[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 draft-ietf-lpwan-schc-over-sigfox

lpwan Working Group                                           JC. Zuniga
Internet-Draft                                                    SIGFOX
Intended status: Informational                                  C. Gomez
Expires: September 12, 2019         Universitat Politecnica de Catalunya
                                                              L. Toutain
                                                          IMT-Atlantique
                                                          March 11, 2019


                         SCHC over Sigfox LPWAN
                 draft-zuniga-lpwan-schc-over-sigfox-06

Abstract

   The Static Context Header Compression (SCHC) specification describes
   a header compression scheme and a fragmentation functionality for Low
   Power Wide Area Network (LPWAN) technologies.  SCHC offers a great
   level of flexibility that can be tailored for different LPWAN
   technologies.

   The present document provides the optimal parameters and modes of
   operation when SCHC is implemented over a Sigfox LPWAN.

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 September 12, 2019.

Copyright Notice

   Copyright (c) 2019 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



Zuniga, et al.         Expires September 12, 2019               [Page 1]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   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.  Static Context Header Compression . . . . . . . . . . . . . .   3
   4.  SCHC over Sigfox  . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  SCHC Rules  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Packet processing . . . . . . . . . . . . . . . . . . . .   4
   5.  Fragmentation . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Fragmentation headers . . . . . . . . . . . . . . . . . .   5
     5.2.  Uplink fragment transmissions . . . . . . . . . . . . . .   5
       5.2.1.  Uplink No-ACK mode  . . . . . . . . . . . . . . . . .   5
       5.2.2.  Uplink ACK-Always mode  . . . . . . . . . . . . . . .   6
       5.2.3.  Uplink ACK-on-Error mode  . . . . . . . . . . . . . .   6
     5.3.  Downlink fragment transmissions . . . . . . . . . . . . .   6
   6.  Padding . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The Static Context Header Compression (SCHC) specification
   [I-D.ietf-lpwan-ipv6-static-context-hc] defines a header compression
   scheme and a fragmentation functionality.  Both can be used on top of
   all the LWPAN systems defined in [RFC8376] . These LPWAN systems 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 systems.  Even though there are a great number of similarities
   between LPWAN technologies, 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.

   This document describes the recommended parameters and modes of
   operation to be used when SCHC is implemented over a Sigfox LPWAN.





Zuniga, et al.         Expires September 12, 2019               [Page 2]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


2.  Terminology

   It is assumed that the reader is familiar with the terms and
   mechanisms defined in [RFC8376] and in
   [I-D.ietf-lpwan-ipv6-static-context-hc].

3.  Static Context Header Compression

   The Static Context Header Compression (SCHC) described in
   [I-D.ietf-lpwan-ipv6-static-context-hc] takes advantage of the
   predictability of data flows existing in LPWAN networks to avoid
   context synchronization.  Nonetheless, these contexts must be stored
   and configured on both ends.  This can be done either by using a
   provisioning protocol, by out of band means, or by pre-provisioning
   them (for instance at manufacturing time).  The way the contexts are
   configured and stored on both ends is out of the scope of this
   document.

        Dev                                                 App
   +----------------+                                  +--------------+
   | APP1 APP2 APP3 |                                  |APP1 APP2 APP3|
   +----------------+                                  +--------------+
   |   UDP  |       |                                  |     UDP      |
   |  IPv6  |       |                                  |    IPv6      |
   +--------+       |                                  |              |
   |SCHC C/D and F/R|                                  |              |
   |                |                                  |              |
   +--------+-------+                                  +-------+------+
            $   +--+     +----+     +-----------+              .
            +~~ |RG| === |NGW | === |   SCHC    |... Internet ..
                +--+     +----+     |F/R and C/D|
                                    +-----------+

                          Figure 1: Architecture

   Figure 1 represents the architecture for compression/decompression
   and fragmentation/reassembly, which is based on [RFC8376]
   terminology, where the Radio Gateway is a Sigfox Base Station and the
   Network Gateway is the Sigfox Cloud.

   The Device is sending applications flows that are compressed and/or
   fragmented by a Static Context Header Compression Compressor/
   Decompressor (SCHC C/D) to reduce headers size and/or fragment the
   packet.  The resulting information is sent over a layer two (L2)
   frame to a LPWAN Radio Gateway (RG) which forwards the frame to a
   Network Gateway (NGW).





Zuniga, et al.         Expires September 12, 2019               [Page 3]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


4.  SCHC over Sigfox

   In the case of the global Sigfox network, RGs (or base stations) are
   distributed over the multiple countries where the Sigfox LPWAN
   service is provided.  On the other hand, the NGW (or Cloud-based Core
   network) is a single entity that connects to all Sigfox base stations
   in the world.

