ATM Modernization, Business & GA, Commercial, Military

Product Focus: Data Communications: Pumping the Bus

By Charlotte Adams | December 1, 2003
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Network-centric warfare applications and integrated architectures are driving the military toward higher-bandwidth onboard interconnects. At the low end, in the Mil-Std-1553 domain, engineers are trying to pump the 1-megabit/sec (Mbit/sec) bus as high as 200 Mbits/sec. At the high end, Fibre Channel and Ethernet data network architectures have emerged. Both commercial standards have been adapted to avionics environments.

There is a great desire to make 1553 run faster in order to use bandwidth-hungry, network-centric applications in aging aircraft. And evolving architectures are creating a need for high-speed networks. In some integrated architectures the "smarts" are being moved out of the sensors and the mission computer is vastly expanding its scope. Moving sensor data back to the core processor requires huge "pipes."

The Society of Automotive Engineers (SAE), which maintains Mil-Std-1553, is finalizing standardization of a 10-Mbit/sec version and is engaged in other efforts, including: High-Speed Mil-Std-1760, for the aircraft/weapon interface; Mil-Std-1394b, a military version of Firewire; and Enhanced Performance 1553.

"We’re not changing the [IEEE] spec," says George Sponsler, SAE’s Avionics Network Subcommittee chairman and Excaliber Systems vice president. "We’re just seeing what we have to do to make it as deterministic and robust as 1553." He expects a draft spec in about six months.

Excalibur plans to have a Mil-Std-1394b test and simulation module by next April in the Magic 4000 line, with Fibre Channel and Gigabit Ethernet products to follow.

SAE also is looking for a protocol to support 100-Mbit/sec data rates through the 1760 connector, Sponsler says. Gigabit Ethernet and Mil-Std-1394b are candidates.

Why such high bandwidth to talk to weapons? An application that could reprogram aircraft weapons in real time via satellite link to hit targets of opportunity is a case in point, he says. A faster bus than 1553 would be needed to download a weapon’s flight operational profile (flight plan) from the aircraft to the weapon in time to hit a pop-up target.

Accelerating 1553

The most ambitious attempt to speed the 1553 bus involves a 200-Mbit/sec-and-higher "Extended 1553" (EB-1553B) capability that would ride on existing cabling. The U.S. Air Force contacted SAE in the past for ideas on how to jump start the bus. The standards body came up with two 200-Mbit/sec systems, "but EMI [electromagnetic interference] killed both of them," Sponsler recalls.

The challenge was taken up by Canadian real-time bus specialist, Edgewater Computer Systems, which has invested "many millions" of its own money in the project, says Edgewater president, Duane Anderson. Edgewater also received Open Systems Joint Task Force FY2001 funding through an Air Force Research Laboratory (AFRL) project. The company aims at backward-compatible technology with a 200-Mbit/sec effective throughput and a bit error rate of 10-12 under Mil-Std-461E testing requirements.

In June Edgewater won a 50/50 cost-shared contract to develop such a technology under AFRL’s Dual Use Science and Technology (DUST) program. While 200 Mbits/sec may sound slow against demands for scores of gigabits, data compression of 20:1 and careful system design could narrow the difference. Edgewater also expects to produce a draft standard document by the end of next year.

The Aeronautical Systems Center’s (ASC’s) Aging Aircraft Division recently hosted an EB-1553 workshop. Under DUST, the division has teamed with organizations such as the Ogden Air Logistics Center’s F-16 program office to accelerate demonstrations of high-bandwidth 1553 capabilities. Interest is keen, given that many Air Force 1553 buses are loaded from 50 to 90 percent, says Bill Wilson, an architecture technology specialist with ASC’s Engineering Directorate. The 200-Mbit/sec technology also would be a candidate for the Universal Armament Interface (UAI). If successful, EB-1553 would be published as an Air Force standard, a tri-service standard, a NATO standard, and finally as an SAE standard.

Edgewater has demonstrated technology performing at 200 Mbits/sec with the required error ratio. But questions abound: Whether the demonstration showed command/response performance; whether the 1-MHz 1553 was running simultaneously with the new technology; how heavily the bus was loaded; what the noise environment was and what susceptibility there was to the noise; and what (if any) interactions occurred between the two signals. Also unknown is what protocol "wraps" the 1553 packets and whether the encoding scheme is proprietary or standard. Additional hardware obviously will be required.

In late October SAE formed an "Enhanced Performance 1553" task group, which will examine noise, latency and other technical issues, as well as possible applications for throughputs of 200 to 500 Mbits/sec, using existing cables and couplers. The group is trying to get as much information as possible prior to the release of the draft spec and draft handbook, which SAE expects in September 2004.

