ISO 20684-1:2021

Intelligent transport systems - Roadside modules SNMP data interface - Part 1: Overview

Field devices are a key component in intelligent transport systems (ITS). Field devices include traffic signals, message signs, weather stations, traffic sensors, roadside equipment for connected ITS (C-ITS) environments, etc. The ISO 20684 series defines data that can be used when field devices need to exchange information with other external entities (called “managers” in this document, even if they are other field devices). Field devices can be quite complex, necessitating the standardization of many data concepts for exchange. As such, the ISO 20684 series is divided into several individual parts. This document (Part 1) introduces the ISO 20684 series and provides normative content that applies to all subsequent parts.

Systèmes de transport intelligents — Interface de données SNMP pour les modules en bord de route — Partie 1: Vue d'ensemble

General Information

• Status: Published
• Publication Date: 22-Apr-2021
• ICS: 03.220.20 - Road transport
• ICS: 35.240.60 - IT applications in transport
• Technical Committee: ISO/TC 204 - Intelligent transport systems
• Drafting Committee: ISO/TC 204/WG 9 - Integrated transport information, management and control
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 05-Jun-2025
• Completion Date: 13-Dec-2025

Overview

ISO 20684-1:2021 - "Intelligent transport systems - Roadside modules SNMP data interface - Part 1: Overview" is the normative introduction to the ISO 20684 series. It defines the common rules, terminology and conformance structure used by later parts that specify SNMP-based management information for ITS field devices. The standard addresses how field devices (traffic signals, variable message signs, weather stations, traffic sensors, and roadside C‑ITS equipment) exchange management and operational data with external entities called managers using SNMP conventions.

Key topics and technical requirements

• Scope and conformance model: Establishes how conformance is defined across the ISO 20684 series and ties requirements to manager-oriented user needs.
• Terminology and symbols: Normative definitions for agents, managers, events, triggers, logs, traps and other SNMP/ITS terms.
• Conventions and data modeling: Prescribes SNMP/SMIv2 and ASN.1 conventions (including reference to IETF RFC 2578) for describing management information.
• Architecture: Describes ITS services, physical and communications views relevant to roadside modules and how these map to the data interface.
• User needs and requirements: Rules for deriving requirements from user needs, including identifiable requirements and structure of data exchange requirements.
• Dialogues (management operations): Generic SNMP dialogues specified for managers to Get/Set elemental or tabular data, manage dynamic table entries, toggle active status, delete entries, and related operations.
• Agent performance and response time: Defines agent behavior expectations (e.g., response time concept) and performance constraints.
• Security: Discusses vulnerabilities and prescriptive topics of authentication, access control, encryption and security recommendations applicable to all parts.
• Annexes: Normative Management Information Base (MIB) definitions (Annex A) and a Requirements Traceability Matrix (RTM) template (Annex B). MIBs are also available electronically from ISO.

Practical applications - who uses this standard

ISO 20684-1 is intended for:

• Device manufacturers designing SNMP-capable roadside modules.
• Systems integrators and software developers implementing SNMP managers and agents for ITS deployments.
• Transportation agencies and procuring authorities specifying open, non‑proprietary field device interfaces to reduce cost and simplify maintenance.
• Network and operations teams responsible for monitoring, configuring and controlling roadside ITS equipment.

Using the ISO 20684 series promotes interoperability, faster deployment, easier expansion and simplified maintenance of ITS field device networks.

Related standards

• ISO 20684 (series) - other parts that specify feature-specific MIBs and requirements.
• ISO 15784-2 - predecessor protocols and approaches for SNMP-based ITS device communication.
• ISO 14813-1 - ITS architecture and services referenced by this document.
• IETF RFC 2578 (SMIv2) - structure of management information used for MIB definitions.

