[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00

MPTCP Working Group                                              F. Wang
Internet-Draft                                                    J. Zuo
Intended Status: Standards Track                                  Z. Cao
Expires: April 29, 2018                                         K. Zheng
                                                                  Huawei
                                                        October 30, 2017

    A Proactive Approach to Avoid Performance Degradation of MPTCP
             draft-zuo-mptcp-degradation-00

Abstract

   One of the goals for MPTCP is utilizing multiple paths to perform at
   least as well as the best path in terms of throughput. However, this
   goal might not be arrived at because of the path asymmetry, which is
   called as the performance-degradation problem of MPTCP in this draft.
   Some existing methods focus on this problem, such as penalizing and
   opportunistic retransmission, which reactively responds to the head-
   of-line blocking for trying their best to send data across all paths.
   In order to efficiently utilize the capabilities of the multiple
   paths, this draft proposes an approach that proactively selects the
   best path(s) to send data instead of always bonding all paths
   together.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Copyright and License Notice




J. Zuo, et al            Expires April 29, 2018                 [Page 1]


INTERNET-DRAFT                                          October 30, 2017


   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2. Acronyms and Terminology  . . . . . . . . . . . . . . . . . . .  3
   3. A Proactive Approach to Avoid MPTCP Performance Degradation . .  3
     3.1 Throughput Measurement . . . . . . . . . . . . . . . . . . .  4
     3.2 Path Selection Strategy  . . . . . . . . . . . . . . . . . .  5
   4. Operation Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     4.1 Slow-Start Stage . . . . . . . . . . . . . . . . . . . . . .  5
     4.2 Congestion-Avoidance Stage . . . . . . . . . . . . . . . . .  6
       4.2.1 Redundant Transmission Mode  . . . . . . . . . . . . . .  6
       4.2.2 Multipath Transmission Mode  . . . . . . . . . . . . . .  7
       4.2.3 Throughput Comparison  . . . . . . . . . . . . . . . . .  7
       4.2.4 Indicator Timer Timeout  . . . . . . . . . . . . . . . .  8
   5. Security Considerations . . . . . . . . . . . . . . . . . . . .  8
   6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  8
   7. References  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1. Normative References  . . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9

1. Introduction

   MultiPath TCP (MPTCP) enables a transport connection across multiple
   paths simultaneously [RFC6824]. According to [RFC6356], one of the
   MPTCP's goals is improving throughput: a multipath flow should
   perform at least as well as a single path flow would on the best of
   the path available to it. However, this goal cannot be always
   achieved due to the head-of-line blocking caused by the path
   asymmetry, e.g. WiFi and LTE in smart phones. To be convenient, this
   phenomenon (that MPTCP performs worse than the best path) is called
   as the performance-degradation problem in this draft.

   The direct solution for this problem is allocating a large enough
   receive buffer. As in [RFC6182], `The RECOMMENDED receive buffer is



J. Zuo, et al            Expires April 29, 2018                 [Page 2]


INTERNET-DRAFT                                          October 30, 2017


   2*sum(BW_i)*RTT_max, which `ensures subflows do not stall when fast
   retransmit is triggered on any subflow'. However, the buffer size can
   be very large to cover all the possible scenarios. In other words,
   the buffer size can be limited and the performance-degradation
   problem is possible to exist. Therefore, it needs a solution for
   MPTCP protocol that can solve this problem. On this issue, some
   reactive methods have been proposed, such as penalizing and
   opportunistic retransmission. They take actions after the head-of-
   line blocking occurring and their purpose is to send data across all
   paths as possible as they can. Experiments show that even with these
   methods, the capabilities of the multiple paths may not be
   efficiently utilized. Meanwhile, instead of bonding all paths
   together, [RFC6182] indicates that it would be better `to only use
   some of the fastest available paths for the MPTCP connection in
   extreme cases'.

   This draft focuses on this problem and proposes a proactive approach,
   which dynamically employs part or all of the paths for higher
   utilization efficiency. In particular, this approach first measures
   the aggregated throughput of the multiple paths and the throughput of
   the best single path in real time. Then, if the performance-
   degradation phenomenon is derived through the throughput comparison,
   only the best path is used to send data.


