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Versions: 00                                                            
lpwan Working Group                                           JC. Zuniga
Internet-Draft                                                    SIGFOX
Intended status: Standards Track                                C. Gomez
Expires: January 10, 2022                                     S. Aguilar
                                    Universitat Politecnica de Catalunya
                                                              L. Toutain
                                                          IMT-Atlantique
                                                             S. Cespedes
                                                              D. Wistuba
                                          NIC Labs, Universidad de Chile
                                                            July 9, 2021


                           SCHC Compound ACK
                 draft-ietf-lpwan-schc-compound-ack-00

Abstract

   The present document describes an extension to the SCHC (Static
   Header Compression and Fragmentation) protocol [RFC8724].  It defines
   a SCHC Compound ACK message format, which is intended to reduce the
   number of downlink transmissions (i.e., SCHC ACKs) by accumulating
   bitmaps of several windows in a single SCHC message (i.e., the SCHC
   Compound ACK).

   The message format is generic, and can be used for instance by any
   the four LWPAN technologies defined in [RFC8376], being Sigfox,
   LoRaWAN, NB-IoT and IEEE 802.15.4w.

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
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   This Internet-Draft will expire on January 10, 2022.






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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
   (https://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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SCHC Compound ACK . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  SCHC Compound ACK Message Format  . . . . . . . . . . . .   3
     3.2.  SCHC Compound ACK Examples  . . . . . . . . . . . . . . .   4
     3.3.  SCHC Compound ACK YANG Data Model . . . . . . . . . . . .   5
   4.  Security considerations . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Generic Framework for Static Context Header Compression and
   Fragmentation (SCHC) specification [RFC8724] describes two
   mechanisms: i) an application header compression scheme, and ii) a
   frame fragmentation and loss recovery functionality.  Either can be
   used on top of radio technologies such as the four LWPAN defined in
   [RFC8376], being Sigfox, LoRaWAN, NB-IoT and IEEE 802.15.4w.  These
   LPWANs have similar characteristics such as star-oriented topologies,
   network architecture, connected devices with built-in applications,
   etc.

   SCHC offers a great level of flexibility to accommodate all these
   LPWAN technologies.  Even though there are a great number of
   similarities between them, some differences exist with respect to the
   transmission characteristics, payload sizes, etc.  Hence, there are
   optimal parameters and modes of operation that can be used when SCHC
   is used on top of a specific LPWAN technology.





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   The present document describes an extension to the SCHC protocol.  It
   defines a SCHC Compound ACK format, which is intended to reduce the
   number of downlink transmissions (i.e., SCHC ACKs) in the ACK-on-
   Error mode of SCHC.  The SCHC Compound ACK extends the SCHC ACK
   message format so that it can contain several bitmaps, each bitmap
   being identified by its corresponding window number.

   The SCHC Compound ACK:

   o  provides feedback only for windows with fragment losses,

   o  has a variable size that depends on the number of windows with
      fragment losses being reported in the single Compound SCHC ACK,

   o  includes the window number (i.e., W) of each bitmap,

   o  has the same SCHC ACK format defined in [RFC8724] when only one
      window with losses is reported,

   o  might not cover all windows with fragment losses of a SCHC Packet,

   o  is distinguishable from the SCHC Receiver-Abort.

2.  Terminology

   It is assumed that the reader is familiar with the terms and
   mechanisms defined in [RFC8376] and in [RFC8724].

3.  SCHC Compound ACK

   The SCHC Compound ACK is a SCHC ACK message that can contain several
   bitmaps, each bitmap being identified by its corresponding window
   number.

   When the ACK-on-Error mode is used for uplink fragmentation, SCHC
   Compound ACKs MAY be used in the downlink responses.

   The SCHC Compound ACK groups the window number (W) with its
   corresponding bitmap.  The included window numbers and corresponding
   bitmaps MUST be ordered from the lowest-numbered to the highest-
   numbered window.

3.1.  SCHC Compound ACK Message Format

   Figure 1 shows the regular SCHC ACK format when all fragments have
   been correctly received (C=1), as defined in [RFC8724].





