GPS Public Interface Control Documents Overview GPS consists of three segments; the Space Segment, Control Segment, and User Segment, commonly known as User Equipment. The communication boundaries that exist between the GPS and other systems, as well as within the GPS itself, are known as interfaces. Interface Control Documents Interfaces are documented in Interface Control Documents. These documents are the formal means of establishing, defining, and controlling interfaces and for documenting detailed interface design definition for the GPS program. For each interface, an ICD typically exists between configuration items to establish and specify interface definition and design. CIs are the contractual responsibility of development, production, and sustainment contractors. These contractors are under the management of their respective government agency program offices. Interface Specifications are specific types of ICDs. ISs specify a single government office or agency as the only necessary and required approval authority for the document. However, the procedure and the process for development, control and maintenance is the same for both ICDs and ISs. Interface Control Working Group The Interface Control Working Group is a specialized technical working group comprised of appropriate technical representatives from the interfacing activities and other interested participating organizations. The ICWG serves as a forum to develop and provide interface requirements as well as focus on interface detail definition and issues. ICWG members include representatives from the GPS Directorate, other government agencies and offices, contractors, and other industry organizations. ICWGS for documents that are publicly releasable are referred to as Public ICWGs. Public ICWGs have additional requirements for coordinating meetings and documents with the public, and anyone with a vested interest in the issues being discussed may participate. The detailed description and requirements of ICWGs are provided in the GPS ICWG Charter.