Avionics Full-Duplex Switched Ethernet
Encyclopedia
Avionics Full-Duplex Switched Ethernet (AFDX) is a data network for safety-critical applications that utilizes dedicated bandwidth while providing deterministic Quality of Service
(QoS). AFDX is based on IEEE 802.3 Ethernet
technology and utilizes commercial off-the-shelf (COTS
) components. It is described specifically by Part 7 of the ARINC
664 Specification, as a special case of a profiled version of an IEEE 802.3 network per parts 1 & 2, which defines how Commercial Off-the-Shelf networking components will be used for future generation Aircraft Data Network
s (ADN). The six primary aspects of AFDX include full duplex, redundancy, deterministic, high speed performance, switched and profiled network.
standard. This standard, developed over thirty years ago and still widely used today, has proven to be highly reliable in safety critical applications. This ADN can be found on a variety of aircraft from Boeing
, Airbus
and Bombardier CSeries
, including the B737
, B747
, B757
, B767
, Airbus A330
, A340
, A380
and the upcoming A350
, Bombardier CSeries CS100 and CS300. ARINC 429 utilizes a unidirectional bus with a single transmitter and up to twenty receivers. A data word consists of 32 bits communicated over a twisted pair cable using the Bipolar Return-to-Zero Modulation. There are two speeds of transmission: high speed operates at 100 kbit/s and low speed operates at 12.5 kbit/s. ARINC 429 operates in such a way that its single transmitter communicates in a point-to-point connection, thus requiring a significant amount of wiring which amounts to added weight.
Another standard, ARINC 629, introduced by Boeing for the 777
provides increased data speeds of up to 2 Mbit/s and allowing a maximum of 120 data terminals. This ADN operates without the use of a bus controller thereby increasing the reliability of the network architecture. The draw back of this system is that it requires custom hardware which can add significant cost to the aircraft. Because of this, other manufactures did not openly accept the ARINC 629 standard.
ARINC 664 is defined as the next-generation aircraft data network (ADN). It is based upon IEEE 802.3 Ethernet and utilizes commercial off-the-shelf hardware thereby reducing costs and development time. AFDX builds on this standard, as is formally defined in Part 7 of the ARINC 664 specification. AFDX was developed by Airbus Industries for the A380
, initially to address real-time issues for flight-by-wire system development. It has since been accepted by Boeing and is used on the Boeing 787 Dreamliner. AFDX bridges the gap on reliability of guaranteed bandwidth from the original ARINC 664 standard. It utilizes a cascaded star topology network, where each switch can be bridged together to other switches on the network. By utilizing this form of network structure, AFDX is able to significantly reduce wire runs thus reducing overall aircraft weight. Additionally, AFDX provides dual link redundancy and Quality of Service (QoS).
, to fix the shortcomings of IEEE 802.3 Ethernet. By adding key elements from Asynchronous Transfer Mode (ATM)
to those already found in Ethernet, and constraining the specification of various options, a highly reliable Full-Duplex deterministic network is created providing guaranteed bandwidth and Quality of Service. Through the use of Full-Duplex Ethernet, the possibility of transmission collisions is eliminated. However, though bandwidth and maximum end-to-end latency and jitter, links are guaranteed, there is no guarantee of packet delivery. A highly intelligent switch, common to the AFDX network, is able to buffer transmission and reception packets. Through the use of twisted pair or fiber optic cables, Full-Duplex Ethernet uses two separate pairs or strands for transmit and receiving data. AFDX extends standard Ethernet to provide high data integrity and deterministic timing. Further a redundant pair of networks is used to improve the system integrity (although a VL may be configured to use one or other network only) It specifies interoperable functional elements at the following OSI Reference Model
layers:
The main elements of an AFDX network are:
Each VL is frozen in specification to ensure that the network has a designed maximum traffic, hence determinism. Also the switch, having a VL configuration table loaded, can reject any erroneous data transmission that may otherwise swamp other branches of the network.
Additionally, there can be sub-virtual links (sub-VLs) that are designed to carry less critical data. Sub-virtual links are assigned to a particular Virtual Link. Data is read in a round robin sequence among the Virtual Links with data to transmit. Also sub-virtual links do not provide guaranteed bandwidth or latency due to the buffering, but AFDX specifies that latency is measured from the traffic regulator function anyway.