Little has been said recently about the EB-1553. Edgewater is co-funding the research, making development details proprietary until a standard is published. Some potential competitors feel frustration, as they will be playing catch-up once the draft standard is issued and the technology is introduced. Edgewater, on the other hand, feels the need to protect its investment.

10-MHz 1553

National Hybrid Inc. (NHI), meanwhile, is pushing toward a 10-Mbit/sec version of 1553 designed for new installations. This higher-speed, multidrop bus will require improved cabling and terminations, as well as different transformers, transceivers and "T" connections. But it is intended to support 10 times the throughput with comparable noise performance.

The company has designed and tested 10-MHz transceiver components that provide higher-speed 1553 protocol communications over more than 300 feet, according to NHI regional sales manager, Seth Freilich. The technology would handle the Mil-Std-1553 command/response protocol, word and message length and format, mode codes, Manchester encoding, 31-remote terminal loading, and half-duplex, asynchronous, and dual-redundant operation.

The new bus is designed to eliminate the need for couplers and for the long wires that connect the couplers to line replaceable units (LRUs). These components can cause reflectance and other noise problems that prevent the bus from running faster. New dual-redundant transceivers and small transformers will be integrated into a 1-by-1-inch (2.5-by-2.5-cm) bus interface module (BIM), to be installed as part of an LRU bus interface card. The LRU then can be wired directly to the main bus cable, using a "T" connection and eliminating long stubs. Regardless of how users want to handle the bus protocol and the subsystem interface, the BIM can save customers space, weight and expense, Freilich contends.

NHI has conducted some testing at 10 MHz with up to 20 terminals at several hundred feet. The company has developed prototype BIM components and a 10-MHz encoder and decoder. It hopes to introduce the 10-MHz parts by the first or second quarter of next year.


The 10-Mbit/sec Extended Bit Rate-1553–more a network than a bus–is expected to become an official SAE standard by year-end, according to Bill Schuh, director of military avionics products for Condor Engineering and SAE’s EBR-1553 task group chairman. Designed for the Small Diameter Bomb (SDB), EBR-1553 also is a contender for the Joint Common Missile and several unmanned air vehicle (UAV) programs.

UAVs may be able to afford the technology because EBR-1553 uses off-the-shelf RS-485 transceivers, which Schuh estimates will cost $1 to $3 in thousands, compared with a "best price" of $45 apiece for conventional 1553 transceivers in similar volumes. Last summer Condor introduced intellectual property (IP) "cores"–logic blocks that are used to program programmable logic devices (PLDs) or create specialized Mil-Std-1553 and EBR-1553 chips. In September the company announced validation of its multifunction Mil-Std-1553 IP core when configured as a single remote terminal. The Mil-Std-1553 core "is like a board-level product in functionality," Schuh says. It supports a bus controller, up to 31 remote terminals, and bus monitor modes simultaneously in a single PLD.

Condor’s EBR-1553 core also implements "link mode," which the company developed to allow systems designers like Boeing to implement the miniature munitions stores interface (MMSI) without using CANbus. This frees up additional pins on the EBR-1553 connector and reduces the chip count required on the interface designs. The Condor implementation resulted from open discussions within SAE and has been added to the notes section of the draft specification, Schuh says.

Boeing, the winner of the SDB program, used Condor products in the competition phase. Although the SDB prime contractor intends to design its own flight interfaces, Condor will continue to provide test and simulation support. Data Device Corp. and Excalibur provide EBR-1553 PC/104 cards (March 2003).

Multipurpose Cards

Ballard Technology is preparing to introduce Omnibus test and simulation cards with twice the number of "cores" or protocol processing engines. Current PCI and cPCI OmniBus boards feature two cores, each of which can manage two independent, dual-redundant 1553 channels, 16 independent ARINC 429 channels or two ARINC 708 channels (weather radar interface). New VME boards–expected by year-end–will accommodate four cores, allowing as many as eight dual-redundant channels of 1553, 64 channels of 429, or eight channels of 708, as well as many combinations of these protocols.

Ballard also plans proprietary-format boards, accommodating four cores and equipped with a Universal Serial Bus (USB) connector, by early next year. The USB board will be used in the BUSBox line of portable test hardware units. An Ethernet core module is planned, as well, but its exact configuration is not available at this time.

Bus and Network Software

SBS Technologies is pushing data bus analyzer software out of the lab and into flight hardware and flight line applications. Onboard data collection software developed under the U.S. Air Force’s Universal Data Acquisition System (UDAS) program may be used for real-time, in-flight engine monitoring on military aircraft.

