CANaerospace

CANaerospace is a higher layer protocol based on Controller Area Network (CAN) which has been developed by Stock Flight Systems in 1998 for aeronautical applications.

A major research aircraft that employs several CANaerospace networks for real-time computer interconnection is the Stratospheric Observatory for Infrared Astronomy (SOFIA), a Boeing 747SP with a 2.5m astronomic telescope.

The CANaerospace interface definition closes the gap between the ISO/OSI layer 1 and 2 CAN protocol (which is implemented in the CAN controller itself) and the specific requirements of distributed systems in aircraft.

The bit timing calculation (baud rate accuracy, sample point definition) and robustness to electromagnetic interference are given special emphasis.

The Bosch CAN specification itself allows messages being transmitted both periodically and aperiodically but does not cover issues like data representation, node addressing or connection-oriented protocols.

The communication channels are therefore arranged according to their relative importance: The majority of the real-time control systems used in aeronautics employ "big endian" processor architectures.

With big endian data representation, the most significant bit of any datum is arranged leftmost and transmitted first on CANaerospace as shown in Figure 2.

The mandatory "Node Identification Service" which each CANaerospace LRU has to respond to allows to scan the network for attached LRUs and their identifier assignment list code to avoid inconsistencies.

An essential characteristic of all flight safety critical systems is that their behavior has to be precisely defined, analyzed and tested to meet formal certification requirements.

The ultimate target to be reached, however, is that it may be demonstrated to certification authorities (i.e. FAA, EASA) that a safety critical system behaves predictably under foreseeable circumstances.

CANaerospace sets forth a concept of managing the available bandwidth of a multi-drop CAN network to ensure predictable behavior for ATM and PTP communication which is called Time Triggered Bus Scheduling.

While Time Triggered Bus Scheduling requires margins and does not optimize network bandwidth usage, it provides a safe and straightforward approach to build certifiable (predictable) systems.

Time Triggered Bus Scheduling ensures adequate flexibility for increasing network traffic during the lifetime of the system if growth potential is planned.