Communications Layer*
The National ITS Architecture provides the framework that ties the transportation and telecommunication worlds together to enable the development and effective implementation of the broad range of ITS User Services. There are multiple communications options available to the system designer. The flexibility in choosing among various options allows each implementer the ability to select the specific technology that meets the local, regional, or national needs. The Communications Layer of the Physical Architecture identifies four major types of communication to support the communications requirements among the 22 subsystems, and between the subsystems and terminators. These are fixed-point - fixed-point, wide area wireless, field - vehicle, and vehicle - vehicle communications. The four communication types are shown as ovals on the Subsystem Diagram. A short description of these four types of communications is given below:
Field - Vehicle Communications
A wireless communications channel used for broadcast and interactive close-proximity communications between vehicles and the immediate infrastructure. It supports location-specific and situation relevant communications for ITS capabilities such as toll collection, transit vehicle management, driver information, and automated commercial vehicle operations as well as connected vehicle applications. This communication channel is supported by technologies such as 5.9 GHz Band Wireless Access in Vehicular Environments (WAVE) / Dedicated Short Range Communications (DSRC), Wi-Fi, WiMAX, and wireless mesh networks.
Fixed Point - Fixed Point Communications
A communications link that provides communications among stationary entities. It may be implemented using a variety of public or private communication networks and technologies. These links support a variety of maintenance, monitoring and management services. It can include, but is not limited to, twisted pair, coaxial cable, fiber optic, microwave relay networks, spread spectrum, etc.
Since the transportation layer defines all information flow as point-to-point transfers between source and destination entities, the architecture appears to recommend a point-to-point network topology. This is not the case. Any physical network topology (including all three provided examples) that can support the identified information transfers is consistent with the communications layer and the National ITS Architecture.
Vehicle - Vehicle Communications
A short range wireless communications link among vehicles (e.g. mobile system to mobile systems). Advanced vehicle services may use this link in the future to support advanced collision avoidance implementations, road condition information sharing, and active coordination between advanced vehicle control systems. Technologies that could support this communications channel include 5.9 GHz Band Wireless Access in Vehicular Environments (WAVE) / Dedicated Short Range Communications (DSRC).
Wide Area Wireless (Mobile) Communications
A wireless communications system that offers broad coverage, enabling communications with vehicles and traveler mobile devices at any location on or off the road network. Both broadcast (one-way) and interactive (two-way) communications services are grouped into wide-area wireless communications in the National ITS Architecture. These links support a range of services in the National ITS Architecture including real-time traveler information and various forms of fleet communications. Technologies supporting this type of link include cellular networks, WiMAX, wireless mesh networks, and any other wireless network technology that offers broad regional coverage.
These four communication interconnect types are a subset of all the possible Architecture Interconnect types described in the National ITS Architecture. Each Physical Architecture Diagram (found by selecting a Physical Entity) identifies the types of interconnects for architecture flows going to or from the entity. For a complete list of possible interconnects select Architecture Interconnects.
