6Lo Working Group J. Hou
Internet-Draft B. Liu
Intended status: Standards Track Huawei Technologies
Expires: October 22, 2021 Y-G. Hong
ETRI
X. Tang
SGEPRI
C. Perkins
Lupin Lodge
April 20, 2021
Transmission of IPv6 Packets over PLC Networks
draft-ietf-6lo-plc-06
Abstract
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
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 October 22, 2021.
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Copyright Notice
Copyright (c) 2021 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
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 . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . 8
4.2. IPv6 Link Local Address . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . . . . . . . . . . . . 11
4.5. Header Compression . . . . . . . . . . . . . . . . . . . 12
4.6. Fragmentation and Reassembly . . . . . . . . . . . . . . 12
5. Internet Connectivity Scenarios and Topologies . . . . . . . 13
6. Operations and Manageability Considerations . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. Security Consideration . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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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)
[SCENA]. The data acquisition devices in these scenarios share
common features such as fixed position, large quantity, low data rate
and low power consumption.
Although PLC technology has evolved over several decades, it has not
been fully adapted for IPv6 based constrained networks. The
resource-constrained IoT 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.
This document provides a brief overview of PLC technologies. Some of
them have LLN (low power and lossy network) characteristics, i.e.
limited power consumption, memory and processing resources. This
document specifies the transmission of IPv6 packets over those
"constrained" PLC networks. The general approach is to adapt
elements of the 6LoWPAN (IPv6 over Low-Power Wireless Personal Area
Network) and 6lo (IPv6 over Networks of Resource-constrained Nodes)
specifications, such as [RFC4944], [RFC6282], [RFC6775] and [RFC8505]
to constrained PLC networks.
2. Requirements Notation and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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 uses the following acronyms and terminologies:
6LoWPAN: IPv6 over Low-Power Wireless Personal Area Network
6lo: IPv6 over Networks of Resource-constrained Nodes
AMI: Advanced Metering Infrastructure
BBPLC: Broadband Power Line Communication
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CID: Context ID
Coordinator: A device capable of relaying messages.
DAD: Duplicate Address Detection
EV: Electric Vehicle
IID: IPv6 Interface Identifier
IPHC: IP Header Compression
LAN: Local Area Network
LLN: Low power and Lossy 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 that 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
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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 | 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
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).
A new PLC standard IEEE 1901.1 [IEEE_1901.1], which aims at the
medium frequency band of 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
G.9903.
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
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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.
+----------------------------------------+
| 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 (join registrar/
coordinator) in CoJP (Constrained Join Protocol)
[I-D.ietf-6tisch-minimal-security].
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]).
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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.
The MTU for ITU-T G.9903 is 400 octets, insufficient for supporting
IPv6's MTU. For this reason, fragmentation and reassembly is
required for G.9903-based networks to adapt IPv6.
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.
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
networks.
4. IPv6 over PLC
6LoWPAN and 6lo standards [RFC4944], [RFC6282], [RFC6775], and
[RFC8505] provides useful functionality including link-local IPv6
addresses, stateless address auto-configuration, neighbor discovery,
header compression, fragmentation and reassembly. However, due to
the different characteristics of the PLC media, the 6LoWPAN
adaptation layer, as it is, cannot perfectly fulfill the requirements
of PLC environments. These considerations suggest the need for a
dedicated adaptation layer for PLC, which is detailed in the
following subsections.
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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
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:
16_bit_PAN:00FF:FE00:16_bit_short_address
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:
YYYY:YYFF:FE00:0XXX
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 from the MAC address SHOULD only
be used for link-local address configuration. A PLC host SHOULD use
the IID derived from 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. As per [RFC8065], when
short addresses are used on PLC links, a shared secret key or version
number from the Authoritative Border Router Option [RFC6775] can be
used to improve the entropy of the hash input, thus the generated IID
can be spread out to the full range of the IID address space while
stateless address compression is still allowed.
