IEC 62056-8-4:2018

IEC 62056-8-4 ®
Edition 1.0 2018-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electricity metering data exchange – the DLMS/COSEM suite –
Part 8-4: Communication profiles for narrow-band OFDM PLC PRIME
neighbourhood networks
Échange des données de comptage de l'électricité – la suite DLMS/COSEM –
Partie 8-4: Profils de communication pour réseaux de voisinage OFDM PLC
PRIME à bande étroite
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IEC 62056-8-4 ®
Edition 1.0 2018-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electricity metering data exchange – the DLMS/COSEM suite –

Part 8-4: Communication profiles for narrow-band OFDM PLC PRIME

neighbourhood networks
Échange des données de comptage de l'électricité – la suite DLMS/COSEM –

Partie 8-4: Profils de communication pour réseaux de voisinage OFDM PLC

PRIME à bande étroite
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 35.110.01; 91.140.50 ISBN 978-2-8322-6334-1

– 2 – IEC 62056-8-4:2018  IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 10
3.1 Terms and definitions . 10
3.2 Abbreviated terms . 10
4 Targeted communication environments . 12
5 Use of the communication layers for this profile . 13
5.1 Information related to the use of the standard specifying the lower layers . 13
5.2 The structure of the communication profiles . 13
5.2.1 Overview . 13
5.2.2 The IEC 61334-4-32 profile . 14
5.2.3 The TCP-UDP/IPv4 profile . 14
5.2.4 The TCP-UDP/IPv6 profile . 14
5.3 Lower protocol layers and their use. 14
5.3.1 General . 14
5.3.2 Physical layer . 14
5.3.3 MAC layer. 15
5.4 Service mapping and convergence layers . 17
5.4.1 Overview . 17
5.4.2 The IEC 61334-4-32 LLC SSCS . 17
5.4.3 The IPv4 SSCS. 19
5.4.4 The IPv6 SSCS. 21
5.5 Registration and connection management . 22
5.5.1 Overview . 22
5.5.2 IEC 61334-4-32 profile . 22
5.5.3 TCP-UDP/IPv4 profile . 27
5.5.4 TCP-UDP/IPv6 profile . 40
6 Identification and addressing schemes . 55
6.1 IEC 61334-4-32 profile addressing . 55
6.1.1 Overview . 55
6.1.2 MAC address . 56
6.1.3 IEC 61334-4-32 SSCS addresses . 56
6.1.4 LLC addresses . 56
6.2 TCP-UDP/IPv4 profile addressing . 57
6.3 TCP-UDP/IPv6 profile addressing . 57
7 Specific consideration for the application layer services . 57
7.1 Overview. 57
7.2 Application Association (AA) establishment and release: ACSE services . 57
7.2.1 AA establishment: IEC 61334-4-32 profile. 57
7.2.2 AA establishment: IP based profile . 58
7.2.3 Application association release . 59
7.3 xDLMS services . 59
7.4 Security mechanisms . 59
7.4.1 DLMS/COSEM security . 59

7.4.2 Lower layers security . 59
7.5 Transferring long application messages . 59
7.6 Media access, bandwidth and timing considerations . 60
7.7 Other considerations . 60
8 Communication configuration and management . 60
9 The COSEM application process . 60
10 Additional considerations for the use of this profile . 60
Annex A (informative) Examples . 61
A.1 Data exchange between two IP communication peers . 61
A.2 Joining a multicast group . 63
A.3 PRIME encoding examples . 63
Annex B (normative) New COSEM interfaces classes and OBIS codes . 76
Annex C (informative) IEC 61334-4-32 profile: Error cases during connection

establishment . 77
Annex D (normative) Convergence layer constants . 78
Bibliography . 79

Figure 1 – Communication architecture . 12
Figure 2 – OFDM PLC PRIME communication profile architectures . 14
Figure 3 – IEC 61334-4-32 SSCS services . 18
Figure 4 – MSC for Data services in the case of logical name referencing . 19
Figure 5 – IEC 61334-4-32 SSCS . 22
Figure 6 – MSC for IEC 61334-4-32 SSCS services . 26
Figure 7 – IPv4 SSCS services . 28
Figure A.1 – MSC of IPv4 SSCS services . 62
Figure A.2 – Joining MSC IPv4 profile . 63
Figure C.1 – Error cases during connection establishment . 77

