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Network Working Group                                     Changqiao Xu
Internet Draft                                                   BUPT
Intended status: Experimental                              Jiuren Qin
Expires: December 2017                                           BUPT
                                                          Hongke Zhang
                                                                 BUPT
                                                        Chunshan Xiong
                                          Huawei Technologies Co., Ltd
                                                              Lei Zhu
                                          Huawei Technologies Co., Ltd
                                                         June 21, 2017


                      A Message-Oriented Extension to
              Multipath Transmission Control Protocol (MPTCP)
                        draft-xu-mptcp-momp-04.txt


Status of this Memo

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   The list of Internet-Draft Shadow Directories can be accessed at
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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
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Abstract

   This memo specifies a message-oriented extension for Multipath TCP
   (MPTCP) which aims to serve high-bandwidth and real-time
   applications. By introducing a message mapping to MPTCP, Message-
   Oriented MPTCP (MO-MPTCP) attaches some message features like
   boundaries, priority and dependency to bytestream. With such
   message-oriented information, MPTCP senders can avoid the waste of
   transmission resources and improve the transmission efficiency.


Table of Contents


   1. Introduction .............................................. 3
   2. Conventions ............................................... 3
   3. New Functionalities provided by MO-MPTCP .................. 3
   4. Message Mapping ........................................... 4


  5. Operations of MO-MPTCP .................................... 6
      5.1. Boundary-Based Packet Scheduling ..................... 6
      5.2. Message-Oriented Transmission Optimization ........... 8
   6. Interface Considerations .................................. 8
   7. Security Considerations ................................... 9
   8. IANA Considerations ....................................... 9
   9. References ................................................ 9
      9.1. Normative References ................................. 9
      9.2. Informative References ............................... 9
   10. Acknowledgments .......................................... 9


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1. Introduction

   With the increasingly demands for bandwidth-intensive services, e.g.,
   high-definition (HD) video, the streaming media data which is
   massive, ordered and delay-sensitive is becoming the main traffic of
   transport layer. Usually, the streaming media data is transferred by
   UDP (User Datagram Protocol) which performs better than TCP
   (Transmission Control Protocol) in improving throughput and reducing
   latency. However, UDP does not have congestion control mechanism and
   may result in network collapses.

   MPTCP which has been standardized in [RFC6824] can greatly improve
   the throughput of one association by concurrently transferring data
   on several TCP subflows. Furthermore, the congestion control
   mechanism provided by MPTCP can make it work without starving TCP.
   With these advantages, MPTCP has the potential to serve the high-
   bandwidth and real-time applications.

   This memo introduces a Message-Oriented MPTCP (MO-MPTCP) which is a


  light and scalable extension to standard MPTCP [RFC6824] and more
   suitable for streaming media transfer. MO-MPTCP specifies a message
   mapping to record the information about message boundaries, priority
   and dependency in the connection level. Based on this mapping, MO-
   MPTCP offers Boundary-Based Packet Scheduling Mechanism which can
   avoid unnecessary transmission and Message-Oriented Transmission
   Optimization which can preferentially ensure the transmission of
   important data.

2. Conventions

   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. New Functionalities provided by MO-MPTCP

   Making the transmission of stream media as an example, the new
   functionalities provided by Message-Oriented MPTCP are as follows:

   o Boundary-Based Packet Scheduling

   In the process of stream media transmission, application layer
   usually delivers the data to the transport layer frame by frame.
   Each frame can be seen as an individual message. However, in the
   transport layer, limited by Maximum Segment Size (MSS) MPTCP tends
   to segment the big messages and splice the small messages. And it
   also splice the small messages into one data packets to reduce


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   transmission overhead. In general, all data are transferred in the
   size of MSS. The segmentation and splicing operation of transport
   layer leads to lose the original message boundaries. MO-MPTCP
   provides a message mapping that can record the features of
   application messages including boundaries, priority and dependency,
   etc.. This mapping can help the sender to avoid unnecessary
   transmissions. For example, stream media can usually tolerate the
   loss of partial packets, which means the sender can give


  transmission up and notify the receiver when a packet is considered
   as time out. This kind of partially reliable mechanism can refer to
   [PRMP]. In this situation, if a packet which contains partial data
   of a frame data is abandoned by the sender, as a result, this frame
   cannot be decoded correctly at receiver side with the absence of
   partial information. Current MPTCP which is based on bytestream
   fails to perceive this situation, and still transmits the remaining
   data of this frame which is a waste of transmission resources. In
   Message-Oriented MPTCP, thanks to the recording of message boundary,
   senders can abandon the remaining data simultaneously and avoid
   unnecessary transmission.

   o Message-Oriented Transmission Optimization

   Traditional transmission ignores the priority and dependency of
   messages and treats them equally as a bytestream, which makes the
   transport blindly. Using an IPMH-like [IPMH] interface, MO-MPTCP can
   get the priority of each message, and record the dependency between
   them. For instance, in the standard MPEG coding, "I" frames are
   essential to the recovery of the whole images and can be decoded
   independently, so they have the "HIGH" priority and Dependency is
   "NULL". Similarly, "P" frames which are decoded based on a previous
   frame have "MEDIUM" priority and Dependency is "PRE". "B" frames
   which are decoded based on both a previous frame and a latter frame
   have "LOW" priority and Dependency is "PRE&LAR". Through some rules,
   TCP packets can determine their own priorities from the messages
   priorities. The reliability and timeliness of high-priority packets
   will be guaranteed first when congestion occurs. When a duplicate
   acknowledgement is received in the subflow level, the sender will
   execute judgment for the missing packet upon their priorities and
   duplicate ACK numbers. The send then will retransmit the packet if
   needed.

