[Search] [txt|pdf|bibtex] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10                 Informational
                                                        IPR declarations
INTAREA/Network Working Group                                   J. Zhu
Internet Draft                                                  Intel
Intended status: Informational                            S. Kanugovi
Expires: October 1,2021                                       Nokia
                                                         April 1, 2021

            Generic Multi-Access (GMA) Encapsulation Protocol
                         draft-zhu-intarea-gma-09


Abstract

   Today, a device can be simultaneously connected to multiple
   networks, e.g. Wi-Fi, LTE, 5G, and DSL. It is desirable to combine
   them seamlessly below transport layer (L4) to improve quality of
   experience for applications that do not have such (multi-path)
   capability built in. Such optimization requires additional control
   information, e.g. Sequence Number, in each (IP) data packet. This
   document presents a new light weight and flexible encapsulation
   protocol for this need. The solution has been developed by the
   authors based on their experiences in multiple standards bodies
   including the IETF and 3GPP, is not an Internet Standard and does
   not represent the consensus opinion of the IETF. This document
   will enable other developers to build interoperable
   implementations.

Status of this Memo

   This Internet-Draft is submitted 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/ietf/1id-abstracts.txt

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




Zhu                    Expires October 1, 2021              [Page 1]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   This Internet-Draft will expire on October 1, 2021.

Copyright Notice

   Copyright (c) 2021 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. Conventions used in this document ............................ 4
   3. Use Case ..................................................... 4
   4. GMA Encapsulation Methods .................................... 5
      4.1. Trailer-based IP Encapsulation .........................6
      4.2. Header-based IP Encapsulation ..........................9
      4.3. (Header-based) non-IP Encapsulation ...................10
   5. Fragmentation ............................................... 10
   6. Concatenation ............................................... 11
   7. Security Considerations ..................................... 12
   8. IANA Considerations ......................................... 13
   9. References .................................................. 13
      9.1. Normative References ..................................13
      9.2. Informative References ................................13

1. Introduction

   Today, a device can be simultaneously connected to multiple
   networks, e.g. Wi-Fi, LTE, 5G, and DSL. It is desirable to combine
   them seamlessly below transport layer (L4) to improve quality of
   experience for applications that do not have such (multi-path)
   capability built in.

   Figure 1 shows the Multi-Access Management Service (MAMS) user-
   plane protocol stack [MAMS], which has been used in today's multi-
   access solutions [ATSSS] [LWIPEP] [GRE]. It consists of two
   layers: convergence and adaptation.

Zhu                    Expires October 1, 2021               [Page 2]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   The convergence layer is responsible for multi-access operations,
   including multi-link (path) aggregation, splitting/reordering,
   lossless switching/retransmission, fragmentation, concatenation,
   etc. It operates on top of the adaptation layer in the protocol
   stack. From the Transmitter perspective, a User Payload (e.g. IP
   packet) is processed by the convergence layer first, and then by
   the adaptation layer before being transported over a delivery
   connection; from the Receiver perspective, an IP packet received
   over a delivery connection is processed by the adaptation layer
   first, and then by the convergence layer.

          +-----------------------------------------------------+
          |   User Payload, e.g., IP Protocol Data Unit (PDU)   |
          +-----------------------------------------------------+
       +-----------------------------------------------------------+
       |  +-----------------------------------------------------+  |
       |  | Multi-Access (MX) Convergence Layer                 |  |
       |  +-----------------------------------------------------+  |
       |  +-----------------------------------------------------+  |
       |  | MX Adaptation   | MX Adaptation   | MX Adaptation   |  |
       |  | Layer           | Layer           | Layer           |  |
       |  | (optional)      | (optional)      | (optional)      |  |
       |  +-----------------+-----------------+-----------------+  |
       |  | Access #1 IP    | Access #2 IP    | Access #3 IP    |  |
       |  +-----------------------------------------------------+  |
       |                            MAMS User-Plane Protocol Stack |
       +-----------------------------------------------------------+

             Figure 1: MAMS User-Plane Protocol Stack [MAMS]

   Today, GRE is used [LWIPEP] [GRE1] [GRE2]as the encapsulation
   protocol at the convergence layer to encode additional control
   information, e.g. Key, Sequence Number. However, there are two
   main drawbacks with this approach:

      o IP-over-IP tunnelling (required for GRE) leads to higher
        overhead especially for small packet;
      o It is difficult to introduce new control fields.

