ETSI EN 302 637-2 V1.4.1 (2019-04)

Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)

EUROPEAN STANDARD
Intelligent Transport Systems (ITS);
Vehicular Communications;
Basic Set of Applications;
Part 2: Specification of Cooperative
Awareness Basic Service
2 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)

Reference
REN/ITS-0010089
Keywords
application, ITS, safety, service, transport
ETSI
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ETSI
3 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 7
Introduction . 7
1 Scope . 8
2 References . 8
2.1 Normative references . 8
2.2 Informative references . 8
3 Definition of terms, symbols and abbreviations . 10
3.1 Terms . 10
3.2 Symbols . 10
3.3 Abbreviations . 10
4 CA basic service introduction . 11
4.1 Background . 11
4.2 Services provided by CA basic service . 11
4.3 Sending CAMs . 12
4.4 Receiving CAMs . 12
5 CA basic service functional description . 12
5.1 CA basic service in the ITS architecture . 12
5.2 CA basic service functional architecture . 13
5.3 Interfaces of the CA basic service . 14
5.3.1 Interface to ITS applications . 14
5.3.2 Interface to data provisioning facilities . 14
5.3.3 Interface to the Networking & Transport Layer . 14
5.3.4 Interfaces protocol stacks of the Networking & Transport Layer . 15
5.3.4.1 Interface to the GeoNetworking/BTP stack . 15
5.3.4.2 Interface to the IPv6 stack and the combined IPv6/GeoNetworking stack . 16
5.3.5 Interface to the Management entity . 16
5.3.6 Interface to the Security entity . 16
6 CAM dissemination . 17
6.1 CAM dissemination concept . 17
6.1.1 CAM dissemination requirements . 17
6.1.2 CA basic service activation and termination . 17
6.1.3 CAM generation frequency management for vehicle ITS-Ss . 17
6.1.4 CAM generation frequency management for RSU ITS-Ss . 18
6.1.5 CAM time requirement . 18
6.1.5.1 CAM generation time . 18
6.1.5.2 CAM Time stamp . 19
6.2 CAM dissemination constraints . 19
6.2.1 General Confidence Constraints . 19
6.2.2 Security constraints . 19
6.2.2.1 Introduction . 19
6.2.2.2 Service Specific Permissions (SSP) . 19
6.2.3 General priority constraints. 21
7 CAM Format Specification . 21
7.1 General Structure of a CAM PDU . 21
7.2 ITS PDU header . 22
7.3 Basic container . 22
7.4 Vehicle ITS-S containers . 22
7.5 RSU ITS-S containers . 23
7.6 CAM format and coding rules . 23
7.6.1 Common data dictionary . 23
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4 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
7.6.2 CAM data presentation . 23
Annex A (normative): ASN.1 specification of CAM . 24
Annex B (normative): Description for data elements and data frames. 26
B.0 General requirements . 26
B.1 header . 26
B.2 cam . 26
B.3 generationDeltaTime . 26
B.4 camParameters . 27
B.5 basicContainer . 27
B.6 highFrequencyContainer . 27
B.7 lowFrequencyContainer . 27
B.8 specialVehicleContainer . 27
B.9 basicVehicleContainerHighFrequency . 27
B.10 basicVehicleContainerLowFrequency . 28
B.11 publicTransportContainer . 28
B.12 specialTransportContainer . 28
B.13 dangerousGoodsContainer . 28
B.14 roadWorksContainerBasic . 28
B.15 rescueContainer . 28
B.16 emergencyContainer . 29
B.17 safetyCarContainer . 29
B.18 stationType . 29
B.19 referencePosition . 29
B.20 performanceClass . 29
B.21 heading . 30
B.22 speed . 30
B.23 vehicleRole . 30
B.24 lanePosition . 30
B.25 driveDirection . 30
B.26 longitudinalAcceleration . 31
B.27 accelerationControl . 31
B.28 lateralAcceleration. 31
B.29 verticalAcceleration. 31
B.30 embarkationStatus . 31
B.31 curvature . 32
B.32 curvatureCalculationMode . 32
B.33 yawRate . 32
B.34 steeringWheelAngle . 32
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5 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
B.35 vehicleLength . 33
B.36 vehicleWidth . 33
B.37 exteriorLights . 33
B.38 pathHistory . 33
B.39 ptActivation . 33
B.40 specialTransportType . 34
B.41 dangerousGoodsBasic . 34
B.42 roadworksSubCauseCode . 34
B.43 closedLanes . 34
B.44 trafficRule . 34
B.45 speedLimit . 35
B.46 lightBarSirenInUse . 35
B.47 incidentIndication . 35
B.48 emergencyPriority . 35
B.49 rsuContainerHighFrequency . 35
B.50 protectedCommunicationZoneRSU . 36
B.51 cenDsrcTollingZone . 36
B.52 protectedZoneLatitude. 36
B.53 protectedZoneLongitude . 36
Annex C (informative): Protocol operation of the CA basic service . 37
C.1 Introduction . 37
C.2 Originating ITS-S operation . 37
C.2.1 Protocol data setting rules . 37
C.2.2 T_CheckCamGen . 37
C.2.3 Originating ITS-S message table . 37
C.2.4 General protocol operation . 38
C.2.5 CAM construction exception . 38
C.3 Receiving ITS-S operation . 38
C.3.1 Protocol data setting rules . 38
C.3.2 General protocol operation . 38
C.3.3 Exception handling . 39
C.3.3.1 CAM decoding exception . 39
Annex D (informative): Flow chart for CAM generation frequency management . 40
Annex E (informative): Extended CAM generation . 44
History . 45

ETSI
6 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
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Foreword
This final draft European Standard (EN) has been produced by ETSI Technical Committee Intelligent Transport
Systems (ITS), and is now submitted for the Vote phase of the ETSI standards EN Approval Procedure.
The present document is part 2 of a multi-part deliverable covering Vehicular Communications; Basic Set of
Applications, as identified below:
ETSI TS 102 637-1: "Functional Requirements";
ETSI EN 302 637-2: "Specification of Cooperative Awareness Basic Service";
ETSI EN 302 637-3: "Specifications of Decentralized Environmental Notification Basic Service".
The specification of the CA basic service was initially developed by the European Car-to-Car Communication
Consortium, see Car2Car Communication Consortium Manifesto [i.2]. The service was evaluated by several initiatives
such as the C2C-CC demonstration in 2008, ETSI Plugtests events and European projects including PRE-DRIVE C2X,
DRIVE C2X, SafeSpot, CVIS, CoVeL, eCoMove, SCOR@F and simTD. These evaluation efforts have provided
feedback to ETSI TC ITS.
The present document replaces ETSI TS 102 637-2 in whole. It includes improvements and enhancements of the CA
basic service specifications in ETSI TS 102 637-2 according to the feedback provided by the various initiatives.

Proposed national transposition dates
Date of latest announcement of this EN (doa): 3 months after ETSI publication
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 6 months after doa
Date of withdrawal of any conflicting National Standard (dow): 6 months after doa

