EE 122: Lecture 15 (Quality of Service)Limitations of IP Architecture in Supporting Resource ManagementService ClassesExample: Integrated ServicesQoS NetworkQoS Network OperationsControl Plane: Admission ControlSlide 8Slide 9Slide 10Data PlaneSlide 12Slide 13Slide 14Service SpecificationHard Real Time: Guaranteed ServicesSoft Real Time: Controlled Load ServiceTraffic and Service CharacterizationToken BucketCharacterizing a Source by Token BucketExamplePer-hop ReservationEnd-to-End ReservationSummaryAdministrative StuffEE 122: Lecture 15(Quality of Service)Ion StoicaOctober 25, [email protected] 2Limitations of IP Architecture in Supporting Resource ManagementIP provides only best effort serviceIP does not participate in resource management-Cannot provide service guarantees on a per flow basis-Cannot provide service differentiation among traffic aggregatesEarly efforts-Tenet group at Berkeley (Ferrari and Verma)-Asynchronous Transfer Mode (ATM) IETF (Internet Engineering Task Force) efforts -Integrated services initiative-Differentiated services [email protected] 3Service ClassesMultiple service classesService can be viewed as a contract between network and communication client-End-to-end service (multicast and anycast)-Other service scopes possible, e.g.,•Aggregates – all packets between to points (not necessary end-hosts) in the InternetThree common services-Best-effort (“elastic” applications)-Hard real-time (“real-time” applications)-Soft real-time (“tolerant” applications)[email protected] 4Example: Integrated ServicesEnhance IP’s service model-Old model: single best-effort service class-New model: multiple service classes, including best-effort and QoS classesCreate protocols and algorithms to support new service models-Old model: no resource management at IP level-New model: explicit resource management at IP levelKey architecture difference-Old model: stateless -New model: per flow state maintained at routers•Used for admission control and scheduling•Set up by signaling [email protected] 5QoS Network Flow or session as QoS abstractionsEach flow has a fixed or stable pathRouters along the path maintain the state of the [email protected] 6QoS Network OperationsControl plane: admission control-Reserve resources (i.e., link capacity and buffer space) at every router along the pathData plane: perform per flow-Classification: classify each packet to the flow it belongs to-Buffer management: decide when and which packet to drop-Packet scheduling: decide when and which packet to [email protected] 7Control Plane: Admission Control SenderReceiverExample: achieve per-flow bandwidth and delay guarantees-Example: guarantee 1MBps and < 100 ms delay to a [email protected] 8Control Plane: Admission Control SenderReceiverAllocate resources - perform per-flow admission [email protected] 9Control Plane: Admission Control SenderReceiverInstall per-flow [email protected] 10 SenderReceiverInstall per flow stateControl Plane: Admission [email protected] 11Data Plane SenderReceiver Per-flow [email protected] 12Data Plane SenderReceiver Per-flow buffer [email protected] 13Data Plane SenderReceiver •Per-flow [email protected] 14Service ClassesMultiple service classesService can be viewed as a contract between network and communication client-End-to-end service-Other service scopes possibleThree common services-Best-effort (“elastic” applications)-Hard real-time (“real-time” applications)-Soft real-time (“tolerant” applications)[email protected] 15Service SpecificationLoss: probability that a flow’s packet is lostDelay: time it takes a packet’s flow to get from source to destinationDelay jitter: maximum difference between the delays experienced by two packets of the flowBandwidth: maximum rate at which the soource can send [email protected] 16Hard Real Time: Guaranteed ServicesService contract-Network to client: guarantee a deterministic upper bound on delay for each packet in a session -Client to network: the session does not send more than it specifiesAlgorithm support-Admission control based on worst-case analysis-Per flow classification/scheduling at [email protected] 17Soft Real Time: Controlled Load ServiceService contract:-Network to client: similar performance as an unloaded best-effort network-Client to network: the session does not send more than it specifiesAlgorithm Support-Admission control based on measurement of aggregates-Scheduling for aggregate [email protected] 18Traffic and Service CharacterizationTo quantify a service one has two know-Flow’s traffic arrival-Service provided by the router, i.e., resources reserved at each routerExamples:-Traffic characterization: token bucket-Service provided by router: fix rate and fix buffer [email protected] 19Token BucketCharacterized by three parameters (b, r, R)-b – token depth-r – average arrival rate-R – maximum arrival rate (e.g., R link capacity)A bit is transmitted only when there is an available token-When a bit is transmitted exactly one token is consumedr tokens per secondb tokens <= R bpsregulatortimebitsb*R/(R-r)slope Rslope [email protected] 20Characterizing a Source by Token BucketArrival curve – maximum amount of bits transmitted by time tUse token bucket to bound the arrival curvetimebitsArrival [email protected] 21ExampleArrival curve – maximum amount of bits transmitted by time tUse token bucket to bound the arrival curvesize of timeintervalbitsArrival curvetimebps01 2 3 4 5121 2 3 4 51234(b=1,r=1,R=2)[email protected] 22Per-hop ReservationGiven b,r,R and per-hop delay dAllocate bandwidth ra and buffer space Ba such that to guarantee d bitsbslope rArrival curvedBaslope [email protected] 23End-to-End ReservationSource S sends a message containing traffic characteristics-r,b,R-This message is used to computes the number of hopsReceiver R sends back this information + worst-case delay (D)Each router along path provide a per-hop delay guarantee and forwards the message -In simplest case routers split the delay
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