Reza Rejaie

1
Architectural Considerations for Playback of
Quality Adaptive Video over the Internet

• Reza Rejaie
• ATT 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)

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

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
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

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

6
Design Principles for Internet App.

• Social behavior
• Being adaptive
• Recovery from losses

7
Social Behavior
Design Principles

• 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

8
Being Adaptive
Design Principles

• 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

9
Recovery from Loss
Design Principles

• 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

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?

11
Congestion Control
Design Space

• Challenge to design an effective Increase,
  Decrease algorithm?
• Goal to be network-friendly
• if TCP traffic dominates gt 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

12
Mechanisms to Adjust Quality
Design Space/Quality Adaptation

• Adaptive encoding
• CPU-intensive
• Switching between multiple encoding
• High storage requirement
• Layered encoding
• Inter-layer decoding dependency
• Suited for multimedia proxy caching

13
Quality Adaptation
Design Space

• 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

14
Error Control
Design Space

• 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

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
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 gt Adjust details of QA
• Change EC mechanism gt Adjust bw sharing between
  QA EC

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

18
Conclusion

• High level architectural insights in design of
  Internet streaming app.
• Key components gt 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

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