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                  |- SCHC ACK Header --|
                  + -------+---+------ + ------------ +
                  | RuleID | W | C=b'1 | b'0-pad(opt) |
                  + ------ + - + ----- + ------------ +


     Figure 1: SCHC Success ACK message format, as defined in RFC8724

   In case SCHC fragment losses are found in any of the windows of the
   SCHC Packet (C=0), the SCHC Compound ACK MAY be used.  The SCHC
   Compound ACK message format is shown in Figure 2.

   The window numbered 00, if present in the SCHC Compound ACK, MUST be
   placed between the Rule ID and the C bit to avoid confusion with
   padding bits.  If padding is needed for the SCHC Compound ACK,
   padding bits MUST be 0 to make subsequent window numbers and bitmaps
   distinguishable.


     |-SCHC ACK Header--| W = x  |...|    W = x + i     |
     +------------------+ ------ +...+ ------- + ------ +------------+
     |RuleID|W=b'x|C=b'0| Bitmap |...| W=b'x+i | Bitmap |b'0-pad(opt)|
     +------+-----+-----+ ------ +...+ ------- + ------ +------------+

                    Losses are found in windows W = x,...,x+i


                Figure 2: SCHC Compound ACK message format

   Each different SCHC LPWAN technology profile MUST specify how the
   SCHC Compound ACK is different from the Receiver-Abort message.

   The SCHC Compound ACK MAY use a Compressed Bitmap, and bitmap fields
   MAY be of variable size.

3.2.  SCHC Compound ACK Examples

   Figure 3 shows an example transmission of a SCHC Packet in ACK-on-
   Error mode using the SCHC Compound ACK.  In the example, the SCHC
   Packet is fragmented in 14 tiles, with N=3, WINDOW_SIZE=7, M=2 and
   two lost SCHC fragments.  Only 1 compound SCHC ACK is generated.










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        Sender                      Receiver
          |-----W=0, FCN=6 ----->|
          |-----W=0, FCN=5 ----->|
          |-----W=0, FCN=4 ----->|
          |-----W=0, FCN=3 ----->|
          |-----W=0, FCN=2 --X-->|
          |-----W=0, FCN=1 ----->|
          |-----W=0, FCN=0 ----->| Bitmap: 1111011
      (no ACK)
          |-----W=1, FCN=6 ----->|
          |-----W=1, FCN=5 ----->|
          |-----W=1, FCN=4 ----->|
          |-----W=1, FCN=3 ----->|
          |-----W=1, FCN=2 ----->|
          |-----W=1, FCN=1 --X-->|
          |-- W=1, FCN=7 + RSC ->| Integrity check: failure
          |<--- Compound ACK ----| C=0, W=0 - Bitmap:1111011, W=1 - Bitmap:1111101
          |-----W=0, FCN=2 ----->|
          |-----W=1, FCN=1 ----->| Integrity check: success
          |<--- ACK, W=1, C=1 ---| C=0
        (End)

           Figure 3: SCHC Compound ACK message sequence example


     |-- SCHC ACK Header ---|- W=00 --|----- W=01 -----|
     + -------------------- + ------- + ---- + ------- + ------------- +
     | RuleID | W=00  | C=0 | 1111011 | W=01 | 1111011 | b'0-pad (opt) |
     + ------ + ------ + -- + ------- + ---- + ------- + ------------- +

      On top are denoted the window numbers of the corresponding bitmap.
      Losses are found in windows 00 and 01.


            Figure 4: SCHC Compound ACK message format example

3.3.  SCHC Compound ACK YANG Data Model

   The present document also extends the YANG data model defined in
   [I-D.ietf-lpwan-schc-yang-data-model] by including a new leaf in the
   Ack-on-Error fragmentation mode to describe the option to use the
   SCHC Compound ACK, as well as its bitmap format.  Figure 5 shows this
   definition:


