CSIT560CSIT560Internet Infrastructure:Internet Infrastructure:Switches and RoutersSwitches and Routers

Active Queue ManagementActive Queue Management

Presented By: Gary Po, Henry Hui and Kenny Chong

AgendaAgenda

Why AQM?Why AQM? In ConsiderationsIn Considerations AQM AlgorithmsAQM Algorithms Commercial EffortCommercial Effort ConclusionsConclusions

Why AQM?Why AQM?

Two Classes of Router Algorithms for Two Classes of Router Algorithms for Congestion ControlCongestion Control

What is Congestion?What is Congestion? Congestion avoidance in TCP, is it Congestion avoidance in TCP, is it

good enough?good enough? Our Choice :Our Choice :

Active Queue ManagementActive Queue Management

What do we consider when What do we consider when implementing AQM?implementing AQM?

QoSQoS– Keep Average queue size smallKeep Average queue size small– Bounded DelayBounded Delay

Link UtilizationLink Utilization– Avoid Global SynchronizationAvoid Global Synchronization– Absorbs bursts without dropping packetsAbsorbs bursts without dropping packets

FairnessFairness– Punishes misbehaving flowsPunishes misbehaving flows– Prevent bias against bursty connectionsPrevent bias against bursty connections

ImplementationImplementation– Ease of ConfigurationsEase of Configurations– Buffer Size Requirement (Large or Small)Buffer Size Requirement (Large or Small)– Per-flow State InformationPer-flow State Information– Computational OverheadComputational Overhead

AQM AlgorithmsAQM Algorithms

FIFO + Drop TailFIFO + Drop Tail

Problems:Problems:– No isolationNo isolation– No policingNo policing– Large queues for high utilizationsLarge queues for high utilizations– Synchronization problemSynchronization problem– Lock-out problemLock-out problem

Define Two Threshold Values

RED (Random Early Detection)RED (Random Early Detection)

FIFO schedulingFIFO scheduling

Min threshMax thresh

Average queuelength

Make Use of Average Queue LengthCase 1:

Average Queue Length < Min. Thresh ValueAdmit the New Packet

RED (Cont’d)RED (Cont’d)

Min threshMax thresh

Average queuelength

Case 2: Average Queue Length betweenMin. and Max. Threshold Value

p

1-p

Admit the New Packet With Probability p…

p

1-p

Or Drop the New Packet With Probability 1-p

RED (Cont’d)RED (Cont’d)

Min threshMax thresh

Average queuelength

Case 3: Avg. Queue Length > Max. Threshold Value

New Packet will be droppedAs no new packets can be admitted,the average queue length decreases.

Until the average queue length drops belowthe max threshold value

New packet could be admitted with a probability p…

or being dropped with a probability 1-p…

RED Flow DiagramRED Flow Diagram

RED (Cont’d)RED (Cont’d)

Queue Size versus TimeQueue Size versus Time

0 5 10 15 20 25 30 35 40 45 500

50

100

150

200

250CHOKe: Queue Size

Time (Seconds)

Siz

e of

Que

ue (

No.

of

Pac

kets

)

Average Queue SizeCurrent Queue Size

Delay is bounded

Delay is bounded

Global Synchronization solvedGlobal Synchronization solved

RED: Queue Size

Unfairness of REDUnfairness of RED

0 5 10 15 20 25 30 350

100

200

300

400

500

600

700

800

900

1000RED's Throughput

Flow Number

Thr

ough

put

(Kbp

s)Idea Fair ShareRED's Throughput

Unresponsive Flow (such

as UDP)

Unresponsive Flow (such

as UDP)

32 TCP Flows1 UDP Flow

32 TCP Flows1 UDP Flow

An unresponsiveflow occupies over 95% of bandwidth

An unresponsiveflow occupies over 95% of bandwidth

CHOKeCHOKe(CHOose and Keep)(CHOose and Keep)

Based on REDBased on RED SimpleSimple Designed for fairnessDesigned for fairness Penalize the unresponsive flowPenalize the unresponsive flow

CHOKe (Cont’d)CHOKe (Cont’d)

MechanismMechanism

CHOKe (Cont’d)CHOKe (Cont’d)

Min threshMax thresh

Average queuelength

Case 1: Average Queue Length < Min. Thresh Value

Admit the New Packet

CHOKe (Cont’d)CHOKe (Cont’d)

Min threshMax thresh

Average queuelength

p

1-p

Case 2: Avg. Queue Length is between Min. and Max. Threshold Values

A packet is randomly chosen from the queue to compare with the new arrival packet

