6Lo Working Group                                                 J. Hou
Internet-Draft                                                    B. Liu
Intended status: Standards Track                     Huawei Technologies
Expires: April 24, 2019                                        Y-G. Hong
                                                                 X. Tang
                                                              C. Perkins
                                                        October 21, 2018

             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, IEEE 1901.2 and IEEE

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 24, 2019.

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Copyright Notice

   Copyright (c) 2018 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
   (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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   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  . . . . . . . . . . . . . .  11
     4.7.  Extension at 6lo Adaptation Layer . . . . . . . . . . . .  12
   5.  Internet Connectivity Scenarios and Topologies  . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   7.  Security Consideration  . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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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
   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.

   The following sections provide a brief overview of PLC, then describe
   transmission of IPv6 packets over PLC networks.  The general approach
   is to adapt elements of the 6LoWPAN specifications [RFC4944],
   [RFC6282], and [RFC6775] to constrained PLC networks.  Compared to
   [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks], this document
   provides a structured and greatly expanded specification of an
   adaptation layer for IPv6 over PLC (6LoPLC) 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

   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

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   Coordinator:  A device capable of relaying messages.

   DAD:  Duplicate Address Detection

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

   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

   PSDU: PHY Service Data Unit

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

   RA:   Router Advertisement

   WAN:  Wide Area Network

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      The terminology used in this draft is aligned with IEEE 1901.2

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

            Table 1: Terminology Mapping between PLC standards

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

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.

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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.

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 fragmentation and reassembly are not needed in these two
   technologies, other 6lo functions like header compression are still
   applicable and useful, particularly in high-noise communication

   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.

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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.

   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.
   Besides, some of the features like fragmentation and reassembly are
   redudant to some PLC technologies.  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.

   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

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   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.

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).

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

           Figure 2: IPv6 Link Local Address for a PLC interface

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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.  6775-update 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

   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.

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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
   [I-D.ietf-6lo-rfc6775-update].  These optimizations support the
   registration of sleeping hosts.  Although PLC devices are
   electrically powered, sleeping mode SHOULD still be used for power

   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

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   in the DIO message.  In this case, the prefix information option
   (PIO) MUST NOT be included in the Router Advertisement.

   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, a PLC host MUST register its address to the
   router using Neighbor Solicitation and Neighbor Advertisement
   messages.  RFC6775-update PLC devices MUST include the EARO with the
   'R' flag set when sending Neighbor Solicitations, and process
   Neighbor Advertisements that include EARO to extract status
   information.  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,
   DAD MUST be performed: RFC6775-only PLC devices MUST perform multihop
   DAD against a 6LBR by using DAR and DAC messages, while for
   RFC6775-update devices, DAD is proxied by a routing registrar, which
   MAY operate according to Optimistic DAD (ODAD) [RFC4429].

   The mesh-under ITU-T G.9903 network SHOULD NOT utilize the address
   registration as described in [RFC6775].  ITU-T G.9903 PLC networks
   MUST use the 6LoWPAN Context Option (6CO) specified in [RFC6775] (see
   clause in [ITU-T_G.9903]), which can be attached in Router
   Advertisements to disseminate Context IDs (CIDs) to use for
   compressing prefixes.

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.

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

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   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, since the MAC layer supports payloads
   of 2031 octets and 1576 octets respectively, fragmentation is not
   needed for IPv6 packet transmission.  The fragmentation and
   reassembly defined in [RFC4944] SHOULD NOT be used in the 6lo
   adaptation layer of IEEE 1901.2.

   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].

4.7.  Extension at 6lo Adaptation Layer

   Apart from the Dispatch and LOWPAN_IPHC headers specified in
   [RFC4944], an additional Command Frame Header is needed for the mesh
   routing procedure in LOADng protocol.  Figure 5 illustrates the
   format of the Command Frame Header [RFC8066].  The ESC dispatch type
   (01000000b) indicates an ESC extension type follows (see [RFC4944]
   and [RFC6282]).  Then this 1-octet dispatch field is used as the
   Command Frame Header and filled with the Command ID.  The Command ID
   can be classified into 4 types:

   o  LOADng message (0x01)

   o  LoWPAN bootstrapping protocol message (0x02)

   o  Reserved by ITU-T (0x03-0x0F)

   o  CMSR protocol messages (0X10-0X1F)

   The LOADng message is used to provide the default routing protocol
   LOADng while the LoWPAN bootstrapping protocol message is for the
   LoWPAN bootstrap procedure.  The CMSR protocol messages are specified
   for the Centralized metric-based source routing [ITU-T G.9905] which
   is out of the scope of this draft.

      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
     |      ESC      |  Command ID   |     Command Payload

           Figure 5: Command Frame Header Format of ITU-T G.9903

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   Command Frame Header appears in the last position if more than one
   header is present in the 6LoWPAN frame [ITU-T_G.9903].  On the other
   hand, this Command Frame Header MUST appear before the LoWPAN_IPHC
   dispatch type as per[RFC8066].

   o  Regarding the order of the command frame header, the inconsistency
      between G.9903 and RFC8066 still exists and is being solved in
      ITU-T SG15/Q15.

   Following these two requirements of header order mentioned above, an
   example of the header order is illustrated in Figure 6 including the
   Fragmentation type, Fragmentation header, ESC dispatch type, ESC
   Extension Type (Command ID), ESC Dispatch Payload (Command Payload),
   LOWPAN_IPHC Dispatch Type, LOWPAN_IPHC header, and Payload.

     |F typ|F hdr| ESC | EET | EDP |Dispatch|LOWPAN_IPHC hdr| Payld|

       Figure 6: A 6LoWPAN packet including the Command Frame Header

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
   [I-D.ietf-6lo-rfc6775-update].  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 7).  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
   topology has been widely applied in the deployment of smart meters,
   especially in apartment buildings.

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

               PLC subnet (IPv6 over PLC)

           Figure 7: 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 8.  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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                          PAN Device
                               \                   +---------
                  PAN Device    \                 /
                       \         \               +
                        \         \              |
                    PAN Device -- PANC ===========+  Internet
                        /         /              |
                       /         /               +
      PAN Device---PAN Device   /                 \
                               /                   +---------
              PAN Device---PAN Device

            PLC subnet (IPv6 over PLC)

           Figure 8: 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 9), 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.

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

            PLC subnet (IPv6 over PLC)

           Figure 9: 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.

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

9.  References

9.1.  Normative References

              Thubert, P., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for 6LoWPAN Neighbor
              Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
              progress), June 2018.

              Anamalamudi, S., Zhang, M., Perkins, C., Anand, S., and B.
              Liu, "Asymmetric AODV-P2P-RPL in Low-Power and Lossy
              Networks (LLNs)", draft-ietf-roll-aodv-rpl-05 (work in
              progress), October 2018.

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              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,

   [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,

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   [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,

9.2.  Informative References

              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>.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,

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

   [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,

   [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,

   [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>.

   [RFC8066]  Chakrabarti, S., Montenegro, G., Droms, R., and J.
              Woodyatt, "IPv6 over Low-Power Wireless Personal Area
              Network (6LoWPAN) ESC Dispatch Code Points and
              Guidelines", RFC 8066, DOI 10.17487/RFC8066, February
              2017, <https://www.rfc-editor.org/info/rfc8066>.

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
   2330 Central Expressway
   Santa Clara  95050
   United States of America

   Email: charliep@computer.org

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