ETSI
7 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Cooperative awareness within road traffic means that road users and roadside infrastructure are informed about each
other's position, dynamics and attributes. Road users are all kind of road vehicles like cars, trucks, motorcycles, bicycles
or even pedestrians and roadside infrastructure equipment including road signs, traffic lights or barriers and gates. The
awareness of each other is the basis for several road safety and traffic efficiency applications with many use cases as
described in ETSI TR 102 638 [i.1]. It is achieved by regular exchange of information among vehicles (V2V, in general
all kind of road users) and between vehicles and road side infrastructure (V2I and I2V) based on wireless networks,
called V2X network and as such is part of Intelligent Transport Systems (ITS).
The information to be exchanged for cooperative awareness is packed up in the periodically transmitted Cooperative
Awareness Message (CAM). The construction, management and processing of CAMs is done by the Cooperative
Awareness basic service (CA basic service), which is part of the facilities layer within the ITS communication
architecture ETSI EN 302 665 [1] supporting several ITS applications.
The CA basic service is a mandatory facility for all kind of ITS-Stations (ITS-S), which take part in the road traffic
(vehicle ITS-S, personal ITS-S, etc.). The present document focuses on the specifications for CAMs transmitted by all
vehicle ITS-Ss participating in the V2X network. Nevertheless, the present document defines the CAM format with
flexibility in order to be easily extendable for the support of other types of ITS-Ss or future ITS applications.
The requirements on the performance of the CA basic service, the content of the CAM and the quality of its data
elements are derived from the Basic Set of Applications (BSA) as defined in ETSI TR 102 638 [i.1] and in particular
from the road safety applications as defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI
TS 101 539-3 [i.10].
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8 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
1 Scope
The present document provides the specifications of the Cooperative Awareness basic service (CA basic service), which
is in support of the BSA road safety application.
This includes definition of the syntax and semantics of the Cooperative Awareness Message (CAM) and detailed
specifications on the message handling.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI EN 302 665 (V1.1.1): "Intelligent Transport Systems (ITS); Communications Architecture".
[2] ETSI TS 102 894-2 (V1.3.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 2: Applications and facilities layer common data dictionary".
[3] SAE J2735 (2009-11-19): "Dedicated Short Range Communications (DSRC) Message Set
Dictionary".
NOTE: Available at http://standards.sae.org/j2735_200911/.
[4] Recommendation ITU-T X.691/ISO/IEC 8825-2 (1997-12): "Information technology - ASN.1
encoding rules: Specification of Packed Encoding Rules (PER)".
[5] ETSI TS 103 097 (V1.3.1): "Intelligent Transport Systems (ITS); Security; Security header and
certificate formats".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TR 102 638 (V1.1.1) (2009-06): "Intelligent Transport Systems (ITS); Vehicular
Communications; Basic Set of Applications; Definitions".
[i.2] Car2Car Communication Consortium (2007-08): "Car2Car Communication Consortium
Manifesto", Version 1.1.
NOTE: Available at http://www.car-to-car.org/.
ETSI
9 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
[i.3] ETSI TR 102 863 (V1.1.1) (2011-06): "Intelligent Transport Systems (ITS); Vehicular
Communications; Basic Set of Applications; Local Dynamic Map (LDM); Rationale for and
guidance on standardization".
[i.4] ETSI TS 102 636-3 (V1.1.1): "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 3: Network architecture".
[i.5] ETSI EN 302 636-4-1: "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 4: Geographical addressing and forwarding for point-to-point and point-to-
multipoint communications; Sub-part 1: Media-Independent Functionality".
[i.6] ETSI TS 102 894-1 (V1.1.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 1: Facility layer structure, functional requirements and specifications".
[i.7] ETSI EN 302 636-5-1: "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 5: Transport Protocols; Sub-part 1: Basic Transport Protocol".
[i.8] ETSI TS 101 539-1 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 1:
Road Hazard Signalling (RHS) application requirements specification".
[i.9] ETSI TS 101 539-2: "Intelligent Transport Systems (ITS); V2X Applications; Part 2: Intersection
Collision Risk Warning (ICRW) application requirements specification".
[i.10] ETSI TS 101 539-3 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 3:
Longitudinal Collision Risk Warning (LCRW) application requirements specification".
[i.11] ETSI TS 102 723-5: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 5: Interface
between management entity and facilities layer".
[i.12] Void.
[i.13] ETSI TS 102 723-11: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 11:
Interface between networking and transport layer and facilities layer".
[i.14] Void.
[i.15] ISO EN 17419: "Intelligent Transport Systems -- Cooperative Systems -- Classification and
management of ITS applications in a global context".
[i.16] ETSI TS 102 724 (V1.1.1): "Intelligent Transport Systems (ITS); Harmonized Channel
Specifications for Intelligent Transport Systems operating in the 5 GHz frequency band".
[i.17] Void.
[i.18] ETSI TR 102 965 (V1.1.1): "Intelligent Transport Systems (ITS);Application Object Identifier
(ITS-AID); Registration list".
[i.19] ISO 1176: "Road vehicles - Masses - Vocabulary and codes".
[i.20] ETSI EN 302 663 (V1.2.1): "Intelligent Transport Systems (ITS); Access layer specification for
Intelligent Transport Systems operating in the 5 GHz frequency band".
[i.21] ETSI TS 103 613 (V1.1.1): "Intelligent Transport Systems (ITS); Access layer specification for
Intelligent Transport Systems using LTE Vehicle to everything communication in the 5,9 GHz
frequency band".
[i.22] ETSI TS 103 574 (V1.1.1): "Intelligent Transport Systems (ITS); Congestion Control Mechanisms
for C-V2X PC5 interface; Access layer part".
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10 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in ETSI EN 302 665 [1], LDM given in ETSI
TR 102 863 [i.3], DE and DF given in SAE J2735 [3] and the following apply:
basic set of applications: group of applications, supported by vehicular communication system
NOTE: The basic set of applications is defined in ETSI TR 102 638 [i.1].
Cooperative Awareness (CA) basic service: facility at the ITS-S facilities layer to generate, receive and process the
CAM
Cooperative Awareness Message (CAM): CA basic service PDU
Cooperative Awareness Message (CAM) data: partial or complete CAM payload
Cooperative Awareness Message (CAM) protocol: ITS facilities layer protocol that operates the CAM transmission
and reception
empty vehicle: complete vehicle kerb mass as defined in ISO 1176, clause 4.6 [i.19]
ITS-G5: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS) as
defined in ETSI EN 302 663 [i.20]
LTE-V2X: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS)
as defined in ETSI TS 103 613 [i.21]
V2X: either vehicle to vehicle (V2V), or vehicle to infrastructure (V2I) and/or infrastructure to vehicle (I2V)
3.2 Symbols
For the purposes of the present document, the following symbols apply:
IF.CAM Interface between CAM basic service and LDM or ITS application
IF.FAC Interface between CAM basic service and other facilities layer entities
IF.N&T Interface between CAM basic service and ITS networking & transport layer
IF.SEC Interface between CAM basic service and ITS security entity
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
API Application Programming Interface
ASN.1 Abstract Syntax Notation 1
BSA Basic Set of Applications
BTP Basic Transport Protocol
CA Cooperative Awareness
CAM Cooperative Awareness Message
DCC Decentralized Congestion Control
DE Data Element
DENM Decentralized Environmental Notification Message
DF Data Frame
FA-SAP Facilities/Applications Service Access Point
GN GeoNetworking
HF High Frequency
HMI Human Machine Interface
I2V Infrastructure-to-Vehicle
ID Identifier
ETSI
11 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
ISO International Organization for Standardization
ITS Intelligent Transport Systems
ITS-S ITS Station
ITS-ST ITS Station Time
LDM Local Dynamic Map
LF Low Frequency
LTE Long Term Evolution
MF-SAP Management/Facilities Service Access Point
MIB Management Information Base
MSB Most Significant Bit
N&T Networking & Transport layer
NF-SAP Networking & Transport/Facilities Service Access Point
OSI Open System Interconnection
PCI Protocol Control Information
PDU Packet Data Unit
PER Packed Encoding Rules
POTI Position and Time management
RSU Road Side Unit
SAE Society of Automotive Engineers
SAP Service Access Point
SF-SAP Security Facilities - Service Access Point
SHB Single-Hop Broadcasting
SSP Service Specific Permissions
TC Technical Committee
TR Technical Report
V2I Vehicle-to-Infrastructure
V2V Vehicle-to-Vehicle
V2X Vehicle-to-Everything
VDP Vehicle Data Provider
4 CA basic service introduction
4.1 Background
Cooperative Awareness Messages (CAMs) are messages exchanged in the ITS network between ITS-Ss to create and
maintain awareness of each other and to support cooperative performance of vehicles using the road network. A CAM
contains status and attribute information of the originating ITS-S. The content varies depending on the type of the
ITS-S. For vehicle ITS-Ss the status information includes time, position, motion state, activated systems, etc. and the
attribute information includes data about the dimensions, vehicle type and role in the road traffic, etc. On reception of a
CAM the receiving ITS-S becomes aware of the presence, type, and status of the originating ITS-S. The received
information can be used by the receiving ITS-S to support several ITS applications. For example, by comparing the
status of the originating ITS-S with its own status, a receiving ITS-S is able to estimate the collision risk with the
originating ITS-S and if necessary may inform the driver of the vehicle via the HMI. Multiple ITS applications may rely
on the CA basic service. It is assigned to domain application support facilities in ETSI TS 102 894-1 [i.6].
Besides the support of applications the awareness of other ITS-S gained by the CA basic service may be used in the
networking & transport layer for the position dependent dissemination of messages, e.g. DENM by GeoBroadcasting as
specified in ETSI EN 302 636-4-1 [i.5]. The generation and transmission of CAM is managed by the CA basic service
by implementing the CAM protocol.
4.2 Services provided by CA basic service
The CA basic service is a facilities layer entity that operates the CAM protocol. It provides two services: sending and
receiving of CAMs. The CA basic service uses the services provided by the protocol entities of the ITS networking &
transport layer to disseminate the CAM.
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12 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
4.3 Sending CAMs
The sending of CAMs comprises the generation and transmission of CAMs. In the course of CAM generation the
originating ITS-S composes the CAM, which is then delivered to the ITS networking & transport layer for
dissemination. The dissemination of CAMs may vary depending on the applied communication system. CAMs may be
sent by the originating ITS-S to all ITS-Ss within the direct communication range. This communication range may, inter
alia, be influenced in the originating ITS-S by changing the transmit power.
CAMs are generated periodically with a frequency controlled by the CA basic service in the originating ITS-S. The
generation frequency is determined taking into account the change of own ITS-Ss status, e.g. change of position or
speed as well as the radio channel load.
4.4 Receiving CAMs
Upon receiving a CAM, the CA basic service makes the content of the CAM available to the ITS applications and/or to
other facilities within the receiving ITS-S, such as a Local Dynamic Map (LDM).
5 CA basic service functional description
5.1 CA basic service in the ITS architecture
Sending CAMs as part of the CA basic service shall be present in all ITS-S, which take part in the road traffic (vehicle
ITS-S, personal ITS-S, etc.).
The CA basic service is a facilities layer entity of the ITS-S architecture as defined in ETSI EN 302 665 [1]. It may
interface with other entities of the facilities layer and with the ITS application layer in order to collect relevant
information for CAM generation and to forward the received CAM content for further processing. The CA basic service
within the ITS-S architecture and the logical interfaces to other layers and potentially to entities within the facility layer
are presented in Figure 1.
In a vehicle ITS-S entities for the collection of data may be the Vehicle Data Provider (VDP) and the Position and Time
management (POTI) and for received data the Local Dynamic Map (LDM) as receiving terminal. The VDP is
connected with the vehicle network and provides the vehicle status information. The POTI , provides the position of the
ITS-S and time information. The LDM as outlined in ETSI TR 102 863 [i.3] is a database in the ITS-S, which may be
updated with received CAM data. ITS applications may retrieve information from the LDM for further processing.
The CA basic service interfaces through the NF-SAP with the networking & transport layer (N&T) for exchanging of
CAM messages with other ITS-Ss, the SF-SAP with the Security entity to access security services for CAM
transmission and CAM reception, the MF-SAP with the Management entity and the FA-SAP with the application layer
if received CAM data are provided directly to the applications.
The functionalities of the CA basic service are defined in clause 5.2, the interfaces in Figure 2 are defined in clause 5.3.
ETSI
13 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)