4. Message Mapping

   MO-MPTCP sets up a Message Mapping in the connection level. The
   Message Mapping which is similar to the Data Sequence Mapping can
   associates message features such as boundary and priority with
   stream features such as DSN. This mapping which is the foundation of
   MO-MPTCP can provide useful information for data scheduling in
   transmission.


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   The Message Mapping consists of a lot of records, and each record
   corresponds to an application message. Its structure sketch is show
   in Figure 1.

                         +----------------------+
                         |   Message Mapping    |
                         +----------------------+
                         |    Message Type 1    |
                         |        DSN 1         |
                         |       Length 1       |
                         |      Priority 1      |
                         |    Dependency 1      |
                         +----------------------+
                         |    Message Type 2    |
                         |        DSN 2         |
                         |       Length 2       |
                         |      Priority 2      |
                         |    Dependency 2      |
                         +----------------------+
                         \          .           /
                         /          .           \
                         +----------------------+
                         |    Message Type N    |
                         |        DSN N         |
                         |       Length N       |
                         |      Priority N      |
                         |    Dependency N      |
                         +----------------------+
                         Figure 1 Message Mapping

   o Message Type is used to distinguish the classes of message. It
     can change its meaning depending on the application. For example,
     in the streaming media transmission, it represents which kind of
     frame this message is.

   o DSN=Data Sequence Number. DSN shows the Data Sequence Number of
     the first byte in an application message.

   o Length shows the number of bytes that this message contains. This
     parameter is usually used with DSN, and can identify the message
     boundaries.

   o Priority shows the importance of this message which usually be
      divided into three priority HIGH, MEDIUM, LOW.





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   o Dependency shows the dependencies between adjacent messages. For
     example, "NULL" means this message is independent; "PRE" means
     this message depends on the previous message to be decoded; "LAT"
     means this message depends on the later message to be decoded.
     "PRE&LAT"means this message depends on both the previous and
     later messages to be decoded.

   The DSN and Length are used to identify the boundary of an
   application message. And, the rest of the parameters which are
   unique nature of messages are used to provide information for the
   transmission optimization.

   MO-MPTCP also provides rules for mapping establishment and removal
   as follows:

   o On receiving an application message, the sender SHOULD add a new
     record containing all necessary parameters to the Message Mapping.
     However these parameters may have different meaning for different
     applications.

   o When receiving an ACK in the MPTCP connection level, the sender
     SHOULD judge whether need to remove some records from the Message
     Mapping. Some messages are larger than the MSS, and may be partly
     acknowledged. MO-MPTCP provisions that the record for a message
     SHOULD be retained until all segments of this message are
     acknowledged.

5. Operations of MO-MPTCP

5.1. Boundary-Based Packet Scheduling

   Boundary-Based Packet Scheduling is used in the situations where the
   applications can tolerate the loss of some packages to meet its
   requirements for timeliness. [PRMP] proposed a partially reliable
   extension to MPTCP called PR-MPTCP, which is designed to deal with
   above situations. However, PR-MPTCP is based on the bytestream and
   can perform better with the help of MO-MPTCP. For instance, if a TCP
   packet containing partial data of a message is determined to be
   discarded, MO-MPTCP can find and discard the remaining data that
   belongs to or relies on this message. The detailed operating steps
   are as follows:

   a) MO-MPTCP offers a function to the sender. When determining to
      discard a packet, the sender SHOULD call thi s function and send
      the starting DSN and length of this packet as parameters to MO-
      MPTCP.



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   b) Every time receiving calling from the sender, MO-MPTCP SHOULD
      search the Message Mapping and record all the messages involved in
      this packet.

   c) Based on the messages selected by step b) MO-MPTCP then refers
      to the Dependency recorded in Message Mapping and extracts some
      other messages which rely on them to be decoded.

   d) MO-MPTCP combines all the messages selected by step b) and c)
      and connects them as one or more bigger messages according to
      their DSNs and Length. Then the new boundaries of these messages
      are obtained.

   e) MO-MPTCP SHOULD return the starting DSN and Length of these new
      messages. Then, the sender can continue its original operations
      and discard the expanded messages according to the new boundaries.