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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
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
Address.
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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.
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
Address.
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.
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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.
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, the IPv6 prefix MAY be disseminated by the
layer 3 routing protocol, such as RPL, which may 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
do not participate to RPL at all, along with RPL-aware PLC devices.
In this case, the prefix dissemination SHOULD use the RS/RA messages.
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
and/or address compression.
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
from 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 link-local neighbors to the 6LBR, DAR/DAC or EDAR/EDAC
messages are not required. A PLC device MUST register its addresses
by sending a unicast NS message with an ARO or EARO. The
registration status is feedbacked via the NA message from the 6LBR.
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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 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.
For IEEE 1901.2 and G.9903, the IP header compression follows the
instruction in [RFC6282]. However, additional adaptation MUST be
considered for IEEE 1901.1 since it has a short address of 12 bits
instead of 16 bits. The only modification is the semantics of the
"Source Address Mode" when set as "10" in the section 3.1 of
[RFC6282], which is illustrated as following.
SAM: Source Address Mode:
If SAC=0: Stateless compression
10: 12 bits. The first 116 bits of the address are elided.The
value of the first 64 bits is the link-local prefix padded with
zeros. The following 64 bits are 0000:00ff:fe00:0XXX, where
XXX are the 12 bits carried in-line.
If SAC=1: stateful context-based compression
10: 12 bits. The address is derived using context information and
the 12 bits carried in-line. Bits covered by context
information are always used. Any IID bits not covered by
context information are taken directly from their corresponding
bits in the 12-bit to IID mapping given by 0000:00ff:fe00:0XXX,
where XXX are the 12 bits carried inline. Any remaining bits
are zero.
4.6. Fragmentation and Reassembly
Constrained PLC MAC layer provides the function of fragmentation and
reassembly, however, 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
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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
as specified in [RFC4944].
[RFC4944] uses a 16-bit datagram tag to identify the fragments of the
same IP packet. [RFC4963] specifies that at high data rates, the
16-bit IP identification field is not large enough to prevent
frequent incorrectly assembled IP fragments. For constranied PLC,
the data rate is much lower than the situation mentioned in RFC4963,
thus the 16-bit tag is sufficient to assemble the fragements
correctly.
5. Internet Connectivity Scenarios and Topologies
The PLC 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. Generally, each PLC network has one
PANC. In some cases, the PLC network can have alternate coordinators
to replace the PANC when the PANC leaves the network for some reason.
Note that the PLC topologies in this section are based on logical
connectivity, not physical links. The term "PLC subnet" refers to a
multilink subnet, in which the PLC devices share the same address
prefix.
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
topology has been widely applied in the deployment of smart meters,
especially in apartment buildings.
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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. Operations and Manageability Considerations
The constrained PLC networks are not managed in the same way as the
enterprise network or carrier network. The constrained PLC networks
as the other IoT networks, are designed to be self-organized and
self-managed. The software or firmware is flushed into the devices
before deployment by the vendor or operator. And during the
deployment process, the devices are bootstrapped, and no extra
configuration is needed to get the device connected to each other.
Once a device becomes offline, it goes back to the bootstrapping
stage and tries to rejoin the network. The onboard status of the
devices and the topology of the PLC network can be visualized via the
gateway. The recently-formed iotops WG in IETF is aming to design
more features for the management of IOT networks.
7. IANA Considerations
There are no IANA considerations related to this document.
8. 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. Thus link layer security
mechanisms are designed in the PLC technologies mentioned in this
document.
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.
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
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frequently changing the global prefix and avoiding unique link-layer
derived IIDs in addresses. [RFC8065] discusses the privacy threats
when interface identifiers (IID) are generated without sufficient
entropy, including correlation of activities over time, location
tracking, device-specific vulnerability exploitation, and address
scanning. Schemes such as limited lease period in DHCPv6 [RFC3315],
Cryptographically Generated Addresses (CGAs) [RFC3972], privacy
extensions [RFC4941], Hash-Based Addresses (HBAs) [RFC5535], or
semantically opaque addresses [RFC7217] SHOULD be considered to
enhance the IID privacy.
