The purpose of this Reference Architecture Document (RAD) is to provide a high-level service model of the GCNet, including a description of its capabilities, and a depiction and description of its target architecture. The GCNet is broken down into its component services. The capabilities of each service will be further described in a separate Service Definition Document (SDD), and the architecture of each will be further described in a separate Technical Architecture Document (TAD), including security and privacy controls.