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Class-Based Queueing: Principles and Link Sharing for Effective Data Management

This document explores Class-Based Queueing (CBQ) as a framework for link sharing, detailing its principles and application in distributing bandwidth according to established hierarchies. Key goals include ensuring that each class, whether interior or leaf, receives its allocated bandwidth during sufficient demand. CBQ offers advantages such as bandwidth protection and priority support for real-time, delay-sensitive services, along with guidelines for regulating classes based on bandwidth utilization. The document also addresses open questions regarding traffic classification and server interaction.

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Class-Based Queueing: Principles and Link Sharing for Effective Data Management

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  1. WebTP Meeting (10/18/1999) Link Sharing Principles Class Based Queueing (CBQ) S. Floyd and V. Jacobson - ToN 1995

  2. Goals • Link Sharing: • Distribute bandwidth according to some hierarchy

  3. Goals • Link Sharing: • Distribute bandwidth according to some hierarchy • CBQ: A unified framework for supporting • Link Sharing • Real-time (delay sensitive) services

  4. Link Sharing between Traffic Classes

  5. Link Sharing Interior Class Leaf Class

  6. Link Sharing Level 3 Level 2 Level 1

  7. Link Sharing between Users

  8. Link Sharing between Users

  9. Link Weights Allocation • Static • Dynamic • network condition • user preferences • adding/removing connections

  10. Link Sharing Goal Over appropriate time-intervals, each interior or leaf class should receive its allocated bandwidth (given sufficient demand)

  11. Link Sharing between Users

  12. Link Sharing between Traffic Classes

  13. CBQ Fundamentals • Scheduling • General scheduler • Link sharing scheduler

  14. CBQ Fundamentals • Scheduling • General scheduler • Link sharing scheduler • Classes • Unregulated • Regulated

  15. CBQ Fundamentals • Scheduling • General scheduler • Link sharing scheduler • Classes • Unregulated • Regulated • Bandwidth Estimator • Exponential weighted moving average

  16. Classes - Definitions • Bandwidth Utilization • Overlimit • Underlimit • At-limit

  17. Classes - Definitions • Bandwidth Utilization • Overlimit • Underlimit • At-limit • Satisfaction • Unsatisfied: Underlimit + persistent backlog • Satisfied

  18. Link Sharing - Guidelines • A class stays unregulated if 1. It is not overlimit

  19. Link Sharing - Guidelines • A class stays unregulated if 1. It is not overlimit, OR 2. It has a not-overlimit ancestor at level j, andthere are no unsatisfied classes in the link-sharing structure at levels lower than j.

  20. Link Sharing - Guidelines • A class stays unregulated if 1. It is not overlimit, OR 2. It has a not-overlimit ancestor at level j, andthere are no unsatisfied classes in the link-sharing structure at levels lower than j. • Otherwise it should be regulated

  21. Link Sharing - Guidelines • A class stays unregulated if 1. It is not overlimit, OR 2. It has a not-overlimit ancestor at level j, andthere are no unsatisfied classes in the link-sharing structure at levels lower than j. • Otherwise it should be regulated • Remark: The root is always not-overlimit

  22. Examples

  23. Example 1 Under Over

  24. Example 2 Under Over

  25. Example 2 Backlog

  26. Example 2 Unsatisfied Unsatisfied

  27. Example 2 Unsatisfied Unsatisfied Regulated

  28. Example 3 Unsatisfied Regulated Overlimit + Backlog

  29. CBQ - Pros • Bandwidth protection • Hierarchy • Support of priorities for delay-sensitive services • flexibility

  30. CBQ - Cons • No deterministic/statistical guarantees on performance measure (delay, throughput) • Many tunable parameters with unknown effects

  31. CBQ and WebTP • Allow sharing of multiple connections with different requirements within a pipe • Allow sharing between multiple users or protocols (FAT pipes) • Open questions: • Traffic classification, admission control • Variable-rate server • interaction with the ADU scheduler

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