   For example, the overhead of IP-over-IP/GRE tunnelling with both
   Key and Sequence Number is 32 Bytes (20 Bytes IP header + 12 Bytes
   GRE header), which is 80% of a 40 Bytes TCP ACK packet;

   This document presents a light-weight GMA encapsulation protocol
   for the convergence layer. It supports three encapsulation


Zhu                    Expires October 1, 2021               [Page 3]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   methods: trailer-based IP encapsulation, header-based IP
   encapsulation, and non-IP encapsulation. Particularly, the IP
   encapsulation methods avoid IP-over-IP tunneling overhead (20
   Bytes), which is 50% of a 40 Bytes TCP ACK packet. Moreover, it
   introduces new control fields to support fragmentation and
   concatenation, which are not available in today's GRE-based
   solutions [LWIPEP] [GRE].

   GMA protocol SHALL only operate between endpoints that have been
   configured to operate with GMA through additional control messages
   and procedures, for example [MAMS]. Moreover, UDP or IPSec
   tunneling MAY be used at the adaptation sublayer to protect GMA
   operation from intermediate nodes.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
   "MAY", and "OPTIONAL" in this document are to be interpreted as
   described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

3. Use Case

                         Multi-Access Aggregation

                    +---+                        +---+
                    | |A|--- LTE Connection -----|C| |
                    |U|-|                        |-|S| Internet
                    | |B|--- Wi-Fi Connection ---|D| |
                    +---+                        +---+
                   Client                Multi-Access Gateway

         A: The adaptation layer endpoint of the LTE connection
         resides in the client

         B: The adaptation layer endpoint of the Wi-Fi connection
         resides in the client

         C: The adaptation layer endpoint of the LTE connection
         resides in the Multi-Access Gateway, aka N-MADP (Network
         Multi-Access Data Proxy) in [MAMS]

         D: The adaptation layer endpoint of the Wi-Fi connection
         resides in the Multi-Access Gateway

         U: The convergence layer endpoint resides in the client

Zhu                    Expires October 1, 2021               [Page 4]


Internet-Draft        GMA Encapsulation Protocol            April 2021


         S: The convergence layer endpoint resides in the Multi-
         Access Gateway

               Figure 2: GMA-based Multi-Access Aggregation

   As shown in Figure 2, a client device (e.g. Smartphone, Laptop,
   etc.) may connect to Internet via both Wi-Fi and LTE connections,
   one of which (e.g. LTE) may operate as the anchor connection, and
   the other (e.g. Wi-Fi) may operate as the delivery connection. The
   anchor connection provides the IP address and connectivity for
   end-to-end Internet access, and the delivery connection provides
   additional path between client and Multi-Access Gateway for multi-
   access optimizations.

   For example, per-packet aggregation allows a single IP flow to use
   the combined bandwidth of the two connections. In another example,
   packets lost due to temporarily link outage may be retransmitted.
   Moreover, packets may be duplicated over multiple connections to
   achieve high reliability and low latency, and duplicated packets
   should be eliminated by the receiving side. Such multi-access
   optimization requires additional control information, e.g.
   Sequence Number, in each IP data packet, which can be supported by
   the GMA encapsulation protocol described in this document.

   The GMA protocol in this document is designed for multiple
   connections, but it may also be used when there is only one
   connection between two end-points. For example, it may be used for
   loss detection and recovery. In another example, it may be used to
   concatenate multiple small packets and reduce per packet overhead.

4. GMA Encapsulation Methods

   The GMA encapsulation protocol supports the following three
   methods:

      o Trailer-based IP Encapsulation (4.1)
      o Header-based IP Encapsulation (4.2)
      o (Header-based) non-IP Encapsulation (4.3)

   Trailer-based IP encapsulation SHOULD be used as long as
   implementation allows.

   Header-based encapsulation SHOULD be used if trailered-based
   encapsulation is not feasible due to any reason, e.g.
   implementation constraints, In this case, if the adaptation layer,
   e.g. UDP tunnelling, supports non-IP packet format, header-based
   non-IP encapsulation SHOULD be used; otherwise, header-based IP
   encapsulation SHOULD be used.

