On-board data bus technology is the interconnection technology used for onboard devices, subsystems, and modules. Understanding it from a computer perspective, various avionic devices are akin to individual microcomputers, while the bus serves as the channel and link connecting these microcomputers, forming a complete functional network for avionic equipment. Traditional bus technologies, represented by MIL-STD-1553b and ARINC429 buses, have been widely applied in military and civilian fields. With continuous technological advancements, the copper cable-based technologies like 1553b are gradually unable to meet the growing data transmission needs. FC (Fibre Channel), introduced by the American National Standards Institute (ANSI) in 1988, is a channel standard aimed at meeting the increasing demand for high-speed data channels within aerospace vehicles.
1. Advantages of Fibre Channel and Introduction to FC-AE-1553
1.1 Advantages of Fibre Channel:
FC (Fibre Channel) possesses dual advantages of a channel and network, allowing current mainstream channel standards and network protocols to operate on the same physical interface. FC serial transmission rates reach 133 megabaud to 1.0625 gigabaud. The enormous data throughput enables the transmission of large amounts of data between different systems; various error handling strategies and a 32-bit CRC support the reliability of Fibre Channel; additionally, Fibre Channel features a flexible topology structure, as shown in the following diagram:
Any topology shown in the diagram can be established using the same devices, satisfying different connection characteristics. Point-to-point communication provides a dedicated line between two computers, representing the most economical topology structure, commonly used to connect radar or electro-optical sensors to their respective processors. The arbitration ring is a closed-loop structure that connects 128 nodes on a shared bandwidth network at a low cost. Each node can act as NC and connect with other nodes. The arbitration ring does not possess fault tolerance capabilities that allow the network to tolerate node or medium failures, and its ability to support multiple operations simultaneously is limited. The switched structure is a network that uses one or multiple interconnected switching components for simultaneous broadband transmission, offering the highest level of functionality. A branch of this switched topology provides an arbitration ring (referred to as a public loop), allowing low-bandwidth nodes (connected to the public ring) to connect with high-bandwidth nodes (directly connected to the structure). The switched structure is currently the most widely used topology.
1.2 FC-AE-1553:
FC-AE is a set of FC protocols designed for the aerospace environment, including FC-AE-1553 high-level protocol, FC-AE-ASM unsigned anonymous message transmission, FC-AEVI virtual interface, FC-AE-FCLP lightweight protocol, and FC-AE-RDMA remote direct memory access protocol. FC-AE-1553 is the most advantageous and technically challenging protocol among the five established protocol specifications, with promising market potential.
FC-AE-1553 stands for Fibre Channel-Avionics Environment-Upper Layer Protocol MIL-STD-1553B Notice 2. FC-AE-1553 implements the upper layer protocol of MIL-STD-1553B, enabling compatibility with existing MIL-STD-1553B bus terminals while integrating the technologies and advantages of Fibre Channel. In terms of performance, FA-AE-1553 technology exhibits the following differences compared to the previous generation MIL-STD-1553b (copper cable):
|
Performance |
MIL-STD-1553b |
FC-AE-1553 |
|
Topology Structure |
Bus |
Point-to-point, Ring, Switched |
|
Allowed Remote/Network Terminal Count |
<25 units |
<224 units |
|
Allowed Subaddress Count |
<25 units |
<232 units |
|
Transmission Encoding |
Manchester Code |
8b/10b Encoding |
|
Transmission Medium |
Copper Cable |
Copper Cable, Fibre |
|
Transmission Rate |
1Mbps |
1/2/4/8Gbps |
|
Word Width |
16bit |
32bit |
|
Message Capacity |
64B |
64KB |
|
Single Message Transmission Time |
Approximately 500-600us |
At a regular 2Gbps rate: 250-300us |
|
Bit Error Rate |
10-7 |
10-12 |
|
Compatibility |
None |
MIL-STD-1553b |
|
Maximum Bytes per Message |
64B |
4.3GB |
FC-AE-1553 and MIL-STD-1553b both implement system data communication in a command-response manner. FC-AE-1553 exhibits an exponential leap in the allowed remote/network terminal count and allowed subaddress count compared to MIL-STD-1553b; since FC-AE-1553 uses fibre as the communication medium, its transmission speed is thousands of times faster than copper cables; the byte count has increased from 5 bits in MIL-STD-1553b to 32 bits, allowing a theoretical maximum transmission of 4.3GB per message; the topology structures of both also differ fundamentally. The bus structure used by MIL-STD-1553b is a point-to-multipoint structure, which has the connectivity of a shared medium while behaving like a point-to-point network at any given moment. In contrast, the point-to-point, switched structure of FC-AE-1553 operates in full-duplex mode, while the arbitration ring structure belongs to the shared medium mode. In terms of both performance and flexible topology, FC-AE-1553 holds a significant and absolute advantage over MIL-STD-1553b.
2. Positioning and Prospects of FC-AE Technology
2.1 Traditional Bus Technology
Modern traditional bus technologies mainly consist of MIL-STD-1553b and ARINC429 buses.