Since AFDX utilizes the Ethernet protocol at the MAC layer, it is possible to use high performance COTS switches with Layer 2 routing as AFDX switches for testing purposes as a cost cutting measure. However some features of a real AFDX switch may be missing such as traffic policing and redundancy functions.
, Boeing 787
, Airbus A400M
, Airbus A350
,
Sukhoi Superjet 100
, AgustaWestland AW101, Irkut MS-21, Bombardier CSeries
.
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS). AFDX is based on IEEE 802.3 Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
technology and utilizes commercial off-the-shelf (COTS
Commercial off-the-shelf
In the United States, Commercially available Off-The-Shelf is a Federal Acquisition Regulation term defining a nondevelopmental item of supply that is both commercial and sold in substantial quantities in the commercial marketplace, and that can be procured or utilized under government contract...
) components. It is described specifically by Part 7 of the ARINC
ARINC
Aeronautical Radio, Incorporated , established in 1929, is a major provider of transport communications and systems engineering solutions for eight industries: aviation, airports, defense, government, healthcare, networks, security, and transportation...
664 Specification, as a special case of a profiled version of an IEEE 802.3 network per parts 1 & 2, which defines how Commercial Off-the-Shelf networking components will be used for future generation Aircraft Data Network
Aircraft Data Network
Aircraft Data Network is a concept introduced by the ARINC Airline Electronics Engineering Committee in the ARINC 664 Specification. The specification proposes data networking standards recommended for use in commercial aircraft installations. The standards provide a means to adapt COTS...
s (ADN). The six primary aspects of AFDX include full duplex, redundancy, deterministic, high speed performance, switched and profiled network.
History
Prior to AFDX, Aircraft Data Networks utilized primarily the ARINC 429ARINC 429
ARINC 429 is the technical standard for the predominant avionics data bus used on most higher-end commercial and transport aircraft. It defines the physical and electrical interfaces of a two-wire data bus and a data protocol to support an aircraft's avionics local area network.-Messages:ARINC 429...
standard. This standard, developed over thirty years ago and still widely used today, has proven to be highly reliable in safety critical applications. This ADN can be found on a variety of aircraft from Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
, Airbus
Airbus
Airbus SAS is an aircraft manufacturing subsidiary of EADS, a European aerospace company. Based in Blagnac, France, surburb of Toulouse, and with significant activity across Europe, the company produces around half of the world's jet airliners....
and Bombardier CSeries
Bombardier CSeries
The Bombardier CSeries is a family of narrow-body, twin-engine, medium-range jet airliners being developed by Canadian manufacturer Bombardier Aerospace. Models are the 110-seat CS100, and the 130-seat CS300...
, including the B737
Boeing 737
The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers...
, B747
Boeing 747
The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...
, B757
Boeing 757
The Boeing 757 is a mid-size, narrow-body twin-engine jet airliner manufactured by Boeing Commercial Airplanes. Passenger versions of the twinjet have a capacity of 186 to 289 persons and a maximum range of , depending on variant and cabin configuration...
, B767
Boeing 767
The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...
, Airbus A330
Airbus A330
The Airbus A330 is a wide-body twin-engine jet airliner made by Airbus, a division of EADS. Versions of the A330 have a range of and can accommodate up to 335 passengers in a two-class layout or carry of cargo....
, A340
Airbus A340
The Airbus A340 is a long-range four-engine wide-body commercial passenger jet airliner. Developed by Airbus Industrie,A consortium of European aerospace companies, Airbus is now fully owned by EADS and since 2001 has been known as Airbus SAS. a consortium of European aerospace companies, which is...
, A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
and the upcoming A350
Airbus A350
The Airbus A350 is a family of long-range, wide-body jet airliners under development by European aircraft manufacturer Airbus.A consortium originally comprising European aerospace companies from the UK, France, Spain and West Germany, Airbus is now fully owned by EADS and since 2001 has been known...
