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Video and Voice over IP performance over a Satellite link Bob Dixon, Ohio State University/OARnet Prasad Calyam, OARnet Joint Techs Workshops, Columbus, OH, July 21 st , 2004. Overview. Terminology E-Model Delay, Jitter, Loss H.323 Beacon Demo Demo Setup Network Performance Bounds
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Video and Voice over IP performance over a Satellite linkBob Dixon, Ohio State University/OARnetPrasad Calyam, OARnetJoint Techs Workshops, Columbus, OH, July 21st, 2004
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
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]
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
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
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
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
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)
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
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!!!
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