    Step b) can be classified into the following situations:

   o Only one message is involved in the packet, which means this
     packet is just a segment of the original message. In this case,
     MO-MPTCP SHOULD search the Message Mapping and record this
     message.

   o Two or more messages are involved in the packet, which means this
     packet contains data comes from different messages. In this case,
     MO-MPTCP SHOULD search the Message Mapping and record all related
     messages.

  When executing step c) there are some notes:

   o Before starting to search the Message Mapping, MO-MPTCP
     preferably checks the priorities of the messages provided by step
     b) and skips the messages which have LOW priority. Because
     there is usually no message relies on them.

   o Although the parameter of Dependency in Message Mapping only
     reflects the relationship between adjacent messages, the lost a
     message with HIGH priority can influence several messages with
     lower priority. For example, if an "I" frame is decided to be
     discarded, the following several frames will be influenced. So,
     the implementation should pay attention to a chain reaction.







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5.2. Message-Oriented Transmission Optimization

   The Message Mapping records the priorities of the messages. Based on
   these priorities, each TCP packet can determine its own priority.
   The basic rules are as follows:

   o If the data of a packet comes from only one message, the packet
     priority is the same with the message priority.

   o If the data of a packet comes from several messages, the packet
     priority is the same with the highest message priority.

   Following the above rules, senders can obtain the packet priority,
   which is an important reference for the transmission optimization.
   The main operations of the optimization are as follows:

   a) Once the sender receives duplicate acknowledgement, it SHOULD
      obtain the priority of those corresponding TCP packets by
      searching the Message Mapping.

   b) MO-MPTCP determines whether these packets need being
      retransmitted immediately based on their priorities and the number
      of duplicate acknowledgments. The packets with HIGH priority
      will not be easily discarded;The packets with LOW priority will be
      discarded first when congestion occurs.

   c) If a TCP packet is judged to need retransmission by step b) the
      senders SHOULD retransmit it immediately. Meanwhile, it SHOULD
      also reset retransmission timer and clear the number of duplicate
      acknowledgment.

   d) If a TCP packet does not need to be transmitted after step b)
      the senders can continue their original works until event in step
      a) happens.

6. Implementation Consideration

   In order to achieve message-oriented control and byte-oriented
   transport, MO-MPTCP records the message information in the Message
   Mapping. In the implementations of MO-MPTCP, hosts have to reserve
   some memory for Message Mapping, which brings additional cost.
   However, with the help of Message Mapping, more intelligent and
   efficient transmission can be achieved. And the additional cost is
   reasonable and tolerable.

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7. Interface Considerations

   MO-MPTCP offers an interface to the upper layer, through which the
   applications can call MO-MPTCP and assign the parameters like
   priority and dependency. The ways in which application obtain these
   parameters can refer to [IPMH].

8. Security Considerations

   This memo develops no new security scheme for MPTCP. MO-MPTCP share
   the same security issues discussed in [RFC6824] with MPTCP.

9. IANA Considerations

   There is no IANA consideration for this memo.

10. References

10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
             "TCP Extensions for Multipath Operation with Multiple
             Addresses", RFC 6824, January 2013.

    10.2. Informative References

   [PRMP]   Changqiao Xu, H. Huang, H. Zhang, C. Xiong, L. Zhu
            "Multipath Transmission Control Protocol (MPTCP) Partial
             Reliability Extension? draft-xu-mptcp-prmp-02, September
             2015.

   [IPMH]    E, Gineste M, Dairaine L, et al. Building self-optimized
             communication systems based on applicative cross-layer
             information. Computer Standards & Interfaces, 2009,
             31(2): 354-361.

11. Acknowledgments

   This Internet Draft is the result of a great deal of constructive
   discussion with several people, notably Man Tang, Hui Huang, and
   Peng Wang.

   This document was prepared using 2-Word-v2.0.template.dot.



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   Authors' Addresses

   Changqiao Xu
   Beijing University of Posts and Telecommunications
   Institute of Network Technology, No. 10, Xitucheng Road,
   Haidian District, Beijing
   P.R. China

   Email: cqxu@bupt.edu.cn


   Jiuren Qin
   Beijing University of Posts and Telecommunications
   Institute of Network Technology, No. 10, Xitucheng Road,
   Haidian District, Beijing
   P.R. China

   Email: jrqin@bupt.edu.cn


   Hongke Zhang
   Beijing University of Posts and Telecommunications
   Institute of Network Technology, No. 10, Xitucheng Road,
   Haidian District, Beijing
   P.R. China

   Email: hkzhang@bupt.edu.cn

   Chunshan Xiong
   Huawei Technologies Co., Ltd
   Science and Technology Demonstration Garden, No. 156, Zhongguancun
   North Qing Road,
   Haidian District, Beijing
   P.R. China

   Email: sam.xiongchunshan@huawei.com

   Lei Zhu
   Huawei Technologies Co., Ltd
   Science and Technology Demonstration Garden, No. 156, Zhongguancun
   North Qing Road,
   Haidian District, Beijing
   P.R. China

   Email: lei.zhu@huawei.com




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