Keywords: ISO 20684-1, SNMP data interface, MIB, Intelligent Transport Systems, roadside modules, field devices, SMIv2, ASN.1, ITS security, conformance.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20684-1
First edition
2021-04
Intelligent transport systems —
Roadside modules SNMP data
interface —
Part 1:
Overview
Systèmes de transport intelligents — Interface de données SNMP pour
les modules en bord de route —
Partie 1: Vue d'ensemble
Reference number
©
ISO 2021
© ISO 2021
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Conformance . 3
6 Conventions . 5
6.1 ASN.1 . 5
6.2 SNMP terminology . 5
7 Architecture . 5
7.1 ITS services . 5
7.2 Physical view . 5
7.3 Communications view . 6
8 User needs . 6
9 Requirements . 7
9.1 Features . 7
9.2 Identifiable requirements. 7
9.3 Structure of data exchange requirements . 7
9.4 Agent performance requirements . 7
10 Dialogues . 8
10.1 General dialogue rules . 8
10.1.1 Manager initiated . 8
10.1.2 Generic and custom dialogues . 8
10.2 Generic dialogues . 8
10.2.1 Get elemental data . 8
10.2.2 Set elemental data . 8
10.2.3 Get tabular data . 8
10.2.4 Set tabular data . 8
10.2.5 Get data column . 9
10.2.6 Get data from dynamic table entry. 9
10.2.7 Get row status of dynamic table entry . 9
10.2.8 Configure entry of a dynamic table . 9
10.2.9 Toggle active status of a dynamic table entry .10
10.2.10 Delete entry from a dynamic table .10
11 Security.11
11.1 Vulnerabilities .11
11.2 Authentication and access control .11
11.3 Encryption .11
11.4 Security recommendation .11
Annex A (normative) Management information base (MIB) .12
Annex B (normative) Requirements traceability matrix (RTM) .19
Bibliography .20
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
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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
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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.
A list of all parts in the ISO 20684 series can be found on the ISO website.
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.
iv © ISO 2021 – All rights reserved

