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INTAREA                                                          J. Zhu
Internet Draft                                                    Intel
Intended status: Standards Track                                 S. Seo
Expires: September 4,2020                                 Korea Telecom
                                                            S. Kanugovi
                                                                  Nokia
                                                                S. Peng
                                                                 Huawei
                                                          March 4, 2020

        User-Plane Protocols for Multiple Access Management Service
                  draft-zhu-intarea-mams-user-protocol-09


Status of this Memo

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

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   This Internet-Draft will expire on September 4,2020.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
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   document must include Simplified BSD License text as described in




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   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Abstract

   Today, a device can be simultaneously connected to multiple
   communication networks based on different technology implementations
   and network architectures like WiFi, LTE, and DSL. In such multi-
   connectivity scenario, it is desirable to combine multiple access
   networks or select the best one to improve quality of experience for
   a user and improve overall network utilization and efficiency. This
   document presents the u-plane protocols for a multi access
   management services (MAMS) framework that can be used to flexibly
   select the combination of uplink and downlink access and core
   network paths having the optimal performance, and user plane
   treatment for improving network utilization and efficiency and
   enhanced quality of experience for user applications.

Table of Contents

   1. Introduction................................................... 3
   2. Terminologies.................................................. 3
   3. Conventions used in this document.............................. 3
   4  MAMS User-Plane Protocols...................................... 4
      4.1   MX Adaptation Sublayer................................... 4
      4.2   GMA-based MX Convergence Sublayer........................ 5
      4.3   MPTCP-based MX Convergence Sublayer...................... 6
      4.4   GRE as MX Convergence Sublayer........................... 6
         4.4.1    Transmitter Procedures.............................7
         4.4.2    Receiver Procedures................................8
      4.5   MX Adaptation and Convergence Co-existence............... 8
   5. MX Convergence Control Message................................. 8
      5.1   Keep-Alive Message....................................... 9
      5.2   Probe Message............................................ 9
      5.3   Acknowledgement (ACK) Message........................... 10
      5.4   Packet Loss Report (PLR) Message........................ 10
      5.5   First Sequence Number (FSN) Message..................... 11
      5.6   Coding Coefficient Update (CCU) Message................. 12
      5.7   Coded MX SDU (CMS) Message.............................. 13
      5.8   Traffic Splitting Update (TSU) Message.................. 14
      5.9   Traffic Splitting Acknowledgement (TSA) Message......... 14
   6  Security Considerations....................................... 15
   7  IANA Considerations........................................... 15
   8  Contributing Authors.......................................... 16
   9  References.................................................... 16
      9.1   Normative References.................................... 16
      9.2   Informative References.................................. 16


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1. Introduction

   Multi Access Management Service (MAMS) [MAMS] is a programmable
   framework to select and configure network paths, as well as adapt to
   dynamic network conditions, when multiple network connections can
   serve a client device. It is based on principles of user plane
   interworking that enables the solution to be deployed as an overlay
   without impacting the underlying networks.

   This document presents the u-plane protocols for enabling the MAMS
   framework. It co-exists and complements the existing protocols by
   providing a way to negotiate and configure the protocols based on
   client and network capabilities. Further it allows exchange of
   network state information and leveraging network intelligence to
   optimize the performance of such protocols. An important goal for
   MAMS is to ensure that there is minimal or no dependency on the
   actual access technology of the participating links. This allows the
   scheme to be scalable for addition of newer access technologies and
   for independent evolution of the existing access technologies.

2. Terminologies

   Anchor Connection: refers to the network path from the N-MADP to the
   Application Server that corresponds to a specific IP anchor that has
   assigned an IP address to the client.

   Delivery Connection: refers to the network path from the N-MADP to
   the C-MADP.

   "Network Connection Manager" (NCM), "Client Connection Manager"
   (CCM), "Network Multi Access Data Proxy" (N-MADP), and "Client Multi
   Access Data Proxy" (C-MADP) in this document are to be interpreted
   as described in [MAMS].

