SureCall: Towards Glitch-Free Real-Time Audio/Video Conferencing

Amit Mondal, Northwestern University Ross Cutler, Microsoft Corporation Cheng Huang, Microsoft Research Jin Li, Microsoft Research Aleksandar Kuzmanovic, Northwestern University

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Physical Presence or United Communications?

• Attending meeting in person is nice, but the overhead due to travel is high & unpredictable

Scheduled

• Seattle  Cape Town Shanghai  Beijing 24 hrs 2 hrs Unified Communications promise

Actual

42 hrs 10 hrs not being there, but better than being there – VoIP service double in next 4 years, with an annual growth rate of 26% ( Infonetics Research, 2008 )

Booming of Unified Communications

• Widely validated in the consumer world • Gradually being adopted by enterprises – Cisco acquired WebEx – Google announced acquisition of GIPS, which powers 3 – Microsoft Unified Communications

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Contributions

• SureCall platform – A distributed measurement and experiment platform for audio/video conferencing • Quantitatively analyze the impact of network over a wide variety of scenarios in fine granularity • Validate new solutions

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SureCall Platform

• A distributed measurement and experiment platform – – SureCall agents installed on volunteers’ machines Measurements & experiments driven by a master controller – – Packet-level traces collected & analyzed Agents upgradeable without user intervention • Available from http://research.microsoft.com/~chengh/SureCall/SureCall.htm

SureCall Measurements

6 • Emulated bidirectional audio/video sessions using UDP – 5-minute session per hour – Audio bitrate : 24 kbps – Video bitrate: 192 kbps – STUN NAT traversal protocol for home users • Network connectivity close to the clients – ICMP packet pair with TTL = 2 • Traceroute to at the beginning and end of each session • Environmental details on client machines – CPU load, network interface type

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SureCall Deployment

• • • Microsoft global enterprise network & many residential networks Current deployment status – 80 unique machines • • Enterprise - 32 Home – 20 • Both – 28 Enterprise trace and Home trace – two separate master controllers (within the enterprise network and on the Internet)

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SureCall Data Set

4,800 hours of packet traces – 4,100 from enterprise – 700 from home 1,968 unique IP addresses – Enterprise - 1212 – Home -756 Trace classification and stratification – Intra-continental vs. inter continental – Wired vs. wireless – Audio-only vs. audio+video Trace preprocessing – Clock skew removal 8 Clock skew in wild 8

Jitter in Enterprise and Home Networks

9 US-US, wired traces Inter-continental, wired traces Home networks have significantly higher jitter compared to enterprise networks and affected greatly by inter continental links.

Correlation between Loss Burst Length and Jitter

Home Enterprise 10 1. End-to-end jitter increases significantly before loss events in both enterprise and home networks (~ 80%) 2. Increase in end-to-end jitter is not a great indicator of loss burst length in enterprise networks.

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Network Audio Diagnostics

• • • Concealed: percent of packets interpolated or extrapolated due to unrecovered packet loss Stretched: percent of packets stretched via time compression Classifier operates as follows • Supervised training with ground-truth objectively determined by PESQ score

Audio Classifier Performance

12 The classifier achieves a true positive rate >80% and false positive rate < 1% for T1=T2=0.07.

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WiFi Relay

• • • Wireless connections experience significantly more packet losses than wired connections Heavy replication is a effective manner to hide packet losses in wireless channel WiFi relay solution

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WiFi Relay

Evaluated on SureCall platform Simultaneous direct and overlay VoIP call – An apple-to-apple comparison 14 WiFi relay greatly reduces packet loss and significantly improves VoIP quality for WiFi users

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Conclusion

• • • SureCall, a distributed measurement and experimental platform, to address the challenges of audio/video communications.

Characterized enterprise and residential networks over a wide variety of network scenarios Two applications of SureCall – Network audio diagnostics – WiFi Relay