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6lpwa                                                 X. Vilajosana, Ed.
Internet-Draft                                              Worldsensing
Intended status: Standards Track                               M. Dohler
Expires: December 5, 2016                          King's College London
                                                            June 3, 2016


                 Transmission of IPv6 Packets over LoRa
                   draft-vilajosana-6lpwa-lora-hc-00

Abstract

   This document describes how IPv6 is transmitted over LoRa using
   6LowPAN techniques.  LoRa is a wireless communication system for
   long-range low-power low-data-rate applications.  LoRa networks
   typically are laid out in a star topology in the field with gateways
   relaying messages between end-devices and a central network server in
   the backend, the complete system referred to as star of stars
   network.

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 December 5, 2016.

Copyright Notice

   Copyright (c) 2016 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
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   to this document.  Code Components extracted from this document must



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   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.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview of LoRa Technology . . . . . . . . . . . . . . . . .   3
   4.  Specification of IPv6 over LoRa . . . . . . . . . . . . . . .   3
     4.1.  Protocol stack  . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Link Model  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Stateless Address Auto-configuration  . . . . . . . . . .   5
       4.3.1.  LoRa Addressing . . . . . . . . . . . . . . . . . . .   5
       4.3.2.  Address Auto-Configuration  . . . . . . . . . . . . .   6
     4.4.  Neighbour Discovery . . . . . . . . . . . . . . . . . . .   7
     4.5.  Header Compression in LoRa  . . . . . . . . . . . . . . .   9
     4.6.  Fragmentation in LoRa . . . . . . . . . . . . . . . . . .   9
   5.  Internet Connectivity Scenarios . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  External Informative References . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   LoRa is a wireless modulation for long-range low-power low-data-rate
   applications developed by Semtech.  LoRa networks typically are
   organized in a star-of-stars topology in which gateways relay
   messages between end-devices and a central network server in the
   backend.  Gateways are connected to the network server via IP links
   while end-devices use single-hop LoRa communication to one or many
   gateways.  All communication is generally bi-directional, although
   uplink communication from end-devices to the network server are
   strongly favoured.

   Communication between end-devices and gateways is spread out among
   different frequency channels and so-called spreading factors.
   Selecting a spreading factor is a trade-off between communication
   range and data rate.  Spreading factors create virtual and orthogonal
   non-interfering communication channels that enable simultaneous
   transmissions.  Depending on the used spreading factor, LoRa data
   rates range from 0.3 kbps to 50 kbps.  To maximize both battery life
   of end-devices and overall network capacity, the LoRa network
   infrastructure manages the data rate and RF output for each end-



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   device individually by means of an adaptive data rate (ADR) scheme.
   End-devices may transmit on any channel available at any time, using
   any available data rate.

   The consolidation of that technology and its important impact in the
   M2M market, is triggering the need for end to end IP connectivity
   from end devices to the backend server without the need of proxying
   roles taken at LoRa Managers or Gateways.  Due to the constrained
   nature of LoRa devices, the compression techniques developed by
   6LowPAN become mandatory.  The present document specifies how IPv6
   and the 6LowPAN architecture run on top of the LoRa MAC layer.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Overview of LoRa Technology

   TODO briefly describe the technology.  Phy layer and modulation.  MAC
   operation and frame formats.

   Figure 1: LoRa Class A transmission and reception window.

   |----------------------------|         |--------|     |--------|
   |             Tx             |         |   Rx   |     |   Rx   |
   |----------------------------|         |--------|     |--------|
                                |---------|
                                 Rx delay 1
                                |------------------------|
                                 Rx delay 2

4.  Specification of IPv6 over LoRa

   The LoRa technology enables low power wide area network coverage at
   the cost of reduced data rate and to obey to strict spectrum
   occupancy regulations.  This imposes strict communication limitations
   that make applications using LoRa to contain the amount of data that
   is transmitted.  6LoWPAN standards RFC4944, RFC6775, and RFC6282
   enable IP connectivity while leverage the overhead of fully IPv6
   headers.  They also provides standard Internet connectivity by
   enabling IPv6 adressing and stateless IPv6 address auto-
   configuration, Neighbour Discovery and most importantly Header
   Compression.  The main difference between IEEE 802.15.4 and LoRa is
   that LoRa builds stars and star of stars networks not requiring a
   routing protocol nor multi-hop operation.  At the same time LoRa is
   subject to bandwidth, data rate, radio duty-cycle regulations and



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   frame size constraints that impose strict limitation in the protocol
   overhead that is supported when compared to IEEE 802.15.4.

