Protocol Analysis

Protocol Analysis

ARINC 818 (also referred to as the Avionics Digital Video Bus (ADVB)) is a protocol that was created for video services in mission critical avionics. ARINC 818 was developed for video that has high bandwidth and low latency. The ARINC 818 White Paper lists a variety of functions where it would be utilized that include, “…infrared and other wave length sensors, optical cameras, radar, flight recorders, map/chart systems, synthetic vision, image fusion systems, heads-up displays and heads-down multifunction displays, video concentrators, ….taxi and take-off assist, cargo loading, navigation, target tracking, collision avoidance, and other critical functions.”

Why?

One of the main problems the protocol was designed to solve was standardizing high speed video systems. Prior to ARINC 818, the Fiber Channel Audio Video (FC-AV) was being used. However, each use of FC-AV was unique to the specific project. Standardization would allow for significant cost savings, and enable different programs to cooperate, applying lessons learned across a variety of platforms.

Another problem ARINC 818 gave priority to was the ever-present aviation concern regarding weight. A calculation featured in the professional publication Military Embedded Systems illustrates the weight reduction that can be expected using this protocol. Assuming that three sets of twisted, shielded cable will be run for command and control signals, and three sets of coax cable will be run to carry video signals (using a 15-meter distance between the sensor and the image processor), ARINC yielded a 62 percent savings in weight from the previous protocol. The formula used included the following specifications: aerospace-grade coax cable weighing 15 g/m, aerospace-grade twisted, shield cable weighing 20 g/m, a sensor interface box weighing 380 grams, and dual-fiber cable weighing 15 g/m.

Latency was also of primary importance in this standard’s design. While the delay from original input to required outcome is important in any high tempo environment, it is of particular concern in aerospace operations. Any gap between the heads-up display (HUD) and the background seen through the cockpit can cause motion sickness and/or vertigo.

Standard Authority

The ARINC Digital Video Committee includes many aircraft manufacturers and avionics developers, including Airbus, Boeing, Honeywell and Lockheed Martin. ARINC stands for Aeronautical Radio, Inc. They were a transportation communications company headquarted in Annapolis, MD that had been in business since 1929, but were acquired by Rockwell Collins in 2013. Although not part of their commercial division, ARINC had developed a reputation for developing standards through three separate committees. ARINC 818 was created by one of these groups, the Airlines Electronic Engineering Committee (AEEC).

As part of the Rockwell Collins’ acquisition, the AEEC was transferred to a non-profit called SAE International Industry Technology Consortia (SAE ITC). This consortia is part of SAE, a global professional organization for engineers. Originally named the Society of Automotive Engineers (SAE), they have since changed their original mission to include representing professionals who work with any type of self-propelled vehicles. SAE International also has a history of creating standards within their areas of expertise.

How?

The payload for ARINC 818 contains either video or video parameters. This payload is encapsulated in packets which have frames that are specified as “ADVB frames.” The maximum payload size is 2,112 bytes. A container is a set of ADVB frames. Four types of objects are defined within a container. These are either video (interlaced odd or even), audio, or ancillary. Odd or even designations allow the video to be sequenced.

ARINC 818 is a point-to-point protocol, so it transports the data in a direct connection between two nodes. Multiple video streams can travel on a single link or a single data stream can move over a dual link. Multiple video streams on a single link allow for sensor fusion. When a video line of data exceeds the maximum payload size, each line is divided into two frames.

Interested Parties

Ideally, protocols do not favor one group or company over another, but are simply put in place to develop best practices. However, any technology standard results in a greater number of purchases being made in one direction or another. At a certain tipping point, people will need to adopt the standard to maintain compliance with the majority.

In the case of ARINC 818, there are several competing standards including National Semiconductor’s Channel Link (Channel Link) and Avionics Full-Duplex Switched Ethernet (AFDX). The main drawback of Channel Link is that it is not compliant with Design Assurance Guidance for Airborne Electronic Hardware (DO-254), a document used by the Federal Aviation Association (FAA) to assess airborne electronic system design. AFDX does not provide the resolution or bandwidth needs that are necessary for modern avionic video.

The creation and evolution of ARINC 818 was originally driven by the industry giants, Airbus and Boeing. They wanted to consolidate several proprietary standards for two programs; the 787 airliner and A400M military transport aircraft. Honeywell, Rockwell Collins, and Thales were all using differing standards in their display manufacturing at the time. The ARINC Digital Video Subcommittee took these proprietary standards, and began to consolidate and enhance them in 2005, leading to ARINC 818’s ratification by 29 companies in 2006.

Present and Future

Cockpit displays in a range of aircraft are using ARINC 818. These include the Boeing 787, and Airbus A350 airliners, the A400M and C-17 military transports, the C-130 military transport Avionics Modernization Program (AMP), and the F-15 and F-18 combat jet upgrades. Many smaller vendors utilize the standard as well, such as France’s TechwaY and America’s EDF.

Since it’s original inception in 2006, ARINC 818 has evolved into a second version that was reviewed in 2013. ARINC 818-2 (Supplement 2) has many changes, including the addition of compression, encryption, data-only links, and video control parameters. Supplement 2 was officially ratified in December 2013.

Originally, ARINC 818 focused only on uncompressed video and audio. It uses Object Class Types from the Fiber Channel Audio Video Specification that the first committee drew from. These have been updated to select either compressed or uncompressed video and audio. Additionally, class types were added to allow for encrypted or unencrypted data.

Supplement 2 added data-only links to its specifications. ARINC 818 often pushes the details of a requirement back to the interface control document (ICD) of whatever system or subsystem is being connected. For example, in the case of data-only links, the object types specify a standard link rate. This link rate may be used, or the link rate from the pertinent ICD may be selected in its stead.

Several control parameters have been added to allow for tiling, and vertical and horizontal banding. Tiling allows for multiple screens to be shown, and one image to be inset within another. For example, a video feed from beneath the airplane could be inset against a forward facing camera. Vertical and horizontal banding can be used in combination to focus on a region-of-interest.

Conclusion

Ongoing worldwide conflicts and the reluctance of the major powers to commit ground troops virtually guarantee increased funding for military avionics development. Given the rapid pace of that development, it is unlikely that manufacturers will experiment with new standards, preferring to use those that are reliable. Since the major aerospace companies pursue both military and civilian contracts, any standards used in military programs may also find increasing influence in civilian programs. ARINC 818 will probably continue to be used in both sectors.