By John McHale
SANTA BARBARA, Calif. - An Ethernet-based technology called AFDX, for Avionics Full-DupleX, is speeding up communications aboard Boeing’s next-generation aircraft, the 787 Dreamliner.
Engineers at Condor Engineering in Santa Barbara, Calif., recently won the bid to support Rockwell Collins in Cedar Rapids, Iowa, in deployment of the 787 Avionics System.
The AFDX device is the CNIC (Condor Network Internet Card). It will be the communications medium for the avionics of the 787, says John Bruno, director of advanced network technology at Condor.
Boeing will use the ARINC 664, Part 7 version of AFDX-which uses fiber optics rather than copper interconnections-in their 787, expected to make its first flight in 2007 and begin service in 2008.
AFDX, developed by Airbus engineers for the A380, “is a standard that defines the electrical and protocol specifications, (IEEE 802.3 and ARINC 664, Part 7) for the exchange of data between avionics subsystems,” Bruno says. “One thousand times faster than its predecessor, ARINC 429; it builds upon the original AFDX concepts introduced by Airbus.
On the other side of the Atlantic, “AFDX will literally take off on board the Airbus A380 when this passenger transport takes its inaugural flight in the first part of this year,” says Jean-Paul Moreaux of Airbus, one of the architects of AFDX. “It is expected that the Airbus A380 will begin service in 2006. AFDX will also be employed for data transmission in the Airbus military transport, the A400M, which will roll out two to four years from now.”
“It is very likely that both AFDX, and its variant ARINC Specification 664, Part 7, will also supplant earlier communications protocols in major airframe retrofits,” Bruno says. This will bring higher speed and greater reliability to aircraft that are in service today.
“One of the reasons that AFDX is such an attractive technology is that it is based upon Ethernet, a mature technology that has been continually enhanced, ever since its inception in 1972,” Bruno explains. “In fact, the investment in Ethernet has been huge compared say, with investment in the development of ARINC 429, MIL-STD-1553, and other data-communications architectures.”
The obvious advantage of AFDX over ARINC 429 is improved speed of more than 100 megabits per second, Bruno says.Ethernet also offers a tremendous advantage for test and simulation applications because standard parts are available right off the shelf, Bruno says.
While it is clear cost reduction is realized in labs and in simulation, when AFDX is airborne it is tougher to gauge because of all the requirements for things like shock and vibration and other environmental concerns, Bruno says.
AFDX makeup
An AFDX system comprises three main components: the avionics subsystems, the AFDX end systems, and the AFDX interconnect. The avionics subsystems are traditional avionics subsystems on board an aircraft, such as the flight-control computer, global-positioning system, tire-pressure monitoring system.
“The AFDX end systems are embedded in each avionics subsystem that connects to the network,” Bruno says. “Their main function is to guarantee a secure and reliable data interchange with the application software. This interface exports an application program interface (API) to the various avionics subsystems, enabling them to communicate with each other through a simple message interface. Each AFDX end system provides an interface between the avionics subsystem and the AFDX interconnect.
The third major component, the AFDX Interconnect, is based upon Ethernet technology. “It is a full-duplex, switched interface that is a departure from the traditional ARINC 429 point-to-point technology and MIL-STD-1553 bus technology.”
The “half duplex” was the cornerstone transmission characteristic of Ethernet, Bruno says. A half-duplex is “a bus structure in which packet transmission takes place in both directions on a single twisted-pair-requiring a contention strategy so that only one packet is sent at any instant, Bruno says. Whereas a full-duplex adds a second twisted-pair so that transmit and receive lines for any interconnection are independent, and therefore, packets flow in only one direction on each pair and can never collide with packets coming in the opposite direction, he continues.
Fewer wires, lower weight
AFDX delivers some additional benefits, compared to ARINC 429.
“In ARINC 429, a twisted pair must link every device, which is to receive the azimuth signal from the inertial platform,” Bruno says. “The point-to-multi-point property of ARINC 429 means that the avionics system must include an ARINC 429 bus for each communication path. In a system with many end points, point-to-point wiring is a major overhead, which can lead to some pretty huge wiring harnesses, with the added weight that goes along with it.
“But in the case of AFDX, each signal is connected to the switch only once so that no matter how many subsystems require the azimuth signal from the inertial platform, they need not be connected individually to the inertial platform,” he continues. “Also in the case of ARINC 429, a transmitter can fan out to only 20 receivers. Whereas in the case of AFDX the number of fan-outs from the inertial platform is limited only by the number of ports on the switch-which can be an arbitrarily large number.”
Condor’s Dual-Port ARINC 664 card supports full throughput simultaneously on all channels. Its two independent full-bandwidth ports can be employed for traffic monitoring, traffic generation, external triggering, and analysis, Condor officials say. The card also offers high-resolution time tagging of incoming Ethernet packets-as well as accurate traffic generation. An IRIG-B receiver/generator is included for synchronization to an external IRIG-B time source and for synchronization between multiple network interface cards. Advanced AFDX traffic generation and end system libraries are included. The end system library implements the complete AFDX protocol stack, and uses an XML-based configuration file approach for specifying an AFDX network, company officials say.
For more information, visit www.condoreng.com.
