AFDX（ARINC664）协议讲解

GE Fanuc Embedded Systems AFDX/ARINC 664 Protocol Tutorial Table of Contents Chapter 1 Overview 4 The Antecedents 4 What is AFDX? 4 Other Avionics Buses 5 ARINC 429 5 MIL-STD-1553 5 Ethernet 6 ALOHA Net 6 The ALOHA Protocol 6 Ethernet Local Area Networks (Broadcast Media) 6 The Ethernet Protocol 6 Ethernet Using Category 5 UTP Copper Twisted Pairs 6 Ethernet Frame Format 6 Chapter 2 Ethernet 6 Full-duplex, Switched Ethernet 7 Doing Away with Contention 7 Reducing Wire Runs and Weight 8 Chapter 3 End Systems and Avionics Subsystems 9 End Systems and Avionics Subsystems 9 Chapter 4 AFDX Communications Ports 10 AFDX Communications Ports 10 Chapter 5 Virtual Links: Packet Routing in AFDX 11 Virtual Links 11 Chapter 6 Message Flows 12 Message Flows 12 Chapter 7 Redundancy Management 13 Redundancy Management 13 Chapter 8 Virtual Link Isolation 14 Virtual Link Isolation 14 Choosing the BAG and Lmax for a Virtual Link 15 Chapter 9 Virtual Link Scheduling 15 Virtual Link Scheduling 15 Chapter 10 Jitter 16 Jitter 16 Chapter 11 AFDX Message Structures 17 Introduction 17 Implicit Message Structures 17 ARINC 429 Labels 18 Chapter 12 The AFDX Protocol Stack 19 The AFDX Protocol Stack 19 Transmission 19 Reception 20 Appendix A AFDX Frame Addressing and Header Structures 21 Ethernet Addressing 21 IP Header Format and Addressing 21 UDP Header Format 22 Appendix B Referenced Documents 23 Reference List 23 List of Figures Figure 1 AFDX Network 4 Figure 2 ARINC 429 Communication Protocol 5 Figure 3 MIL-STD-1553 Bus Communication Protocol 5 Figure 4 ALOHA Net 6 Figure 5 Ethernet Local Area Networks (Broadcast Media) 6 Figure 6 Ethernet Frame Format 6 Figure 7 Full-Duplex, Switched Ethernet Example 7 Figure 8 AFDX versus ARINC 429 architecture 8 Figure 9 End Systems and Avionics Subsystems Example 9 Figure 10 Sampling Port at Receiver 10 Figure 11 Queuing Port at Receiver 10 Figure 12 Format of Ethernet Destination Address in AFDX Network 11 Figure 13 Packet Routing Example 11 Figure 14 Message Sent to Port 1 by the Avionics Subsystem 12 Figure 15 Ethernet Frame with IP and UDP Headers and Payloads 12 Figure 16 A and B Networks 13 Figure 17 AFDX Frame and Sequence Number 13 Figure 18 Receive Processing of Ethernet Frames 13 Figure 19 Three Virtual Links Carried by a Physical Link 14 Figure 20 Virtual Link Scheduling 15 Figure 21 Virtual Link Scheduling 15 Figure 22 Role of Virtual Link Regulation 16 Figure 23 Two Message Structures 17 Figure 24 ARINC 664 Message Structures 18 Figure 25 AFDX Tx Protocol Stack 19 Figure 26 AFDX Rx Protocol Stack 20 Figure 27 Ethernet Source Address Format 21 Figure 28 IP Header Format 21 Figure 29 IP Unicast Address Format 21 Figure 30 IP Multicast Address Format 21 Figure 31 UDP Header Format 22 4 One of the reasons that AFDX is such an attractive tech- nology is that it is based upon Ethernet , a mature technol- ogy that has been continually enhanced, ever since its inception in 1972 In fact , the commercial investment and advancements in Ethernet have been huge compared say, to ARINC 429, MIL-STD-1553, and other specialized data- communications technologies As shown in Figure 1, an AFDX system comprises the follow- ing components:  Avionics Subsystem: The traditional Avionics Subsystems on board an aircraft, such as the flight control com- puter, global positioning system, tire pressure monitoring system, etc An Avionics Computer System provides a computational environment for the Avionics Subsystems Each Avionics Computer System contains an embedded End System that connects the Avionics Subsystems to an AFDX Interconnect  AFDX End System (End System): Provides an “interface” between the Avionics Subsystems and the AFDX Intercon- nect Each Avionics Subsystem the End System interface to guarantee a secure and reliable data interchange with other Avionics Subsystems This interface exports an ap- plication program interface (API) to the various Avionics Subsystems, enabling them to communicate with each other through a simple