Access & radio
The link that puts a message on the air: either ITS-G5 (802.11p) or C-V2X PC5 / NR-V2X. Everything above is written so this layer can be swapped without touching it.
EN 302 663 · EN 303 798 · 3GPP Rel-14 → Rel-17 ITS-G5 vs C-V2X →
What is in a
V2X stack.
A V2X stack has the same shape whoever builds it. The ETSI ITS reference architecture (EN 302 665) sets it out: four layers from the radio up to the applications, and two planes, security and management, that cross all of them. It lines up, layer for layer, with the TCP/IP model every network engineer already knows.
Mapped to TCP/IP
The same shape
as TCP/IP.
The C-ITS stack lines up with TCP/IP layer by layer: BTP is its transport, GeoNetworking its network layer, ITS-G5 or C-V2X its link. The difference sits at the top, where ITS splits the application layer into a facilities layer, its message set, and the applications above it, and adds two planes, security and management, that TCP/IP has no equivalent for.
Networking & transport
GeoNetworking routes by geography instead of by address, and the Basic Transport Protocol carries the payload above it.
EN 302 636 · BTP (EN 302 636-5-1)
Facilities
The ETSI C-ITS message set on one shared message and codec layer: awareness, hazard, collective perception, signalised intersection, priority.
CAM · DENM · CPM · VAM · SPATEM · MAPEM · IVIM · SREM · SSEM · POIM
Applications
The C-ITS services a driver actually meets, built on those messages: road-works and hazard warnings, in-vehicle signage, green-light optimal speed, collision warnings and more, drawn from the ETSI basic set of applications.
TR 102 638 (Basic Set of Applications) · TS 101 539
Cross-layer planes
These two do not sit between two layers. They run the full height of the stack, touching every layer above.
Security & trust
Every message is signed and verified against a certificate, and a PKI issues and manages those certificates. It spans every layer, from the access link up to the application.
TS 102 940 · TS 103 097 · IEEE 1609.2 · TS 102 941Management
Station management, decentralised congestion control that keeps a shared channel usable under load, and a Local Dynamic Map that holds a live, geo-indexed picture of what has been received.
ISO 24102 · TS 102 687 (DCC) · EN 302 895 (LDM)Why it matters
One stack, or
many vendors.
These layers and planes can come from one codebase, or be assembled from a radio vendor, a networking library, a facilities SDK and a separate PKI. Assembled, the seams between them are where conformance and interoperability break.
The SkyV2X stack is one codebase. Facilities, the security and management planes and the Local Dynamic Map are ours, over a radio that stays interchangeable, so the layers are tested together and conformance is measured across the whole stack at once.
See the full V2X stackFAQ
Questions,
answered.
- What are the layers of the ETSI ITS station architecture?
- Four horizontal layers — Access and radio, Networking and transport, Facilities, and Applications — crossed by two vertical planes: Security and trust, and Management. The reference model is EN 302 665.
- How does the C-ITS stack map to the TCP/IP model?
- Layer for layer: Applications and Facilities sit at the application layer, BTP at transport, GeoNetworking at the network layer, and the access and radio layer at the link layer.
- What is the difference between the Facilities and Applications layers?
- The Facilities layer builds and manages the standard messages — CAM, DENM, CPM, VAM and the infrastructure messages. The Applications layer is the use cases that consume them, such as road hazard warning or green-light optimal speed.
- Are Security and Management layers in the C-ITS stack?
- No, they are cross-layer planes rather than stacked layers. Security and trust, and Management, run alongside all four horizontal layers instead of sitting between them.
See the stack running.
Every layer and plane above runs, live, behind a public digital twin and four reachable testbeds.