ISO 21217:2020

INTERNATIONAL ISO
STANDARD 21217
Third edition
Intelligent transport systems —
Station and communication
architecture
Systèmes de transport intelligents — Architecture du station et du
communication
PROOF/ÉPREUVE
Reference number
ISO 21217:2020(E)
©
ISO 2020

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ISO 21217:2020(E)

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© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 21217:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 7
5 Requirements .10
6 Overview of ITS communications .10
6.1 ITS services and applications .10
6.2 ITS communication technologies .11
6.3 ITS communication characteristics .12
6.4 Localized and networked communications .13
6.5 Hybrid communications .13
6.6 ITS communication networks .13
6.7 ITS station interconnection scenarios .14
6.8 Communication paths and data flows .16
7 ITS station — overview .17
7.1 ITS station — concept .17
7.2 ITS station architecture .18
7.2.1 Generalized OSI model . .18
7.2.2 ITS station nodes .21
7.2.3 Protocol and service data units in the ITS-S protocol stack .22
7.2.4 Distributed implementations of ITS-S roles .23
8 Details of elements of ITS-S reference architecture.25
8.1 ITS-S interfaces .25
8.1.1 Implementation habits .25
8.1.2 ITS-S management interfaces .25
8.1.3 ITS-S security interfaces .26
8.1.4 ITS-S communications interfaces .26
8.1.5 ITS-S application programming interface .26
8.2 ITS-S access layer .26
8.2.1 Access technologies .26
8.2.2 Details of the ITS-S access layer .27
8.2.3 Logical channels .28
8.2.4 Prioritization of transmission requests .29
8.3 ITS-S networking and transport layer .30
8.3.1 ITS-S networking and transport layer details .30
8.3.2 Networking protocols .31
8.3.3 Transport protocols .31
8.4 ITS-S facilities layer .32
8.4.1 ITS-S facilities layer details .32
8.4.2 ITS-S facilities services .33
8.5 ITS-S management entity .34
8.5.1 Management entity details .34
8.5.2 Management functionality .36
8.6 ITS-S security entity .36
8.6.1 Security entity details .36
8.6.2 Functionality .38
8.7 ITS-S applications .38
8.7.1 ITS-S applications details .38
8.7.2 ITS service .40
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9 Typical implementations of ITS-SUs .41
Annex A (informative) Illustration of typical ITS-SU implementations .42
Annex B (informative) ITS-S configurations .46
Bibliography .50
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ISO 21217:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 204, Intelligent transport systems.
This third edition cancels and replaces the second edition (ISO 21217:2014), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— many general alignments with other standards (e.g. on terms and abbreviations, and on references)
revised or developed since the publication of the second edition of this document;
— prioritization in the receive path added;
— more details on hybrid communications included;
— details on security requirements added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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Introduction
This document provides the intelligent transport systems (ITS) station and communication reference
architecture that is referenced in a family of deliverables from standard development organizations
(SDOs) for cooperative intelligent transport systems (C-ITS), which is a subset of standards for ITS.
ITS aims to improve surface transportation in terms of:
— safety
e.g. crash avoidance, obstacle detection, emergency calls, dangerous goods;
— efficiency
e.g. navigation, green wave, priority, lane access control, contextual speed limits, car sharing;
— comfort
e.g. telematics, parking, electric vehicle charging, infotainment; and
— sustainability,
by applying information and communication technologies (ICT).
ITS specifications are in general developed to address a specific ITS service domain (see ISO 14813-1),
such as public transport, road safety, freight and logistics, public emergencies or electronic fee
collection.
To support interoperability, C-ITS specifications are developed to exchange and share information
amongst ITS applications of a given application domain and even between application domains.
C-ITS services are based on the exchange of data between vehicles of any category (cars, trucks, buses,
emergency and specialized vehicles, etc.), the roadside and urban infrastructure (traffic lights, road
tolls, variable message signs, etc.), control and services centres (traffic control centre, service providers,
map providers, etc.), and other road users (pedestrians, cyclists, etc.).
Some ITS services require cooperation by vehicles with their surrounding environment (other vehicles,
other road users, roadside and urban infrastructure, etc.) while other ITS services require connectivity
to remote service platforms (road traffic control centres, map providers, service providers, fleet
managers, equipment manufacturers, etc.).
In order to support:
— a large variety of C-ITS services with diverging requirements, and
— efficient sharing of information maintained by individual service applications,
it is necessary to combine multiple access technologies and communication protocols with distinct
performance characteristics (communication range, available bandwidth, end-to-end transmission
delay, quality of service, security, etc.); see Figure 1.
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Figure 1 — Examples of ITS communications
Combining multiple access technologies and communication protocols requires a common approach
to the way communications and data are securely managed, which is specified in this document (see
Figure 2).
