User-Plane Protocols for Multiple Access Management Service
draft-zhu-intarea-mams-user-protocol-07

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INTAREA                                                          J. Zhu
Internet Draft                                                    Intel
Intended status: Standards Track                                 S. Seo
                                                Expires: October 3,2019
                                                          Korea Telecom
                                                             S. Kanugovi
                                                                   Nokia
                                                                 S. Peng
                                                                  Huawei
                                                           April 3, 2019

        User-Plane Protocols for Multiple Access Management Service
                  draft-zhu-intarea-mams-user-protocol-07

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   respect to this document. Code Components extracted from this
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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   Co-existence of MX Adaptation and MX Convergence Sublayers
            8
   5. MX Convergence Control Message.................................8
      5.1   Keep-Alive Message.......................................9
      5.2   Probe Message............................................9
      5.3   Packet Loss Report (PLR) Message........................10
      5.4   First Sequence Number (FSN) Message.....................11
      5.5   Coded MX SDU (CMS) Message..............................12
      5.6   Traffic Splitting Update (TSU) Message..................13
      5.7   Acknowledgement Message.................................14
   6  Security Considerations.......................................14
   7  IANA Considerations...........................................15
   8  Contributing Authors..........................................15
   9  References....................................................15
      9.1   Normative References....................................15
      9.2   Informative References..................................15

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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 trailer-based convergence capability in the discovery
and capability exchange procedures [MAMS].

          +-----------------------------------------------------+
          |                        IP PDU                       |
          |-----------------------------------------------------|
          |     Trailer-based 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   Co-existence of MX Adaptation and MX Convergence Sublayers

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. Figure 6 shows the MX
control PDU format with the following fields:

o Type (1 Byte): the type of the MX control message
o CID (1 Byte): the connection ID of the delivery connection for
  sending out the MX control message
o MX Control Message (variable): the payload of the MX control message

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Figure 7 shows the MX convergence control protocol stack, and MX
control PDU goes through the MX adaptation sublayer the same way as MX
data PDU.

                        <----MX Control PDU Payload --------------->
+------------------------------------------------------------------+
| IP header | UDP Header| Type | CID |       MX Control Message    |
+------------------------------------------------------------------+
                      Figure 6: MX Control PDU Format

          |-----------------------------------------------------|
          |          MX Convergence Control Messages            |
          |-----------------------------------------------------|
          |                  UDP/IP                             |
          |-----------------------------------------------------|
          | MX Adaptation  | MX Adaptation | MX Adaptation      |
          | Sublayer       | Sublayer      | Sublayer           |
          | (optional)     | (optional)    | (optional)         |
          |-----------------------------------------------------|
          | Access #1 IP   | Access #2 IP  | Access #3 IP       |
          +-----------------------------------------------------+
              Figure 7: 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 Keep-Alive 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 milliseconds.

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 Probing 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: a bit flag to indicate the presence of the Reverse
          Connection ID (R-CID) field.
       + Bit #3~7: 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 milliseconds.
  o Padding (variable)

The "R-CID" field is only present if both Bit #0 and Bit #2 of the
"Probing Flag" field are set to "1". Moreover, Bit #2 of the "Probing
Flag" field SHOULD be set to "0" if the Bit #0 is "0", indicating the
ACK message is not expected.

If the "R-CID" field is not present but the Bit #0 of the "Probing
Flag" field is set to "1", 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  Packet Loss Report (PLR) Message

The "Type" field is set to "2" 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 Connection ID (1 Byte): an unsigned integer to identify the anchor
     connection which the ACK message is for;
  o Traffic Class ID (1 Byte): an unsigned integer to identify the
     traffic class of the anchor connection which the ACK message is
     for;
  o ACK number (4 Bytes): the next (in-order) sequence number (SN)
     that the sender of the PLR message is expecting
  o Number of Loss Bursts (1 Byte)

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     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 8: MAMS Retransmission Procedure

Figure 8 shows the MAMS retransmission procedure in an example where
the lost packet is found and retransmitted.

