Transcript SureCall: Towards Glitch-Free Real

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
Physical Presence or United
Communications?
• Attending meeting in person is nice, but the
overhead due to travel is high & unpredictable
Seattle  Cape Town
Shanghai  Beijing
Scheduled
24 hrs
2 hrs
Actual
42 hrs
10 hrs
• Unified Communications promise
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)
2
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
– Microsoft Unified Communications
3
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
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 collected & analyzed
– Agents upgradeable without user intervention
• Available from
http://research.microsoft.com/~chengh/SureCall/SureCall.htm
5
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
6
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)
7
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. intercontinental
– 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
US-US, wired traces
Inter-continental, wired traces
Home networks have significantly higher jitter compared
to enterprise networks and affected greatly by intercontinental links.
9
Correlation between Loss Burst Length
and Jitter
Home
10
Enterprise
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.
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
11
Audio Classifier Performance
The classifier achieves a true positive rate >80%
and false positive rate < 1% for T1=T2=0.07.
12
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
13
WiFi Relay
• 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
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