Playback-buffer Equalization for Streaming Media using Stateless Transport Prioritization

1. Playback-buffer Equalization for Streaming Media using Stateless Transport Prioritization Dan Tan, HPL, Palo Alto Weidong Cui, UC Berkeley John Apostolopoulos, HPL, Palo Alto

2. Streaming Server High Capacity Core Network Bottleneck Streaming Server Reducing “Pauses” in Playback • Problem: frequent “pauses” in playback • Goal: reduce “pauses” via smart routing in common bottleneck • Client transparency • No server coordination • Stateless smart routing in bottleneck Packet Video Workshop 2003, Nantes, France

3. How “Pauses” Occur No Control Received:network condition Consumed:constant Packet Video Workshop 2003, Nantes, France

4. TCP Feedback b1 b1 Streaming Server b1 See Better Channel TCP Data High Capacity Core Network Smart Router Smart Router High Capacity Core Network Bottleneck b2 Bottleneck b2 b2 Streaming Server Want “Equalized” buffer Problem: Independent loops, cannot optimize across streams How: Better service for packet triggers higher sending rate Pros:Client transparency, Server coordination-free, Stateless smart router Our Solution Packet Video Workshop 2003, Nantes, France

5. 100 Mbps bottleneck 10.1.0.15 10 Mbps 10.2.0.1 10.1.0.1 10.2.0.23 Receiver 10.1.0.25 Servers Testbed Encoding buffer Occupancy into TOS in IP header 1 0 2 3 4 5 6 7 Label 0 2 4 8 16 32 64 Buffer occupancy (s) Smart Router: - mostly priority queuing (smallest b first) - every 20 packets perform round-robin Packet Video Workshop 2003, Nantes, France

6. Large buffer spread Results: First-In-First-Out (FIFO) Buf data deadline pause Packet Video Workshop 2003, Nantes, France

7. Small buffer spread Results: Playback Buffer Equalization (PBE) Packet Video Workshop 2003, Nantes, France

8. Simulation Study • More control in size and parameters of topology • Large number of runs • Various simulated load by adjusting Poisson arrival rate of independent sessions, • Media duration according to empirical distribution of trace from HP Media Services 80 ms 40 ms bottleneck 20 ms 10 Mbps Servers Receiver 10 ms Packet Video Workshop 2003, Nantes, France

9. Results: NS Simulation Results FIFO pauses Improves fairness! PBE pauses load Moderate load Over-load no reduction 10x reduction Packet Video Workshop 2003, Nantes, France

10. Priority Queue: • Works most of the time • Starvation  bad TCP behavior • DiffServ Expedited Forwarding • 10 Mbps bottleneck, 3Mbps max high priority • Dynamically choose threshold T to limit high priority traffic ( b < T ) • Few starvation despite threshold-based classification • Steady state: purely FIFO operation • New flows given high initial throughput to quickly arrive at steady state. • Medium spread in buffer occupancy Other Characteristics • No harmful effects over non-bottleneck links • Reduction factor in “pauses” roughly constant and independent of round-trip delay • Other Smart Router designs examined: Packet Video Workshop 2003, Nantes, France

11. Summary Playback Buffer Equalization (PBE) • Reduces pauses for sessions behind a common bottleneck • Client-transparent • No server coordination • Stateless operation at “Smart Router” • Experiments & simulations for TCP (HTTP) streaming Future Work • Using existing QoS mechanisms in current switches, e.g, HP Procurve 530x series switches • Extension to non-TCP rate control Packet Video Workshop 2003, Nantes, France