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Versions: (draft-farrell-lpwan-overview) 00 01 02 03 04 05 06 07 08 09 10 RFC 8376

lpwan                                                    S. Farrell, Ed.
Internet-Draft                                    Trinity College Dublin
Intended status: Informational                         February 27, 2017
Expires: August 31, 2017


                             LPWAN Overview
                      draft-ietf-lpwan-overview-01

Abstract

   Low Power Wide Area Networks (LPWAN) are wireless technologies with
   characteristics such as large coverage areas, low bandwidth, possibly
   very small packet and application layer data sizes and long battery
   life operation.  This memo is an informational overview of the set of
   LPWAN technologies being considered in the IETF and of the gaps that
   exist between the needs of those technologies and the goal of running
   IP in LPWANs.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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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 31, 2017.

Copyright Notice

   Copyright (c) 2017 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
   (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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  LPWAN Technologies  . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  LoRaWAN . . . . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Provenance and Documents  . . . . . . . . . . . . . .   4
       2.1.2.  Characteristics . . . . . . . . . . . . . . . . . . .   4
     2.2.  Narrowband IoT (NB-IoT) . . . . . . . . . . . . . . . . .  11
       2.2.1.  Provenance and Documents  . . . . . . . . . . . . . .  11
       2.2.2.  Characteristics . . . . . . . . . . . . . . . . . . .  11
     2.3.  SIGFOX  . . . . . . . . . . . . . . . . . . . . . . . . .  15
       2.3.1.  Provenance and Documents  . . . . . . . . . . . . . .  15
       2.3.2.  Characteristics . . . . . . . . . . . . . . . . . . .  15
     2.4.  Wi-SUN Alliance Field Area Network (FAN)  . . . . . . . .  19
       2.4.1.  Provenance and Documents  . . . . . . . . . . . . . .  19
       2.4.2.  Characteristics . . . . . . . . . . . . . . . . . . .  20
   3.  Generic Terminology . . . . . . . . . . . . . . . . . . . . .  23
   4.  Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . . .  24
     4.1.  Naive application of IPv6 . . . . . . . . . . . . . . . .  24
     4.2.  6LoWPAN . . . . . . . . . . . . . . . . . . . . . . . . .  25
       4.2.1.  Header Compression  . . . . . . . . . . . . . . . . .  25
       4.2.2.  Address Autoconfiguration . . . . . . . . . . . . . .  26
       4.2.3.  Fragmentation . . . . . . . . . . . . . . . . . . . .  26
       4.2.4.  Neighbor Discovery  . . . . . . . . . . . . . . . . .  27
     4.3.  6lo . . . . . . . . . . . . . . . . . . . . . . . . . . .  27
     4.4.  6tisch  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     4.5.  RoHC  . . . . . . . . . . . . . . . . . . . . . . . . . .  28
     4.6.  ROLL  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     4.7.  CoAP  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     4.8.  Mobility  . . . . . . . . . . . . . . . . . . . . . . . .  29
     4.9.  DNS and LPWAN . . . . . . . . . . . . . . . . . . . . . .  29
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  30
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  33
   Appendix A.  Changes  . . . . . . . . . . . . . . . . . . . . . .  37
     A.1.  From -00 to -01 . . . . . . . . . . . . . . . . . . . . .  37
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   [[Ed: Editor comments/queries are in double square brackets like
   this.]]




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   This document provides background material and an overview of the
   technologies being considered in the IETF's Low Power Wide-Area
   Networking (LPWAN) working group.  We also provide a gap analysis
   between the needs of these technologies and currently available IETF
   specifications.

   Most technologies in this space aim for similar goals of supporting
   large numbers of low-cost, low-throughput devices at very low-cost
   and with very-low power consumption, so that even battery-powered
   devices can be deployed for years.  LPWAN devices also tend to be
   constrained in their use of bandwidth, for example with limited
   frequencies being allowed to be used within limited duty-cycles
   (usually expressed as a percentage of time/hour that the device is
   allowed to transmit.)  [[Ed: is that right?]] And as the name
   implies, coverage of large areas is also a common goal.  So, by and
   large, the different technologies aim for deployment in very similar
   circumstances.

   Existing pilot deployments have shown huge potential and created much
   industrial interest in these technolgies.  As of today, [[Ed: with
   the possible exception of Wi-SUN devices?]] essentially no LPWAN
   devices have IP capabilities.  Connecting LPWANs to the Internet
   would provide significant benefits to these networks in terms of
   interoperability, application deployment, and management, among
   others.  The goal of the LPWAN WG is to, where necessary, adapt IETF
   defined protocols, addressing schemes and naming to this particular
   constrained environment.

   This document is largely the work of the people listed in Section 7.
   Discussion of this document should take place on the lp-wan@ietf.org
   list.

2.  LPWAN Technologies

   This section provides an overview of the set of LPWAN technologies
   that are being considered in the LPWAN working group.  The text for
   each was mainly contributed by proponents of each technology.

   Note that this text is not intended to be normative in any sesne, but
   simply to help the reader in finding the relevant layer 2
   specifications and in understanding how those integrate with IETF-
   defined technologies.  Similarly, there is no attempt here to set out
   the pros and cons of the relevant technologies.








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2.1.  LoRaWAN

   Text here is largely from [I-D.farrell-lpwan-lora-overview] which may
   have been updated since this was published.

2.1.1.  Provenance and Documents

   LoRaWAN is a wireless technology for long-range low-power low-data-
   rate applications developed by the LoRa Alliance, a membership
   consortium.  <https://www.lora-alliance.org/> This draft is based on
   version 1.0.2 [LoRaSpec] of the LoRa specification.  Version 1.0,
   which has also seen some deployment, is available at [LoRaSpec1.0].

2.1.2.  Characteristics

   In LoRaWAN networks, end-device transmissions may be received at
   multiple gateways, so during nominal operation a network server may
   see multiple instances of the same uplink message from an end-device.

   The LoRaWAN network infrastructure manages the data rate and RF
   output power for each end-device individually by means of an adaptive
   data rate (ADR) scheme.  End-devices may transmit on any channel
   allowed by local regulation at any time, using any of the currently
   available data rates.

   LoRaWAN networks are typically 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 that can be received at one or more gateways.  All
   communication is generally bi-directional, although uplink
   communication from end-devices to the network server are favoured in
   terms of overall bandwidth availability.

   Figure 1 shows the entities involved in a LoRaWAN network.
















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   +----------+
   |End-device| * * *
   +----------+       *   +---------+
                        * | Gateway +---+
   +----------+       *   +---------+   |   +---------+
   |End-device| * * *                   +---+ Network +--- Application
   +----------+       *                 |   | Server  |
                        * +---------+   |   +---------+
   +----------+       *   | Gateway +---+
   |End-device| * * *   * +---------+
   +----------+
       Key: *      LoRaWAN Radio
            +---+  IP connectivity

                      Figure 1: LoRaWAN architecture

   o  End-device: a LoRa client device, sometimes called a mote.
      Communicates with gateways.

   o  Gateway: a radio on the infrastructure-side, sometimes called a
      concentrator or base-station.  Communicates with end-devices and,
      via IP, with a network server.

   o  Network Server: The Network Server (NS) terminates the LoRaWAN MAC
      layer for the end-devices connected to the network.  It is the
      center of the star topology.

   o  Uplink message: refers to communications from end-device to
      network server or appliction via one or more gateways.

   o  Downlink message: refers to communications from network server or
      application via one gateway to a single end-device or a group of
      end-devices (considering multicasting).

   o  Application: refers to application layer code both on the end-
      device and running "behind" the network server.  For LoRaWAN,
      there will generally only be one application running on most end-
      devices.  Interfaces between the network server and application
      are not further described here.

   LoRaWAN radios make use of industrial, scientific and medical (ISM)
   bands, for example, 433MHz and 868MHz within the European Union and
   915MHz in the Americas.

   The end-device changes channel in a pseudo-random fashion for every
   transmission to help make the system more robust to interference and/
   or to conform to local regulations.




