《Performance Optimization of VoIP》.ppt

Performance Optimization of VoIP Using an Overlay Network Raj Kumar Rajendran Samrat Ganguly Rauf Izmailov Dan Rubenstein Motivation VoIP traffic poised to grow rapidly FCC projects 27 million residential VoIP lines by 2010 Corporate VoIP usage to go from 4% to 44% by 2010 Skype had 10 billion minutes of calls in first year Internet not engineered for delay-sensitive applications Skype is proprietary Not clear how it works Hypothesized that VoIP performance can be improved by Path-Diversity Error-coding Challenge Design VoIP-specific overlay network Implement Path-Diversity Parity-coding Deploy Test performance Design test tools and methodology Test usefulness of overlay Effect of Path-Diversity Tradeoffs of Redundancy and Error-Coding Measuring VoIP Performance ITU-T E-Model R-factor System Architecture Estimating Link-Quality Link Quality-Probe 8 second talk-spurt (1000 132Byte packets) is sent and we estimate Average Delay (d) Network Loss-rate (n) Jitter Loss-rate (j) Delay loss Loss Clustering (c) Estimating Path-Quality R-factor is not linear so is not additive ! We cannot just add the R-factor of the links The Routing Algorithm Do (Every T seconds) Measure quality of direct-path to beacon, overlay nodes Repeat Exchange delay, loss( network,cluster) of best-path with other overlay-nodes If better-path exists through another overlay-node, update best-path Until (paths don’t change) Done Experimental Setup System Implemented on PlanetLab 35 nodes spread over US, Europe, Asia 11 nodes were chosen to be overlay-nodes Tests Used the G.711 codec 120 Byte frames every 15 ms (133 f/s) Each call 170Kbps (Frame+RTP+UDP+IP) Results: Overlay Performance Overlay run for 1 day uninterrupted Routing algorithm rerun every 10 minutes % Paths that improved Avg. R-factor improvement % Paths where R-factor Improved from low to medium ( 70 to 70) Improved from medium to high ( 80 to 80) Usefulness of Path-Diversity Can we put through more calls if we use multiple p