6Lo Working Group                                                 J. Hou
Internet-Draft                                                    B. Liu
Intended status: Standards Track                     Huawei Technologies
Expires: December 5, 2020                                      Y-G. Hong
                                                                 X. Tang
                                                              C. Perkins
                                                            June 3, 2020

             Transmission of IPv6 Packets over PLC Networks


   Power Line Communication (PLC), namely using the electric-power lines
   for indoor and outdoor communications, has been widely applied to
   support Advanced Metering Infrastructure (AMI), especially smart
   meters for electricity.  The inherent advantage of existing
   electricity infrastructure facilitates the expansion of PLC
   deployments, and moreover, a wide variety of accessible devices
   raises the potential demand of IPv6 for future applications.  This
   document describes how IPv6 packets are transported over constrained
   PLC networks, such as ITU-T G.9903, IEEE 1901.1 and IEEE 1901.2.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 5, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation and Terminology . . . . . . . . . . . .   3
   3.  Overview of PLC . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Protocol Stack  . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Addressing Modes  . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Maximum Transmission Unit . . . . . . . . . . . . . . . .   6
     3.4.  Routing Protocol  . . . . . . . . . . . . . . . . . . . .   7
   4.  IPv6 over PLC . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Stateless Address Autoconfiguration . . . . . . . . . . .   7
     4.2.  IPv6 Link Local Address . . . . . . . . . . . . . . . . .   8
     4.3.  Unicast Address Mapping . . . . . . . . . . . . . . . . .   9
       4.3.1.  Unicast Address Mapping for IEEE 1901.1 . . . . . . .   9
       4.3.2.  Unicast Address Mapping for IEEE 1901.2 and ITU-T
               G.9903  . . . . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Neighbor Discovery  . . . . . . . . . . . . . . . . . . .  10
     4.5.  Header Compression  . . . . . . . . . . . . . . . . . . .  11
     4.6.  Fragmentation and Reassembly  . . . . . . . . . . . . . .  12
   5.  Internet Connectivity Scenarios and Topologies  . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Security Consideration  . . . . . . . . . . . . . . . . . . .  15
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The idea of using power lines for both electricity supply and
   communication can be traced back to the beginning of the last
   century.  With the advantage of existing power grid, Power Line
   Communication (PLC) is a good candidate for supporting various
   service scenarios such as in houses and offices, in trains and
   vehicles, in smart grid and advanced metering infrastructure (AMI).
   The data acquisition devices in these scenarios share common features

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   such as fixed position, large quantity, low data rate and low power

   Although PLC technology has evolved over several decades, it has not
   been fully adapted for IPv6 based constrained networks.  The 6lo
   related scenarios lie in the low voltage PLC networks with most
   applications in the area of Advanced Metering Infrastructure (AMI),
   Vehicle-to-Grid communications, in-home energy management and smart
   street lighting.  IPv6 is important for PLC networks, due to its
   large address space and efficent address auto-configuration.  A
   comparison among various existing PLC standards is provided to
   facilitate the selection of the most applicable standard in
   particular scenarios.

   This specification provides a brief overview of PLC technologies.
   Some of them have LLN characteristics, i.e. limited power
   consumption, memory and processing resources.  This specification is
   focused on the transmission of IPv6 packets over those "constrained"
   PLC networks.  The general approach is to adapt elements of the
   6LoWPAN specifications [RFC4944], [RFC6282], and [RFC6775] to
   constrained PLC networks.  There was work previously proposed as
   [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks], which did not
   reach consensus.  This document provides a more structured
   specification than the previous work, expanding to a larger variety
   of PLC networks.

2.  Requirements Notation and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document often uses the following acronyms and terminologies:

   6LoWPAN:  IPv6 over Low-Power Wireless Personal Area Network

   AMI:  Advanced Metering Infrastructure

   BBPLC:  Broadband Power Line Communication

   CID:  Context ID

   Coordinator:  A device capable of relaying messages.