message interface  AFDX Interconnect: A full-duplex, switched Ethernet in- terconnect It generally consists of a network of switches that forward Ethernet frames to their appropriate destina- tions This switched Ethernet technology is a departure from the traditional ARINC 429 unidirectional, point-to- point technology and the MIL-STD-1553 bus technology Chapter 1 Overview The Antecedents Moving information between avionics subsystems on board an aircraft has never been more crucial, and it is here that electronic data transfer is playing a greater role than ever before Since its entry into commercial airplane service on the Airbus A320 in 1988, the all-electronic fly-by-wire system has gained such popularity that it is becoming the only control system used on new airliners But there are a host of other systems — inertial platforms, communication systems, and the like — on aircraft, that demand high-reliability, high-speed communications, as well Control systems and avionics in particular, rely on having complete and up-to-date data delivered from source to re- ceiver in a timely fashion For safety-critical systems, reliable real-time communications links are essential That is where AFDX comes in Initiated by Airbus in the evolu- tion of its A380 Aircraft, they coined the term, AFDX, for Avion- ics Full-DupleX, switched Ethernet AFDX brings a number of improvements such as higher-speed data transfer — and with regard to the host airframe — significantly less wiring, thereby reducing wire runs and the attendant weight What is AFDX? Avionics Full DupleX Switched Ethernet (AFDX) is a standard that defines the electrical and protocol specifications (IEEE 802 3 and ARINC 664, Part 7) for the exchange of data be- tween Avionics Subsystems One thousand times faster than its predecessor, ARINC 429, it builds upon the original AFDX concepts introduced by Airbus Figure 1. AFDX Network Controllers Actuators Sensors Controllers Actuators Sensors Gateway Avionics Computer System AFDX Interconnect End System Avionics Subsystem Avionics Subsystem End System End System Avionics Computer System Avionics Computer System Internet 5 As shown in the example in Figure 1, two of the End Systems provide communication interfaces for three avionics sub- systems and the third End System supplies an interface for a Gateway application It, in turn, provides a communications path between the Avionics Subsystems and the external IP network and, typically, is used for data loading and logging The following sections provide an overview of the AFDX ar- chitecture and protocol But first we briefly review two of the traditional avionics communications protocols Other Avionics Buses This section compares AFDX to two earlier Avionics data com- munication protocols: ARINC 429 and MIL-STD-1553 ARINC 429 Receiver ReceiverReceiverReceiver Source Bit rates are either 100 Kbps or 12 5 Kbps 32-bit messages Figure 2. ARINC 429 Communication Protocol ARINC 429 implements a single-source, multi-drop bus with up to 20 receivers (see Figure 2) Messages consist of 32-bit words with a format that includes five primary fields The Label field determines the interpretation of the fields in the re- mainder of the word, including the method of translation The point to multi-point property of ARINC 429 requires the Avion- ics system to include an ARINC 429 bus for each pair-wise communication Refer to the GE Fanuc Embedded Systems ARINC Tutorial for more details MIL-STD-1553 Bit-rate 1 Mbps 20-bit data word Figure 3. MIL-STD-1553 Bus Communication Protocol MIL-STD-1553 (see Figure 3) implements a bus architecture in which all the devices attached to the bus are capable of receiving and transmitting data The Avionics subsystems at- tach to the bus through an interface called a remote terminal (RT) The Tx and Rx activity of the bus is managed by a bus controller, that acts to ensure that no two devices ever trans- mit simultaneously on the bus The communication is half duplex and asynchronous For more information, refer