Providing Controlled Quality Assurance in Video Streaming across the Internet Yingfei Dong, Zhi-Li Zhang and Rohit Rakesh Computer Networking and Multimedia Research Group Dept. of Computer Science and Engineering University of Minnesota

Motivations  The Internet: Service-Oriented Network  Service Requirement: End-to-End QoS  Service Delivery System: Content Distribution Networks  On-Demand Large Stored Video Streaming --- High Bandwidth requirements oWide-Area Stored Video Delivery System Common Approach --- Proxy Server System

Proxy Content Delivery Architecture Proxy Server + VPN

Virtual Private Network(VPN)  Network- Layer VPN not Leased-Lines, but Service Level Agreements, oCoarse-grain average : T3 VPN, 99.9% available, 120 ms average RTT monthly average oNo rate guarantee for individual flows oNo packet loss/delay guarantee Application-level Traffic Management is needed.

System Constraints and Challenge  Constraints  Limited Buffer Space v.s. Huge Video Volume Streaming from central servers is required.  Aggregate B/W v.s. Individual Flow Requirement Bandwidth management must be present.  Stringent Timing v.s. No Delay/Loss Guarantee Reliably prefetching is necessary.  Challenge oQuality Assurance across Best-Effort Networks

Outline  Motivations and Background  Staggered Two-Flow Streaming  Control Bandwidth Sharing  Conclusion and Current Work

Objective and Approaches Controlled Quality Assurance in streaming on the best-effort Internet by exploiting o Application Information, such as the priority structure in videos (frame-dependency), and flow rate o Coarse-grain bandwidth assurance of VPN o Storage / processing capacity of proxy servers

Priority Structure in Videos Two flows in a video session:  A Reliable Flow for essential data (e.g., I frames)  An Unreliable Flow for enhanced data (e.g., P/B)

Segment and Staggered Delivery The Reliable Flow is one segment ahead

Staggered Two-Flow Streaming  Reliable Flow: I-frame segments, prefetched and cached at proxy.  Unreliable Flow: P/B-frames segments, real-time delivery subject to adaptation when congestion in the soft VPN pipe.  Merging both flows at Proxy Server, then send to clients

Prefetching Cache Illustration To user k k+1 Unreliable Delivery Reliable Prefetching k k+1 k k Proxy ServerCentral Server best-effort VPN Merging k Competition!!

Interesting Issues  Data Plane Issues   Bandwidth Competition  Unreliable-Flow  Unreliable-Flow Rate Adaptation  Control Plane Issues o o Application-aware Resource Management e.g., Admission Control, VPN management, Video placement and migration  Implementation Issues

Application-Aware Controlled Bandwidth Sharing Stable and Predictable transport protocols  Controlled TCP (cTCP)  Application-aware throughput control: A variant of TCP Reno using a simple TCP model to regulate the injection rate.  Rate-Controlled UDP(rUDP)  Generating Piece-wise CBR traffic: Extending UDP on FreeBSD with a periodical injection mechanism limited by a leaky-bucket Both are implemented in FreeBSD kernel.

TCP: reliable but not fit to our setting  Sliding Window (W) Injection Control W packets per RTT  AIMD oFluctuation: Greedily Increase, back off to half when loss oFairness regardless of flow requirements Packet losses even when sufficient B/W

cTCP: a variant of TCP Reno  Flow Target Rate T cTCP  Target Window Size W target ousing a simple TCP bandwidth model to limit the injection to the flow requirement oIf packet loss oelse No slow-start. No packet losses when given sufficient B/W.

Two cTCP Flows v.s. Two TCP Flows On a 64KBps link, the 1st flow with a target rate 13KBps starts 12 seconds earlier than the 2nd flow with a target rate 27KBps

Experimental Environment  Controlled Testbed on FreeBSD4.1  3 PCs on a dedicated Gbps Ethernet switch  A central server and a proxy server  A bandwidth-and-delay control unit emulates a VPN pipe in between, running IP Dummynet  Testing Video: a 60-minute MPEG-2 video clip Target Rate of I frames, 52 KBps Target Rate of P/B frames, 200 KBps

Multiple Sessions: cTCP/rUDP v.s. TCP/rUDP RXs in TCP or cTCP rUDP Losses A video session of two flows (cTCP/rUDP or TCP/rUDP)

Multiple Sessions (Arrival / Departure) : cTCP/rUDP v.s. TCP/rUDP C = Max_Rate  Starting with 4 sessions;  Then, add one more;  Later, terminate two. Compare the variations of packet RXs and losses

Summary of Controlled BW Sharing  Practical quality assurance of the essential data over best-effort networks  None / Low Packet Losses  Stable, Predictable System Performance Providing chances for applying simple application-aware traffic management  TCP-firendly: do not grab BW from others  Patent Pending

Current and Future Work Quality Assurance issues in Service-Oriented Networks  Scalability in data plane  Aggregation at the levels of video, session, and flow.  Network parameters sharing among sessions.  Service-Oriented B/W Management in control plane  Application-ware admission control  Proxy Placement utilizing the topology info.  Proxy Caching and Video Placement / Migration.  High-Quality VOD on Cable Broadband Networks.