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Overview

Explore E-Model components, delay, jitter, loss effects on VoIP over satellite links, and evaluate audiovisual quality. Learn about MOS ranking, H.323 Beacon, and network performance bounds. Understand testing techniques and optimization tips.

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Overview

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Presentation Transcript

  1. Video and Voice over IP performance over a Satellite linkBob Dixon, Ohio State University/OARnetPrasad Calyam, OARnetJoint Techs Workshops, Columbus, OH, July 21st, 2004

  2. Overview • Terminology • E-Model • Delay, Jitter, Loss • H.323 Beacon • Demo • Demo Setup • Network Performance Bounds • H.323 Beacon Server-to-Server Test Module • Conclusion

  3. Evaluating Audiovisual Quality • Two approaches • Subjective Measurements • Involve human participants to rate audiovisual quality Can you hear me now? • Mean Opinion Score (MOS) Ranking technique (ITU-T P.800) Not just “Good”! • Objective Measurements • Automated techniques to rate audiovisual quality • Perceptual Assessment of Speech Quality (PESQ) [ITU-T P.862] • “E-Model” [ITU-T G.107]

  4. MOS Rankings

  5. E-Model • A computational model that uses transmission parameters to predict user perceived voice quality • Uses a psycho-acoustic R-scale (0-100) that can be mapped to MOS rankings (1-5) • E-Model Components R = Ro – Is – Id – Ie + A ≈ 94 – Id –Ie

  6. E-Model Components • Ro→ Effects of noise and loudness • Is → Simultaneous Impairment Factor • Impairments occurring simultaneously with the speech signal • Id → Delay Impairment Factor • Impairments that are delayed with respect to the speech signal • Ie → Equipment Impairment Factor • Impairments caused by transmission equipment • A → Advantage Factor • Used to compensate for the allowance users make for poor quality in return for the ease of access; e.g. cell phone or satellite phone

  7. Understanding Delay… • Delay is the amount of time that a packet takes to travel from the sender’s application to reach the receiver’s destination application • Caused by codecs, router queuing delays, … • One-way delay requirement is stringent for H.323 Videoconferencing to maintain good interaction between both ends

  8. Understanding Jitter… • Jitter is the variation in delay of the packets arriving at the receiving end • Caused by congestion, insufficient bandwidth, varying packet sizes in the network, out of order packets, … • Excessive jitter may cause packet loss in the receiver jitter buffers thus affecting the playback of the audio and video streams

  9. Understanding Loss… • Packet Loss is the packets discarded deliberately (RED, TTL=0) or non-deliberately by intermediate links, nodes and end-systems along a given transmission path • Caused by line properties (Layer 1), full buffers (Layer 3) or late arrivals (at the application)

  10. Network Performance Bounds for MOS Grades • Delay (Least Problematic) • Good (0ms - 150ms) • Acceptable (150ms - 300ms) • Poor (> 300ms) • Jitter (Most problematic) • Good (0ms - 20ms) • Acceptable (20ms - 50ms) • Poor (> 50ms) • Loss • Good (0% - 0.5%) • Acceptable (0.5% - 1.5%) • Poor (> 1.5%) http://www.cl.cam.ac.uk/Research/SRG/netos/pam2004/papers/222.pdf

  11. H.323 Traffic performance characterization Testing Sites More than 500 one-on-one subjective quality assessments from Videoconferencing end-users and corresponding traffic traces were obtained from the Testing!!!

  12. H.323 Beaconhttp://www.itecohio.org/beacon • An H.323 application related end-to-end performance troubleshooting tool • Can be used to obtain H.323-protocol specific evidence and other network information necessary for troubleshooting • Latest Version 1.4 released on Sourceforge.net • Developed by OARnet and supported by Internet2 and Ohio Board of Regents

  13. Demo Setup

  14. Questions?

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