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Time-Shifted Streaming Time-Shifted Streaming in a P2P Video Multicast Systemin a P2P Video Multicast System
JeongJeonghhun Nohun Noh, Aditya Mavlankar, , Aditya Mavlankar,
Pierpaolo BaccichetPierpaolo Baccichet11, and Bernd Girod, and Bernd Girod
Information Systems LaboratoryInformation Systems Laboratory
Stanford UniversityStanford University
11Now with OnLive Inc.Now with OnLive Inc.
22J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Playback Control in P2P SystemPlayback Control in P2P System• To pause/resume video• To rewind or fast-forward
Video server
Users watching live video
33J. Noh et al. : Time-shifted streaming in a P2P video multicast system
OutlineOutline• System overview• Video availability
– Modeling– Comparison with simulation results
• Improving video availability– Fast prefetching– Simulation results
44J. Noh et al. : Time-shifted streaming in a P2P video multicast system
SPPM: Stanford P2P MulticastSPPM: Stanford P2P Multicast
55J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Live Streaming in SPPMLive Streaming in SPPM
[Setton et al., P2PMMS 2005][Baccichet et al., ICME 2007]
Tree 1
Tree 2
… …Video stream
LS peers watching live video
Video server
66J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Buffer:
Time-Shifted Streaming in SPPMTime-Shifted Streaming in SPPM
…Video frames
2 3 4 5 6 7 8
Buffer: 4 5 6 7 8
Server
Buffer: 2 3 4
2 3 4 5 6 7 8
Live Stream
Time-Shifted
77J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Video AvailabilityVideo Availability
Time
Video position Live stream
t
x (t, x)
• 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
88J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Video Availability ModelVideo 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
99J. Noh et al. : Time-shifted streaming in a P2P video multicast system
• 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 Video Availability Model (cont.)(cont.)
1010J. Noh et al. : Time-shifted streaming in a P2P video multicast system
• Peer arrival rate: 1.2 per second• Average peer lifetime: 120 second• 50% TS peers, 50% LS peers
t = 900s At time t = 900s
Video Availability Model Video Availability Model (cont.)(cont.)
1111J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Comparing with Simulation ResultsComparing with Simulation ResultsModel 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
1212J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Server LoadServer Load
70 LS peers and 70 TS peersServer Uplink: 20R (2R reserved for LS)Averaged 10 simulations
1313J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Improving Video AvailabilityImproving 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
1414J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Fast PrefetchingFast Prefetching
Child 1
Time
Video position
Parent
x1
t1 t2
x2
Child 2
T
Uplink = 2R
Child 1 (no fast prefetching)
Video trajectory Overlay structure
• Improves video availability in the system• Reduces playback disruption due to more buffering
1515J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Server LoadServer Load
70 LS peers and 70 TS peersServer Uplink: 20R (2R reserved for LS)D = 10s, averaged 10 simulations
1616J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Parent Selection for TS PeersParent Selection for TS Peers
Time
Video position
t t + D
• Parent candidate Pi
• Buffered video length:
• Download rate:
• Upload rate:
• : look ahead time
• For each Pi, child C computes
• Select the best candidate by
Download:
Upload:
1717J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Server LoadServer Load
70 LS peers and 70 TS peersServer Uplink: 20R (2R reserved for LS)D = 10s, averaged 10 simulations
1818J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Video AvailabilityVideo Availability
No fast prefetching Fast prefetching
TS peers only. 100 simulations
1919J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Video QualityVideo Quality
Averaged over first 900 secondsVideo: Mother & daughter encoded at 420 kbps
2020J. Noh et al. : Time-shifted streaming in a P2P video multicast system
ConclusionsConclusions• 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
2121J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Thank you!Jeong-hun Noh
2222J. Noh et al. : Time-shifted streaming in a P2P video multicast system
P2P Time-Shifted StreamingP2P 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)
T1
X2
Peer 2 (LS, TS)
T2
2323J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Uplink Bandwidth AllocationUplink Bandwidth Allocation– Allocate tree bitrate r to LS peers
U
UT r
– Allocate r to TS peers with full prefetch
UT
UT’
r
r
– Allocate equal BW to remaining TS peers
UT’
r’ r’
2424J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Fast Prefetch ExampleFast Prefetch Example• TS peers watch from position 0s• Peer uplink bandwidth: Ur=3R (homogeneous)
Peer 1
Peer 2 Peer 3Peer 4
Peer 6Peer 5 Peer 7
2525J. Noh et al. : Time-shifted streaming in a P2P video multicast system
P2P Time-Shifted StreamingP2P 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
Peer 1 (LS)
T1
X2
Peer 2 (TS)
T2
Peer 3 (TS)
T3
X3
2626J. Noh et al. : Time-shifted streaming in a P2P video multicast system
Coverage ConditionsCoverage Conditions• Determine (arrival time, video position) for possessing
video of position x at time t
time
Video position
Live stream
t
x
t-x
TS peer
time
Video positionLive stream
t
x
LS peer
x
(t, x) (t, x)
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