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

Goals Link Sharing: –Distribute bandwidth according to some hierarchy

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

Link Sharing between Traffic Classes

Link Sharing Leaf Class Interior Class

Link Sharing Level 1 Level 2 Level 3

Link Sharing between Users

Link Weights Allocation Static Dynamic –network condition –user preferences –adding/removing connections

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

Link Sharing between Users

Link Sharing between Traffic Classes

CBQ Fundamentals Scheduling –General scheduler –Link sharing scheduler

CBQ Fundamentals Scheduling –General scheduler –Link sharing scheduler Classes –Unregulated –Regulated

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

Classes - Definitions Bandwidth Utilization –Overlimit –Underlimit –At-limit

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

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

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

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

Link Sharing - Guidelines A class stays unregulated if 1. It is not overlimit, OR 2. It has a not-overlimit ancestor at level j, and there 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

Examples

Example 1 Under Over

Example 2 Under Over

Example 2 Backlog

Example 2 Unsatisfied

Example 2 Regulated Unsatisfied

Example 3 Unsatisfied Overlimit + Backlog Regulated

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

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

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