Department of Computer Science & Engineering The Chinese University of Hong Kong Constructing Robust and Resilient Framework for Cooperative Video Streaming Louis Shi Lu, Microsoft Shanghai Michael R. Lyu, The Chinese University of Hong Kong Presented by: Jiangchuan Liu, Simon Fraser University 2006 International Conference on Multimedia & Expo July 9-12, 2006 Toronto, Ontario, Canada

Department of Computer Science & Engineering The Chinese University of Hong Kong Outline Introduction Motivation Related work Challenges The p2p streaming framework Overview Peer control overlay Data transfer protocol Peer local optimization Topology optimization Experiments Empirical experience in CUHK Experiments on PlanetLab Conclusion

Department of Computer Science & Engineering The Chinese University of Hong Kong Motivation Video over Internet is pervasive today New challenge: on-line TV broadcasting fails on traditional client-server architecture  500Kbps, theoretical limitation for a 100Mbps Server is 200 concurrent users Is there any efficient way to support video broadcasting to a large group of network users?

Department of Computer Science & Engineering The Chinese University of Hong Kong Why Client/Server fail Traditional client/server solution is not scalable 3 bottlenecks  Server load The server bandwidth is the major bottleneck  Edge capacity One connection to one client The connection may degrade  End to end bandwidth Scalability?

Department of Computer Science & Engineering The Chinese University of Hong Kong Related work Peer-to-Peer file sharing system  BitTorrent, eMule, DC++  Peer collaborate with each other  Without (or with very little) needs to dictated resources Why not suitable for video broadcasting  Without in-bound rate requirement  Without real-time requirement

Department of Computer Science & Engineering The Chinese University of Hong Kong Related work Content Distribution Network (CDN)  Install a lot of dictated servers on the edge of the Internet  Requests are directed to the best servers  Very high cost on purchasing servers Tree-based overlay  Coopnet, NICE  Rigid structure, not robust to node-failures and network condition changes Other Mesh-based systems  CoolStreaming, pplive, ppStream

Department of Computer Science & Engineering The Chinese University of Hong Kong Challenges Bandwidth  In-bound data bandwidth is not less than the video rate  In-bound bandwidth should not have large fluctuations Network dynamics  Network bandwidth and latency may change  Peer nodes may leave and join at any time  Peer nodes may fail or shut down Real-time requirement  All media packets must be fetched before its playback deadline

Department of Computer Science & Engineering The Chinese University of Hong Kong Goals For each peer:  Provide satisfying in-bound bandwidth  Assign its traffic in a balanced and fair manner For the whole network:  Keep it as one-piece while peer may fail/leave  Keep the shape of the overlay from degrading  Keep the radius small

Department of Computer Science & Engineering The Chinese University of Hong Kong P2P based solution: Overview Collaboration between client peers Source server alleviated Better scalability Better reliability

Department of Computer Science & Engineering The Chinese University of Hong Kong Infrastructure Video source  Windows media encoder, RealProducer …  Source peer Takes content from the video streaming server and feed it to the p2p network Wrap packets, add seq no. Look-up service (tracker)  Track the peers viewing each channel  Help new peers to join the broadcast Client peers (organized into a random graph)  Schedule and dispatch the video packets  Adapt to the network condition  Optimize the performance  Support the local video player

Department of Computer Science & Engineering The Chinese University of Hong Kong Peer join Peer join: Obtain a peer list Establish connections  Neighborhood selection Random IP matching Peer depth Peer performance Register its own service

Department of Computer Science & Engineering The Chinese University of Hong Kong The connection pool “ No one is reliable ”  A peer tries its best for better performance  A peer maintains a pool of active connections to peers  A peer keeps trying new peers when the incoming bandwidth is not reached  A peer keeps trying new connections after that, but in a slower manner  Update peer list  Others may establish new connections

Department of Computer Science & Engineering The Chinese University of Hong Kong Connection pool maintenance For each connection, define connection utility  Recent bandwidth (I/O)  Recent latency  Peer depth  Peer recent progress When connections are more than  Drop several bad connections Out-rate bound Peer depth (distance to source)

