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Effective Communication in Computer Networks

Learn about the layers of the OSI model and how they enable effective communication in computer networks. Explore the protocols and technologies used in each layer.

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Effective Communication in Computer Networks

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  1. Computer Networks0010-ISO-OSI Gergely Windisch windisch.gergely@nik.uni-obuda.hu

  2. Howcanwedoeffectivecommunication? • Take a lookattheclient-server image fromthepreviouslecture • Whereshouldallthecommunicationtakeplace?

  3. Protocolhierarchy

  4. Layers, Layerseverywhere

  5. Why OSI? • Networkswere being developedatdifferentplaces • universities, companies, researchinstitutions • differenttechnology, differentnamingconventions – howaretheygoingtotalktoeachother? • ISO – common standard modelshould be created • Open System Interconnect • openmeansthatthedetails of implementationareopenlyavaliable – notnecessarily free and canalso be tied to a vendor • Tohave a commonbase – samenomenclaturesothatpeoplecancollaborate

  6. OSI – Open System Interconnect • 7 layershavebeendefined • number of layers is arbitrary, implementationsdonothavetofollow • Havinglayers is important • inside is a blackbox • layerseparation is important – layersshould be asindependentfromeachotheraspossible - makesurethattheyareseparatedwell • Layersare service providers

  7. OSI model source: http://www.infocellar.com/networks/osi-model.htm Learntehesebyheart. You’llthankmelater.

  8. Sidenote: mnemonicstohelpyouremember • All People Seem To Need Data Processing • Princess Diana Never Tried Screwing Prince Andrew • Please Do Not Take Sales People's Advice • Philys Did Networking Till She Passed Away • American Presidents Should Try New Dating Practices • All Penguins Stand Too Near Deep Pools • Angus Prefers Sausages To Nibbling Dried Pork • A Pathetic Silly Trick Never Does Please • People Don't Need This Stuff Presented Anyway • Programmers Do Not Throw Sausage Pizza Away • Arse Pounders Seem To Neglect Delicious Pussy • All Parents Should Teach New Dads Parenting • Apply Proper Sense To Network Data Path • People Don't Need To Study Protocol Analysis • Please Do Not Touch Steve's Pet Alligator • Phil Donahue Never Televises Sick People Anymore • Please Dear, Not Tonight, Soft Penis Already • All People Studying This Need Drastic Psychotherapy • People Design Networks To Send Packets Accurately • Australian Post Sucks They Never Deliver Parcels • Philosophers Deign Not To Solipstically Ponder Anachronisms • Please Don't Network These Stupid People Again • Any Person Standing Totally Nude Doesn't Perspire • All Pussy Seems To Need Douching Periodically

  9. Layer 1 - Physical • Transfersbitstotheotherside • Access medium is handledonthePhysicallayer • light • radiosignals • electricalimpulse • Physicallayer is notreliable, bitsgetlost, duplicated, corrupted

  10. Layer 2 – Data link • Usestheservices of thedumbphyisicallayertosendbits • Providesthe service of sendinglargechunksofbitstotheothersidereliably • createsframes, addssynchronizingbitstothebeginning of theframe and crctothe end • CRC is usedforerrordetection • Errorcorrection has beenusedearlier, butphysicallayersaretooreliablenow – errorcorrectionbecameextinct • 1 wrong bit in 1 billion

  11. Layer 3 – Network • Receivespackets and sendsthemtoanyhostintheworld* • Interestingquestionsthatmightarise • howdoweknowwhowewanttosenditto? • howthehelldowegetthere? *: For a givenvalue of any

  12. Layer 3 – Network • Receivespackets and sendsthemtoanyhostintheworld* • Interestingquestionsthatmightarise • howdoweknowwhowewanttosenditto? • howthehelldowegetthere? • Interestinganswerstotheinterestingquestions • logicaladdressing (IP) • routingprotocols • Routingprotocolshelpfindthedestination – onehopat a time • howmanyhopsdoesittaketogetfromthisroomto a computer labinchina? *: For a givenvalue of any

  13. Layer 4 – Transport • Layer 3 cantransportindividualpackets, butwearenotinthe business of transferringpackets – wewanttotransferdata – documents, musicfiles (onlylegalofcourse), cutepicturesofcats, video files of ourfavoriteBritneySpearsconcert and soon. • The transportlayertakesthedataapart, createsdatagrams and givesthemtoLayer 3 fortransportation. • Transportlayerhelpsforthedatatogettothegivenapplication • ports • TCP and UDP arethe most importantprotocols

  14. Layer 5 – Session • Session layerhandlestheconnectionpropertiesbetweentwocomputers • usernames, passwords, whatnot

  15. Layer 6 – Presentation • Data conversion • byte orderforexample, codepages • encodingifnecessary (session layerhandleskeyexcange, presentationlayerusesthem)

  16. Layer 7 – Application • The actual program thattheuseruses • Thereare an infiniteamount of applicationprotocols – ftp, http, smtp and manyothers

  17. Encapsulation source: http://www.infocellar.com/networks/osi-model.htm

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