   DAD:  Duplicate Address Detection

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   EV:   Electric Vehicle

   IID:  IPv6 Interface Identifier

   IPHC: IP Header Compression

   LAN:  Local Area Network

   MSDU: MAC Service Data Unit

   MTU:  Maximum Transmission Unit

   NBPLC:  Narrowband Power Line Communication

   OFDM: Orthogonal Frequency Division Multiplexing

   PANC: PAN Coordinator, a coordinator which also acts as the primary
         controller of a PAN.

   PLC:  Power Line Communication

   PLC device:  An entity follows the PLC standards and implements the
         protocol stack described in this draft.

   PSDU: PHY Service Data Unit

   RPL:  IPv6 Routing Protocol for Low-Power and Lossy Networks

   RA:   Router Advertisement

   WAN:  Wide Area Network

      The terminology used in this draft is aligned with IEEE 1901.2

   |  IEEE 1901.2  |  IEEE 1901.1   |   ITU-T G.9903   | This document |
   |      PAN      |    Central     | PAN Coordinator  |      PAN      |
   |  Coordinator  |  Coordinator   |                  |  Coordinator  |
   |               |                |                  |               |
   |  Coordinator  |     Proxy      |  Full-function   |  Coordinator  |
   |               |  Coordinator   |      device      |               |
   |               |                |                  |               |
   |     Device    |    Station     |    PAN Device    |   PLC Device  |

            Table 1: Terminology Mapping between PLC standards

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3.  Overview of PLC

   PLC technology enables convenient two-way communications for home
   users and utility companies to monitor and control electric plugged
   devices such as electricity meters and street lights.  Due to the
   large range of communication frequencies, PLC is generally classified
   into two categories: Narrowband PLC (NBPLC) for automation of sensors
   (which have low frequency band and low power cost), and Broadband PLC
   (BBPLC) for home and industry networking applications.

   Various standards have been addressed on the MAC and PHY layers for
   this communication technology, e.g., BBPLC (1.8-250 MHz) including
   IEEE 1901 and ITU-T G.hn, and NBPLC (3-500 kHz) including ITU-T
   G.9902 (G.hnem), ITU-T G.9903 (G3-PLC) [ITU-T_G.9903], ITU-T G.9904
   (PRIME), IEEE 1901.2 [IEEE_1901.2] (combination of G3-PLC and PRIME
   PLC) and IEEE 1901.2a [IEEE_1901.2a] (an amendment to IEEE 1901.2).

   Moreover, recently a new PLC standard IEEE 1901.1 [IEEE_1901.1],
   which aims at the medium frequency band less than 12 MHz, has been
   published by the IEEE standard for Smart Grid Powerline Communication
   Working Group (SGPLC WG).  IEEE 1901.1 balances the needs for
   bandwidth versus communication range, and is thus a promising option
   for 6lo applications.

   This specification is focused on IEEE 1901.1, IEEE 1901.2 and ITU-T

3.1.  Protocol Stack

   The protocol stack for IPv6 over PLC is illustrated in Figure 1.  The
   PLC MAC/PHY layer corresponds to IEEE 1901.1, IEEE 1901.2 or ITU-T
   G.9903.  The 6lo adaptation layer for PLC is illustrated in
   Section 4.  For multihop tree and mesh topologies, a routing protocol
   is likely to be necessary.  The routes can be built in mesh-under
   mode at layer 2 or in route-over mode at layer 3, as explained in
   Section 3.4.