SBS also hopes to use the data collection software developed under UDAS as the core of a bus analysis tool for flight line technicians and system developers. Because "PASS Lite" would run on SBS’ flight cards, it could assist in hangar-level debug. The project will require a new graphical user interface (GUI).

The UDAS code was developed for the embedded Linux operating system to meet open source code requirements, but SBS has established a migration path to LynxOS, which has a Linux-compatible Unix kernel that is flight-certified, SBS says.

UK-based YED, meanwhile, is launching a benchtop, first-line 1553 data bus analyzer. The DATAIR-1500-i/DR allows users to connect to the bus and view active traffic. Weighing less than 1 pound (0.45 kg), the Windows-based unit features a four-line liquid crystal display controlled by three push-buttons. The command-and-status screen indicates the message repetition rate in milliseconds. Data can be presented in engineering units.

Excalibur plans a rugged, Compaq iPAQ-based handheld computer bus tool. Running over Windows CE, the unit will have a USB plug and a 5-gigabyte hard drive, so that aircraft 429 and 1553 bus anomalies can be stored for later analysis on Exalibur’s Exalt program.

AIM GmbH, the German bus specialist, provides a portable bus analyzer, fdXplorer, for use with the Avionics Full-Duplex Switched Ethernet (AFDX) data network. Systems based on the fdXplorer will be supplied to Airbus as standard equipment.

Basic 1553 Hardware

Products for Mil-Std-1553 continue to evolve. Consider the following:

  • AIM GmbH has introduced a rugged-connector 1553 PCMCIA test and simulation card that dissipates 3 watts.

  • NHI has Mil-Std-1553/1760 156xx terminals that connect directly to a 32-bit PCI bus, using an internal PCI bridge. New 2-MHz 157xx terminals allow 1-MHz and 2-MHz operation simultaneously on a legacy 1553 bus.

  • Excalibur is introducing a conduction-cooled PC/104 card enclosure, including a processor and power supply.

  • Radstone Technology has refreshed its 1553 PMC line. The PMC1553E, a single- or dual-channel mezzanine, adds 66-MHz PCI bridging.

  • Dy 4 Systems single-board computer, the DMV-182, features two, dual-redundant 1553 channels on the base card. The addition of two PMCs adds four more channels.

  • The 1553 Bus Exchange Switch by Data Bus Products now includes an Internet Protocol (IP) address, allowing engineers to remotely access the switch when it is hooked to an organization’s intranet. LRUs can be added to or extracted from the bus from another site.

  • BCF Designs’ 1553 harness testers now support the U.S. C-130J program and the C-5 avionics modernization program. The tester also has been selected for the F-22 Raptor and the Eurofighter Typhoon platforms.

Future of Ethernet

Ethernet has a bright future in avionics. A version of Ethernet 10/100BaseT, known as AFDX–Avionics Full Duplex Switched Ethernet–will serve as the avionics backbone on the Airbus 380. (AFDX is an Airbus implementation of the emerging ARINC 664 data networks standard.) Gigabit Ethernet is the chosen standard for the U.S. Army’s Future Combat System (FCS), which ranges from large combat vehicles to tube-launched, unmanned air vehicles (UAVs).

Rockwell Collins provides AFDX switches and end systems for the A380 and, with partner General Dynamics, will develop a scalable architecture for FCS, based on Gigabit Ethernet. Collins also is using Ethernet 10/100BaseT–in a non-AFDX, ARINC 664 implementation–to modernize U.S. Air Force KC-135s and U.S. Army Special Operations MH-60, MH-47 and AH/MH-6 helicopters.

Traditionally Ethernet faced challenges because it doesn’t support attributes needed in an avionics environment. ARINC 664, however, takes the IEEE 802.3 standard and "profiles" it, "subtracting" non-avionics-quality services and adding new features such as bounded latency and guaranteed bandwidth. Collins says the ARINC 664-based technology that the company uses in its military applications maintains interoperability with most commercial Ethernet equipment.

At the same time, commercial users in the telecom and banking industries are demanding low-latency, predictable performance, motivating commercial suppliers of Ethernet products to provide quality-of-service (QOS) features in their hardware. Because of such improvements, Collins plans to use IEEE 802.3-compliant, commercial off-the-shelf (COTS) solutions in FCS.