3. Conventions used in this document

   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 [RFC2119].

   The terminologies "Network Connection Manager" (NCM), "Client
   Connection Manager" (CCM), "Network Multi Access Data Proxy" (N-
   MADP), and "Client Multi Access Data Proxy" (C-MADP) in this
   document are to be interpreted as described in [MAMS].





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4  MAMS User-Plane Protocols

Figure 1 shows the MAMS u-plane protocol stack as specified in [MAMS].
             +-----------------------------------------------------+
             |      User Payload (e.g. IP PDU)                     |
             |-----------------------------------------------------|
          +--|-----------------------------------------------------|--+
          |  |-----------------------------------------------------|  |
          |  | Multi-Access (MX) Convergence Sublayer              |  |
          |  |-----------------------------------------------------|  |
          |  |-----------------------------------------------------|  |
          |  | MX Adaptation  | MX Adaptation | MX Adaptation      |  |
          |  | Sublayer       | Sublayer      | Sublayer           |  |
          |  | (optional)     | (optional)    | (optional)         |  |
          |  |-----------------------------------------------------|  |
          |  | Access #1 IP   | Access #2 IP  | Access #3 IP       |  |
          |  +-----------------------------------------------------+  |
          +-----------------------------------------------------------+
                 Figure 1: MAMS U-plane Protocol Stack
It consists of the following two Sublayers:

o Multi-Access (MX) Convergence Sublayer: This layer performs multi-
  access specific tasks, e.g., access (path) selection, multi-link
  (path) aggregation, splitting/reordering, lossless switching,
  fragmentation, concatenation, keep-alive, and probing etc.
o Multi-Access (MX) Adaptation Sublayer: This layer performs functions
  to handle tunneling, network layer security, and NAT.

The MX convergence sublayer operates on top of the MX adaptation sublayer
in the protocol stack. From the Transmitter perspective, a User Payload
(e.g. IP PDU) is processed by the convergence sublayer first, and then by
the adaptation sublayer before being transported over a delivery access
connection; from the Receiver perspective, an IP packet received over a
delivery connection is processed by the MX adaptation sublayer first, and
then by the MX convergence sublayer.

4.1  MX Adaptation Sublayer

The MX adaptation sublayer supports the following mechanisms and
protocols while transmitting user plane packets on the network path:

o UDP Tunneling: The user plane packets of the anchor connection can be
  encapsulated in a UDP tunnel of a delivery connection between the N-
  MADP and C-MADP.


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o IPsec Tunneling: The user plane packets of the anchor connection are
  sent through an IPsec tunnel of a delivery connection.
o Client Net Address Translation (NAT): The Client IP address of user
  plane packet of the anchor connection is changed, and sent over a
  delivery connection.
o Pass Through: The user plane packets are passing through without any
  change over the anchor connection.

The MX adaptation sublayer also supports the following mechanisms and
protocols to ensure security of user plane packets over the network
path.

o IPsec Tunneling: An IPsec [RFC7296] tunnel is established between the
  N-MADP and C-MADP on the network path that is considered untrusted.
o DTLS: If UDP tunneling is used on the network path that is considered
  "untrusted", DTLS (Datagram Transport Layer Security) [RFC6347] can
  be used.

The Client NAT method is the most efficient due to no tunneling
overhead. It SHOULD be used if a delivery connection is "trusted" and
without NAT function on the path.

The UDP or IPsec Tunnelling method SHOULD be used if a delivery
connection has a NAT function placed on the path.

4.2  GMA-based MX Convergence Sublayer

Figure 2 shows the MAMS u-plane protocol stack based on trailer-based
encapsulation [GMA]. Multiple access networks are combined into a
single IP connection. If NCM determines that N-MADP is to be
instantiated with GMA as the MX Convergence Protocol, it exchanges the
support of GMA convergence capability in the discovery and capability
exchange procedures [MAMS].