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                    |           Application Layer            |
                    |                TCP/UDP                 |
                    |                                        |
                    |                  IPv6                  |
                    |                                        |
                    |   Adaptation layer for IPv6 over PLC   |
                    |             PLC MAC Layer              |
                    |             PLC PHY Layer              |

                       Figure 1: PLC Protocol Stack

3.2.  Addressing Modes

   Each PLC device has a globally unique long address of 48-bit
   ([IEEE_1901.1]) or 64-bit ([IEEE_1901.2], [ITU-T_G.9903]) and a short
   address of 12-bit ([IEEE_1901.1]) or 16-bit ([IEEE_1901.2],
   [ITU-T_G.9903]).  The long address is set by the manufacturer
   according to the IEEE EUI-48 MAC address or the IEEE EUI-64 address.
   Each PLC device joins the network by using the long address and
   communicates with other devices by using the short address after
   joining the network.  Short addresses can be assigned during the
   onboarding process, by the PANC or the JRC in CoJP

3.3.  Maximum Transmission Unit

   The Maximum Transmission Unit (MTU) of the MAC layer determines
   whether fragmentation and reassembly are needed at the adaptation
   layer of IPv6 over PLC.  IPv6 requires an MTU of 1280 octets or
   greater; thus for a MAC layer with MTU lower than this limit,
   fragmentation and reassembly at the adaptation layer are required.

   The IEEE 1901.1 MAC supports upper layer packets up to 2031 octets.
   The IEEE 1901.2 MAC layer supports the MTU of 1576 octets (the
   original value of 1280 bytes was updated in 2015 [IEEE_1901.2a]).
   Though these two technologies can support IPv6 natively without
   fragmentation and reassembly, it is possible to configure a smaller
   MTU in high-noise communication environment.  Thus the 6lo functions,
   including header compression, fragmentation and reassembly, are still
   applicable and useful.

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   The MTU for ITU-T G.9903 is 400 octets, insufficient for supporting
   IPv6's MTU.  For this reason, fragmentation and reassembly as per
   [RFC4944] MUST be enabled for G.9903-based networks.

3.4.  Routing Protocol

   Routing protocols suitable for use in PLC networks include:

   o  RPL (Routing Protocol for Low-Power and Lossy Networks) [RFC6550]
      is a layer 3 routing protocol.  AODV-RPL [I-D.ietf-roll-aodv-rpl]
      updates RPL to include reactive, point-to-point, and asymmetric
      routing.  IEEE 1901.2 specifies Information Elements (IEs) with
      MAC layer metrics, which can be provided to L3 routing protocol
      for parent selection.  For IPv6-addressable PLC networks, a
      layer-3 routing protocol such as RPL and/or AODV-RPL SHOULD be
      supported in the standard.

   o  IEEE 1901.1 supports L2 routing.  Each PLC node maintains a L2
      routing table, in which each route entry comprises the short
      addresses of the destination and the related next hop.  The route
      entries are built during the network establishment via a pair of
      association request/confirmation messages.  The route entries can
      be changed via a pair of proxy change request/confirmation
      messages.  These association and proxy change messages MUST be
      approved by the central coordinator (PANC in this document).

   o  LOADng is a reactive protocol operating at layer 2 or layer 3.
      Currently, LOADng is supported in ITU-T G.9903 [ITU-T_G.9903], and
      the IEEE 1901.2 standard refers to ITU-T G.9903 for LOAD-based

4.  IPv6 over PLC

   6LoWPAN standards [RFC4944], [RFC6775], and [RFC6282] provides useful
   functionality including link-local IPv6 addresses, stateless address
   auto-configuration, neighbor discovery and header compression.
   However, due to the different characteristics of the PLC media, the
   6LoWPAN adaptation layer cannot perfectly fulfill the requirements.
   These considerations suggest the need for a dedicated adaptation
   layer for PLC, which is detailed in the following subsections.

4.1.  Stateless Address Autoconfiguration

   To obtain an IPv6 Interface Identifier (IID), a PLC device performs
   stateless address autoconfiguration [RFC4944].  The autoconfiguration
   can be based on either a long or short link-layer address.

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   The IID can be based on the device's 48-bit MAC address or its EUI-64
   identifier [EUI-64].  A 48-bit MAC address MUST first be extended to
   a 64-bit Interface ID by inserting 0xFFFE at the fourth and fifth
   octets as specified in [RFC2464].  The IPv6 IID is derived from the
   64-bit Interface ID by inverting the U/L bit [RFC4291].

