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Network Working Group                                        A. Minaburo
Internet-Draft                                                    Acklio
Intended status: Informational                                L. Toutain
Expires: December 25, 2016     Institut MINES TELECOM ; TELECOM Bretagne
                                                           June 23, 2016

                           LPWAN GAP Analysis


   Low Power Wide Area Networks (LPWAN) are different technologies
   covering different applications based on long range, low bandwidth
   and low power operation.  The use of IETF protocols in the LPWAN
   technologies should contribute to the deployment of a wide number of
   applications in an open and standard environment where actual
   technologies will be able to communicate.  This document makes a
   survey of the principal characteristics of these technologies and
   covers a cross layer analysis on how to adapt and use the actual IETF
   protocols, but also the gaps for the integration of the IETF protocol
   stack in the LPWAN technologies.

Status of This Memo

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   This Internet-Draft will expire on December 25, 2016.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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1.  Introduction

   LPWAN (Low-Power Wide Area Network) technologies are a kind of
   constrained and challenged networks [RFC7228].  They can operate in
   license or license-exempt bands to provide connectivity to a vast
   number of battery-powered devices requiring limited communications.
   If the existing pilot deployments have shown the huge potential and
   the industrial interest in their capabilities, the loose coupling
   with the Internet makes the device management and network operation
   complex.  More importantly, LPWAN devices are, as of today, with no
   IP capabilities.  The goal is to adapt IETF defined protocols,
   addressing schemes and naming spaces to this constrained environment.

2.  Problem Statement

   The LPWANs are large-scale constrained networks in the sense of
   [RFC7228] with the following characteristics:

   o  very small frame payload as low as 12 bytes.  Typical traffic
      patterns are composed of a large majority of frames with payload
      size around 15 bytes and a small minority of up to 100 byte
      frames.  Some nodes will exchange less than 10 frames per day.

   o  very low bandwidth, most LPWAN technologies offer a throughput
      between 50 bit/s to 250 kbit/s, with a duty cycle of 0.1% to 10%
      on some ISM bands.

   o  high packet loss, which can be the result of bad transmission
      conditions or collisions between nodes.

   o  variable MTU for a link depending on the used L2 modulation.

   o  highly asymmetric and in some cases unidirectional links.

   o  ultra dense networks with thousands to tens of thousands of nodes.

   o  different modulations and radio channels.

   o  sleepy nodes to preserve energy.

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   In the terminology of [RFC7228], these characteristics put LP-WANs
   into the "challenged network" category where the IP connectivity has
   to be redefined or modified.  Therefore, LP-WANs need to be
   considered as a separate class of networks.  The intrinsic
   characteristics, current usages and architectures will allow the
   group to make and justify the design choices.  Some of the desired
   properties are:

   o  keep compatibility with current Internet:

      *  preserve the end-to-end communication principle.

      *  maintain independence from L2 technology.

      *  use or adapt protocols defined by IETF to this new environment
         that could be less responsive.

      *  use existing addressing spaces and naming schemes defined by

   o  ensure the correspondence with the stringent LPWAN requirements,
      such as:

      *  limited number of messages per device.

      *  small message size, with potentially no L2 fragmentation.

      *  RTTs potentially orders of magnitude bigger than existing
         constrained networks.

   o  optimize the protocol stack in order to limit the number of
      duplicated functionalities; for instance acknowledgements should
      not be done at several layers.

3.  Identified gaps in current IETF groups concerning LPWANs

3.1.  IPv6 and LPWAN

   IPv6 [RFC2460] has been designed to allocate addresses to all the
   nodes connected to the Internet.  Nevertheless the 40 bytes of
   overhead introduced by the protocol are incompatible with the LPWAN
   constraints.  If IPv6 were used, several LPWAN frames will be needed
   just to carry the header.  Another limitation comes from the MTU
   limit, which is 1280 bytes required from the layer 2 to carry IPv6
   packet [RFC1981].  This is a side effect of the PMTU discovery
   mechanism, which allows intermediary routers to send to the source an
   ICMP message (packet too big) to reduce the size.  An attacker will
   be able to forge this message and reduce drastically the transmission

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   performances.  This limit allows to mitigate the impact of this

   IPv6 needs a configuration protocol (neighbor discovery protocol, NDP
   [RFC4861]) to learn network parameters, and the node relation with
   its neighbor.  This protocol generates a regular traffic with a large
   message size that does not fit LPWAN constraints.

