The scope of this document addresses top-level functions necessary for the delivery of AIS and MET data link services, as depicted in Figure 1-1. The functions are described in RTCA DO-308/EUROCAE ED-151, RTCA DO-324/EUROCAE ED-175, RTCA DO-339, and RTCA DO-340; however, they are further decomposed and described in Section 3.3.2 of this document.