Implementation and Validation of TCP Options andCongestion Control Algorithms for ns-3

Maurizio Casoni, Carlo Augusto Grazia, Martin Klapez,Natale Patriciello

Department of Engineering Enzo FerrariUniversity of Modena and Reggio Emilia

Casteldefels, 14 May 2015WNS3 ’15

N.Patriciello (UNIMORE) WNS3 ’15 14 May 2015 1 / 23

Talk overview

1 IntroductionHistory timeState of the Art

2 Background on congestion control

3 Results

4 Conclusions

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Section 1

Introduction

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TCP Options recap

whatTCP Options: defined in RFC 793, Window Scale and Timestampspresented in RFC 1323

whyTo improve performance over large bandwidth*delay product pathsand to provide reliable operation over very high-speed paths

whereNS-3 TCP implementation under src/internet

N.Patriciello (UNIMORE) WNS3 ’15 14 May 2015 4 / 23

TCP variants recap

whatCongestion control algorithms for high-delay links still missing anative implementation for ns-3 (Hybla, Highspeed, ...). Otherwell-known variant (Bic, Cubic, ...) are in ns-2 but not ported in ns-3

whyThe purpose for adding these versions is to update internet module totoday’s standard

whereNS-3 TCP implementation under src/internet

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Important TCP options

Window scaleEnable the peers to utilize more than 65535 bytes for the slidingwindow

TimestampsBetter RTT estimation, protection for wrap-around sequence number

SACKSelective ACK: explicit knowledge about the segments lost in thenetwork (Breaking news: wns3 2015 poster...)

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Most used TCP congestion control algorithms

CUBIC/BICDefault algorithm in Linux (BIC from 2.6.8 to 2.6.19, CUBIC from2.6.19 to date)

HighspeedEvolution of NewReno to address its issues in Fast Long-DistanceNetworks

HyblaEvolution of NewReno to remove its performance dependency fromRTT

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Section 2

Background on congestion control

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TCP BIC

What is TCP BIC?It views the congestion avoidance as a search problem. Thecongestion window is updated thanks to a binary search, performedfrom the actual value up to the highest measured value

Why TCP BIC?Forerunner of CUBIC, Linux default congestion control algorithm for2 years

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TCP CUBIC

What is TCP CUBIC?Less aggressive and more systematic derivative of BIC, in which thewindow is a cubic function of time since the last congestion event,with the inflection point set to the window prior to the event.

Why TCP CUBIC?Linux default congestion control algorithm since 2006.

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TCP Highspeed

What is TCP Highspeed?AIMD parameters changes in function of the current window value.The window will grow faster than standard TCP and also recoverfrom losses more quickly.

Why TCP Highspeed?Often chosed as a reference benchmark for newer algorithms

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TCP Hybla

What is TCP Hybla?The key idea is to obtain for long RTT connections the sameinstantaneous transmission rate of a reference TCP connection withlower RTT

Why TCP Hybla?Often chosed as a reference benchmark for satellite-based network

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TCP Noordwijk

What is TCP Noordwijk?

A burst-based TCP variant for satellite networks, designedto:

Optimize transmission of short objectGuarantee a fair behavior with competing flowsOperate efficiently over DVB-RCS schemes

Why TCP Noordwijk?

Some interesting ideas for high-delay networks

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Section 3

Results

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Results: Window scale

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Time (s)WinScale disabledWinScale enabled

Please note, the max cwnd is determined by the TCP Tx/Rxbuffer!

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Results: BIC

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Bic cWndBic ssThresh

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Bic cWndBic ssThresh

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Results: CUBIC

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Cubic cWndCubic ssThresh

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Results: Highspeed

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HighSpeed-100msNewReno-100ms

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HighSpeed-100msNewReno-100ms

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Results: Hybla

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Hybla-350msNewReno-25ms

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Hybla-25msHybla-100ms

Hybla-350msNewReno-25ms

NewReno-100msNewReno-350ms

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Results: Noordwijk

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Noordwijk flow 0Noordwijk flow 1

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Noordwijk flow 0Noordwijk flow 1

Noordwijk aggregateNewReno single flow

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Section 4

Conclusions

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Conclusions

RecapPresented (and validated) TCP Options infrastructurePresented (and validated) TCP congestion control algorithms

Validation MethodComparison between simulation results with the theoretically expectedbehaviors

Lesson learnedVarious aspect of TCP still missing testing/validationCritical aspect in the TCP layer design

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Future Works

Directions to take

Re-design some part of the internet module to easilyextends the TCP (and UDP) testing platform (GSoC’15 accepted)Test TCP for RFC-complianceCompare ns-3 and real implementations

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Any questions ?

natale.patriciello@unimore.it

Why not a comparison with a real stack?

DCEAt the time, DCE was missing the cwnd/ssth tracing capabilities

Real networkTwo computer connected with an ethernet cable.

side-effects between queue and shaping with tcheavy-optimized TCP (SACK, persistent tables, and so on)really unfair comparison