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Versions: 00 01                                                         
Network Working Group                                        A. Minaburo
Internet-Draft                                                  A. Pelov
Intended status: Informational                                    Acklio
Expires: August 27, 2016                                      L. Toutain
                               Institut MINES TELECOM ; TELECOM Bretagne
                                                       February 24, 2016

                          LP-WAN GAP Analysis


   Low Power Wide Area Networks (LP-WAN) are different technologies
   covering different applications based on long range, low bandwidth
   and low power operation.  The use of IETF protocols in the LP-WAN
   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 LP-WAN technologies.

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
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   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 August 27, 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
   Provisions Relating to IETF Documents

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   (http://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 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.

1.  Introduction

   LP-WAN (Low-Power Wide Area Network) technologies are a kind of
   constrained and challenged networks [RFC7228].  They can operate in
   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, LP-WAN 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 LP-WANs 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 LP-WAN 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 LP-WAN 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 LP-WANs

3.1.  IPv6 and LP-WAN

   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 LP-WAN
   constraints.  If IPv6 were used, several LP-WAN 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 LP-WAN constraints.

3.2.  6LoWPAN, 6lo and LP-WAN

   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 LP-WAN 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 LP-WANs it is the network itself
   that imposes the most stringent constraint.

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

3.3.  6tisch and LP-WAN


   Describe why 6tisch is complementary to LP-WAN

   A key element of 6tisch is the use of synchronization to enable
   determinism.  An LP-WAN 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 with a deterministic slotted

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3.4.  ROLL and LP-WAN

   The LP-WANs 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 LP-WAN WG.

3.5.  CORE and LP-WAN


   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.

3.6.  Security and LP-WAN


3.7.  Mobility and LP-WAN


   LP-WAN nodes can be mobile.  However, LP-WAN mobility is different
   than the one studied in the context of Mobile IP.  LP-WAN implies
   sporadic traffic and will rarely be used for high-frequency, real-
   time communications.

4.  Annex A -- survey of LP-WAN technologies

   Different technologies can be included under the LP-WAN 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-LTE       |< 15 km        | < 150 kbps   | < 200 B|

                  Figure 1: Survey of LP-WAN 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.  Acknowledgements

   Thanks you very much for the discussion and feedback on the LP-WAN
   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.

6.  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

   Alexander Pelov
   2bis rue de la Chataigneraie
   35510 Cesson-Sevigne Cedex

   Email: a@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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