Flow Control and Reliability Control in WebTP Ye Xia 10/24/00.
WebTP Meeting (10/18/1999) Link Sharing Principles Class Based Queueing (CBQ) S. Floyd and V....
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Transcript of 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