1. On Peer-to-Peer Media Streaming Dongyan Xu Mohamed Heffeda Susanne Hamrusch Bharat Bhargava 2002 International Conference on Distributed Computing Systems

2. Outline Introduction P2P Media Streaming Model Optimal Media Data Assignment Fast System Capacity Amplification Simulation Conclusion

3. Introduction Category of P2P system Main difference between a general P2P system and a P2P media system is the data sharing mode –Open-after-downloading mode –Play-while-downloading mode

4. Introduction Characteristics of a P2P media system Self-growing The more peers it serves ， the larger the capacity it will have Server-less Such as opening a large number of simultaneous connection Heterogeneous Different out-bound bandwidth contribution to the system

5. Introduction Characteristics of a P2P media system Many-to-one Multiple supplying peers in one real-time streaming session

6. Introduction Problems of P2P media system Media data assignment for a multi-supplier peer-to-peer streaming session Fast amplification of the P2P streaming capacity

7. P2P Media Streaming Model Roles of peers Each supplying peer participates in at most one P2P streaming session at any time Bandwidth of peers –R 0 : denote the playback rate of the media data –R in (P r ) = R 0 –R out (P s ) = R 0 /2 n (R 0 /2, R 0 /4, …. R 0 /2 N )

8. P2P Media Streaming Model Classes of peers –Classify the peers into N classes according to their out-bound bandwidth offer –Class-n peer : offer out-bound bandwidth R 0 /2 n (1 ≦ n ≦ N ) Capacity of the P2P streaming system Segments of media data –Media data be partitioned into small sequential segments of equal sizes –δt of each segment is the same

9. Optimal Media Data Assignment Bad Case Requesting peer : P r Supplying peers : P 1 s, P 2 s, P 3 s, P 4 s ( R 0 /2, R 0 /4, R 0 /8, R 0 /8) P 1 s : 8k+1, 8k+2, 8k+3, 8k+4 P 2 s : 8k+4, 8k+5 P 3 s : 8k+6 P 4 s : 8k+7 ( k = 0, 1, 2, 3, …. )

10. Optimal Media Data Assignment Optimal Case Requesting peer : P r Supplying peers : P 1 s, P 2 s, P 3 s, P 4 s ( R 0 /2, R 0 /4, R 0 /8, R 0 /8) (1)The lowest class among supplying peer is class-n (2)Computes the assignment of the first 2 n segments

11. Optimal Media Data Assignment The algorithm OTS p2p compute an optimal media data assignment achieves the minimum buffering delay The minimum buffering delay

12. Fast System Capacity Amplification Waiting time : interval between requesting peer first streaming request and the earliest time it can be admitted T : duration of the P2P streaming session Class-1 : P 3 s, P 4 s, P 3 r Class-2 : P 1 s, P 2 s, P 1 r, P 2 r Average waiting time (0+T+2T)/3 = T

13. Fast System Capacity Amplification Average waiting time (T+T+0)/3 = 2T/3 Different admission decisions lead to different growth of streaming capacity Higher-class requesting peers will lead to a faster amplification of the system capacity

14. Fast System Capacity Amplification Distributed admission control protocol (DAC p2p ) Key features –Supplying peer can decides whether or not to participate in a streaming session by probability –Requesting peer may send a reminder to a busy supplying peer P s

15. Fast System Capacity Amplification DAC p2p – Supplying Peers Each Ps maintains an admission probability vector How to determine probability vector 1.Suppose P s is class-k peer P r [i] = 1.0 when 1 ≦ i ≦ k P r [i] = 1/2 i-k when k<i ≦ N class i is favored class of Ps, if Pr[i] =1.0 2.If P s idle ， then probability vector will be updated after a period of T out k < i ≦ N, Pr[i] = Pr[i]*2

16. Fast System Capacity Amplification DAC p2p – Supplying Peers (3) If Ps finished serving a streaming ， will update its probability vector During the streaming session ， did not receive any request of its favored class k < i ≦ N, Pr[i] = Pr[i]*2 If received one request of its favored class ， request peer left a reminder to P s ， if k is the highest favored class of requesting peer which left a reminder P r [i] = 1.0 when 1 ≦ i ≦ k P r [i] = 1/2 i-k when k<i ≦ N

17. Fast System Capacity Amplification DAC p2p – Requesting Peers P r obtains a list of M randomly supplying peers ， and directly contact the candidate from high to low classes P r will be admitted –Pass the probabilistic admission test –R sum = R 0 P r will be rejected –P r will leave a reminder to a busy P s who currently favors the class of P r –Backoff for at least a period of T bkf befor making the request again

18. Simulation Number of requesting peers : 50000 Number of seed supplying peers : 100 Each seed peers is a class-1 peer Show time of video : 60 min Class distribution of requesting peers class-1 : 10% class-2 : 10% class-3 : 40% class-4 : 40% M = 8 T out = 20 min T bkf = 10 min Simulate period : 144 hours During the first 72 hours ， the 50000 peers make their first streaming requests

19. Simulation System capacity amplification

20. Simulation Request admission rate DAC p2p NDAC p2p

21. Simulation Average buffering delay DAC p2p NDAC p2p

22. Conclusion Algorithm OTS p2p which computes optimal media data assignments for P2P media streaming Algorithm DAC p2p which achieves fast system capacity amplification and creates an incentive for peers to offer their truly available out-bound bandwidth