History
Many commercial aircraft use the ARINC 429 standard buses. This standard was developed in 1977 and is widely used today, has proven to be highly reliable in safety critical applications. This data bus topology can be found on a variety of aircraft from Boeing, Airbus and Bombardier CSeries, including the B737, B747, B757, B767, Airbus A330, A340, A380 and the upcoming A350, Bombardier CSeries CS100 and CS300. ARINC 429 utilizes a unidirectional bus with a single transmitter and up to twenty receivers. A data word consists of 32 bits communicated over a twisted pair cable using the Bipolar Return-to-Zero Modulation. There are two speeds of transmission: high speed operates at 100 kbit/s and low speed operates at 12.5 kbit/s. ARINC 429 operates in such a way that its single transmitter communicates in a point-to-point connection, thus requiring a significant amount of wiring which amounts to added weight.
Another standard, ARINC 629, introduced by Boeing for the 777 provides increased data speeds of up to 2 Mbit/s and allowing a maximum of 120 data terminals. This ADN operates without the use of a bus controller thereby increasing the reliability of the network architecture. The draw back of this system is that it requires custom hardware which can add significant cost to the aircraft. Because of this, other manufactures did not openly accept the ARINC 629 standard.
AFDX is a next-generation aircraft data network (ADN). It is based upon IEEE 802.3 Ethernet and utilizes commercial off-the-shelf hardware thereby reducing costs and development time. AFDX is one implementation of deterministic Ethernet defined by ARINC Specification 664 Part 7. AFDX was developed by Airbus Industries for the A380, initially to address real-time issues for flight-by-wire system development. A similar implementation of deterministic Ethernet is used on the Boeing 787 Dreamliner. AFDX bridges the gap on reliability of guaranteed bandwidth from the original ARINC 664 standard. It utilizes a cascaded star topology network, where each switch can be bridged together to other switches on the network. By utilizing this form of network structure, AFDX is able to significantly reduce wire runs thus reducing overall aircraft weight. Additionally, AFDX provides dual link redundancy and Quality of Service (QoS).
Read more about this topic: Avionics Full-Duplex Switched Ethernet
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