   For IEEE 1901.2 and ITU-T G.9903, a 48-bit "pseudo-address" is formed
   by the 16-bit PAN ID, 16 zero bits and the 16-bit short address.
   Then, the 64-bit Interface ID MUST be derived by inserting 16-bit
   0xFFFE into as follows:


   For the 12-bit short addresses used by IEEE 1901.1, the 48-bit
   pseudo-address is formed by 24-bit NID (Network IDentifier, YYYYYY),
   12 zero bits and a 12-bit TEI (Terminal Equipment Identifier, XXX).
   The 64-bit Interface ID MUST be derived by inserting 16-bit 0xFFFE
   into this 48-bit pseudo-address as follows:


   Since the derived Interface ID is not global, the "Universal/Local"
   (U/L) bit (7th bit) and the Individual/Group bit (8th bit) MUST both
   be set to zero.  In order to avoid any ambiguity in the derived
   Interface ID, these two bits MUST NOT be used to generate the PANID
   (for IEEE 1901.2 and ITU-T G.9903) or NID (for IEEE 1901.1).  In
   other words, the PANID or NID MUST always be chosen so that these
   bits are zeros.

   For privacy reasons, the IID derived by the MAC address SHOULD only
   be used for link-local address configuration.  A PLC host SHOULD use
   the IID derived by the link-layer short address to configure the IPv6
   address used for communication with the public network; otherwise,
   the host's MAC address is exposed.  Implementations should look at
   [RFC8064] as well, in order to generate a stable IPv6 address using
   an opaque IID.

4.2.  IPv6 Link Local Address

   The IPv6 link-local address [RFC4291] for a PLC interface is formed
   by appending the IID, as defined above, to the prefix FE80::/64 (see
   Figure 2).

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       10 bits           54 bits                   64 bits
     |1111111010|        (zeros)        |    Interface Identifier    |

           Figure 2: IPv6 Link Local Address for a PLC interface

4.3.  Unicast Address Mapping

   The address resolution procedure for mapping IPv6 unicast addresses
   into PLC link-layer addresses follows the general description in
   section 7.2 of [RFC4861].  [RFC6775] improves this procedure by
   eliminating usage of multicast NS.  The resolution is realized by the
   NCEs (neighbor cache entry) created during the address registration
   at the routers.  [RFC8505] further improves the registration
   procedure by enabling multiple LLNs to form an IPv6 subnet, and by
   inserting a link-local address registration to better serve proxy
   registration of new devices.

4.3.1.  Unicast Address Mapping for IEEE 1901.1

   The Source/Target Link-layer Address options for IEEE_1901.1 used in
   the Neighbor Solicitation and Neighbor Advertisement have the
   following form.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    |     Type      |    Length=1   |              NID              :
    :NID (continued)|  Padding (all zeros)  |          TEI          |

             Figure 3: Unicast Address Mapping for IEEE 1901.1

   Option fields:

   Type: 1 for Source Link-layer Address and 2 for Target Link-layer

   Length:  The length of this option (including type and length fields)
         in units of 8 octets.  The value of this field is 1 for the
         12-bit IEEE 1901.1 PLC short addresses.

   NID:  24-bit Network IDentifier

   Padding:  12 zero bits

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   TEI:  12-bit Terminal Equipment Identifier

   In order to avoid the possibility of duplicated IPv6 addresses, the
   value of the NID MUST be chosen so that the 7th and 8th bits of the
   first byte of the NID are both zero.

