SureCall: Towards Glitch-FreeReal-Time Audio/Video Conferencing

Amit Mondal, Northwestern UniversityRoss Cutler, Microsoft CorporationCheng Huang, Microsoft Research

Jin Li, Microsoft ResearchAleksandar Kuzmanovic, Northwestern University

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

• Unified Communications promise

– VoIP service double in next 4 years, with an annual growth rate of 26% (Infonetics Research, 2008)

Scheduled ActualSeattle Cape Town 24 hrs 42 hrsShanghai Beijing 2 hrs 10 hrs

Physical Presence or United Communications?

not being there, but better than being therenot being there, but better than being there

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• Gradually being adopted by enterprises– Cisco acquired WebEx– Google announced acquisition of GIPS, which powers

– Microsoft Unified Communications

Booming of Unified Communications

• Widely validated in the consumer world

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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

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SureCall Measurements• 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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• 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

8Clock skew in wild8

SureCall Data Set

Jitter in Enterprise and Home Networks

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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.

Home networks have significantly higher jitter compared to enterprise networks and affected greatly

by inter-continental links.

Correlation between Loss Burst Length and Jitter

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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.

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.

EnterpriseHome

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

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Audio Classifier Performance

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

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

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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• Evaluated on SureCall platform• Simultaneous direct and overlay VoIP call– An apple-to-apple comparison

WiFi relay greatly reduces packet loss and significantly improves VoIP quality for WiFi users

WiFi relay greatly reduces packet loss and significantly improves VoIP quality for WiFi users

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WiFi Relay

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

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