   Uplink Sigfox transmissions occur in repetitions over different times
   and frequencies.  Besides these time and frequency diversities, the
   Sigfox network also provides space diversity, as potentially an
   uplink message will be received by several base stations.  Since all
   messages are self-contained and base stations forward them all back
   to the same Core network (NGW), multiple input copies can be combined
   at the NGW and hence provide for extra reliability based on the
   triple diversity (i.e. time, space and frequency).  A detailed
   description of the Sigfox Radio Protocol can be found in
   [sigfox-spec].

   The NGW communicates with the Network SCHC C/D for compression/
   decompression and/or for fragmentation/reassembly.  The Network SCHC
   C/D shares the same set of rules as the Dev SCHC C/D.  The Network
   SCHC C/D can be collocated with the NGW or it could be in another
   place, as long as a tunnel is established between the NGW and the
   SCHC C/D.  After decompression and/or reassembly, the packet can be
   forwarded over the Internet to one (or several) LPWAN Application
   Server(s) (App).

   The SCHC C/D process is bidirectional, so the same principles can be
   applied on both uplink and downlink.

4.1.  SCHC Rules

   The RuleID MUST be sent at the beginning of the SCHC header.  The
   total number of rules to be used affects directly the Rule ID field
   size, and therefore the total size of the fragmentation header.  For
   this reason, it is recommended to keep the number of rules that are
   defined for a specific device to the minimum possible.

4.2.  Packet processing

   TBD

5.  Fragmentation

   The SCHC specification [I-D.ietf-lpwan-ipv6-static-context-hc]
   defines a generic fragmentation functionality that allows sending
   data packets larger than the maximum size of a Sigfox data frame.



Zuniga, et al.         Expires September 12, 2019               [Page 4]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   The functionality also defines a mechanism to send reliably multiple
   frames, by allowing to resend selectively any lost frames.

   The SCHC fragmentation supports several modes of operation.  These
   modes have different advantages and disadvantages depending on the
   specifics of the underlying LPWAN technology and Use Case.  This
   section describes how the SCHC fragmentation functionality should
   optimally be implemented when used over a Sigfox LPWAN for the most
   typical use case applications.

5.1.  Fragmentation headers

   A list of fragmentation header fields, their sizes as well as
   suggested modes for SCHC fragmentation over Sigfox are provided in
   this section.

5.2.  Uplink fragment transmissions

   Uplink transmissions are completely asynchronous and can take place
   in any random frequency of the allowed uplink bandwidth allocation.
   Hence, devices can go to deep sleep mode, and then wake up and
   transmit whenever there is a need to send any information to the
   network.  In that way, there is no need to perform any network
   attachment, synchronization, or other procedure before transmitting a
   data packet.  All data packets are self contained with all the
   required information for the network to process them accordingly.

   Since uplink transmissions occur asynchronously, an SCHC fragment can
   be transmitted at any given time by the Dev.

5.2.1.  Uplink No-ACK mode

   No-ACK is RECOMMENDED to be used for transmitting short, non-critical
   packets that require fragmentation.

   The recommended Fragmentation Header size is 8 bits, and it is
   composed as follows:

   The recommended Rule ID size is: 2 bits

   The recommended DTag size (T) is: 2 bits

   Fragment Compressed Number (FCN) size (N): 4 bits

   As per [I-D.ietf-lpwan-ipv6-static-context-hc], in the No-ACK mode
   the W (window) field is not present.





Zuniga, et al.         Expires September 12, 2019               [Page 5]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   When fragmentation is used to transport IP frames, the Message
   Integrity Check (MIC) size, M: TBD bits

   The algorithm for computing the MIC field MUST be TBD.

5.2.2.  Uplink ACK-Always mode

   TBD

5.2.3.  Uplink ACK-on-Error mode

   ACK-on-Error is RECOMMENDED for larger packets that need to be sent
   reliably, since it leads to a reduced number of ACKs in the lower
   capacity downlink channel.

   In the most generic case, the Fragmentation Header size is 8 bits and
   it is composed as follows:

   The recommended Rule ID size is: 2 bits.

   The recommended DTag size (T) is: 1 bit.

   The recommended Window (W) size is: 2 bits.

   Fragment Compressed Number (FCN) size (N): 3 bits.

   For the ACK-on-Error fragmentation mode(s), a single window size is
   RECOMMENDED.

   The value of MAX_ACK_REQUESTS SHOULD be 2, and the value of
   MAX_WIND_FCN SHOULD be 6 (or 0b110, which allows a maximum window
   size of 7 fragments).

   When fragmentation is used to transport IP frames, the Message
   Integrity Check (MIC) size, M: TBD bits

   The algorithm for computing the MIC field MUST be TBD.