          +-----------------------------------------------------+
          |                        IP PDU                       |
          |-----------------------------------------------------|
          |               GMA  Convergence Sublayer             |
          |-----------------------------------------------------|
          | MX Adaptation  | MX Adaptation | MX Adaptation      |
          | Sublayer       | Sublayer      | Sublayer           |
          | (optional)     | (optional)    | (optional)         |
          |-----------------------------------------------------|
          | Access #1 IP   | Access #2 IP  | Access #3 IP       |
          +-----------------------------------------------------+
 Figure 2: MAMS U-plane Protocol Stack with GMA as MX Convergence Layer

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Figure 3 shows the trailer-based Multi-Access (MX) PDU (Protocol Data
Unit) format [GMA]. If the MX adaptation method is UDP tunneling and
"MX header optimization" in the "MX_UP_Setup_Configuration_Request"
message [MAMS] is true, the "IP length" and "IP checksum" header fields
of the MX PDU SHOULD remain unchanged. Otherwise, they should be
updated after adding or removing the GMA trailer in the convergence
sublayer.

          +------------------------------------------------------+
          | IP hdr |        IP payload             | GMA Trailer |
          +------------------------------------------------------+
                         Figure 3: GMA PDU Format

4.3  MPTCP-based MX Convergence Sublayer

Figure 4 shows the MAMS u-plane protocol stack based on MPTCP. Here, MPTCP
is reused as the "MX Convergence Sublayer" protocol. Multiple access
networks are combined into a single MPTCP connection. Hence, no new u-
plane protocol or PDU format is needed in this case.

          |-----------------------------------------------------|
          |                       MPTCP                         |
          |-----------------------------------------------------|
          |  TCP           |   TCP         |      TCP           |
          |-----------------------------------------------------|
          | MX Adaptation  | MX Adaptation | MX Adaptation      |
          | Sublayer       | Sublayer      | Sublayer           |
          | (optional)     | (optional)    | (optional)         |
          |-----------------------------------------------------|
          | Access #1 IP   | Access #2 IP  | Access #3 IP       |
          +-----------------------------------------------------+
    Figure 4: MAMS U-plane Protocol Stack with MPTCP as MX Convergence
                                   Layer


If NCM determines that N-MADP is to be instantiated with MPTCP as the MX
Convergence Protocol, it exchanges the support of MPTCP capability in the
discovery  and  capability  exchange  procedures  [MAMS].  MPTCP  proxy
protocols [MPProxy][MPPlain] SHOULD be used to manage traffic steering
and aggregation over multiple delivery connections.

4.4  GRE as MX Convergence Sublayer

Figure 5 shows the MAMS u-plane protocol stack based on GRE (Generic
Routing Encapsulation) [GRE2784]. Here, GRE is reused as the "MX
Convergence sub-layer" protocol. Multiple access networks are combined


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into a single GRE connection. Hence, no new u-plane protocol or PDU format
is needed in this case.

          +-----------------------------------------------------+
          |      User Payload (e.g. IP PDU)                     |
          |-----------------------------------------------------|
          |              GRE as MX Convergence Sublayer         |
          |-----------------------------------------------------|
          |        GRE Delivery Protocol (e.g. IP)              |
          |-----------------------------------------------------|
          | MX Adaptation  | MX Adaptation | MX Adaptation      |
          | Sublayer       | Sublayer      | Sublayer           |
          | (optional)     | (optional)    | (optional)         |
          |-----------------------------------------------------|
          | Access #1 IP   | Access #2 IP  | Access #3 IP       |
          +-----------------------------------------------------+
     Figure 5: MAMS U-plane Protocol Stack with GRE as MX Convergence
                                   Layer


If NCM determines that N-MADP is to be instantiated with GRE as the MX
Convergence Protocol, it exchanges the support of GRE capability in the
discovery and capability exchange procedures [MAMS].

