<Performance Issues with MPTCP>
draft-khalili-mptcp-performance-issues-02

Multipath TCP                                              Ramin Khalili
INTERNET-DRAFT                                          T-Labs/TU-Berlin
Intended Status: Standard Track                             Nicolas Gast
Expires: August 21, 2013                                Miroslav Popovic
                                                     Jean-Yves Le Boudec
                                                               EPFL-LCA2
                                                       February 17, 2013

                    <Performance Issues with MPTCP> 
               draft-khalili-mptcp-performance-issues-02

Abstract

   We show, by measurements over a testbed and by mathematical analysis,
   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; and (P2) MPTCP users can be
   excessively aggressive towards TCP users. We attribute these problems
   to the "Linked Increases" Algorithm (LIA) of MPTCP [4], and more
   specifically, to an excessive amount of traffic transmitted over
   congested paths. Our results show that these problems are important
   and can be mitigated. We believe that the design of the congestion
   control of MPTCP should be improved.  

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on August 22, 2013.

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Copyright and License Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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Table of Contents

   1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1 Requirements Language  . . . . . . . . . . . . . . . . . . .  4
     1.2 Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  4
   2 MPTCP's LIA  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3 Testbed Setup  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4 Scenario A: MPTCP can penalize regular TCP users . . . . . . . .  7
   5 Scenario B: MPTCP can penalize other MPTCP users . . . . . . . . 10
   6 Scenario C: MPTCP is excessively aggressive towards TCP users  . 12
   7 Can the suboptimality of MPTCP with LIA be fixed?  . . . . . . . 14
   8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1 Normative References . . . . . . . . . . . . . . . . . . . . 17
     9.2 Informative References . . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

 

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1 Introduction

   Regular TCP uses a window-based congestion-control mechanism to
   adjust the transmission rate of users [2]. It always provides a
   Pareto-optimal allocation of resources: it is impossible to increase
   the throughput of one user without decreasing the throughput of
   another or without increasing the congestion cost [5]. It also
   guarantees a fair allocation of bandwidth among the users but favors
   the connections with lower RTTs [6].

   Various mechanisms have been used to build a multipath transport
   protocol compatible with the regular TCP. Inspired by utility
   maximization frameworks, [7, 8] propose a family of algorithms. These