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A Survey of Recent High Speed TCP Variants. Philip Fisher-Ogden U.C. Davis March 16 th , 2007. Outline. Why do we need high speed TCP variants? Three recent variants Compound TCP CUBIC TCP-Adaptive Reno Recent Evaluations Q&A. Standard TCP - advantages. Widely used Standardized

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a survey of recent high speed tcp variants

A Survey of Recent High Speed TCP Variants

Philip Fisher-Ogden

U.C. Davis

March 16th, 2007

outline
Outline
  • Why do we need high speed TCP variants?
  • Three recent variants
    • Compound TCP
    • CUBIC
    • TCP-Adaptive Reno
  • Recent Evaluations
  • Q&A
standard tcp advantages
Standard TCP - advantages
  • Widely used
  • Standardized
  • Promises, promises
    • Guaranteed, in-order delivery
    • Avoids congestion collapse
  • Evolved: Tahoe, Reno/NewReno, SACK
standard tcp disadvantages
Standard TCP - disadvantages
  • Underutilization of the bandwidth in fast long distance networks (FLDnets)
  • Low window size resiliency to packet loss in FLDnets
prior high speed tcps
Prior High Speed TCPs
  • Effectively use available bandwidth
  • Unfriendly – “doesn’t play nicely with others”
  • Unfair to different RTT flows
  • Examples: HSTCP, STCP, BIC-TCP
goals
Goals
  • TCP friendly
    • Minimize bandwidth-stolen
  • RTT fair
    • Co-existing flows with different RTTs are treated fairly
  • Efficient use of available bandwidth
compound tcp motivation
Compound TCP - Motivation
  • Loss-based - uses packet loss as an indicator of congestion and modifies the increase/decrease congestion avoidance TCP parameters.
  • Delay-based - infers congestion and bottleneck queue size from changes in the RTT and modifies the transfer rates to mitigate the effects of congestion.
  • Combine both approaches
  • Focus on efficiency & friendliness
compound tcp design
Compound TCP - Design
  • Maintains a delay window and a congestion window – uses both to determine send window
  • Estimates the bottleneck queue size:
    • Diff = (Expected – Actual) * baseRTT
  • Has a threshold, γ, at which it says “the network is congested”
compound tcp design11
Compound TCP - Design
  • Builds on loss-based (standard) TCP
  • Reverts to standard TCP at low window sizes
  • Uses gamma-auto tuning to dynamically adjust γ, the estimated number of packets that indicate a bottleneck in the queue, based on the network configuration
cubic motivation
CUBIC - Motivation
  • Enhance BIC!
    • Maintain BIC’s scalability & stability
    • Simplify the window control
    • Improve BIC’s friendliness
    • Use real-time, rather than ACK-clocked, updates to window
  • Improve the detection of the “TCP Region”
cubic design
CUBIC - Design
  • Based on BIC:
cubic design16
CUBIC - Design
  • Window growth function:
cubic design aspects
CUBIC – Design Aspects
  • Stability – The window grows slowly around Wmax.
  • Scalability – It experiences fast “probing” growth away from Wmax.
  • Intra-protocol fairness - Two competing CUBIC flows will converge to fair share window sizes.
  • Fairness – The window growth rate is time dependent and RTT independent, allowing for fairer sharing.
cubic design aspects18
CUBIC – Design Aspects
  • Standard TCP outperforms CUBIC’s window growth function in short RTT networks.
  • CUBIC emulates the time-independent TCP window adjustment algorithm so that it can select the greater of the two windows (emulated versus cubic) to use.
tcp areno motivation
TCP-AReno - Motivation
  • Enhance TCP-Westwood-BBE
  • Improve on TCP-Reno’s response function by incorporating a congestion estimate that is based on RTT measurements.
  • Identify if a packet loss was due to congestion or not.
tcp areno design
TCP-AReno - Design
  • Congestion Estimate
    • RTTcong = the RTT that would indicate a congestion event.
    • Classifies packet losses as due to congestion or not
    • RTT values vary between RTTmin and RTTcong. The distance of recent RTT measurements from RTTcong and RTTmin determines the level of congestion in the network.
tcp areno design23
TCP-AReno - Design
  • Congestion Window Increase
tcp areno design24
TCP-AReno - Design
  • Congestion Window Reduction
recent evaluations linux beats windows28
Recent EvaluationsLinux beats Windows!
  • BIC/CUBIC are over aggressive and steal bandwidth.
  • Serious unfairness
recent evaluations experimental evaluation of cubic tcp
Recent EvaluationsExperimental Evaluation of Cubic-TCP
  • Conducted partially in response to “should CUBIC be adopted in Linux?”
  • CUBIC suffers from a slow convergence of congestion windows.
  • Controversial! A rebuttal was issued by Injong Rhee (CUBIC co-author)
recent evaluations assessing interactions among legacy high speed tcps
Recent EvaluationsAssessing Interactions among Legacy & High-Speed TCPs
  • Evaluated efficiency, fairness, & friendliness
recent evaluations assessing interactions among legacy high speed tcps32
Recent EvaluationsAssessing Interactions among Legacy & High-Speed TCPs
  • Delay-based control are not effective in improving RTT-fairness due to the slow-start behavior of short flows that induces RTT measurement problems
  • TCP-AReno was modified to avoid having the short flow problem impact its delay based mechanism.
  • TCP-AReno outperformed all others.
  • Compound TCP came close, but experienced the delay-based control problem.