6lpwa X. Vilajosana, Ed.
Internet-Draft Worldsensing
Intended status: Standards Track M. Dohler
Expires: January 9, 2017 King's College London
A. Yegin
July 8, 2016

Transmission of IPv6 Packets over LoRaWAN


This document describes how IPv6 is transmitted over LoRaWAN using 6LowPAN techniques. LoRaWAN is a wireless communication system for long-range low-power low-data-rate applications. LoRaWAN 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.

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Table of Contents

1. Introduction

LoRa is a wireless technology for long-range low-power low-data-rate applications developed by Semtech, which is used in LoRaWAN networks. LoRaWAN 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 LoRaWAN 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 required link budget and data rate. Spreading factors create virtual and orthogonal non-interfering communication channels that enable simultaneous transmissions. Depending on the used spreading factor, LoRaWAN data rates range from 0.3 kbps to 50 kbps. To maximize both battery life of end-devices and overall network capacity, the LoRaWAN network infrastructure manages the data rate and RF output for each end-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 Gateways. Due to the constrained nature of LoRaWAN devices, the compression techniques developed by 6LowPAN become mandatory. The present document specifies how IPv6 and the 6LowPAN architecture run on top of the LoRaWAN 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 LoRaWAN Technology

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

Figure 1: LoRaWAN Class A transmission and reception window.

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

4. Specification of IPv6 over LoRaWAN

The LoRaWAN 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 LoRaWAN 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 addressing and stateless IPv6 address auto-configuration, Neighbour Discovery and most importantly Header Compression. The main difference between IEEE 802.15.4 and LoRaWAN is that LoRaWAN builds stars and star of stars networks not requiring a routing protocol nor multi-hop operation. At the same time LoRaWAN is subject to bandwidth, data rate, radio duty-cycle regulations and 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 LoRaWAN

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

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

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 LoRaWAN the IPv6 layer is designed to enable transmission of IPv6 packets over LoRaWAN links. The LoRaWAN protocol is in charge of establishing the pairwise communication between the LoRaWAN gateway and the LoRaWAN 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.

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 Neighbor Solicitation (NS) is expected in the upcoming revision. The IPv6 payload length can be derived from the LoRaWAN MAC header length and the possibly elided IPv6 address can be reconstructed from the link-layer address, used at the time of LoRaWAN 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.

LoRaWAN 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 LoRaWAN node and the LoRaWAN gateway have established the LoRaWAN 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 LoRaWAN 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 LoRaWAN nodes determine the address to be used and how this address is bound to the 6LBR node (or Gateway).

4.3.1. LoRaWAN Addressing

The DevEUI is a global end-device ID in IEEE EUI64 address space that uniquely identifies the end-device. The DevEUI is preconfigured at each node.

A LoRaWAN 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 (join-request and join-response). The latter assumes that device address and security keys are pre-programmed at the nodes and the DevEUI is not mandatory. Lately, the LoRa Alliance is considering to mandate DevEUI in ABP mode.

Figure 3: DevEUI

|  Bit#      |    [63..0]     | 
| DevEUI     |     DevEUI     |

4.3.2. Address Auto-Configuration

A LoRaWAN end device performs stateless address auto-configuration as per [RFC4862]. A 64-bit Interface identifier (IID) for a LoRaWAN interface MAY be formed by utilizing the 64-bit LoRaWAN DevEUI. 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 LoRaWAN-enabled devices MUST be formed on the basis of 64 bits long and constructed using the EUI-64 format. LoRaWAN End Device Addresses MUST follow a stateless address auto-configuration with the 64 bit DevEUI.

[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 LoRaWAN 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.

LoRaWAN IPv6 Network Prefix is build using the link-local prefix FE80::/64. The IPv6 link-local address for a LoRaWAN-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.

For non-link-local addresses a 64-bit IID MAY be formed by utilizing the 64-bit LoRaWAN DevEUI as described in this section. 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 LoRaWAN

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

4.4. Neighbour Discovery

Neighbour Discovery is addressed following the classical ND approach as defined by [RFC4861] , [RFC4862] and [RFC6775]. As LoRaWAN networks can be organized in star topologies or star of stars topologies the LoRaWAN manager can take two differentiated roles. For single star topologies the LoRaWAN 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.

Figure 5: ND Procedure for a single star topology

 LoRaWAN node                      LoRaWAN 6LR/6LBR
      |    Router Solicitation (RS)     |
      |                                 |
      |    Router Advertisement (RA)    |
      |                                 |
      |    Neighbour Solicitation (NS)  |
      |                                 |
      |    Neighbour Advertisement (NA) |
      |                                 |

When a LoRaWAN 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 NS 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 NS. As LoRaWAN might use very low data rates it is recommended to use large Lifetime configurations assuming that LoRaWAN 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.

Future versions of this document should consider the ND approach described in [efficient-nd]

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.

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

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

4.5. Header Compression in LoRaWAN


4.6. Fragmentation in LoRaWAN


5. Internet Connectivity Scenarios


6. Security Considerations

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

7. IANA Considerations

There are no IANA considerations related to this document.

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.
[RFC6775] Shelby, Z., 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.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011.
[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.
[RFC4862] Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007.
[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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005.
[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.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

9.2. External Informative References

[LoRaSpec] LoRa Alliance, "LoRaWAN Specification Rev.3", April 2014.
[efficient-nd] Thubert, P., Nordmark, E. and S. Chakrabarti, "An Update to 6LoWPAN ND", draft-thubert-6lo-rfc6775-update-00 , May 2016.

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
Alper Yegin Actility Paris, Paris FR EMail: alper.yegin@actility.com