4.4.1            Transmitter Procedures

Transmitter is the N-MADP or C-MADP instance, instantiated with GRE as
the convergence protocol that transmits the GRE packets. The Transmitter
receives the User Payload (e.g. IP PDU), encapsulates it with a GRE header
and Delivery Protocol (e.g. IP) header to generate the GRE Convergence
PDU.

When IP is used as the GRE delivery protocol, the IP header information
(e.g. IP address) can be created using the IP header of the user payload
or a virtual IP address. The "Protocol Type" field of the delivery header
is set to 47 (or 0X2F, i.e. GRE)[IANA].

The GRE header fields are set as specified below,

  - If the transmitter is a C-MADP instance, then sets the LSB 16 bits
     to the value of Connection ID for the Anchor Connection associated
     with the user payload or sets to 0xFFFF if no Anchor Connection ID
     needs to be specified.
  - All other fields in the GRE header including the remaining bits in
     the key fields are set as per [GRE_2784][GRE_2890].




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4.4.2            Receiver Procedures

Receiver is the N-MADP or C-MADP instance, instantiated with GRE as the
convergence protocol that receives the GRE packets. The receiver
processes the received packets per the GRE procedures [GRE_2784,
GRE_2890] and retrieves the GRE header.

  - If the Receiver is an N-MADP instance,
       o Unless the LSB 16 Bits of the Key field are 0xFFFF, they are
          interpreted as the Connection ID of Anchor Connection for the
          user payload. This is used to identify the network path over
          which the User Payload (GRE Payload) is to be transmitted.
  - All other fields in the GRE header, including the remaining bits
     in the Key fields, are processed as per [GRE_2784][GRE_2890].

The GRE Convergence PDU is passed onto the MX Adaptation Layer (if
present) before delivery over one of the network paths.

4.5   MX Adaptation and Convergence Co-existence

MAMS u-plane protocols support multiple combinations and instances of
user plane protocols to be used in the MX Adaptation and the
Convergence sublayers.

For example, one instance of the MX Convergence Layer can be MPTCP
Proxy [MPProxy][MPPlain] and another instance can be Trailer-based. The
MX Adaptation for each can be either UDP tunnel or IPsec. IPsec may be
set up for network paths considered as untrusted by the operator, to
protect the TCP subflow between client and MPTCP proxy traversing that
network path.

Each of the instances of MAMS user plane, i.e. combination of MX
Convergence and MX Adaptation layer protocols, can coexist
simultaneously and independently handle different traffic types.

5. MX Convergence Control Message

A UDP connection may be configured between C-MADP and N-MADP to
exchange control messages for keep-alive or path quality estimation.
The N-MADP end-point IP address and UDP port number of the UDP
connection is used to identify MX control PDU. A MX control PDU
consists of the following fields:

  o Type (1 Byte): the MX control message type
  o CID (1 Byte): an unsigned integer to identify the anchor and delivery
     connection of the MX control message
       + Anchor Connection ID (MSB 4 Bits): an unsigned integer to
       identify the anchor connection

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       + Delivery Connection ID (LSB 4 Bits): an unsigned integer to
       identify the delivery connection
  o MX Control Message (variable): the payload of the MX control message

Figure 6 shows the MX convergence control protocol stack, and MX
control PDU goes through the MX sublayers the same way as MX data PDU.

          |-----------------------------------------------------|
          |          MX Convergence Control Messages            |
          |-----------------------------------------------------|
          |                  UDP/IP                             |
         |-----------------------------------------------------|
         |             MX Convergence Sublayer                 |
          |-----------------------------------------------------|
          | MX Adaptation  | MX Adaptation | MX Adaptation      |
          | Sublayer       | Sublayer      | Sublayer           |
          | (optional)     | (optional)    | (optional)         |
          |-----------------------------------------------------|
          | Access #1 IP   | Access #2 IP  | Access #3 IP       |
          +-----------------------------------------------------+
              Figure 6: MX Convergence Control Protocol Stack

5.1  Keep-Alive Message

The "Type" field is set to "0" for Keep-Alive messages. C-MADP may send
out Keep-Alive message periodically over one or multiple delivery
connections, especially if UDP tunneling is used as the adaptation method
for the delivery connection with a NAT function on the path.

