MPTCP is not pareto-optimal: performance issues and a possible solution
MPTCP is not pareto-optimal: performance issues and a possible solution
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DOI：
10.1145/2413176.2413178
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发表时间：
2012-12
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影响因子：
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通讯作者：
R. Khalili;Nicolas Gast;M. Popovic;U. Upadhyay;J. Le Boudec
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作者：
R. Khalili;Nicolas Gast;M. Popovic;U. Upadhyay;J. Le Boudec
MPTCP是最近提出的一种机制，用于透明地支持到应用层的多个连接。IETF正在讨论这个问题。然而，我们发现当前的MPTCP协议存在两个问题：(P1)将一些TCP用户升级到MPTCP会降低其他用户的吞吐量，而对升级后的用户没有任何好处，这是不是帕累托最优的症状；(P2)MPTCP用户可能对TCP用户过于咄咄逼人。我们将这些问题归因于MPTCP的链接增加算法(LIA)，更具体地说，归因于在拥塞路径上传输的过多流量。LIA的设计要求在最优资源池和响应速度之间进行权衡。我们重新讨论了这个问题，并证明了同时提供这两个性质是可能的。我们在Linux内核中实现了机会主义链接增加算法(OLIA)，并通过模拟和理论分析在我们的试验台上研究了它的性能。我们证明了Olia是Pareto最优的，并且满足MPTCP的设计目标。因此，它可以避免问题P1和P2。我们的测量和模拟表明，带有OLIA的MPTCP与带有LIA的MPTCP一样具有响应性和非浮动性，并且它解决了问题P1和P2。
MPTCP has been proposed recently as a mechanism for supporting transparently multiple connections to the application layer. It is under discussion at the IETF. We show, however, that the current MPTCP suffers from two problems: (P1) Upgrading some TCP users to MPTCP can reduce the throughput of others without any benefit to the upgraded users, which is a symptom of not being Pareto-optimal; and (P2) MPTCP users could be excessively aggressive towards TCP users. We attribute these problems to the linked-increases algorithm (LIA) of MPTCP and, more specifically, to an excessive amount of traffic transmitted over congested paths. The design of LIA forces a tradeoff between optimal resource pooling and responsiveness. We revisit the problem and show that it is possible to provide these two properties simultaneously. We implement the resulting algorithm, called opportunistic linked increases algorithm (OLIA), in the Linux kernel, and we study its performance over our testbed, by simulations and by theoretical analysis. We prove that OLIA is Pareto-optimal and satisfies the design goals of MPTCP. Hence it can avoid the problems P1 and P2. Our measurements and simulations indicate that MPTCP with OLIA is as responsive and non-flappy as MPTCP with LIA, and that it solves problems P1 and P2.