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Quality of Service - applications

Quality of Service - applications. Henning Schulzrinne with Wenyu Jiang Dept. of Computer Science Columbia University NSF QoS workshop, April 2002. Application requirements. What kind of applications? What matters? What doesn't? How do we know?.

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Quality of Service - applications

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  1. Quality of Service - applications Henning Schulzrinne with Wenyu Jiang Dept. of Computer Science Columbia University NSF QoS workshop, April 2002

  2. Application requirements • What kind of applications? • What matters? • What doesn't? • How do we know?

  3. Applications – the diminishing set (or the cynics view of QoS) • video-on-demand  80 GB disk + P2P-over-TCP • voice-over-IP  where? • multimedia conferencing  still waiting, after 50 years... • network games  latency kills

  4. QoS evaluation • Problem: no tool for reliably evaluating quality end-to-end • network (PSTN & Internet) + hardware + operating system • depends on packet loss, jitter (playout buffer), FEC, loss correlation • need subjective evaluation, but too expensive • applicability of objective measures (PSQM, etc.) • use speech recognition as measure • e-model

  5. Voice quality vs. packet loss

  6. MOS vs. loss for FEC and LBR

  7. Myth: TCP loves lossy networks Lakshman/Madow/Suter ToN 2000

  8. Rrel as Universal MOS Predictor • Mapping from relative recognition ratio Rrel to MOS

  9. Human Recognition Results • Listeners are asked to transcribe what they hear in addition to MOS grading. • Human recognition result curves are less “smooth” than MOS curves.

  10. Research infrastructure • After 10 years, still no low-latency audio research application • existing applications (rat/vat) have erratic latency behavior • no good access to audio queuing information for lip-sync • no good diagnostic tools  blame network

  11. QoS is about reliability • can’t sell premium service that’s unavailable one day a year • auxiliary cost of failure: people scheduling, interruption, embarrassment, ... • consistent 5% packet loss is much better than 5% probability that network is unavailable for seconds • BGP convergence time ~ minutes • conjecture: applications (conferencing, VoIP) don't migrate for lack of predictability

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