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Figure 2 — ITS-S reference architecture
Similarly to the ISO Open Systems Interconnection (OSI) 7-layer architecture, the ITS station
architecture is divided into three independent communication layers (namely the ITS station access
layer, the ITS station networking and transport layer and the ITS station facilities layer) on top of which
the ITS Applications entity is located. Additional cross-layer entities in charge of the management
activities (management of ITS station units, of communications and security) support communications
and applications.
An implementation of this ITS station architecture is referred to as an “ITS station unit" (ITS-SU). The
functionalities available in an ITS-SU can be implemented in one or multiple physical units, referred to
as “ITS station communication units” (ITS-SCUs). The various ITS-SCUs of one single ITS-SU may even
be split over a large geographical area, e.g. along a motorway several tens of kilometres in length.
ITS-SUs conformant with this document may be deployed in various environments, including vehicles
of any kind (vehicle ITS station), on the roadside infrastructure (roadside ITS station), in data centres
(central ITS station) or in nomadic devices (personal ITS station), as illustrated in Figure 3.
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Figure 3 — Typical implementations of ITS station units
Details of the following functional building blocks of the ITS station architecture are specified in a set
of related standards:
— ITS station management,
— ITS communication, application (service) and station security,
— ITS station facilities layer protocols,
— ITS station networking and transport layer protocols,
— communication interfaces (CIs) designed specifically for ITS applications and services such as those
designed specifically for safety of life and property,
— interfacing existing access technologies into ITS stations,
— distributed implementations of ITS stations, and
— interfacing ITS stations to existing communication networks and communicating with nodes
thereon.
As C-ITS deals with safety of human life and property, ITS station units are designed for supporting
the secure provision of the C-ITS services and secure allocation of resources with prioritized access.
Security means covering the two essential operational modes:
a) Authentication of the sender of a broadcast message used for information dissemination.
b) Secure session establishment and maintenance.
Due to the diverging requirements from the multiplicity of already known and continuously emerging
ITS applications, multiple communication technologies that are fundamentally different may be
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supported in a specific ITS-SU. Supporting multiple access technologies and communication protocols,
also referred to as “hybrid communications”, is a design principle of the ITS station architecture. The
ITS station architecture is thus specified with no pre-defined mandatory communication technologies.
It can support any type of existing and forthcoming technology, on the condition that:
1) it respects the same design principles;
2) its integration into the ITS station architecture is specified in a support standard, and
3) it preserves backward compatibility with existing standards.
Presently, specifications have been developed to support a number of access technologies, for example:
— all kinds of cellular access technologies (e.g. specified at 3GPP with profile standards from other
SDOs tailoring them to the ITS station reference architecture);
— satellite communications;
— other technologies such as infrared, millimetre wave (ultra wideband communications), vehicular
Wi-Fi (ITS-G5/US-DSRC/ITS-M5: all profiles of IEEE 802.11 OCB) and optical light communications;
and several flavours of communication protocol suites:
— GeoNetworking / Basic Transport Protocol from ETSI;
— FNTP from ISO;
— WSMP from IEEE; and
— the suite of IPv6 protocols from IETF with supporting specifications from ISO.
The ITS station architecture actually combines:
a) localized communications,
i.e. communications to nearby stations without involving networking from a source station through
nodes of a network to a final destination station – also referred to as “ad-hoc communications”, and
b) networked communications.
NOTE While networked communications (e.g. cellular communications and access to internet) can apply the
principle of “Technology Neutrality” (allowing simultaneous usage of a mix of incompatible access technologies),
it is necessary for localized communication between ITS station units to be based on a specific access technology
per service (or service domain) in order to enable interoperability.
EXAMPLE ITS-M5 (ISO 21215) with FNTP (ISO 29281-1) is an example of a protocol stack for localized
communications. Cellular network access to internet (ISO 17515-1) with IPv6 (ISO 21210) is an example of a
protocol stack for networked communications.
Unlike many legacy applications, the choice of the access technology and communication protocol
can be made transparent to the applications, i.e. ITS applications are technology-agnostic. This is
achieved through a number of functionalities across the ITS station architecture in support of hybrid
communications, and is illustrated in Figure 4.
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Figure 4 — Architecture of communication profile and path selection
Before transmitting data, applications provide their communication requirements (level of priority,
amount of data to be transmitted, expected level of security, expected end-to-end transmission delay,
etc.) to the management entity of the ITS-SU for each type of communication flow. In the meantime,
the management entity maintains various elements of information (local regulation enforcing the use
of a specific communication profile, existing capabilities of the ITS-SU and their status, characteristics
and load of available radio technologies, current load of the ITS-SU, etc.). Based on the communication
requirement and the current view of the management, the uppermost relevant communication profile
(uniquely identified by an ITS-S communication profile identifier) is selected and ITS station resources
are securely committed for identified communication flow.