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   Figure 2 below shows that after a transmission slot a Class A device
   turns on its receiver for two short receive windows that are offset
   from the end of the transmission window.  End-devices can only
   transmit a subsequent uplink frame after the end of the associated
   receive windows.  When a device joins a LoRaWAN network, there are
   similar timeouts on parts of that process.

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

        Figure 2: LoRaWAN Class A transmission and reception window

   Given the different regional requirements the detailed specification
   for the LoRaWAN physical layer (taking up more than 30 pages of the
   specification) is not reproduced here.  Instead and mainly to
   illustrate the kinds of issue encountered, in Table 1 we present some
   of the default settings for one ISM band (without fully explaining
   those here) and in Table 2 we describe maxima and minima for some
   parameters of interest to those defining ways to use IETF protocols
   over the LoRaWAN MAC layer.

   +------------------------+------------------------------------------+
   |       Parameters       |              Default Value               |
   +------------------------+------------------------------------------+
   |       Rx delay 1       |                   1 s                    |
   |                        |                                          |
   |       Rx delay 2       |    2 s (must be RECEIVE_DELAY1 + 1s)     |
   |                        |                                          |
   |      join delay 1      |                   5 s                    |
   |                        |                                          |
   |      join delay 2      |                   6 s                    |
   |                        |                                          |
   |     868MHz Default     | 3 (868.1,868.2,868.3), data rate: 0.3-5  |
   |        channels        |                   kbps                   |
   +------------------------+------------------------------------------+

                Table 1: Default settings for EU868MHz band









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   +-----------------------------------------------+--------+----------+
   | Parameter/Notes                               |  Min   |   Max    |
   +-----------------------------------------------+--------+----------+
   | Duty Cycle: some but not all ISM bands impose |   1%   | no-limit |
   | a limit in terms of how often an end-device   |        |          |
   | can transmit. In some cases LoRaWAN is more   |        |          |
   | stringent in an attempt to avoid congestion.  |        |          |
   |                                               |        |          |
   | EU 868MHz band data rate/frame-size           |  250   |  50000   |
   |                                               | bits/s | bits/s : |
   |                                               |  : 59  |   250    |
   |                                               | octets |  octets  |
   |                                               |        |          |
   | US 915MHz band data rate/frame-size           |  980   |  21900   |
   |                                               | bits/s | bits/s : |
   |                                               |  : 19  |   250    |
   |                                               | octets |  octets  |
   +-----------------------------------------------+--------+----------+

         Table 2: Minima and Maxima for various LoRaWAN Parameters

   Note that in the case of the smallest frame size (19 octets), 8
   octets are required for LoRa MAC layer headers leaving only 11 octets
   for payload (including MAC layer options).  However, those settings
   do not apply for the join procedure - end-devices are required to use
   a channel and data rate that can send the 23 byte Join-request
   message for the join procedure.

   Uplink and downlink higher layer data is carried in a MACPayload.
   There is a concept of "ports" (an optional 8 bit value) to handle
   different applications on an end-device.  Port zero is reserved for
   LoRaWAN specific messaging, such as the configuration of device's
   network parameters (available channels, data rates, ADR parameters,
   RX1/2 delay, etc.).

   In addition to carrying higher layer PDUs there are Join-Request and
   Join-Response (aka Join-Accept) messages for handling network access.
   And so-called "MAC commands" (see below) up to 15 bytes long can be
   piggybacked in an options field ("FOpts").

   There are a number of MAC commands for: link and device status
   checking, ADR and duty-cycle negotiation, managing the RX windows and
   radio channel settings.  For example, the link check response message
   allows the network server (in response to a request from an end-
   device) to inform an end-device about the signal attenuation seen
   most recently at a gateway, and to also tell the end-device how many
   gateways received the corresponding link request MAC command.




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   Some MAC commands are initiated by the network server.  For example,
   one command allows the network server to ask an end-device to reduce
   its duty-cycle to only use a proportion of the maximum allowed in a
   region.  Another allows the network server to query the end-device's
   power status with the response from the end-device specifying whether
   it has an external power source or is battery powered (in which case
   a relative battery level is also sent to the network server).

   A LoRaWAN network has a short network identifier ("NwkID") which is a
   seven bit value.  A private network (common for LoRaWAN) can use the
   value zero.  If a network wishes to support "foreign" end-devices
   then the NwkID needs to be registered with the LoRA Alliance, in
   which case the NwkID is the seven least significant bits of a
   registered 24-bit NetID.  (Note however, that the methods for
   "roaming" are defined in the upcoming LoRaWAN 1.1 specification.

   In order to operate nominally on a LoRaWAN network, a device needs a
   32-bit device address, which is the catentation of the NwkID and a
   25-bit device-specific network address that is assigned when the
   device "joins" the network (see below for the join procedure) or that
   is pre-provisioned into the device.

   End-devices are assumed to work with one or a quite limited number of
   applications, identified by a 64-bit AppEUI, which is assumed to be a
   registered IEEE EUI64 value.  In addition, a device needs to have two
   symmetric session keys, one for protecting network artefacts
   (port=0), the NwkSKey, and another for protecting application layer
   traffic, the AppSKey.  Both keys are used for 128 bit AES
   cryptographic operations.  So, one option is for an end-device to
   have all of the above, plus channel information, somehow
   (pre-)provisioned, in which case the end-device can simply start
   transmitting.  This is achievable in many cases via out-of-band means
   given the nature of LoRaWAN networks.  Table 3 summarises these
   values.

















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   +---------+---------------------------------------------------------+
   | Value   | Description                                             |
   +---------+---------------------------------------------------------+
   | DevAddr | DevAddr (32-bits) =  NwkId (7-bits) + device-specific   |
   |         | network address (25 bits)                               |
   |         |                                                         |
   | AppEUI  | IEEE EUI64 naming the application                       |
   |         |                                                         |
   | NwkSKey | 128 bit network session key for use with AES            |
   |         |                                                         |
   | AppSKey | 128 bit application session key for use with AES        |
   +---------+---------------------------------------------------------+

              Table 3: Values required for nominal operation

   As an alternative, end-devices can use the LoRaWAN join procedure in
   order to setup some of these values and dynamically gain access to
   the network.  To use the join procedure, an end-device must still
   know the AppEUI, and in addition, a different (long-term) symmetric
   key that is bound to the AppEUI - this is the application key
   (AppKey), and is distinct from the application session key (AppSKey).
   The AppKey is required to be specific to the device, that is, each
   end-device should have a different AppKey value.  And finally, the
   end-device also needs a long-term identifier for itself,
   syntactically also an EUI-64, and known as the device EUI or DevEUI.
   Table 4 summarises these values.

     +---------+----------------------------------------------------+
     | Value   | Description                                        |
     +---------+----------------------------------------------------+
     | DevEUI  | IEEE EUI64 naming the device                       |
     |         |                                                    |
     | AppEUI  | IEEE EUI64 naming the application                  |
     |         |                                                    |
     | AppKey  | 128 bit long term application key for use with AES |
     +---------+----------------------------------------------------+

                Table 4: Values required for join procedure

   The join procedure involves a special exchange where the end-device
   asserts the AppEUI and DevEUI (integrity protected with the long-term
   AppKey, but not encrypted) in a Join-request uplink message.  This is
   then routed to the network server which interacts with an entity that
   knows that AppKey to verify the Join-request.  All going well, a
   Join-accept downlink message is returned from the network server to
   the end-device that specifies the 24-bit NetID, 32-bit DevAddr and
   channel information and from which the AppSKey and NwkSKey can be




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   derived based on knowledge of the AppKey.  This provides the end-
   device with all the values listed in Table 3.

   All payloads are encrypted and have data integrity.  MAC commands,
   when sent as a payload (port zero), are therefore protected.  MAC
   commands piggy-backed as frame options ("FOpts") are however sent in
   clear.  Any MAC commands sent as frame options and not only as
   payload, are visible to a passive attacker but are not malleable for
   an active attacker due to the use of the MIC.

   For LoRaWAN version 1.0.x, the NWkSkey session key is used to provide
   data integrity between the end-device and the network server.  The
   AppSKey is used to provide data confidentiality between the end-
   device and network server, or to the application "behind" the network
   server, depending on the implementation of the network.