Figure 1: CA basic service within the ITS-S architecture
5.2 CA basic service functional architecture
The CA basic service is part of the Application Support domain of the Facilities Layer according to ETSI
TS 102 894-1 [i.6]. Figure 2 shows the functional block diagram with the functional blocks of the CA basic service and
interfaces to other facilities and layers, which are detailed in the following. The interfaces to other entities and layers are
defined in clause 5.3.
Figure 2: Functional block diagram of the CA basic service
For sending and receiving CAMs, the CA basic service shall provide the following sub-functions:
• Encode CAM:
This sub-function constructs the CAM according to the format specified in annex A. The most recent in-
vehicle data shall be included in CAM.
• Decode CAM:
This sub-function decodes the received CAMs.
ETSI
14 Final draft ETSI EN 302 637-2 V1.4.1 (2019-01)
• CAM transmission management:
This sub-function implements the protocol operation of the originating ITS-S, as specified in clause C.1,
including in particular:
- Activation and termination of CAM transmission operation.
- Determination of the CAM generation frequency.
- Trigger the generation of CAM.
• CAM reception management:
This sub-function implements the protocol operation of the receiving ITS-S, as specified in clause C.2,
including in particular:
- Trigger the "decode CAM" function at the reception of CAM.
- Provision of the received CAM data to LDM or ITS applications of the receiving ITS-S.
- Optionally, checking the information of received CAMs.
5.3 Interfaces of the CA basic service
5.3.1 Interface to ITS applications
An ITS application is an application layer entity that implements the logic for fulfilling one or more ITS use cases. ITS
applications are defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI TS 101 539-3 [i.10].
For the provision of received data the CA basic service provides the interface IF.CAM to LDM or to ITS application
layer, as illustrated in Figure 2.
NOTE: The interface to the ITS application layer may be implemented as API and data are exchanged between
the CA basic service and ITS applications via this API. In another possible implementation, the interface
to the application layer may be implemented as FA-SAP. Specifications of the FA-SAP and the
corresponding protocols and APIs are out of scope of the present document.
5.3.2 Interface to data provisioning facilities
For the generation of CAMs, the CA basic service interacts with other facilities layer entities in order to obtain the
re
...

EUROPEAN STANDARD
Intelligent Transport Systems (ITS);
Vehicular Communications;
Basic Set of Applications;
Part 2: Specification of Cooperative
Awareness Basic Service
2 ETSI EN 302 637-2 V1.4.1 (2019-04)

Reference
REN/ITS-0010089
Keywords
application, ITS, safety, service, transport
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16

Siret N° 348 623 562 00017 - NAF 742 C
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° 7803/88

Important notice
The present document can be downloaded from:
http://www.etsi.org/standards-search
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
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© ETSI 2019.
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ETSI
3 ETSI EN 302 637-2 V1.4.1 (2019-04)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 7
Introduction . 7
1 Scope . 8
2 References . 8
2.1 Normative references . 8
2.2 Informative references . 8
3 Definition of terms, symbols and abbreviations . 10
3.1 Terms . 10
3.2 Symbols . 10
3.3 Abbreviations . 10
4 CA basic service introduction . 11
4.1 Background . 11
4.2 Services provided by CA basic service . 11
4.3 Sending CAMs . 12
4.4 Receiving CAMs . 12
5 CA basic service functional description . 12
5.1 CA basic service in the ITS architecture . 12
5.2 CA basic service functional architecture . 13
5.3 Interfaces of the CA basic service . 14
5.3.1 Interface to ITS applications . 14
5.3.2 Interface to data provisioning facilities . 14
5.3.3 Interface to the Networking & Transport Layer . 14
5.3.4 Interfaces protocol stacks of the Networking & Transport Layer . 15
5.3.4.1 Interface to the GeoNetworking/BTP stack . 15
5.3.4.2 Interface to the IPv6 stack and the combined IPv6/GeoNetworking stack . 16
5.3.5 Interface to the Management entity . 16
5.3.6 Interface to the Security entity . 16
6 CAM dissemination . 17
6.1 CAM dissemination concept . 17
6.1.1 CAM dissemination requirements . 17
6.1.2 CA basic service activation and termination . 17
6.1.3 CAM generation frequency management for vehicle ITS-Ss . 17
6.1.4 CAM generation frequency management for RSU ITS-Ss . 18
6.1.5 CAM time requirement . 18
6.1.5.1 CAM generation time . 18
6.1.5.2 CAM Time stamp . 19
6.2 CAM dissemination constraints . 19
6.2.1 General Confidence Constraints . 19
6.2.2 Security constraints . 19
6.2.2.1 Introduction . 19
6.2.2.2 Service Specific Permissions (SSP) . 19
6.2.3 General priority constraints. 21
7 CAM Format Specification . 21
7.1 General Structure of a CAM PDU . 21
7.2 ITS PDU header . 22
7.3 Basic container . 22
7.4 Vehicle ITS-S containers . 22
7.5 RSU ITS-S containers . 23
7.6 CAM format and coding rules . 23
7.6.1 Common data dictionary . 23
ETSI
4 ETSI EN 302 637-2 V1.4.1 (2019-04)
7.6.2 CAM data presentation . 23
Annex A (normative): ASN.1 specification of CAM . 24
Annex B (normative): Description for data elements and data frames. 26
B.0 General requirements . 26
B.1 header . 26
B.2 cam . 26
B.3 generationDeltaTime . 26
B.4 camParameters . 27
B.5 basicContainer . 27
B.6 highFrequencyContainer . 27
B.7 lowFrequencyContainer . 27
B.8 specialVehicleContainer . 27
B.9 basicVehicleContainerHighFrequency . 27
B.10 basicVehicleContainerLowFrequency . 28
B.11 publicTransportContainer . 28
B.12 specialTransportContainer . 28
B.13 dangerousGoodsContainer . 28
B.14 roadWorksContainerBasic . 28
B.15 rescueContainer . 28
B.16 emergencyContainer . 29
B.17 safetyCarContainer . 29
B.18 stationType . 29
B.19 referencePosition . 29
B.20 performanceClass . 29
B.21 heading . 30
B.22 speed . 30
B.23 vehicleRole . 30
B.24 lanePosition . 30
B.25 driveDirection . 30
B.26 longitudinalAcceleration . 31
B.27 accelerationControl . 31
B.28 lateralAcceleration. 31
B.29 verticalAcceleration. 31
B.30 embarkationStatus . 31
B.31 curvature . 32
B.32 curvatureCalculationMode . 32
B.33 yawRate . 32
B.34 steeringWheelAngle . 32
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5 ETSI EN 302 637-2 V1.4.1 (2019-04)
B.35 vehicleLength . 33
B.36 vehicleWidth . 33
B.37 exteriorLights . 33
B.38 pathHistory . 33
B.39 ptActivation . 33
B.40 specialTransportType . 34
B.41 dangerousGoodsBasic . 34
B.42 roadworksSubCauseCode . 34
B.43 closedLanes . 34
B.44 trafficRule . 34
B.45 speedLimit . 35
B.46 lightBarSirenInUse . 35
B.47 incidentIndication . 35
B.48 emergencyPriority . 35
B.49 rsuContainerHighFrequency . 35
B.50 protectedCommunicationZoneRSU . 36
B.51 cenDsrcTollingZone . 36
B.52 protectedZoneLatitude. 36
B.53 protectedZoneLongitude . 36
Annex C (informative): Protocol operation of the CA basic service . 37
C.1 Introduction . 37
C.2 Originating ITS-S operation . 37
C.2.1 Protocol data setting rules . 37
C.2.2 T_CheckCamGen . 37
C.2.3 Originating ITS-S message table . 37
C.2.4 General protocol operation . 38
C.2.5 CAM construction exception . 38
C.3 Receiving ITS-S operation . 38
C.3.1 Protocol data setting rules . 38
C.3.2 General protocol operation . 38
C.3.3 Exception handling . 39
C.3.3.1 CAM decoding exception . 39
Annex D (informative): Flow chart for CAM generation frequency management . 40
Annex E (informative): Extended CAM generation . 44
History . 45

