Overview

The Aviation Satellite Communication System (satcom) is a worldwide mobile communications system providing voice and data communications services between aircraft subnetworks and ground subnetworks.

The satellite network, in conjunction with avionics implemented in accordance with this document, provides air-ground packet-switched data services and voice communications using conventions and capabilities which are standardized worldwide. The use of circuit-switched channels for data and facsimile services is also possible.

The goal of satcom is to provide the civil aviation community with worldwide, highquality safety and non-safety communications services. It is intended to accommodate Air Traffic Services (ATS), Airline Operational Control (AOC), Airline Administrative Communications (AAC), and Airline Passenger Communications (APC). These four categories are recognized by the International Civil Aviation Organization (ICAO) and the International Telecommunications Union (ITU) which have assigned them priorities for communications purposes (Radio Regulation Article S44 and ICAO Annex 10, Volume II, 5.1.8). The system is to be designed to ensure that aeronautical communications for safety and regularity of flight are not delayed by the transmission and reception of other types of messages.

The satcom architecture defines system characteristics to assure a worldwide level of communications interoperability. Satcom is to be compatible and interoperable with external systems. This presumes the implementation of well-defined gateways and peer-to-peer protocols. Routing and addressing schemes used are to be compatible worldwide. The ICAO 24-bit aircraft address is to be used throughout satcom to ensure compatibility between organizations and systems.

For packet-mode data services, two modes of operation are permitted. These modes are referred to as Data-2 and Data-3 to be consistent with industry standards. Data-2 operation does not include subnetwork layer protocol functions. User data packets are transparently enveloped with a two-octet header and use the RLS link layer services directly. Data-3 operation supports a Switched Virtual Circuit (SVC) subnetwork layer service which operates over the RLS link layer service.

Interoperability has been accomplished by applying the International Standards Organization's (ISO) Open Systems Interconnection (OSI) Basic Reference Model (ISO 7498). Satcom data services are expected to conform, in the future, with guidelines for the Aeronautical Telecommunications Network (ATN) currently being developed.

For circuit-mode services, interoperability has been accomplished through the use of layered design techniques in accordance with International Telecommunication Union Telecommunication Standardization Sector (ITU-T) design principles.