   All MAC layer messages have an outer 32-bit Message Integrity Code
   (MIC) calculated using AES-CMAC calculated over the ciphertext
   payload and other headers and using the NwkSkey.  Payloads are
   encrypted using AES-128, with a counter-mode derived from IEEE
   802.15.4 using the AppSKey.  Gateways are not expected to be provided
   with the AppSKey or NwkSKey, all of the infrastructure-side
   cryptography happens in (or "behind") the network server.  When
   session keys are derived from the AppKey as a result of the join
   procedure the Join-accept message payload is specially handled.

   The long-term AppKey is directly used to protect the Join-accept
   message content, but the function used is not an aes-encrypt
   operation, but rather an aes-decrypt operation.  The justification is
   that this means that the end-device only needs to implement the aes-
   encrypt operation.  (The counter mode variant used for payload
   decryption means the end-device doesn't need an aes-decrypt
   primitive.)

   The Join-accept plaintext is always less than 16 bytes long, so
   electronic code book (ECB) mode is used for protecting Join-accept
   messages.  The Join-accept contains an AppNonce (a 24 bit value) that
   is recovered on the end-device along with the other Join-accept
   content (e.g.  DevAddr) using the aes-encrypt operation.  Once the
   Join-accept payload is available to the end-device the session keys
   are derived from the AppKey, AppNonce and other values, again using
   an ECB mode aes-encrypt operation, with the plaintext input being a
   maximum of 16 octets.








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2.2.  Narrowband IoT (NB-IoT)

   Text here is largely from [I-D.ratilainen-lpwan-nb-iot] which may
   have been updated since this was published.

2.2.1.  Provenance and Documents

   Narrowband Internet of Things (NB-IoT) is developed and standardized
   by 3GPP.  The standardization of NB-IoT was finalized with 3GPP
   Release-13 in June 2016, but further enhancements for NB-IoT are
   worked on in the following releases, for example in the form of
   multicast support.  For more information of what has been specified
   for NB-IoT, 3GPP specification 36.300 [TGPP36300] provides an
   overview and overall description of the E-UTRAN radio interface
   protocol architecture, while specifications 36.321 [TGPP36321],
   36.322 [TGPP36322], 36.323 [TGPP36323] and 36.331 [TGPP36331] give
   more detailed description of MAC, RLC, PDCP and RRC protocol layers
   respectively.  Note that the description below assumes familiarity
   with numerous 3GPP terms.

2.2.2.  Characteristics

   [[Ed: Not clear what minimum/worst-case MTU might be.]]

   Specific targets for NB-IoT include: Less than US$5 module cost,
   extended coverage of 164 dB maximum coupling loss, battery life of
   over 10 years, ~55000 devices per cell and uplink reporting latency
   of less than 10 seconds.

   NB-IoT supports Half Duplex FDD operation mode with 60 kbps peak rate
   in uplink and 30 kbps peak rate in downlink, and a maximum size MTU
   of 1600 bytes.  As the name suggests, NB-IoT uses narrowbands with
   the bandwidth of 180 kHz in both, downlink and uplink.  The multiple
   access scheme used in the downlink is OFDMA with 15 kHz sub-carrier
   spacing.  On uplink multi-tone SC-FDMA is used with 15 kHz tone
   spacing or as a special case of SC-FDMA single tone with either 15kHz
   or 3.75 kHz tone spacing may be used.

   NB-IoT can be deployed in three ways.  In-band deployment means that
   the narrowband is multiplexed within normal LTE carrier.  In Guard-
   band deployment the narrowband uses the unused resource blocks
   between two adjacent LTE carriers.  Also standalone deployment is
   supported, where the narrowband can be located alone in dedicated
   spectrum, which makes it possible for example to refarm the GSM
   carrier at 850/900 MHz for NB-IoT.  All three deployment modes are
   meant to be used in licensed bands.  The maximum transmission power
   is either 20 or 23 dBm for uplink transmissions, while for downlink




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   transmission the eNodeB may use higher transmission power, up to 46
   dBm depending on the deployment.

   For signaling optimization, two options are introduced in addition to
   legacy RRC connection setup, mandatory Data-over-NAS (Control Plane
   optimization, solution 2 in [TGPP23720]) and optional RRC Suspend/
   Resume (User Plane optimization, solution 18 in [TGPP23720]).  In the
   control plane optimization the data is sent over Non Access Stratum,
   directly from Mobility Management Entity (MME) in core network to the
   UE without interaction from base station.  This means there are no
   Access Stratum security or header compression, as the Access Stratum
   is bypassed, and only limited RRC procedures.

   The RRC Suspend/Resume procedures reduce the signaling overhead
   required for UE state transition from Idle to Connected mode in order
   to have a user plane transaction with the network and back to Idle
   state by reducing the signaling messages required compared to legacy
   operation

   With extended DRX the RRC Connected mode DRX cycle is up to 10.24
   seconds and in RRC Idle the DRX cycle can be up to 3 hours.

   NB-IoT has no channel access restrictions allowing up to a 100% duty-
   cycle.

   3GPP access security is specified in [TGPP33203].

   +--+
   |UE| \              +------+      +------+
   +--+  \             | MME  |------| HSS  |
          \          / +------+      +------+
   +--+    \+-----+ /      |
   |UE| ----| eNB |-       |
   +--+    /+-----+ \      |
          /          \ +--------+
         /            \|        |    +------+     Service PDN
   +--+ /              |  S-GW  |----| P-GW |---- e.g. Internet
   |UE|                |        |    +------+
   +--+                +--------+

                    Figure 3: 3GPP network architecture

   Mobility Management Entity (MME) is responsible for handling the
   mobility of the UE.  MME tasks include tracking and paging UEs,
   session management, choosing the Serving gateway for the UE during
   initial attachment and authenticating the user.  At MME, the Non
   Access Stratum (NAS) signaling from the UE is terminated.




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   Serving Gateway (S-GW) routes and forwards the user data packets
   through the access network and acts as a mobility anchor for UEs
   during handover between base stations known as eNodeBs and also
   during handovers between other 3GPP technologies.

   Packet Data Node Gateway (P-GW) works as an interface between 3GPP
   network and external networks.

   Home Subscriber Server (HSS) contains user-related and subscription-
   related information.  It is a database, which performs mobility
   management, session establishment support, user authentication and
   access authorization.

   E-UTRAN consists of components of a single type, eNodeB. eNodeB is a
   base station, which controls the UEs in one or several cells.

   The illustration of 3GPP radio protocol architecture can be seen from
   Figure 4.

   +---------+                                       +---------+
   | NAS     |----|-----------------------------|----| NAS     |
   +---------+    |    +---------+---------+    |    +---------+
   | RRC     |----|----| RRC     | S1-AP   |----|----| S1-AP   |
   +---------+    |    +---------+---------+    |    +---------+
   | PDCP    |----|----| PDCP    | SCTP    |----|----| SCTP    |
   +---------+    |    +---------+---------+    |    +---------+
   | RLC     |----|----| RLC     | IP      |----|----| IP      |
   +---------+    |    +---------+---------+    |    +---------+
   | MAC     |----|----| MAC     | L2      |----|----| L2      |
   +---------+    |    +---------+---------+    |    +---------+
   | PHY     |----|----| PHY     | PHY     |----|----| PHY     |
   +---------+         +---------+---------+         +---------+
               LTE-Uu                         S1-MME
       UE                     eNodeB                     MME

                Figure 4: 3GPP radio protocol architecture

   The radio protocol architecture of NB-IoT (and LTE) is separated into
   control plane and user plane.  Control plane consists of protocols
   which control the radio access bearers and the connection between the
   UE and the network.  The highest layer of control plane is called
   Non-Access Stratum (NAS), which conveys the radio signaling between
   the UE and the EPC, passing transparently through radio network.  It
   is responsible for authentication, security control, mobility
   management and bearer management.

