A3XX: Headlong Into Ethernet Technology

By Charlotte Adams | October 1, 2000
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When, as seems likely, Europe’s giant new A3XX airliner program is launched, it will set records in data, as well as passenger transport. Although the avionics architecture–and the data network that underpins it–have not yet been completely defined, the Airbus partners have decided to employ 100-megabits per second (Mbits/s) full duplex, switched Ethernet technology to link avionics boxes aboard the 500+ passenger airliner. The ARINC-429 databus may still be used, but the main avionics data pipe will be Ethernet, better known as a local area network (LAN) technology in the commercial world.

Ethernet is attractive in the avionics world. It promises to accommodate future systems’ bandwidth demands, increase flexibility in avionics design and procurement, and reduce aircraft wire counts, thus lowering aircraft weight and operating costs.

Invented in 1972, Ethernet is the network standard used to connect computers within countless office buildings worldwide. Since its introduction, Ethernet has become universally accepted commercially at 10- and 100-Mbits/s data rates. The technology is widely understood, and components are readily available. (Commercial components can be used on aircraft if they are properly screened and qualified.)

Ethernet is not new to the aircraft environment. Boeing pioneered 10-Mbits/s Ethernet on its B777 to transport non-flight-critical data. Rockwell Collins provides a real-time, flight-critical display system using 10-Mbits/s Ethernet on the Boeing 767-400ER (see May 2000). That system was certified by the U.S. Federal Aviation Administration (FAA) and Europe’s Joint Aviation Authority (JAA) in July.

The use of Ethernet technology translates into greater flexibility in avionics architecture design and lower aircraft construction and operational costs, proponents say. The A3XX design will greatly advance the use of Ethernet in avionics architectures. Unlike the 767-400ER, the A3XX will use Ethernet as the main avionics data backbone. The flight-critical Ethernet will connect flight management, flight warning, display and other avionics computers aboard the new aircraft, says Jean-Francois Saint-Etienne, an avionics engineer with the European Aeronautics Defense and Space Co. (EADS).

Ethernet is the baseline for communications, Saint-Etienne says. Some of the avionics processing units for the A3XX’s integrated modular avionics architecture also will be new, procured as a "standard computing resource," he adds. Participants expect a standard computing unit to process data for multiple applications.

Airbus intends to freeze the network’s definition by mid-2001, Saint-Etienne says. Airbus has been working internally and with avionics suppliers such as Honeywell, Rockwell Collins, Sextant, Smiths Industries, Teldix and BGT, to help define the overall avionics architecture. The Airbus implementation of an Ethernet-based avionics backbone on the A3XX is known as the avionics full duplex switched network, or AFDX.

A3XX will incorporate several enhancements to standard Ethernet. For example, "We have some requirements in terms of safety, segregation and partitioning that oblige us to make some modifications of the Ethernet switch," Saint-Etienne explains.

Avionics Ethernets need to do such things as guarantee and control bandwidth allocation to users on the network and ensure that the right data arrives at the right destination at the right time. And there will be "some extra electrical requirements on the cable" to support the higher frequency, he says. "We can’t just make a cut-and-paste of the IEEE [Institute of Electrical and Electronic Engineers] standards." There will also be redundant networks, Saint-Etienne says.

One attraction of 100-Mbits/s Ethernet is its ability to allow for aircraft systems’ bandwidth growth. "Next-generation ground proximity warning systems, for example, may want to combine map and air traffic data, terrain information, weather radar returns, information on man-made obstacles, and imagery on the airport environment, and fuse it into one 3-dimensional representation," says Bruce Ray, a director of advanced programs at Rockwell Collins.

Such a move could increase pilot situational awareness, but would dramatically increase display processing and data bandwidth requirements, he adds. "Avionics data is no longer just a question of airspeed, altitude and pitch," Ray continues. "It now includes the terrain of Wyoming or an approach chart for JFK [Airport in New York] or a picture of weather on the other side of the world."

