical energy.. It powersIt powerselectronic deviceselectronic devices.. It providesIt provides light. (light. (33)) It isIt isinstantly controllable at the point of use—itinstantly controllable at the point of use—ittakes only a flick of a switch to turn antakes only a flick of a switch to turn anelectrical device on or offelectrical device on or off..
  • 35. advantageadvantage1. television after World War II, many1. television after World War II, manybroadcasters predicted the complete demisebroadcasters predicted the complete demiseof radioof radio.. A reliance on sound, when imagesA reliance on sound, when imageswere available, seemed an anachronismwere available, seemed an anachronism.. In time, it became apparent that the mediumIn time, it became apparent that the mediumhad many unique characteristics that helpedhad many unique characteristics that helpeddistinguish it from both the press anddistinguish it from both the press andtelevisiontelevision.. Some of these characteristics seem more likeSome of these characteristics seem more likelimitations, but many can also be turned tolimitations, but many can also be turned tothe medium’s.the medium’s.
  • 36. 2 .Food processors and manufacturers2 .Food processors and manufacturers, who will, who willbenefit from produce with a longer shelf-life,benefit from produce with a longer shelf-life,and better properties for processing andand better properties for processing andmanufacture.manufacture.3 .3 . ConsumersConsumers, who will have cheaper and, who will have cheaper andmore plentiful food as a result of themore plentiful food as a result of theadvantages to growers and processors, asadvantages to growers and processors, aswell as possibly better rape) have beenwell as possibly better rape) have beendesigned to modify the proportions ofdesigned to modify the proportions ofdifferent polyunsaturated fatty acids, and sodifferent polyunsaturated fatty acids, and soimprove the nutritional quality of the oilimprove the nutritional quality of the oil
  • 37. DisadvantageDisadvantage GrowersGrowers, who will benefit from the, who will benefit from theresistance of crops to insect pests,resistance of crops to insect pests,viruses, and fungi, by theviruses, and fungi, by theintroduction of natural insecticidesintroduction of natural insecticidesor fungicides from other species, soor fungicides from other species, soreducing the need for application ofreducing the need for application ofagricultural chemicals, hence alsoagricultural chemicals, hence alsoan environmental gain;an environmental gain;
  • 38. Local governmentLocal government Each of the 24 countiesEach of the 24 counties ((länlän)) in Swedenin Swedenis governed by an administrative boardis governed by an administrative boardappointed by the central government, inappointed by the central government, inconjunction with a popularly electedconjunction with a popularly electedcounty councilcounty council.. Towns, cities, and ruralTowns, cities, and ruraldistricts within the counties constitutedistricts within the counties constitutecommunes and also have popularlycommunes and also have popularlyelected councilselected councils..
  • 39. communicationcommunication Early telegraph andEarly telegraph and telephonetelephone systems relied upon a directsystems relied upon a directconnection between source and destination, usually throughconnection between source and destination, usually throughcopper wires or cablescopper wires or cables.. The development ofThe development of radioradio mademadepossible “wireless”possible “wireless” communicationcommunication, and, later, the development, and, later, the developmentofof televisiontelevision transmissiontransmission.. These inventions have also enabled the development of theThese inventions have also enabled the development of theInternetInternet, and digital systems combined with radio have, and digital systems combined with radio haveproducedproduced cellularcellular mobile telephone networksmobile telephone networks.. They have also made possibleThey have also made possible communications satellitecommunications satellitesystems, the satellitesystems, the satellite--basedbased global positioning system (global positioning system (GPSGPS)),,and advanced military and commercialand advanced military and commercial radarradar systemssystems.. TheThelatest application is multichannel digital radio and televisionlatest application is multichannel digital radio and televisionbroadcasting systems, which will soon replace the old analoguebroadcasting systems, which will soon replace the old analoguesystemssystems..
  • 40. Cellular RadioCellular Radio mobile radiomobile radio telephonetelephone system, which has rapidlysystem, which has rapidlysupplementedlandlinetelecommunications as asupplementedlandlinetelecommunications as ameans of two-way personal communications. Cellularmeans of two-way personal communications. Cellularradio works on the principle and uses the physics ofradio works on the principle and uses the physics oftwo-waytwo-way radioradio communications and is named aftercommunications and is named afterthe unit “cell” into which an area is dividedthe unit “cell” into which an area is divided Each cell has a radius of about 1.5 to 2.4 km (1 to 2.5Each cell has a radius of about 1.5 to 2.4 km (1 to 2.5mi) and is equipped with a radiomi) and is equipped with a radio transmitter thattransmitter thatemploys its own range of radio frequenciesemploys its own range of radio frequencies..
  • 41.  Thank YouThank You