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Performance Evaluation of VoIP in Different Settings

Performance Evaluation of VoIP in Different Settings. Tom Christiansen Ioannis Giotis Shobhit Raj Mathur. Outline. How does VoIP work in the Internet today? How is VoIP quality measured? Which network parameters affect the performance of VoIP?

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Performance Evaluation of VoIP in Different Settings

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  1. Performance Evaluation of VoIP in Different Settings Tom Christiansen Ioannis Giotis Shobhit Raj Mathur

  2. Outline • How does VoIP work in the Internet today? • How is VoIP quality measured? • Which network parameters affect the performance of VoIP? • How does the speech quality of VoIP depend on these parameters? • How can the existing VoIP technology be improved?

  3. How does VoIP work? Audio Sampling Audio Decoding 128 kbps Audio Encoding Codec 5 – 30 kbps Network Protocol Network Protocol RTP over UDP

  4. VoIP Quality Metrics • Signaling quality • Measure of the call setup performance • Delivery quality • Latency • Jitter • Packet Loss • Call quality • Perceived quality • E-model – Analytical model which generates an R-value • MOS (Mean Opinion Score) – Related to the R-value

  5. VoIP Quality Metrics

  6. VoIP Measurements • Using Brix Networks’ VoIP testing tool • A total of 600 experiments were run over a period of two weeks. • Types of networks • UW Gigabit Ethernet • Wireless 802.11 at UW • Cable (Comcast) • Dial-up from home • Destinations • Boston • Helsinki • London • Montreal • San Jose • Sydney

  7. Quantifying the quality degradation UW LAN average MOS, G.711 Cable average MOS, G.711 802.11 average MOS, G.729 Dial-up average MOS, G.729

  8. Traceroute Analysis • Edges are the bottlenecks in today’s Internet. • Last hop delay in the case of a dialup connection is the same as the intercontinental delay! • On slow networks like dialups, an increase in the geographical distance degrades the MOS due to higher latency. UW LAN to London Dial-up to London

  9. What we can conclude • LAN>Cable>802.11>dial-up, as expected. • LAN and cable are great ! • Negligible degradation due to the network • Dial-up is somewhat useable. • Main cause of degradation is latency, caused due to the delay over the last hop • 802.11 is in-between and has lots of issues. • Main cause of degradation is packet discards (delayed packets and garbled packets). • Other traffic causes serious degradation even on cable • Background downloads severely affect speech quality

  10. Future improvements • Adaptive VoIP clients • Variable codec parameters based on network condition • QoS guarantees from the OS • Priority over other traffic at the end hosts • Forward Error Correction • Research shows that we can achieve significantly better quality with FEC in “lossy” connections • Especially useful for 802.11 • Adaptive FEC (variable code rate)

  11. Conclusions • It does work ! • But still not ready to take over land lines. • In our report • More details on VoIP quality metrics • Explicit quantification of the degradation factors for each type of networks. • Possible improvements to VoIP based on our analysis of the experimental results

  12. Thank You Questions?

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