   Access Stratum (AS) is the functional layer below NAS, and in control
   plane it consists of Radio Resource Control protocol (RRC)



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   [TGPP36331], which handles connection establishment and release
   functions, broadcast of system information, radio bearer
   establishment, reconfiguration and release.  RRC configures the user
   and control planes according to the network status.  There exists two
   RRC states, RRC_Idle or RRC_Connected, and RRC entity controls the
   switching between these states.  In RRC_Idle, the network knows that
   the UE is present in the network and the UE can be reached in case of
   incoming call.  In this state the UE monitors paging, performs cell
   measurements and cell selection and acquires system information.
   Also the UE can receive broadcast and multicast data, but it is not
   expected to transmit or receive singlecast data.  In RRC_Connected
   the UE has a connection to the eNodeB, the network knows the UE
   location on cell level and the UE may receive and transmit singlecast
   data.  RRC_Connected mode is established, when the UE is expected to
   be active in the network, to transmit or receive data.  Connection is
   released, switching to RRC_Idle, when there is no traffic to save the
   UE battery and radio resources.  However, a new feature was
   introduced for NB-IoT, as mentioned earlier, which allows data to be
   transmitted from the MME directly to the UE, while the UE is in
   RRC_Idle transparently to the eNodeB.

   Packet Data Convergence Protocol's (PDCP) [TGPP36323] main services
   in control plane are transfer of control plane data, ciphering and
   integrity protection.

   Radio Link Control protocol (RLC) [TGPP36322] performs transfer of
   upper layer PDUs and optionally error correction with Automatic
   Repeat reQuest (ARQ), concatenation, segmentation and reassembly of
   RLC SDUs, in-sequence delivery of upper layer PDUs, duplicate
   detection, RLC SDU discard, RLC-re-establishment and protocol error
   detection and recovery.

   Medium Access Control protocol (MAC) [TGPP36321] provides mapping
   between logical channels and transport channels, multiplexing of MAC
   SDUs, scheduling information reporting, error correction with HARQ,
   priority handling and transport format selection.

   Physical layer [TGPP36201] provides data transport services to higher
   layers.  These include error detection and indication to higher
   layers, FEC encoding, HARQ soft-combining.  Rate matching and mapping
   of the transport channels onto physical channels, power weighting and
   modulation of physical channels, frequency and time synchronization
   and radio characteristics measurements.

   User plane is responsible for transferring the user data through the
   Access Stratum.  It interfaces with IP and consists of PDCP, which in
   user plane performs header compression using Robust Header
   Compression (RoHC), transfer of user plane data between eNodeB and



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   UE, ciphering and integrity protection.  Lower layers in user plane
   are similarly RLC, MAC and physical layer performing tasks mentioned
   above.

   Under worst-case conditions, NB-IoT may achieve data rate of roughly
   200 bps.  For downlink with 164 dB coupling loss, NB-IoT may achieve
   higher data rates, depending on the deployment mode.  Stand-alone
   operation may achieve the highest data rates, up to few kbps, while
   in-band and guard-band operations may reach several hundreds of bps.
   NB-IoT may even operate with higher maximum coupling loss than 170 dB
   with very low bit rates.

2.3.  SIGFOX

   Text here is largely from
   [I-D.zuniga-lpwan-sigfox-system-description] which may have been
   updated since this was published.

2.3.1.  Provenance and Documents

   The SIGFOX LPWAN is in line with the terminology and specifications
   being defined by the ETSI ERM TG28 Low Throughput Networks (LTN)
   group [etsi_ltn].  As of today, SIGFOX's network has been fully
   deployed in 6 countries, with ongoing deployments on 18 other
   countries, in total a geography containing 397M people.

2.3.2.  Characteristics

   SIGFOX LPWAN autonomous battery-operated devices send only a few
   bytes per day, week or month, in principle allowing them to remain on
   a single battery for up to 10-15 years.  The capacity of a SIGFOX
   base station mainly depends on the number of messages generated by
   the devices, and not on the number of devices.  The battery life of
   devices also depends on the number of messages generated by the
   device, but it is important to keep in mind that these devices are
   designed to last several years, some of them even buried underground.
   The coverage of the cell also depends on the link budget and on the
   type of deployment (urban, rural, etc.), which can vary from sending
   less than one message per device per day to dozens of messages per
   device per day.

   The radio interface is compliant with the following regulations:

      Spectrum allocation in the USA [fcc_ref]

      Spectrum allocation in Europe [etsi_ref]

      Spectrum allocation in Japan [arib_ref]



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   The SIGFOX LTN radio interface is also compliant with the local
   regulations of the following countries: Australia, Brazil, Canada,
   Kenya, Lebanon, Mauritius, Mexico, New Zealand, Oman, Peru,
   Singapore, South Africa, South Korea, and Thailand.

   The radio interface is based on Ultra Narrow Band (UNB)
   communications, which allow an increased transmission range by
   spending a limited amount of energy at the device.  Moreover, UNB
   allows a large number of devices to coexist in a given cell without
   significantly increasing the spectrum interference.

   Both uplink and downlink communications are possible with the UNB
   solution.  Due to spectrum optimizations, different uplink and
   downlink frames and time synchronization methods are needed.

   The main radio characteristics of the UNB uplink transmission are:

   o  Channelization mask: 100 Hz (600 Hz in the USA)

   o  Uplink baud rate: 100 baud (600 baud in the USA)

   o  Modulation scheme: DBPSK

   o  Uplink transmission power: compliant with local regulation

   o  Link budget: 155 dB (or better)

   o  Central frequency accuracy: not relevant, provided there is no
      significant frequency drift within an uplink packet

   In Europe, the UNB uplink frequency band is limited to 868,00 to
   868,60 MHz, with a maximum output power of 25 mW and a maximum mean
   transmission time of 1%.

   The format of the uplink frame is the following:

   +--------+--------+--------+------------------+-------------+-----+
   |Preamble|  Frame | Dev ID |     Payload      |Msg Auth Code| FCS |
   |        |  Sync  |        |                  |             |     |
   +--------+--------+--------+------------------+-------------+-----+


                       Figure 5: Uplink Frame Format

   The uplink frame is composed of the following fields:

   o  Preamble: 19 bits




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   o  Frame sync and header: 29 bits

   o  Device ID: 32 bits

   o  Payload: 0-96 bits

   o  Authentication: 16-40 bits

   o  Frame check sequence: 16 bits (CRC)

   The main radio characteristics of the UNB downlink transmission are:

   o  Channelization mask: 1.5 kHz

   o  Downlink baud rate: 600 baud

   o  Modulation scheme: GFSK

   o  Downlink transmission power: 500 mW (4W in the USA)

   o  Link budget: 153 dB (or better)

   o  Central frequency accuracy: Centre frequency of downlink
      transmission are set by the network according to the corresponding
      uplink transmission.

   In Europe, the UNB downlink frequency band is limited to 869,40 to
   869,65 MHz, with a maximum output power of 500 mW with 10% duty
   cycle.

   The format of the downlink frame is the following:

   +------------+-----+---------+------------------+-------------+-----+
   |  Preamble  |Frame|   ECC   |     Payload      |Msg Auth Code| FCS |
   |            |Sync |         |                  |             |     |
   +------------+-----+---------+------------------+-------------+-----+


                      Figure 6: Downlink Frame Format

   The downlink frame is composed of the following fields:

   o  Preamble: 91 bits

   o  Frame sync and header: 13 bits

   o  Error Correcting Code (ECC): 32 bits




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   o  Payload: 0-64 bits

   o  Authentication: 16 bits

   o  Frame check sequence: 8 bits (CRC)

   The radio interface is optimized for uplink transmissions, which are
   asynchronous.  Downlink communications are achieved by querying the
   network for existing data from the device.

   A device willing to receive downlink messages opens a fixed window
   for reception after sending an uplink transmission.  The delay and
   duration of this window have fixed values.  The LTN transmits the
   downlink message for a given device during the reception window.  The
   LTN selects the base station (BS) for transmitting the corresponding
   downlink message.

   Uplink and downlink transmissions are unbalanced due to the
   regulatory constraints on the ISM bands.  Under the strictest
   regulations, the system can allow a maximum of 140 uplink messages
   and 4 downlink messages per device.  [[Ed: in what duration?]] These
   restrictions can be slightly relaxed depending on system conditions
   and the specific regulatory domain of operation.