Table 1 – Result values for SSCS services . 25
Table 2 – AR_REGISTER_S message format . 36
Table 3 – AR_REGISTER B message format . 36
Table 4 – AR_UNREGISTER_S message format . 36
Table 5 – AR_MCAST_REG_S message format . 36
Table 6 – AR_MCAST_REG_B message format . 37
Table 7 – AR_MCAST_UNREG_S message format . 37
Table 8 – AR_MCAST_UNREG_B message format . 37
Table 9 – AR_LOOKUP_S message format . 38
Table 10 – AR_LOOKUP_B message format . 38
Table 11 – IPv4 packet format without header compression negotiated . 38
Table 12 – IPv4 packet format with VJ header compression . 39
Table 13 – Connection data sent by the initiator . 39
Table 14 – Connection data sent by the responder . 40
Table 15 – IPv6 SSCS table entry . 44
Table 16 – Mapping IPv6 precedence to PRIME MAC priority . 45

– 4 – IEC 62056-8-4:2018  IEC 2018
Table 17 – AR_REGISTERv6_S message format . 51
Table 18 – AR_REGISTERv6_B message format . 51
Table 19 – AR_UNREGISTERv6_S message format . 51
Table 20 – AR_UNREGISTERv6_B message format . 52
Table 21 – AR_LOOKUPv6_S message format . 52
Table 22 – AR_LOOKUPv6_B message format . 52
Table 23 – AR_MCAST_REGv6_S message format . 53
Table 24 – AR_MCAST_REGv6_B message format . 53
Table 25 – AR_MCAST_UNREGv6_B message format . 53
Table 26 – IPv6 Packet format without negotiated header compression . 54
Table 27 – UDP/IPv6 Packet format with LOWPAN_IPHC header compression and
LOWPAN_NHC . 54
Table 28 – IPv6 Packet format with LOWPAN_IPHC negotiated header compression . 54
Table 29 – IPv6 Connection signalling data sent by the initiator . 55
Table 30 – IPv6 Connection signalling data sent by the responder . 55
Table 31 – Client service access point values . 57
Table 32 – Server service access point values . 57
Table 33 – Application associations and data exchange in the IEC 61334-4-32 profile . 58
Table D.1 – TYPE value assignment . 78

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICITY METERING DATA EXCHANGE –
THE DLMS/COSEM SUITE –
Part 8-4: Communication profiles for narrow-band
OFDM PLC PRIME neighbourhood networks

FOREWORD
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed that compliance
with this International Standard may involve the use of a maintenance service concerning the stack of protocols on
which the present standard IEC 62056-8-4 is based.
The IEC takes no position concerning the evidence, validity and scope of this maintenance service.
The provider of the maintenance service has assured the IEC that he is willing to provide services under
reasonable and non-discriminatory terms and conditions for applicants throughout the world. In this respect, the
statement of the provider of the maintenance service is registered with the IEC. Information may be obtained from:
PRIME Alliance
2-12, Avenue de la Renaissance
1000, Brussels/ (BE)
www.prime-alliance.org.com
International Standard IEC 62056-8-4 has been prepared by IEC technical committee 13:
Electrical energy measurement and control.

– 6 – IEC 62056-8-4:2018  IEC 2018
The text of this standard is based on the following documents:
CDV Report on voting
13/1749/CDV 13/1763/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62056 series, published under the general title Electricity metering
data exchange – The DLMS/COSEM suite, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
As defined in IEC 62056-1-0, the IEC 62056 DLMS/COSEM suite provides specific
communication profile standards for communication media relevant for smart metering.
Such communication profile standards specify how the COSEM data model and the
DLMS/COSEM application layer can be used on the lower, communication media-specific
protocol layers.
Communication profile standards refer to communication standards that are part of the
IEC 62056 DLMS/COSEM suite or to any other open communication standard.
This International Standard specifies DLMS/COSEM communication profiles using
Recommendation ITU-T G.9904:2012 Narrow-band orthogonal frequency division multiplexing
power line communication transceivers for PRIME networks. It applies for devices installed on
the neighbourhood network.
It follows the rules defined in IEC 62056-5-3:2017, Annex A, and in IEC 62056-1-0 and the
IEC TS 62056-1-1 recommendations for its structure.
The communication profile specified in this document is based on the results of the European
OPEN Meter project, Topic Energy 2008.7.1.1, Project no.: 226369, www.openmeter.com, and
has been prepared by the PRIME Alliance Technical Working Group, www.prime-alliance.org.