to the GE Fanuc Embedded Systems “MIL-STD-1553 Tutorial” BC RT RTRTRT MIL-STD 1553 DATA BUS 6 Ethernet This chapter provides a brief description of the origins of Ethernet, the Ethernet frame format and the role of switched Ethernet in avionics applications ALOHA Net In 1970, the University of Hawaii deployed a packet radio system called the “ALOHA network” [Norman Abramson; see Figure 4] to provide data communications between stations located on different islands There was no centralized control among the stations; thus, the potential for collisions (simulta- neous transmission by two or more stations) existed Chapter 2 Ethernet Figure 4. ALOHA Net The ALOHA Protocol 1 If you have a message to send, send the message, and 2 If the message collides with another transmission, try resending the message later using a back-off strategy Issues • No central coordination • Collisions lead to non-deterministic behavior Ethernet Local Area Networks (Broadcast Media) In 1972, Robert Metcalfe and David Boggs at Xerox Palo Alto Research Center built upon the ALOHA network idea and used a coaxial cable as the communication medium and invented Ethernet (see Figure 5) Ethernet is similar to the ALOHA protocol in the sense that there is no centralized control and transmissions from different stations (hosts) could collide The Ethernet communication protocol is referred to as “CSMA/ CD” (Carrier Sense, Multiple Access, and Collision Detection) Carrier Sense means that the hosts can detect whether the medium (coaxial cable) is idle or busy Multiple Access means that multiple hosts can be connected to the common me- dium Collision Detection means that, when a host transmits, it can detect whether its transmission has collided with the transmission of another host (or hosts) The original Ethernet data rate was 2 94Mbps Station Station Station Ether Figure 5. Ethernet Local Area Networks (Broadcast Media) The Ethernet Protocol 1 If you have a message to send and the medium is idle, send the message 2 If the message collides with another transmission, try sending the message later using a suitable back-off strategy Issues • No central coordination • Collisions lead to non-deterministic behavior Ethernet Using Category 5 UTP Copper Twisted Pairs The most common electrical form of Ethernet today is based on the use of twisted pair copper cables Typically, cables are point-to-point, with hosts directly connected to a switch In the case of Fast Ethernet (100Mbps), two pairs of Category 5 UTP copper wire are used for Tx and Rx, respectively In the case of transmission, each 4-bit nibble of data is encoded by 5 bits prior to transmission This is referred to as “4B/5B encoding” and results in a transmission clock frequency of 125Mbps, since 5 bits are sent for every 4 bits of data Since there are twice as many 5-bit patterns as 4-bit ones, it is possible to ensure that every transmitted pattern is able to provide good clock synchronization (not too many 0’s or 1’s in a row) for reliable transmission of data Some of the 5-bit patterns are used to represent control codes Host HostHostHost Coaxial Cable (Bus Architecture) Ethernet Frame Format As Figure 6 illustrates, IEEE 802 3 defines the format of an Ethernet transmission to include a 7-byte Preamble, a Start Frame Delimiter (SFD), the Ethernet frame itself, and an Inter-Frame Gap (IFG) consisting of at least 12 bytes of idle symbols The Ethernet frame begins with the Ethernet header, Preamble Ty pe IFGPayloadSourceAddress Destination Address byte 7 1 6 6 2 46 - 1500 4 12 FC S SF D Ethernet Frame Figure 6. Ethernet Frame Format 7 Doing Away with Contention To do away with contention (collisions), and hence the indeterminacy regarding how long a packet takes to travel from sender to receiver, it is necessary to move to Full-duplex Switched Ethernet Full-duplex Switched Ethernet eliminates the possibility of transmission collisions like the ones that occur when using Half-duplex Based Ethernet As shown in Figure 7, each Avionics S