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

page 2April 29, 2003 Packet Video Workshop 2003, Nantes, France 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 Bottleneck Streaming Server High Capacity Core Network Streaming Server

page 3April 29, 2003 Packet Video Workshop 2003, Nantes, France How “Pauses” Occur Consumed: constant Received: network condition No Control

page 4April 29, 2003 Packet Video Workshop 2003, Nantes, France Our Solution Bottleneck Streaming Server High Capacity Core Network Streaming Server b2b2 b1b1 Want “Equalized” buffer Problem: Independent loops, cannot optimize across streams TCP Data TCP Feedback See Better Channe l b2b2 b1b1 Smart Router How: Better service for packet triggers higher sending rate Bottleneck High Capacity Core Network b2b2 b1b1 Smart Router Pros: Client transparency, Server coordination-free, Stateless smart router

page 5April 29, 2003 Packet Video Workshop 2003, Nantes, France Testbed Servers Receiver bottleneck 100 Mbps 10 Mbps Buffer occupancy (s) Label Smart Router: - mostly priority queuing (smallest b first) - every 20 packets perform round-robin Encoding buffer Occupancy into TOS in IP header

page 6April 29, 2003 Packet Video Workshop 2003, Nantes, France Results: First-In-First-Out (FIFO) deadline pause Buf data Large buffer spread

page 7April 29, 2003 Packet Video Workshop 2003, Nantes, France Results: Playback Buffer Equalization (PBE) Small buffer spread

page 8April 29, 2003 Packet Video Workshop 2003, Nantes, France 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 Servers Receiver bottleneck 10 ms 10 Mbps 20 ms 40 ms 80 ms

page 9April 29, 2003 Packet Video Workshop 2003, Nantes, France pauses Results: NS Simulation Results load pauses Moderate loadOver-load 10x reduction no reduction FIFO PBE Improves fairness!

page 10April 29, 2003 Packet Video Workshop 2003, Nantes, France 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: 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

page 11April 29, 2003 Packet Video Workshop 2003, Nantes, France 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