Reliable and LowLatency Multicast for Group Collaboration in Wireless LAN

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Reliable and Low-Latency Multicast for Group
Collaboration in Wireless LAN

• Jingtao Wang
• jingtaow_at_cs.berkeley.edu

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Motivation

• Overcome real-world data synchriozation problems
  encountered in developing collaborative learning
  applications in Wireless LAN
• Unstable network connectivity
• High packet loss rate
• Long synchronization latency
• Traffic congestions

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Evolution of LiveNotes
Version 2
Version 1
Livenotes enables collaborative learning and
note-taking in classroom environments by using
wirelessly Tablet PCs/PDAs
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Design Trade-offs
Priority

• Resilience to packet loss, network failures and
  membership changes
• Low-Latency Delivery of small data packages
• Resilience to workload bursts
• Data consistency
• Scalability
• In-sequence delivery

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Related Works

• SRM ( Scalable Reliable Multicast)
• Erasure Correcting Scalable Reliable Multicast
  (ECSRM)
• RMDP (Reliable Multicast data Distribution
  Protocol)
• OverQoS

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Backgrounds - ARQ and FEC
ARQ
FEC
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Proposed Implementation

• Reliability and Low Latency
• Adaptive Utilization of FEC and NACK by using
  application level knowledge
• Packet Size
• Packet Content
• Packet Owner
• Respond to Repeat Requests from Machines Other
  than the Sender

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Proposed Implementation contd

• Congestion Avoidance
• Exploit Application Knowledge to Adjust
  Parameters Before the Starting of Congestions
• Synchronizing Lecture Slides
• Collecting Survey Answers
• Collecting Lecture Notes

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Current Status

• LiveNotes 2 is being implemented by C and
  TabletPC SDK
• A Baseline System using raw IP Multicast has been
  Implemented
• Ported two FEC algorithms to C
• Reed-Solomon (based on Christian Schuler's C
  code)
• Vandermonde matrices (based on Luigi Rizzos C
  code)