4.1.  Protocol stack

   Figure 2: Protocol Stack for IPv6 over LoRa


      +----------------------------------------+ ------------------
      |                                        |     Transport and
      |         Upper Layer Protocols          |  Application Layer
      +----------------------------------------+ ------------------
      |                                        |         |
      |                 IPv6                   |         |
      |                                        |      Network
      +----------------------------------------+       Layer
      |   Adaptation Layer for IPv6 over LoRa  |         |
      +----------------------------------------+ ------------------
      |                                        |
      |      IPv6-LOR Addressing Binding       |   LoRa Link Layer
      |                                        |         |
      +----------------------------------------+ ------------------
      |                                        |         |
      |               Activities               |        LoRa
      |            Digital Protocol            |   Physical Layer
      |               RF Analog                |         |
      |                                        |         |
      +----------------------------------------+ ------------------

   Adaptation layer for IPv6 over LoRa SHALL support neighbour discovery,
   address auto-configuration, header compression, and fragmentation and
   reassembly.


4.2.  Link Model

   According to RFC 4861 [RFC4861] a link is "a communication facility
   or medium over which nodes can communicate at the link layer, i.e.,
   the layer immediately below IPv6."

   In LoRa the IPv6 layer is designed to enable transmission of IPv6
   packets over LoRa links.  The LoRa protocol is in charge of
   establishing the pairwise communication between the LoRa gateway and
   the LoRa device.  The IPv6 adaptation layer however is in charge of
   managing header compression and packet fragmentation in order to deal
   with different spreading factors and allowed packet payload at the
   underlying MAC layer.




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   Per this specification, the IPv6 header compression format specified
   in RFC 6282 MUST be used [RFC6282] but more drastic compression based
   on provisioning an extended context in the NS is expected in the
   upcoming revision.  The IPv6 payload length can be derived from the
   LoRa MAC header length and the possibly elided IPv6 address can be
   reconstructed from the link-layer address, used at the time of LoRa
   connection establishment.  As described in Section 4.5 context
   information or more aggressive compression formats such as RoHC
   [RFC3095] SHOULD be used at the 6LBR in order to compress well-known
   network prefixes and indicated at the specific field of the IPHC
   header.  This compression will be defined in the upcomming revisions.

   LoRa networks form star topologies or star of stars, having a point-
   to-point nature.  Address assignment is managed by the 6LBR that
   ensures that collisions do not occur.  Broadcast features are used
   mainly by the 6LBR.  6LN to 6LN communications are always carried out
   through the 6LBR and hence it is in charge of relaying link local
   packets.

   After the LoRa node and the LoRa gateway have established the LoRa
   connection, the link is enabled and IPv6 address configuration and
   subsequent transmission are able to start.

4.3.  Stateless Address Auto-configuration

   Nodes (both hosts and routers) in a LoRa network MAY use the address
   auto-configuration process.  This process relies in the ability for a
   node to generate a link-local address for the communication
   interface.  A link-local address is formed by appending an identifier
   of the interface to the well-known link-local prefix [RFC4291].
   Before the link-local address can be assigned to an interface and
   used, a node must attempt to verify that this "tentative" address is
   not already in use by another node on the link.  This section
   describes how LoRa nodes determine the address to be used and how
   this address is bound to the 6LBR node (or LoRa Manager or Gateway).

4.3.1.  LoRa Addressing

   LoRa device addressing can be conducted in two ways.  Over the air
   activation (OTAA) and Activation by personalization (ABP).  The
   former requires 2 MAC layer messages to establish the network address
   and security keys.  The latter assumes that device address and
   security keys are pre-programmed at the nodes.  In the case of OTAA
   the joining negotiation establishes a unique 4 Bytes DevAddr.  When
   ABP is used the DevAddr is pre-configured at the node.