A Keep-Alive message is 6 Bytes long, and consists of the following
fields:

  o Sequence Number (2 Bytes): the sequence number of the keep-alive
     message
  o Timestamp (4 Bytes): the current value of the timestamp clock of the
     sender in the unit of 100 microseconds.

5.2  Probe Message

The "Type" field is set to "1" for Probe messages.

N-MADP may send out the Probe message for path quality estimation. In
response, C-MADP may send back the ACK message.

A Probe message consists of the following fields:



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  o Sequence Number (2 Bytes): the sequence number of the Probe REQ
     message
  o Probing Flag (1 Byte):
       + Bit #0: a ACK flag to indicate if the ACK message is expected
          (1) or not (0);
       + Bit #1: a Probe Type flag to indicate if the Probe message is
          sent during the initialization phase (0) when the network path
          is not included for transmission of user data or the active
          phase (1) when the network path is included for transmission of
          user data;
       + Bit #2~7: reserved
  o Reverse Connection ID (1 Byte): the connection ID of the delivery
     connection for sending out the ACK message on the reverse path
  o Timestamp (4 Bytes): the current value of the timestamp clock of the
     sender in the unit of 100 microseconds.
  o Padding (variable)

The "R-CID" field is valid only if Bit #0 of the "Probing Flag" field is
set to "1". If the "R-CID" field is set to all "1"s, the ACK message
SHOULD be sent over the same delivery connection as the Probe message.

The "Padding" field is used to control the length of Probe message.

5.3  Acknowledgement (ACK) Message

The "Type" field is set to "2" for ACK messages. The ACK message
consists of the following fields:

  o Acknowledgment Number (2 Bytes): the sequence number of the
     received message.
  o Timestamp (4 Bytes): the current value of the timestamp clock of the
     sender in the unit of 100 microseconds.

5.4  Packet Loss Report (PLR) Message

The "Type" field is set to "3" for PLR messages.

C-MADP may send out the PLR messages to report lost MX SDU for example
during handover. In response, C-MADP may retransmit the lost MX SDU
accordingly.

A PLR message consists of the following fields:

  o Sequence Number (2 Bytes): the sequence number of the PLR message
  o Flow ID (1 Byte): an unsigned integer to identify the traffic
     flow;
  o ACK number (4 Bytes): the next (in-order) sequence number (SN) that
     the sender of the PLR message is expecting

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  o Number of Loss Bursts (1 Byte)
     For each loss burst, include the following
       + Sequence Number of the first lost MX SDU in a burst (4 Bytes)
       + Number of consecutive lost MX SDUs in the burst (1 Byte)


          C-MADP                                             N-MADP
              |                                                 |
              |<------------------ MX SDU (data packets)--------|
              |                                                 |
             +---------------------------------+                |
             |Packet Loss detected             |                |
             +---------------------------------+                |
              |                                                 |
              |----- PLR Message ------------------------------>|
              |<-------------retransmit(lost)MX SDUs -----------|

                Figure 7: MAMS Retransmission Procedure

Figure 7 shows the MAMS retransmission procedure in an example where
the lost packet is found and retransmitted.

5.5  First Sequence Number (FSN) Message

The "Type" field is set to "4" for FSN messages.

N-MADP may send out the FSN messages to indicate the oldest MX SDU in its
buffer if a lost MX SDU is not found in the buffer after receiving the
PLR message from C-MADP. In response, C-MADP SHALL only report packet
loss with SN not smaller than FSN.