ETSI
6 ETSI EN 302 637-2 V1.4.1 (2019-04)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This European Standard (EN) has been produced by ETSI Technical Committee Intelligent Transport Systems (ITS).
The present document is part 2 of a multi-part deliverable covering Vehicular Communications; Basic Set of
Applications, as identified below:
ETSI TS 102 637-1: "Functional Requirements";
ETSI EN 302 637-2: "Specification of Cooperative Awareness Basic Service";
ETSI EN 302 637-3: "Specifications of Decentralized Environmental Notification Basic Service".
The specification of the CA basic service was initially developed by the European Car-to-Car Communication
Consortium, see Car2Car Communication Consortium Manifesto [i.2]. The service was evaluated by several initiatives
such as the C2C-CC demonstration in 2008, ETSI Plugtests events and European projects including PRE-DRIVE C2X,
DRIVE C2X, SafeSpot, CVIS, CoVeL, eCoMove, SCOR@F and simTD. These evaluation efforts have provided
feedback to ETSI TC ITS.
The present document replaces ETSI TS 102 637-2 in whole. It includes improvements and enhancements of the CA
basic service specifications in ETSI TS 102 637-2 according to the feedback provided by the various initiatives.

National transposition dates
Date of adoption of this EN: 1 April 2019
Date of latest announcement of this EN (doa): 31 July 2019
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 January 2020
Date of withdrawal of any conflicting National Standard (dow): 31 January 2020

