Instruments in an aircraft typically communicate over an ARINC 429 data bus that uses simplex communication, supports data rates up to 100 kbps, and can transmit 23 bits of data with each message. If two instruments need to send data back and forth, then two ARINC 429 buses must be used. As a result, adding more devices that must communicate with each other quickly increases the number of necessary buses, and because of the low data-transfer rate, the amount of real-time data using this approach has to be kept to a minimum.
With the adoption of the AFDX (avionics full-duplex switched Ethernet) standard network, all devices can communicate on a single bus at much higher data rates (1000 times higher with the use of 100-Mbps Ethernet). This allows for much greater versatility and higher data throughput, so devices can communicate in real time. For the system designer, however, it introduces another set of challenges, since communications become time-division multiplexed and timing must be controlled.
The added complexity also creates a greater possibility for system-level problems, and the architecture of the bus, which includes multiple links and systems, makes it difficult to troubleshoot an issue. There is no simple method for monitoring all the data traffic, since multiple data paths are possible. This has led test companies to develop innovative tools for addressing AFDX test.
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