The ITS station — four layers and two verticals.
The reason a European CAM works identically over ITS-G5 and over C-V2X PC5 is architectural, not accidental. ETSI EN 302 665 defines an ITS station as a layered stack with the access technology isolated at the bottom, so that changing the radio changes nothing above it. Anyone designing V2X hardware should be able to draw this from memory.
Four of them, with the access technology isolated at the bottom.
| Layer | OSI | Contents |
|---|---|---|
| Applications | — | Road safety, traffic efficiency, other applications — the three-way split stated at clause 5.1 of EN 302 665, and the reason V2X has a benefit case beyond crash reduction. What V2X is for |
| Facilities | 5–7 | Application support, information support including the Local Dynamic Map, communication and session support. The message services live here: CA basic service, DEN basic service, CP service, VRU basic service. Also HMI support and position-and-time (PoTi). |
| Networking & transport | 3–4 | GeoNetworking (EN 302 636 series) and BTP, and/or IPv6; TCP/UDP |
| Access | 1–2 | PHY and data link — ITS-G5, C-V2X PC5, cellular Uu, Ethernet |
Management and security, both crossing every layer.
- Management entity — cross-layer configuration, service advertisement, congestion control (DCC), application deployment, the MIB.
- Security entity — firewall and intrusion management, authentication, authorisation, certificate and key management, the SIB.
The interfaces are named: MA, MN, MF, MI and MS for management; SA, SN, SF and SI for security; IN and NF connecting layers vertically.
Station types: vehicle ITS-S (the on-board unit), roadside ITS-S (the roadside unit), central ITS-S (the back office), and personal ITS-S (a VRU device). In the European trust model, vehicle and roadside stations are both end entities under the same PKI with different permissions — an important design property, and one worth copying. The trust models compared →
The security entity is a vertical, not a peripheral.
The security entity touches every layer. In a real device that means the secure element is not “a chip on the SPI bus that the security library talks to”; it is a boundary that the facilities layer, the networking layer and the management layer all reach through. Getting that interface right — what crosses it, how often, and at what latency — is most of the integration work on an on-board unit. Hardware root of trust →
Questions this page answers.
What is an ITS station?
The ETSI term for any node participating in cooperative ITS — a vehicle on-board unit, a roadside unit, a central back office, or a personal device carried by a vulnerable road user. All four are defined by the same layered reference architecture in ETSI EN 302 665 and, in the European trust model, vehicle and roadside stations are both end entities under the same PKI with different permissions.
What is the Local Dynamic Map?
A facilities-layer database inside an ITS station holding a continuously updated picture of the surrounding environment, assembled from received V2X messages, static map data and the station's own sensors. It is what the safety applications actually query — they do not read raw messages off the radio.
Why is V2X architecture layered this way?
So the message set is independent of the radio. The access layer is isolated at the bottom of the stack, which is why an identical ETSI CAM can ride ITS-G5 or C-V2X PC5 without changing a byte above it. That separation is what allows a jurisdiction to change radio technology without rewriting its application layer.