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Transcript

  • 1. TCP Video Streaming to Bandwidth-Limited Access Links Puneet Mehra and Avideh Zakhor Video and Image Processing Lab University of California, Berkeley
  • 2. Talk Outline
    • Goals & Motivation
    • Our Approach
    • Experimental Results
    • Related Work
    • Conclusion
  • 3. Goal
    • Efficient video streaming using TCP to bandwidth-limited receivers
    • Key Assumptions:
      • Receivers have limited-bandwidth last mile connections to Internet
      • … and run multiple concurrent TCP networking apps
    • Constraints:
      • Should not modify senders or network infrastructure
  • 4. Motivation
    • Increasingly access links are the net. Bottleneck!
      • Limited Bandwidth (B/W)  Less than 1.5MBps
      • Users run concurrent apps  compete for limited B/W
    • Most Traffic on Internet is TCP [HTTP, P2P, FTP]
      • TCP handles recovery of lost packets
      • TCP has congestion control
      • UDP Streaming difficult w/ firewalls
    • Problem: TCP shares bottleneck B/W according to RTT
      • May Not provide enough B/W for streaming apps
  • 5. Example Situation High RTT Med. RTT Low RTT Congestion Most Bandwidth!
  • 6. Talk Outline
    • Motivation & Goals
    • Our Approach
    • Experimental Results
    • Related Work
    • Conclusion
  • 7. Our Approach
    • We developed a receiver-based bandwidth sharing system (BWSS) for TCP [INFOCOM 2003]
    • Key Idea: Break fairness among TCP flows to allow user-specified B/W allocation
    • Approach: Limit throughput of low-priority connections to provide B/W for high-priority ones
      • Ensures full utilization of access link
      • Doesn’t require changes to TCP/senders or infrastructure
  • 8. BWSS Overview
  • 9. Target Rate Allocation Subsystem
    • Some apps need minimum guaranteed rate(video), others don’t (ftp)
    • User assigns each flow:
      • Priority, minimum rate and weight
    • Bandwidth allocation algorithm:
      • Satisfy minimum rate in decreasing order of priority
      • Remaining B/W shared according to weight
    T 1 User Prefs. σ T n
  • 10. Flow Control System (FCS) w – TCP window RTT – Flow RTT MSS – TCP MSS
  • 11. σ – Calculation Subsystem
    • Goal: Choose σ to maximize link utilization. U = Σ i R i ( σ )
    • Approach: Use increase/decrease in measured throughput to guide increase/decrease of σ
    R 1 R N σ = Σ i T i T 1 = R 1 σ U W 2 W 1 Link Capacity T 2 = R 2 T 1 = R 1 T 2 ≠ R 2 T 2 = R 2
  • 12. Talk Outline
    • Motivation & Goals
    • Our Approach
    • Experimental Results
    • Related Work
    • Conclusion
  • 13. Experimental Setup RUDE
  • 14. Experimental Details Invisible to Apps User Level App  easy to deploy ETH0 NIST NET Emulator BW = 960 Kbps Delay = 30 ms BWSS – Shared Library APP_1 APP_n APP_2
  • 15. TCP vs BWSS Internet Experiments
    • Video streamed at 496Kbps
    • Congestion on access link from 30s to 60s
    • Standard TCP not good enough during congestion
    TCP BWSS
  • 16. BWSS Reduces Required Pre-Buffering
    • BWSS provides 4X reduction in pre-buffering over standard TCP
  • 17. SureStream TM Experimental Setup RUDE
  • 18. RealVideo SureStream TM Internet Experiments
    • Takeaway: standard TCP not good enough for streaming
    TCP TCP w/ BWSS
    • Video encoded at 450Kbps, 350Kbps, 260Kbps & 64Kbps
    • Congestion on access link from 60s to 100s (320Kbps)
    Despite congestion, video streams at steady rate. Poor streaming quality
  • 19. RealVideo SureStream TM Internet Experiments UDP TCP w/ BWSS
    • Takeaway: BWSS can break fairness among flows locally, and provide additional B/W for video apps.
    UDP SureStream unable to stream at 450KBps till after congestion Constant streaming at 450Kbps
  • 20. Related Work – TCP Streaming
    • Network-Based Approaches
      • Receiver-based Delay Control (RDC) [NOSSDAV 2001]
        • receivers delay ACK packets based on router feedback
        • Mimic a CBR connection
    • End-Host Approaches
      • Time-lined TCP (T-TCP) [ICNP 2002]
      • TCP Real-Time Mode (TCP-RTM) [ICNP 2002]
      • Must modify both sender & receiver to allow skipping “late” packets
  • 21. Conclusions
    • BWSS allows flexible allocation of link B/W
      • Breaks fairness among TCP flows “locally” in manner unavailable to TCP-Friendly UDP protocols
    • BWSS enables efficient video streaming over TCP to bandwidth-limited receivers
      • Better performance than standard TCP
      • In some cases, better performance than congestion-aware UDP
    • Future Work: Incorporating UDP flows
  • 22. Questions?