5.4  First Sequence Number (FSN) Message

The "Type" field is set to "3" 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 Connection ID (1 Byte): an unsigned integer to identify the anchor
     connection which the FSN message is for;
  o Traffic Class ID (1 Byte): an unsigned integer to identify the
     traffic class of the anchor connection which the FSN message is
     for;
  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 9 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 9: MAMS Retransmission Procedure with FSN

5.5  Coded MX SDU (CMS) Message

The "Type" field is set to "4" 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 Connection ID (1 Byte): an unsigned integer to identify the anchor
     connection of the coded MX SDU;
  o Traffic Class ID (1 Byte): an unsigned integer to identify the
     traffic class of the coded MX;
  o Sequence Number (4 Bytes): the sequence number of the first
     (uncoded) MX SDU used to generate the coded MX SDU.
  o Fragmentation Control (FC) (1 Byte): to provide necessary
     information for re-assembly, only needed if the coded MX SDU is
     too long to transport in a single MX control PDU.
  o N (1 Byte): the number of consecutive MX SDUs used to generate the
     coded MX SDU
  o K (1 Byte): the length (in terms of bits) of the coding
     coefficient field
  o Coding Coefficient ( N x K / 8 Bytes)
       + a(i): the coding coefficient of the i-th (uncoded) MX SDU
       + padding
  o Coded MX SDU (variable): the coded MX SDU

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If K = 0, the simple XOR method is used to generate the Coded MX SDU
from N consecutive uncoded MX SDUs, and the a(i) fields are not
included in the message.

If the coded MX SDU is too long, it can be fragmented, and transported
by multiple MX control PDUs. The N, K, and a(i) fields are only
included in the MX PDU carrying the first fragment of the coded MX SDU.

          C-MADP                                             N-MADP
              |                                                 |
              |<------------------ MX SDU #1 -------------------|
              |      lost<-------- MX SDU #2 -------------------|
              |<---- CMS Message (MX SDU #1 XOR MX SDU #2)------|
             +----------------------+                           |
             | MX SDU #2 recovered  |                           |
             +----------------------+                           |
              |                                                 |

       Figure 10: MAMS Packet Recovery Procedure with XOR Coding

5.6  Traffic Splitting Update (TSU) Message

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

N-MADP (or C-MADP) may send out a TSU message if downlink (or uplink)
traffic splitting configuration has changed.

A TSU message consists of the following fields:

  o Connection ID (1 Byte): an unsigned integer to identify the anchor
     connection;
  o Traffic Class ID (1 Byte): an unsigned integer to identify the
     traffic class;
  o Sequence Number (2 Bytes): an unsigned integer to identify the TSU
     message.
  o Flags (1 Byte)
       + Bit #0: a Reverse Path bit flag to indicate if the traffic
          splitting configuration is for the reverse path (1) or not
          (0);
       + Bit #1: a Bit-Reversal bit flag to indicate if bit-reversal is
          used in traffic splitting
       + Others: reserved.
  o Traffic Splitting Configuration Parameters ( 5 + (N -1) Bytes):
       + StartSN (4 Bytes): the sequence number of the first MX SDU
          using the traffic splitting configuration provided by the TSU
          message

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       + L (1 Byte): the traffic splitting burst size
       + K(i): the traffic splitting threshold of the i-th delivery
          connection, where connections are ordered according to their
          Connection ID.

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.

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

Wherein, 1 < or = i < N, K[0]=0, and K[N]=L.

N is the total number of connections for delivering a data flow,
identified by (anchor) Connection ID and Traffic Class ID.

When the bit-reversal bit is set to 1, the burst size L MUST be a power
of 2, and the traffic splitting function is

         f(x)=i,  if K[i-1]< or = F(mod(x - StartSN, L)) < K[i]

Wherein F(.) is the bit reversal function [BITR] of the input variable.

5.7  Acknowledgement Message

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

C-MADP (or N-MADP) SHOULD send out the ACK message in response to the
successful reception of a PLR, FSN, or TSU message.

C-MADP SHOULD send out the ACK message in response to a Probe message
with the ACK flag set to "1".

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 milliseconds.

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].

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7  IANA Considerations

This draft makes no requests of IANA.

8  Contributing Authors

The editors gratefully acknowledge the following additional
contributors in alphabetical order: Salil Agarwal/Nokia, Hema
Pentakota/Nokia.

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

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   [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

   [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

   [BITR] Alan H. Karp, "Bit reversal on uniprocessors", SIAM Review,
             38 (1): 1-26, 1996.

Authors' Addresses

   Jing Zhu

   Intel

   Email: jing.z.zhu@intel.com

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   SungHoon Seo

   Korea Telecom

   Email: sh.seo@kt.com

   Satish Kanugovi

   Nokia

   Email: satish.k@nokia.com

   Shuping Peng

   Huawei

   Email: pengshuping@huawei.com

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