4.3.2.  Unicast Address Mapping for IEEE 1901.2 and ITU-T G.9903

   The Source/Target Link-layer Address options for IEEE_1901.2 and
   ITU-T G.9903 used in the Neighbor Solicitation and Neighbor
   Advertisement have the following form.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |     Type      |    Length=1   |             PAN ID            |
     |       Padding (all zeros)     |         Short Address         |

             Figure 4: Unicast Address Mapping for IEEE 1901.2

   Option fields:

   Type: 1 for Source Link-layer Address and 2 for Target Link-layer

   Length:  The length of this option (including type and length fields)
         in units of 8 octets.  The value of this field is 1 for the
         16-bit IEEE 1901.2 PLC short addresses.

   PAN ID:  16-bit PAN IDentifier

   Padding:  16 zero bits

   Short Address:  16-bit short address

   In order to avoid the possibility of duplicated IPv6 addresses, the
   value of the PAN ID MUST be chosen so that the 7th and 8th bits of
   the first byte of the PAN ID are both zero.

4.4.  Neighbor Discovery

   Neighbor discovery procedures for 6LoWPAN networks are described in
   Neighbor Discovery Optimization for 6LoWPANs [RFC6775] and [RFC8505].
   These optimizations support the registration of sleeping hosts.
   Although PLC devices are electrically powered, sleeping mode SHOULD
   still be used for power saving.

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   For IPv6 address prefix dissemination, Router Solicitations (RS) and
   Router Advertisements (RA) MAY be used as per [RFC6775].  If the PLC
   network uses route-over mesh, the IPv6 prefix MAY be disseminated by
   the layer 3 routing protocol, such as RPL which includes the prefix
   in the DIO message.  As per [I-D.ietf-roll-unaware-leaves], it is
   possible to have PLC devices configured as RPL-unaware-leaves, which
   don't not participate to RPL at all, along with RPL-aware PLC
   devices.  In this case, the prefix dissemination SHOULD use the RS/RA

   For context information dissemination, Router Advertisements (RA)
   MUST be used as per [RFC6775].  The 6LoWPAN context option (6CO) MUST
   be included in the RA to disseminate the Context IDs used for prefix

   For address registration in route-over mode, a PLC device MUST
   register its addresses by sending unicast link-local Neighbor
   Solicitation to the 6LR.  If the registered address is link-local,
   the 6LR SHOULD NOT further register it to the registrar (6LBR, 6BBR).
   Otherwise, the address MUST be registered via an ARO or EARO included
   in the DAR ([RFC6775]) or EDAR ([RFC8505]) messages.  For RFC8505
   compliant PLC devices, the 'R' flag in the EARO MUST be set when
   sending Neighbor Solicitaitons in order to extract the status
   information in the replied Neighbor Advertisements from the 6LR.  If
   DHCPv6 is used to assign addresses or the IPv6 address is derived by
   unique long or short link layer address, Duplicate Address Detection
   (DAD) MUST NOT be utilized.  Otherwise, the DAD MUST be performed at
   the 6LBR (as per [RFC6775]) or proxied by the routing registrar (as
   per [RFC8505]).  The registration status is feedbacked via the DAC or
   EDAC message from the 6LBR and the Neighbor Advertisement (NA) from
   the 6LR.

   For address registration in mesh-under mode, since all the PLC
   devices are the link-local neighbors to the 6LBR, DAR/DAC or EDAR/
   EDAC messages are not required.  A PLC device MUST register its
   addresses by sending the unicast NS message with an ARO or EARO.  The
   registration status is feedbacked via the NA message from the 6LBR.

4.5.  Header Compression

   The compression of IPv6 datagrams within PLC MAC frames refers to
   [RFC6282], which updates [RFC4944].  Header compression as defined in
   [RFC6282] which specifies the compression format for IPv6 datagrams
   on top of IEEE 802.15.4, is included in this document as the basis
   for IPv6 header compression in PLC.  For situations when PLC MAC MTU
   cannot support the 1280-octet IPv6 packet, headers MUST be compressed
   according to [RFC6282] encoding formats.