                +--+
                |EP| *                    +------+
                +--+   *                  |  RA  |
                         *                +------+
                +--+       *                 |
                |EP| * * *   *               |
                +--+       *   +----+        |
                             * | BS | \  +--------+
                +--+       *   +----+  \ |        |
        DA -----|EP| * * *               |   SC   |----- NA
                +--+       *           / |        |
                             * +----+ /  +--------+
                +--+       *   | BS |/
                |EP| * * *   * +----+
                +--+         *
                           *
                +--+     *
                |EP| * *
                +--+

                       Figure 7: SIGFOX architecture

   Figure 7 depicts the different elements of the SIGFOX architecture.




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   SIGFOX has a "one-contract one-network" model allowing devices to
   connect in any country, without any notion of roaming.

   The architecture consists of a single core network, which allows
   global connectivity with minimal impact on the end device and radio
   access network.  The core network elements are the Service Center
   (SC) and the Registration Authority (RA).  The SC is in charge of the
   data connectivity between the Base Station (BS) and the Internet, as
   well as the control and management of the BSs and End Points.  The RA
   is in charge of the End Point network access authorization.

   The radio access network is comprised of several BSs connected
   directly to the SC.  Each BS performs complex L1/L2 functions,
   leaving some L2 and L3 functionalities to the SC.

   The devices or End Points (EPs) are the objects that communicate
   application data between local device applications (DAs) and network
   applications (NAs).

   EPs (or devices) can be static or nomadic, as they associate with the
   SC and they do not attach to a specific BS.  Hence, they can
   communicate with the SC through one or many BSs.

   Due to constraints in the complexity of the EP, it is assumed that
   EPs host only one or very few device applications, which communicate
   to one single network application at a time.

   The radio protocol provides mechanisms to authenticate and ensure
   integrity of the message.  This is achieved by using a unique device
   ID and a message authentication code, which allow ensuring that the
   message has been generated and sent by the device with the ID claimed
   in the message.

   Security keys are independent for each device.  These keys are
   associated with the device ID and they are pre-provisioned.
   Application data can be encrypted by the application provider.

2.4.  Wi-SUN Alliance Field Area Network (FAN)

   [[Ed: Text here is via personal communication from Bob Heile
   (bheile@ieee.org) and was authored by Bob and Sum Chin Sean.  Many
   references to specifications are still needed here.]]

2.4.1.  Provenance and Documents

   The Wi-SUN Alliance <https://www.wi-sun.org/> is an industry alliance
   for smart city, smart grid, smart utility, and a broad set of general
   IoT applications.  The Wi-SUN Alliance Field Area Network (FAN)



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   profile is open standards based (primarily on IETF and IEEE802
   standards) and was developed to address applications like smart
   municipality/city infrastructure monitoring and management, electric
   vehicle (EV) infrastructure, advanced metering infrastructure (AMI),
   distribution automation (DA), supervisory control and data
   acquisition (SCADA) protection/management, distributed generation
   monitoring and management, and many more IoT applications.
   Additionally, the Alliance has created a certification program to
   promote global multi-vendor interoperability.

   The FAN profile [[Ed: reference (really really:-) needed!]] is an
   IPv6 frequency hopping wireless mesh network with support for
   enterprise level security.  The frequency hopping wireless mesh
   topology aims to offer superior network robustness, reliability due
   to high redundancy, good scalability due to the flexible mesh
   configuration and good resilience to interference.  Very low power
   modes are in development permitting long term battery operation of
   network nodes.  [[Ed: details welcome.]]

2.4.2.  Characteristics

   [[Ed: this really needs the references.]] The FAN profile is based on
   various open standards in IETF, IEEE802 and ANSI/TIA for low power
   and lossy networks.  The FAN profile specification provides an
   application-independent IPv6-based transport service for both
   connectionless (i.e.  UDP) and connection-oriented (i.e.  TCP)
   services.  There are two possible methods for establishing the IPv6
   packet routing: mandatory Routing Protocol for Low-Power and Lossy
   Networks (RPL) at the Network layer or optional Multi-Hop Delivery
   Service (MHDS) at the Data Link layer.  Table 5 provides an overview
   of the FAN network stack.

   The Transport service is based on User Datagram Protocol (UDP)
   defined in RFC768 or Transmission Control Protocol (TCP) defined in
   RFC793.

   The Network service is provided by IPv6 defined in RFC2460 with
   6LoWPAN adaptation as defined in RC4944 and RFC6282.  Additionally,
   ICMPv6 as defined in RFC4443 is used for control plane in information
   exchange.

   The Data Link service provides both control/management of the
   Physical layer and data transfer/management services to the Network
   layer.  These services are divided into Media Access Control (MAC)
   and Logical Link Control (LLC) sub-layers.  The LLC sub-layer
   provides a protocol dispatch service which supports 6LoWPAN and an
   optional MAC sub-layer mesh service.  The MAC sub-layer is
   constructed using data structures defined in IEEE802.15.4-2015.



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   Multiple modes of frequency hopping are defined.  The entire MAC
   payload is encapsulated in an IEEE802.15.9 Information Element to
   enable LLC protocol dispatch between upper layer 6LoWPAN processing,
   MAC sublayer mesh processing, etc.  These areas will be expanded once
   IEEE802.15.12 is completed

   The PHY service is derived from a sub-set of the SUN FSK
   specification in IEEE802.15.4-2015.  The 2-FSK modulation schemes,
   with channel spacing range from 200 to 600 kHz, are defined to
   provide data rates from 50 to 300 kbps, with Forward Error Coding
   (FEC) as an optional feature.  Towards enabling ultra-low-power
   applications, the PHY layer design is also extendable to low energy
   and critical infrastructure monitoring networks, such as
   IEEE802.15.4k.





































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   +------------------------------+------------------------------------+
   | Layer                        | Description                        |
   +------------------------------+------------------------------------+
   | IPv6 protocol suite          | TCP/UDP                            |
   |                              |                                    |
   |                              | 6LoWPAN Adaptation + Header        |
   |                              | Compression                        |
   |                              |                                    |
   |                              | DHCPv6 for IP address management.  |
   |                              |                                    |
   |                              | Routing using RPL.                 |
   |                              |                                    |
   |                              | ICMPv6.                            |
   |                              |                                    |
   |                              | Unicast and Multicast forwarding.  |
   |                              |                                    |
   | MAC based on IEEE 802.15.4e  | Frequency hopping                  |
   | + IE extensions              |                                    |
   |                              |                                    |
   |                              | Discovery and Join                 |
   |                              |                                    |
   |                              | Protocol Dispatch (IEEE 802.15.9)  |
   |                              |                                    |
   |                              | Several Frame Exchange patterns    |
   |                              |                                    |
   |                              | Optional Mesh Under routing (ANSI  |
   |                              | 4957.210).                         |
   |                              |                                    |
   | PHY based on 802.15.4g       | Various data rates and regions     |
   |                              |                                    |
   | Security                     | 802.1X/EAP-TLS/PKI                 |
   |                              | Authentication.                    |
   |                              |                                    |
   |                              | 802.11i Group Key Management       |
   |                              |                                    |
   |                              | Optional ETSI-TS-102-887-2 Node 2  |
   |                              | Node Key Management                |
   +------------------------------+------------------------------------+

                      Table 5: Wi-SUN Stack Overivew

   The FAN security supports Data Link layer network access control,
   mutual authentication, and establishment of a secure pairwise link
   between a FAN node and its Border Router, which is implemented with
   an adaptation of IEEE802.1X and EAP-TLS as described in RFC5216 using
   secure device identity as described in IEEE802.1AR.  Certificate
   formats are based upon RFC5280.  A secure group link between a Border
   Router and a set of FAN nodes is established using an adaptation of



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   the IEEE802.11 Four-Way Handshake.  A set of 4 group keys are
   maintained within the network, one of which is the current transmit
   key.  Secure node to node links are supported between one-hop FAN
   neighbors using an adaptation of ETSI-TS-102-887-2.  FAN nodes
   implement Frame Security as specified in IEEE802.15.4-2015.

