Intelligent transport systems -- Station and communication architecture

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.

Systèmes de transport intelligents -- Architecture du station et du communication

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Status
Published
Publication Date
16-Dec-2020
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
09-Dec-2020
Completion Date
09-Dec-2020
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INTERNATIONAL ISO
STANDARD 21217
Third edition
2020-12
Intelligent transport systems —
Station and communication
architecture
Systèmes de transport intelligents — Architecture du station et du
communication
Reference number
ISO 21217:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 21217:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
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

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 21217:2020(E)

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

iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 21217:2020(E)
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.
vi © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 21217:2020(E)
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).
© ISO 2020 – All rights reserved vii
---------------------- Page: 7 ----------------------
ISO 21217:2020(E)
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.

viii © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 21217:2020(E)
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

© ISO 2020 – All rights reserved ix
---------------------- Page: 9 ----------------------
ISO 21217:2020(E)

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.
x © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 21217:2020(E)
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.

© ISO 2020 – All rights reserved xi
---------------------- Page: 11 ----------------------
ISO 21217:2020(E)

Early deployments have proven the need to deploy C-ITS services using a range 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.

xii © ISO 2020 – All rights reserved
---------------------- Page: 12 ----------------------
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 available as CEN/TS 21177.

ETSI TS 103 097, Intelligent Transport Systems (ITS); Security; Security header and certificate formats

3 Terms and definitio
...

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
---------------------- Page: 1 ----------------------
ISO 21217:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
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

© ISO 2020 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
ISO 21217:2020(E)

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

iv PROOF/ÉPREUVE © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO 2020 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
ISO 21217:2020(E)
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.
vi PROOF/ÉPREUVE © ISO 2020 – All rights reserved
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ISO 21217:2020(E)
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
...

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