ETSI
7 ETSI EN 302 637-2 V1.4.1 (2019-04)
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Cooperative awareness within road traffic means that road users and roadside infrastructure are informed about each
other's position, dynamics and attributes. Road users are all kind of road vehicles like cars, trucks, motorcycles, bicycles
or even pedestrians and roadside infrastructure equipment including road signs, traffic lights or barriers and gates. The
awareness of each other is the basis for several road safety and traffic efficiency applications with many use cases as
described in ETSI TR 102 638 [i.1]. It is achieved by regular exchange of information among vehicles (V2V, in general
all kind of road users) and between vehicles and road side infrastructure (V2I and I2V) based on wireless networks,
called V2X network and as such is part of Intelligent Transport Systems (ITS).
The information to be exchanged for cooperative awareness is packed up in the periodically transmitted Cooperative
Awareness Message (CAM). The construction, management and processing of CAMs is done by the Cooperative
Awareness basic service (CA basic service), which is part of the facilities layer within the ITS communication
architecture ETSI EN 302 665 [1] supporting several ITS applications.
The CA basic service is a mandatory facility for all kind of ITS-Stations (ITS-S), which take part in the road traffic
(vehicle ITS-S, personal ITS-S, etc.). The present document focuses on the specifications for CAMs transmitted by all
vehicle ITS-Ss participating in the V2X network. Nevertheless, the present document defines the CAM format with
flexibility in order to be easily extendable for the support of other types of ITS-Ss or future ITS applications.
The requirements on the performance of the CA basic service, the content of the CAM and the quality of its data
elements are derived from the Basic Set of Applications (BSA) as defined in ETSI TR 102 638 [i.1] and in particular
from the road safety applications as defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI
TS 101 539-3 [i.10].
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8 ETSI EN 302 637-2 V1.4.1 (2019-04)
1 Scope
The present document provides the specifications of the Cooperative Awareness basic service (CA basic service), which
is in support of the BSA road safety application.
This includes definition of the syntax and semantics of the Cooperative Awareness Message (CAM) and detailed
specifications on the message handling.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI EN 302 665 (V1.1.1): "Intelligent Transport Systems (ITS); Communications Architecture".
[2] ETSI TS 102 894-2 (V1.3.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 2: Applications and facilities layer common data dictionary".
[3] SAE J2735 (2009-11-19): "Dedicated Short Range Communications (DSRC) Message Set
Dictionary".
NOTE: Available at http://standards.sae.org/j2735_200911/.
[4] Recommendation ITU-T X.691/ISO/IEC 8825-2 (1997-12): "Information technology - ASN.1
encoding rules: Specification of Packed Encoding Rules (PER)".
[5] ETSI TS 103 097 (V1.3.1): "Intelligent Transport Systems (ITS); Security; Security header and
certificate formats".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TR 102 638 (V1.1.1) (2009-06): "Intelligent Transport Systems (ITS); Vehicular
Communications; Basic Set of Applications; Definitions".
[i.2] Car2Car Communication Consortium (2007-08): "Car2Car Communication Consortium
Manifesto", Version 1.1.
NOTE: Available at http://www.car-to-car.org/.
ETSI
9 ETSI EN 302 637-2 V1.4.1 (2019-04)
[i.3] ETSI TR 102 863 (V1.1.1) (2011-06): "Intelligent Transport Systems (ITS); Vehicular
Communications; Basic Set of Applications; Local Dynamic Map (LDM); Rationale for and
guidance on standardization".
[i.4] ETSI TS 102 636-3 (V1.1.1): "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 3: Network architecture".
[i.5] ETSI EN 302 636-4-1: "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 4: Geographical addressing and forwarding for point-to-point and point-to-
multipoint communications; Sub-part 1: Media-Independent Functionality".
[i.6] ETSI TS 102 894-1 (V1.1.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 1: Facility layer structure, functional requirements and specifications".
[i.7] ETSI EN 302 636-5-1: "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 5: Transport Protocols; Sub-part 1: Basic Transport Protocol".
[i.8] ETSI TS 101 539-1 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 1:
Road Hazard Signalling (RHS) application requirements specification".
[i.9] ETSI TS 101 539-2: "Intelligent Transport Systems (ITS); V2X Applications; Part 2: Intersection
Collision Risk Warning (ICRW) application requirements specification".
[i.10] ETSI TS 101 539-3 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 3:
Longitudinal Collision Risk Warning (LCRW) application requirements specification".
[i.11] ETSI TS 102 723-5: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 5: Interface
between management entity and facilities layer".
[i.12] Void.
[i.13] ETSI TS 102 723-11: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 11:
Interface between networking and transport layer and facilities layer".
[i.14] Void.
[i.15] ISO EN 17419: "Intelligent Transport Systems -- Cooperative Systems -- Classification and
management of ITS applications in a global context".
[i.16] ETSI TS 102 724 (V1.1.1): "Intelligent Transport Systems (ITS); Harmonized Channel
Specifications for Intelligent Transport Systems operating in the 5 GHz frequency band".
[i.17] Void.
[i.18] ETSI TR 102 965 (V1.1.1): "Intelligent Transport Systems (ITS);Application Object Identifier
(ITS-AID); Registration list".
[i.19] ISO 1176: "Road vehicles - Masses - Vocabulary and codes".
[i.20] ETSI EN 302 663 (V1.2.1): "Intelligent Transport Systems (ITS); Access layer specification for
Intelligent Transport Systems operating in the 5 GHz frequency band".
[i.21] ETSI TS 103 613 (V1.1.1): "Intelligent Transport Systems (ITS); Access layer specification for
Intelligent Transport Systems using LTE Vehicle to everything communication in the 5,9 GHz
frequency band".
[i.22] ETSI TS 103 574 (V1.1.1): "Intelligent Transport Systems (ITS); Congestion Control Mechanisms
for C-V2X PC5 interface; Access layer part".
ETSI
10 ETSI EN 302 637-2 V1.4.1 (2019-04)
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in ETSI EN 302 665 [1], LDM given in ETSI
TR 102 863 [i.3], DE and DF given in SAE J2735 [3] and the following apply:
basic set of applications: group of applications, supported by vehicular communication system
NOTE: The basic set of applications is defined in ETSI TR 102 638 [i.1].
Cooperative Awareness (CA) basic service: facility at the ITS-S facilities layer to generate, receive and process the
CAM
Cooperative Awareness Message (CAM): CA basic service PDU
Cooperative Awareness Message (CAM) data: partial or complete CAM payload
Cooperative Awareness Message (CAM) protocol: ITS facilities layer protocol that operates the CAM transmission
and reception
empty vehicle: complete vehicle kerb mass as defined in ISO 1176, clause 4.6 [i.19]
ITS-G5: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS) as
defined in ETSI EN 302 663 [i.20]
LTE-V2X: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS)
as defined in ETSI TS 103 613 [i.21]
V2X: either vehicle to vehicle (V2V), or vehicle to infrastructure (V2I) and/or infrastructure to vehicle (I2V)
3.2 Symbols
For the purposes of the present document, the following symbols apply:
IF.CAM Interface between CAM basic service and LDM or ITS application
IF.FAC Interface between CAM basic service and other facilities layer entities
IF.N&T Interface between CAM basic service and ITS networking & transport layer
IF.SEC Interface between CAM basic service and ITS security entity
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
API Application Programming Interface
ASN.1 Abstract Syntax Notation 1
BSA Basic Set of Applications
BTP Basic Transport Protocol
CA Cooperative Awareness
CAM Cooperative Awareness Message
DCC Decentralized Congestion Control
DE Data Element
DENM Decentralized Environmental Notification Message
DF Data Frame
FA-SAP Facilities/Applications Service Access Point
GN GeoNetworking
HF High Frequency
HMI Human Machine Interface
I2V Infrastructure-to-Vehicle
ID Identifier
ETSI
11 ETSI EN 302 637-2 V1.4.1 (2019-04)
ISO International Organization for Standardization
ITS Intelligent Transport Systems
ITS-S ITS Station
LDM Local Dynamic Map
LF Low Frequency
LTE Long Term Evolution
MF-SAP Management/Facilities Service Access Point
MIB Management Information Base
MSB Most Significant Bit
N&T Networking & Transport layer
NF-SAP Networking & Transport/Facilities Service Access Point
OSI Open System Interconnection
PCI Protocol Control Information
PDU Packet Data Unit
PER Packed Encoding Rules
POTI Position and Time management
RSU Road Side Unit
SAE Society of Automotive Engineers
SAP Service Access Point
SF-SAP Security Facilities - Service Access Point
SHB Single-Hop Broadcasting
SSP Service Specific Permissions
TC Technical Committee
TR Technical Report
V2I Vehicle-to-Infrastructure
V2V Vehicle-to-Vehicle
V2X Vehicle-to-Everything
VDP Vehicle Data Provider
4 CA basic service introduction
4.1 Background
Cooperative Awareness Messages (CAMs) are messages exchanged in the ITS network between ITS-Ss to create and
maintain awareness of each other and to support cooperative performance of vehicles using the road network. A CAM
contains status and attribute information of the originating ITS-S. The content varies depending on the type of the
ITS-S. For vehicle ITS-Ss the status information includes time, position, motion state, activated systems, etc. and the
attribute information includes data about the dimensions, vehicle type and role in the road traffic, etc. On reception of a
CAM the receiving ITS-S becomes aware of the presence, type, and status of the originating ITS-S. The received
information can be used by the receiving ITS-S to support several ITS applications. For example, by comparing the
status of the originating ITS-S with its own status, a receiving ITS-S is able to estimate the collision risk with the
originating ITS-S and if necessary may inform the driver of the vehicle via the HMI. Multiple ITS applications may rely
on the CA basic service. It is assigned to domain application support facilities in ETSI TS 102 894-1 [i.6].
Besides the support of applications the awareness of other ITS-S gained by the CA basic service may be used in the
networking & transport layer for the position dependent dissemination of messages, e.g. DENM by GeoBroadcasting as
specified in ETSI EN 302 636-4-1 [i.5]. The generation and transmission of CAM is managed by the CA basic service
by implementing the CAM protocol.
4.2 Services provided by CA basic service
The CA basic service is a facilities layer entity that operates the CAM protocol. It provides two services: sending and
receiving of CAMs. The CA basic service uses the services provided by the protocol entities of the ITS networking &
transport layer to disseminate the CAM.
ETSI
12 ETSI EN 302 637-2 V1.4.1 (2019-04)
4.3 Sending CAMs
The sending of CAMs comprises the generation and transmission of CAMs. In the course of CAM generation the
originating ITS-S composes the CAM, which is then delivered to the ITS networking & transport layer for
dissemination. The dissemination of CAMs may vary depending on the applied communication system. CAMs may be
sent by the originating ITS-S to all ITS-Ss within the direct communication range. This communication range may, inter
alia, be influenced in the originating ITS-S by changing the transmit power.
CAMs are generated periodically with a frequency controlled by the CA basic service in the originating ITS-S. The
generation frequency is determined taking into account the change of own ITS-Ss status, e.g. change of position or
speed as well as the radio channel load.
4.4 Receiving CAMs
Upon receiving a CAM, the CA basic service makes the content of the CAM available to the ITS applications and/or to
other facilities within the receiving ITS-S, such as a Local Dynamic Map (LDM).
5 CA basic service functional description
5.1 CA basic service in the ITS architecture
Sending CAMs as part of the CA basic service shall be present in all ITS-S, which take part in the road traffic (vehicle
ITS-S, personal ITS-S, etc.).
The CA basic service is a facilities layer entity of the ITS-S architecture as defined in ETSI EN 302 665 [1]. It may
interface with other entities of the facilities layer and with the ITS application layer in order to collect relevant
information for CAM generation and to forward the received CAM content for further processing. The CA basic service
within the ITS-S architecture and the logical interfaces to other layers and potentially to entities within the facility layer
are presented in Figure 1.
In a vehicle ITS-S entities for the collection of data may be the Vehicle Data Provider (VDP) and the Position and Time
management (POTI) and for received data the Local Dynamic Map (LDM) as receiving terminal. The VDP is
connected with the vehicle network and provides the vehicle status information. The POTI , provides the position of the
ITS-S and time information. The LDM as outlined in ETSI TR 102 863 [i.3] is a database in the ITS-S, which may be
updated with received CAM data. ITS applications may retrieve information from the LDM for further processing.
The CA basic service interfaces through the NF-SAP with the networking & transport layer (N&T) for exchanging of
CAM messages with other ITS-Ss, the SF-SAP with the Security entity to access security services for CAM
transmission and CAM reception, the MF-SAP with the Management entity and the FA-SAP with the application layer
if received CAM data are provided directly to the applications.
The functionalities of the CA basic service are defined in clause 5.2, the interfaces in Figure 2 are defined in clause 5.3.
ETSI
13 ETSI EN 302 637-2 V1.4.1 (2019-04)