Zhu                    Expires October 1, 2021               [Page 5]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   If non-IP encapsulation is configured, GMA header SHOULD always be
   present in every packet. In comparison, if IP encapsulation is
   configured, GMA header or trailer may be added dynamically on per-
   packet basis, and it indicates the presence of GMA header (or
   trailer) to set the protocol type of the GMA PDU to "114".

   The GMA endpoints MAY configure the GMA encapsulation method
   through control signalling or pre-configuration. For example, the
   "MX UP Setup Configuration Request" message as specified in Multi-
   Access Management Service [MAMS] includes "MX Convergence Method
   Parameters", which provides the list of parameters to configure
   the convergence layer, and can be extended to indicate the GMA
   encapsulation method.

4.1. Trailer-based IP Encapsulation

          |<---------------------GMA PDU ----------------------->|
          +------------------------------------------------------+
          | IP hdr |        IP payload             | GMA Trailer |
          +------------------------------------------------------+
          |<------- GMA SDU (user payload)-------->|


       Figure 3: GMA PDU Format with Trailer-based IP Encapsulation

   Figure 3 shows the trailer-based IP encapsulation GMA PDU
   (protocol data unit) format. A (GMA) PDU may carry one or multiple
   IP packets, aka (GMA) SDUs (service data unit), in the payload, or
   a fragment of the SDU.

   The Protocol Type field in the IP header of the GMA PDU MUST be
   changed to 114 (Any 0-Hop Protocol) [IANA] to indicate the
   presence of the GMA trailer.

   If the original IP packet is IPv4, the following three IP header
   fields SHOULD be changed:

     o IP Length: add the length of "GMA Trailer" to the length of
        the original IP packet
     o Time To Live (TTL): set to "1"
     o IP checksum: recalculate after changing "Protocol Type", "TTL"
        and "IP Length"

   If the original IP packet is IPv6, the following two IP header
   fields SHOULD be changed:



Zhu                    Expires October 1, 2021               [Page 6]


Internet-Draft        GMA Encapsulation Protocol            April 2021


     o IP Length: add the length of "GMA Trailer" to the length of
        the original IP packet
     o Hop-Limit (HL): set the HL field to "0"

   The GMA (Generic Multi-Access) trailer MUST consist of two
   mandatory fields (the last 3 bytes): Next Header and Flags,
   defined as follows:

     o Next Header (1 Byte): the IP protocol type of the (first) SDU
        in a PDU, and it stores the value before it was overwritten to
        114.
     o Flags (2 Bytes): Bit 0 is the most significant bit (MSB), and
        Bit 15 is the least significant bit (LSB)
        + Checksum Present (bit 0): If the Checksum Present bit is set
        to 1, then the Checksum field is present;
        + Concatenation Present (bit 1): If the Concatenation Present
        bit is set to 1, then the PDU carries multiple SDUs, and the
        First SDU Length field is present;
        + Connection ID Present (bit 2): If the Connection ID Present
        bit is set to 1, then the Connection ID field is present;
        + Flow ID Present (bit 3): If the Flow ID Present bit is set
        to 1, then the Flow ID field is present;
        + Fragmentation Present (bit 4): If the Fragmentation Present
        bit is set to 1, then the PDU carry a fragment of the SDU and
        the Fragmentation Control field is present;
        + Delivery SN Present (bit 5): If the Delivery SN (Sequence
        Number) Present bit is set to 1, then the Delivery SN field is
        present and contains the valid information;
        + Flow SN Present (bit 6): If the Flow SN Present bit is set
        to 1, then the Sequence Number field is present;
        + Timestamp Present (bit 7): If the Timestamp Present bit is
        set to 1, then the Timestamp field is present;
        + TTL Present (bit 8): If the TTL Present bit is set to 1,
        then the TTL field is present;
        + Reserved (bit 9-12): set to "0" and ignored on receipt;
        + Version (bit 13~15): GMA version number, set to 0 for the
        GMA encapsulation protocol specified in this document.