A FSN message consists of the following fields:

  o Sequence Number (2 Bytes): the sequence number of the FSN message
  o Flow ID (1 Byte): an unsigned integer to identify the traffic
     flow;
  o First Sequence Number (4 Bytes): the sequence number (SN) of the
     oldest MX SDU in the (retransmission) buffer of the sender of the
     FSN message.

Figure 8 shows the MAMS retransmission procedure in an example where
the lost packet is not found.

          C-MADP                                             N-MADP
              |                                                 |


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              |<------------------ MX SDU (data packets)--------|
              |                                                 |
             +---------------------------------+                |
             |Packet Loss detected             |                |
             +---------------------------------+                |
              |                                                 |
              |----- PLR Message ------------------------------>|
              |                              +---------------------+
              |                              |Lost packet not found|
              |                              +---------------------+
              |<-------------FSN message -----------------------|

            Figure 8: MAMS Retransmission Procedure with FSN

5.6  Coding Coefficient Update (CCU) Message

The "Type" field is set to "5" for CCU messages.

N-MADP (or C-MADP) may send out the CCU message to support downlink (or
uplink) packet loss recovery through coding, e.g. [CRLNC], [CTCP],
[RLNC]. In response, C-MADP (or N-MADP) SHALL send out the ACK message
to indicate the successful reception. A CCU message consists of the
following fields:

  o Sequence Number (2 Bytes): the sequence number of the CCU message
  o Flow ID (1 Byte): an unsigned integer to identify the traffic flow
  o Fragmentation Control (FC) (1 Byte): to provide necessary
     information for re-assembly
       + Bit #7: a More Fragment (MF) flag to indicate if the fragment
          is the last one (0) or not (1)
       + Bit #0~#6: Fragment Offset (in units of fragments) to specify
          the offset of a particular fragment relative to the beginning
          of the SDU
  o Type (1 Byte): the coding coefficient generation method type
       + 0: none (if XOR is used for coding)
       + 1: deterministic
       + 2: random
       + Others: reserved
  o L (1 Bytes): the length of coding coefficient (in Bytes), included
     only if "Type" is 1 or 2
  o K (4 Bytes): the total number of coding coefficients, included
     only if "Type" is 1
  o Coding Coefficients (K x L Bytes): the list of coding
     coefficients, included only if "Type" is 1
  o Random Seed (8 Bytes): the random seed to generate coding
     coefficients, included only if "Type" is 2

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If the CCU message is too long, it can be fragmented and transported by
multiple MX control PDUs. Only the first MX control PDU carries Type, K,
and L.

5.7  Coded MX SDU (CMS) Message

The "Type" field is set to "6" for CMS messages.

N-MADP (or C-MADP) may send out the CMS message to support downlink (or
uplink) packet loss recovery through coding, e.g. [CRLNC], [CTCP],
[RLNC]. A coded MX SDU is generated by applying a network coding
algorithm to multiple consecutive (uncoded) MX SDUs, and it is used for
fast recovery without retransmission if any of the MX SDUs is lost.

A Coded MX SDU message consists of the following fields:

  o Sequence Number (2 Bytes): the sequence number of the CMS message
  o Flow ID (1 Byte): an unsigned integer to identify the traffic flow
  o Flag (1 Byte)
       + Bit #0: to indicate if the CMS message uses the same set of
          coding coefficients as its previous CMS message or not. This
          bit is flipped whenever a new set of coding coefficients is
          used
       + Bit #1: to indicate if the FC field is present or not
       + Bit #2: to indicate if the SDU-SN field is present or not
       + Bit #3: to indicate if the K field is present or not
       + Bit #4~7: reserved
  o Fragmentation Control (FC) (1 Byte): to provide necessary
     information for re-assembly
       + Bit #7: a More Fragment (MF) flag to indicate if the fragment
          is the last one (0) or not (1)
       + Bit #0~#6: Fragment Offset (in units of fragments) to specify
          the offset of a particular fragment relative to the beginning
          of the SDU
  o SDU-SN (4 Bytes): the sequence number of the first (uncoded) MX
     SDU used to generate the coded MX SDU
  o K (4 Bytes): with linear network coding, this field indicates the
     coding coefficient index for the first MX SDU; with XOR, this
     field is not included.
  o N (1 Byte): the number of consecutive MX SDUs used to generate the
     coded MX SDU
  o Coded MX SDU (variable): the coded MX SDU