2. Acronyms and Terminology

   MPTCP: Multiple Path Transport Control Protocol

   RTT: Round-robin Transmit Time

   PLR: Packet Loss Ratio

   BW: BandWidth

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


3. A Proactive Approach to Avoid MPTCP Performance Degradation

   This section introduces the basic principles of the proposed
   approach: 1) how to efficiently measure the characteristics of
   multiple paths; 2) how to select the path(s). More details regarding
   to this approach can be found in Section 4. Briefly, through
   measuring and comparing the path characteristics, the best path(s) is
   selected to satisfy a special purpose, such as the high throughput or



J. Zuo, et al            Expires April 29, 2018                 [Page 3]


INTERNET-DRAFT                                          October 30, 2017


   low RTT. In theory, path characteristics can be RTT, throughput,
   congestion window, etc., while only throughput is considered in this
   draft for a case study. As shown in Figure 1, the proposed approach
   is implemented in the Performance-Degradation-Free Module of the MP
   layer.

3.1 Throughput Measurement

   This section describes the method of the throughput measurement for
   multipath transmissions. As shown in [CMT-SCTP], one possible method
   is modeling the aggregated throughput of multiple paths and measuring
   the related path characteristics, i.e. buffer size, PLR, BW and RTT.
   However, it is hard to accurately model the throughput, since 1)
   lacking of BW evaluation methods, 2) and the small PLR can be
   obtained only after a huge number of data exchanging.

   This draft proposes a method that directly measures the multipath and
   best-single-path throughputs, in order to avoid the measurements of
   BW and PLR. At first, two modes are defined for the throughput
   measurement:

   1) Redundant transmission mode: Multiple paths transmit the same
   data;

   2) MultiPath (MP) transmission mode: Multiple paths transmit
   different data with using a MPTCP scheduling scheme, such as minRTT
   (the default scheduling method) in version 0.92. By the way, the
   opportunistic retransmission and penalization mechanisms can be
   enabled in MP mode.

   The redundant transmission mode is a kind of scheduling scheme in
   MPTCP v0.92, which is usually used to achieve lower packet delay than
   that of a single path. Because of wasting bandwidth (BW), the
   redundant transmission mode is ignored when MPTCP aggregates the BWs
   of multiple paths. However, this draft utilizes the redundant
   transmission mode to measure the throughputs of each path and the
   best single path, while using the multipath transmission mode to
   measure the aggregated throughput. To be convenient, the redundant/MP
   transmission mode is also called as the redundant/MP mode in the
   following part of this draft. Moreover, the throughput measurement is
   executed during the data transmission without introducing extra
   packets, and is periodic for self-adapting to the dynamic network
   environment.

   The Figure 1 briefly shows the relationship between the two
   transmission modes and our Performance-Degradation-Free Module in MP
   layer.




J. Zuo, et al            Expires April 29, 2018                 [Page 4]


INTERNET-DRAFT                                          October 30, 2017


       +---------------------------------------+
       |                  APP                  |
       +---------------------------------------+
       |                MP Layer               |
       | +- - - - - - - - - - - - - - - - - -+ |
       | |Performance-Degradation-Free Module| |
       | +- - - - - - - - -+- - - - - - - - -+ |
       | |  Redundant Mode |     MP Mode     | |
       | +- - - - - - - - -+- - - - - - - - -+ |
       +-------------------+-------------------+
       |     Path 1        |     Path 2        |
       +---------------------------------------+


   Figure 1: The performance-degradation-free module in the MP layer.

3.2 Path Selection Strategy

   All these paths or the best one of them are used to send data
   depending on the corresponding throughput.

4. Operation Overview

   Section 3 presents the main principles, i.e. throughput measurement
   and path selection. This section introduces how the proposed approach
   works in details. According to different congestion-control schemes,
   the proposed approach may have slow-start stage and congestion-
   control stage. At the first stage, the approach ensures that the slow
   start of the scheme has been finished. At the second stage, the
   approach periodically measures the average throughputs of multiple
   paths and the best path, and employs the suitable path(s) through
   throughput comparisons.