   The Flags field is at the end of the PDU, and the Next Header
   field is the second last. The Receiver SHOULD first decode the
   Flags field to determine the length of the GMA trailer, and then
   decode each optional field accordingly. The GMA (Generic Multi-
   Access) trailer MAY consist of the following optional fields:

     o Checksum (1 Byte): to contain the (one's complement) checksum
        sum of all the 8 bits in the trailer. For purposes of
        computing the checksum, the value of the checksum field is


Zhu                    Expires October 1, 2021               [Page 7]


Internet-Draft        GMA Encapsulation Protocol            April 2021


        zero. This field is present only if the Checksum Present bit
        is set to one.
     o First SDU Length (2 Bytes): the length of the first IP packet
        in the PDU, only included if a PDU contains multiple IP
        packets. This field is present only if the Concatenation
        Present bit is set to one.
     o Connection ID (1 Byte): an unsigned integer to identify the
        anchor and delivery connection of the GMA PDU. This field is
        present only if the Connection ID Present bit is set to one.
        + Anchor Connection ID (MSB 4 Bits): an unsigned integer to
        identify the anchor connection
        + Delivery Connection ID (LSB 4 Bits): an unsigned integer to
        identify the delivery connection
     o Flow ID (1 Byte): an unsigned integer to identify the IP flow
        that a PDU belongs to, for example Data Radio Bearer (DRB) ID
        [LWIPEP] for a cellular (e.g. LTE) connection. This field is
        present only if the Flow ID Present bit is set to one.
     o Fragmentation Control (FC) (e.g. 1 Byte): to provide necessary
        information for re-assembly, only needed if a PDU carries
        fragments. This field is present only if the Fragmentation
        Present bit is set to one. Please refer to section 5 for its
        detailed format and usage.
     o Delivery SN (1 Byte): an auto-incremented integer to indicate
        the GMA PDU transmission order on a delivery connection.
        Delivery SN is needed to measure packet loss of each delivery
        connection and therefore generated per delivery connection per
        flow. This field is present only if the Delivery SN Present
        bit is set to one.
     o Flow SN (3 Bytes): an auto-incremented integer to indicate the
        GMA SDU (IP packet) order of a flow. Flow SN is needed for
        retransmission, reordering, and fragmentation. It SHALL be
        generated per flow. This field is present only if the Flow SN
        Present bit is set to one.
     o Timestamp (4 Bytes): to contain the current value of the
        timestamp clock of the transmitter in the unit of 1
        millisecond. This field is present only if the Timestamp
        Present bit is set to one.
     o TTL (1 Byte): to contain the TTL value of the original IP
        header if the GMA SDU is IPv4, or the Hop-Limit value of the
        IP header if the GMA SDU is IPv6. This field is present only
        if the TTL Present bit is set to one.

   Figure 4 shows the GMA trailer format with all the fields present,
   and the order of the GMA control fields SHALL follow the bit order
   in the Flags field. For example, Bit 0 (the MSB) of the Flags
   field is the Checksum Present bit, and the Checksum field is the
   last in the trailer except of the two mandatory fields. Bit 1 is


Zhu                    Expires October 1, 2021               [Page 8]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   the Concatenation present bit, and the FSL field is the second
   last.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     TTL       |                   Timestamp
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |                   Flow SN                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Delivery SN  |    FC         |   Flow ID     | Connection ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      First SDU Length (FSL)   |   Checksum    |  Next Header  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Flags                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 4: GMA Trailer Format

4.2. Header-based IP Encapsulation

   Figure 5 shows the header-based IP encapsulation format. Here, the
   GMA header is inserted right after the IP header of the GMA SDU,
   and the IP header fields of the GMA PDU SHOULD be changed in the
   same way as trailered-based IP encapsulation.

          +-----------------------------------------------+
          |IP hdr | GMA Header  |       IP payload        |
          +-----------------------------------------------+
       Figure 5: GMA PDU Format with Header-based IP Encapsulation

   Figure 6 shows the GMA header format. In comparison to GMA
   trailer, the only difference is that the Flags field is now in the
   front so that the Receiver can first decode the Flags field to
   determine the GMA header length. Moreover, the IP header fields of
   the GMA SDU SHOULD be changed the same way as in trailer-based IP
   encapsulation.

