1. A Utility-based Approach to Scheduling Multimedia Streams in P2P Systems Fang Chen Computer Science Dept. University of California, Riverside fchen@cs.ucr.edu

2. Fang ChenUniv. of California, Riverside2 Roadmap What is a P2P system What is a P2P system System model System model Optimization problem Optimization problem Related work Related work Current status Current status

3. Fang ChenUniv. of California, Riverside3 Physical Network Overlay Network What is a Peer-to-Peer (P2P) System ? Overlay network built on top of a large number of heterogeneous computers Attractive for large scale distributed applications

4. Fang ChenUniv. of California, Riverside4 P2P Systems today Unstructured P2P systems Gnutella, Kazaa, etc. Focus on object sharing (e.g., files, video clips) Search objects by flooding query messages Structured P2P systems Maintain topology structures using distributed hash tables (DHTs) Message routing to a neighbor with the closest key Minimize number of hops (typically O(logN) )

5. Fang ChenUniv. of California, Riverside5 Why Multimedia Streaming in P2P? Multimedia streaming is necessary for Video conference applications Collaborative applications Audio/video broadcasting

6. Fang ChenUniv. of California, Riverside6 Challenges of Distributed Real- Time Multimedia Applications Satisfy end-to-end QoS requirements of real-time multimedia tasks (e.g. delay, jitter, drop rate, etc.) Support heterogeneous users Bandwidth constraints Computing power constraints Software constraints Support multimedia tasks with both computation and communication requirements (e.g., transcoding tasks) Streaming data may need to be processed before it is delivered to end users

7. Fang ChenUniv. of California, Riverside7 Steps for Multimedia Streaming Service paths constructed during initialization phase Powerful nodes must provide computation services Transcoding, encryption, watermarking, etc. Resources must be managed end-to-end to satisfy the QoS requirements of competing tasks Transcoder Video source Receiver Video playback in P2P environment. Data from video source needs transcoding service before reaching the thin client

8. Fang ChenUniv. of California, Riverside8 System Model Each multimedia stream consists of periodical independent tasks (e.g. GOP transcoding in MPEG streams) with period Weight set to differentiate tasks based on importance Each task requires an operation, associated with QoS levels With QoS level, has a utility values and resource requirements

9. Fang ChenUniv. of California, Riverside9 System Model (cont.) CPU offers cycles every second, each communication link k has an available bandwidth of A 0/1 function is derived for each task, indicating the outgoing path Transcoding Peer Stream Input Stream output

10. Fang ChenUniv. of California, Riverside10 Problem Formulation Maximize Subject to Objective: Optimize the overall utility value for the system, while ensuring that resource constraints are met

11. Fang ChenUniv. of California, Riverside11 Architecture Resource monitor measures CPU and bandwidth usage Task Scheduler selects tasks and enforces scheduling policy Connection Manager responsible for service path construction and topology maintenance Priority queue Thread scheduler Task queue Service Manager Connection Manager Scheduler Resource Monitor User Interface

12. Fang ChenUniv. of California, Riverside12 Resource Monitoring Monitor current CPU load Available CPU cycles affected by other applications running in the same host Periodical CPU profiling (e.g., /proc/ readings) Monitor available bandwidth of connections Based on TCP congestion feedback Increase estimated value periodically Peak value when TCP writes block Other techniques Packet-pair Trend of round-trip time

13. Fang ChenUniv. of California, Riverside13 Local Scheduling EDF based scheduler to assign higher priorities to selected tasks with earlier deadlines Make scheduling decisions at each peer when New tasks arrive Tasks finish execution Select task set at each peer to maximize current system utility when making scheduling decisions Rejected tasks are forwarded along their outgoing paths and will be processed by other peers

14. Fang ChenUniv. of California, Riverside14 Prototype Efforts Implementation of a prototype P2P system using Gnutella messaging protocol A simple transcoding service based on libavcodec Transcode GOPs of mpeg-1 streams Different quality levels of bit-rate reduction Deployment on Emulab, a configurable test- bed for distributed applications in wide-area environments

15. Fang ChenUniv. of California, Riverside15 Preliminary Results Operation cost of transcoding a GOP (50KB) with different quality levels Dynamic bandwidth estimation at run-time

16. Fang ChenUniv. of California, Riverside16 Related Work Layered streaming [ Cui03 ] Utility based quality adaptation [Liao01] Stream transcoding in active networks [Guo03] Server transcoding for universal access [Vidhya03] General scheduling [Brandt03], user specified scheduling of multimedia streams [Hicks03] Utility accrual scheduling [Jensen03] Adaptive service composition [Fu01, Gu2003] P2P Multimedia broadcasting [PeerCast]

17. Fang ChenUniv. of California, Riverside17 Current Status Building a P2P system that supports multimedia streaming Evaluate our method on the prototype Extensions: Minimize QoS level fluctuations of individual multimedia streams Optimization for a cluster of transcoding peers in the vicinity

18. Fang ChenUniv. of California, Riverside18 A Utility-based Approach to Scheduling Multimedia Streams in P2P Systems Fang Chen Computer Science Dept. University of California, Riverside fchen@cs.ucr.edu http://www.cs.ucr.edu/~fchen