The ITS station architecture serves as a reference for numerous C-ITS services developed around the
world, and more particularly, in Europe. Early deployments of C-ITS services conforming to the ITS
[115]
station architecture have been initiated in Europe under the framework of the C-ROADS and
InterCor initiatives supported by the European Commission. National pilot deployments are underway
all across Europe (for example, SCOOP in France, NordicWay in Scandinavia, the C-ITS corridor
project between The Netherlands, Germany, and Austria) and in other regions such as Austroads in
Australia and New Zealand, and in Israel. These early deployment projects are typically focused on
road safety and traffic efficiency services that rely on the exchange of data between vehicles and the
roadside infrastructure. This data exchange is performed through both localized communications and
networked communications.
In these European deployments, localized communications, also known as V2X, are performed using
the ITS-G5 access technology within the 5.9 GHz frequency band, a Wi-Fi profile designed for vehicular
communications. Networked communications are typically performed using a cellular technology (e.g.
LTE). Other technologies may of course be used in the future (e.g. 5G, infrared, etc.) provided that they
conform to the ITS station architecture and related standards defining technology building blocks.
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Early deployments have proven the need to deploy C-ITS services using a diversity of access
technologies, for example either ITS-G5 or LTE, or a combination of both. For instance, the French pilot
deployment (SCOOP) uses ITS-G5 between vehicle and roadside ITS stations to inform about immediate
dangers (CAM, DENM) and LTE is used by patrol vehicles to provide information to road control centres.
In Scandinavia, the scarce population has driven NordicWay to deploy roadside ITS stations only at
critical locations and to rely on LTE to deliver environmental information (DENM) from road control
centres to vehicles.
Further on, at the early stage of deployment of C-ITS services, the density of vehicle ITS stations
equipped with ITS-G5 capabilities is scarce, whereas roadside ITS stations are only deployed in
critical areas. Similarly, many areas anywhere in the world do not have the benefit of sufficient cellular
network coverage. While some time critical road safety C-ITS services are best served by localized
communications (e.g. notification of immediate danger requiring emergency breaking), there are not
always vehicles equipped with the ITS-G5 technology or roadside equipment in the vicinity able to relay
the notification immediately to nearby vehicles. In such a situation, using networked communications
(e.g. cellular) to provide the information to road control centres, and then from them back to vehicles in
a specific area, prevents the successive occurrence of road accidents.
All of these experiences, gained through early deployments, demonstrate that it is not possible
to provide the same level of services to all vehicles in all locations. The type of service and the
performance of the service depends on national decisions, the local road environment, the density of
population, the density of vehicles equipped, cellular coverage, and numerous other factors. In addition,
and importantly, the roadside infrastructure equipment and vehicles have a life expectancy that far
exceeds the innovation cycle of new radio and communication technologies. Equipment at the roadside
and in vehicles is therefore likely to have to accommodate new communications technologies during its
lifetime.
The ITS station and communication architecture specified in this document and its functionalities in
support of hybrid communications provide an answer to these concerns and enable a future-proof and
sustainable deployment of C-ITS services.
This architecture document is complemented by
— a business-oriented architecture specified in ISO 17427-1;
— testing architectures specified in ISO/TS 20026 and ETSI EG 202 798; and
— data registration procedures for ITS safety and emergency messages specified in ISO 24978.
Further on, guidelines on the topics related to this document are provided in the ISO 17427 series and
in the ISO 21186 series.
The Bibliography at the end of this document provides information on standards, draft standards
and new standard work items from various SDOs, and about other documentation relevant to ITS.
The information given there does not claim to be complete. There can be further standards and
documentation relevant to ITS, either already in existence, or available in the future.
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INTERNATIONAL STANDARD ISO 21217:2020(E)
Intelligent transport systems — Station and
communication architecture
1 Scope
This document describes the communications reference architecture of nodes called “ITS station
units” designed for deployment in intelligent transport systems (ITS) communication networks. The
ITS station reference architecture is described in an abstract manner. While this document describes
a number of ITS station elements, whether or not a particular element is implemented in an ITS station
unit depends on the specific communication requirements of the implementation.
This document also describes the various communication modes for peer-to-peer communications over
various networks between ITS communication nodes. These nodes can be ITS station units as described
in this document or any other reachable nodes.
This document specifies the minimum set of normative requirements for a physical instantiation of the
ITS station based on the principles of a bounded secured managed domain.
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.
ISO/TS 21177, Intelligent transport systems — ITS station security services for secure session establishment
and authentication between trusted devices
NOTE Document also
...