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CMU CS 15441 - Intserv, Diffserv, RSVP

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15-441 Computer NetworkingMotivationApplication TypesImproving QOS in IP NetworksOverviewPrinciples for QOS GuaranteesPrinciples for QOS Guarantees (more)Slide 8Slide 9Slide 10SummaryA Short History of Internet QoSSlide 13IETF IntservComponents of Integrated ServicesService ModelsSlide 17Service InterfacePacket schedulingCall AdmissionSlide 21Differentiated ServicesDiffserv - MotivationDiffserv - DiscussionEdge Router/Host FunctionsClassification and ConditioningCore FunctionsForwarding (PHB)Slide 29Slide 30Example of EF: A Virtual Leased Line ServiceDifferentiated Services IssuesSlide 33Slide 34Role of RSVPReservation Protocol: RSVPRSVP GoalsReceiver-Initiated ReservationSoft StateRSVP Service ModelBasic Message TypesPATH MessagesRESV MessagesRouter Handling of RESV MessagesRSVP reservationsReservation StylesExampleWildcard Filter ReservationFixed Filter ReservationDynamic Filter ReservationChanging ReservationRouting ChangesState in SwitchesRSVP - Review115-441 Computer NetworkingIntserv, Diffserv, RSVPLecture 22: 11/20/2001 2Motivation•Internet currently provides only single class of “best-effort” service.•No admission control and no assurances about delivery•Existing applications are elastic.•Tolerate delays and losses•Can adapt to congestion•Future “real-time” applications may be inelastic.•Should we modify these applications to be more adaptive or should we modify the Internet to support inelastic behavior?Lecture 22: 11/20/2001 3Application Types•Elastic applications.•Wide range of acceptable rates, although faster is better•E.g., data transfers such as FTP•Continuous media applications.•Lower and upper limit on acceptable performance•Sometimes called “tolerant real-time” since they can adapt to the performance of the network•E.g., changing frame rate of video stream•“Network-aware” applications•Hard real-time applications.•Require hard limits on performance – “intolerant real-time”•E.g., control applicationsLecture 22: 11/20/2001 4Improving QOS in IP Networks•IETF groups are working on proposals to provide better QOS control in IP networks, i.e., going beyond best effort to provide some assurance for QOS.•Work in Progress includes RSVP, Differentiated Services, and Integrated Services.Lecture 22: 11/20/2001 5Overview•Principles for QoS•Integrated Services (Intserv)•Differentiated Services (Diffserv)•Resource ReSerVation Protocol (RSVP)Lecture 22: 11/20/2001 6Principles for QOS Guarantees•Simple model for sharing and congestion studies (“dumbell topology”):Lecture 22: 11/20/2001 7Principles for QOS Guarantees (more)•Consider a phone application at 1Mbps and an FTP application sharing a 1.5 Mbps link. •Bursts of FTP can congest the router and cause audio packets to be dropped.•Want to give priority to audio over FTP.•PRINCIPLE 1: Marking of packets is needed for router to distinguish between different classes; and new router policy to treat packets accordingly.Lecture 22: 11/20/2001 8Principles for QOS Guarantees (more)•Applications misbehave (audio sends packets at a rate higher than 1Mbps assumed above).•PRINCIPLE 2: provide protection (isolation) for one class from other classes.•Require Policing Mechanisms to ensure sources adhere to bandwidth requirements; Marking and Policing need to be done at the edges:Lecture 22: 11/20/2001 9Principles for QOS Guarantees (more)•Alternative to Marking and Policing: allocate a set portion of bandwidth to each application flow; can lead to inefficient use of bandwidth if one of the flows does not use its allocation.•PRINCIPLE 3: While providing isolation, it is desirable to use resources as efficiently as possible.Lecture 22: 11/20/2001 10Principles for QOS Guarantees (more)•Cannot support traffic beyond link capacity.•PRINCIPLE 4: Need a Call Admission Process; application flow declares its needs, network may block call if it cannot satisfy the needs .Lecture 22: 11/20/2001 11SummaryLecture 22: 11/20/2001 12A Short History of Internet QoS•Lots of initial research in the late 80s and early 90s.•Often takes a telecommunications view of the network.•ATM QoS and Integrated services were developed based on these results.•Focus on per-flow, hard QoS.•Effort was driven by perceived application needs.•In the last 5 years, the focus has shifted towards Differentiated services.•Focus is on QoS for flow aggregates, e.g., all the flows belonging to one customer.Lecture 22: 11/20/2001 13Overview•Motivation for QoS•Integrated Services (Intserv)•Differentiated Services (Diffserv)•Resource ReSerVation Protocol (RSVP)Lecture 22: 11/20/2001 14IETF Intserv•Focus on per-flow QoS.•Support specific applications such as video streaming.•Based on mathematical guarantees.•Many concerns:•Complexity•Scalability•Business model•ChargingLecture 22: 11/20/2001 15Components of Integrated Services•Type of service model•What does the network promise?•Service interface•How does the application describe what it wants?•Packet scheduling•How does the network meet promises?•Establishing the guarantee•How is the promise communicated to/from the network?•How is admission of new applications controlled?Lecture 22: 11/20/2001 16Service Models•Network can support traffic streams with different “quality of service”.•Best effort•Predictive or differentiated services•Strong guarantees on the level of service (real-time)•The set of services that is supported on a specific network can be viewed as a service model.•Model that can be used to select a service•E.g., cost versus performance tradeoffs•Network architecture that supports the set of services•Considers interactions between servicesLecture 22: 11/20/2001 17Service Models•Guaranteed service•Targets hard real-time applications.•User specifies traffic characteristics and a service requirement.•Requires admission control at each of the routers.•Can mathematically guarantee bandwidth, delay, and jitter.•Controlled load.•Targets applications that can adapt to network conditions within a certain performance window.•User specifies traffic characteristics and bandwidth.•Requires admission control at each of the routers.•Guarantee not as strong as with the guaranteed service.•e.g., measurement-based admission control.•Best effortLecture 22: 11/20/2001 18Service Interface•Session must first declare its QoS requirement and characterize


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