EE 368C Project Multi-stream Audio Transmission with Path DiversityThe IncentivesOutlinePlayout Scheduling AlgorithmsMulti-stream Audio PlayoutDetermine the Playout ScheduleMDC over Multiple StreamsComparison: Single-stream with FECExperiments over the Internet (I)Results of Experiment I (1)Results of Experiment I (2)Results of Experiment I (3)Experiments over the Internet (II)Results of Experiment II (1)Results of Experiment II (2)More Comments on Our ExperimentsSimulations Using Network SimulatorLoss ReductionDelay ReductionConclusions and Future WorkCoupling of Multiple PathsLosses over Coupled PathsYi LiangMar. 8, 2001EE 368C Project Multi-stream Audio Transmission with Path DiversityMulti-stream Audio Transmission with Path Diversity Yi LiangThe IncentivesBest-effort services vs. strict QoS requirements of real-time speech communication, e.g. latency, loss, delay variation etc.Low data rate of the voice streamWhy alternative path/multi-path?Exists a superior alt. path in 30-80% cases [Savage, 99’]Path diversity – network behavior averaged; burst loss converted to isolated loss; outage probability decreased [Apostolopoulos, 01’]Multi-path – independent jitter behaviorRealization: explicitly path selection using relay serversDSRelayRelay12DatatrafficDatatrafficThe bottleneckVoice trafficMulti-stream Audio Transmission with Path Diversity Yi LiangOutlineBackground on media playout scheduling algorithmsAdaptive playout for multiple streamsMeasurements over the Internet and resultsNs simulation and resultsPerformance analysis of multi-stream transmissionMulti-stream Audio Transmission with Path Diversity Yi LiangFixed playout deadlinePlayout Scheduling AlgorithmsTradeoff between delay and loss, wish to reduce bothThe adaptive playout scheme for single stream – jitter adaptationlate lossAdaptive playoutMulti-stream Audio Transmission with Path Diversity Yi LiangMulti-stream Audio PlayoutCan always take the packet with lower delayAdaptive playout and speech scaling make seamless switching between streams possible; question: setting playout schedule? Multiple description coding; question: audio quality?Multi-stream Audio Transmission with Path Diversity Yi LiangDetermine the Playout ScheduleTo minimize the Lagrange cost functionC = delay + 1 p (packet from both streams lost) + 2 p (one packet lost) (audio quality degrad. when losing one packet)= d + 1 lp1 lp2 + 2 [lp1 (1- lp2)+lp2 (1- lp1)] SNRdegradMaintaining history for both streams; loss probability determined by delay and past history (order statistics)Greater 1 results in lower loss rate at the cost of higher delayGreater 2 results in both lower loss rate and better audio quality, at the cost of higher delayIncreasing 1 without big 2 leads to lower loss rate, but not necessarily better sound qualitySmall 1 and 2 result in low delayStream 1 ds1lp1lp2Stream 2 ds2dFreqMulti-stream Audio Transmission with Path Diversity Yi LiangMulti-stream with MDCStream 1: Even samples: quantized in finer resolution (8-bit) Odd samples: quantized in coarser resolution (4-bit)Stream 2: the other way [Jiang, 00’]SNR degradationMDC over Multiple StreamsEs1s2OEOEOOEOEOEPackets in multi-streamsStream 1 Stream 2 SNRdegrad(dB)0 -21-21-27 (after conceal.)Multiple description coding (MDC): generates multiple descriptions of equal importance for the same source signalEOMulti-stream Audio Transmission with Path Diversity Yi LiangComparison: Single-stream with FEC 2 3 411 2 3 2 411 32 3 41Stream received with packet lossStream reconstructed3Stream sentFEC protected single-streamFor fair comparison Primary copy: quantized in finer resolution (8-bit) Secondary copy quantized in coarser resolution (4-bit)SNR degradationSame data rate as multi-stream MDCPackets protected with FECPrimary Second - SNRdegrad(dB)0 -24-27 (after conceal.)FEC: adds redundancy by sending multiple copies of the source signal in the following packet(s) [Bolot, 96’]Multi-stream Audio Transmission with Path Diversity Yi LiangExperiments over the Internet (I)Path 1 (direct): Netergy – MITPath 2 (alternative): Netergy – Harvard – MITDirect path: 30ms UDP packets sent from source to dest.; routes determined by routing algorithmAlt. path: packets sent from source to relay server, then forwarded to dest.Exodus Comm.Exodus Comm.BBN PlanetBBN PlanetQwestQwestNetergy networks192.84.16.176MIT18.184.0.50Harvard140.247.62.110(5)(45)(40) (5)(5)Multi-stream Audio Transmission with Path Diversity Yi LiangResults of Experiment I (1)Delay – loss curve obtained by varying 1 while keeping 2 small and fixed.Mean delays (ms): 72.4/60.3Link loss rate: 0.02%/0.85% Observed significant reduction in delay and loss rate by using multiple streams.Total/burst loss rate greatly reduced since jitter averaged.Path 1 (direct): Netergy – MITPath 2 (alt): Netergy – Harvard - MITMulti-stream Audio Transmission with Path Diversity Yi LiangResults of Experiment I (2)Results obtained by varying 2 while keeping 1 fixedWith higher delay: better chances to play both descriptionsObserved lower playout rate variation by using multiple streams Jitter averaged; lower STD of min(di , dj)Multi-stream Audio Transmission with Path Diversity Yi LiangResults of Experiment I (3)Playout of packets from multiple streamsMulti-stream Audio Transmission with Path Diversity Yi LiangExperiments over the Internet (II)VBNS IP Backbone ServiceVBNS IP Backbone ServiceDANTE OperationsDANTE OperationsUUNET Tech.UUNET Tech.New Jersey165.230.227.81Germany131.188.130.136Harvard140.247.62.110(7)(40)AT&TAT&T(5)(5)Path 1 (direct): N. J. – GermanyPath 2 (alternative): N. J. – Harvard – Germany(10)Multi-stream Audio Transmission with Path Diversity Yi LiangResults of Experiment II (1)Path 1 (direct): N. J. – GermanyPath 2 (alternative): N. J. – Harvard – GermanyMean delays (ms):61.3/65.0Link loss rate: 0.6%/1.1% Burst loss rate can still be reduced by more than 3%, since jitter averaged.Multi-stream Audio Transmission with Path Diversity Yi LiangResults of Experiment II (2)Multi-stream Audio Transmission with Path
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