Cooperative Intelligent Transportation Systems (ITS) are systems where the vehicles, the roadside infrastructure, central control centers and other entities exchange information in order to achieve better road safety, traffic efficiency and comfort of the road users. This exchange of information must rely on a common communication architecture. The ITS Station reference architecture has thus been specified in ISO and ETSI. It allows vehicles and roadside ITS stations to organize themselves into Vehicular Ad-hoc Network (VANET), presumably through IPv6 GeoNetworking using IEEE802.11p and to connect seamlessly to the Internet through any available access technology. Several paths may thus be available at a given vehicle ITS station to communicate with other ITS stations. Paths are of three types: direct path, optimize path and anchor path. The objective of the study is to optimize the communication between ITS Stations by selecting the best available communication path. This requires first to gather information available locally at the ITS station (position, speed, application requirements, media characteristics, capabilities, path status, ...) and collected from neighbors ITS stations (position, speed, services, ...) and then to process this information through a decision-making algorithm. First, we define a network module allowing the combination of IPv6 together with GeoNetworking. Second, we propose a cross-layer path selection management module. Our contributions are mapped to the ITS station reference architecture by defining the relation between the ITS station network and transport layer (which hosts our IPv6 GeoNetworking contribution) and the vertical ITS station cross-layer entity (which hosts the path selection decision-making algorithm). We specify the functions allowing the exchange of parameters through the Service Access Point (SAP) between the network layer and the management entity (MN-SAP). The parameters used at the cross layer ITS station management entity are abstracted in a way so that they are agnostic to the protocols used at the ITS station network and transport layer, therefrom allowing easy replacement of protocol elements (e.g. replacing NEMO by other mobility support protocol) or permutation of the network stack (IPv6 or GeoNetworking, a combination of both or other network stack).