// --- Bitmap format

    identity bitmap-format-base-type {



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        description "Define how the bitmap is defined in ACK messages.";
    }

    identity RFC8724-bitmap {
        base bitmap-format-base-type;
        description "Bitmap as defined in RFC8724.";
    }

   identity compound-ack-bitmap {
        base bitmap-format-base-type;
        description "Compound Ack.";
    }

    typedef bitmap-format-type {
        type identityref {
            base RCS-algorithm-base-type;
        }
        description "type used in rules";
    }

       choice mode {
            case no-ack;
            case ack-always;
            case ack-on-error {
                leaf tile-size {
                    type uint8;
                    description "size in bit of tiles, if not specified or set to 0: tile fills the fragment.";
                }
                leaf tile-in-All1 {
                    type schc:all1-data-type;
                    description "When true, sender and receiver except a tile in All-1 frag";
                }
                leaf ack-behavior {
                    type schc:ack-behavior-type;
                    description "Sender behavior to acknowledge, after All-0, All-1 or when the
                    LPWAN allows it (Always)";
                }
                leaf bitmap-format {
                    type schc:bitmap-format-type,
                    default schc:RFC8724-bitmap;
                    description "how the bitmaps are included in the Ack message.";
                }
            }
        description "RFC 8724 defines 3 fragmentation modes";


                Figure 5: SCHC Compound ACK YANG Data Model




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4.  Security considerations

   The current document specifies a message format extension for SCHC.
   Hence, the same Security Considerations defined in [RFC8724] apply.

5.  Acknowledgements

   Carles Gomez has been funded in part by the Spanish Government
   through the Jose Castillejo CAS15/00336 grant, the TEC2016-79988-P
   grant, and the PID2019-106808RA-I00 grant, and by Secretaria
   d'Universitats i Recerca del Departament d'Empresa i Coneixement de
   la Generalitat de Catalunya 2017 through grant SGR 376.

   Sergio Aguilar has been funded by the ERDF and the Spanish Government
   through project TEC2016-79988-P and project PID2019-106808RA-I00,
   AEI/FEDER, EU.

   Sandra Cespedes has been funded in part by the ANID Chile Project
   FONDECYT Regular 1201893 and Basal Project FB0008.

   Diego Wistuba has been funded by the ANID Chile Project FONDECYT
   Regular 1201893.

   The authors would like to thank Rafael Vidal, Julien Boite, Renaud
   Marty, and Antonis Platis for their useful comments and
   implementation design considerations.

6.  Normative References

   [I-D.ietf-lpwan-schc-yang-data-model]
              Minaburo, A. and L. Toutain, "Data Model for Static
              Context Header Compression (SCHC)", draft-ietf-lpwan-schc-
              yang-data-model-04 (work in progress), Feb 2021.

   [RFC8376]  Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
              Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
              <https://www.rfc-editor.org/info/rfc8376>.

   [RFC8724]  Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zuniga, "SCHC: Generic Framework for Static Context Header
              Compression and Fragmentation", RFC 8724,
              DOI 10.17487/RFC8724, April 2020,
              <https://www.rfc-editor.org/info/rfc8724>.








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Authors' Addresses

   Juan Carlos Zuniga
   SIGFOX
   Montreal  QC
   Canada

   Email: JuanCarlos.Zuniga@sigfox.com
   URI:   http://www.sigfox.com/


   Carles Gomez
   Universitat Politecnica de Catalunya
   C/Esteve Terradas, 7
   08860 Castelldefels
   Spain

   Email: carlesgo@entel.upc.edu


   Sergio Aguilar
   Universitat Politecnica de Catalunya
   C/Esteve Terradas, 7
   08860 Castelldefels
   Spain

   Email: sergio.aguilar.romero@upc.edu


   Laurent Toutain
   IMT-Atlantique
   2 rue de la Chataigneraie
   CS 17607
   35576 Cesson-Sevigne Cedex
   France

   Email: Laurent.Toutain@imt-atlantique.fr


   Sandra Cespedes
   NIC Labs, Universidad de Chile
   Av. Almte. Blanco Encalada 1975
   Santiago
   Chile

   Email: scespedes@niclabs.cl





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   Diego Wistuba
   NIC Labs, Universidad de Chile
   Av. Almte. Blanco Encalada 1975
   Santiago
   Chile

   Email: wistuba@niclabs.cl












































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