1 Computer Communications - CSCI 551 Copyright © William C. ChengCS551Differentiated Services(DiffServ)Bill Chenghttp://merlot.usc.edu/cs551-f12Tune applications to network services rather thannetwork services to applications Traffic classes instead of flows2Key Ideas Computer Communications - CSCI 551 Copyright © William C. ChengForwarding behaviors instead of end-to-end serviceguaranteesNo resource reservationDiscrete v.s. continuous spaceSomewhere between Best Effort and IntServairline service, first class, coach, various restrictions oncoach as a function of payment Analogy:3Service Differentiation Computer Communications - CSCI 551 Copyright © William C. ChengBest-effort expected to make up bulk of traffic, butrevenue from first class important to economic base (will payfor more plentiful bandwidth overall)Not motivated by real-time but by economics and assurancesadmitted based on peak ratePremium service: (type P)4Types of Service Computer Communications - CSCI 551 Copyright © William C. Chengconservative, virtual wire servicesunused premium goes to best effort (subsidy!)based on expected capacity usage profilesAssured service: (type A)traffic unlikely to be dropped if user maintains profileout-of-profile traffic marked traffic is in or out (of profile)police traffic to keep in within limitsuse provisioning and/or admission control to limit amoutof inpreferentially drop out trafficNo need for reservations: just mark packets5Differences With Integrated Services Computer Communications - CSCI 551 Copyright © William C. ChengPacket marking done at administrative boundaries beforeinjecting packets into networkSignificant savings in signaling, much simpler overallCS551A Two-bit DifferentiatedServices Architecture[Nichols99a]Bill Chenghttp://merlot.usc.edu/cs551-f126 Computer Communications - CSCI 551 Copyright © William C. ChengAppropriate for intolerant and rigid applicationsPremium packets receive virtual circuit type of treatment7Premium vs. Assured Forwarding Behaviors Computer Communications - CSCI 551 Copyright © William C. ChengAppropriate for adaptive applicationsAssured packets receive "better than best effort" type oftreatmentPrecedence field encodes P & A type packets82-bit Differentiated Service Computer Communications - CSCI 551 Copyright © William C. ChengP packets are BW limited, shaped and queued at higherpriority than ordinary best effortA packets treated preferentially with respect to droppingprobability in the normal queueLeaf and border routers have input and output tasks -other routers just outputUser sends within profile, network commits to deliverywith requested profileSimple forwarding: classify packet in one of two queues,use priorityShaping at trust boundaries only, using token bucket Signaling, admission control may get more elaborate, butstill not end-to-end9 Computer Communications - CSCI 551 Copyright © William C. Cheng Premium Service10 Computer Communications - CSCI 551 Copyright © William C. Cheng Premium Traffic Flowinternalrouterborderrouterfirst hoprouterhostborderrouterPremium packet flowrestricted to R bytes/secUnmarkedpacket flowPackets in premiumflows have bit setCompany AISPMarkers: service class, rate, permissible burst size11First-hop Router Input Functionality Computer Communications - CSCI 551 Copyright © William C. ChengClearA & P bitsPacketclassifierArrivingpacketForwardingengineMarker 1Marker NBest effortFlow 1Flow NFirst-hop routers have traffic profiles - they classify packetsbased on packet header12Marker Function in Routers Computer Communications - CSCI 551 Copyright © William C. Chengif no profile present, pass as best effortmark packets in or out (in-profile packets with A,forward others unmarked)if profile is for A:delay or drop out-of -profile packets to shape into profileif profile is for P:Routers at administrative boundariesmust make sure traffic exchange agreements are met13Markers to Implement Two Different Services Computer Communications - CSCI 551 Copyright © William C. ChengTest iftokenSet A bitPacketoutputtokenPacketinputNo tokendelay or drop out-of -profile packets to shape into profileif profile is for P:Wait fortokenSet P bitPacketinputPacketoutputDrop on overflow14Markers to Implement Two Different Services Computer Communications - CSCI 551 Copyright © William C. ChengTest iftokenSet A bitPacketoutputtokenPacketinputNo tokenWait fortokenSet P bitPacketinputPacketoutputDrop on overflowmark packets in or out (in-profile packets with A,forward others unmarked)if profile is for A:if no profile present, pass as best effortdrop P packets out of profileAt border routers profile meters test marked flows:unmark A packets15 Computer Communications - CSCI 551 Copyright © William C. Cheng Border Router Input Interface Profile MetersForwardingengineClear A-bitTokenavailable?Tokenavailable?Is packetmarked?ArrivingpacketA setP settokentokennonoNot markedDrop packet2 queues: P packets on higher priority queue16Output Forwarding Computer Communications - CSCI 551 Copyright © William C. ChengLower priority queue implements RED "In or Out" scheme(RIO) [Clark98a]P-bit set? High-priority QLow-priority QIf A-bit setincr A_cntIf A-bit set decr A_cntRIO queuemanagementPackets outyesnoFor Assured Services17Red With In or Out (RIO) Computer Communications - CSCI 551 Copyright © William C. ChengSimilar to RED, but with two separate probability curvesHas two classes, "In" and "Out" (of profile)"Out" class has lower Minthresh, so packets are droppedfrom this class firstAs avg queuelength increases,"in" packets aredropped[Clark98a]Maxin1.0PmaxAvgLenP(drop)MininMaxoutMinoutinoutMore dropprobability curves(WRED)Define behavior of individual routers rather thanend-to-end services18Per-hop Behaviors (PHBs) Computer Communications - CSCI 551 Copyright © William C. ChengMultiple behaviors - need more than one bit in the headerSix bits from IP tos field are taken for Diffserv codepoints (DSCP)there may be much more services than behaviorsstatic (long-term):done out-of-bandWhere?19Signaling Computer Communications - CSCI 551 Copyright © William C. Chengdynamic:from leaf to Bandwidth Brokerand from BB in one domain to another BBnot clear, but maybe RSVPHow?20Signaling: BBs Computer Communications - CSCI 551 Copyright © William C. ChengResources to aggregated traffic, not flows21Diffserv vs. Intserv Summary Computer Communications - CSCI 551 Copyright © William C. ChengTraffic policing at the edges, class forwarding in
View Full Document
Unlocking...