Quality of ServiceOverviewWhat is QoS?Service provider QoS goalsWhy a New Service Model?“Today”: Elastic appsInelastic ApplicationsUtility curve – Elastic trafficAdmission ControlUtility Curves – Inelastic trafficSlide 11So?Components of Integrated Services1. Type of commitmentPlayback ApplicationsCharacteristics of Playback ApplicationsApplication VariationApplications VariationsType of CommitmentsSlide 20Scheduling for Guaranteed TrafficToken Bucket FilterToken Bucket OperationToken Bucket CharacteristicsToken Bucket SpecsPossible Token Bucket UsesGuarantee Proven by ParekhPredicted ServiceSlide 29Key Principles of QoSQuality of ServiceOverview•Why QoS? When QoS?•One model: Integrated services•Contrast to Differentiated Services (more modern; more practical; not covered)What is QoS?•Providing guarantees (or rough bounds) on various network properties:–Available bandwidth for flows–Delay bounds–Low jitter (variation in delay)–Packet lossService provider QoS goals •Traffic classes for customers for differential pricing (“Gold”, “Silver”, …)–Gets particular Service Level Agreement (SLC) about b/w, delay, etc.–Costs more. •SLAs that specify rate guarantees, max rates, priorities, etc.•Control who gets to use the network (admission control) (maybe, maybe not)Why a New Service Model?•What is the basic objective of network design?–Maximize total bandwidth? Minimize latency?–Shenker argues: Maximize user satisfaction – the total utility given to users•What does utility vs. bandwidth look like?–Must be non-decreasing function –Shape depends on application“Today”: Elastic apps•Internet currently (mostly) provides one single class of “best-effort” service–No assurances about delivery•Most existing applications are elastic–Tolerate delays and losses–Can adapt to congestion•Some “real-time” applications are inelasticInelastic Applications•Continuous media applications–Lower and upper limit on acceptable performance.–BW below which video and audio are not intelligible–Internet telephones, teleconferencing with high delay (200 - 300ms) impair human interaction•Hard real-time applications–Require hard limits on performance–E.g. control applications•Claim: These apps are not as elastic or adaptive. Don’t typically react to congestion. This is a bit questionable, but telephony has some of these attributes.•Note about jitter: More jitter == more buffering == delay + memory.Utility curve – Elastic trafficBandwidthUElasticDoes equal allocation of bandwidth maximize total utility?Admission Control•If U(bandwidth) is concave  elastic applications–Incremental utility is decreasing with increasing bandwidth–Is always advantageous to have more flows with lower bandwidth•No need of admission control; This is why the Internet works!BWUElasticUtility Curves – Inelastic trafficBWUHard real-timeBWUDelay-adaptiveDoes equal allocation of bandwidth maximize total utility?Admission Control•If U is convex  inelastic applications–U(number of flows) is no longer monotonically increasing–Need admission control to maximize total utility•Admission control  deciding when the addition of new people would result in reduction of utility–Basically avoids overloadBWUDelay-adaptiveSo?•Right answer depends on a lot of factors: –Cost of complexity vs. cost of bandwidth–Can applications become adaptive?•Well worth thinking about!–Even if the answer is “best effort is mostly okay”•Important features:–Maximizing V doesn’t necessarily maximize Ui•In fact, it almost can’t! It takes away from elastic Us to add to inelastic Us–Keep in mind: Only so much you can do if underprovisioned•Much depends on the cost of adding b/w vs. the user benefit –Should you add capacity to support traffic? (VoIP? BitTorrent?)–Internet economics are not directly passed on to customer•Makes some economic models of reservations hardComponents of Integrated Services1. Type of commitment What does the network promise?2. Packet scheduling How does the network meet promises?3. Service interface How does the application describe what it wants?4. Establishing the guarantee How is the promise communicated to/from the network How is admission of new applications controlled?1. Type of commitment What kind of promises/services should network offer? Depends on the characteristics of the applications that will use the network ….Playback Applications•Sample signal  packetize  transmit  buffer  playback–Fits most multimedia applications•Performance concern:–Jitter – variation in end-to-end delay•Delay = fixed + variable = (propagation + packetization) + queuing•Solution: –Playback point – delay introduced by buffer to hide network jitterCharacteristics of Playback Applications–In general lower delay is preferable.–Doesn’t matter when packet arrives as long as it is before playback point–Network guarantees (e.g. bound on jitter) would make it easier to set playback point–Applications can tolerate some lossApplication Variation•Rigid & adaptive applications –Rigid – set fixed playback point –Adaptive – adapt playback point•Gamble that network conditions will be the same as in the past•Are prepared to deal with errors in their estimate•Will have an earlier playback point than rigid applications•Tolerant & intolerant applications–Tolerance to brief interruptions in service•4 combinationsApplications VariationsReally only two classes of applications1) Intolerant and rigid2) Tolerant and adaptiveOther combinations make little sense3) Intolerant and adaptive - Cannot adapt without interruption4) Tolerant and rigid - Missed opportunity to improve delay So what service classes should the network offer?Type of Commitments•Guaranteed service–For intolerant and rigid applications–Fixed guarantee, network meets commitment as long as clients send at match traffic agreement•Predicted service–For tolerant and adaptive applications–Two components•If conditions do not change, commit to current service•If conditions change, take steps to deliver consistent performance (help apps minimize playback delay)•Implicit assumption – network does not change much over time•Datagram/best effort serviceComponents of Integrated Services1. Type of commitment What does the network promise?2. Packet scheduling How does