CS551Internet Architecture[Clark88a]Bill Chenghttp://merlot.usc.edu/cs551-f121 Computer Communications - CSCI 551 Copyright © William C. ChengA style and method of design and construction2Architecture: Definition Computer Communications - CSCI 551 Copyright © William C. ChengOrderly arrangement of partsThe manner of construction of something and the dispositionof its partsDesign, the way components fit togetherEx: railway system, airline systemA single architecture can have many implementationsEx:hub-and-spoke and United/American/Deltadirect-flights and Southwest/JetBlue3 Computer Communications - CSCI 551 Copyright © William C. Cheng The Interneta system of store-and-forward packet-switched gatewaysthat provides unreliable packet delivery between any twonodes in the networkARPANET, NSFNet, DECNet, etc.The Internet is one implementation of a particular architectureThe original Internet architecturethere have been other implementations of this architecturea virtual circuit based architecture: XUNETOther architecturesDefinitions are vague, so we need guiding principles - butcan people agree on what these are?4Architecture Principles Computer Communications - CSCI 551 Copyright © William C. ChengThe debate is raging on! Just browse www.ietf.org sometimeNow: original principlesEnd of class: look at current debate about InternetarchitectureConnect a number of distinguishable networksTop-level goal:5Internet Architecture Goals[Clark88a] Computer Communications - CSCI 551 Copyright © William C. ChengPacket switched networkBasic design:Store and forward gateways between component networksMultiple applications and services over the InternetIf a path exists, communication continues transparentlySurvivability6IP Design Principles Computer Communications - CSCI 551 Copyright © William C. ChengFate sharingIP makes minimal assumptions about underlying medium,and doesn’t get in the way of applicationsHourglass designRobust way to identify communication flowsSoft-stateHelps survivabilityEach network owned and managed separatelyAutonomous systemsPerfection is achieved not when there is no longer anythingto add, but when there is no longer anything to take awayAntoine de Saint-Exupery7Slogans For Computer Network Design Computer Communications - CSCI 551 Copyright © William C. ChengThe simplest explanation is the bestOccam’s razorBe liberal in what you accept, and conservative in what yousendJon PostelIn allocating resources, strive to avoid a disaster rather thanto achieve an optimumButler Lampsonrobust to network/gateway failureHeterogeneous networks8The Internet Architecture Computer Communications - CSCI 551 Copyright © William C. ChengMultiplexing via packet switchingSub-goals:multiple kinds of trafficmultiple kinds of networksdistributed managementinexpensivelow effort to add hostresource accountingAvian Carriers April Fools day RFCMultiple wired LANs, last mile, POP-to-POP, satellite,terrestrial wireless (802.11, Bluetooth) technologies9Heterogeneous Networks Computer Communications - CSCI 551 Copyright © William C. Cheng"Two cans and a string"Need to run over existing networkseasier to get started and growpay for what you needdifferent technologies (e.g. ethernet, token ring)different capabilities (e.g., wired vs. wireless)decentralized managementEfficient: resources used on demandstatistical multiplexing Interleave packets from different sources10Packet Switching Computer Communications - CSCI 551 Copyright © William C. ChengGeneralmultiple types of applicationsAccommodates bursty trafficthe "router"(Aunt Mable)1920s telephony: circuits---a physical wire from one end tothe other11Back in the Old Days... Computer Communications - CSCI 551 Copyright © William C. Chengthe wire12Then Came TDM... Computer Communications - CSCI 551 Copyright © William C. Cheng... but keeps the idea of a fixedpipe (circuit) the right size fora telephone conversationTime Division Multiplexingmux demux13And FDM and CDM... Computer Communications - CSCI 551 Copyright © William C. Chengα α α α α α α α α α α αFrequency Division MultiplexingCode Division Multiplexinga a a a a a a a a a a14Circuit Switching Computer Communications - CSCI 551 Copyright © William C. ChengFixed size pipe from her to himperfect for voicereliable conversations (QoS - Quality of Service)provisioning, good engineeringdumb end points, smart networkevolved for 100 years (analog to digital)15Packet Switching (Internet) Computer Communications - CSCI 551 Copyright © William C. ChengBut:QoS is much harderend-points are more expensiveDifferences:packets as low-level componentmultiple kinds of trafficsmart edges, dumb networkCircuit switching: can support 10 users.1 Mbps link; Users require 0.1 mbps when transmitting; Usersactive only 10% of the time.16Statistical Multiplexing Gain Computer Communications - CSCI 551 Copyright © William C. ChengPacket switching: with 35 users, probability that >=10are transmitting at the same time = 0.0004.Packets are self contained unitsStore and forward17Characteristics of Packet Switching Computer Communications - CSCI 551 Copyright © William C. ChengCan use alternate paths - reorderingCongestionContentionDelayall state at endpointsApplications should not see transient failures18Robust to Failures Computer Communications - CSCI 551 Copyright © William C. ChengIntermediate nodes faillater: soft-state in the network and refreshed periodically(if lost, regenerated)datagramsno hard-state in the networkfate-sharing: connection shares fate with the endpoints(it’s okay to lose the connection if an endpoint fails)state information stored at end hostsvarying needs in speed, latency, reliabilityOriginally just NCP, but split to {TCP,UDP}/IP soon after19Multiple Types of Service Computer Communications - CSCI 551 Copyright © William C. ChengWhy?not just bi-directional reliable data "virtual circuit"interactive,low-latencyIP: best effort datagramTCPbulk deliverybad if link layer wants to do too muchlightweightUDPallows out-of-order to userlow-latency & jitter, RT possiblefor voicereliability is biggest source of jitterwebClasses of apps20Multiple Applications Computer Communications - CSCI 551 Copyright © William C. Chengfile transfer (Napster, etc.)remote loginstreaming audiointeractive audiostreaming/interactive videocomputer appliancesdistributed gamesloss resilienceRequirements:delay/jitter sensitivitybursty/smoothpoint-to-point vs.
View Full Document
Unlocking...