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4.6.  Fragmentation and Reassembly

   PLC differs from other wired technologies in that the communication
   medium is not shielded; thus, to successfully transmit data through
   power lines, PLC Data Link layer provides the function of
   segmentation and reassembly.  A Segment Control Field is defined in
   the MAC frame header regardless of whether segmentation is required.
   The number of data octets of the PHY payload can change dynamically
   based on channel conditions, thus the MAC payload segmentation in the
   MAC sublayer is enabled and guarantees a reliable one-hop data
   transmission.  Fragmentation and reassembly is still required at the
   adaptation layer, if the MAC layer cannot support the minimum MTU
   demanded by IPv6, which is 1280 octets.

   In IEEE 1901.1 and IEEE 1901.2, the MAC layer supports payloads as
   big as 2031 octets and 1576 octets respectively.  However when the
   channel condition is noisy, it is possible to configure smaller MTU
   at the MAC layer.  If the configured MTU is smaller than 1280
   octects, the fragmentation and reassembly defined in [RFC4944] MUST
   be used.

   In ITU-T G.9903, the maximum MAC payload size is fixed to 400 octets,
   so to cope with the required MTU of 1280 octets by IPv6,
   fragmentation and reassembly at 6lo adaptation layer MUST be provided
   referring to [RFC4944].

5.  Internet Connectivity Scenarios and Topologies

   The network model can be simplified to two kinds of network devices:
   PAN Coordinator (PANC) and PAN Device.  The PANC is the primary
   coordinator of the PLC subnet and can be seen as a master node; PAN
   Devices are typically PLC meters and sensors.  The PANC also serves
   as the Routing Registrar for proxy registration and DAD procedures,
   making use of the updated registration procedures in [RFC8505].  IPv6
   over PLC networks are built as tree, mesh or star according to the
   use cases.  Every network requires at least one PANC to communicate
   with each PAN Device.  Note that the PLC topologies in this section
   are based on logical connectivity, not physical links.

   The star topology is common in current PLC scenarios.  In single-hop
   star topologies, communication at the link layer only takes place
   between a PAN Device and a PANC.  The PANC typically collects data
   (e.g., a meter reading) from the PAN devices, and then concentrates
   and uploads the data through Ethernet or LPWAN (see Figure 5).  The
   collected data is transmitted by the smart meters through PLC,
   aggregated by a concentrator, sent to the utility and then to a Meter
   Data Management System for data storage, analysis and billing.  This

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   topology has been widely applied in the deployment of smart meters,
   especially in apartment buildings.

                   PLC Device   PLC Device
                         \        /           +---------
                          \      /           /
                           \    /           +
                            \  /            |
          PLC Device ------ PANC ===========+  Internet
                            /  \            |
                           /    \           +
                          /      \           \
                         /        \           +---------
                   PLC Device   PLC Device

               PLC subnet (IPv6 over PLC)

           Figure 5: PLC Star Network connected to the Internet

   A tree topology is useful when the distance between a device A and
   PANC is beyond the PLC allowed limit and there is another device B in
   between able to communicate with both sides.  Device B in this case
   acts both as a PAN Device and a Coordinator.  For this scenario, the
   link layer communications take place between device A and device B,
   and between device B and PANC.  An example of PLC tree network is
   depicted in Figure 6.  This topology can be applied in the smart
   street lighting, where the lights adjust the brightness to reduce
   energy consumption while sensors are deployed on the street lights to
   provide information such as light intensity, temperature, humidity.
   Data transmission distance in the street lighting scenario is
   normally above several kilometers thus the PLC tree network is
   required.  A more sophisticated AMI network may also be constructed
   into the tree topology which is depicted in [RFC8036].  A tree
   topology is suitable for AMI scenarios that require large coverage
   but low density, e.g., the deployment of smart meters in rural areas.
   RPL is suitable for maintenance of a tree topology in which there is
   no need for communication directly between PAN devices.

