traffic sensitive active queue management - mark claypool, robert kinicki, abhishek kumar dept. of...

Traffic Sensitive Active Queue Management

- Mark Claypool, Robert Kinicki, Abhishek Kumar

Dept. of Computer Science

Worcester Polytechnic Institute

Presenter – Ashish Samant

8th IEEE Global Internet Symposium

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IntroductionIntroduction

Internet was not designed to support application based quality of service (QoS).

– Best effort model– No performance guarantees

Active Queue Management (AQM) helps deal with congestion at routers, but is not enough.

– No per application QoS– Not sensitive to delay/throughput needs

Our goal, “to add per application based QoS to AQM, over current best effort Internet”.


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Spectrum of QoS Requirements of ApplicationsT

hrou

ghpu

t S

ens

itivi

ty

Delay Sensitivity

Electronic Mail

File TransferWeb-browsing Streaming Audio

Streaming Video

Gaming

Interactive Video

Interactive Audio


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Problems with previous approaches to AQM:– Static classification– Per flow state maintenance– Pricing, policing overhead

Features of Traffic Sensitive QoS (TSQ):– Allows applications to indicate delay/throughput sensitivity

at packet level.– Can be deployed over existing AQM schemes.– No significant addition to overhead at routers.


5

OutlineOutline

Introduction

TSQ Mechanism

Application Quality Metrics

Experiments and Results

Future Work


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TSQ MechanismTSQ Mechanism

Router

RoutingTable

Packetqueue

1

23

4


7


AQM

Packet queue

10 Mbps

10 Mbps

5 Mbps

q

q’=

TSQ

(hint)

q’p +

p’

=

+ q+Rate

+


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On receiving each packet, router calculates a weight :w = (d * td ) / 2N + ta

d = delay limittd = drain time

N = no. of bits used to represent delay hintsta = arrival time

Weight of packet determines it’s position in router queue.

Lower delay hint leads to lower weight. Time of arrival prevents starvation.


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TSQ Mechanism TSQ Mechanism

TSQ uses “cut-in-line” scheme to insert packets with high delay sensitivity (higher weights) towards the front of the queue.

Packets from throughput sensitive application are delegated to the back of the queue

Packets that “cut-in-line” are dropped with a higher probability to ensure fairness.

Thus, advantage of labeling packets with high delay hints is neutralized with higher drop rates.


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The underlying AQM has a drop probability (p) that is applied uniformly to all packets.

Delay sensitive packets receive higher drop probability :

p’ = [(l + q)2 * p ] / (l + q’)2

l = one way delayq = instantaneous queue position

q’ = new queue positionp = drop probability calculated by underlying AQM

Packets that “cut-in-line” more will have a higher drop probability.


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OutlineOutline

Introduction

TSQ Mechanism



Conclusion and Future Work


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Application Quality MetricsApplication Quality Metrics

Based on previous work, we measure application quality as minimum of it’s delay quality (Qd) and throughput quality (Qt) :

Q(d,t) = min(Qd, Qt) { 0 ≤ Q(d,t) }

Higher value of Qd indicates the application is more sensitive to delay and vice versa.

Application quality is normalized between 0 and 1 - 1 indicates highest quality and 0 means no quality

at all.


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Excellent Quality Good Quality

Bad Quality

Excellent Quality

Good QualityBad Quality

Interactive Audio Delay Quality Refs [Act02][IKK93]


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Interactive Audio Throughput Quality Refs[Cor98]


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OutlineOutline

Introduction

TSQ Mechanism



Conclusion and Future Work


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Experimental SetupExperimental Setup

Network TopologyS1

S2

SN-1

SN

Queue Size

PI, PI+TSQAQM

800 packets

qref200 packets

R1

50 Mbps, 50 ms

D1

D2

DN-1

DN

R2

50 Mbps, 50 ms

B Mbps


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Experimental Setup Experimental Setup

PI parameters : a = 0.00001822, b = 0.00001816, w = 170 Hz, qref = 200 packets, qmax = 800 packets.

Average packet size = 1000 bytes.

All experiments run for 100 seconds

TSQ parameters : l = 40 ms. This is one-way delay constant parameter.


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Experiment – Interactive AudioExperiment – Interactive Audio

Experiment 1: Interactive Audio

– Bottleneck link bandwidth = 15 Mbps– 100 sources and 100 destinations. One

way propagation delay = 150 ms– 99 TCP based file transfer flows using

delay hint = 16– 1 TCP friendly CBR source sending at 128

Kbps, with varying delay hints.


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Analysis – Interactive AudioAnalysis – Interactive Audio

Analysis - Interactive Audio ( Delay )

• Low median queuing delay for lower delay hint.

• Less variation in queuing delay at lower delay hints.

•Delay Quality increases as delay hints decrease.


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Analysis – Interactive AudioAnalysis – Interactive Audio

• Throughput measured every RTT (300 ms).

• Median throughput low for lower delay hints.


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Analysis – Interactive Audio Analysis – Interactive Audio

Overall Quality

• Overall quality is minimum of delay and throughput quality.

• Maximum quality occurs when delay hint is 6.


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ConclusionsConclusions

TSQ provides a per-packet QoS to Internet applications.

It is a best-effort service without any guarantees.

Trade-off between throughput and delay is maintained by adjusting queue position and drop probability.

Does not require complex modifications at the router, over those needed for the AQM.


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Future WorkFuture Work

Derive quality metrics for other applications like network games, instant messaging, peer to peer.

Develop applications to dynamically change their delay hints.

Investigate optimum number of bits to be used for delay hints.

Apply TSQ to other domains, for e.g. wireless.


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Questions or Comments ?

Thank you !

traffic sensitive active queue management - mark claypool, robert kinicki, abhishek kumar dept. of...

Documents

tsq mechanism tsq

introduction internet

queue packets

delay quality q d

tsq mechanism aqm packet

q rate slide

mbps q q

tsq hint q p p