If they are from different flows, the samelogic in RED applies

If they are from the same flow, both packets will be dropped

CHOKe (Cont’d)CHOKe (Cont’d)

Min threshMax thresh

Average queuelength

Case 3:Avg. Queue Length > Max. Threshold Value

A random packet will be chosen forcomparison

If they are from different flows, the new packet will be droppedIf they are from the same flow,

both packets will be dropped

Evaluate CHOKe’s Evaluate CHOKe’s performance using NS-2performance using NS-2

Simulation ScenarioSimulation Scenario

10Mbps

1Mbps

10Mbps

UDP

TCP

UDP

TCP

source destination

router router

• Topology: Dumb-bell• Metrics: throughput and queue size

Performance of CHOKePerformance of CHOKe

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35

40

Flow Number

Thr

ough

put

(Kbp

s)

CHOKe: Throughput Per Flow

Ideal Fair ShareCHOKe

Fair Share Level

Fair Share Level

Bandwidth is evenly shared

Bandwidth is evenly shared

Unresponsive Flow (UDP)Unresponsive Flow (UDP)

32 TCP Flows1 UDP Flow

32 TCP Flows1 UDP Flow

ParametersParameters

Number of responsive/unresponsive Number of responsive/unresponsive flowsflows

Transfer rate of different flowsTransfer rate of different flows Number of random candidates Number of random candidates

chosen for comparisonchosen for comparison

CHOKe SimulationCHOKe Simulation

Different Parameters, different performanceDifferent Parameters, different performance

0 5 10 15 20 25 30 350

50

100

150

200

250CHOKe 1: Throughput Per Flow

Flow Number

Thr

ough

put

(Kbp

s)

Ideal Fair ShareCHOKe 1

0 5 10 15 20 25 30 350

50

100

150CHOKE 2: Throughput with 3 UDP with Different Rate

Flow Number

Thr

ough

put

Ideal Fair ShareCHOKE 2

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35

40

45

50CHOKe 2: Throughput Per Flow (with 4x UDP rate)

Flow Number

Thr

ough

put

(Kbp

s)

Ideal Fair ShareCHOKe 2

0 5 10 15 20 25 30 350

50

100

150

200

250CHOKe 2: Throuhput Per Flow (with 3 UDP Flows)

Flow Number

Thr

ough

put

(Kbp

s)

Ideal Fair ShareCHOKe 2

CHOKe-132 TCPs1 UDP

CHOKe-132 TCPs1 UDP

CHOKe-232 TCPs,1 UDP of high rate

CHOKe-232 TCPs,1 UDP of high rate

CHOKe-232 TCPs,3 UDPs of

different rate

CHOKe-232 TCPs,3 UDPs of

different rate

CHOKe-232 TCPs,3 UDPs of same rate

CHOKe-232 TCPs,3 UDPs of same rate

Evolutions of AQM AlgorithmsEvolutions of AQM Algorithms

FIFO+FIFO+DropTailDropTail

REDRED

FREDFRED

CHOKeCHOKe SACSAC

BLUEBLUE SFBSFB

SREDSRED

REM, AVQ, PI ControllerREM, AVQ, PI Controller REDRED– MeritsMerits

Early congestion Early congestion detectiondetection

No bias against No bias against bursty trafficbursty traffic

No global No global synchronizationsynchronization

– DrawbacksDrawbacks Difficulty in Difficulty in

parameter settingparameter setting Insensitivity to traffic Insensitivity to traffic

load and drain ratesload and drain rates

REDRED– MeritsMerits

Early congestion Early congestion detectiondetection

No bias against No bias against bursty trafficbursty traffic

No global No global synchronizationsynchronization

– DrawbacksDrawbacks Difficulty in Difficulty in

parameter settingparameter setting Insensitivity to traffic Insensitivity to traffic

load and drain ratesload and drain rates

SREDSRED– MeritsMerits

Stabilized queue Stabilized queue occupancyoccupancy

Protection from Protection from misbehaving flowsmisbehaving flows

– DrawbacksDrawbacks Some per-flow state Some per-flow state

(zombie list)(zombie list) RED disadvantagesRED disadvantages

SREDSRED– MeritsMerits

Stabilized queue Stabilized queue occupancyoccupancy

Protection from Protection from misbehaving flowsmisbehaving flows

– DrawbacksDrawbacks Some per-flow state Some per-flow state

(zombie list)(zombie list) RED disadvantagesRED disadvantages

FREDFRED– MeritsMerits

Good protection from Good protection from misbehaving flowsmisbehaving flows

– DrawbacksDrawbacks Per-flow statePer-flow state RED disadvantagesRED disadvantages