If the CMS message is too long, it can be fragmented and transported by
multiple MX control PDUs. SDU-SN, N and K are only included in the MX
PDU carrying the first fragment of the coded MX SDU.



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          C-MADP                                             N-MADP
              |                                                 |
              |<-----------------CCU Message (Type = XOR)-------|
              |------ACK Message ------------------------------>|
              |                                                 |
              |<------------------ MX SDU #1 -------------------|
              |      lost<-------- MX SDU #2 -------------------|
              |<---- CMS Message (MX SDU #1 XOR MX SDU #2)------|
             +----------------------+                           |
             | MX SDU #2 recovered  |                           |
             +----------------------+                           |
              |                                                 |

        Figure 9: MAMS Packet Recovery Procedure with XOR Coding

5.8  Traffic Splitting Update (TSU) Message

The "Type" field is set to "7" for TSU messages.

N-MADP (or C-MADP) may send out a TSU message to change the traffic
splitting configuration of the reverse path.

A TSU message consists of the following fields:

  o Sequence Number (2 Bytes): the sequence number of the TSU message;
  o Flow ID (1 Byte): an unsigned integer to identify the flow;
  o N (1 Byte): number of delivery connections;
  o Traffic Splitting Parameters (N Bytes): the traffic splitting
     threshold K(i) of the i-th delivery connection, where connections
     are ordered according to their Connection ID, where i=1, 2, ...,
     N, and N is the number of delivery connections.

Let's use f(x) to denote the traffic splitting function, which maps a
MX SDU Sequence Number "x" to the i-th delivery connection, and f(x)
MAY be given by

           f(x)=i, if K[i-1] . mod(x - StartSN, K[N]) < K[i]

Wherein, i=1,2,...,N and K[0]=0. Please refer to 5.9 for the definition
of "StartSN".

5.9  Traffic Splitting Acknowledgement (TSA) Message

The "Type" field is set to "8" for TSA messages. N-MADP (or C-MADP)
SHALL send out a TSC message in response to a received TSU message. A
TSA message consists of the following fields:

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  o SN Number (2 Bytes): the sequence number of the corresponding TSU
     message;
  o StartSN (4 Bytes): the sequence number of the first MX SDU
     using  the  traffic  splitting  configuration  provided  by  the
     corresponding TSU message.

Figure 10 shows the traffic splitting update procedure for downlink
traffic, where C-MADP performs path quality measurement based on received
packets and determines traffic splitting parameters. Once update is
needed, C-MADP will send the TSU message carrying the new traffic
splitting parameters to N-MADP. N-MADP will send back the TSA message in
response, and perform traffic splitting accordingly. The TSA message
carries the "StartSN" parameter to indicate the first packet using the
new configuration so that C-MANDP can perform measurements accordingly.

For uplink traffic, N-MADP performs measurements, determines traffic
splitting parameters, and sends out the TSU message. C-MADP sends back
the TSA message and performs traffic splitting.

          C-MADP                                             N-MADP
              |                                                 |
              |<------------------ MX SDU #1 -------------------|
              |<------------------ MX SDU #2 -------------------|
  +--------------------------+                                  |
  | path quality measurement |                                  |
  +--------------------------+                                  |
              |------------------ TSU ------------------------->|
              |<------------------------- TSA(StartSN: 3) ------|
              |<------------------ MX SDU #3 -------------------|
              |<------------------ MX SDU #4 -------------------|

         Figure 10: Downlink Traffic Splitting Update Procedure

6  Security Considerations

User data in MAMS framework rely on the security of the underlying
network transport paths.  When this cannot be assumed, NCM configures
use of appropriate protocols for security, e.g. IPsec [RFC4301]
[RFC3948], DTLS [RFC6347].

