ISSN 2319-8885 Vol.02,Issue.19, December-2013, Pages:2161-2164 www.semargroups.org, www.ijsetr.com Safety-Critical Ethernet/AFDX–Concept, Design, Implementation and Beyond 1 2 PRAJYOD KUMAR ARUDRA , ARUN KUMARI.B 1PG Scholar, Dept of CSE, MLR Institute of Technology, Dundigal, Hyderabad, AP-INDIA, E-mail: [email protected]. 2Assoc Prof, Dept of CSE, MLR Institute of Technology, Dundigal, Hyderabad, AP-INDIA, E-mail: [email protected]. Abstract: Avionic Full-Duplex Switched Ethernet” (AFDX), is a specification for a deterministic aircraft data network bus for aero-nautical, railway and military systems. The network is based on standard IEEE 802.3 Ethernet technology. The benefits from using commercial-off-the-shelf (COTS) Ethernet components include reduced overall costs, faster system development and less-costly maintenance for the system network. Hardware components, cables and test equipment for Ethernet are field proven and much more affordable than “built-to-spec” avionics solutions. Standard commercial grade Ethernet won’t meet avionics network requirements. Therefore, AFDX extends the Ethernet standard by adding Quality of Service (QoS) and deterministic behavior with a guaranteed dedicated band-width. AFDX™ is currently used in the Airbus A380 and A400M as well as in the Boeing 787 Dream liner. Keywords: Quality of Service (QoS), Commercial-Off-The-Shelf (COTS). I. HISTORY OF AVIONICS DATA BUSSES a serial data bus. It was originally designed for use with Aircraft control systems generally consist of a number military avionics, but has also become commonly used in of sensors to read environmental or inertial data, an spacecraft on-board data handling (OBDH) subsystems, avionic system performing a certain flight relevant control both military and civil. It features a dual redundant function and outputs, for instance to control actuators to balanced line physical layer, a (differential) network perform rudder or flap movements. There always has been interface, time division multiplexing, half-duplex a need to interconnect between these components and command/response protocol and up to 31 remote terminals traditionally, a set of sensors and actuators have been (devices). The communication speed rated up to 1 Mbit per connected to one avionics function. The main data busses second. All communication on the bus is initiated by the used for these purposes where ARINC-429 and MIL-STD bus controller, which polls the remote terminals to send or 1553. The following sections will give a brief overview of receive data. It was first published as a U.S. Air Force these technologies. standard in 1973, and was first used on the F-16 Fighting Falcon fighter aircraft. It is widely used now by all A. ARINC-429 branches of the U.S. military and has been adopted by ARINC-429 is a two-wire data bus that is application- NATO as STANAG 3838 AVS. specific for commercial and transport aircraft. The connection wires are twisted pairs. Words are 32 bits in C. IMA requires new communication capabilities length and most messages consist of a single data word. A number of innovations and changes are delivering The specification defines the electrical and data new capabilities to aircraft operations. Modern aircrafts are characteristics and protocols. ARINC 429 uses a equipped with numerous electronic components. Some of unidirectional data bus standard (Tx and Rx are on separate them – like flight control and guidance systems – provide ports) known as the Mark 33 Digital Information Transfer flight critical functions, while others may provide System (DITS). Messages are trans-mitted at either 12.5 or assistance services that are not critical to maintain 100 Kbit/s to other system elements that are monitoring the airworthiness, but reduce the workload of the crew. The bus messages. The transmitter is always transmitting either amount of capabilities is increasing, and so is the amount 32-bit data words or the NULL state. No more than 20 of information that needs to be processed and displayed. receivers can be connected to a single bus (wire pair). The industry more and more requires a flexible and scalable standard architecture to support the broad B. MIL-STD 1553 spectrum of capabilities and performance with MIL-STD-1553 is military standard published by the standardized interfaces to fit a wide range of aircrafts. United States Department of Defense (DoD) that defines Simultaneously a need exists to improve factors like the mechanical, electrical and functional characteristics of system dispatchability, reliability and maintainability while Copyright @ 2013 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved. PRAJYOD KUMAR ARUDRA, ARUN KUMARI.B at the same time reducing the physical dimensions of size, working group. ARINC-664 