Bestavros, Azer

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1http://www.cs.bu.edu/groups/wingAccelerating Internet Streaming Media Delivery usingNetwork-Aware Partial CachingAzer BestavrosandShudong JinBoston UniversityInternational Conference on Distributed Computing SystemsVienna, Austria — July 3, 20022002.07.03 Network-Aware Partial Caching 2Scalable Content Delivery: Why?? Need to manage resource usage as demand goes up? Server load: ? CPU, memory, etc.? Network load:? Bytes, Byte-Hops, etc.? Also need to worry about QoS to clients? Delay, response time, jitter, etc.Offered Load (N)Resources Used?2002.07.03 Network-Aware Partial Caching 3Scalable Content Delivery: How?Replicate It!2002.07.03 Network-Aware Partial Caching 4Scalable Content Delivery: How?? Replicate it from the client side? Client caching/prefetching, proxy caching, cooperative caching, server selection, etc.? Replicate it from the server side? Servers on steroids, server farms, reverse proxy caching and CDNs, etc.? Replicate it in the network? Network caches, multicast, anycast, traffic engineering, etc.2002.07.03 Network-Aware Partial Caching 5Scalable Content Delivery: What?? Streaming content? Emerging as largest sink of net resources? Potential for savings is huge due to more predictable access patterns ? QoS of delivery to client is key? Complicated by the bursty nature of network and server conditions? Further complicated by the increasingly peer-to-peer nature of content deliveryA gold mine of R&D problems!2002.07.03 Network-Aware Partial Caching 6Streaming Media Replication? Two flavors of replication? Caching: Replicate the artifact by storing it at an alternate location (server, CDN, proxy, or client)? Multicast: Duplicate content en route to destinations, either in the network (IP multicast) or at edges (end-system multicast)InefficientExcellent ~MulticastUnexplored!Poor ~CachingQoSScalability) 6.0(O n)(O   ) (logO nn ↔We advocate the use of caching primarily to control QoS of streaming delivery22002.07.03 Network-Aware Partial Caching 7Streaming Media ReplicationTraditional Caching? Whole objectPrefix Caching? Leading portion? [SenEtAl:98]Pipelined Caching? Sliding window? [RejaieEtAl:00]Partial Caching? Content from origin and from cache are disjoint? Cache an arbitrary portion of the object (prefix, layers, frames, random coded words …) Cache is in-line2002.07.03 Network-Aware Partial Caching 8Caches: Proxies vs AcceleratorsCacheNetwork[JinBestavros:ICDCS’02]CacheNetwork[SalehiEtAl:Sigmetrics’96][WangEtAl:Infocom’98][SenEtAl:Infocom’99][Rejaie:Infocom’00] …2002.07.03 Network-Aware Partial Caching 9Partial Caching? Cache is not the only source: Content served from many sources (“manycast”)? Provides cache management with a new dimension to decide “worth” of caching? All or none: Either cache A or B? Partial: Cache 40% of A and 60% of B? Cache “allocation” versus “replacement”2002.07.03 Network-Aware Partial Caching 10Partial Caching: ArchitectureCacheStreamsClientsNetworkAssumptions “for now”Client-side Caching:Bandwidth from cache to all clients is largeHomogeneous Clientele:Same bandwidth from an origin server to all clients2002.07.03 Network-Aware Partial Caching 11Partial Caching: Model? N objects? For object i? Duration = Ti  sec? CBR = ri Mb/sec? Access Freq =  λi? B/W to origin = bi Mb/sec? Cache size is C with xi of object i in cacheri Tibixiλi2002.07.03 Network-Aware Partial Caching 12Partial Caching: Startup DelayTimeBytesReceivedxiFromCacheStreamedin Real-timeri TiPlayout time (Ti)Startup Delayribi32002.07.03 Network-Aware Partial Caching 13Partial Caching: Startup DelayTimeBytesReceivedxiFromCacheStreamedin Real-time ri TiribiPlayout time (Ti)Delay2002.07.03 Network-Aware Partial Caching 14Partial Caching: Immediate PlayTimeBytesReceivedxiFromCacheStreamedin Real-time ri TiribiPlayout time (Ti)2002.07.03 Network-Aware Partial Caching 15Partial Caching: FormulationA constrained optimization Problem? Populate the cache by finding a set of xivalues that minimizes the average delay (or other cost functions) over all N objectsMinimizeSuch that                    and 2002.07.03 Network-Aware Partial Caching 16Partial Caching: Solution? Can be reduced to a fractional knapsack problem [JinBestavrosIyengar:ICDCS’02]? Optimal solution? Sort objects in order of their          ratio? Cache up to                  of each such object until cache is full? But, how do we find    and    ? Are they even static?2002.07.03 Network-Aware Partial Caching 17Partial Caching: Approximating λi? Assuming that λi is stationary (over some reasonable time scale or period), it can be approximated using the frequency of access over that period.? Cache needs to keep track of access frequencies—efficient techniques exist (sketches).? Need to periodically update cache content based on measured frequencies.2002.07.03 Network-Aware Partial Caching 18Partial Caching: Measuring bi? Many techniques exist for the estimation of bi  (e.g., using packet-pairs, cartouche probing, TCP equation, etc.) which could be done by origin servers periodically? Need to periodically update cache content based on measured bandwidths? But, bandwidth is not constant over any interesting time scale! Need to deal with bandwidth variability 42002.07.03 Network-Aware Partial Caching 19Partial Caching: bi  Variabilitybi/mean(bi) for NLANR transfers# of Observations2002.07.03 Network-Aware Partial Caching 20Partial Caching: bi  Variability? Over Provisioning: ? Level of over provisioning should be tied to distribution