===== What is C-ITS? =====
**C-ITS** stands for **Cooperative Intelligent Transport Systems**: vehicles and infrastructure communicate with one another.

Typical C-ITS participants are:

**Stationary [[en:c-its:rsu|RSUs - Road Side Units]]**
  - Traffic lights (traffic signal installations)
  - Roadworks signs
  - Toll gantries on motorways

**Vehicles, OBUs (On-Board Units)**
  - Trams
  - Buses
  - Cars
  - Emergency vehicles

C-ITS packets are transmitted on **5.9 GHz**. The packets are unencrypted, but they can be signed.

An overview of which vehicles and infrastructure actually send C-ITS: [[en:c-its:senders|Who is sending C-ITS?]]


===== C-ITS Messages =====
Various types of messages are sent via C-ITS.

The most important ones are: \\
| Message Type | Meaning |
| **[[en:c-its:messages:cam|CAM]]** | Cooperative Awareness Message: periodic status message sent by vehicles |
| **[[en:c-its:messages:denm|DENM]]** | Warning about exceptional situations, e.g. roadworks, traffic jams, stationary vehicles |
| **[[en:c-its:messages:mapem|MAPEM]]** | Description of intersections, lane geometry |
| **[[en:c-its:messages:spatem|SPATEM]]** | Signal states and timings of traffic lights |
| **[[en:c-its:messages:ivim|IVIM]]** | Road signs, infrastructure information |