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                          PLC Device
                               \                   +---------
                  PLC Device    \                 /
                       \         \               +
                        \         \              |
                   PLC Device -- PANC ===========+  Internet
                        /         /              |
                       /         /               +
      PLC Device---PLC Device   /                 \
                               /                   +---------
              PLC Device---PLC Device

            PLC subnet (IPv6 over PLC)

           Figure 6: PLC Tree Network connected to the Internet

   Mesh networking in PLC is of great potential applications and has
   been studied for several years.  By connecting all nodes with their
   neighbors in communication range (see Figure 7), mesh topology
   dramatically enhances the communication efficiency and thus expands
   the size of PLC networks.  A simple use case is the smart home
   scenario where the ON/OFF state of air conditioning is controlled by
   the state of home lights (ON/OFF) and doors (OPEN/CLOSE).  AODV-RPL
   enables direct PAN device to PAN device communication, without being
   obliged to transmit frames through the PANC, which is a requirement
   often cited for AMI infrastructure.

                PLC Device---PLC Device
                    / \        / \                   +---------
                   /   \      /   \                 /
                  /     \    /     \               +
                 /       \  /       \              |
          PLC Device--PLC Device---PANC ===========+  Internet
                 \       /  \       /              |
                  \     /    \     /               +
                   \   /      \   /                 \
                    \ /        \ /                   +---------
                PLC Device---PLC Device

            PLC subnet (IPv6 over PLC)

           Figure 7: PLC Mesh Network connected to the Internet

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6.  IANA Considerations

   There are no IANA considerations related to this document.

7.  Security Consideration

   Due to the high accessibility of power grid, PLC might be susceptible
   to eavesdropping within its communication coverage, e.g., one
   apartment tenant may have the chance to monitor the other smart
   meters in the same apartment building.  For security consideration,
   link layer security is guaranteed in every PLC technology.

   Malicious PLC devices could paralyze the whole network via DOS
   attacks, e.g., keep joining and leaving the network frequently, or
   multicast routing messages containing fake metrics.  A device may
   also join a wrong or even malicious network, exposing its data to
   illegal users.  Mutual authentication of network and new device can
   be conducted during the onboarding process of the new device.
   Methods include protocols such as [RFC7925] (exchanging pre-installed
   certificates over DTLS) , [I-D.ietf-6tisch-minimal-security] (which
   uses pre-shared keys), and
   [I-D.ietf-6tisch-dtsecurity-zerotouch-join] (which uses IDevID and
   MASA service).  It is also possible to use EAP methods such as
   [I-D.ietf-emu-eap-noob] via transports like PANA [RFC5191].  No
   specific mechanism is specified by this document as an appropriate
   mechanism will depend upon deployment circumstances.  The network
   encryption key appropriate for the layer-2 can also be acquired
   during the onboarding process.

   IP addresses may be used to track devices on the Internet; such
   devices can in turn be linked to individuals and their activities.
   Depending on the application and the actual use pattern, this may be
   undesirable.  To impede tracking, globally unique and non-changing
   characteristics of IP addresses should be avoided, e.g., by
   frequently changing the global prefix and avoiding unique link-layer
   derived IIDs in addresses.  [RFC3315], [RFC3972], [RFC4941],
   [RFC5535], [RFC7217], and [RFC8065] provide valuable information for
   IID formation with improved privacy, and are RECOMMENDED for IPv6

8.  Acknowledgements

   We gratefully acknowledge suggestions from the members of the IETF
   6lo working group.  Great thanks to Samita Chakrabarti and Gabriel
   Montenegro for their feedback and support in connecting the IEEE and
   ITU-T sides.  Authors thank Scott Mansfield, Ralph Droms, Pat Kinney
   for their guidance in the liaison process.  Authors wish to thank

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   Stefano Galli, Thierry Lys, Yizhou Li, Yuefeng Wu and Michael
   Richardson for their valuable comments and contributions.