3.  Generic Terminology

   LPWAN technologies, such as those discussed above, have similar
   architectures but different terminology.  We can identify different
   types of entities in a typical LPWAN network:

   o  The Host, which are the devices or the things (e.g. sensors,
      actuators, etc.), they are named differently in each technology
      (End Device, User Equipment or End Point).  There can be a high
      density of hosts per radio gateway.

   o  The Radio Gateway, which is the end point of the constrained link.
      It is known as: Gateway, Evolved Node B or Base station.

   o  The Network Gateway or Router is the interconnection node between
      the Radio Gateway and the Internet.  It is known as: Network
      Server, Serving GW or Service Center.

   o  AAA Server, which controls the user authentication, the
      applications.  It is known as: Join-Server, Home Subscriber Server
      or Registration Authority.  [[Ed: I'm not clear that AAA server is
      the right generic term here.]]

   o  At last we have the Application Server, known also as Packet Data
      Node Gateway or Network Application.




















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 +---------------------------------------------------------------------+
 | Function/    |           |            |             |               |
 | Technology   |  LORAWAN  |    NB-IOT  |   SIGFOX    |      IETF     |
 +--------------+-----------+------------+-------------+---------------+
 |    Sensor,   |           |            |             |               |
 |  Actuator,   |     End   |     User   |     End     |     Thing     |
 |device, object|   Device  | Equipment  |    Point    |     (HOST)    |
 +--------------+-----------+------------+-------------+---------------+
 | Transceiver  |           |   Evolved  |    Base     |     RADIO     |
 |  Antenna     |  Gateway  |   Node B   |   Station   |    GATEWAY    |
 +--------------+-----------+------------+-------------+---------------+
 |  Server      |  Network  |  Serving-  |   Service   |Network Gateway|
 |              |  Server   |  Gateway   |   Center    |   (ROUTER)    |
 +--------------+-----------+------------+-------------+---------------+
 |   Security   |    Join   |   Home     |Registration |               |
 |    Server    |   Server  | Subscriber | Authority   |      AAA      |
 |              |           |  Server    |             |    SERVER     |
 +--------------+-----------+------------+-------------+---------------+
 | Application  |Application| Packet Data|  Network    |  APPLICATION  |
 |              |   Server  |Node Gateway| Application |    SERVER     |
 +---------------------------------------------------------------------+

                 Figure 8: LPWAN Architecture Terminology

 ()    ()   ()         |                         +------+
   ()  () () ()       / \         +---------+    | AAA  |
() () () () () ()    /   \========|    /\   |====|Server|  +-----------+
 ()  ()   ()        |             | <--|--> |    +------+  |Application|
()  ()  ()  ()     / \============|    v    |==============|   Server  |
  ()  ()  ()      /   \           +---------+              +-----------+
 HOSTS         Radio Gateways   Network Gateway

                       Figure 9: LPWAN Architecture

   In addition to the names of entities, LPWANs are also subject to
   possibly regional frequency band regulations.  Those may include
   restrictions on the duty-cycle, for example requiring that hosts only
   transmit for a certain percentage of each hour.  [[Ed: Are these
   duty-cycle percentages always per-hour?  Could a host amortise it's
   transmits per day?]]

4.  Gap Analysis

4.1.  Naive application of IPv6

   IPv6 [RFC2460] has been designed to allocate addresses to all the
   nodes connected to the Internet.  Nevertheless, the header overhead
   of at least 40 bytes introduced by the protocol is incompatible with



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   LPWAN constraints.  If IPv6 with no further optimization were used,
   several LPWAN frames would be needed just to carry the IP header.
   Another problem arises from IPv6 MTU requirements, which require the
   layer below to support at least 1280 byte packets [RFC2460].

   IPv6 has a configuration protocol - neighbor discovery protocol,
   (NDP) [RFC4861]).  For a node to learn network parameters NDP
   generates regular traffic with a relatively large message size that
   does not fit LPWAN constraints.

   In some LPWAN technologies, layer two multicast is not supported.  In
   that case, if the network topology is a star, the solution and
   considerations of section 3.2.5 of [RFC7668] may be applied.

   Other key protocols such as DHCPv6 [RFC3315], IPsec [RFC4301] and TLS
   [RFC5246] have similarly problematic properties in this context.
   Each of those require relatively frequent round-trips between the
   host and some other host on the network.  In the case of
   cryptographic protocols such as IPsec and TLS, in addition to the
   round-trips required for secure session establishment, cryptographic
   operations can require padding and addition of authenticators that
   are problematic when considering LPWAN lower layers.

4.2.  6LoWPAN

   Several technologies that exhibit significant constraints in various
   dimensions have exploited the 6LoWPAN suite of specifications
   [RFC4944], [RFC6282], [RFC6775] to support IPv6 [I-D.hong-6lo-use-
   cases].  However, the constraints of LPWANs, often more extreme than
   those typical of technologies that have (re)used 6LoWPAN, constitute
   a challenge for the 6LoWPAN suite in order to enable IPv6 over LPWAN.
   LPWANs are characterised by device constraints (in terms of
   processing capacity, memory, and energy availability), and specially,
   link constraints, such as:

   o  very low layer two payload size (from ~10 to ~100 bytes),

   o  very low bit rate (from ~10 bit/s to ~100 kbit/s), and

   o  in some specific technologies, further message rate constraints
      (e.g.  between ~0.1 message/minute and ~1 message/minute) due to
      regional regulations that limit the duty cycle.

4.2.1.  Header Compression

   6LoWPAN header compression reduces IPv6 (and UDP) header overhead by
   eliding header fields when they can be derived from the link layer,
   and by assuming that some of the header fields will frequently carry



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   expected values. 6LoWPAN provides both stateless and stateful header
   compression.  In the latter, all nodes of a 6LoWPAN are assumed to
   share compression context.  In the best case, the IPv6 header for
   link-local communication can be reduced to only 2 bytes.  For global
   communication, the IPv6 header may be compressed down to 3 bytes in
   the most extreme case.  However, in more practical situations, the
   smallest IPv6 header size may be 11 bytes (one address prefix
   compressed) or 19 bytes (both source and destination prefixes
   compressed).  These headers are large considering the link layer
   payload size of LPWAN technologies, and in some cases are even bigger
   than the LPWAN PDUs. 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, which may or may not be duty-cycled.

4.2.2.  Address Autoconfiguration

   Traditionally, Interface Identifiers (IIDs) have been derived from
   link layer identifiers [RFC4944] . This allows optimisations such as
   header compression.  Nevertheless, recent guidance has given advice
   on the fact that, due to privacy concerns, 6LoWPAN devices should not
   be configured to embed their link layer addresses in the IID by
   default.

4.2.3.  Fragmentation

   As stated above, IPv6 requires the layer below to support an MTU of
   1280 bytes [RFC2460].  Therefore, given the low maximum payload size
   of LPWAN technologies, fragmentation is needed.

   If a layer of an LPWAN technology supports fragmentation, proper
   analysis has to be carried out to decide whether the fragmentation
   functionality provided by the lower layer or fragmentation at the
   adaptation layer should be used.  Otherwise, fragmentation
   functionality shall be used at the adaptation layer.

   6LoWPAN defined a fragmentation mechanism and a fragmentation header
   to support the transmission of IPv6 packets over IEEE 802.15.4
   networks [RFC4944].  While the 6LoWPAN fragmentation header is
   appropriate for IEEE 802.15.4-2003 (which has a frame payload size of
   81-102 bytes), it is not suitable for several LPWAN technologies,
   many of which have a maximum payload size that is one order of
   magnitude below that of IEEE 802.15.4-2003.  The overhead of the
   6LoWPAN fragmentation header is high, considering the reduced payload
   size of LPWAN technologies and the limited energy availability of the
   devices using such technologies.  Furthermore, its datagram offset
   field is expressed in increments of eight octets.  In some LPWAN
   technologies, the 6LoWPAN fragmentation header plus eight octets from
   the original datagram exceeds the available space in the layer two



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   payload.  In addition, the MTU in the LPWAN networks could be
   variable which implies a variable fragmentation solution.

