Architectural Considerations for Playback of Quality Adaptive Video over the Internet

1. Architectural Considerations for Playback of Quality Adaptive Video over the Internet Reza Rejaie AT&T Labs – Research Menlo Park, CA. http://www.research.att.com/~reza ICON 2000 In collaboration with Mark Handley(ACIRI at ICSI) Deborah Estrin (ISI/USC) Reza Rejaie AT&T Labs - Research

2. Motivation • Rapid growth in client-server streaming over the Internet • Internet applications should deploy end-to-end congestion control • Streaming applications require QoS • Most of the existing solutions do not properly integrate congestion control into Internet streaming applications Reza Rejaie AT&T Labs - Research

3. Unicast Streaming Applications • Delay-sensitive • Semi-reliable • Rate-based • Require QoS from the end-to-end point of view Encoder Adaptation Source Server Internet TCP TCP Buffer Decoder Display Reza Rejaie AT&T Labs - Research

4. Goal of this paper • To provide high level architectural insights in the design of unicast Internet streaming applications • Guidelines for Internet streaming application designers Reza Rejaie AT&T Labs - Research

5. Outline • Design principles for Internet applications • Key components • Design space for key components of Internet streaming applications • An architecture • Generalizing the architecture • Conclusion & future directions Reza Rejaie AT&T Labs - Research

6. Design Principles for Internet App. • Social behavior • Being adaptive • Recovery from losses Reza Rejaie AT&T Labs - Research

7. Design Principles Social Behavior • Network resources are shared • End-systems should adjust their tx rate based on state of the network • Rapidly decrease when congestion occurs • Periodically increase to probe for spare capacity • End-to-end Congestion Control • Congestion control should result in fairness, stability and high utilization • Congestion control is network-dependent Reza Rejaie AT&T Labs - Research

8. Design Principles Being Adaptive • Bandwidth heterogeneity • Shared resources • Internet applications should be able to: • operate over wide range of available bw • cope with wide & unpredictable variations in bw • Internet applications should be quality adaptive • Quality adaptation is application-specific Reza Rejaie AT&T Labs - Research

9. Design Principles Recovery from Loss • Packets are pseudo-randomly lost in the network mainly due to congestion • Internet applications should be able to recover from losses • to meet required level of reliability • Error control • Error control is application-specific Reza Rejaie AT&T Labs - Research

10. Key Components • Congestion Control(CC) • Quality Adaptation(QA) • Error Control(EC) • What is the design space for each key component in the context of Internet streaming applications? Reza Rejaie AT&T Labs - Research

11. Design Space Congestion Control • Challenge: to design an effective Increase, Decrease algorithm? • Goal: to be network-friendly • if TCP traffic dominates => TCP-friendly • Additive Inc., Multiplicative Dec. • Slope of increase & decreasing factor • Some existing TCP-friendly CC schemes: • SCP, LDA, RAP, TFRC • Performing CC results in unpredictable and potentially wide variations in bandwidth Reza Rejaie AT&T Labs - Research

12. Design Space/Quality Adaptation Mechanisms to Adjust Quality • Adaptive encoding • CPU-intensive • Switching between multiple encoding • High storage requirement • Layered encoding • Inter-layer decoding dependency • Suited for multimedia proxy caching Reza Rejaie AT&T Labs - Research

13. Design Space Quality Adaptation • Adjust delivered quality with long-term changes in available bandwidth • receiver buffering only absorbs short-term changes in bandwidth • Challenge: frequent changes in delivered quality degrades perceptual quality • encoding-specific • More buffering allows smoother variations in delivered quality • Buffering strategy? • QA is the least understood aspect of streaming applications Reza Rejaie AT&T Labs - Research

14. Design Space Error Control • Streaming applications require quality instead of complete reliability • Techniques for loss repair are well understood • Appropriate EC mechanism depends on: • Required level of reliability by encoding • Accepted delay for loss recovery • Expected/measured loss pattern • EC & QA should share the available bw in order to maximize delivered quality • Encoding-specific Reza Rejaie AT&T Labs - Research

15. End-to-End Architecture Error Control Quality Adaptation Cong. Control Acker Playback Buffer Internet Buffer Manager Buffer Manager Transmission Buffer Decoder Archive Adaptation Buffer Server Client Data path Control path Reza Rejaie AT&T Labs - Research

16. Generalizing the Architecture • Architecture is generic. Knowing: • Designated func. to each component • Design space for each component • Effect of each design choice on other components • Replace algorithms in each module • Address implications on other modules • Examples: • Use a new CC mechanism => Adjust details of QA • Change EC mechanism => Adjust bw sharing between QA & EC Reza Rejaie AT&T Labs - Research

17. Natural Design Steps • Select a network-friendly CC scheme • Select an EC mechanism that satisfies application requirements • Design a QA mechanism that bridges the gap between app. requirements & CC • maximizes perceptual quality for a given encoding • Design a bandwidth sharing strategy for QA and EC mechanisms Reza Rejaie AT&T Labs - Research

18. Conclusion • High level architectural insights in design of Internet streaming app. • Key components => designated func. • Design space of each component • Inter-dependency among key components • Set of high level design guidelines for streaming applications • Applicable to live but non-interactive streaming applications Reza Rejaie AT&T Labs - Research

19. Future Directions • Prototyping a sample architecture • MPEG4 encoding • Layered QA • TCP-friendly • Retx-based error control • Extending the arch to include multimedia proxy caches (mcaches) • To deliver high quality streams in a large scale • Utility-based QA and • More details: http://www.research.att.com/~reza Reza Rejaie AT&T Labs - Research