FREDFRED– MeritsMerits

Good protection from Good protection from misbehaving flowsmisbehaving flows

– DrawbacksDrawbacks Per-flow statePer-flow state RED disadvantagesRED disadvantages

BLUEBLUE– MeritsMerits

SimplicitySimplicity High throughputHigh throughput

– DrawbacksDrawbacks No early congestion No early congestion

detection (Pdrop detection (Pdrop updated only on updated only on queue overflow or queue overflow or link idle events)link idle events)

Slow response and Slow response and dependence on dependence on historyhistory

BLUEBLUE– MeritsMerits

SimplicitySimplicity High throughputHigh throughput

– DrawbacksDrawbacks No early congestion No early congestion

detection (Pdrop detection (Pdrop updated only on updated only on queue overflow or queue overflow or link idle events)link idle events)

Slow response and Slow response and dependence on dependence on historyhistory

REMREM– MeritsMerits

Low delay and small Low delay and small queuesqueues

Independence of the Independence of the number of usersnumber of users

– DrawbacksDrawbacks Some complexity due to Some complexity due to

parametersparameters Low throughput for Web Low throughput for Web

traffictraffic Inconsistency with TCP Inconsistency with TCP

sender mechanism; sender mechanism; works best with ECNworks best with ECN

REMREM– MeritsMerits

Low delay and small Low delay and small queuesqueues

Independence of the Independence of the number of usersnumber of users

– DrawbacksDrawbacks Some complexity due to Some complexity due to

parametersparameters Low throughput for Web Low throughput for Web

traffictraffic Inconsistency with TCP Inconsistency with TCP

sender mechanism; sender mechanism; works best with ECNworks best with ECN

LDCLDC– MeritsMerits

Sensitivity to traffic load Sensitivity to traffic load and drain rateand drain rate

Low delayLow delay Target delay achievedTarget delay achieved Intuitive parameters, Intuitive parameters,

meaningful to users meaningful to users (target delay)(target delay)

– DrawbacksDrawbacks Some complexity due to Some complexity due to

parametersparameters Low throughput in some Low throughput in some

casescases

LDCLDC– MeritsMerits

Sensitivity to traffic load Sensitivity to traffic load and drain rateand drain rate

Low delayLow delay Target delay achievedTarget delay achieved Intuitive parameters, Intuitive parameters,

meaningful to users meaningful to users (target delay)(target delay)

– DrawbacksDrawbacks Some complexity due to Some complexity due to

parametersparameters Low throughput in some Low throughput in some

casescases

Commercial Efforts & Commercial Efforts & ConclusionConclusion

Commercial Efforts & Commercial Efforts & Conclusion (Cont’d)Conclusion (Cont’d)

““ Applying AQM over 3G wireless Applying AQM over 3G wireless network” – a paper supported by network” – a paper supported by Motorola Canada Ltd. (Mar. 2003)Motorola Canada Ltd. (Mar. 2003)

3G network, real-time applications 3G network, real-time applications have hard time deadlines for packet have hard time deadlines for packet delivery at the receiver.delivery at the receiver.

Use AQM to avoid long queuing delay Use AQM to avoid long queuing delay and prevent expiring packets.and prevent expiring packets.

Commercial Efforts & Commercial Efforts & Conclusion (Cont’d)Conclusion (Cont’d)

AQM improves overall system AQM improves overall system performance by increasing performance by increasing throughput and reducing end-to-end throughput and reducing end-to-end delay.delay.

Commercial Efforts & Commercial Efforts & Conclusion (Cont’d)Conclusion (Cont’d)

““ Effect of AQM on Web Effect of AQM on Web Performance” – a paper supported by Performance” – a paper supported by Cisco Systems and IBM. (Aug. 2003)Cisco Systems and IBM. (Aug. 2003)

Proportional Integrator (PI) controllerProportional Integrator (PI) controller Random Exponential Marking (REM)

controller Adaptive Random Early Detection (ARED). IETF proposed standard :

Explicit Congestion Notification (ECN)

Commercial Efforts & Commercial Efforts & Conclusion (Cont’d)Conclusion (Cont’d)

ECN has significant impact with AQM ECN has significant impact with AQM scheme in web performance.scheme in web performance.

Many researches and efforts are Many researches and efforts are going on in the field of AQM.going on in the field of AQM.

Simple and Easy to implement Simple and Easy to implement