LEDBAT+AQM code

Nowadays, due to excessive queuing, delays on the Internet can grow longer than several round trips between the Moon and the Earth – for which the ‘‘bufferbloat’’ term was recently coined. Some point to active queue management (AQM) as the solution. Others propose end-to-end low-priority congestion control (LPCC) true techniques . Under both approaches, promising advances have been made in recent times: notable examples are CoDel for AQM, and LEDBAT for LPCC. In this project, we study the impact that Active Queue Management (AQM) techniques have on LEDBAT (and other LPCCs such as NICE, TCP-LP, etc.). To promote cross-comparison, we make our simulation code and experimental code available to the research community.

The phenomenon

While LPCC and AQM both try to solve the buffer inflation problem, however a potentially fateful interaction arise when AQM and LPCC techniques are combined true, namely:

• AQM resets the relative level of priority between best effort and low-priority congestion control protocols;
• while reprioritization generally equalizes the priority of LPCC and TCP, we also find that some AQM settings may actually lead best effort TCP to starvation.

The problem is illustrated in the following figure, showing a breakdown of the TCP vs LEDBAT throughput for 10 flows sharing the same bottleneck under FIFO Droptail (left) vs RED (right).

Contributions

By an extended set of experiments true conducted on both controlled testbeds and on the Internet, we show the problem to hold in the real world for any tested combination of AQM policies and LPCC protocols. To further validate the generality of our findings, we complement our experiments with packet-level simulation, to cover cases of other popular AQM and LPCC that are not available in the Linux kernel true.

To gather fundamental insights on the problem

• we resort to a control theoretic modeling to analyze the system dynamics true (that was shortlisted for, but finally did not win, the best paper award ) that we extend in true (a little known but very cool paper!)
• finally, we propose true and implement true a solution able to reinstate the relative levels of priority between heterogeneous congestion contro, while avoiding the bufferbloat problem at the same time.

Experiments

Note: PhD-grade skills are required to run the experiments and tweak the experimental settings

• scripts for launching experiments and bare-bone visualization of result described in true, including a short howto ]]

Simulation

Note: PhD-grade ns2 skills are required to modify and build the ns2 source tree; modification includes our own implementation of the LEDBAT and TCP-NICE low priority congestion control (LPCC), plus Choke and CoDel (AQM) from the respective authors, packaged here for commodity.

• tarball of needed modification to ns2
• scripts for launching simulations and post-processing results described in true (including a short howto on the workflow
• scripts of the proof-of-concept solution to the reprioritization described in true
• Of historical interest, we also provide a copy of the initial student project slides (that made their way up to Van Jacobson!) of YiXi on the topic

References

• [LCN-10] Carofiglio, G. and Muscariello, L. and Rossi, D. and Testa, C., A hands-on Assessment of Transport Protocols with Lower than Best Effort Priority 35th IEEE Conference on Local Computer Networks (LCN’10) oc. 2010, conference Bibtex

  @inproceedings{DR:LCN-10,
    title = {A hands-on Assessment of Transport Protocols with Lower than Best Effort Priority},
    author = {Carofiglio, G. and Muscariello, L. and Rossi, D. and Testa, C.},
    booktitle = {35th IEEE Conference on Local Computer Networks (LCN'10)},
    address = {Denver, CO, USA},
    month =  oc,
    year = {2010},
    annote = {category=inproceedings state=published project=trans},
    note = {keyword=ledbat,trans,congestion control},
    url = {http://www.enst.fr/~drossi/paper/rossi10lcn.pdf},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi10lcn.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi10lcn.pdf}
  }
  

• [CONEXT-12] , Interaction or Interference: can AQM and Low Priority Congestion Control Successfully Collaborate ACM CoNEXT’12 Student Workshop dec. 2012, conference Abstract Bibtex
  Heterogeneity in the Internet ecosystem sometimes turns interaction into interference. Over the years, active queue management (AQM) and end-to-end low-priority congestion control (LPCC) have been proposed as alternative solutions to counter the persistently full buffer problem – that recently became popular under the "bufferbloat" term. In this work, we point out the existence of a negative interplay among AQM and LPCC techniques. Intuitively, as AQM is designed to penalize the most aggressive flows it mainly hit best effort TCP: it follows that LPCC is not able to maintain its low priority, thus becoming as aggressive as TCP. By an extended set of simulation on various AQM policies and LPCC protocols, including the very recent CoDel AQM and LEDBAT LPCC proposals, we point out that this interference is quite universal and deserves further attention.

