Purpose: The purpose of this document is to provide the framework for developing a compilation of requirements for an airplane-wide avionics network. This document is intended to provide system-level considerations for the development of such a network. The avionics network may include a mix of standard data buses and private data buses.

This document is written for the "avionics network developer" involved with the systems engineering process and the selection of existing data standards and protocols for use in an airborne environment. It presumes that existing standards such as ARINC Specification 429 and ARINC Specification 629 will be considered in the network definition.

This document applies to the digital data communication between identifiable sources and sinks that include, but are not limited to Line Replaceable Units (LRUs), Line Replaceable Modules (LRMs), and Integrated Modular Avionics (IMA) cabinets on a single airplane. Other resources such as power distribution, cooling, mechanical support are outside the scope of this document. However, this document may affect the definition of those resources.

This document represents a top-down approach for the selection of data bus and protocol standards applied to an avionics network. As a secondary role, this document is expected to be useful in the development of AEEC standards for data communication. This includes data bus standards, protocol standards and, where applicable, network standards. It establishes the criteria for selecting proven data communication standards used elsewhere in the electronics industry that meet the expectations of airline users. Depending on the type of avionics application, the resulting network may fully or only partially refer to existing data communication standards and protocol definitions. These standards describe the physical layer, data link layer and the appropriate elements of the network layer of the Open Systems Interconnect (OSI) reference model published by the International Organization for Standardization (ISO).

For instance, for deterministic flight critical data transfers, a communication stack that is less complex than the OSI stack may be preferred, and a specific upper layer protocol may be developed. Where compatibility with the OSI standards is needed (i.e., for air to ground communications) the full OSI stack may be used. Both approaches could be implemented at the same time on a given network, different stacks would be used for different types of exchanges.

The functions to be performed by upper layers of the OSI reference model are defined in ARINC Specification 638, "OSI Upper Layer Specification." ARINC Specification 638 refers to numerous ISO documents that pertain to the OSI reference model.