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Page 1: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

MaxNet NetLab PresentationHailey Lam 08.08.08

Page 2: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Outline

• MaxNet as an alternative to TCP

• Linux implementation of MaxNet

• Demonstration of fairness, quick convergence, etc.

• Incorporating ADPM with MaxNet

Page 3: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Shortcomings of TCP

Sensitivity to losses

Round-trip time (RTT) unfairness

Slow start-up times for small flows

RFC 793 – Transmission Control Protocol

2

2

1

1

2

RTT

RTT

rate

rate

Page 4: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

MaxNet Overview

Router ReceiverSender

Transmission rate(congestion window)

Price

Echo price

Adjust window

Page 5: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

MaxNet Benefits from Explicit Feedback

• Avoid queueing, loss instead of reacting to it▫ Avoid hindering flows

• Flows achieve max-min fairness

▫ Maximize the minimum transfer rate

▫ Without affecting minimum, maximize second minimum rate, repeat.

Andrew, Jacobsson, et al. - "MaxNet: Theory and Implementation", Technical Report

Page 6: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Max-Min Fairness

Page 7: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Other Protocols using Explicit Feedback

• XCP (Katabi, Handley, Rohrs 2002)▫ At capacity, new flow bandwidth allocation too slow

• RCP (Dukkipatti, Kobayashi, Zhan-Shen, Mckeown 2005)

▫ Signals RTT for more responsiveness

• REM, JetMax, RED/ECN, many others

Page 8: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

TC on Routers to Implement MaxNet

Packet Arrival

Packet Parsed with MaxNet

field

Packet forwarded

TC calls MaxNet code

Price Update Calculation

• Update based on rate of traffic since last update

Packet Price Update

• Only if router price > packet price

Packet now has price data

Page 9: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Choice of Host Kernel

• Linux kernel version 2.6.23.1

▫ Benefits from improvements in SACK (selective acknowledgements)

• Modular Framework

▫ Consolidates much of MaxNet code

Page 10: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Linux Modular Framework

Hooks from Modular Framework

Cwnd_event – Extracts MaxNet Option

Cong_avoid – Changes congestion window per algorithm

Ssthresh – Sets threshold for slowstart

Many Others…

Page 11: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

TCP Header

Andrew, Jacobsson, et al. - "MaxNet: Theory and Implementation", Technical Report

TCP Header

SACK Header

SACK 1 SACK 2 SACK 3MaxNetOption

Page 12: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

MaxNet Option Format

MaxNet Option (42)

1 byte

Option Size (6)

1 byte

Echo Price

(3 bytes)

Price

(3 bytes)

Page 13: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Sender Targets for Equilibrium

• Equilibrium Rate (log scale for constant relative precision)

• Variable ξ for stability

• Host keeps track of variables: ξ, price

▫ Values in fixed point format

Tpriceex /

max

Page 14: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Sender Acknowledgement Arrival

ACK Arrival

Packet Parsed with MaxNet

option

Next Packet Transmitted

cong_avoidhook to

MaxNet code

Price Updated

• Take price from ACK

Congestion window Update

• Recalculate window based on new price

Page 15: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Receiver Data Arrival

Packet Arrival

Packet Parsed with MaxNet

option

ACK Transmitted

Echo price in ACK Packet

Solution: Have MaxNet treat delayed ACKs as increase in RTT, not congestion

Page 16: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Experiment Topology

Legend:Hardware RouterSoftware RouterServer

Page 17: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Experiment Topology

Legend:Hardware RouterSoftware RouterServer

Page 18: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Experiment Topology

Legend:Hardware RouterSoftware RouterServer

Page 19: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Experiment Topology

Legend:Hardware RouterSoftware RouterServer

Page 20: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Example Data – Fairness and Quick Convergence

Page 21: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Bursty Data Flows

• Data transmitted/received in bursts

• Router price and CPU load increase temporarily

• Results in slower transfer rates

• TCP Pacing as a solution

Page 22: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Future enhancements

• “Incompatibility” with TCP

▫ Greedy TCP will hog bandwidth

▫ MaxNet backs off and stops sending

• Encrypted packets▫ MaxNet option in TCP header – routers cannot use

Page 23: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Advanced Deterministic Packet Marking (ADPM)

• Single bit (ECN) in IP header marks packets

• Determine bit value with IPid field hash

• More packets passed yield closer estimate to actual price

Andrew, Hanly, et al. – Adaptive Deterministic Packet Marking

Page 24: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

ADPM

• Benefits

▫ Enables MaxNet to work with encrypted packets

▫ Routers should not look inside TCP layer

• Drawbacks

▫ Decreases accuracy of congestion level estimation

Page 25: MaxNet NetLab Presentationnetlab.caltech.edu › maxnet › MaxNetNetLabPresentation2008.pdfMaxNet NetLab Presentation Hailey Lam 08.08.08. Outline •MaxNet as an alternative to TCP

Summary

• MaxNet: Router assisted scheme

▫ Avoids some pitfalls of TCP

• MaxNet ported to 2.6.23.1

▫ Modular framework

▫ Improved SACK handling

• Address packet encryption with ADPM