Figure 1: CA basic service within the ITS-S architecture
5.2 CA basic service functional architecture
The CA basic service is part of the Application Support domain of the Facilities Layer according to ETSI
TS 102 894-1 [i.6]. Figure 2 shows the functional block diagram with the functional blocks of the CA basic service and
interfaces to other facilities and layers, which are detailed in the following. The interfaces to other entities and layers are
defined in clause 5.3.
Figure 2: Functional block diagram of the CA basic service
For sending and receiving CAMs, the CA basic service shall provide the following sub-functions:
• Encode CAM:
This sub-function constructs the CAM according to the format specified in annex A. The most recent in-
vehicle data shall be included in CAM.
• Decode CAM:
This sub-function decodes the received CAMs.
ETSI
14 ETSI EN 302 637-2 V1.4.1 (2019-04)
• CAM transmission management:
This sub-function implements the protocol operation of the originating ITS-S, as specified in clause C.1,
including in particular:
- Activation and termination of CAM transmission operation.
- Determination of the CAM generation frequency.
- Trigger the generation of CAM.
• CAM reception management:
This sub-function implements the protocol operation of the receiving ITS-S, as specified in clause C.2,
including in particular:
- Trigger the "decode CAM" function at the reception of CAM.
- Provision of the received CAM data to LDM or ITS applications of the receiving ITS-S.
- Optionally, checking the information of received CAMs.
5.3 Interfaces of the CA basic service
5.3.1 Interface to ITS applications
An ITS application is an application layer entity that implements the logic for fulfilling one or more ITS use cases. ITS
applications are defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI TS 101 539-3 [i.10].
For the provision of received data the CA basic service provides the interface IF.CAM to LDM or to ITS application
layer, as illustrated in Figure 2.
NOTE: The interface to the ITS application layer may be implemented as API and data are exchanged between
the CA basic service and ITS applications via this API. In another possible implementation, the interface
to the application layer may be implemented as FA-SAP. Specifications of the FA-SAP and the
corresponding protocols and APIs are out of scope of the present document.
5.3.2 Interface to data provisioning facilities
For the generation of CAMs, the CA basic service interacts with other facilities layer entities in order to obtain the
required data. This set of facilities that provides data for CAM generation is referred to as data provisioning facilities.
Data are exchanged between the data provisioning facilities and the CA basic service via the interface IF.FAC.
NOTE: Specifications of the interface to
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Inteligentni transportni sistemi - Komunikacija med vozili - Osnovni nabor aplikacij - 2. del: Specifikacija osnovne storitve kooperativne izmenjave podatkov o vozilihIntelligent Transport Systems (ITS) - Vehicular Communications - Basic Set of Applications - Part 2: Specification of Cooperative Awareness Basic Service35.240.60Uporabniške rešitve IT v prometuIT applications in transportICS:Ta slovenski standard je istoveten z:ETSI EN 302 637-2 V1.4.1 (2019-04)SIST EN 302 637-2 V1.4.1:2019en01-junij-2019SIST EN 302 637-2 V1.4.1:2019SLOVENSKI
STANDARD
EUROPEAN STANDARD SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 2
Reference REN/ITS-0010089 Keywords application, ITS, safety, service, transport ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE
Tel.: +33 4 92 94 42 00
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Important notice The present document can be downloaded from: http://www.etsi.org/standards-search The present document may be made available in electronic versions and/or in print. The content of any electronic and/or print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI deliverable is the one made publicly available in PDF format at www.etsi.org/deliver. Users of the present document should be aware that the document may be subject to revision or change of status. Information on the current status of this and other ETSI documents is available at https://portal.etsi.org/TB/ETSIDeliverableStatus.aspx If you find errors in the present document, please send your comment to one of the following services: https://portal.etsi.org/People/CommiteeSupportStaff.aspx Copyright Notification No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm except as authorized by written permission of ETSI. The content of the PDF version shall not be modified without the written authorization of ETSI. The copyright and the foregoing restriction extend to reproduction in all media.
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DECTTM, PLUGTESTSTM, UMTSTM and the ETSI logo are trademarks of ETSI registered for the benefit of its Members. 3GPPTM and LTETM are trademarks of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of the oneM2M Partners. GSM® and the GSM logo are trademarks registered and owned by the GSM Association. SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 3 Contents Intellectual Property Rights . 6 Foreword . 6 Modal verbs terminology . 7 Introduction . 7 1 Scope . 8 2 References . 8 2.1 Normative references . 8 2.2 Informative references . 8 3 Definition of terms, symbols and abbreviations . 10 3.1 Terms . 10 3.2 Symbols . 10 3.3 Abbreviations . 10 4 CA basic service introduction . 11 4.1 Background . 11 4.2 Services provided by CA basic service . 11 4.3 Sending CAMs . 12 4.4 Receiving CAMs . 12 5 CA basic service functional description . 12 5.1 CA basic service in the ITS architecture . 12 5.2 CA basic service functional architecture . 13 5.3 Interfaces of the CA basic service . 14 5.3.1 Interface to ITS applications . 14 5.3.2 Interface to data provisioning facilities . 14 5.3.3 Interface to the Networking & Transport Layer . 14 5.3.4 Interfaces protocol stacks of the Networking & Transport Layer . 15 5.3.4.1 Interface to the GeoNetworking/BTP stack . 15 5.3.4.2 Interface to the IPv6 stack and the combined IPv6/GeoNetworking stack . 16 5.3.5 Interface to the Management entity . 16 5.3.6 Interface to the Security entity . 16 6 CAM dissemination . 17 6.1 CAM dissemination concept . 17 6.1.1 CAM dissemination requirements . 17 6.1.2 CA basic service activation and termination . 17 6.1.3 CAM generation frequency management for vehicle ITS-Ss . 17 6.1.4 CAM generation frequency management for RSU ITS-Ss . 18 6.1.5 CAM time requirement . 18 6.1.5.1 CAM generation time . 18 6.1.5.2 CAM Time stamp . 19 6.2 CAM dissemination constraints . 19 6.2.1 General Confidence Constraints . 19 6.2.2 Security constraints . 19 6.2.2.1 Introduction . 19 6.2.2.2 Service Specific Permissions (SSP) . 19 6.2.3 General priority constraints. 21 7 CAM Format Specification . 21 7.1 General Structure of a CAM PDU . 21 7.2 ITS PDU header . 22 7.3 Basic container . 22 7.4 Vehicle ITS-S containers . 22 7.5 RSU ITS-S containers . 23 7.6 CAM format and coding rules . 23 7.6.1 Common data dictionary . 23 SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 4 7.6.2 CAM data presentation . 23 Annex A (normative):
ASN.1 specification of CAM . 24 Annex B (normative):
Description for data elements and data frames. 26 B.0 General requirements . 26 B.1 header . 26 B.2 cam . 26 B.3 generationDeltaTime . 26 B.4 camParameters . 27 B.5 basicContainer . 27 B.6 highFrequencyContainer . 27 B.7 lowFrequencyContainer . 27 B.8 specialVehicleContainer . 27 B.9 basicVehicleContainerHighFrequency . 27 B.10 basicVehicleContainerLowFrequency . 28 B.11 publicTransportContainer . 28 B.12 specialTransportContainer . 28 B.13 dangerousGoodsContainer . 28 B.14 roadWorksContainerBasic . 28 B.15 rescueContainer . 28 B.16 emergencyContainer . 29 B.17 safetyCarContainer . 29 B.18 stationType . 29 B.19 referencePosition . 29 B.20 performanceClass . 29 B.21 heading . 30 B.22 speed . 30 B.23 vehicleRole . 30 B.24 lanePosition . 30 B.25 driveDirection . 30 B.26 longitudinalAcceleration . 31 B.27 accelerationControl . 31 B.28 lateralAcceleration. 31 B.29 verticalAcceleration. 31 B.30 embarkationStatus . 31 B.31 curvature . 32 B.32 curvatureCalculationMode . 32 B.33 yawRate . 32 B.34 steeringWheelAngle . 32 SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 5 B.35 vehicleLength . 33 B.36 vehicleWidth . 33 B.37 exteriorLights . 33 B.38 pathHistory . 33 B.39 ptActivation . 33 B.40 specialTransportType . 34 B.41 dangerousGoodsBasic . 34 B.42 roadworksSubCauseCode . 34 B.43 closedLanes . 34 B.44 trafficRule . 34 B.45 speedLimit . 35 B.46 lightBarSirenInUse . 35 B.47 incidentIndication . 35 B.48 emergencyPriority . 35 B.49 rsuContainerHighFrequency . 35 B.50 protectedCommunicationZoneRSU . 36 B.51 cenDsrcTollingZone . 36 B.52 protectedZoneLatitude. 36 B.53 protectedZoneLongitude . 36 Annex C (informative):
Protocol operation of the CA basic service . 37 C.1 Introduction . 37 C.2 Originating ITS-S operation . 37 C.2.1 Protocol data setting rules . 37 C.2.2 T_CheckCamGen . 37 C.2.3 Originating ITS-S message table . 37 C.2.4 General protocol operation . 38 C.2.5 CAM construction exception . 38 C.3 Receiving ITS-S operation . 38 C.3.1 Protocol data setting rules . 38 C.3.2 General protocol operation . 38 C.3.3 Exception handling . 39 C.3.3.1 CAM decoding exception . 39 Annex D (informative):
Flow chart for CAM generation frequency management . 40 Annex E (informative):
Extended CAM generation . 44 History . 45
ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 6 Intellectual Property Rights Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (https://ipr.etsi.org/). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Trademarks The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners. ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks. Foreword This European Standard (EN) has been produced by ETSI Technical Committee Intelligent Transport Systems (ITS). The present document is part 2 of a multi-part deliverable covering Vehicular Communications; Basic Set of Applications, as identified below: ETSI TS 102 637-1:
"Functional Requirements"; ETSI EN 302 637-2: "Specification of Cooperative Awareness Basic Service"; ETSI EN 302 637-3:
"Specifications of Decentralized Environmental Notification Basic Service". The specification of the CA basic service was initially developed by the European Car-to-Car Communication Consortium, see Car2Car Communication Consortium Manifesto [i.2]. The service was evaluated by several initiatives such as the C2C-CC demonstration in 2008, ETSI Plugtests events and European projects including PRE-DRIVE C2X, DRIVE C2X, SafeSpot, CVIS, CoVeL, eCoMove, SCOR@F and simTD. These evaluation efforts have provided feedback to ETSI TC ITS.
The present document replaces ETSI TS 102 637-2 in whole. It includes improvements and enhancements of the CA basic service specifications in ETSI TS 102 637-2 according to the feedback provided by the various initiatives.
National transposition dates Date of adoption of this EN: 1 April 2019 Date of latest announcement of this EN (doa): 31 July 2019 Date of latest publication of new National Standard or endorsement of this EN (dop/e):
31 January 2020 Date of withdrawal of any conflicting National Standard (dow): 31 January 2020
ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 7 Modal verbs terminology In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). "must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation. Introduction Cooperative awareness within road traffic means that road users and roadside infrastructure are informed about each other's position, dynamics and attributes. Road users are all kind of road vehicles like cars, trucks, motorcycles, bicycles or even pedestrians and roadside infrastructure equipment including road signs, traffic lights or barriers and gates. The awareness of each other is the basis for several road safety and traffic efficiency applications with many use cases as described in ETSI TR 102 638 [i.1]. It is achieved by regular exchange of information among vehicles (V2V, in general all kind of road users) and between vehicles and road side infrastructure (V2I and I2V) based on wireless networks, called V2X network and as such is part of Intelligent Transport Systems (ITS). The information to be exchanged for cooperative awareness is packed up in the periodically transmitted Cooperative Awareness Message (CAM). The construction, management and processing of CAMs is done by the Cooperative Awareness basic service (CA basic service), which is part of the facilities layer within the ITS communication architecture ETSI EN 302 665 [1] supporting several ITS applications. The CA basic service is a mandatory facility for all kind of ITS-Stations (ITS-S), which take part in the road traffic (vehicle ITS-S, personal ITS-S, etc.). The present document focuses on the specifications for CAMs transmitted by all vehicle ITS-Ss participating in the V2X network. Nevertheless, the present document defines the CAM format with flexibility in order to be easily extendable for the support of other types of ITS-Ss or future ITS applications. The requirements on the performance of the CA basic service, the content of the CAM and the quality of its data elements are derived from the Basic Set of Applications (BSA) as defined in ETSI TR 102 638 [i.1] and in particular from the road safety applications as defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI TS 101 539-3 [i.10]. SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 8 1 Scope The present document provides the specifications of the Cooperative Awareness basic service (CA basic service), which is in support of the BSA road safety application. This includes definition of the syntax and semantics of the Cooperative Awareness Message (CAM) and detailed specifications on the message handling. 