iCON² : Internet Congestion Control, in Retrospect.
Aditya Akella, Richard Karp, Christos Papadimitriou, Srini Seshan, Scott Shenker and Ion Stoica.

• The pioneering theoretical analysis of Chiu and Jain has resulted in the widespread belief that linear additive-increase-multiplicative-decrease (AIMD) control algorithms should be used in the Internet. However, these early congestion control design decisions were made in a context where loss recovery was fairly primitive (e.g. TCP Reno) and often timed-out when more than a few losses occurred. Moreover, routers were almost always FIFO drop-tail.
  In subsequent years, there has been significant improvement in TCP loss recovery algorithms. For instance, TCP SACK can absorb many losses without timing out. In addition, there have been many proposals for improved router behavior: RED active queue management, Explicit Congestion Notification (ECN), and per-flow packet scheduling (DRR and fair queueing).
  In this Work, we evaluate the four linear congestion control styles -- AIMD, AIAD, MIMD, MIAD -- in the context of these various loss recovery and router algorithms. We find that in the traditional context of TCP Reno loss recovery and FIFO drop-tail routers, AIMD is clearly the superior design choice. However, when we include the more modern developments of better loss recovery and queue management schemes, we find quite a different story. In particular, AIAD seems to be a reasonable alternative choice. We also show that with minor modifications, AIAD can also be made fair, a problem that AIAD faces with FIFO drop-tail buffers.
• The "socially responsible" congestion control behavior, that is implemented by the bulk of Internet end-points, has been given credit for the continued stability of the network. This paper is an attempt to understand if these social congestion control algorithms were aptly credited. We answer whether greedy behavior by network end-points actually results in unstable network conditions such as congestion collapse or does socially responsible congestion control behavior actually match the best interests of greedy end-users performing reliable data transfer. The answer to this question has important implications to network operation. If the answer is that greedy behavior results in instability, then the reason that the Internet is functioning correctly is either that end-users are consciously socially responsible or that it is too difficult to modify end-hosts to behave greedily. Clearly, network operators cannot rely on either of these conditions persisting and they must deploy new network mechanisms to ensure that network end-points do not behave greedily in the future. On the other hand, if selfishness does not result in poor network behavior, then we need no such mechanisms deployed and there are reasons beyond just the social congestion control algorithms of TCP that perhaps contribute to stability in the face of greedy network end-point behavior.
  In this part of our analysis of congestion control algorithms, we adopt a game-theoretic analysis of TCP to show the following
  • In certain situations, greedy end-point behavior is identical to the socially optimal behavior. In particular, these behaviors overlap in the historically significant setting of TCP-Reno end-points in a network of drop-tail routers.
  • Unfortunately, our analysis also shows that most situations that are typical of current conditions, e.g., TCP-SACK end-points with either drop-tail or RED routers, encourage greedy flows to exhibit undesirable behavior. This results in Nash Equilibria with poor overall network efficiency.
  • It is possible, as we have shown, to design simple, scalable queue management algorithms to ensure that the advantage gained by greedy flows is more than offset by a high packet loss rate. Another valuable upshot of our analysis of the TCP Game has been the development of simple schemes to evaluate the effectiveness of active queue management techniques in containing aggressive end-user behavior.

• Selfish Behavior and Stability of the Internet: A Game-Theoretic Analysis of TCP [ps] [pdf]
  Aditya Akella, Richard Karp, Christos Papadimitriou, Srinivasan Seshan and Scott Shenker.
  ACM SIGCOMM 2002, Pittsburgh PA.
  Slides from the talk [ppt] [pdf].
• Exploring Congestion Control [ps] [pdf]
  Aditya Akella, Srinivasan Seshan, Scott Shenker and Ion Stoica.
  CMU SCS Technical Report Number CMU-CS-02-139.
• Exploring Congestion Control [ppt]
  At CMU Systems Seminar, Nov 2001.