1、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,Attending meeting in person is nice, but the overhead due
2、 to travel is high & unpredictableUnified Communications promiseVoIP service double in next 4 years, with an annual growth rate of 26% (Infonetics Research, 2008),Physical Presence or United Communications?,not being there, but better than being there,2,Gradually being adopted by enterprises Cisco a
3、cquired WebEx Google announced acquisition of GIPS, which powersMicrosoft Unified Communications,Booming of Unified Communications,Widely validated in the consumer world,3,Contributions,SureCall platform A distributed measurement and experiment platform for audio/video conferencing Quantitatively an
4、alyze the impact of network over a wide variety of scenarios in fine granularity Validate new solutions,4,SureCall Platform,A distributed measurement and experiment platform SureCall agents installed on volunteers machines Measurements & experiments driven by a master controller Packet-level traces
5、collected & analyzed Agents upgradeable without user interventionAvailable from http:/ 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 usersNetwork connectivity close to
6、the clients ICMP packet pair with TTL = 2Traceroute to at the beginning and end of each sessionEnvironmental details on client machines CPU load, network interface type,6,SureCall Deployment,Microsoft global enterprise network & many residential networks Current deployment status 80 unique machines
7、Enterprise - 32 Home 20 Both 28 Enterprise trace and Home trace two separate master controllers (within the enterprise network and on the Internet),7,4,800 hours of packet traces 4,100 from enterprise 700 from home 1,968 unique IP addresses Enterprise - 1212 Home -756 Trace classification and strati
8、fication Intra-continental vs. inter-continental Wired vs. wireless Audio-only vs. audio+video Trace preprocessing Clock skew removal,8,Clock skew in wild,8,SureCall Data Set,Jitter in Enterprise and Home Networks,9,US-US, wired traces,Inter-continental, wired traces,Home networks have significantly
9、 higher jitter compared to enterprise networks and affected greatly by inter-continental links.,Correlation between Loss Burst Length and Jitter,10,End-to-end jitter increases significantly before loss events in both enterprise and home networks ( 80%) Increase in end-to-end jitter is not a great in
10、dicator of loss burst length in enterprise networks.,Enterprise,Home,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 followsSupervised training with
11、 ground-truth objectively determined by PESQ score,11,Audio Classifier Performance,12,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
12、effective manner to hide packet losses in wireless channel WiFi relay solution,13,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,14,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,15,
