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  • Problem setting: time-shifted streaming in P2P LIVE STREAMING SYSTEM. We want to preserver the scalability of the P2P system. How? Make use of peer’s local storage in addition to their uplink bandwidths!
  • System overview: SPPM for LS, and its extension Explain “video availability Intro to Fast prefetching as parent selection algorithm Video availability Server load Video quality
  • SPPM originally supports live streaming to a population of peers
  • Define LS peers
  • Peer database at the server Peer identifier, join time, initial video time-stamp Latest video time-stamp is estimated (and periodically corrected) Peers cache received video packets Protocol can handle video time-stamp
  • Explain time-video plot. But, no needs for explaining “video trajectory”! Needs for defense on the two assumptions?
  • 150 peers. 90% of them are active -> 135. Maximum # of LS reach 60.
  • Explain how to interpret the video availability plot. Each point. Higher, better. Latest part is covered by LS peers. In early stage, all portion of video is well covered. Averaged 100 simulations. Intro to NS2 simulator (packet-level)
  • Say: 2R is sufficient to support 100 LS peers. For 100 TS peers, more than 20R bandwidth required.
  • Explain time-video plot again. Explain “video trajectory”! A peer can receive video faster than playout speed Why fast prefetching? Data are available. BW is available. (good use of peer resources) Benefit: Good for children ( relaxed playout deadline) Larger video coverage -> may reduce server load
  • How to maximize fast prefetching? LS peer parent selection: number of logical hops to server -> it’s not optimal here. Learn more about parent candidates and choose the best for maximum expected throughput
  • EXPLAIN COLORS EXPLAIN SIMULATION SETTINGS
  • Time 0 ~ 900s : server loads are almost the same for different schemes. But, there is a difference in video quality!
  • Define TS peers Explain time-video plot. Explain live stream trajectory, LS, TS trajectory
  • At the last step, the child download rate >= r’
  • Peers discard cached packets only when they leave the system Uniform access: worst case video random access
  • Weight the region with lifetime probability

Improving Capacity and End-to-end delay of P2P Video ... Improving Capacity and End-to-end delay of P2P Video ... Presentation Transcript

  • Time-Shifted Streaming in a P2P Video Multicast System Jeong h un Noh , Aditya Mavlankar, Pierpaolo Baccichet 1 , and Bernd Girod Information Systems Laboratory Stanford University 1 Now with OnLive Inc.
  • Playback Control in P2P System
    • To pause/resume video
    • To rewind or fast-forward
    Video server Users watching live video
  • Outline
    • System overview
    • Video availability
      • Modeling
      • Comparison with simulation results
      • Improving video availability
      • Fast prefetching
      • Simulation results
  • SPPM: Stanford P2P Multicast
  • Live Streaming in SPPM [ Setton et al., P2PMMS 2005] [Baccichet et al., ICME 2007] Tree 1 Tree 2 LS peers watching live video Video server … … Video stream
  • Time-Shifted Streaming in SPPM … Video frames 2 3 4 5 6 7 8 4 5 6 7 8 Server 2 3 4 Live Stream Time-Shifted Buffer: Buffer: Buffer: 2 3 4 5 6 7 8
  • Video Availability
    • How many peers are available for serving
    • video of position x at time t ?
    • Assumptions for analytical model
      • TS peer requests video position x,
      • uniformly drawn from 0  x < t
      • Poisson peer arrival
      • Exponential peer lifetime
    t Time Video position Live stream t x (t, x)
  • Video Availability Model
    • Peer arrival rate: 1.2 per second
    • Average peer lifetime: 120 second
    • 50% TS peers, 50% LS peers
    t = 300s At time t = 300s
  • Video Availability Model (cont.)
    • Peer arrival rate: 1.2 per second
    • Average peer lifetime: 120 second
    • 50% TS peers, 50% LS peers
    t = 600s At time t = 600s
  • Video Availability Model (cont.)
    • Peer arrival rate: 1.2 per second
    • Average peer lifetime: 120 second
    • 50% TS peers, 50% LS peers
    t = 900s At time t = 900s
  • Comparing with Simulation Results Model Simulation
    • Simulation in NS-2 simulator
    • 1 real instance
    • Peer arrival rate: 1.2 per second
    • Average peer lifetime: 120 second
    • 50% TS peers, 50% LS peers
    • Simulation in NS-2 simulator
    • Averaged 100 simulations
  • Server Load 70 LS peers and 70 TS peers Server Uplink: 20R (2R reserved for LS) Averaged 10 simulations
  • Improving Video Availability
    • Server load increases over time
      • Video availability decreases
      • More TS peers connect to server
    • Can we reduce server load?
      • Live stream vs time-shifted streams
      • Redundant peer uplink bandwidths
  • Fast Prefetching Child 1 Time Video position Parent Child 2 T Uplink = 2 R Child 1 (no fast prefetching) Video trajectory Overlay structure x 1 t 1 t 2 x 2
    • Improves video availability in the system
    • Reduces playback disruption due to more buffering
  • Server Load 70 LS peers and 70 TS peers Server Uplink: 20R (2R reserved for LS) D = 10s, averaged 10 simulations
  • Parent Selection for TS Peers Time Video position t t + D
    • Parent candidate P i
      • Buffered video length :
      • Download rate:
      • Upload rate:
    • : look ahead time
    • For each Pi, child C computes
    • Select the best candidate by
    Download: Upload:
  • Server Load 70 LS peers and 70 TS peers Server Uplink: 20R (2R reserved for LS) D = 10s, averaged 10 simulations
  • Video Availability No fast prefetching Fast prefetching TS peers only. 100 simulations
  • Video Quality Averaged over first 900 seconds Video: Mother & daughter encoded at 420 kbps
  • Conclusions
    • A tree-based live streaming P2P (e.g., SPPM) can be extended to support time-shifted streaming
    • Analysis of video availability
      • Over time, more TS peers have to connect to the server
      • More peers and longer peer lifetime reduce server load
    • Fast prefetching disseminates data faster
      • Renders TS peers less susceptible to peer churn
      • Reduces server load
    • Thank you!
    • Jeong-hun Noh
    • [email_address]
  • P2P Time-Shifted Streaming
    • Streaming live stream shifted in time in P2P networks
    • For TS peers, packets are asynchronously delivered
    Time Video position Live stream Peer 1 (LS) T 1 X 2 Peer 2 (LS, TS) T 2
  • Uplink Bandwidth Allocation
      • Allocate tree bitrate r to LS peers
    U U T r
      • Allocate r to TS peers with full prefetch
    U T U T ’ r r
      • Allocate equal BW to remaining TS peers
    U T ’ r’ r’
  • Fast Prefetch Example
    • TS peers watch from position 0s
    • Peer uplink bandwidth: Ur=3R (homogeneous)
    Peer 1 Peer 2 Peer 3 Peer 4 Peer 6 Peer 5 Peer 7
  • P2P Time-Shifted Streaming
    • For TS peers, packets are asynchronously delivered
    • Time-Shifted Streaming (TSS): Streaming live stream shifted in time over the network
    Time Video position Live stream X 3 Peer 1 (LS) T 1 X 2 Peer 2 (TS) T 2 Peer 3 (TS) T 3
  • Coverage Conditions
    • Determine (arrival time, video position) for possessing video of position x at time t
    x (t, x) (t, x) time Video position Live stream t x t-x TS peer time Video position Live stream t x LS peer