MPTCP Is Not Pareto-Optimal: Performance Issues and a Possible Solution

Abstract

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 Paretooptimal; 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.

Use Cases and Operational Experience with Multipath TCP

“…It is also an adaptation of the NewReno single path congestion-control scheme to support multiple paths. Simulations [CONEXT12] and measurements [CONEXT13] have shown that it provides some performance benefits compared to the default coupled congestion-control scheme.…”

“…The second congestion-control scheme is OLIA [CONEXT12]. It is also an adaptation of the NewReno single path congestion-control scheme to support multiple paths.…”

Advanced Measurements of the Aggregation Capability of the MPT Network Layer Multipath Communication Library

“…MTPCP is actively researched and analyzed from different viewpoints see e.g. [8] and its references or count the Google Scholar hits for "Multipath TCP".…”

An implementation of multipath TCP in ns3

“…1 MPTCP should be pareto optimal, i.e., it should not harm any TCP user while improving the situation for MPTCP users. Achieving pareto optimality is still a problem for MPTCP [2] though improvements have been made [6]. Several techniques exist in the literature, such as watching the loss correlation between subflows to infer if they shared a bottleneck, but such methods make assumptions about the network that prevent them from being holistic.…”

“…Several congestion control algorithms have been proposed such as LinkedIncrease Algorithm (LIA [14]) or Opportunistic LIA [6] (OLIA). They couple the increase MPTCP congestion window with the congestion window of its subflows:…”