3.2.  6LoWPAN, 6lo and LPWAN

   6LoWPAN only resolves the IPv6 constraints by drastically reducing
   IPv6 overhead to about 4 bytes for ND traffic, but the header
   compression is not better for an end-to-end communications using
   global addresses (up to 20 bytes). 6LoWPAN has been initially
   designed for IEEE 802.15.4 networks with a frame size up to 127 bytes
   and a throughput of up to 250 kb/s with no duty cycle regarding the
   usage of the network.

   IEEE 802.15.4 is a CSMA/CA protocol which means that every unicast
   frame is acknowledged.  Because IEEE 802.15.4 has its own reliability
   mechanism by retransmission, 6LoWPAN does not have reliable delivery.
   Some LPWAN technologies do not provide such acknowledgements at L2
   and would require other reliability mechanisms.

   6lo extends the usage of 6LoWPAN to other technologies (BLE, DECT,
   ...), with similar characteristics to IEEE 802.15.4.  The main
   constraint in these networks comes from the nature of the devices
   (constrained devices), whereas in LPWANs it is the network itself
   that imposes the most stringent constraint.

   6LoWPAN has optimized Neighbor Discovery by reducing the message
   size, the periodic exchanges and removing multicast message for
   point-to-point exchanges with border router.

3.3.  6tisch and LPWAN

   6TiSCH is complementary to LPWA technologies.

   A key element of 6tisch is the use of synchronization to enable
   determinism.  TSCH and 6TiSCH may provide a standard scheduling
   function.  An LPWA may or may not support synchronization like the
   one used in 6tisch.  The 6tisch solution is dedicated to mesh
   networks that operate using 802.15.4e MAC with a deterministic
   slotted channel.  The TSCH can help to reduce collisions and to
   enable a better balance over the channels.  It improves the battery
   life by avoiding the idle listening time for the return channel.

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3.4.  ROLL and LPWAN

   The LPWANs considered by the WG are based on a star topology, which
   eliminates the need for routing.  Future works may address additional
   use-cases which may require the adaptation of existing routing
   protocols or the definition of new ones.  For the moment, the work
   done at the ROLL WG and other routing protocols are out of scope of
   the LPWAN WG.

3.5.  CORE and LPWAN

   CoRE provides a resource-oriented application intended to run on
   constrained IP networks.  It may be necessary to adapt the protocols
   to take into account the duty cycling and the potentially extremely
   limited throughput.  For example, some of the timers in CoAP may need
   to be redefined.  Taking into account CoAP acknowledgements may allow
   the reduction of L2 acknowledgements.  The actual work in progress in
   the CoRE WG where the COMI/CoOL network management interface which
   uses Structured Identifiers (SID) to reduce payload size over CoAP
   proves to be a good solution for the LPWA technologies.  The overhead
   is reduced by adding a dictionary which match a URI to a small
   identifier and a compact mapping of the YANG model into the CBOR
   binary representation.

3.6.  Security and LPWAN

   Most of the LPWA integrate some authentication or encryption
   mechanisms that may not have been defined by the IETF.  The working
   group will work to integrate these mechanisms to unify management.
   For the technologies which are not integrating natively security
   protocols, the group will adapt existing mechanisms to the LPWA
   constraints.  The AAA infrastructure brings a scalable solution.  It
   offers a central management for the security processes, draft-garcia-
   dime-diameter-lorawan-00 and draft-garcia-radext-radius-lorawan-00
   explains the possible security process for a LORAWAN network.  The
   mechanisms basically are divided by: key management protocols,
   encryption and integrity algorithms used.  Most of the solutions do
   not present a key management procedure to derive specific keys for
   securing network and or data information.  In most cases it is
   assumed a pre-shared key between the smart object and the
   communication endpoint.

3.7.  Mobility and LPWAN

   LPWA nodes can be mobile.  However, LPWAN mobility is different than
   the one specified for Mobile IP.  LPWAN, implies sporadic traffic and
   will rarely be used for high-frequency, real-time communications.
   The applications do not generate a flow, they need to save energy and

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   most of the time the node will be down.  The mobility will imply most
   of the time a group of devices, which represent a network itself, the
   the mobility concerns more the gateway than the devices.

3.8.  DNS and LPWAN

   The purpose of the DNS is to enable applications to name things that
   have a global unique name.  Lots of protocols are using DNS to
   identify the objects, especially REST and applications using CoAP.
   Therefore, things should be registred in DNS.  DNS is probably a good
   point of research for the LPWA technologies, while the matching of
   the name and the IP information can be used to configured the LPWA

4.  Annex A -- survey of LPWAN technologies

   Different technologies can be included under the LPWAN acronym.  The
   following list is the result of a survey among the first participant
   to the mailing-list.  It cannot be exhaustive but is representative
   of the current trends.