Avionics Ethernet

In "full duplex, switched Ethernet" ARINC 664 implementations, such as Collins deploys, the network allows simultaneous receive and transmit communications at each node via switches. According to Rich Eisenhart, director of engineering for Rockwell Collins Government Systems, this approach "completely avoids" traditional Ethernet "collisions." (In a collision, transmissions, like people in a crowded hall, collide with each other and take more time than planned to reach their destinations.) This unpredictability of arrival time is to be avoided in safety critical avionics.

Airborne Ethernet networks provide predictable performance. Collins has certified an Ethernet architecture on KC-135s and on Army helicopters. "We’ve proved avionics-quality Ethernet networks can be created that maintain high data throughput while achieving deterministic performance," says Eisenhart. In flight critical applications, the company has demonstrated "bounded latency, determinism and guaranteed availability" to the customer.

Making Ethernet do avionics jobs exacts a performance penalty. Current implementations of 100-Mbit/sec systems yield an effective throughput of about 80 Mbits/sec per node. But a 100-Mbit/sec, ARINC 664-compliant system loaded to 40 or 50 percent of capacity is still much faster than ARINC 629 and Mil-Std-1553. The 100BaseT Ethernet standard also would permit a much larger number of nodes. And, unlike 1553 or ARINC 629, total system bandwidth increases by 100 Mbits/sec for each added node. As the military transitions to Gigabit Ethernet, work required to maintain determinism will be fairly constant, predicts Steve Tyson, Collins Government Systems’ principal systems engineer for integrated applications. "We’re also trying to improve throughput all the time by going to better TCP/IP offload engine coprocessors and utilizing improvements in the commercial standards," he says. (TCP/IP stands for transmission control protocol/Internet protocol.) Driven by commercial investment, Ethernet technology has advanced more rapidly than Fibre Channel, for example, and Ethernet switches are less costly. In the commercial world, thanks to the Internet, Ethernet is the medium and standard over which most IP-based data is being transmitted. And the military is evolving toward an IP-based, network-centric system, Eisenhart asserts.

COTS Migration Path

Collins Government Systems sees a migration path to "straight-up COTS implementations" of Gigabit Ethernet for some types of avionics systems. The company is conducting studies "to show how far up on the safety-criticality levels we will be able to utilize a pure COTS implementation of Gigabit Ethernet," Eisenhart says. "We recognize we will not get to a [DO-178B], Level A, certification," so flight control applications won’t be using COTS Gigabit Ethernet.

But, based on technical studies, "we believe that a pure COTS solution for Gigabit Ethernet will be able to support Level C criticality," he adds. Level C is associated with avionics such as mission computing and flight management systems (FMS). COTS Gigabit Ethernet will be able to get to Level C certification because of the "huge bandwidth and quality of service features being implemented in COTS products," Tyson says. Ethernet will get to Level A, adds Tyson, but "that’s when you have to employ ARINC 664 and profile [it]."

Fibre Channel

Fibre Channel, a 2-Gbit/sec interconnection technology, is used as the avionics backbone on the F-35 Joint Strike Fighter, providing communications between the integrated core processor and the sensors, com/nav/identification (CNI) system, and the displays. JSF uses the Fibre Channel-Avionics Environment anonymous subscriber messaging protocol (FC-AE- ASM) and both point-to-point and switched fabric topologies. Fibre Channel also will be retrofitted to legacy aircraft.

Data Device Corp.’s new FibreAccess series of network interface controllers (NICs) supports the FC-AE-1553 protocol, which allows Fibre Channel networks to pull information from 1553. Because the two communications systems can share data, customers can preserve their investment in legacy system software, legacy 1553 buses and boxes, while adding Fibre Channel networks with higher data rates and vastly increased size. FibreAccess also supports FC-AE-ASM.

Built in a conduction-cooled PCI mezzanine card (PMC) format, the FC-75000 series supports the use of copper or fiber media. DDC stresses having used its own intellectual property to develop FibreAccess technology. This, asserts the company, allows products to be supported through long military life cycles. The cards can be used with point-to-point, arbitrated loop and switched fabric implementations.

AIM’s Test Card

AIM-USA, meanwhile, has developed a Fibre Channel test and simulation card with IRIG-B timing and three levels of error injection. The APG-FC2 also allows "snooping" of network traffic, to look for specific messages and events, with triggers for parameters of snooped data. This allows engineers to make real-time decisions on the data and generate data based on those decisions, the company says.

AIM will offer the card initially as a PCI module, which will ship in January 2004 to the Joint Strike Fighter program. The unit supports FC-AE-1553 and FC-AE-ASM. fcXplorer, a Windows-based user interface, will allow customers to set up monitoring and simulation features.

Sanmina-SCI also offers a PC/104 test card that is FC-AE-1553-compliant.


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