, Bombardier CSeries CS100 and CS300. ARINC 429 utilizes a unidirectional bus with a single transmitter and up to twenty receivers. A data word consists of 32 bits communicated over a twisted pair cable using the Bipolar Return-to-Zero Modulation. There are two speeds of transmission: high speed operates at 100 kbit/s and low speed operates at 12.5 kbit/s. ARINC 429 operates in such a way that its single transmitter communicates in a point-to-point connection, thus requiring a significant amount of wiring which amounts to added weight.
Another standard, ARINC 629, introduced by Boeing for the 777
Boeing 777
The Boeing 777 is a long-range, wide-body twin-engine jet airliner manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet and is commonly referred to as the "Triple Seven". The aircraft has seating for over 300 passengers and has a range from , depending on model...
provides increased data speeds of up to 2 Mbit/s and allowing a maximum of 120 data terminals. This ADN operates without the use of a bus controller thereby increasing the reliability of the network architecture. The draw back of this system is that it requires custom hardware which can add significant cost to the aircraft. Because of this, other manufactures did not openly accept the ARINC 629 standard.
ARINC 664 is defined as the next-generation aircraft data network (ADN). It is based upon IEEE 802.3 Ethernet and utilizes commercial off-the-shelf hardware thereby reducing costs and development time. AFDX builds on this standard, as is formally defined in Part 7 of the ARINC 664 specification. AFDX was developed by Airbus Industries for the A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
, initially to address real-time issues for flight-by-wire system development. It has since been accepted by Boeing and is used on the Boeing 787 Dreamliner. AFDX bridges the gap on reliability of guaranteed bandwidth from the original ARINC 664 standard. It utilizes a cascaded star topology network, where each switch can be bridged together to other switches on the network. By utilizing this form of network structure, AFDX is able to significantly reduce wire runs thus reducing overall aircraft weight. Additionally, AFDX provides dual link redundancy and Quality of Service (QoS).
Overview of AFDX
AFDX adopted concepts (token bucket) from the telecom standard, Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
, to fix the shortcomings of IEEE 802.3 Ethernet. By adding key elements from Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
to those already found in Ethernet, and constraining the specification of various options, a highly reliable Full-Duplex deterministic network is created providing guaranteed bandwidth and Quality of Service. Through the use of Full-Duplex Ethernet, the possibility of transmission collisions is eliminated. However, though bandwidth and maximum end-to-end latency and jitter, links are guaranteed, there is no guarantee of packet delivery. A highly intelligent switch, common to the AFDX network, is able to buffer transmission and reception packets. Through the use of twisted pair or fiber optic cables, Full-Duplex Ethernet uses two separate pairs or strands for transmit and receiving data. AFDX extends standard Ethernet to provide high data integrity and deterministic timing. Further a redundant pair of networks is used to improve the system integrity (although a VL may be configured to use one or other network only) It specifies interoperable functional elements at the following OSI Reference Model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
layers:
- Data LinkData link layerThe data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
(MACMedia Access ControlThe media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
and Virtual Link addressing concept); - NetworkNetwork LayerThe network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
(IPInternet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
and ICMPInternet Control Message ProtocolThe Internet Control Message Protocol is one of the core protocols of the Internet Protocol Suite. It is chiefly used by the operating systems of networked computers to send error messages indicating, for example, that a requested service is not available or that a host or router could not be...
); - TransportTransport layerIn computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
(UDPUser Datagram ProtocolThe User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
and optionally TCPTransmission Control ProtocolThe Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
) - Application (Network)Application layerThe Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....
(Sampling, Queuing, SAPService Access PointA Service Access Point is an identifying label for network endpoints used in Open Systems Interconnection networking.When using the OSI Network Layer , the base for constructing an address for a network element is an NSAP address, similar in concept to an IP address...
, TFTP and SNMPSimple Network Management ProtocolSimple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
).