5.3.  Downlink fragment transmissions

   In some LPWAN technologies, as part of energy-saving techniques,
   downlink transmission is only possible immediately after an uplink
   transmission.  This allows the device to go in a very deep sleep mode
   and preserve battery, without the need to listen to any information
   from the network.  This is the case for Sigfox-enabled devices, which
   can only listen to downlink communications after performing an uplink
   transmission and requesting a downlink.




Zuniga, et al.         Expires September 12, 2019               [Page 6]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   When there are fragments to be transmitted in the downlink, an uplink
   message is required to trigger the downlink communication.  In order
   to avoid potentially high delay for fragmented datagram transmission
   in the downlink, the fragment receiver MAY perform an uplink
   transmission as soon as possible after reception of a downlink
   fragment that is not the last one.  Such uplink transmission MAY be
   triggered by sending a SCHC message, such as a SCHC ACK.  However,
   other data messages can equally be used to trigger DL communications.

   For reliable downlink fragment transmission, the ACK-Always mode is
   RECOMMENDED.

   The recommended Fragmentation Header size is: 8 bits

   The recommended Rule ID size is: 2 bits.

   The recommended DTag size (T) is: 2 bits.

   Fragment Compressed Number (FCN) size (N): 3 bits.

   As per [I-D.ietf-lpwan-ipv6-static-context-hc], in the ACK-Always
   mode a Window (W) 1-bit field must be present.

   For the ACK-Always fragmentation mode(s), a single window size is
   RECOMMENDED.

   The value of MAX_ACK_REQUESTS SHOULD be 2, and the value of
   MAX_WIND_FCN SHOULD be 6 (or 0b110, which allows a maximum window
   size of 7 fragments).

   When fragmentation is used to transport IP frames, the Message
   Integrity Check (MIC) size, M: TBD bits

   The algorithm for computing the MIC field MUST be TBD.

   Sigfox downlink frames have a fixed length of 8 bytes, which means
   that default SCHC algorithm for padding cannot be used.  Therefore,
   the 3 last bits of the fragmentation header are used to indicate in
   bytes the size of the padding.  A size of 000 means that the full
   ramaining frame is used to carry payload, a value of 001 indicates
   that the last byte contains padding, and so on.

6.  Padding

   The Sigfox payload fields have different characteristics in uplink
   and downlink.





Zuniga, et al.         Expires September 12, 2019               [Page 7]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   Uplink frames can contain a payload size from 0 to 96 bits, that is 0
   to 12 bytes.  The radio protocol allows sending zero bits or one
   single bit of information for binary applications (e.g. status), or
   an integer number of bytes.  Therefore, for 2 or more bits of payload
   it is required to add padding to the next integer number of bytes.
   The reason for this flexibility is to optimize transmission time and
   hence save battery consumption at the device.

   Downlink frames on the other hand have a fixed length.  The payload
   length must be 64 bits (i.e. 8 bytes).  Hence, if less information
   bits are to be transmitted, padding would be necessary and it should
   be performed as described in the previous section.

7.  Security considerations

   The radio protocol authenticates and ensures the integrity of each
   message.  This is achieved by using a unique device ID and an AES-128
   based message authentication code, ensuring that the message has been
   generated and sent by the device with the ID claimed in the message.

   Application data can be encrypted at the application level or not,
   depending on the criticality of the use case.  This flexibility
   allows providing a balance between cost and effort vs. risk.  AES-128
   in counter mode is used for encryption.  Cryptographic keys are
   independent for each device.  These keys are associated with the
   device ID and separate integrity and confidentiality keys are pre-
   provisioned.  A confidentiality key is only provisioned if
   confidentiality is to be used.

   The radio protocol has protections against reply attacks, and the
   cloud-based core network provides firewalling protection against
   undesired incoming communications.

8.  Acknowledgements

   Carles Gomez has been funded in part by the ERDF and the Spanish
   Government through project TEC2016-79988-P.

9.  Informative References

   [I-D.ietf-lpwan-ipv6-static-context-hc]
              Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zuniga, "LPWAN Static Context Header Compression (SCHC)
              and fragmentation for IPv6 and UDP", draft-ietf-lpwan-
              ipv6-static-context-hc-17 (work in progress), October
              2018.





Zuniga, et al.         Expires September 12, 2019               [Page 8]


Internet-Draft           SCHC over Sigfox LPWAN               March 2019


   [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>.

   [sigfox-spec]
              Sigfox, "Sigfox Radio Specifications",
              <https://build.sigfox.com/
              sigfox-device-radio-specifications>.

Authors' Addresses

   Juan Carlos Zuniga
   SIGFOX
   425 rue Jean Rostand
   Labege  31670
   France

   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


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

   Email: Laurent.Toutain@imt-atlantique.fr













Zuniga, et al.         Expires September 12, 2019               [Page 9]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/