2 References 2.1 Normative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which are not found to be publicly available in the expected location might be found at https://docbox.etsi.org/Reference. NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee their long term validity. The following referenced documents are necessary for the application of the present document. [1] ETSI EN 302 665 (V1.1.1): "Intelligent Transport Systems (ITS); Communications Architecture". [2] ETSI TS 102 894-2 (V1.3.1): "Intelligent Transport Systems (ITS); Users and applications requirements; Part 2: Applications and facilities layer common data dictionary". [3] SAE J2735 (2009-11-19): "Dedicated Short Range Communications (DSRC) Message Set Dictionary". NOTE: Available at http://standards.sae.org/j2735_200911/. [4] Recommendation ITU-T X.691/ISO/IEC 8825-2 (1997-12): "Information technology - ASN.1 encoding rules: Specification of Packed Encoding Rules (PER)". [5] ETSI TS 103 097 (V1.3.1): "Intelligent Transport Systems (ITS); Security; Security header and certificate formats". 2.2 Informative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee their long term validity. The following referenced documents are not necessary for the application of the present document but they assist the user with regard to a particular subject area. [i.1] ETSI TR 102 638 (V1.1.1) (2009-06): "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of Applications; Definitions". [i.2] Car2Car Communication Consortium (2007-08): "Car2Car Communication Consortium Manifesto", Version 1.1. NOTE: Available at http://www.car-to-car.org/. SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 9 [i.3] ETSI TR 102 863 (V1.1.1) (2011-06): "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of Applications; Local Dynamic Map (LDM); Rationale for and guidance on standardization". [i.4] ETSI TS 102 636-3 (V1.1.1): "Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking; Part 3: Network architecture". [i.5] ETSI EN 302 636-4-1: "Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking; Part 4: Geographical addressing and forwarding for point-to-point and point-to-multipoint communications; Sub-part 1: Media-Independent Functionality". [i.6] ETSI TS 102 894-1 (V1.1.1): "Intelligent Transport Systems (ITS); Users and applications requirements; Part 1: Facility layer structure, functional requirements and specifications". [i.7] ETSI EN 302 636-5-1: "Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking; Part 5: Transport Protocols; Sub-part 1: Basic Transport Protocol". [i.8] ETSI TS 101 539-1 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 1: Road Hazard Signalling (RHS) application requirements specification". [i.9] ETSI TS 101 539-2: "Intelligent Transport Systems (ITS); V2X Applications; Part 2: Intersection Collision Risk Warning (ICRW) application requirements specification". [i.10] ETSI TS 101 539-3 (V1.1.1): "Intelligent Transport Systems (ITS); V2X Applications; Part 3: Longitudinal Collision Risk Warning (LCRW) application requirements specification". [i.11] ETSI TS 102 723-5: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 5: Interface between management entity and facilities layer". [i.12] Void. [i.13] ETSI TS 102 723-11: "Intelligent Transport Systems (ITS); OSI cross-layer topics; Part 11: Interface between networking and transport layer and facilities layer". [i.14] Void. [i.15] ISO EN 17419: "Intelligent Transport Systems -- Cooperative Systems -- Classification and management of ITS applications in a global context". [i.16] ETSI TS 102 724 (V1.1.1): "Intelligent Transport Systems (ITS); Harmonized Channel Specifications for Intelligent Transport Systems operating in the 5 GHz frequency band". [i.17] Void. [i.18] ETSI TR 102 965 (V1.1.1): "Intelligent Transport Systems (ITS);Application Object Identifier (ITS-AID); Registration list". [i.19] ISO 1176: "Road vehicles - Masses - Vocabulary and codes". [i.20] ETSI EN 302 663 (V1.2.1): "Intelligent Transport Systems (ITS); Access layer specification for Intelligent Transport Systems operating in the 5 GHz frequency band". [i.21] ETSI TS 103 613 (V1.1.1): "Intelligent Transport Systems (ITS); Access layer specification for Intelligent Transport Systems using LTE Vehicle to everything communication in the 5,9 GHz frequency band". [i.22] ETSI TS 103 574 (V1.1.1): "Intelligent Transport Systems (ITS); Congestion Control Mechanisms for C-V2X PC5 interface; Access layer part". SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 10 3 Definition of terms, symbols and abbreviations 3.1 Terms For the purposes of the present document, the terms given in ETSI EN 302 665 [1], LDM given in ETSI TR 102 863 [i.3], DE and DF given in SAE J2735 [3] and the following apply: basic set of applications: group of applications, supported by vehicular communication system NOTE: The basic set of applications is defined in ETSI TR 102 638 [i.1]. Cooperative Awareness (CA) basic service: facility at the ITS-S facilities layer to generate, receive and process the CAM Cooperative Awareness Message (CAM): CA basic service PDU Cooperative Awareness Message (CAM) data: partial or complete CAM payload Cooperative Awareness Message (CAM) protocol: ITS facilities layer protocol that operates the CAM transmission and reception empty vehicle: complete vehicle kerb mass as defined in ISO 1176, clause 4.6 [i.19] ITS-G5: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS) as defined in ETSI EN 302 663 [i.20] LTE-V2X: access technology to be used in frequency bands dedicated for European intelligent transport System (ITS) as defined in ETSI TS 103 613 [i.21] V2X: either vehicle to vehicle (V2V), or vehicle to infrastructure (V2I) and/or infrastructure to vehicle (I2V) 3.2 Symbols For the purposes of the present document, the following symbols apply: IF.CAM Interface between CAM basic service and LDM or ITS application IF.FAC Interface between CAM basic service and other facilities layer entities IF.N&T Interface between CAM basic service and ITS networking & transport layer IF.SEC Interface between CAM basic service and ITS security entity 3.3 Abbreviations For the purposes of the present document, the following abbreviations apply: API Application Programming Interface ASN.1 Abstract Syntax Notation 1 BSA Basic Set of Applications BTP Basic Transport Protocol CA Cooperative Awareness CAM Cooperative Awareness Message DCC Decentralized Congestion Control DE Data Element DENM Decentralized Environmental Notification Message DF Data Frame FA-SAP Facilities/Applications Service Access Point GN GeoNetworking HF High Frequency HMI Human Machine Interface I2V Infrastructure-to-Vehicle ID Identifier SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 11 ISO International Organization for Standardization ITS Intelligent Transport Systems ITS-S ITS Station LDM Local Dynamic Map LF Low Frequency LTE Long Term Evolution MF-SAP Management/Facilities Service Access Point MIB Management Information Base MSB Most Significant Bit N&T Networking & Transport layer NF-SAP Networking & Transport/Facilities Service Access Point
OSI Open System Interconnection PCI Protocol Control Information PDU Packet Data Unit PER Packed Encoding Rules POTI Position and Time management RSU Road Side Unit SAE Society of Automotive Engineers SAP Service Access Point SF-SAP Security Facilities - Service Access Point SHB Single-Hop Broadcasting SSP Service Specific Permissions TC Technical Committee TR Technical Report V2I Vehicle-to-Infrastructure V2V Vehicle-to-Vehicle V2X Vehicle-to-Everything VDP Vehicle Data Provider 4 CA basic service introduction 4.1 Background Cooperative Awareness Messages (CAMs) are messages exchanged in the ITS network between ITS-Ss to create and maintain awareness of each other and to support cooperative performance of vehicles using the road network. A CAM contains status and attribute information of the originating ITS-S. The content varies depending on the type of the
ITS-S. For vehicle ITS-Ss the status information includes time, position, motion state, activated systems, etc. and the attribute information includes data about the dimensions, vehicle type and role in the road traffic, etc. On reception of a CAM the receiving ITS-S becomes aware of the presence, type, and status of the originating ITS-S. The received information can be used by the receiving ITS-S to support several ITS applications. For example, by comparing the status of the originating ITS-S with its own status, a receiving ITS-S is able to estimate the collision risk with the originating ITS-S and if necessary may inform the driver of the vehicle via the HMI. Multiple ITS applications may rely on the CA basic service. It is assigned to domain application support facilities in ETSI TS 102 894-1 [i.6]. Besides the support of applications the awareness of other ITS-S gained by the CA basic service may be used in the networking & transport layer for the position dependent dissemination of messages, e.g. DENM by GeoBroadcasting as specified in ETSI EN 302 636-4-1 [i.5]. The generation and transmission of CAM is managed by the CA basic service by implementing the CAM protocol.
4.2 Services provided by CA basic service The CA basic service is a facilities layer entity that operates the CAM protocol. It provides two services: sending and receiving of CAMs. The CA basic service uses the services provided by the protocol entities of the ITS networking & transport layer to disseminate the CAM.
ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 12 4.3 Sending CAMs The sending of CAMs comprises the generation and transmission of CAMs. In the course of CAM generation the originating ITS-S composes the CAM, which is then delivered to the ITS networking & transport layer for dissemination. The dissemination of CAMs may vary depending on the applied communication system. CAMs may be sent by the originating ITS-S to all ITS-Ss within the direct communication range. This communication range may, inter alia, be influenced in the originating ITS-S by changing the transmit power. CAMs are generated periodically with a frequency controlled by the CA basic service in the originating ITS-S. The generation frequency is determined taking into account the change of own ITS-Ss status, e.g. change of position or speed as well as the radio channel load. 4.4 Receiving CAMs Upon receiving a CAM, the CA basic service makes the content of the CAM available to the ITS applications and/or to other facilities within the receiving ITS-S, such as a Local Dynamic Map (LDM). 5 CA basic service functional description 5.1 CA basic service in the ITS architecture Sending CAMs as part of the CA basic service shall be present in all ITS-S, which take part in the road traffic (vehicle ITS-S, personal ITS-S, etc.).
The CA basic service is a facilities layer entity of the ITS-S architecture as defined in ETSI EN 302 665 [1]. It may interface with other entities of the facilities layer and with the ITS application layer in order to collect relevant information for CAM generation and to forward the received CAM content for further processing. The CA basic service within the ITS-S architecture and the logical interfaces to other layers and potentially to entities within the facility layer are presented in Figure 1. In a vehicle ITS-S entities for the collection of data may be the Vehicle Data Provider (VDP) and the Position and Time management (POTI) and for received data the Local Dynamic Map (LDM) as receiving terminal. The VDP is connected with the vehicle network and provides the vehicle status information. The POTI , provides the position of the ITS-S and time information. The LDM as outlined in ETSI TR 102 863 [i.3] is a database in the ITS-S, which may be updated with received CAM data. ITS applications may retrieve information from the LDM for further processing. The CA basic service interfaces through the NF-SAP with the networking & transport layer (N&T) for exchanging of CAM messages with other ITS-Ss, the SF-SAP with the Security entity to access security services for CAM transmission and CAM reception, the MF-SAP with the Management entity and the FA-SAP with the application layer if received CAM data are provided directly to the applications. The functionalities of the CA basic service are defined in clause 5.2, the interfaces in Figure 2 are defined in clause 5.3. SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 13
Figure 1: CA basic service within the ITS-S architecture 5.2 CA basic service functional architecture The CA basic service is part of the Application Support domain of the Facilities Layer according to ETSI TS 102 894-1 [i.6]. Figure 2 shows the functional block diagram with the functional blocks of the CA basic service and interfaces to other facilities and layers, which are detailed in the following. The interfaces to other entities and layers are defined in clause 5.3.
Figure 2: Functional block diagram of the CA basic service For sending and receiving CAMs, the CA basic service shall provide the following sub-functions: • Encode CAM:
This sub-function constructs the CAM according to the format specified in annex A. The most recent in-vehicle data shall be included in CAM. • Decode CAM:
This sub-function decodes the received CAMs. SIST EN 302 637-2 V1.4.1:2019