   The LoRa device address uses 32 bits and identifies the end-device
   within the current network.  The most significant 7 bits are used as



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   network identifier (NetworkID) to separate addresses of territorially
   overlapping networks or networks managed by different network
   operators.  The least significant 25 bits are referred to as the
   network address (NetworkAddress) of the end-device and can be
   arbitrarily assigned by the network manager.

   Figure 3: End Device Address

   +------------+----------------+----------------+
   |  Bit#      |    [31..25]    |     [24..0]    |
   +------------+----------------+----------------+
   | DevAddr    |   NetworkID    |    End Device  |
   |            |                | NetworkAddress |
   +------------+----------------+----------------+

4.3.2.  Address Auto-Configuration

   A LoRa end device performs stateless address auto-configuration as
   per [RFC4862].  A 64-bit Interface identifier (IID) for a LoRa
   interface MAY be formed by utilizing the 32-bit LoRa DevAddr.  That
   IID MAY guarantee a stable IPv6 address and MUST be used along the
   lifetime of the network.

   According to [RFC7136], interface IIDs of all unicast addresses for
   LoRa-enabled devices MUST be formed on the basis of 64 bits long and
   constructed using the EUI-64 format.  LoRa End Device Addresses MUST
   follow a stateless address auto-configuration that requires 32 zeros
   and 32 bit DevAddr.

   [RFC4291] indicates the use of a "Universal/Local" scope bit that
   identifies the network device to be locally accessible or globally
   accessible.  The former SHOULD be followed and LoRa end-devices
   SHOULD set to 0 the "Universal/Local" bit.  In the case that a
   Universally accessible IPv6 address needs to be used a Neighbor
   Discovery mechanism and a network commissioning procedure is
   required.  This procedure is described in Section 4.4.

   LoRa IPv6 Network Prefix is build using the link-local prefix
   FE80::/64.  The IPv6 link-local address for a LoRa-enabled device is
   formed by appending the IID, to the prefix, as depicted in Figure 4.

   Duplicate address detection for link-local addresses is performed by
   the 6LBR.

   Once a 6LN has established its own link-local address, it starts
   sending Router Solicitation messages as described in [RFC4861]
   Section 6.3.7.




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   For non-link-local addresses a 64-bit IID MAY be formed by utilizing
   the 32-bit LoRa DevAddr as described in Section TODO.  A 6LN can also
   use a the EUI-64 generated IID from the MAC Layer.  The non-link-
   local addresses generated by the 6LN MUST be registered with the
   6LBR.

   The mechanism by which the 6LBR obtains an IPv6 prefix is out of
   scope of this document but can for example be accomplished by using
   Unique Local IPv6 Unicast Addresses (ULA) [RFC4193].  As 6LNs MUST
   always communicate to the 6LBR, the "on-link" flag (L) MUST be set to
   zero in the Prefix Information Option [RFC4861].  This will always
   happen even when the destination is another 6LN using the same
   prefix.

   Figure 4: IPv6 link-local address in LoRa

     0          0                 0               0                1
     0          1                 6               9                2
     0          0                 4               6                7
     +----------+-----------------+---------------+----------------+
     |1111111010|      zeros      |     zeros     |    DevAddr     |
     +----------+-----------------+---------------+----------------+
     |                                                             |
     | /-------------------------- 128 bits ----------------------/|
     |                                                             |


4.4.  Neighbour Discovery

   Neighbour Discovery is addressed following the classical ND approach
   as defined by [RFC4861] , [RFC4862] and [RFC6775].  As LoRa networks
   can be organized in star topologies or star of stars topologies the
   LoRa manager can take two differentiated roles.  For single star
   topologies the LoRa manager will act as a 6LBR and MUST keep track of
   the nodes addresses within the link, otherwise it acts as 6LR and
   forwards Node Solicitation and ARO requests to the 6LBR in the
   network.