MIL-STD-1553b: Mainly used in military aircraft. Since the U.S. military announced the MIL-STD-1553b bus in 1973, it has been rapidly adopted in U.S. military aircraft such as the F-16, F-18, and B1. Subsequently, MIL-STD-1553b occupied the vast majority of military aircraft buses. However, the entire system communication of 1553b is conducted under the command of the system controller, which poses a potential single point of failure risk; if the controller fails, the entire bus system will collapse. Additionally, since the copper cable material of 1553b cannot meet the communication needs of modern military flight systems.
ARINC429 Bus: Mainly used in civilian aircraft. ARINC429 was drafted based on ARINC419, primarily aimed at standardizing various aircraft buses in the market, with advantages of convenient interfaces and reliable data transmission. ARINC429 is currently the most widely used bus in the civil aviation sector: Airbus A310, A330/A340, Boeing 727, 737, 747, 757, 767, and McDonnell Douglas MD-11 all utilize the ARINC429 bus. It is also applied in missiles and radar fields.
2.2 Next Generation Aerospace Bus Technology
With the continuous development of aviation technology, traditional bus technologies can no longer meet the current aerospace vehicles’ needs for low latency and high throughput data communication. Next-generation bus technologies are gradually replacing traditional bus technologies. Currently, new military and civilian aerospace electronic systems abroad are beginning to shift towards Fibre Channel (FC), Avionics Full-Duplex Switched Ethernet (AFDX), SpaceWire, Time-Triggered Protocol (TTP), and Time-Triggered Ethernet (TTE). Next-generation aerospace bus technologies can effectively meet the technical design requirements of modern aerospace vehicles.
2.2.1 Fibre Channel
Fibre Channel (FC) was proposed by the ANSI X3T11 group in 1988, featuring a flexible topology structure, fast data transmission rates, strong reliability, and good compatibility with 1553b. The main applications of FC in aerospace electrical systems include the FC-AE and FC-AV (ARINC818) protocol branches.
FC-AE Protocol Set: Currently, FC has been applied in models such as FC-35, B1-B, F18E/F, V22, Apache, and is one of the representative technologies of the fourth and fifth generation fighter jets. Domestically, MIL-STD-1553b bus is still commonly used, while FC-AE-ASM is still in the pre-research and validation stage, with some improvements made to international standards.
FC-AV (ARINC818) Protocol: The FC-AV protocol was officially released in 2002. Based on the large data transmission characteristics of FC, this protocol primarily targets industrial-grade audio and video data stream transmission and is widely used in models such as F18 and C-130 AMP. With the continuous development of avionic technologies, the U.S. and Europe have shifted to the ARINC818 protocol published by the AEEC in 2007 for model video system designs. This protocol is mainly used for transmitting critical uncompressed digital video to complete critical safety video tasks, applied in Boeing 787, A400M, and A350XWB models.
2.2.2 Other Technologies
AFDX: Avionics Full-Duplex Switched Ethernet. AFDX resolves the delay issues present in IEEE802.3 Ethernet by adopting telecommunication standard Asynchronous Transfer Mode (ATM). This technology originated from the communication backbone design of the Airbus A380 and has been successfully applied in the A380. Domestically, AFDX has been used as a communication backbone in military aircraft and large aircraft projects.
SpaceWire: Proposed by the European Space Agency, based on IEEE1355-1995 and IEEE1596.3 (LVDS) commercial standards, SpaceWire has improved reliability and power consumption compared to IEEE1355. SpaceWire employs a full-duplex, point-to-point structure, allowing multiple buses to be used within the same network, increasing data transmission speeds by adding bus quantities. SpaceWire is currently mainly applied in several spacecraft of ESA (European Space Agency). Domestic aerospace manufacturing units have also begun promoting it, primarily in the satellite and spacecraft fields.
TTP: Time-Triggered Protocol, jointly developed by Vienna University of Technology and TTTech. The TTP/C protocol provides synchronization and fault-tolerance mechanisms, primarily applied in critical safety real-time systems. The bus-type transmission rate is 5Mbps, while the star structure is 25Mbps. Time-Triggered ensures determinism and reliability. Due to its important position in critical safety control buses, several aerospace manufacturing units have begun establishing laboratories.
TTE: Time-Triggered Ethernet, the latest bus technology based on Ethernet. TTE combines the advantages of Ethernet and TTP, enabling compatibility with TTE network data streams, ordinary network data streams, and AFDX data streams on the same network platform, possessing the highest level of safety, reliability, determinism, and strong fault tolerance. TTE supports 100Mbps and 1000Mbps, significantly improving data transmission speeds compared to TTP. Currently, this technology is still in the promotion stage domestically.
2.3 Summary
Currently, the widely adopted technology domestically is still the previous generation MIL-STD-1553b technology, but it is in a transitional phase towards next-generation bus technologies. In the current environment, China has basically identified FC and AFDX as the development directions, and several research institutions and companies have entered the debugging, pre-research, and development stages. Among them, the main application areas of FC will be in the six major sectors of missiles, arrows, stars, machines, vehicles, and ships, with broad future market potential.
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Author: Lu Han, Foundation of Cornerstone
