1 Node Selection For a Fault- Tolerant Streaming Service On A Peer-to-Peer Network Hyunjoo Kim, Sooyong Kang and Yeom H.Y.

2 Agenda  Introduction  P2P Service Model  Server Selection Schemes Larger available outbound Bandwidth First (LBF) Smaller available outbound Bandwidth First (SBF) Playback Node First (PNF) Playback Node First with Prefetching (PNF-P)  Simulation Results  Conclusion

3 Introduction  QoS degradation due to node failures is critical in streaming services  Schemes to cope with node/link failures Redundant data Reallocation of data sending rate from sever nodes Special encoding for graceful quality degradation Service migration

4 Introduction  The paper focus on server selection schemes Nodes are autonomous and have different bandwidth QoS depends greatly on the selection scheme  The Fact Failure probability of a node currently being served is lower than that of a node not being served

5 P2P Service Model  Assumptions A node can receive/transmit data from/to multiple nodes simultaneously Client node knows all the data placement CBR media objects which segmented into equal size

6 P2P Service Model  When server receive a request, tell client the available outbound bandwidth  Based on the selection scheme, tell the server whether it is selected  If the server is not selected, it send update information to client when available bandwidth changes

7 P2P Service Model  For each selected server, i Prefetch for t d seconds Store t d r i amount of data for each server Monitor the size of buffer to detect fault Fault detection threshold, s d is segment size, δ is predicted migration time Replace the failed node by one or more server nodes

8 Server Selection Schemes  Larger available outbound Bandwidth First (LBF)  Smaller available outbound Bandwidth First (SBF)  Playback Node First (PNF)  Playback Node First with Prefetching (PNF-P)

9 Larger available bandwidth first (LBF)  Select the nodes that can provide larger available outbound bandwidth first  Minimize the number of servers needed  Probability of encountering a node/link failure is smaller  But individual node/link failure probability is still the same  Fault recovery generally involve multiple nodes, so overhead is larger

10 Smaller available bandwidth first (SBF)  Select the nodes that can provide smaller available outbound bandwidth first  Maximize the number of servers needed  Probability of encountering a node/link failure is larger  But individual node/link failure probability is still the same  Fault recovery generally involve one node only, so overhead is smaller

11 Playback Node First (PNF)  The Fact Failure probability of a node currently being served is lower than that of a node not being served  Based on LBF but nodes that are currently being served is selected first  Node that has the longer remaining playback time is selected first

12 Playback Node First (PNF) TRTR TRTR TRTR N0N0 N2N2 N1N1 N3N3 t0t0 t1t1 t2t2 t3t3 time server selection priority T R =2500 B=150 T R =1700 B=70 T R =1000 B=150 T R =0 B=80 Request for 300Kbps Selection: N 0 (150), N 1 (70), N 2 (80)

13 Playback Node First with Prefetching (PNF-P)  Node failure probability increases after the server finishes its own service  Client node receive future data in advance into the storage  Use PNF for selecting one or more servers for prefetching  Prefetch data are transmit in reverse direction, from end of segment to the start

14 Simulation Results ParametersValues Number of initial servers20 Outbound bandwidth 30 – 100 Kbps Number of objects20 Object playback rate300 Kbps Segment size10 Kb Object size3600 seconds Buffering time5 seconds Predicted migration time ( δ ) 2 seconds Request arrival rateExp. Distr. w/ mean Network congestion interval10000 seconds Network congestion duration50 seconds Normal state migration timeExp. Distr. w/ mean 0.1 sec Congestion state migration time Exp. Distr. w/ mean 1 sec MTBF 6250 – seconds Simulation time86400 seconds (24 hours)

15 Simulation Results

16 Simulation Results

17 Simulation Results

18 Simulation Results

19 Conclusion  New node selection schemes for a service migration-based fault-tolerant streaming service on P2P networks.  PNF and PNF-P decrease the average number of node failures and increase the probability of stable service.

20 Comments  The “ Fact ” is the fact?  Prefetching method is not good enough