webtp meeting (10/18/1999) link sharing principles class based queueing (cbq) s. floyd and v....

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

C onn . 150%

R T - V ideo50%

C onn . 215%

C onn . 310%

T ext, C G I25%

C onn . 412 .5%

C onn . 512 .5%

G IF , JP EG25%

L ink (P ipe)

Link Sharing

C onn . 150%

R T - V ideo50%

C onn . 215%

C onn . 310%

T ext, C G I25%

C onn . 412 .5%

C onn . 512 .5%

G IF , JP EG25%

L ink (P ipe)

Leaf Class

Interior Class

Link Sharing

C onn . 150%

R T - V ideo50%

C onn . 215%

C onn . 310%

T ext, C G I25%

C onn . 412 .5%

C onn . 512 .5%

G IF , JP EG25%

L ink (P ipe)

Level 1

Level 2

Level 3

Link Sharing between Users

U ser 150%

U ser 250%

L ink (P ipe)

Link Sharing between Users

V ideo10%

F T P40%

U ser 150%

V ideo40%

F T P10%

U ser 250%

L ink (P ipe)

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

110%

240%

U ser 150%

140%

210%

U ser 250%

L ink (P ipe)

Link Sharing between Traffic Classes

C onn . 150%

R T - V ideo50%

C onn . 215%

C onn . 310%

T ext, C G I25%

C onn . 412 .5%

C onn . 512 .5%

G IF , JP EG25%

L ink (P ipe)

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 if1. It is not overlimit

Link Sharing - Guidelines

• A class stays unregulated if1. 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 if1. 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 if1. 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

1 2

A

1 2

B

L ink

Example 1

1 2

A

1 2

B

L ink

Under

Over

Example 2

1 2

A

1 2

B

L ink

Under

Over

Example 2

1 2

A

1 2

B

L ink

Backlog

Example 2

1 2

A

1 2

B

L ink

Unsatisfied

Unsatisfied

Example 2

1 2

A

1 2

B

L ink

Regulated

Unsatisfied

Unsatisfied

Example 3

1 2

A

1 2

B

L ink

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