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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 10, 2022. Zuniga, et al. Expires January 10, 2022 [Page 1] Internet-Draft SCHC Compound ACK July 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 (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. Zuniga, et al. Expires January 10, 2022 [Page 2] Internet-Draft SCHC Compound ACK July 2021 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]. Zuniga, et al. Expires January 10, 2022 [Page 3] Internet-Draft SCHC Compound ACK July 2021 |- 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. Zuniga, et al. Expires January 10, 2022 [Page 4] Internet-Draft SCHC Compound ACK July 2021 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 { Zuniga, et al. Expires January 10, 2022 [Page 5] Internet-Draft SCHC Compound ACK July 2021 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 Zuniga, et al. Expires January 10, 2022 [Page 6] Internet-Draft SCHC Compound ACK July 2021 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, . [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, . Zuniga, et al. Expires January 10, 2022 [Page 7] Internet-Draft SCHC Compound ACK July 2021 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 Zuniga, et al. Expires January 10, 2022 [Page 8] Internet-Draft SCHC Compound ACK July 2021 Diego Wistuba NIC Labs, Universidad de Chile Av. Almte. Blanco Encalada 1975 Santiago Chile Email: wistuba@niclabs.cl Zuniga, et al. Expires January 10, 2022 [Page 9]