Department of Computer Science & Engineering The Chinese University of Hong Kong The peer control overlay Random-graph shape  Evolving with time  Radius: will not degrade since all peers are trying to minimize its depth  Integrity: will not be broken into pieces Data transfer  The data transfer path is determined from the control overlay  Each data packet is transferred along a tree  Determined just-in-time from the control overlay

Department of Computer Science & Engineering The Chinese University of Hong Kong Data transfer protocol Receiver driven  While exchanging data, data availability information is also exchanged  The data receiver determine which block from which neighbor Driven by data distribution information  Peer knows where the missing data is  Peer issues data request Peer synchronization  Content fetching progress

Department of Computer Science & Engineering The Chinese University of Hong Kong Data transfer protocol Data transfer load scheduling Several factors:  Latency  Bandwidth  Data availability Connection status (busy, free)  Data request issued (->busy)  Data arrived (->free) Scheduling time: on data arrival  Get a packet that is recent available  Estimate the latency  The playback deadline is before the expected latency

Department of Computer Science & Engineering The Chinese University of Hong Kong Data transfer protocol Connection status Busy standby Data request issued data arrived When data arrive:  Measure the latency of the previous packet  Get a weighted delay  Find if the packet whose playback deadline is ok for that delay  Issue request (  busy) Critical block

Department of Computer Science & Engineering The Chinese University of Hong Kong Data transfer protocol Multicast tree  Each data packet would not go by a peer twice  For each data packet, a multicast tree is constructed  The tree is built just-in-time To adapt to the transient properties of the network links  Each data packet may have different trees

Department of Computer Science & Engineering The Chinese University of Hong Kong Neighborhood management Performance monitoring:  Measured every once an interval (e.g. 10 sec.)  Avg. in-bound data rate  Avg. out-bound data rate  Avg. data packet latency Neighborhood goodness Neighborhood number  Lower bound of Nb  Upper bound of Nb

Department of Computer Science & Engineering The Chinese University of Hong Kong Peer control protocol Consideration: Data distribution and performance  While in-bound data rate is not enough  While neighbor number is lower than lower bound Establish new connections  While neighbor number is higher than upper bound Discard the worst connection The benefit is two-fold: both sides release something bad.

Department of Computer Science & Engineering The Chinese University of Hong Kong Overlay integrity Peers may leave or fail The overlay shall not be broken into pieces Maintain the connectivity of the overlay Solution: Peers try to connect to neighbors with lower depth Since each peer tries to lower its depth, the probability for (articulation) critical points to occur becomes small …… Source peer, depth = 0

Department of Computer Science & Engineering The Chinese University of Hong Kong Overlay integrity Playback progress difference:  Higher depth difference  higher playback progress difference  The attempt to reduce local peer depth may reduce that progress difference

Department of Computer Science & Engineering The Chinese University of Hong Kong Experiments Planet-Lab  300+ nodes deployed worldwide Performance test  Data smoothness The ratio of the data packets that can be fetched before its playback deadline  Dynamic experiment Peer sojourn time is exponential distributed (unstable) A. All peers are unstable B. A potion of the peers are unstable  Overlay size  Peer local buffer size

Department of Computer Science & Engineering The Chinese University of Hong Kong Static performance The impact of overlay size and peer buffer size

Department of Computer Science & Engineering The Chinese University of Hong Kong Dynamic performance The impact of peer stability The peers ’ sojourn time is exponential distributed The longer the mean, the more stable the peers are

Department of Computer Science & Engineering The Chinese University of Hong Kong Observations More users, better performance Resilient in dynamic network environment Robust to peer join-leave More stable, better performance Bigger buffer increases coherence

Department of Computer Science & Engineering The Chinese University of Hong Kong Benefits Low cost:  Without any extra hardware expenditure  Purely software solution Scalable: can support theoretically infinite users Reliable and resilient to user join/leave  Multiple connections  Intelligent content scheduling between peers  Quick adapt to the change of network conditions Solution for:  Low-cost large scale live broadcast

Department of Computer Science & Engineering The Chinese University of Hong Kong Conclusions In this presentation, we have:  Introduced the challenges in the p2p streaming system  Defined several goals that a p2p system to support real- time video broadcast  Proposed a solution for large-scale p2p video streaming service Future work  Distributed look-up service  Content copyright protection (Identity authentication, data encryption)  Overlay topology control (Traffic localization)  Possible VOD system based on this infrastructure