4.2.4.  Neighbor Discovery

   6LoWPAN Neighbor Discovery [RFC6775] defined optimizations to IPv6
   Neighbor Discovery [RFC4861], in order to adapt functionality of the
   latter for networks of devices using IEEE 802.15.4 or similar
   technologies.  The optimizations comprise host-initiated interactions
   to allow for sleeping hosts, replacement of multicast-based address
   resolution for hosts by an address registration mechanism, multihop
   extensions for prefix distribution and duplicate address detection
   (note that these are not needed in a star topology network), and
   support for 6LoWPAN header compression.

   6LoWPAN Neighbor Discovery may be used in not so severely constrained
   LPWAN networks.  The relative overhead incurred will depend on the
   LPWAN technology used (and on its configuration, if appropriate).  In
   certain LPWAN setups (with a maximum payload size above ~60 bytes,
   and duty-cycle-free or equivalent operation), an RS/RA/NS/NA exchange
   may be completed in a few seconds, without incurring packet
   fragmentation.

   In other LPWANs (with a maximum payload size of ~10 bytes, and a
   message rate of ~0.1 message/minute), the same exchange may take
   hours or even days, leading to severe fragmentation and consuming a
   significant amount of the available network resources.  6LoWPAN
   Neighbor Discovery behavior may be tuned through the use of
   appropriate values for the default Router Lifetime, the Valid
   Lifetime in the PIOs, and the Valid Lifetime in the 6CO, as well as
   the address Registration Lifetime.  However, for the latter LPWANs
   mentioned above, 6LoWPAN Neighbor Discovery is not suitable.

4.3.  6lo

   The 6lo WG has been reusing and adapting 6LoWPAN to enable IPv6
   support over link layer technologies such as Bluetooth Low Energy
   (BTLE), ITU-T G.9959, DECT-ULE, MS/TP-RS485, NFC IEEE 802.11ah.  (See
   <https://tools.ietf.org/wg/6lo> for details.)  These technologies are
   similar in several aspects to IEEE 802.15.4, which was the original
   6LoWPAN target technology.

   6lo has mostly used the subset of 6LoWPAN techniques best suited for
   each lower layer technology, and has provided additional
   optimizations for technologies where the star topology is used, such
   as BTLE or DECT-ULE.





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   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 constraints.  [[Ed: I'm not
   sure that conclusion follows from the information provided in this
   section - is more needed?.]]

4.4.  6tisch

   The 6tisch solution is dedicated to mesh networks that operate using
   802.15.4e MAC with a deterministic slotted channel.  The time slot
   channel (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.

   A key element of 6tisch is the use of synchronization to enable
   determinism.  TSCH and 6TiSCH may provide a standard scheduling
   function.  The LPWAN networks probably will not support
   synchronization like the one used in 6tisch.

4.5.  RoHC

   Robust header compression (RoHC) is a header compression mechanism
   [RFC3095] developed for multimedia flows in a point to point channel.
   RoHC uses 3 levels of compression, each level having its own header
   format.  In the first level, RoHC sends 52 bytes of header, in the
   second level the header could be from 34 to 15 bytes and in the third
   level header size could be from 7 to 2 bytes.  The level of
   compression is managed by a sequence number, which varies in size
   from 2 bytes to 4 bits in the minimal compression.  SN compression is
   done with an algorithm called W-LSB (Window- Least Signifiant Bits).
   This window has a 4 bit size representing 15 packets, so every 15
   packets RoHC needs to slide the window in order to receive the
   correct sequence number, and sliding the window implies a reduction
   of the level of compression.  When packets are lost or errored, the
   decompressor loses context and drops packets until a bigger header is
   sent with more complete information.  To estimate the performance of
   RoHC, an average header size is used.  This average depends on the
   transmission conditions, but most of the time is between 3 and 4
   bytes.

   RoHC has not been adapted specifically to the constrained hosts and
   networks of LPWANs: it does not take into account energy limitations
   nor the transmission rate, and RoHC context is synchronised during
   transmission, which does not allow better compression.  [[Ed: this
   seems to conflict a bit with what was said about 6tisch which puzzled
   me.]]





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4.6.  ROLL

   Most technologies considered by the lpwan WG are based on a star
   topology, which eliminates the need for routing at that layer.
   Future work may address additional use-cases that may require
   adaptation of existing routing protocols or the definition of new
   ones.  As of the time of writing, work similar to that done in the
   ROLL WG and other routing protocols are out of scope of the LPWAN WG.

4.7.  CoAP

   CoAP [RFC7252] provides a RESTful framework for applications intended
   to run on constrained IP networks.  It may be necessary to adapt CoAP
   or related protocols to take into account for the extreme duty cycles
   and the potentially extremely limited throughput of LPWANs.

   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.  On the other hand, the current 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 LPWAN technologies.  The
   overhead is reduced by adding a dictionary which matches a URI to a
   small identifier and a compact mapping of the YANG model into the
   CBOR binary representation.

4.8.  Mobility

   LPWANs nodes can be mobile.  However, LPWAN mobility is different
   from 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
   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 mobility concerns more the gateway than the devices.

   NEMO [RFC3963] Mobility solutions may be used in the case where some
   hosts belonging to the same Network gateway will move from one point
   to another and that they are not aware of this mobility.

4.9.  DNS and LPWAN

   [[Ed: the WG probably need to decide what to say about DNS, there's
   not much content here so far.]]

   The Domain Name System (DNS) DNS [RFC1035], enables applications to
   name things with a globallly resolvable name.  Many protocols use the
   DNS to identify hosts for example applications using CoAP.



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   The DNS query/answer protocol as a pre-cursor to other communication
   within the time-to-live (TTL) of a DNS answer is clearly problematic
   in an LPWAN, say where only one round-trip per hour can be used, and
   with a TTL that is less than 3600.  It is currently unclear [[Ed: to
   me anyway:-)]] whether and hw DNS-like functionality might be
   provided in LPWANs.

5.  Security Considerations

   [[Ed: be good to add stuff here about a) privacy and b) difficulties
   with getting current security protocols to work in this context.  For
   a) maybe try find nice illustrations, e.g. extremecom instrumeted-
   igloo traces (temperature change allowing one to infer when someone
   took a pee:-).  For b) things like IPsec/(D)TLS/OCSP and NTP to work
   in these environments.  Not sure how much of that is known or useful
   for the WG.  Probably worth noting the IAB statement on
   confidentiality and to ponder the impact of more than one layer of
   encryption in this context.  Text below is basically from the "gaps"
   draft.]]

   Most LPWAN technologies integrate some authentication or encryption
   mechanisms that were defined outside the IETF.  The working group may
   need to do work to integrate these mechanisms to unify management.  A
   standardized Authentication, Accounting and Authorization (AAA)
   infrastructure [RFC2904] may offer a scalable solution for some of
   the security and management issues for LPWANs.  AAA offers
   centralized management that may be of use in LPWANs, for example
   [I-D.garcia-dime-diameter-lorawan] and
   [I-D.garcia-radext-radius-lorawan] suggest possible security
   processes for a LoRaWAN network.  Similar mechanisms may be useful to
   explore for other LPWAN technologies.

6.  IANA Considerations

   There are no IANA considerations related to this memo.

7.  Contributors

   As stated above this document is mainly a collection of content
   developed by the full set of contributors listed below.  The main
   input documents and their authors were:

   o  Text for Section 2.1 was provieded by Alper Yegin and Stephen
      Farrell in [I-D.farrell-lpwan-lora-overview].

   o  Text for Section 2.2 was provided by Antti Ratilainen in
      [I-D.ratilainen-lpwan-nb-iot].




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   o  Text for Section 2.3 was provided by Juan Carlos Zuniga and Benoit
      Ponsard in [I-D.zuniga-lpwan-sigfox-system-description].

   o  Text for Section 2.4 was provided via personal communication from
      Bob Heile (bheile@ieee.org) and was authored by Bob and Sum Chin
      Sean.  There is no Internet draft for that at present.

   o  Text for Section 4 was provided by Ana Minabiru, Carles Gomez,
      Laurent Toutain, Josep Paradells and Jon Crowcroft in
      [I-D.minaburo-lpwan-gap-analysis].  Additional text from that
      draft is also used elsewhere above.