of bandwidth variability? Instead of using the “mean” bandwidth, one could use a more conservative estimate (e.g., 10th percentile)? Integral Caching:? Over provisioning in the extreme reduces “partial” caching to “integral” caching? Cache entire objects with highest          ratio2002.07.03 Network-Aware Partial Caching 21Evaluation MethodologyModelsCharacterizationAnalysisGenerationValidationTrace-drivenEvaluationParametricEvaluationObservations ArtifactsProtocolDistributions of Random VariablesSynthetic WorkloadsLogs and TracesCaching, Multicast, …2002.07.03 Network-Aware Partial Caching 22GISMO Workload Generator? GISMO: A toolkit to generate synthetic streamed media workloads [JinBestavros:PER’02]? GISMO generates? A set of “placeholder” streaming media objects, which can be installed on servers? Requests to these objects, initiated by clients subject to a prescribed access modelhttp://csr.bu.edu/gismo2002.07.03 Network-Aware Partial Caching 23GISMO: ComponentsProgrammableAgentsStandardElements2002.07.03 Network-Aware Partial Caching 24GISMO: Standard ParametersParameter Setting Popularity Zipf-like Temporal Correlation Truncated Pareto Seasonal Access Patterns User-defined Partial Access Truncated Pareto Media Object Size (S) Power Law VBR Long-Range Dependence Self-similar VBR Marginal Distribution - Body Lognormal VBR Marginal Distribution - Tail Pareto RequestsObjects52002.07.03 Network-Aware Partial Caching 25Partial Caching: Performance ? Used GISMO to generate synthetic workload (objects & request stream)2002.07.03 Network-Aware Partial Caching 26Partial Caching: Performance ? Implemented GISMO agents to model network bandwidth and UDP transfersMean(bi) in Kbps bi/Mean(bi)2002.07.03 Network-Aware Partial Caching 27Partial Caching: Performance Algorithms? Partial Bandwidth-based (PB) ? Integral Bandwidth-based (IB)? Integral Frequency-based (IF)Metrics? Average Service DelayAverage playout delay over all requests? Average Stream Quality% of stream that yields immediate playout? Traffic Reduction RatioRatio of traffic without cache to that with cache2002.07.03 Network-Aware Partial Caching 28Partial Caching: Performance Partial Caching significantly improves the timeliness of stream delivery!2002.07.03 Network-Aware Partial Caching 29Partial Caching: Performance Partial caching improves immediate playout quality.2002.07.03 Network-Aware Partial Caching 30Partial Caching: Performance Partial caching does not result in significant reduction in traffic (a feature not a bug!)62002.07.03 Network-Aware Partial Caching 31Partial Caching: Performance Bandwidth variability reduces relative performance of PB vs IB (as expected)Low bandwidth variability High bandwidth variability2002.07.03 Network-Aware Partial Caching 32Partial Caching: ExtensionsDealing with heterogeneous clientele? Cluster clients into “equivalence classes”– Using BGP data [KrishnamurthyEtAl:Infocom’01]– Using DNS clustering [BestavrosMehrotra:WWC’01]– Using MINT caricatures [BestavrosEtAl:Infocom’02]? For each equivalence class j estimate λij and bijand minimize ∑∑∑∑ +−−i j iji ijiijiiij ijbxbTrTλλ /][2002.07.03 Network-Aware Partial Caching 33Partial Caching: ExtensionsDealing with finite cache-to-client bandwidth? If cache-to-client bandwidth for class j is then playout delay is:? Reformulation of optimization problem is possible ⎟⎟⎠⎞⎜⎜⎝⎛ −−'  , maxjiijiijiiibxbxbTrT'jb2002.07.03 Network-Aware Partial Caching 34Partial Caching: ExtensionsDealing with multi-cache downloadsCachesStreamsClientsNetwork2002.07.03 Network-Aware Partial Caching 35Partial Caching: Multi-Cache ? For a given class of clients j, caches are sorted in order of? Caches as a hierarchy: Cache at one level is origin server to those at lower levels? Problems: ? Need to account for bottleneck bandwidth sharing between caches and clients? Estimate shared bottleneck bandwidth [Harfoush:PhD’02]? Need to make sure that content received from multiple caches is not redundant? Use RS or Tornado encoded content [ByersEtAl:Sigcomm’98]'jb2002.07.03 Network-Aware Partial Caching 36Take-Home Conclusions? New caching architectures in wake of the proliferation of streaming media content? Caching cannot be studied in isolation of other enabling protocols/technologies (e.g., multicast, network measurements, coding …)? Characterization (of access patterns, topology, etc.) is key to the evaluation of novel protocols and architectures72002.07.03 Network-Aware Partial Caching 37Related Linkshttp://www.cs.bu.edu/groups/winghttp://www.cs.bu.edu/~best2002.07.03 Network-Aware Partial Caching 38Scalable Content Delivery: What?? Static bulk content? Early focus of scalable content delivery work? Moderate savings (~ 40% max) possible? Diminishing % of today’s web transactions? Dynamic bulk content? Need to worry about freshness of content? Fairly straightforward…Case closed for bulk content replication!2002.07.03 Network-Aware Partial Caching 39Scalable Content Delivery: What?? Dynamic “tailor-made” content? Not a unidirectional content exchange!? Replicate assembly process vs content? Complicated by issues of consistency, coherence, trust, security, code safety, etc.Wide open!2002.07.03 Network-Aware Partial Caching 40On Consistency [BradleyBestavros:GI’02]June 21st03:25 am

Accelerating internet streaming media delivery using network-aware partial caching

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Accelerating internet streaming media delivery using network-aware partial caching

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