ETSI ETSI EN 302 637-2 V1.4.1 (2019-04) 14 • CAM transmission management:
This sub-function implements the protocol operation of the originating ITS-S, as specified in clause C.1, including in particular: - Activation and termination of CAM transmission operation. - Determination of the CAM generation frequency. - Trigger the generation of CAM.
• CAM reception management:
This sub-function implements the protocol operation of the receiving ITS-S, as specified in clause C.2, including in particular: - Trigger the "decode CAM" function at the reception of CAM.
- Provision of the received CAM data to LDM or ITS applications of the receiving ITS-S. - Optionally, checking the information of received CAMs. 5.3 Interfaces of the CA basic service 5.3.1 Interface to ITS applications An ITS application is an application layer entity that implements the logic for fulfilling one or more ITS use cases. ITS applications are defined in ETSI TS 101 539-1 [i.8], ETSI TS 101 539-2 [i.9] and ETSI TS 101 539-3 [i.10].
For the provision of received data the CA basic service provides the interface IF.CAM to LDM or to ITS application layer, as illustrated in Figure 2.
NOTE: The interface to the ITS application layer may be implemented as API and data are exchanged between the CA basic service and ITS applications via this API. In another possible implementation, the interface to the application layer may be implemented as FA-SAP. Specifications of the FA-SAP and the corresponding protocols and APIs are out of scope of the present document. 5.3.2 Interface to data provisioning facilities For the generation of CAMs, the CA basic service interacts with other facilities layer entities in order to obtain the required data. This set of facilities that provides data for CAM generation is referred to as data provisioning facilities. Data are exchanged between the data provisioning facilities and the CA basic service via the interface IF.FAC.
NOTE: Specifications of the interface to the data provisioning facilities and the corresponding protocols are out of scope of the present document. 5.3.3 Interface to the Networking & Transport Layer The CA basic servi
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