An Introduction to Computer NetworksChapter OutlineThis LectureSlide 8Two ways to shareInternet Traffic Is BurstyPacket switching also show reorderingSlide 18The mail systemCharacteristics of the mail systemSlide 21The InternetCharacteristics of the InternetBest EffortDifferences Between Circuit & Packet SwitchingSlide 261An Introduction to Computer NetworksSome slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden Prof. Dina KatabiChapter 72Chapter OutlineIntroduction (slides and 7.A)Layered Architecture (slides and 7.B & 7.D)Routing (slides and 7.D)Reliable Transmission & Flow Control (slides and read 7.E)Congestion Control (slides and read 7.F)3This LectureWhat is a network?Sharing the infrastructureCircuit switching Packet switchingBest Effort ServiceAnalogy: the mail systemInternet’s Best Effort Service8This LectureWhat is a network?Sharing the infrastructureCircuit switching Packet switchingBest Effort ServiceAnalogy: the mail systemInternet’s Best Effort Service9Two ways to shareCircuit switching (isochronous)Packet switching (asynchronous)13Internet Traffic Is BurstyDaily traffic at an MIT-CSAIL routerMax In:12.2Mb/s Avg. In: 2.5Mb/sMax Out: 12.8Mb/s Avg. Out: 3.4 Mb/s17Packet switching also show reorderingHost AHost BHost EHost DHost CNode 1Node 2Node 3Node 4Node 5Node 6Node 7Packets in a flow may not follow the same path (depends on routing as we will see later) packets may be reordered18This LectureWhat is a network?Sharing the InfrastructureCircuit switching Packet switchingBest Effort ServiceAnalogy: the mail systemInternet’s Best Effort Service19The mail systemDina NickMITStanfordAdmin Admin20Characteristics of the mail systemEach envelope is individually routedNo time guarantee for deliveryNo guarantee of delivery in sequenceNo guarantee of delivery at all!Things get lostHow can we acknowledge delivery?RetransmissionHow to determine when to retransmit? Timeout?If message is re-sent too soon duplicates21The mail systemDina NickMITStanfordAdmin Admin22 The InternetDina NickNms.csail.mit.eduLeland.Stanford.eduO.S. O.S.HeaderData HeaderDataPacketPacket23Characteristics of the InternetEach packet is individually routedNo time guarantee for deliveryNo guarantee of delivery in sequenceNo guarantee of delivery at all!Things get lostAcknowledgementsRetransmissionHow to determine when to retransmit? Timeout?If packet is re-transmitted too soon duplicate24Best EffortNo Guarantees:Variable Delay (jitter)Variable ratePacket lossDuplicatesReordering(notes also state maximum packet length)25Differences Between Circuit & Packet SwitchingCircuit-switching Packet-SwitchingGuaranteed capacity No guarantees (best effort)Capacity is wasted if data is burstyMore efficientBefore sending data establishes a pathSend data immediatelyAll data in a single flow follow one pathDifferent packets might follow different pathsNo reordering; constant delay; no pkt dropsPackets may be reordered, delayed, or dropped26This LectureWe learned how to share the network infrastructure between many connections/flowsWe also learned about the implications of the sharing scheme (circuit or packet switching) on the service that the traffic
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