– 8 – IEC 62056-8-4:2018  IEC 2018
ELECTRICITY METERING DATA EXCHANGE –
THE DLMS/COSEM SUITE –
Part 8-4: Communication profiles for narrow-band
OFDM PLC PRIME neighbourhood networks

1 Scope
This part of IEC 62056 specifies DLMS/COSEM communication profiles for narrow-band
OFDM power line carrier PRIME neighbourhood networks using the modulation as specified in
Recommendation ITU-T G.9904:2012.
Three communication profiles are specified:
• a profile using the IEC 61334-4-32 LLC layer;
• a profile using TCP-UDP/IPv4;
• a profile using TCP-UDP/IPv6.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 61334-4-32:1996, Distribution automation using distribution line carrier systems – Part 4:
Data communication protocols – Section 32: Data link layer – Logical link control (LLC)
IEC 61334-4-511:2000, Distribution automation using distribution line carrier systems – Part
4-511: Data communication protocols – Systems management – CIASE protocol
IEC 62056-1-0, Electricity metering data exchange – The DLMS/COSEM suite – Part 1-0:
Smart metering standardization framework
IEC TS 62056-1-1, Electricity metering data exchange – The DLMS/COSEM suite – Part 1-1:
Template for DLMS/COSEM communication profile standards
IEC 62056-4-7:2015, Electricity metering data exchange – The DLMS/COSEM suite – Part 4-
7: DLMS/COSEM transport layer for IP networks
IEC 62056-5-3:2017, Electricity metering data exchange – The DLMS/COSEM suite – Part 5-
3: DLMS/COSEM application layer
IEC 62056-6-1, Electricity metering data exchange – The DLMS/COSEM suite – Part 6-1:
Object identification system (OBIS)
IEC 62056-6-2:2017, Electricity metering data exchange – The DLMS/COSEM suite – Part 6-
2: COSEM interface classes
IEC 62056-9-7:2013, Electricity metering data exchange – The DLMS/COSEM suite – Part 9-
7: Communication profile for TCP-UDP/IP networks

Recommendation ITU-T G.9904:2012, Series G: Transmission systems and media, digital
systems and networks Access networks – In premises networks. Narrowband orthogonal
frequency division multiplexing power line communication transceivers for PRIME networks
STD0005 – Internet Protocol
Author: J. Postel
Date: September 1981
Also: RFC0791, RFC0792, RFC0919, RFC0922, RFC0950, RFC1112
Available from: http://www.ietf.org/rfc/rfc0791.txt
STD0006 – User Datagram Protocol
Author: J. Postel
Date: 28 August 1980
Also: RFC 768
Available from: http://www.ietf.org/rfc/rfc0768.txt
STD0007 – Transmission Control Protocol
Author: J. Postel
Date: September 1981
Available from: http://www.ietf.org/rfc/rfc0793.txt
RFC 1144, Compressing TCP/IP Headers for Low Speed serial Link
Author: V. Jabobson
Date: February 1990
Available from https://tools.ietf.org/rfc/rfc1144.txt
RFC 2460, Internet Protocol, Version 6 (IPv6) Specification
Authors: S. Deering, Cisco, R. Hinden Nokia
Date: December 1998
Available from: http://www.ietf.org/rfc/rfc2460.txt
RFC 2464, Transmission of IPv6 Packets over Ethernet Networks
Authors M. Crawford Fermilab
Date: December 1998
Available from: http://www.ietf.org/rfc/rfc2464.txt
RFC 3315, Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Authors R. Droms, E J. Bound, B. Volz, T. Lemon, C. Perkins, M. Carney
Date: July 2003
Available from: www.ietf.org/rfc/rfc3315.txt
RFC 4291, IP Version 6 Addressing Architecture
Authors R. Hinden Nokia, S. Deering Cisco Systems
Date: February 2006.
Available from: http://www.ietf.org/rfc/rfc4291.txt
RFC 4862, IPv6 Stateless Address Configuration
Authors S. Thomson, Cisco, T. Narten IBM, T. Jinmei, Toshiba
Date: September 2007.
Available from: www.ietf.org/rfc/rfc4862.txt
RFC 6282, Compression Format for IPv6 Datagrams over IEEE 802.15.4–Based Networks
Authors J. Hui, Ed. Arch Rock Corporation P. Thubert Cisco
Date: September 2011.
Available from: http://www.ietf.org/rfc/rfc6282.txt

