EE 122 Lecture 15 Quality of Service Ion Stoica October 25 2001 Limitations of IP Architecture in Supporting Resource Management IP provides only best effort service IP does not participate in resource management Cannot provide service guarantees on a per flow basis Cannot provide service differentiation among traffic aggregates Early efforts Tenet group at Berkeley Ferrari and Verma Asynchronous Transfer Mode ATM IETF Internet Engineering Task Force efforts Integrated services initiative Differentiated services initiative istoica cs berkeley edu 2 Service Classes Multiple service classes Service 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 Internet Three common services Best effort elastic applications Hard real time real time applications Soft real time tolerant applications istoica cs berkeley edu 3 Example Integrated Services Enhance IP s service model Old model single best effort service class New model multiple service classes including best effort and QoS classes Create protocols and algorithms to support new service models Old model no resource management at IP level New model explicit resource management at IP level Key architecture difference Old model stateless New model per flow state maintained at routers Used for admission control and scheduling Set up by signaling protocol istoica cs berkeley edu 4 QoS Network Flow or session as QoS abstractions Each flow has a fixed or stable path Routers along the path maintain the state of the flow istoica cs berkeley edu 5 QoS Network Operations Control plane admission control Reserve resources i e link capacity and buffer space at every router along the path Data 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 send istoica cs berkeley edu 6 Control Plane Admission Control Example achieve per flow bandwidth and delay guarantees Example guarantee 1MBps and 100 ms delay to a flow Receiver Sender istoica cs berkeley edu 7 Control Plane Admission Control Allocate resources perform per flow admission control Receiver Sender istoica cs berkeley edu 8 Control Plane Admission Control Install per flow state Receiver Sender istoica cs berkeley edu 9 Control Plane Admission Control Install per flow state Receiver Sender istoica cs berkeley edu 10 Data Plane Per flow classification Receiver Sender istoica cs berkeley edu 11 Data Plane Per flow buffer management Receiver Sender istoica cs berkeley edu 12 Data Plane Per flow scheduling Receiver Sender istoica cs berkeley edu 13 Service Classes Multiple service classes Service can be viewed as a contract between network and communication client End to end service Other service scopes possible Three common services Best effort elastic applications Hard real time real time applications Soft real time tolerant applications istoica cs berkeley edu 14 Service Specification Loss probability that a flow s packet is lost Delay time it takes a packet s flow to get from source to destination Delay jitter maximum difference between the delays experienced by two packets of the flow Bandwidth maximum rate at which the soource can send traffic istoica cs berkeley edu 15 Hard Real Time Guaranteed Services Service 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 specifies Algorithm support Admission control based on worst case analysis Per flow classification scheduling at routers istoica cs berkeley edu 16 Soft Real Time Controlled Load Service Service contract Network to client similar performance as an unloaded best effort network Client to network the session does not send more than it specifies Algorithm Support Admission control based on measurement of aggregates Scheduling for aggregate possible istoica cs berkeley edu 17 Traffic and Service Characterization To quantify a service one has two know Flow s traffic arrival Service provided by the router i e resources reserved at each router Examples Traffic characterization token bucket Service provided by router fix rate and fix buffer space istoica cs berkeley edu 18 Token Bucket Characterized 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 consumed r tokens per second b tokens bits slope r b R R r slope R R bps regulator istoica cs berkeley edu time 19 Characterizing a Source by Token Bucket Arrival curve maximum amount of bits transmitted by time t Use token bucket to bound the arrival curve bps bits Arrival curve time istoica cs berkeley edu time 20 Example Arrival curve maximum amount of bits transmitted by time t Use token bucket to bound the arrival curve bits b 1 r 1 R 2 Arrival curve 2 5size of time 4 bps 3 2 2 1 1 0 1 2 3 4 5 time istoica cs berkeley edu 1 3 4 interval 21 Per hop Reservation Given b r R and per hop delay d Allocate bandwidth ra and buffer space Ba such that to guarantee d slope ra bits slope r Arrival curve b d Ba istoica cs berkeley edu 22 End to End Reservation Source S sends a message containing traffic characteristics r b R This message is used to computes the number of hops Receiver 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 D num hops S S b r R b r R 0 0 S1 S1 S2 S2 b r R 2 D d1 b r R 1 D d1 d2 b r R 3 S3 S3 R R b r R 3 D worst case delay istoica cs berkeley edu 23 Summary Service a contract between end hosts and network QoS goal provide better than best effort services to support new applications with more stringent delay and bandwidth requirements e g IP telephony videoconferencing QoS requires to manage flows aggregates both on data and control plane Two major proposals Integrated Services this is mostly what we did this lecture we ll do more next lecture Differentiated Services see next lectures istoica cs berkeley edu 24 Administrative Stuff 2nd midterm exam next Tuesday November 6 Similar to the 1st midterm exam Conceptual questions Problems similar to the ones in homeworks Close books All material up to and
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