Introduction
0.1  Background
The need for standardized communication with ITS field devices is growing around the world. Several
countries have adopted SNMP-based field device communication standards.
There is a growing view and empirical evidence that standardizing this activity will result in improved
ITS performance, reduced cost, reduced deployment time and improved maintainability. The ISO 20684
series extends ISO 15784-2 by defining the management information necessary to monitor, configure
and control features of field devices. The data elements defined in all parts of the ISO 20684 series may
be used with any relevant protocol, but were designed with an expectation that they would be used
with one of the ISO 15784-2 protocols.
By using this approach, agencies can specify open procurements and systems can be expanded
geographically in an open and non-proprietary manner, which reduces costs, speeds up deployment
and simplifies integration.
0.2  Overview
SNMP is a collection of well-thought-out and well-proven concepts and principles. SNMP employs the
sound principles of abstraction and standardization. This has led to SNMP being widely accepted as the
prime choice for communication between management systems and devices on the internet and other
communications networks.
The original implementation of SNMP was used to manage network devices such as routers and
switches. Since then, the use of SNMP has grown into many areas of application on the internet and has
also been used successfully over various serial communications networks.
This document defines management information for ITS field devices following the SNMP conventions.
0.3  Document approach and layout
This document defines:
a) How conformance is defined in subsequent parts of the ISO 20684 series (Clause 5);
b) Terminology and symbols used throughout the various parts of the ISO 20684 series (Clause 3 and
Clause 4);
c) Conventions used throughout the various parts of the ISO 20684 series (Clause 6);
d) The ITS architectural services defined in ISO 14813-1 that are addressed by the ISO 20684 series
(Clause 7);
e) The rules used by other parts of the ISO 20684 series in defining the user needs that drive the
definition of requirements (Clause 8);
f) The rules used by other parts of the ISO 20684 series in defining requirements and constraints
(Clause 9);
g) A set of generic dialogues that are referenced by other parts of the ISO 20684 series (Clause 10);
h) A discussion of security that applies to all devices conforming to the ISO 20684 series (Clause 11);
i) The management information base (MIB) for the features defined by this document (Annex A);
j) A description of the requirements traceability matrix that is provided in each subsequent part of
the ISO 20684 series that traces defined requirements to the required design elements (Annex B).
In addition, the MIBs are available electronically at https:// standards .iso .org/ iso/ 20684/ -1/ ed -1/ en.
INTERNATIONAL STANDARD ISO 20684-1:2021(E)
Intelligent transport systems — Roadside modules SNMP
data interface —
Part 1:
Overview
1 Scope
Field devices are a key component in intelligent transport systems (ITS). Field devices include traffic
signals, message signs, weather stations, traffic sensors, roadside equipment for connected ITS (C-ITS)
environments, etc.
The ISO 20684 series defines data that can be used when field devices need to exchange information
with other external entities (called “managers” in this document, even if they are other field devices).
Field devices can be quite complex, necessitating the standardization of many data concepts for
exchange. As such, the ISO 20684 series is divided into several individual parts. This document (Part 1)
introduces the ISO 20684 series and provides normative content that applies to all subsequent parts.
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.
IETF RFC 2578, Structure of Management Information Version 2 (SMIv2), April 1999.
3 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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
agent
entity (3.2) that can respond to get and set requests
3.2
entity
device or “thing” that becomes part of an intelligent transport system
3.3
event
information captured when a trigger (3.13) fires (3.6) within an agent (3.1)
Note 1 to entry: Events are often transmitted in notifications or stored in logs.
3.4
exception
condition that creates an event (3.3) that a user can want to store in a log (3.7) or transmit in a
notification (3.9)
3.5
field device
fixed or portable roadside module that includes an agent (3.1)
3.6
fire
to start a process when a trigger (3.13) value transitions from false to true
3.7
log
registry of events (3.3) within an agent (3.1) that can be retrieved by a manager (3.8)
3.8
manager
entity (3.2) that can generate get and set requests and/or can receive report, trap, and/or other inform
messages
[SOURCE: ISO 15784-2:2015, 4.9 — modified.]
3.9
notification
listing of one or more events (3.3) that the agent (3.1) can send to one or more managers (3.8)
3.10
response time
time from the receipt of the last byte of a Confirmed Class pduType to the start of the transmission of
the first byte of the response message (when access is allowed by lower layers)
3.11
target
entity (3.1) to which the field device (3.5) can need to send requests or notifications
Note 1 to entry: Field devices often need to send notifications to managers when triggers fire.
Note 2 to entry: Field devices can be configured to request data from other field devices to use in their expression
or trigger logic.
Note 3 to entry: Field devices can be configured to control other field devices in response to a trigger firing.
3.12
trap
notification (3.9) sent from an SNMP agent (3.1) to a SNMP manager (3.8) without an immediately
preceding request from the manager or any expectation of an acknowledgement
3.13
trigger
condition that evaluates to a Boolean value
4 Symbols and abbreviated terms
ASN.1 abstract syntax notation one
BER basic encoding rules
IAB Internet Architecture Board
2 © ISO 2021 – All rights reserved

