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    PV Powerpoint PV Powerpoint Presentation Transcript

    • TCP Video Streaming to Bandwidth-Limited Access Links Puneet Mehra and Avideh Zakhor Video and Image Processing Lab University of California, Berkeley
    • Talk Outline
      • Goals & Motivation
      • Our Approach
      • Experimental Results
      • Related Work
      • Conclusion
    • 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
    • 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
    • Example Situation High RTT Med. RTT Low RTT Congestion Most Bandwidth!
    • Talk Outline
      • Motivation & Goals
      • Our Approach
      • Experimental Results
      • Related Work
      • Conclusion
    • 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
    • BWSS Overview
    • 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
    • Flow Control System (FCS) w – TCP window RTT – Flow RTT MSS – TCP MSS
    • 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
    • Talk Outline
      • Motivation & Goals
      • Our Approach
      • Experimental Results
      • Related Work
      • Conclusion
    • Experimental Setup RUDE
    • 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
    • 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
    • BWSS Reduces Required Pre-Buffering
      • BWSS provides 4X reduction in pre-buffering over standard TCP
    • SureStream TM Experimental Setup RUDE
    • 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
    • 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
    • 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
    • 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
    • Questions?