Aviation is moving from low-bandwidth "data" to high-bandwidth "information," he explains. These collections of data, which will be transferred around the airplane, will be gigabytes in size. Another attraction of Ethernet, advocates say, is its promise to free avionics data transfer in integrated avionics systems from the logistical limitations of a backplane bus–the special-purpose communications bus linking computing modules inside of a physical enclosure. In the Boeing 777, for example–which pioneered integrated avionics, although not with Ethernet–computing modules are tightly integrated inside a fixed space. This restricts flexibility in placing computing resources.

"With this [Ethernet] bus, it’s as easy to talk to a module at the other end of the aircraft as it is to the one sitting next to you," says Denis Weale, technical manager in Smiths’ Future Systems Group. "You don’t have to interface to a bus on a backplane in a cabinet."

"Ethernet allows you more choice and greater flexibility in where you install boxes," Ray adds. Moreover, independence from a physical enclosure will give Airbus more flexibility in choosing avionics suppliers. "A closed rack tends to have ‘a single-point supplier.’ It’s a little bit more constrained," says Weale.

Because Ethernet is a "switched" architecture–a network rather than a point-to-point link–aircraft designers can create redundant subnetworks, Ray explains. Faults can be isolated and analyzed without impacting the system as a whole.

Moving from one-way, low-bandwidth links like ARINC-429 to a high-speed, bi-directional network like Ethernet will also "reduce considerably the number of wires on an aircraft," Saint-Etienne says. This, in turn, will reduce weight, save fuel, and simplify wiring layout, making planes easier to both build and repair, proponents say.

The Ethernet switch that routes data from box to box is the single most important item of on-board, aviation Ethernets. Although it has nothing to do with flying the airplane, the switch "enables communication and also ensures that communications are safe communications," Smiths’ Weale says.

Smiths and Rockwell Collins are potential providers of switch components, which Airbus is expected to obtain in a procurement separate from the other systems.

Generically, a switch receives data and routes it to its destination. But an avionics Ethernet switch serves as a kind of data traffic cop, regulating the concept of the network. It verifies messages’ integrity, enforces bandwidth limitations on subscriber boxes, and guarantees predictable, predetermined data flows. In short, the double-deck A3XX is expected to do more than push the passenger-bearing envelope. It is intended to accelerate in-aircraft data communications, as well.

View from Boeing

Boeing made use of Ethernet in air transport aircraft, first with the B777 and more recently with the B767-400ER. What does the trend-setter think of moving ahead to 100 Mbits/s?

"The day is coming when we’ll need to do that," says Chuck Royalty, lead engineer for network systems with the Avionics Organization of the Boeing Commercial Airplanes Group. He sees it happening first in non-safety-related areas, to support new functions for maintenance and flight crews.

"If there’s ever a need on the flight controls or display side" for 100 Mbits/s Ethernet, "we’ll have had the experience," Royalty adds. "But current avionics display and flight-control applications don’t need such high bandwidth, so my expectation would be, it’s unlikely we’ll see 100 Mbits/s Ethernet copper wiring go in unless there was some other reason." Such a reason might be cost savings.

But use of 100 Mbits/s Ethernet presents challenges, such as electromagnetic interference (EMI), he says. "Any time you put a high frequency on a wire, it radiates. Making it not radiate too much is the big problem with 100 Mbits/s."

ARINC currently is working on standards for cabling to support 100 Mbits/s speeds. Boeing officials agree that Ethernet has a lot going for it. The idea of a fixed, point-to-point bus is fading away, Royalty says.

"The idea that we ought to be able to route data wherever it’s needed without having to make major changes to the airplane is part of what’s driving the [Ethernet] network." He foresees passenger cabin applications, such as video-on-demand (VOD), or on the avionics side, the need for higher speed data transfer to the ground, driving the need for greater data transmission speed.

Boeing and other companies are working with ARINC on an airborne server specification and an aircraft data-network standard, Royalty says, adding that both specs would encompass Ethernet at 10 and 100 Mbits/s.

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