IP internet protocol
ITS intelligent transport systems
MIB management information base
OER octet encoding rules
OID object identifier
PDU protocol data unit
RFC request for comments
NOTE Specifically, RFCs published by the Internet Engineering Task Force
RTM requirements traceability matrix
SMIv2 structure of management information version 2
SNMP simple network management protocol
STD IAB standard
TLS transport layer security
UDP user datagram protocol
USM user-based security model
5 Conformance
Conformance to each part of the ISO 20684 series is defined as per the conformance section of each
part, which is written using the structure defined in this clause.
Conformance is driven by defined user needs. Each part of the ISO 20684 series may define user needs
and the design to fulfil the user need. User needs are written from the perspective of a manager for the
field device.
NOTE Some parts of the ISO 20684 series do not define any user needs, but only provide reusable design
elements that can be referenced by other parts of the ISO 20684 series.
Table 1 of each part of the ISO 20684 series (other than this document) identifies the user needs
associated with the part and indicates whether they are mandatory or optional for conformance to that
part. Each user need is also traced to a set of features. A feature is a high-level, architectural concept
that represents a coherent capability of the device that can support multiple user needs.
Table 2 of each part of the ISO 20684 series (other than this document) traces each feature to the
requirements for that feature.
Each user need, feature and requirement is identified by name and a reference. The reference can be
within the same part, a different part, or a different standard. When references are made to other
documents, all details and remaining traceability shall be defined in the referenced document.
Both tables indicate conformance for an item using one of the following conformance codes:
a) M – indicates the item is mandatory when an implementation claims conformance to its parent
item.
b) O – indicates the item is optional when an implementation claims conformance to its parent item
and if no other parent item makes the item mandatory.
Parent items are defined as follows:
a) The part is the parent item of each user need defined within it.
b) Each user need is a parent item for one or more features as shown by the indentation in Table 1. A
user need may trace to multiple features and a feature may trace from multiple user needs.
c) Each feature is a parent item for one or more requirements as shown by the indentation in Table 2.
A feature may trace to multiple requirements; a requirement may trace from multiple user needs
but typically only traces from one feature.
Note that a feature defined in one part of the ISO 20684 series can have a parent defined in another
part. Features should not be defined until at least one user need exists for the feature.
A qualifier may precede a conformance code. In such cases, the qualifier shall be a term followed by a
colon. The term shall be defined in Table 3 of each part as a reference to a specific clause in a specific
standard. The meaning of this notation is that the conformance code only applies when the referenced
clause is supported by an implementation.
EXAMPLE The code “condition:M” means that the indicated row is “mandatory” if the clause referenced by
the term “condition” is supported by the implementation.
An option group expression may follow the “O” conformance code. The option group expression is of
the form “. ()”, where group shall be a sequential number that groups a number of
options together and shall be a range of integers that indicate the number of options that
may be supported by an implementation from the option group.
EXAMPLE The code “O.2 (1.*)” means that the indicated row is optional, but one or more options from
option group 2 are to be supported.
The requirements referenced by Table 2 are written as “shall” statements. However, the “shall” only
applies if the conformance table indicates that the feature is required.
NOTE This document defines the rules to be followed by subsequent parts of the ISO 20684 series; it does
not define any user needs or features itself and therefore does not contain Tables 1-3.
Each requirement specifying a need for a data exchange shall trace to one dialogue and one or more
data elements that an implementation claiming conformance to the requirement shall support. The
traceability from requirements to dialogues and data elements shall be defined in a requirements
traceability matrix (RTM) contained in Annex B of each part of the ISO 20684 series. The RTM may
include references to dialogues and data elements defined in other documents; any locally defined
dialogues shall be defined in the body of the standard while all locally defined data elements shall be
defined in Annex A of the document using a management information base (MIB) conforming to the
format defined in IETF RFC 2578. If the implementation supports SNMP, all supported data element
instances (i.e. SNMP objects) shall be accessible via any dialogue that meets the requirements of SNMP
and the data element definition.
NOTE The dialogues defined in the ISO 20684 series are specified to promote a common interface for testing
purposes and are not intended to restrict otherwise allowable requests or notifications.
Annex A of this document defines a set of object identities (i.e. nodes on the OID tree) and textual
conventions (i.e. useful data types) that should be imported as needed by other MIB modules contained
in other parts of the ISO 20684 series.
As this document does not contain any user needs, the Annex B of this document does not contain an
RTM; however, it does provide additional requirements that shall be applicable related to the RTMs
contained in other parts of the ISO 20684 series.
4 © ISO 2021 – All rights reserved