       +------------------------------------------------------+
       | Flags | other fields (TTL, Timestamp, Flow SN, etc.) |
       +------------------------------------------------------+
                       Figure 6: GMA Header Format




Zhu                    Expires October 1, 2021               [Page 9]


Internet-Draft        GMA Encapsulation Protocol            April 2021


4.3. (Header-based) non-IP Encapsulation

   Figure 7 shows the header-based non-IP encapsulation format. Here,
   "UDP Tunnelling" is configured at the MX adaptation layer. "TTL",
   "FSL", and "Next Header" are no longer needed. Moreover, the IP
   header fields of the GMA SDU remain unchanged.

    +-------------------------------------------------------------+
    | IP hdr | UDP hdr  | GMA Header | IP hdr |    IP payload     |
    +-------------------------------------------------------------+
                                    |<------- GMA SDU------------>|
                        |<------------------- GMA PDU------------>|

            Figure 7: GMA PDU Format with Non-IP Encapsulation

5. Fragmentation

   The convergence layer MAY support fragmentation if a delivery
   connection has a smaller maximum transmission unit (MTU) than the
   original IP packet (SDU). The fragmentation procedure at the
   convergence sublayer is similar to IP fragmentation [RFC791] in
   principle, but with the following two differences for less
   overhead:

     o The fragment offset field is expressed in number of fragments
     o The maximum number of fragments per SDU is 2^7 (=128)

   The Fragmentation Control (FC) field in the GMA trailer (or
   header) contains the following bits:

     o Bit #7: a More Fragment (MF) flag to indicate if the fragment
        is the last one (0) or not (1)
     o Bit #0~#6: Fragment Offset (in units of fragments) to specify
        the offset of a particular fragment relative to the beginning
        of the SDU

   A PDU carries a whole SDU without fragmentation if the FC field is
   set to all "0"s or the FC field is not present in the trailer.
   Otherwise, the PDU contains a fragment of the SDU.

   The Flow SN field in the trailer is used to distinguish the
   fragments of one SDU from those of another. The Fragment Offset
   (FO) field tells the receiver the position of a fragment in the
   original SDU. The More Fragment (MF) flag indicates the last
   fragment.



Zhu                    Expires October 1, 2021              [Page 10]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   To fragment a long SDU, the transmitter creates n PDUs and copies
   the content of the IP header fields from the long PDU into the IP
   header of all the PDUs. The length field in the IP header of PDU
   SHOULD be changed to the length of the PDU, and the protocol type
   SHOULD be changed to 114.

   The data of the long SDU is divided into n portions based on the
   MTU size of the delivery connection. The first portion of the data
   is placed in the first PDU. The MF flag is set to "1", and the FO
   field is set to "0". The i-th portion of the data is placed in the
   i-th PDU. The MF flag is set to "0" if it is the last fragment and
   set to "1" otherwise. The FO field is set to i-1.

   To assemble the fragments of a SDU, the receiver combines PDUs
   that all have the same Flow SN. The combination is done by placing
   the data portion of each fragment in the relative order indicated
   by the Fragment Offset in that fragment's GMA trailer (or header).
   The first fragment will have the Fragment Offset set to "0", and
   the last fragment will have the More-Fragments flag set to "0".

   GMA fragmentation operates above the IP layer of individual access
   connection (Wi-Fi, LTE) and between the two end points of
   convergence layer. The convergence layer end points (client,
   multi-access gateway) SHOULD obtain the MTU of individual
   connection through either manual configuration or implementing
   PMTUD as suggested in [RFC8900].

6. Concatenation

   The convergence sublayer MAY support concatenation if a delivery
   connection has a larger maximum transmission unit (MTU) than the
   original IP packet (SDU). Only the SDUs with the same client IP
   address, and the same Flow ID MAY be concatenated.

   If the (trailer or header based) IP encapsulation method is used,
   the First SDU Length (FSL) field SHOULD be included in the GMA
   trailer (or header) to indicate the length of the first SDU.
   Otherwise, the FSL field SHOULD not be included.

     +-----------------------------------------------------------+
     |IP hdr| IP payload    |IP hdr|   IP payload  | GMA Trailer |
     +-----------------------------------------------------------+
        Figure 8: Example of GMA PDU Format with Concatenation and
                      Trailer-based IP Encapsulation

   To concatenate two or more SDUs, the transmitter creates one PDU
   and copies the content of the IP header field from the first SDU

Zhu                    Expires October 1, 2021              [Page 11]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   into the IP header of the PDU. The data of the first SDU is placed
   in the first portion of the data of the PDU. The whole second SDU
   is then placed in the second portion of the data of the PDU
   (Figure 8). The procedure continues till the PDU size reaches the
   MTU of the delivery connection. If the FSL field is present, the
   IP length field of the PDU SHOULD be updated to include all
   concatenated SDUs and the trailer (or header), and the IP checksum
   field SHOULD be recalculated if the packet is IPv4.