describes air-craft data weight, number of connectors, etc. To reduce lifecycle and networks (AND) and part 7 specifically deals with AFDX. construction costs, the usage of common system building blocks with high levels of reuse is aimed at. Consequently, II. FLEXIBLE NETWORK TOPOLOGY the aircraft manufacturers as well as the main function Normal Ethernet technology uses a topology where suppliers for avionic subsystems have been thinking about each node is treated equally. If a peer wants to transmit a a new architecture for avionic systems, providing a packet on the network and the media is occupied, a standardized hosting platform for avionic applications. The collision occurs, the peer backs up and tries again, until the idea of “Integrated Modular Avionic” (IMA) was born and transmission is successful, or a predefined amount of time it is quite simple: has elapsed. This behavior introduces variable length A general purpose computing platform provides the latency, which is not tolerable in safety critical computational power. applications. In order to avoid collisions on the network, a The interfaces to sensors and actuators are switched full duplex topology is introduced. The following standardized and provided on separate I/O boards. figures 1 and 2 shows the AFDX topology overview and The computing platform provides a real-time sent redundant of AFDX messages. operating sys-tem (RTOS) with a standard interface (API) to avionic applications. The IMA approach introduces a number of advantages over the traditional solutions, as resources can now be shared, computational power can be added to the system, if growth concepts requires additional performance. Standardized platform software provides standard functionality common to all subsystems, like maintenance functions, data loading functions, BITE, etc. The IMA concept goes as far as allowing multiple avionic applications to execute on one computing module in so called partitions. To retain fault containment within partition boundaries, the underlying operating system is required to provide strict partitioning of CPU-time and other resources, like memory, common I/O channels, or communication paths. While most of the avionic software Figure 1: AFDX Topology Overview applications still anticipate data communication and distribution over ARINC-429, a new network infrastructure was needed to reflect the new flexibility in aircraft system design and cope with the mere number of interconnections between avionic subsystems. D. AFDX, the next generation avionic data network The solution to the new challenge is to use commercially proven hardware base technology and apply a protocol to it, capable of delivering the reliability in packet transport and timing. Asynchronous Full Duplex Switched Ethernet (AFDX) is based on standard IEEE 802.3 10/100 Mbit Ethernet hardware. This is a well known standard and it is widely used. The packets are enveloped as IP and UDP packets, a software protocol known from the internet. How-ever, the base requirements for a network for avionics applications are not covered by Figure 2: AFDX messages are sent redundant standard technology: Reliable packet transport Regular switches forward packets according to a Bounded transport latency connection table, which is build and updated while the switch is in operation; it “learns” and “forgets” about the Special extensions to the network protocol and a fixed peers connected to it. Of course, this technique is very topology are needed to meet these requirements. The appropriate in a network with temporary peers that attach AFDX protocol has been standardized by an ARINC and detach from the net. The process of learning however, International Journal of Scientific Engineering and Technology Research Volume.02, IssueNo.19, December-2013, Pages:2161-2164 Safety-Critical Ethernet/AFDX–Concept, Design, Implementation and Beyond introduces variable latency and has to be eliminated in an connection. The VL-bundle is de-multiplexed at the avionic data network. Consequently, an AFDX switch destination switch and forwarded to the appropriate End forwards packets according to a static table. This is, in Systems. fact, a general policy in this network to statically define all peers and their respective network addresses. There is B. Queuing Ports no address resolution protocol (ARP) necessary to resolve As shown in figure 3 Queuing Port is message MAC addresses from IP addresses. To increase oriented; a queue with a preconfigured depth accepts availability of the network, it is build using redundancy messages until all space is occupied. Further attempts to on the physical layer. Each packet is transmitted place a message in the queue will result in the simultaneously by two Ethernet controllers onto separate