   The full list of contributors are:


      Jon Crowcroft
      University of Cambridge
      JJ Thomson Avenue
      Cambridge, CB3 0FD
      United Kingdom

      Email: jon.crowcroft@cl.cam.ac.uk


      Carles Gomez
      UPC/i2CAT
      C/Esteve Terradas, 7
      Castelldefels 08860
      Spain

      Email: carlesgo@entel.upc.edu


      Bob Heile
      Wi-Sun Alliance
      11 Robert Toner Blvd, Suite 5-301
      North Attleboro, MA  02763
      USA

      Phone: +1-781-929-4832
      Email: bheile@ieee.org


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



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      Email: ana@ackl.io


      Josep PAradells
      UPC/i2CAT
      C/Jordi Girona, 1-3
      Barcelona 08034
      Spain

      Email: josep.paradells@entel.upc.edu


      Benoit Ponsard
      SIGFOX
      425 rue Jean Rostand
      Labege  31670
      France

      Email: Benoit.Ponsard@sigfox.com
      URI:   http://www.sigfox.com/


      Antti Ratilainen
      Ericsson
      Hirsalantie 11
      Jorvas  02420
      Finland

      Email: antti.ratilainen@ericsson.com


      Chin-Sean SUM
      Wi-Sun Alliance
      20, Science Park Rd
      Singapore  117674

      Phone: +65 6771 1011
      Email: sum@wi-sun.org


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

      Email: Laurent.Toutain@telecom-bretagne.eu



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      Alper Yegin
      Actility
      Paris, Paris
      FR

      Email: alper.yegin@actility.com


      Juan Carlos Zuniga
      SIGFOX
      425 rue Jean Rostand
      Labege  31670
      France

      Email: JuanCarlos.Zuniga@sigfox.com
      URI:   http://www.sigfox.com/


8.  Acknowledgements

   Thanks to all those listed in Section 7 for the excellent text.
   Errors in the handling of that are solely the editor's fault.

   In addition to the contributors above, thanks are due to Jiazi Yi,
   [your name here] for comments.

   Stephen Farrell's work on this memo was supported by the Science
   Foundation Ireland funded CONNECT centre <https://connectcentre.ie/>.

9.  Informative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

   [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>.

   [RFC2904]  Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
              Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
              D. Spence, "AAA Authorization Framework", RFC 2904,
              DOI 10.17487/RFC2904, August 2000,
              <http://www.rfc-editor.org/info/rfc2904>.







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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>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, DOI 10.17487/RFC3963, January 2005,
              <http://www.rfc-editor.org/info/rfc3963>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <http://www.rfc-editor.org/info/rfc4301>.

   [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>.

   [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>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [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>.

   [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>.




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   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

   [RFC7668]  Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
              Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
              <http://www.rfc-editor.org/info/rfc7668>.

   [I-D.farrell-lpwan-lora-overview]
              Farrell, S. and A. Yegin, "LoRaWAN Overview", draft-
              farrell-lpwan-lora-overview-01 (work in progress), October
              2016.

   [I-D.minaburo-lpwan-gap-analysis]
              Minaburo, A., Gomez, C., Toutain, L., Paradells, J., and
              J. Crowcroft, "LPWAN Survey and GAP Analysis", draft-
              minaburo-lpwan-gap-analysis-02 (work in progress), October
              2016.

   [I-D.zuniga-lpwan-sigfox-system-description]
              Zuniga, J. and B. PONSARD, "SIGFOX System Description",
              draft-zuniga-lpwan-sigfox-system-description-01 (work in
              progress), October 2016.

   [I-D.ratilainen-lpwan-nb-iot]
              Ratilainen, A., "NB-IoT characteristics", draft-
              ratilainen-lpwan-nb-iot-00 (work in progress), July 2016.

   [I-D.garcia-dime-diameter-lorawan]
              Garcia, D., Lopez, R., Kandasamy, A., and A. Pelov,
              "LoRaWAN Authentication in Diameter", draft-garcia-dime-
              diameter-lorawan-00 (work in progress), May 2016.

   [I-D.garcia-radext-radius-lorawan]
              Garcia, D., Lopez, R., Kandasamy, A., and A. Pelov,
              "LoRaWAN Authentication in RADIUS", draft-garcia-radext-
              radius-lorawan-02 (work in progress), October 2016.

   [TGPP36300]
              3GPP, "TS 36.300 v13.4.0 Evolved Universal Terrestrial
              Radio Access (E-UTRA) and Evolved Universal Terrestrial
              Radio Access Network (E-UTRAN); Overall description; Stage
              2", 2016,
              <http://www.3gpp.org/ftp/Specs/2016-09/Rel-14/36_series/>.





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   [TGPP36321]
              3GPP, "TS 36.321 v13.2.0 Evolved Universal Terrestrial
              Radio Access (E-UTRA); Medium Access Control (MAC)
              protocol specification", 2016.

   [TGPP36322]
              3GPP, "TS 36.322 v13.2.0 Evolved Universal Terrestrial
              Radio Access (E-UTRA); Radio Link Control (RLC) protocol
              specification", 2016.

   [TGPP36323]
              3GPP, "TS 36.323 v13.2.0 Evolved Universal Terrestrial
              Radio Access (E-UTRA); Packet Data Convergence Protocol
              (PDCP) specification (Not yet available)", 2016.

   [TGPP36331]
              3GPP, "TS 36.331 v13.2.0 Evolved Universal Terrestrial
              Radio Access (E-UTRA); Radio Resource Control (RRC);
              Protocol specification", 2016.

   [TGPP36201]
              3GPP, "TS 36.201 v13.2.0 - Evolved Universal Terrestrial
              Radio Access (E-UTRA); LTE physical layer; General
              description", 2016.

   [TGPP23720]
              3GPP, "TR 23.720 v13.0.0 - Study on architecture
              enhancements for Cellular Internet of Things", 2016.

   [TGPP33203]
              3GPP, "TS 33.203 v13.1.0 - 3G security; Access security
              for IP-based services", 2016.

   [etsi_ltn]
              "ETSI Technical Committee on EMC and Radio Spectrum
              Matters (ERM) TG28 Low Throughput Networks (LTN)",
              February 2015.

   [fcc_ref]  "FCC CFR 47 Part 15.247 Telecommunication Radio Frequency
              Devices - Operation within the bands 902-928 MHz,
              2400-2483.5 MHz, and 5725-5850 MHz.", June 2016.

   [etsi_ref]
              "ETSI EN 300-220 (Parts 1 and 2): Electromagnetic
              compatibility and Radio spectrum Matters (ERM); Short
              Range Devices (SRD); Radio equipment to be used in the 25
              MHz to 1 000 MHz frequency range with power levels ranging
              up to 500 mW", May 2016.



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   [arib_ref]
              "ARIB STD-T108 (Version 1.0): 920MHz-Band Telemeter,
              Telecontrol and data transmission radio equipment.",
              February 2012.

   [LoRaSpec]
              LoRa Alliance, "LoRaWAN Specification Version V1.0.2",
              July 2016, <http://portal.lora-
              alliance.org/DesktopModules/Inventures_Document/
              FileDownload.aspx?ContentID=1398>.

   [LoRaSpec1.0]
              LoRa Alliance, "LoRaWAN Specification Version V1.0", Jan
              2015, <https://www.lora-alliance.org/portals/0/specs/
              LoRaWAN%20Specification%201R0.pdf>.

Appendix A.  Changes

A.1.  From -00 to -01

   o  WG have stated they want this to be an RFC.

   o  WG clearly want to keep the RF details.

   o  Various changes made to remove/resolve a number of editorial notes
      from -00 (in some cases as per suggestions from Ana Minaburo)

   o  Merged PR's: #1...

   o  Github repo is at: https://github.com/sftcd/lpwan-ov

Author's Address

   Stephen Farrell (editor)
   Trinity College Dublin
   Dublin  2
   Ireland

   Phone: +353-1-896-2354
   Email: stephen.farrell@cs.tcd.ie











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