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   Figure 5: ND Procedure for a single star topology


     LoRa node                         LoRa 6LR/6LBR
         |    Router Solicitation (RS)     |
         |-------------------------------->|
         |                                 |
         |    Router Advertisement (RA)    |
         |<--------------------------------|
         |                                 |
         |    Neighbour Solicitation (NS)  |
         |-------------------------------->|
         |                                 |
         |    Neighbour Advertisement (NA) |
         |<--------------------------------|
         |                                 |


   When a LoRa node joins a network, it sends an RS to the 6LR
   containing its IID as described in Section 4.3.2.  The 6LBR router
   answers with a RA containing its IIDs and prefixes.  Hosts receive
   Router Advertisement messages containing the Authoritative Border
   Router Option (ABRO), the IIDs of the 6LR or 6LBR and MAY optionally
   contain one or more 6LoWPAN Context Options (6COs).  They also
   contain the existing Prefix Information Options (PIOs) as described
   in [RFC4861].

   When a host has configured a non-link-local IPv6 address, it
   registers that address with one or more of its default routers using
   the Address Registration Option (ARO) in an RS message.  The host
   chooses a lifetime of the registration and repeats the ARO
   periodically (before the lifetime runs out) to maintain the
   registration.  The host needs to refresh its prefix and context
   information by sending a new unicast RS.  As LoRa might use very low
   data rates it is recommended to use large Lifetime configurations
   assuming that LoRa devices are not mobile.  According to [RFC6775]
   the maximum Router Lifetime is about 18 hours, whereas the maximum
   Registration Lifetime is about 45.5 days.

   The ND Procedure for star of stars follows the multi-hop ND approach
   described by [RFC6775].  The multihop distribution relies on RS
   messages and RA messages sent between routers, and using the ABRO
   version number to control the propagation of the information
   (prefixes and context information) that is being sent in the RAs.







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   Figure 6: ND Procedure for star of stars in LoRa.


  LoRa node                         LoRa 6LR                          LoRa 6LBR
      |    Router Solicitation (RS)    |                                  |
      |------------------------------->|                               |
      |                                |                                  |
      |    Router Advertisement (RA)   |                                  |
      |<-------------------------------|                               |
      |                                |                                  |
      |    Node Registration (NR)      |                                  |
      |------------------------------->|                               |
      |                                |  Neighbour Solicitation (NS)     |
      |                                |-------------------------------->|
      |                                |                                  |
      |                                |   Neighbour Advertisement (NA)   |
      |                                |<--------------------------------|
      |    Node Confirmation (NC)      |                                  |
      |<------------------------------|                                |
      |                                |                                  |


4.5.  Header Compression in LoRa

   TODO.

4.6.  Fragmentation in LoRa

   TODO.

5.  Internet Connectivity Scenarios

   TODO.

6.  Security Considerations

   The transmission of IPv6 over LoRa links has similar requirements and
   concerns for security as for IEEE 802.15.4.  LoRa Link Layer security
   considerations are covered by the LoRa Specification [LoRaSpec].

7.  IANA Considerations

   There are no IANA considerations related to this document.








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8.  Acknowledgements

   The authors would like to acknowledge the guidance and input provided
   by Pascal Thubert.

9.  References

9.1.  Normative References

   [RFC7136]  Carpenter, B. and S. Jiang, "Significance of IPv6
              Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
              February 2014, <http://www.rfc-editor.org/info/rfc7136>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <http://www.rfc-editor.org/info/rfc6775>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <http://www.rfc-editor.org/info/rfc6282>.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
              <http://www.rfc-editor.org/info/rfc4944>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <http://www.rfc-editor.org/info/rfc4862>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <http://www.rfc-editor.org/info/rfc4291>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
              <http://www.rfc-editor.org/info/rfc4193>.





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   [RFC3095]  Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
              Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
              K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
              Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
              Compression (ROHC): Framework and four profiles: RTP, UDP,
              ESP, and uncompressed", RFC 3095, DOI 10.17487/RFC3095,
              July 2001, <http://www.rfc-editor.org/info/rfc3095>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

9.2.  External Informative References

   [LoRaSpec]
              LoRa Alliance, "LoRa Specification Rev.3", April 2014.

Authors' Addresses

   Xavier Vilajosana (editor)
   Worldsensing
   483 Arago 4th floor
   Barcelona, Catalonia  08013
   Spain

   Email: xvilajosana@worldsensing.com


   Mischa Dohler
   King's College London
   London, London
   UK

   Email: mischa.dohler@kcl.ac.uk












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