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ISM 50 - Business Information SystemsLecture 18Instructor: John MusacchioUC Santa CruzNovember 30, 2010AnnouncementsFINAL EXAMMonday December 6Time: 7:30-10:30pmReview SessionsWed Dec 1, 20105:00PM to 6:45PMThimann 003Fri Dec 3 20105:00PM to 6:45PMNat Sci Annex 101Student PresentationPost Office AnalogyAlice Smith1156 High StSanta Cruz 95064Bob in New YorkNY Post OfficePlane to LondonPlane to SFOSFOPost OfficeTruck toSanta CruzTruck toSanta RosaLook at beginningof zip code.Make forwarding decisionLook at addressMake forwardingdecisionSanta CruzPost OfficeTruck toHigh StTruck to41st AveAliceNetwork LayerHost AHost BHost CHost DLink 1Link 2Link 3128.114.60.200128.114.60.201128.114.60.202128.114.60.203Header Payload DataDestination Address: 128.114.60.202(IP Address)Network LayerHost AHost BHost CHost DLink 1Link 2Link 3128.114.60.200128.114.60.201128.114.60.202128.114.60.203Header Payload Data128.114.60.202 A uses Link 1 to send to B B looks atPacket Header Routing TableAddress Next Hop128.114.60.202 Link 2128.114.60.203 Link 3Routing in the Internet Many feasible paths from source to destination.Host BHost AHost CRoutingRoutingUpdating the routing tableObjective: each packet gets closer to destinationPacket forwardingTransmitting each packet on the appropriate output linkBased on routing tableRouting AlgorithmsRouters talk to each other to build their routing tablesHost BHost AHost CHUB114.211.1.2114.211.1.1114.211.1.3114.211.1.4I am acceptingTraffic to 114.211.1.XWild CardRouting Table has Wild Cards Host BHost AHost CHUB114.211.1.2114.211.1.1114.211.1.3114.211.1.4114.211.1.X Link 11200.261.19.X Link 22ROUTING TABLEInternet Routing is HierarchicalAutonomousSystem (AS)Backbone or NSP: (MCI, ATT)ASISP or IAP(CRUZIO, AOL)Customer ASASISPRouting Concerns Long routes Circular routes Hijacking routes Route flappingIP Addresses vs Mac Addresses HierarchicalThe beginning bits tell you which network the host is onEx: UCSC addresses start with 128.114.X.XThe last bits tell you which host of the network ChangeableChanges with location of Host 4 bytes Only 4.2 billion Not HierarchicalBeginning bits tell nothing useful Not Changeable 6 bytes 281 TrillionLink and Network Layer InteractionHost AHost BEthernetHubRouterRouterRouterRouterEthernetHubHost C128.114.60.202MAC address00-A4-B7-34-57-23MACHeaderIP HeaderIP PayloadEthernet FrameStrip MAC header off frame.Forward IP packet based onRouting table.IP HeaderIPPayloadPayloadTransport Protocols The Internet is unreliableIt will make a best effort to get your packet to its destination Packets can be lost because ofCongestionLink errorsRouting problemsPhysicalLinkNetworkTransportSessionPresentationApplicationTransmission Control Protocol (TCP) Retransmit mechanism for reliabilityReceiver sends acknowledgements to senderIf a packet is lost, source fails to get ACK, and then retransmits. Congestion controlIf congestion perceived (by lost packets)Source reduces its send rate When loss, sender reduces send rate by half Otherwise slowly increasesACKPacket 1?Packet 2Packet 2TCP contd TCP port numbersTCP Header has a port number fieldHelps host sort out how to route packets to applicationsPort 80 PacketTCP HeaderIP HeaderPayload Email ClientPort 80Port 143Your ComputerAudiocoderAudiodecoderStream ofpacketsUDP For some applications packet retransmissions are not worthwhileWhy? For those applications, we use UDP UDP is a transport protocol thatDoes not do retransmissionsDoes not do congestion controlCongestion Control When networks are congested, certain sessions (Source-destination pairs) should reduce offered rates.Today all TCP sessions slow down when they detect packet losses.UDP sessions do not slow down. What are some alternative strategies?Have those whose applications arent as sensitive slow down more? How would we know which are less sensitivePricing within the Internet Customer pays an ISPOften Flat Rate per month ISP pays a backbone ASOften just flat rate, dependent on access link speed.Sometimes based on total usage Backbone NSPs peer with each otherOften for free if they exchange comparable amounts of traffic. OverallInternet billing today is much more course grained than telephone billing.ISP(Cruzio)Backbone NSP$Flat Rate$Flat Rate orsimple usage basedBackbone NSPPeering RelationshipDomain NamesIP addresses are inconvenient for people32 bits hard to remember128 bits very hard to rememberDomain namese.g. argus.eecs.berkeley.eduEasier to remember than IP addressesHowever, we need some way of mapping domain names to IP addresses.Domain Name System (DNS)BerkeleyName ServerEECS Name ServerRootName ServerUCSCName ServerSoEName ServerHierarchy in Addresses vs. NamesAddresses hierarchical in topologyMaximize wild cards and distribute address administrationNames hierarchical in administrationSingle administered organizations often distributed topologically (e.g. ibm.com)Transport Protocols The Internet is unreliableIt will make a best effort to get your packet to its destination Packets can be lost because ofCongestionLink errorsRouting problemsPhysicalLinkNetworkTransportSessionPresentationApplicationOSI Layers PhysicalLinkNetworkTransportSessionPresentationApplicationModulation Schemes: QAM, OFDM, etcEthernet, Wi-Fi, SONNET, Internet Protocol (IP), TCP, UDPInternet Explorer, Outlook Email,Real Player, Some Typical TopologiesHome NetworkDSL Modem TelephoneLineRouterEthernet Switch(to localOffice)Small/Medium BusinessRouterwith FirewallT1 LineT1 ModemEthernetSwitchWeb Site ServerTo LocalOfficeISP TopologyTelephone CompanyLocal OfficeLocal LoopTelephoneSwitchLocal LoopLocal LoopDSL ModemDSL ModemDSL ModemDSLAMLeasedLine to NAPToTelephoneNetworkISP Point of PresenceNetwork Service ProviderNetworkAccessPointNetworkAccessPointLarge E-BusinessCustomersMerchandiseOrdersDatabasesApplication ServersWeb ServersLoad BalancerIncoming HTTPRequestsPresentation Logic(AssemblingWeb page)LogicFlow ofInteractionInterconnectedwith Gigabit Ethernet orother technologyWeb Caching Speed up web page loading by storing previously seen components locallyhttp://www.ucsc.eduCache on Hard DriveWebserverAkamai CaseAkamai Case1) Akamais technology can be best classified asA) Enterprise Resource PlanningB) Content Delivery NetworkC) Thin


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