lpwan Working Group JC. Zuniga Internet-Draft SIGFOX Intended status: Standards Track C. Gomez Expires: 13 June 2022 S. Aguilar Universitat Politècnica de Catalunya L. Toutain IMT-Atlantique S. Céspedes D. Wistuba NIC Labs, Universidad de Chile 10 December 2021 SCHC Compound ACK draft-ietf-lpwan-schc-compound-ack-02 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 of 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 13 June 2022. Zuniga, et al. Expires 13 June 2022 [Page 1] Internet-Draft SCHC Compound ACK December 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised 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 Behaviour . . . . . . . . . . . . . . . 4 3.2.1. Sender Behaviour . . . . . . . . . . . . . . . . . . 5 3.2.2. Receiver Behaviour . . . . . . . . . . . . . . . . . 5 3.3. SCHC Compound ACK Examples . . . . . . . . . . . . . . . 5 3.4. SCHC Compound ACK YANG Data Model . . . . . . . . . . . . 6 3.4.1. SCHC YANG Data Model Extension . . . . . . . . . . . 6 3.4.2. SCHC YANG Tree Extension . . . . . . . . . . . . . . 9 4. SCHC Compound ACK Parameters . . . . . . . . . . . . . . . . 9 5. Security considerations . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 7. Normative References . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The Generic Framework for Static Context Header Compression and Fragmentation (SCHC) specification [RFC8724] describes two mechanisms: i) a protocol 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 Zuniga, et al. Expires 13 June 2022 [Page 2] Internet-Draft SCHC Compound ACK December 2021 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. 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: * provides feedback only for windows with fragment losses, * has a variable size that depends on the number of windows with fragment losses being reported in the single Compound SCHC ACK, * includes the window number (i.e., W) of each bitmap, * has the same SCHC ACK format defined in [RFC8724] when only one window with losses is reported, * might not cover all windows with fragment losses of a SCHC Packet, * and 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. The SCHC Compound ACK groups the window number (W) with its corresponding bitmap. Windows do not need to be contiguous. However, the window numbers and corresponding bitmaps included in the SCHC Compound ACK message 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 13 June 2022 [Page 3] Internet-Draft SCHC Compound ACK December 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, 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. |--SCHC ACK Header--| W = w1 |...| W = wi | +-------------------+ ------ +...+ ------- + ------ +------------+ |RuleID|W=b'w1|C=b'0| Bitmap |...| W=b'wi | Bitmap |b'0-pad(opt)| +------+------+-----+ ------ +...+ ------- + ------ +------------+ Losses are found in windows W = w1,...,wi; where w1| |-----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=0, FCN=2 ----->| W=1 - Bitmap:1111101] |-----W=1, FCN=1 ----->| Integrity check: success |<--- ACK, W=1, C=1 ---| C=1 (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) | + ------ + ------ + -- + ------- + ---- + ------- + ------------- + Figure 4: SCHC Compound ACK message format example: Losses are found in windows 00 and 01 3.4. SCHC Compound ACK YANG Data Model The present document also extends the SCHC 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 both the option to use the SCHC Compound ACK, as well as its bitmap format. 