# BIM-Based Description of Intelligent Transportation Systems for Roads
## 2 Knowledge Sources for Semantic Modeling of ITS
### ITS Communications  
On-board communication capabilities allow ITS intelligent infrastructure to cooperatively connect to network nodes and to share resources without the need for a middleware or coordinating infrastructure, entailing cooperative ITS (C-ITS) communication [48]. Wireless communication is the cornerstone of C-ITS communication and is leveraged by scalability and easy deployment in vehicular environments. The ETSI TR 101 607 technical report lists standards, protocols, and specifications applied to C-ITS communications in Europe with respect to traffic efficiency and road safety requirements [49]. The architecture of ITS communication networks, to be reflected in the semantic model, is illustrated in Figure 3. Based on [50], ITS communication networks are in general categorized into ITS station internal networks and ITS station external networks; the latter include an ITS domain and a generic domain, as will be illuminated in the following paragraphs.  
An ITS station internal network denotes communications within one ITS station. ITS station internal networks are defined in terms of a reference architecture based on layered communication protocols consisting of applications, facilities, networking and transport, access, management, and security layers. Each layer characterizes different functionalities and protocols relevant to ITS stations. For example, the ITS-G5 protocol characterizes access layer specifications for dedicated short-range communications in the 5.9 GHz frequency band [51], and GeoNetworking is a family of networking protocols that transports data packets based on geographical positions of the network nodes [50]. Every ITS station internal network possesses physical on-board equipment and devices, such as sensors, transceivers, and mechanical and/or electrical actuators, which are characterized and presented by the proprietary network. Only an ITS station internal network can access the proprietary network of the same ITS station.  
ITS station external networks are composed of a generic domain and an ITS domain. The generic domain includes an access network to provide information to ITS users publicly, i.e., through public access networks, an access point to provide authorized closed groups of users with specific data, i.e., through private access networks, and a core network that provides access to the Internet, i.e., through core networks. In the ITS domain, the ITS ad-hoc network ensures wireless C-ITS communication between ITS stations, and the ITS access network provides direct connections between ITS station internal networks and the generic domain in ITS station external networks.  
ITS station external networks exploit ITS station internal networks for combining on-board under-utilized resources of ITS stations, for transmitting data, and eventually for performing ITS applications. Therefore, ITS station external and internal networks, representing key components of ITS communications, are of notable importance for understanding ITS operations. As a result, direct implications for ITS communications are reflected by introducing ITS station external and internal networks in the semantic model.  
Figure 3: ITS communication networks.