– 10 – IEC 62056-8-4:2018  IEC 2018
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
NOTE See also Recommendation ITU-T G.9904:2012.
3.1.1
base node
master node which controls and manages the resources of a subnetwork
3.1.2
registration
process by which a service node is accepted as member of the subnetwork and allocated with
an LNID
3.1.3
service node
any one node of a subnetwork which is not a base node
3.1.4
unregistration
process by which a service node leaves a subnetwork
3.2 Abbreviated terms
Abbreviation Meaning
AA Application Association
AARE Application Association Response
AARQ Application Association Request
ACSE Application Control Service Element
AL Application Layer
AP Application Process
APDU Application Protocol Data Unit
ARQ Automatic Repeat Request
CL Convergence Layer
.cnf Confirm service primitive
COSEM Companion Specification for Energy Metering
CPCS Common Part Convergence Sublayer
CSMA/CA Carrier Sense Multiple Access – Collision Avoidance
D8PSK Differential Eight-Phase Shift Keying
DBPSK Differential Binary Phase Shift Keying
DGW Default Gateway
Abbreviation Meaning
DHCP Dynamic Host Configuration Protocol
DLMS Device Language Message Specification
DQPSK Differential Quaternary Phase Shift Keying
EUI-48 48-bit Extended Unique Identifier
FU Firmware Upgrade
FW Firmware
IANA Internet Assigned Numbers Authority
IGMP Internet Group Management Protocol
.ind Indication service primitive
IP Internet Protocol
IPv4 Internet Protocol, version 4
IPv6 Internet Protocol version 6
LCID Local Connection Identifier
LD Logical Device
LLC Logical Link Control (sub-layer)
LNID Local Node Identifier
MAC Medium Access Control, MAC sublayer entity
MLME MAC Layer Management Entity
MPDU MAC Protocol Data Unit
NAT Network Address Translation
NHC Next Header Compression
NL Noise Level
OBIS OBject Identification System
OFDM Orthogonal Frequency Division Multiplexing
OSI Open System Interconnection
PHY Physical Layer entity
PLC Power Line Communication
PIB PLC Information Base
PLME Physical Layer Management Entity
PPDU PHY Protocol Data Unit
.req Request service primitive
RFC Request For Comment
.rsp Response service primitive
SDU Service Data Unit
SID Switch Identifier
SNA Subnetwork Address
SNR Signal-to-Noise Ratio
SSCS Service Specific Convergence Sublayer

– 12 – IEC 62056-8-4:2018  IEC 2018
Abbreviation Meaning
TCP Transmission Control Protocol
TOS Type Of Service
UDP User Datagram Protocol
xDLMS_ASE extended DLMS Application Service Element
ZCT Zero Crossing Time
4 Targeted communication environments
The DLMS/COSEM communication profiles for narrow-band OFDM PLC PRIME
neighbourhood networks are intended for remote data exchange on Neighbourhood Networks
(NN) between Neighbourhood Network Access Points (NNAPs) and Local Network Access
Points (LNAPs) or End Devices using OFDM PLC technology over the low voltage electricity
distribution network as a communication medium. The functional reference architecture is
shown Figure 1.
IEC
Figure 1 – Communication architecture
End devices – typically electricity meters – comprise application functions and communication
functions. They may be connected directly to the NNAP via the C interface, or to an LNAP via
an M interface, while the LNAP is connected to the NNAP via the C interface. The LNAP
function may be co-located with the metering functions.
A NNAP comprises gateway functions and it may comprise concentrator functions. Upstream,
it is connected to the Metering Head End System (HES) using suitable communication media
and protocols.
End devices and LNAPs may communicate to different NNAPs, but to one NNAP only at a
time. From the PLC communication point of view, the NNAP acts as the base node while end
devices and LNAPs act as service nodes.