3.4.1. SCHC YANG Data Model Extension Zuniga, et al. Expires 13 June 2022 [Page 6] Internet-Draft SCHC Compound ACK December 2021 file "ietf-compound-ack@2021-12-10.yang" module ietf-schc-compound-ack { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-schc-compound-ack"; prefix schc-compound-ack; import ietf-schc { prefix schc; } organization "IETF IPv6 over Low Power Wide-Area Networks (lpwan) working group"; contact "WG Web: WG List: Editor: Laurent Toutain Editor: Juan Carlos Zuniga "; description " Copyright (c) 2021 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. *************************************************************** This module extends the ietf-schc module to include the Compound ACK behavior for ACK-on-Error as defined in RFC YYYY. It introduces a new leaf for ACK-on-Error defining the format of the SCHC Compound ACK, adding the possibility to send several bitmaps in a single SCHC ACK message."; revision 2021-12-08 { description Zuniga, et al. Expires 13 June 2022 [Page 7] Internet-Draft SCHC Compound ACK December 2021 "Initial version for RFC YYYY "; reference "RFC YYYY: SCHC Compound ACK"; } identity bitmap-format-base-type { description "Define how the bitmap is formed in ACK messages."; } identity bitmap-RFC8724 { base bitmap-format-base-type; description "Bitmap by default as defined in RFC8724."; } identity bitmap-compound-ack { base bitmap-format-base-type; description "Compound ACK."; } typedef bitmap-format-type { type identityref { base bitmap-format-base-type; } description "type used in rules"; } augment "/schc:schc/schc:rule/schc:nature/schc:fragmentation/schc:mode/schc:ack-on-error" { leaf bitmap-format { when "derived-from(../schc:fragmentation-mode, 'schc:fragmentation-mode-ack-on-error')"; type schc-compound-ack:bitmap-format-type; default "schc-compound-ack:bitmap-RFC8724"; description "How the bitmaps are included in the Ack message."; } description "added to SCHC rules"; } } Figure 5: SCHC YANG Data Model - Compound ACK extension Zuniga, et al. Expires 13 June 2022 [Page 8] Internet-Draft SCHC Compound ACK December 2021 3.4.2. SCHC YANG Tree Extension augment /schc:schc/schc:rule/schc:nature/schc:fragmentation/schc:mode/schc:ack-on-error: +--rw bitmap-format? schc-compound-ack:bitmap-format-type Figure 6: SCHC YANG Tree - Compound ACK extension 4. SCHC Compound ACK Parameters This section lists the parameters related to the SCHC Compound ACK usage that need to be defined in the Profile, in addition to the ones listed in Annex D of [RFC8724]. * Usage or not of the SCHC Compound ACK message. * Usage or not of the compressed bitmap format in the last window of the SCHC Compound ACK message. * Differentiation between SCHC Receiver-Abort and SCHC Compound ACK message, e.g., Receiver-Abort message padded with 1s with an extra byte appended at the end, while the SCHC Compound ACK is 0-padded. 5. Security considerations The current document specifies a message format extension for SCHC. Hence, the same Security Considerations defined in [RFC8724] apply. 6. 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. Zuniga, et al. Expires 13 June 2022 [Page 9] Internet-Draft SCHC Compound ACK December 2021 The authors would like to thank Rafael Vidal, Julien Boite, Renaud Marty, Antonis Platis, Dominique Barthel and Pascal Thubert for their very useful comments, reviews and implementation design considerations. 7. Normative References [I-D.ietf-lpwan-schc-yang-data-model] Minaburo, A. and L. Toutain, "Data Model for Static Context Header Compression (SCHC)", Work in Progress, Internet-Draft, draft-ietf-lpwan-schc-yang-data-model-04, February 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, . Authors' Addresses Juan Carlos Zúñiga SIGFOX Montreal QC Canada Email: JuanCarlos.Zuniga@sigfox.com URI: http://www.sigfox.com/ Carles Gomez Universitat Politècnica de Catalunya C/Esteve Terradas, 7 08860 Castelldefels Spain Email: carlesgo@entel.upc.edu Zuniga, et al. Expires 13 June 2022 [Page 10] Internet-Draft SCHC Compound ACK December 2021 Sergio Aguilar Universitat Politècnica 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 Céspedes NIC Labs, Universidad de Chile Av. Almte. Blanco Encalada 1975 Santiago Chile Email: scespedes@niclabs.cl Diego Wistuba NIC Labs, Universidad de Chile Av. Almte. Blanco Encalada 1975 Santiago Chile Email: wistuba@niclabs.cl Zuniga, et al. Expires 13 June 2022 [Page 11]