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

Outline Background Transmission Scheduling Performance Evaluation Summary

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

Transmission Scheduling On Request Scheduling Staggered Scheduling Randomized Scheduling

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

On Request Scheduling r i : request from node i r1r1 r2r2 r1r1 r2r2 Node 0 Node 1 Node 9 r1r1 r2r

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

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

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

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

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

Performance Evaluation Cluster Size Router Buffer Size Queueing Delay

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

Cluster Size

Router Buffer Size

Queueing Delay

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

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