9.  References

9.1.  Normative References

              IEEE-SA Standards Board, "Standard for Medium Frequency
              (less than 15 MHz) Power Line Communications for Smart
              Grid Applications", IEEE 1901.1, May 2018,

              IEEE-SA Standards Board, "IEEE Standard for Low-Frequency
              (less than 500 kHz) Narrowband Power Line Communications
              for Smart Grid Applications", IEEE 1901.2, October 2013,

              International Telecommunication Union, "Narrowband
              orthogonal frequency division multiplexing power line
              communication transceivers for G3-PLC networks",
              ITU-T G.9903, February 2014,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,

   [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,

   [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,

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   [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,

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,

   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8505]  Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,

9.2.  Informative References

              Richardson, M., "6tisch Zero-Touch Secure Join protocol",
              draft-ietf-6tisch-dtsecurity-zerotouch-join-04 (work in
              progress), July 2019.

              Vucinic, M., Simon, J., Pister, K., and M. Richardson,
              "Constrained Join Protocol (CoJP) for 6TiSCH", draft-ietf-
              6tisch-minimal-security-15 (work in progress), December

              Aura, T. and M. Sethi, "Nimble out-of-band authentication
              for EAP (EAP-NOOB)", draft-ietf-emu-eap-noob-01 (work in
              progress), June 2020.

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              Anamalamudi, S., Zhang, M., Perkins, C., Anand, S., and B.
              Liu, "AODV based RPL Extensions for Supporting Asymmetric
              P2P Links in Low-Power and Lossy Networks", draft-ietf-
              roll-aodv-rpl-08 (work in progress), May 2020.

              Thubert, P. and M. Richardson, "Routing for RPL Leaves",
              draft-ietf-roll-unaware-leaves-15 (work in progress),
              April 2020.

              Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets
              over IEEE 1901.2 Narrowband Powerline Communication
              Networks", draft-popa-6lo-6loplc-ipv6-over-
              ieee19012-networks-00 (work in progress), March 2014.

              IEEE-SA Standards Board, "IEEE Standard for Low-Frequency
              (less than 500 kHz) Narrowband Power Line Communications
              for Smart Grid Applications - Amendment 1", IEEE 1901.2a,
              September 2015, <https://standards.ieee.org/findstds/

   [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, <https://www.rfc-editor.org/info/rfc3315>.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,

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

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC5191]  Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H.,
              and A. Yegin, "Protocol for Carrying Authentication for
              Network Access (PANA)", RFC 5191, DOI 10.17487/RFC5191,
              May 2008, <https://www.rfc-editor.org/info/rfc5191>.

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   [RFC5535]  Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535,
              DOI 10.17487/RFC5535, June 2009,

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,

   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,

   [RFC8036]  Cam-Winget, N., Ed., Hui, J., and D. Popa, "Applicability
              Statement for the Routing Protocol for Low-Power and Lossy
              Networks (RPL) in Advanced Metering Infrastructure (AMI)
              Networks", RFC 8036, DOI 10.17487/RFC8036, January 2017,

   [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
              "Recommendation on Stable IPv6 Interface Identifiers",
              RFC 8064, DOI 10.17487/RFC8064, February 2017,

   [RFC8065]  Thaler, D., "Privacy Considerations for IPv6 Adaptation-
              Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
              February 2017, <https://www.rfc-editor.org/info/rfc8065>.

Authors' Addresses

   Jianqiang Hou
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012

   Email: houjianqiang@huawei.com

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   Bing Liu
   Huawei Technologies
   No. 156 Beiqing Rd. Haidian District,
   Beijing 100095

   Email: remy.liubing@huawei.com

   Yong-Geun Hong
   Electronics and Telecommunications Research Institute
   161 Gajeong-Dong Yuseung-Gu
   Daejeon 305-700

   Email: yghong@etri.re.kr

   Xiaojun Tang
   State Grid Electric Power Research Institute
   19 Chengxin Avenue
   Nanjing 211106

   Email: itc@sgepri.sgcc.com.cn

   Charles E. Perkins

   Email: charliep@computer.org

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