7  IANA Considerations

This draft makes no requests of IANA.




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8  Contributing Authors

The editors gratefully acknowledge the following additional
contributors in alphabetical order: Salil Agarwal/Nokia, Wei Mao/Intel,
Hema Pentakota/Nokia, and Menglei Zhang/Intel.

9  References

9.1  Normative References

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

   [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
             Internet Protocol", RFC 4301, DOI10.17487/RFC4301,
             December 2005, <http://www.rfc-editor.org/info/rfc4301>.

9.2  Informative References

   [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
             Security Version 1.2", RFC 6347, January 2012,
             <http://www.rfc-editor.org/info/rfc6347>.

   [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
             Kivinen, "Internet Key Exchange Protocol Version 2
             (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
             2014, <http://www.rfc-editor.org/info/rfc7296>.

   [RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
             Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC
             3948, DOI 10.17487/RFC3948, January 2005, <http://www.rfc-
             editor.org/info/rfc3948>.

   [MPProxy] X. Wei, C. Xiong, and E. Lopez, "MPTCP proxy mechanisms",
             https://tools.ietf.org/html/draft-wei-mptcp-proxy-
             mechanism-02

   [MPPlain] M. Boucadair et al, "An MPTCP Option for Network-Assisted
             MPTCP", https://www.ietf.org/id/draft-boucadair-mptcp-
             plain-mode-09.txt

   [MAMS] S. Kanugovi, S. Vasudevan, F. Baboescu, and J. Zhu, "Multiple
             Access Management Protocol",
             https://tools.ietf.org/html/draft-kanugovi-intarea-mams-
             protocol-03




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   [GMA] J. Zhu, "Trailer-based Encapsulation Protocols for Generic
             Multi-Access Convergence",
             https://tools.ietf.org/html/draft-zhu-intarea-gma-01

   [GRE2784] D. Farinacci, et al., "Generic Routing Encapsulation
             (GRE)", RFC 2784 March 2000, <http://www.rfc-
             editor.org/info/rfc2784>.

   [GRE2890] G. Dommety, "Key and Sequence Number Extensions to GRE",
             RFC 2890 September 2000, <http://www.rfc-
             editor.org/info/rfc2890>.

   [IANA]    https://www.iana.org/assignments/protocol-
             numbers/protocol-numbers.xhtml

   [LWIPEP] 3GPP TS 36.361, "Evolved Universal Terrestrial Radio Access
             (E-UTRA); LTE-WLAN Radio Level Integration Using Ipsec
             Tunnel (LWIP) encapsulation; Protocol specification"

   [RFC791] Internet Protocol, September 1981

   [CRLNC] S Wunderlich, F Gabriel, S Pandi, et al. Caterpillar RLNC
             (CRLNC): A Practical Finite Sliding Window RLNC Approach,
             IEEE Access, 2017

   [CTCP] M. Kim, et al. Network Coded TCP (CTCP), eprint
             arXiv:1212.2291, 2012

   [RLNC] J. Heide, et al. Random Linear Network Coding (RLNC)-Based
             Symbol Representation, https://www.ietf.org/id/draft-
             heide-nwcrg-rlnc-00.txt

Authors' Addresses

   Jing Zhu

   Intel

   Email: jing.z.zhu@intel.com

   SungHoon Seo

   Korea Telecom

   Email: sh.seo@kt.com

   Satish Kanugovi


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   Nokia

   Email: satish.k@nokia.com

   Shuping Peng

   Huawei

   Email: pengshuping@huawei.com








































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