4.1 Slow-Start Stage

   During the slow-start stage, MPTCP schedules the data in the
   redundant mode, where the same data are transmitted across multiple
   paths. After each round, we get a measured throughput from the view
   of MP layer, where the round time could be from sending a packet
   until receiving its responsive ACK. The throughput (defined as
   `B_rd') is calculated by dividing the total number of delivered data
   with the time period of this round. We define a threshold `h', where
   h belongs to (0,1), e.g. h=0.2. As shown in Figure 2, if the measured
   throughput is h times larger than the last measured value (i.e.
   B_rd(i) >= h * B_rd(i-1) ) , keep the redundant mode and set the
   round counter Nr as 0, or else increase the round counter (defined as
   Nr) by 1.




J. Zuo, et al            Expires April 29, 2018                 [Page 5]


INTERNET-DRAFT                                          October 30, 2017


4.2 Congestion-Avoidance Stage

   If the round counter Nr > N (e.g. N = 3), then the transmission
   switches to the congestion-avoidance stage, as shown in Figure 2. Two
   timers are set to decide when we need measure the throughputs of the
   redundant and MP modes again. Two indicators of updating the
   redundant and MP measurement values, Indicator_Redundant and
   Indicator_MP, are both set as 1. The indicator timers for the
   redundant mode and MP modes are set as REDUNDANT_MODE_TIMER and
   MP_MODE_TIMER, separately. The timeout of both timers is set as a
   period of time TIMEOUT (e.g. 10s).

   At first, the redundant mode is used to measure the throughput.

                    +-------------------------------------+
                    |                                     |
                    v                         +---------------------------+
                                 Nr <= N      |   If B_rd(i)= h*B_rd(i-1) |
            +----------------+                |      Nr++;                |
            |Slow-Start Stage+--------------> |   Else                    |
            +----------------+                |      Nr=0;                |
   Nr > N           |                         +---------------------------+
                    |
          +---------v----------------+
          |Congestion-Avoidance Stage|
          +--------------------------+

  Figure 2: Stage transition from slow start to congestion avoidance.


4.2.1 Redundant Transmission Mode

   As shown in Figure 3, when running the redundant mode, MP layer and
   each path would calculate the average throughputs during a period of
   time (e.g. 1s). Meanwhile, the timer REDUNDANT_MODE_TIMER is reset
   and the variable Indicator_Redundant is set as 0. Before sending each
   segment, if Indicator_MP = 1, the redundant mode is switched to the
   MP mode to measure the throughput, as described in Section 4.2.2.
   Otherwise, the two throughputs obtained from the redundant and MP
   modes are compared, which is introduced in Section 4.2.3.











J. Zuo, et al            Expires April 29, 2018                 [Page 6]


INTERNET-DRAFT                                          October 30, 2017


+--------------------------------+                         +-------------------------+
|        Redundant Mode          |                         |        MP Mode          |
+--------------------------------+                         +-------------------------+
|      +-------------------+     | Indicator_MP = 1        |  +-------------------+  |
|      |  after a period of|     +------------------------->  |  after a period of|  |
|      |  time (e.g. 1s)   |     |                         |  |  time (e.g. 1s)   |  |
|      +---------+---------+     |                         |  +--------+----------+  |
|                |               <-------------------------+           |             |
| +--------------v-------------+ | Indicator_Redundant = 1 | +---------v------------ |
| | Indicator_Redundant = 0;   | |                         | | Indicator_MP = 0;   | |
| | Reset REDUNDANT_MODE_TIMER | |                         | | Reset MP_MODE_TIMER | |
| +----------------------------+ |                         | +---------------------- |
|                                |                         |                         |
+--------+------+----------------+                         +-----------+----^-----^--+
         ^      |                                                      |    |     |
         |      |        +---------------------------------------+     |    |     |
         |      +-------->                                       <-----+    |     |
         |               | Comparison of the Measured Throughput |          |     |
         |               |                                       +----------+     |
         |               +-------------------+-------------------+ select MP mode |
         |                                   |                                    |
         |             select redundant mode |                                    |
         |                          +--------v--------+                           |
         |                          |transmit data    |                           |
         +--------------------------+in the best path +---------------------------+
           Indicator_Redundant = 1  +-----------------+     Indicator_MP = 1

Figure 3: The redundant-and-MP mode transition when the corresponding indicator is equal to 1.

