Quality of Service EECS 122 Lecture 15 Department of Electrical Engineering and Computer Sciences University of California Berkeley Qos Mechanisms Policing at the edge of the network controls the amount of traffic the network layer has to allocate Scheduling in conjunction with packet dropping control performance within a router Scheduling mechanisms determine how the bandwidth of an output port is shared Model of router queues A t Mainly used to manage delay Signaling allows for flows March 7 2006 EECS122 Lecture 15 AKP A1 t R f1 A2 t R f2 D t AM t R fM Scheduling Discipline 2 1 Flow Set up Flow signals to the network its Statistics e g 24Mb s constant bit rate Token Buckets If the network cannot fulfill the requirement it rejects the flow Traffic Spec Service Level requirement Max average 95 level etc May suggest a change Admission Control If the network can fulfill the requirement it reserves resources to carry the flow traffic and accepts the flow Resource Reservation March 7 2006 EECS122 Lecture 15 AKP 3 Today End to End QoS Network Layer Multiple routers Intserv Diffserv Application Layer Adaptive Playback Buffers March 7 2006 Streaming Voice EECS122 Lecture 15 AKP 4 2 IETF Integrated Services architecture for providing QOS guarantees in IP networks for individual application sessions resource reservation routers maintain state info a la VC of allocated resources QoS req s admit deny new call setup requests Question can newly arriving flow be admitted with performance guarantees while not violated QoS guarantees made to already admitted flows March 7 2006 EECS122 Lecture 15 AKP 5 Intserv QoS guarantee scenario Resource reservation call setup signaling RSVP traffic QoS declaration per element admission control request reply QoS sensitive scheduling e g WFQ March 7 2006 EECS122 Lecture 15 AKP 6 3 Call Admission Arriving session must declare its QOS requirement R spec defines the QOS being requested characterize traffic it will send into network T spec defines traffic characteristics signaling protocol needed to carry R spec and Tspec to routers where reservation is required RSVP Resource Reservation Protocol will cover this when we discuss multicast March 7 2006 7 EECS122 Lecture 15 AKP Intserv QoS Service models rfc2211 rfc 2212 Controlled load service Guaranteed service worst case traffic arrival leakybucket policed source simple mathematically provable bound on delay Parekh 1992 Cruz 1988 arriving traffic a quality of service closely approximating the QoS that same flow would receive from an unloaded network element token rate r bucket size b per flow rate R WFQ D b R max March 7 2006 EECS122 Lecture 15 AKP 8 4 Intserv Example Goal achieve per flow bandwidth and delay guarantees Receiver Sender March 7 2006 9 EECS122 Lecture 15 AKP Step 1 Ask Permission Example achieve per flow bandwidth and delay guarantees Sender sends Tspec Rspec Receiver Sender March 7 2006 EECS122 Lecture 15 AKP 10 5 Step 2 Establish Path RSVP Signaling Protocol Path established Receiver Sender March 7 2006 EECS122 Lecture 15 AKP 11 Step 3 Reserve buffer resources Configure router queues Sender Per flow state on all routers in path Receiver What about DATAGRAM routing March 7 2006 EECS122 Lecture 15 AKP 12 6 Step 4 Traffic Flows We will discuss joins later Receiver Sender Per flow classification on each router March 7 2006 EECS122 Lecture 15 AKP 13 Traffic Flows Receiver Sender Per flow classification on each router March 7 2006 EECS122 Lecture 15 AKP 14 7 Traffic Flows Per flow scheduling on each router Receiver Sender March 7 2006 EECS122 Lecture 15 AKP 15 Token Bucket WFQ Delay Bound No packet has a queueing delay of more than b R seconds arriving traffic token rate r bucket size b per flow rate R WFQ D b R max March 7 2006 EECS122 Lecture 15 AKP 16 8 IETF Differentiated Services Concerns with Intserv Scalability signaling maintaining per flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Also want qualitative service classes behaves like a wire relative service distinction Platinum Gold Silver Diffserv approach simple functions in network core relatively complex functions at edge routers or hosts Don t define define service classes provide functional components to build service classes March 7 2006 17 EECS122 Lecture 15 AKP Diffserv Architecture Edge router r marking scheduling per flow traffic management marks packets as in profile and out profile b Core router per class traffic management buffering and scheduling based on marking at edge preference given to in profile packets Assured Forwarding March 7 2006 EECS122 Lecture 15 AKP 18 9 Edge router Packet Marking profile pre negotiated rate A bucket size B packet marking at edge based on per flow profile Rate A B User packets Possible usage of marking class based marking packets of different classes marked differently intra class marking conforming portion of flow marked differently than non conforming one March 7 2006 EECS122 Lecture 15 AKP 19 Classification and Shaping may be desirable to limit traffic injection rate of some class user declares traffic profile e g rate burst size traffic metered shaped if non conforming March 7 2006 EECS122 Lecture 15 AKP 20 10 Forwarding Per Hop Behaviors PHBs Try to control QoS per router hop rather than end to end PHB specifies observable measurable forwarding performance behavior E g Don t any packets of class 11 by more than 20ms PHB does not specify what mechanisms to use to ensure required PHB performance behavior Examples Class A gets x of outgoing link bandwidth over time intervals of a specified length Class A packets leave first before packets from class B March 7 2006 EECS122 Lecture 15 AKP 21 Classification and Conditioning Packet is marked in the Type of Service TOS in IPv4 and Traffic Class in IPv6 6 bits used for Differentiated Service Code Point DSCP and determine PHB that the packet will receive 2 bits are currently unused March 7 2006 EECS122 Lecture 15 AKP 22 11 Forwarding PHB PHBs being developed Expedited Forwarding pkt departure rate of a class equals or exceeds specified rate logical link with a minimum guaranteed rate Assured Forwarding 4 classes of traffic each guaranteed minimum amount of bandwidth each with three drop preference partitions March 7 2006 23 EECS122 Lecture 15 AKP Comparison Best Effort Diffserv Intserv Service Connectivity No isolation No guarantees Per aggregate isolation Per aggregate guarantee Per flow
View Full Document
Unlocking...