Paper review : Charge-Sensitive TCP and Rate Control in the Internet (LA00)

• Goal
  To provide a network-independent algorithm which optimizes the system rates and the total user utility.
  

• Contribution
  This paper extends Kelly et al.'s work, which is rate-based, to the class of window-based (TCP/Vegas) algorithms.

• Main ideas
  • The system optimization problem can be decomposed into two subproblems, network and user problems, in order to get a feedback-insensitive solution.
  • When users update their parameters by solving their own optimization problem, at an equilibrium the system optimum is achieved.
  • In the case of a single bottleneck, there exists a unique Nash equilibria when we model the problem as a noncooperative game.

• Evaluation
  • Significance rating: 1
    Most of the work in this paper are based on several previous work, especially on Kelly's seminal work. The formalization and the analysis of the problem are copies, in some sense, of the original work under the window-based case. And the authors do not provide enough arguments to show the advantages and/or feasibility of their approach.
    

  • Convincing rating
    The authors create and analyze their model for the optimization problem with considerable mathematical teniques. They also use Network Simulator (NS) to simulate their results.
    However, the authors do not test their algorithm on the Internet; so the feasibility of the algorithm on the realistic scale is still a question. Also, their simulation uses the similar utility functions Ui, which is not so convincing for the possiblity of the various Internet users. It seems to me not clear that why they can suppose the user's utility function as multiple of log x.
    There're also too many assumptions in this paper. Actually, this is partly caused by the assumptions made by previous works, such as Kelly's and the TCP/Vegas protocol. Anyway, the authors do not tell us whether the model/algorithm is still practical when it satisifies so many restrictions. Some of the assumptions are not trivial, in my eyes, such as each user has only a fixed route and a single bottleneck in the model.
    

  • Limitation
    This work is done in a relatively simple model, e.g., it's only designed for unicast.
    The authors should also consider how to combine their work with the currently dominant TCP protocols, such as TCP/Tahoe or TCP/Reno. Since they cannot expect TCP/Vegas can be more prominent by their paper.

• Conclusion
  Pricing mechanism for a distributed system is complex. Appropriately modelling the system and proposing a resonable and feasible definition of fairness, hence providing an effective (network-insensitive) algorithm needs a lot of work.

  10/29/01