4.2.2 Multipath Transmission Mode

   As shown in Figure 3, when running the MP mode, MP layer would
   calculate its average throughput during a period of time (e.g. 1s).
   Meanwhile, the timer MP_MODE_TIMER is reset and the variable
   Indicator_MP is set as 0. Before sending each segment, if
   Indicator_Redundant = 1, the MP mode is switched to the redundant
   mode to measure the throughputs (refer to Section 4.2.1). Otherwise,
   the two throughputs obtained from the redundant and MP modes are
   compared (see Section 4.2.3).


4.2.3 Throughput Comparison

   By comparing the throughputs measured by the redundant and MP modes,
   a transmission mode corresponding to the larger throughput would be
   selected.

   If the redundant mode (described in Section 4.2.1) is selected, the



J. Zuo, et al            Expires April 29, 2018                 [Page 7]


INTERNET-DRAFT                                          October 30, 2017


   path with the highest throughput is employed for data transmission.
   Before sending each segment, if Indicator_redundant = 1 or
   Indicator_MP = 1, we will go back to the redundant mode or the MP
   mode to measure the corresponding throughput(s). If both of the
   indicators are 0, keep transmitting data at the best path.

   If the MP mode (described in Section 4.2.2) is selected, the multiple
   paths are bonded together to achieve the aggregated throughput.


4.2.4 Indicator Timer Timeout

   During data transmission, if the timer for the redundant/MP mode is
   timeout, set Indicator_Redundant/Indicator_MP = 1 and reset the timer
   of the redundant/MP mode.


5. Security Considerations

   TBD.


6. IANA Considerations


7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, DOI
             10.17487/RFC2119, March 1997, <http://www.rfc-
             editor.org/info/rfc2119>.

   [RFC6356] Raiciu, C., Handly, M., and Wischikf, D., "Coupled
             Congestion Control for Multipath Transport Protocols", RFC
             6356, DOI 10.17487/RFC6356, October 2011, <https://rfc-
             editor.org/rfc/rfc6356.txt>.

   [RFC6824] Ford, A., Raiciu, C., Handley, M., and Bonaventure, O.,
             "TCP Extensions for Multipath Operation with Multiple
             Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
             <http://www.rfc-editor.org/info/rfc6824>.

   [RFC6182] Ford, A., Raiciu, C., Handley, M., Barre, S., Iyengar, J.,
             "Architectural Guidelines for Multipath TCP Development",
             RFC 6182, DOI 10.17487/RFC6182, March 2011,



J. Zuo, et al            Expires April 29, 2018                 [Page 8]


INTERNET-DRAFT                                          October 30, 2017


             <http://www.rfc-editor.org/info/rfc6182>.

7.2. Informative References

   [CMT-SCTP] Yang, W., Li, H., Li, F., Wu, Q., & Wu, J., "RPS: range-
             based path selection method for concurrent multipath
             transfer", June 2010, In Proceedings of the 6th
             International Wireless Communications and Mobile Computing
             Conference (pp. 944-948). ACM.


Author's Addresses

             Fanzhao Wang
             Huawei Technologies
             Bantian, Longgang District,
             Shenzhen 518129 P.R. China
             EMail: wangfanzhao@huawei.com

             Jing Zuo
             Huawei Technologies
             Bantian, Longgang District,
             Shenzhen 518129 P.R. China
             EMail: jing.zuo@huawei.com

             Zhen Cao
             Huawei Technologies
             No.156 Beiqing Rd. Haidian District,
             Beijing 100095 P.R. China
             EMail: zhencao.ietf@gmail.com

             Kai Zheng
             Huawei Technologies
             No.156 Beiqing Rd. Haidian District,
             Beijing 100095 P.R. China
             EMail: kai.zheng@huawei.com
















J. Zuo, et al            Expires April 29, 2018                 [Page 9]


Html markup produced by rfcmarkup 1.126, available from https://tools.ietf.org/tools/rfcmarkup/