  @inproceedings{DR:CONEXT-12,
    title = {Interaction or Interference: can AQM and Low Priority
    Congestion Control Successfully Collaborate},
    author = {},
    year = {2012},
    booktitle = {ACM CoNEXT'12 Student Workshop},
    annote = {category=article state=published project=mplane},
    note = {keyword=bufferbloat,ledbat},
    month = dec,
    pages = {25-26},
    url = {http://www.enst.fr/~drossi/paper/rossi12conext.pdf},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi12conext.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi12conext.pdf}
  }
  

• [TMA-13b] Gong, Y. and Rossi, D. and Testa, C. and Valenti, S. and Taht, D., Fighting the bufferbloat: on the coexistence of AQM and low priority congestion control IEEE INFOCOM Workshop on Traffic Measurement and Analysis (TMA’13) apr. 2013, conference Abstract Bibtex
  Nowadays, due to excessive queuing, delays on the Internet can grow longer than several round trips between the Moon and the Earth, for which the "bufferbloat" term was recently coined. Some point to active queue management (AQM) as the solution. Others propose end-to-end low-priority congestion control techniques (LPCC). Under both approaches, promising advances have been made in recent times: notable examples are CoDel for AQM, and LEDBAT for LPCC. In this paper, we warn of a potentially fateful interaction when AQM and LPCC techniques are combined: namely (i) AQM resets the relative level of priority between best effort and low-priority congestion control protocols; (ii) while reprioritization generally equalizes the priority of LPCC and TCP, we also find that some AQM settings may actually lead best effort TCP to starvation. By an extended set of experiments conducted on both controlled testbeds and on the Internet, we show the problem to hold in the real world for all tested combination of AQM policies and LPCC protocols. To further validate the generality of our findings, we complement our experiments with packet-level simulation, to cover cases of other popular AQM and LPCC that are not available in the Linux kernel. To promote cross-comparison, we make our scripts and dataset available to the research community.

  @inproceedings{DR:TMA-13b,
    author = {Gong, Y. and Rossi, D. and Testa, C. and Valenti, S. and Taht, D.},
    title = {Fighting the bufferbloat: on the coexistence of AQM and low priority congestion control},
    booktitle = {IEEE INFOCOM Workshop on Traffic Measurement and Analysis (TMA'13)},
    year = {2013},
    address = {Turin, Italy},
    month = apr,
    annote = {category=article state=published project=mplane},
    url = {http://www.enst.fr/~drossi/paper/rossi13tma-b.pdf},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi13tma-b.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi13tma-b.pdf},
    note = {keyword=ledbat,bufferbloat,mplane}
  }
  

• [ITC-13] Gong, YiXi and Rossi, Dario and Leonardi, Emilio, Modeling the interdependency of low-priority congestion control and active queue management The 25th International Teletraffic Congress (ITC25), Runner-up for Best Paper Award sep. 2013, conference Award Abstract Bibtex
  Recently, a negative interplay has been shown to arise when scheduling/AQM techniques and low-priority conges- tion control protocols are used together: namely, AQM resets the relative level of priority among congestion control protocols. This work explores this issue by (i) studying a fluid model that describes system dynamics of heterogeneous congestion control protocols competing on a bottleneck link governed by AQM and (ii) proposing a system level solution able to reinstate priorities among protocols.

  @inproceedings{DR:ITC-13,
    title = {Modeling the interdependency of low-priority
    congestion control and active queue management},
    author = {Gong, YiXi and Rossi, Dario and Leonardi, Emilio},
    booktitle = {The 25th International Teletraffic Congress (ITC25), Runner-up for Best Paper Award},
    year = {2013},
    month = sep,
    annote = {category=article state=published project=mplane},
    note = {keyword=ledbat,bestpaperrunnerup},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi13itc.pdf},
    url = {http://www.enst.fr/~drossi/paper/rossi13itc.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi13itc.pdf}
  }
  