NNAPs and similarly LNAPs may communicate to each other, but this is out of the scope of
this document, which covers the C interface only.
When the NNAP has concentrator functions, it acts as a DLMS/COSEM client. When the
NNAP has gateway functionality only, then the HES plays the role of a DLMS/COSEM client.
The end devices or the LNAPs play the role of DLMS/COSEM servers.
A mixed architecture is also possible, i.e. both the HES and the NNAP can act as a client.
5 Use of the communication layers for this profile
5.1 Information related to the use of the standard specifying the lower layers
Recommendation ITU-T G.9904:2012 defines PHY and MAC layers for power line
communication using OFDM. At the top of the MAC layer it defines also a number of
Convergence layers, the purpose of which is to match the lower protocol layers with the
higher protocol layers.
This document makes use of the entire part of the PHY and MAC layers. Additionally, it
defines – in 5.5 – the use of the respective Convergence layers.
5.2 The structure of the communication profiles
5.2.1 Overview
The proposed protocol stacks use the following OSI layers as shown in Figure 2.
• the DLMS/COSEM Application layer as specified in IEC 62056-5-3 covering the
Application, Presentation and Session functionalities;
• the LLC sublayer as specified in IEC 61334-4-32, used with the DLMS/COSEM 61334-4-
32 profile over PRIME networks;
• the DLMS/COSEM transport layer for IP networks as specified in IEC 62056-4-7:2015
used with the DLMS/COSEM TCP-UDP/IPv4 and TCP-UDP/IPv6 profiles over PRIME
networks;
• the PRIME MAC layer, the CPCS and the corresponding SSCS, according to the selected
profile (IEC 61334-4-32, TCP-UDP/IPv4 or TCP-UDP/IPv6);
• the PRIME Physical layer.
Following this reference model, three distinct profiles can be identified, all of them using the
PRIME PHY, MAC layers as lower layers and the Common Part Convergence Sublayer on
one hand, and the DLMS/COSEM Application layer specified in IEC 62056-5-3 and the
COSEM object model specified in IEC 62056-6-1 and IEC 62056-6-2 on the other hand. Lower
layers – meaning PHY and MAC – are based on the principles of IEEE 802.15.4.
NOTE The COSEM interface classes for setting up and managing data exchange over narrow-band OFDM PLC
PRIME network are specified in IEC 62056-6-2.