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   |Technology   |range          | Throughput   |MAC MTU |
   |LoRa         |2-5 km urban   |0.3 to 50 kbps|256 B   |
   |             |<15 km suburban|              |        |
   |SIGFOX       |10 km urban    |100 bps       |12 B    |
   |             |50 km rural    |              |        |
   |IEEE802.15.4k| < 20 km LoS   |1.5 bps to    |16/24/  |
   |LECIM        | < 5 km NoLoS  | 128 kbps     | 32 B   |
   |IEEE802.15.4g| 2-3 km LoS    | 4.8 kbps to  |2047 B  |
   |SUN          |               |800 kbps      |        |
   |RPMA         | 65 km LoS     |  up: 624kbps |64 B    |
   |             | 20 km NoLoS   |down: 156kbps |        |
   |             |               | mob: 2kbps   |        |
   |DASH-7       | 2 km          |    9 kbps    |256 B   |
   |             |               |   55.55 kbps |        |
   |             |               |  166.66 kbps |        |
   |Weightless-w | 5 km urban    | 1 kbps to    |min 10 B|
   |             |               | 10 Mbps      |        |
   |Weightless-n |<5 km urban    | 30 kbps to   |max 20 B|
   |             |<30 km suburban| 100kbps      |        |
   |Weightless-p |> 2 km urban   | up to 100kbps|        |
   | NB-IoT   *  |        <15 km |  ~  200kbps  | >1000B |
   * supports segmentation

                  Figure 1: Survey of LPWAN technologies

   The table Figure 1 gives some key performance parameters for some
   candidate technologies.  The maximum MTU size must be taken
   carefully, for instance in LoRa, it take up to 2 sec to send a 50
   Byte frame using the most robust modulation.  In that case the
   theoretical limit of 256 B will be impossible to reach.

   Most of the technologies listed in the Annex A work in the ISM band
   and may be used for private a public networks.  Weightless-W uses
   white spaces in the TV spectrum and NB-LTE will use licensed
   channels.  Some technologies include encryption at layer 2.

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5.  Annex B -- Security in LPWAN technologies


   LoRaWAN provides a joining procedure called "Over the Air Activation"
   that enables a smart object to securely join the network, deriving
   the necessary keys to perform the communications securely.  The
   messages are integrity protected and the application information is
   ciphered with the derived keys from the joining procedure.

   The joining procedure consists of one exchange, that entails a join-
   request message and a join-accept message.  Upon successful
   authentication, the smart- object and the network-server are able to
   derive two keys to secure the communications (AppSKey and NwkSKey)


   SIGFOX provides secure communications, providing integrity of the
   messages and ciphered application information.  No information about
   how the keys are distributed to the end devices.

   IEEE802.15.4k and IEEE802.15.4g

   There is no mention of acquiring key material to secure the


   DASH-7 defines 2 keys for specific users (root, user) and a network
   key.  Provides network security, integrity and encryption.  The
   process of how these keys are distributed is not explained.


   They use security algorithms and provides for mutual device
   authentication, message authentication and message confidentiality.
   No mention of how the key material is distributed.


   They offer a joining procedure to network by authenticating the smart
   object.  Integrity of the messages, encryption and key distribution


   ToDo.  Not Access to the specification.

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6.  Acknowledgements

   Thanks you very much for the discussion and feedback on the LPWAN
   mailing list, namely, Pascal Thubert, Carles Gomez, Samita
   Chakrabarti, Xavier Vilajosana, Misha Dohler, Florian Meier, Timothy
   J.  Salo, Michael Richardson, Robert Cragie, Paul Duffy, Pat Kinney,
   Joaquin Cabezas and Bill Gage.

   We would like also to thanks the input made for the security part to
   Dan Garcia Carrillo et Rafael Marin Lopez

7.  Normative References

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
              1996, <http://www.rfc-editor.org/info/rfc1981>.

   [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>.

   [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,

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,

Authors' Addresses

   Ana Minaburo
   2bis rue de la Chataigneraie
   35510 Cesson-Sevigne Cedex

   Email: ana@ackl.io

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   Laurent Toutain
   Institut MINES TELECOM ; TELECOM Bretagne
   2 rue de la Chataigneraie
   CS 17607
   35576 Cesson-Sevigne Cedex

   Email: Laurent.Toutain@telecom-bretagne.eu

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