Functional requirements are a description of WHAT the system has to do. In the architecture, functions are defined at several different levels. Each inventory element is mapped to one or more subsystems and terminators from the National ITS Architecture. The general descriptions associated with these entities identify functionality in a very general sense. At the next level of detail, most of the ITS elements have been mapped to one or more "Functional Areas" that provide additional functional detail. At the most detailed level, each functional area includes several specific Functional Requirements that precisely specify the functions to be performed. All three levels of detail are available on this web site. The subsystems and functional areas that are associated with the regional ITS architecture are listed in the table below. Each table entry is a link to more detailed descriptions and functional requirements.