6 Conventions
6.1 ASN.1
This document contains MIBs, which are written in the form of ASN.1. This document also contains
references to and explanations of ASN.1 data concepts within its text. In all cases, the ASN.1 terms are
presented in a fixed width font (e.g. such as this) to distinguish these terms from normal English.
6.2 SNMP terminology
Terminology between the different versions of SNMP is slightly different. For the purposes of the
ISO 20684 series, the terminology of SNMPv3 is adopted.
7 Architecture
7.1 ITS services
The ISO 20684 series defines mechanisms by which ITS field devices can be monitored, configured and
controlled. ITS field devices may be used to support almost any ITS service, defined in ISO 14813-1,
with a roadside component.
7.2 Physical view
Figure 1 depicts the physical view of this interface using the graphical conventions defined by the
[19]
architecture reference for cooperative and intelligent transportation and also documented in
ISO 14813-5:2020, Annex B.
Figure 1 — Physical view of interface
The manager of the field device is shown in grey indicating that it can be any type of physical object,
such as a central system, another field device, a maintenance laptop or any other device that supports
the defined interface.
The field device is shown in orange, indicating that it is located in the field (e.g. along the roadside).
It shall have a connection to the manager and may have any number of connections to other ITS-S or
external systems.
The figure indicates two information transfers between these physical objects. The first is the
“configuration and commands” information flow from the manager to the field device. The second is
the “status and notifications” information flow from the field device to the manager. Both flows are
shown in green indicating that authentication is required and both are shown with a single arrowhead
indicating a unicast transfer.
Subsequent parts of the ISO 20684 series define needs, requirements and design details for various
field device capabilities.
NOTE This document is based on the use of SNMP, which implements a GET/SET paradigm where
there is a manager and an agent. However, a single field device entity can act as both a manager (e.g. sending
requests to other field devices) and as an agent (e.g. responding to requests from a centre or other field device)
simultaneously.
7.3 Communications view
Figure 2 depicts how the ISO 20684 series is intended to relate to other standards using the ITS Station
architecture, as defined in ISO 21217.
Figure 2 — Typical communications stack
Parts 2-9 of the ISO 20684 series are reserved for features that are a part of the Management Plane of
an ITS Station. These standards do not define end-device functionality; rather they define management
services that may support end-device functionality. The management layer typically also supports
other data to manage the communications stack as defined by a variety of SNMPv3 MIBs.
Parts 10 and above of the ISO 20684 series will address the end-device functionality and are considered
part of the definition of ITS-S applications.
The information defined for the Management Plane and ITS-S applications can theoretically be
exchanged over any communications stack, but is designed to be exchanged using SNMPv3, as described
in ISO 15784-2, with certificate-based security using TLS for SNMP. SNMPv3 is typically exchanged
using well-known internet protocols, such as UDP/IP over any number of access layers to media.
8 User needs
Specific user needs are defined in subsequent parts of the ISO 20684 series. Each user need should be
written from the perspective of a manager and provide a definition with a justification for the need.
The definition of the user need may be followed with an explanation of how the user need is fulfilled
using defined features.
6 © ISO 2021 – All rights reserved

9 Requirements
9.1 Features
Within each part of the ISO 20684 series, requirements should be grouped by feature. This will reduce
the amount of cross-referencing of requirements. Within a feature, requirements may be further
grouped by type of requirement (e.g. data exchange, functional, performance, etc.).
9.2 Identifiable requirements
Each logical requirement shall be written as a “shall” statement and be contained within its own
subclause. A requirement may include a list of items, where a letter identifies each item. Multiple
“shall” statements should be avoided in a subclause, unless the secondary “shall” statement(s) further
refines the initial “shall”. The applicability of a subclause to the definition of conformance is separately
defined in the conformance section (Clause 5). Placing each requirement in a separate subclause
allows easy referencing of requirements within traceability tables. The subclause may contain
additional explanatory text to assist the reader in understanding the requirement and/or to justify the
requirement.
9.3 Structure of data exchange requirements
Due to the nature of SNMP, data exchange requirements within the ISO 20684 series are generally
requirements for the agent to allow a manager to perform operations. Each such data exchange
requirement shall follow the following structure, to the extent possible:
the field device shall allow a manager to
The action is a required component and should typically be something similar to “determine”, “retrieve”,
“configure”, “toggle”, “reset”, “clear”, “control”, “or “confirm”.
The target is a required component and shall identify the information that is the recipient of the action.
The constraints are optional. If there are two constraints that apply to the entire requirement, they
should generally be placed at opposite ends of the sentence to avoid ambiguities. If there are more than
two constraints, great care should be taken and consideration given to restructuring the requirement.
NOTE Ambiguities someti
...