9. 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, Yuefeng Wu and Michael
Richardson for their valuable comments and contributions.
10. References
10.1. Normative References
[IEEE_1901.1]
IEEE-SA Standards Board, "Standard for Medium Frequency
(less than 15 MHz) Power Line Communications for Smart
Grid Applications", IEEE 1901.1, May 2018,
<https://ieeexplore.ieee.org/document/8360785>.
[IEEE_1901.2]
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,
<https://standards.ieee.org/findstds/
standard/1901.2-2013.html>.
[ITU-T_G.9903]
International Telecommunication Union, "Narrowband
orthogonal frequency division multiplexing power line
communication transceivers for G3-PLC networks",
ITU-T G.9903, February 2014,
<https://www.itu.int/rec/T-REC-G.9903>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[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,
<https://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,
<https://www.rfc-editor.org/info/rfc4944>.
[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,
<https://www.rfc-editor.org/info/rfc6282>.
[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,
<https://www.rfc-editor.org/info/rfc6550>.
[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,
<https://www.rfc-editor.org/info/rfc6775>.
[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,
<https://www.rfc-editor.org/info/rfc8505>.
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10.2. Informative References
[EUI-64] IEEE-SA Standards Board, "Guidelines for 64-bit Global
Identifier (EUI-64) Registration Authority", IEEE EUI-64,
March 1997, <https://standards.ieee.org/content/dam/ieee-
standards/standards/web/documents/tutorials/eui.pdf>.
[I-D.ietf-6tisch-dtsecurity-zerotouch-join]
Richardson, M., "6tisch Zero-Touch Secure Join protocol",
draft-ietf-6tisch-dtsecurity-zerotouch-join-04 (work in
progress), July 2019.
[I-D.ietf-6tisch-minimal-security]
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
2019.
[I-D.ietf-emu-eap-noob]
Aura, T., Sethi, M., and A. Peltonen, "Nimble out-of-band
authentication for EAP (EAP-NOOB)", draft-ietf-emu-eap-
noob-03 (work in progress), December 2020.
[I-D.ietf-roll-aodv-rpl]
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.
[I-D.ietf-roll-unaware-leaves]
Thubert, P. and M. Richardson, "Routing for RPL Leaves",
draft-ietf-roll-unaware-leaves-30 (work in progress),
January 2021.
[IEEE_1901.2a]
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/
standard/1901.2a-2015.html>.
[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>.
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[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[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,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[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>.
[RFC5535] Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535,
DOI 10.17487/RFC5535, June 2009,
<https://www.rfc-editor.org/info/rfc5535>.
[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,
<https://www.rfc-editor.org/info/rfc7217>.
[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,
<https://www.rfc-editor.org/info/rfc7925>.
[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,
<https://www.rfc-editor.org/info/rfc8036>.
[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>.
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[SCENA] Cano, C., Pittolo, A., Malone, D., and L. Lampe, "State of
the Art in Power Line Communications: From the
Applications to the Medium", July 2016,
<https://ieeexplore.ieee.org/document/7467440>.
Authors' Addresses
Jianqiang Hou
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Email: houjianqiang@huawei.com
Bing Liu
Huawei Technologies
No. 156 Beiqing Rd. Haidian District,
Beijing 100095
China
Email: remy.liubing@huawei.com
Yong-Geun Hong
Electronics and Telecommunications Research Institute
161 Gajeong-Dong Yuseung-Gu
Daejeon 305-700
Korea
Email: yghong@etri.re.kr
Xiaojun Tang
State Grid Electric Power Research Institute
19 Chengxin Avenue
Nanjing 211106
China
Email: itc@sgepri.sgcc.com.cn
Charles E. Perkins
Lupin Lodge
Email: charliep@computer.org
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