1. On Transmission Scheduling in a Server-less Video-on- Demand System

2. Outline Background Transmission Scheduling Performance Evaluation Summary

3. Playback Internet (N – 1) nodes STB Server-less VoD System Network delay Packet Loss Access router  Transmission Scheduling is required

4. Transmission Scheduling On Request Scheduling Staggered Scheduling Randomized Scheduling

5. On Request Scheduling At receiver side  Initiate a video session  Send requests to all nodes at the same time At sender side  Admit requests  Reserve a timeslots for each request  First come, first serve

6. On Request Scheduling r i : request from node i r1r1 r2r2 r1r1 r2r2 Node 0 Node 1 Node 9 r1r1 r2r2 11 11 11 2 22 22

7. On Request Scheduling Simple algorithm Minimize start-up latency However,  Timeslots assigned by different nodes to the same request are usually close together  Bursty traffic at the receiver side  Congestion and packet loss

8. Staggered Scheduling Why not spreading out the transmission in advance?  Non-overlapping timeslots for each request  Pre-allocation of timeslots Algorithm  Node i serves node j at timeslot (i – j – 1) mod N

9. Staggered Scheduling 12345782345786901690 Node 0 Node 1 Node 9 12345782345786901690 12345782345786901690 Node i serves node j at timeslot (i – j – 1) mod N

10. Staggered Scheduling Assumption  Nodes are clock synchronized Two implications  Performance depends on clock synchronization accuracy  Assumptions may not always be feasible

11. Randomized Scheduling Motivation  Eliminate the requirement of synchronization  Decorrelate the transmission time Randomized  Timeslots to each request  Timeslots in each round

12. Performance Evaluation Cluster Size Router Buffer Size Queueing Delay

13. Simulation Model ParametersDefault Values Cluster size500 Video block size8KB Video bitrate, R v 4Mbps Access network bandwidth1.1R v Router buffer size (per node)32KB Mean propagation delay0.005s Variance of propagation delay10 -6 Mean router queueing delay0.005s Variance of clock jitter10 -6

14. Cluster Size

15. Router Buffer Size

16. Queueing Delay

17. Summary Transmission scheduling is required to resolve the congestion Staggered scheduling  can achieve near-zero packet loss rate with small network delay variation and clock synchronization Randomized scheduling  can achieve consistent performance for any delay variation  Without clock synchronization  suitable for serverless system

18. Current and Future Works Deterministic scheduling  Optimal schedule for any given delay profile  Using QQP Stochastic scheduling  Schedule based on stochastic information  Receiver messaging feedback