**2. Architecture**

In co-operative systems the specification of a unified communication architecture plays a central role for further deployment. As a result of the deployment of co-operative systems the road users will benefit from improved safety, reduced traffic congestion, environmental friendly driving and much more. The key to achieving these benefits lies in the specification of a common and standardized communication architecture among the various components of such systems. This architecture comprises four main components which can be composed arbitrarily to form a co-operative intelligent transport system. To form such a system there is no need to have all these four components available but a subset of them is sufficient. The components can communicate with each other either directly within the same communication network or indirectly across several communication networks. These four components are depicted in Figure 2 and are briefly described in the following. For a more detailed description one can refer to (Bechler et al., 2010; ETSI, 2010).

Fig. 2. Communication Architecture Components.