The main elements of an AFDX network are:
- AFDX End Systems
- AFDX Switches
- AFDX Links
Virtual links
The central feature of an AFDX network are its Virtual Links (VL). In one abstraction, it is possible to visualise the VLs as an ARINC 429 style network each with one source and one or more destinations. Virtual Links are unidirectional logic path from the source end-system to all of the destination end-systems. Unlike that of a traditional Ethernet switch which switches frames based on the Ethernet destination or MAC address, AFDX routes packets using a Virtual Link ID. The Virtual Link ID is a 16-bit Unsigned integer value that follows the constant 32-bit field. The switches are designed to route an incoming frame from one, and only one, End System to a predetermined set of End Systems. There can be one or more receiving End Systems connected within each Virtual Link. Each Virtual Link is allocated dedicated bandwidth [sum of all VL Bandwidth Allocation Gap (BAG)rates x MTU] with the total amount of bandwidth defined by the system integrator. However total bandwidth cannot exceed the maximum available bandwidth on the network. Bi directional communications must therefore require the specification of a complimentary VL.Each VL is frozen in specification to ensure that the network has a designed maximum traffic, hence determinism. Also the switch, having a VL configuration table loaded, can reject any erroneous data transmission that may otherwise swamp other branches of the network.
Additionally, there can be sub-virtual links (sub-VLs) that are designed to carry less critical data. Sub-virtual links are assigned to a particular Virtual Link. Data is read in a round robin sequence among the Virtual Links with data to transmit. Also sub-virtual links do not provide guaranteed bandwidth or latency due to the buffering, but AFDX specifies that latency is measured from the traffic regulator function anyway.
BAG Rate
BAG stands for Bandwidth Allocation Gap, this is one of the main features of the AFDX protocol. This is the maximum rate data can be sent, and it is guaranteed to be sent at that interval. When setting the BAG rate for each VL, care must be taken so there will be enough bandwidth for other VL's and the total speed cannot exceed 100Mbps.Switching of Virtual Links
Each switch has filtering, policing, and forwarding functions that should be able to process at least 4096 VLs (this seems like a system specific derived requirement in part 7). Therefore, in a network with multiple switches (cascaded star topology), the total number of Virtual Links is nearly limitless. There is no specified limit to the number of Virtual Links that can be handled by each End System, although this will be determined by the BAG rates and max frame size specified for each VL versus the Ethernet data rate. However, the number sub-VLs that may be created in a single Virtual Link is limited to four. The switch must also be non-blocking at the data rates that are specified by the system integrator, and in practise this may mean that the switch shall have a switching capacity that is the sum of all of its physical ports.Since AFDX utilizes the Ethernet protocol at the MAC layer, it is possible to use high performance COTS switches with Layer 2 routing as AFDX switches for testing purposes as a cost cutting measure. However some features of a real AFDX switch may be missing such as traffic policing and redundancy functions.
Usage
The AFDX bus is used in Airbus A380Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
, Boeing 787
Boeing 787
The Boeing 787 Dreamliner is a long-range, mid-size wide-body, twin-engine jet airliner developed by Boeing Commercial Airplanes. It seats 210 to 290 passengers, depending on the variant. Boeing states that it is the company's most fuel-efficient airliner and the world's first major airliner to use...
, Airbus A400M
Airbus A400M
The Airbus A400M, also known as the Atlas, is a multi-national four-engine turboprop military transport aircraft. It was designed by Airbus Military as a tactical airlifter with strategic capabilities. The aircraft's maiden flight, originally planned for 2008, took place on 11 December 2009 in...
, Airbus A350
Airbus A350
The Airbus A350 is a family of long-range, wide-body jet airliners under development by European aircraft manufacturer Airbus.A consortium originally comprising European aerospace companies from the UK, France, Spain and West Germany, Airbus is now fully owned by EADS and since 2001 has been known...
,
Sukhoi Superjet 100
Sukhoi Superjet 100
The Sukhoi Superjet 100 is a modern, fly-by-wire regional jet in the 75- to 95-seat category. With development starting in 2000, the plane was designed by the civil aircraft division of the Russian aerospace company Sukhoi in co-operation with Western partners...
, AgustaWestland AW101, Irkut MS-21, Bombardier CSeries
Bombardier CSeries
The Bombardier CSeries is a family of narrow-body, twin-engine, medium-range jet airliners being developed by Canadian manufacturer Bombardier Aerospace. Models are the 110-seat CS100, and the 130-seat CS300...
.
External links
- ARINC Tutorials and Products by Ballard Technology, Inc.
- ARINC-664 part 7(AFDX) Tutorial (video) from Excalibur Systems Inc.
- Embvue AFDX | Arinc 664 by Embvue