• [COMNET-14b] Gong, YiXi and Rossi, Dario and Testa, Claudio and Valenti, Silvio and Taht, Dave, Fighting the bufferbloat: on the coexistence of AQM and low priority congestion control (extended version) In Computer Networks, Vol. 65, No. 0, pp.255 – 267, 2014, journal Abstract Bibtex
  Nowadays, due to excessive queuing, delays on the Internet can grow longer than the round trip time between the Moon and the Earth – for which the “bufferbloa t” term was recently coined. Some point to active queue management (AQM) as the solution. Others propose end-to-end low-priority congestion control techniques (LPCC). Under both approaches, promising advances have been made in recent times: notable examples are CoDel for AQM, and LEDBAT for LPCC. In this paper, we warn of a potentially fateful interaction when AQM and LPCC techniques are combined: namely, AQM resets the relative level of priority between best-effort and low-priority congestion control protocols. We validate the generality of our findings by an extended set of experiments with packet-level ns2 simulation, considering 5 AQM techniques and 3 LPCC protocols, and carry on a thorough sensitivity analysis varying several parameters of the networking scenario. We complete the simulation via an experimental campaign conducted on both controlled testbeds and on the Internet, confirming the reprioritization issue to hold in the real world at least under all combination of AQM policies and LPCC protocols available in the Linux kernel. To promote cross-comparison, we make our scripts and dataset available to the research community.

  @article{DR:COMNET-14b,
    author = {Gong, YiXi and Rossi, Dario and Testa, Claudio and Valenti, Silvio and Taht, Dave},
    title = {{Fighting the bufferbloat: on the coexistence of AQM and low priority congestion control (extended version)}},
    note = {keyword=measurement,ledbat,tengineer,mplane},
    journal = {Computer Networks},
    volume = {65},
    number = {0},
    pages = {255 -- 267},
    year = {2014},
    issn = {1389-1286},
    annote = {category=article state=published project=mplane},
    url = {http://www.enst.fr/~drossi/paper/rossi14comnet-b.pdf},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi14comnet-b.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi14comnet-b.pdf}
  }
  

• [TOMPECS-16] De Cicco, Luca and Gong, Yixi and Rossi, Dario and Leonardi, Emilio, A control theoretic analysis of low-priority congestion control reprioritization under AQM In ACM Transactions on Modeling and Performance Evaluation of Computer Systems, Vol. 1, pp.17:1–17:33, sep. 2016, journal Abstract Bibtex
  Recently, a negative interplay has been shown to arise when scheduling/Active Queue Management (AQM) techniques and low-priority congestion control protocols are used together; namely, AQM resets the relative level of priority among congestion control protocols. This work explores this issue by carrying out a control-theoretic analysis of the dynamical system to prove some fundamental properties that fully characterize the reprioritization phenomenon. In particular, (i) we provide the closed-form solution of the equilibrium in the open loop (i.e., fixing a target loss probability p); (ii) we provide a stability analysis and a characterization of the reprioritization phenomenon when closing the loop with AQM (i.e., that dynamically adjusts the system loss probability). Our results are important as the characterization of the reprioritization phenomenon is not only quantitatively accurate for the specific protocols and AQM considered but also qualitatively accurate for a broader range of congestion control protocol and AQM combinations. Finally, while we find a sufficient condition to avoid the reprioritization phenomenon, we also show, at the same time, such conditions to be likely impractical: Therefore, we propose a simple and practical system-level solution that is able to reinstate priorities among protocols.

  @article{DR:TOMPECS-16,
    title = {A control theoretic analysis of low-priority congestion control
    reprioritization under AQM},
    author = {De Cicco, Luca and Gong, Yixi and Rossi, Dario and Leonardi, Emilio},
    year = {2016},
    month = sep,
    journal = {ACM Transactions on Modeling and Performance Evaluation of Computer Systems},
    note = {keyword=newnet,ledbat},
    volume = {1},
    issue = {4},
    pages = {17:1--17:33},
    url = {http://www.enst.fr/~drossi/paper/rossi16tompecs.pdf},
    howpublished = {http://www.enst.fr/~drossi/paper/rossi16tompecs.pdf},
    www_txt_url = {http://www.enst.fr/~drossi/paper/rossi16tompecs.pdf}
  }