**3. Wireless technologies**

The wireless technologies used for the continuous communication among different vehicles and between vehicles and the road infrastructure are the cornerstone of co-operative systems. These technologies concern the *networking & transport* and *access* layers of the reference protocol stack of an ITS station (Figure 3) and can be divided into two main categories: general and vehicular specific communication technologies.

Therefore, for the connection among vehicles and the road infrastructure a mixture of general and vehicular specific technologies is needed. Some of these technologies are already in use, while some others are still under development.