– 14 – IEC 62056-8-4:2018  IEC 2018
IEC
Figure 2 – OFDM PLC PRIME communication profile architectures
5.2.2 The IEC 61334-4-32 profile
The IEC 61334-4-32 profile uses the PRIME IEC 61334-4-32 SSCS making the necessary
adaptation between the PRIME PHY and MAC layers and the DLMS/COSEM application
layer.
5.2.3 The TCP-UDP/IPv4 profile
The TCP-UDP/IPv4 profile uses the PRIME IPv4 SSCS making the necessary adaptation
between the PRIME PHY and MAC layers and the IPv4 layer, supporting the DLMS/COSEM
transport layer and application layer.
5.2.4 The TCP-UDP/IPv6 profile
The TCP-UDP/IPv6 profile uses the PRIME IPv6 SSCS making the necessary adaptation
between the PRIME PHY and MAC layers and the IPv6 layer, supporting the DLMS/COSEM
transport layer and application layer.
5.3 Lower protocol layers and their use
5.3.1 General
All three profiles specified in this document share the same PHY and MAC layers.
5.3.2 Physical layer
5.3.2.1 General
This layer provides the interface between the equipment and the physical transmission
medium that is the electricity distribution network. It transmits and receives MPDUs between
neighbour nodes.
5.3.2.2 PRIME PHY data plane services
PHY DATA services are generated / used by the MAC layer entity whenever data – PPDUs –
have to be transmitted to / received from (a) peer MAC entity(ies) using the PHY transmission
procedures. See Recommendation ITU-T G.9904:2012, 7.10.2.
5.3.2.3 PRIME PHY control plane services
PRIME PHY control plane services are used to control the physical layer by the MAC layer.
See Recommendation ITU-T G.9904:2012, 7.10.3. They are the following:
• PHY_AGC: allows the MAC layer entity to set or get the Automatic Gain Mode of the PHY;
• PHY_TIMER: allows the MAC layer entity to get the time at which the transmission has to
be started;
• PHY_CD: allows the MAC layer entity to look for the carrier detect signal, in order to
detect if the physical medium is free;
• PHY_NL: allows the MAC layer entity to get the floor noise level value present on the
power line;
• PHY_SNR: allows the MAC layer entity to get the value of the signal-to-noise ratio, in
order to find the appropriate degree of robustness needed for data exchange;
• PHY_ZCT: allows the MAC layer entity to get the zero crossing time of the mains and the
time between the last transmission or reception and the zero crossing of the mains.
5.3.2.4 PRIME PHY management plane services
PRIME PHY management plane services are used to manage the physical layer by the MAC
layer. See Recommendation ITU-T G.9904:2012, 7.10.4. They are the following:
• PLME_RESET: allows the MAC layer entity to request the PHY layer to reset its present
functional state. As a result of this primitive, the PHY should reset all internal states and
flush all buffers to clear any queued receive or transmit data;
• PLME_SLEEP: allows the MAC layer entity to request the PHY layer to suspend its
present activities including all reception functions. The PHY layer should complete any
pending transmission before entering into a sleep state;
• PLME_RESUME: allows the MAC layer entity to request the PHY layer to resume its
suspended activities. As a result of this primitive, the PHY layer should start its normal
transmission and reception functions;
• PLME_TESTMODE: allows the MAC layer entity to put the PHY layer into some non-
default functional modes. Specific functional mode out of the various possible modes is
provided as an input parameter. Following the reception of this primitive, the PHY layer
should complete any pending transmissions in its buffer before entering the test mode
requested;
• PLME_GET: allows the MAC layer entity to query information about a given attribute of the
PRIME Information Base.
5.3.3 MAC layer
5.3.3.1 Overview – main features and functions
A subnetwork can be seen as a tree structure with two types of nodes, the base node and
service nodes. The base node is at the root of the tree and acts as the master node that
provides the subnetwork with connectivity. There is one and only one base node in a
subnetwork. Any other subnetwork node is a service node. Service nodes are either leaves or
branch points (switches) of the tree structure.
The base node is initially the subnetwork itself and all other nodes should follow a registration
process to enrol themselves on the subnetwork.

– 16 – IEC 62056-8-4:2018  IEC 2018
Service nodes start in a “Disconnected” state and they try to find a base node or a switch
node to register themselves to the subnetwork. After this, they become leaves of the tree.
Service nodes may change their state dynamically from “Terminal” functions to “Switch”
functions and vice-versa. These changes occur on the basis of certain pre-defined events on
the network. Service nodes in “Switch” state become branch points of the tree, capable of
switching their neighbours’ data to propagate connectivity.
The three functional states of service nodes are:
• Disconnected: all nodes are in this state initially or after a restart. In this state, a node is
not capable to participate in the network. The primary function of a service node in this
state is to search for an operational network in its proximity and try to register itself on it;
• Terminal: In this state a service node is part of the network and is capable of
communicating its traffic by establishing connections, but it is not capable of switching the
traffic of any other node; and finally:
• Switch: In this state a service node is capable of performing all “Terminal” functions.
Additionally, it is capable of forwarding data to and from other devices on the subnetwork.
The events and associated processes that trigger changes from one functional state to
another are registration, unregistration, promotion and demotion.
Other functions of the MAC layer are:
• address resolution and broadcast and multicast addressing;
• CSMA/CA algorithm implementation;
• promoting service nodes from “Terminal” state to “Switch” state or demoting them from the
“Switch” state to “Terminal” state;
• establishing direct connections from one service node to another;
• packet aggregation;
• security functions, such as encryption and security keys management;
• PHY robustness management in order to select the best modulation schema for a given
situation;
• ARQ mechanism.
5.3.3.2 Services used by base node and service nodes
The MAC connection and data services used by base nodes and service nodes are the
following (see Recommendation ITU-T G.9904:2012, 8.5.2 and 8.5.4:
• MAC_ESTABLISH: is used to manage the connection establishment at MAC layer;
• MAC_RELEASE: is used to release a connection at MAC layer;
• MAC_JOIN: is used to join to a broadcast or multicast connection and allow the reception
of such packets;
• MAC_LEAVE: is used to leave a broadcast or multicast connection;
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