   To disaggregate a PDU, if the (header or trailer based) IP
   encapsulation method is used, the receiver first obtains the
   length of the first SDU from the FSL field and decodes the first
   SDU. The receiver then obtains the length of the second SDU based
   on the length field in the second SDU IP header and decodes the
   second SDU. The procedure continues till no byte is left in the
   PDU. If the non-IP encapsulation method (Figure 7) is used, the IP
   header of the first SDU will not change during the encapsulation
   process, and the receiver SHOULD obtain the length of the first
   SDU directly from its IP header (Figure 9).

                                    |<-------1st GMA SDU------------
   +---------------------------------------------------------------+
   | IP hdr | UDP hdr  | GMA Header | IP hdr |       IP payload    |
   +---------------------------------------------------------------+
            | IP hdr |           IP payload    |
   +-------------------------------------------+
   -------->|<-------2nd GMA SDU--------------->

    Figure 9: Example of GMA PDU Format with Concatenation and Header-
                     based Non-IP (UDP) Encapsulation

   If a PDU contains multiple SDUs, the Flow SN field is for the last
   SDU, and the Flow SN of other SDU carried by the same PDU can be
   obtained according to its order in the PDU. For example, if the SN
   field is 6 and a PDU contains 3 SDUs (IP packets), the SN is 4, 5,
   and 6 for the first, second, and last SDU respectively.

   GMA concatenation can be used for packing small packets of a
   single application, e.g. TCP ACKs, or from multiple applications.
   Notice that a single GMA flow may carry multiple application flows
   (TCP, UDP, etc.).

7. Security Considerations

   Security in a network using GMA should be relatively similar to
   security in a normal IP network. The GMA protocol at the
   convergence sublayer is a 0-hop protocol and relies on the

Zhu                    Expires October 1, 2021              [Page 12]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   security of the underlying network transport paths. When this
   cannot be assumed, appropriate security protocols (IPsec, DTLS,
   etc.) SHOULD be configured at the adaptation sublayer. On the
   other hand, packet filtering requires either that a firewall looks
   inside the GMA packet or that the filtering is done on the GMA
   endpoints. In those environments in which this is considered to be
   a security issue it may be desirable to terminate the GMA
   operation at the firewall.

   Local-only packet leak prevention (HL=0, TTL=1) SHOULD be on
   preventing the leak of the local-only GMA PDUs outside the "local
   domain" to the Internet or to another domain which could use the
   same IP protocol type, i.e. 114.

8. IANA Considerations

   This draft makes no requests of IANA

9. References

9.1. 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, <https://www.rfc-
             editor.org/info/rfc2119>.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174
             May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [GRE1] Dommety, G., "Key and Sequence Number Extensions to GRE",
             <https://www.rfc-editor.org/info/rfc2890> .

9.2. Informative References

   [MAMS] S. Kanugovi, F. Baboescu, J. Zhu, and S. Seo "Multi-Access
             Management Services
             (MAMS)https://tools.ietf.org/rfc/rfc8743.txt

   [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"


Zhu                    Expires October 1, 2021              [Page 13]


Internet-Draft        GMA Encapsulation Protocol            April 2021


   [RFC791] Internet Protocol, September 1981

   [ATSSS] 3GPP TR 23.793, Study on access traffic steering, switch
             and splitting support in the 5G system architecture.

   [GRE2] RFC 8157, Huawei's GRE Tunnel Bonding Protocol, May 2017

   [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan,
             O., and F. Gont, "IP Fragmentation Considered Fragile",
             BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
             <https://www.rfc-editor.org/info/rfc8900>.

Authors' Addresses

   Jing Zhu

   Intel

   Email: jing.z.zhu@intel.com

   Satish Kanugovi

   Nokia

   Email: satish.k@nokia.com
























Zhu                    Expires October 1, 2021              [Page 14]