Since its entry into commercial airplane service on the Airbus A in , 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 many electronic subsystems are on board large aircraft, such as inertial plat- forms, control systems, sensors systems, and communication systems. They all demand high- reliability, high-speed information transfer. Control systems and avionics, in particular, rely on complete and up-to-date data delivery from source to receiver in a timely fashion. For safety-critical systems, reliable real-time communications links are essential.
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AFDX is based on Ethernet technology and adapted to the avionics environment. This interface exports an API to these subsystems, thereby enabling them to communicate with each other through a simple message interface. Each Address is 48 bits wide. The Destination Address identifies the Virtual Link. The source address is a unicast address. The Destination address is a multicast address. Destination Port : This the port number of the addressed application on the destination computer.
This means that the minimum value of length is 8, and maximum value is This is the actual payload data.
Virtual Links: In a Traditional Ethernet Switch, incoming Ethernet frames are routed to output links based on the Ethernet destination address.
The mbps link of an end system can support multiple virtual links. Each virtual link is assigned to parameters. Jitter : jitter is introduced due to switches. But we can maintain zero-jitter by using scheduling method at Virtual links The difference between the minimum and maximum time from when a source node sends a message to when the sink node receives the message.
AFDX message are sent in 1 Frame, data may be lost or overwritten. Each sampling port must provide an indication of the freshness of the message contained in the port buffer. Without this indication, it is impossible to tell whether the transmitting Avionics subsystem has stopped transmitting or is repeatedly sending the message.
Queuing Port: For Bi-Directional Communication and no data lost A queuing port has sufficient storage for a fixed number of messages a Configuration parameter , and new messages are appended to the queue. Reading from a queuing port removes the message from the queue FIFO.
For a Bidirectional communication, ports should be used in queuing mode. These numbers are determined by the system configuration and are fixed for each AFDX communications port. The IP header is added and IP checksum is calculated for each fragment. The VL layer is responsible for scheduling the Ethernet frames for transmission, adding the sequence numbers on a per-VL basis , and passing the frames to the Redundancy Management Unit, where the frames are replicated if necessary and the Ethernet source address is updated with the physical port ID on which the frame is transmitted.
These steps are carried out at the virtual link level. The resulting IP packet is passed on to the IP network level. The network level is responsible for checking the IP checksum field and the UDP packet reassembly, if necessary. Redundancy Management: An AFDX implementation requires two redundant switch networks, A and B, and that each packet be replicated and sent out on both networks. End systems need a way to identify the corresponding packets that arrive on the A and B networks.
In AFDX, all packets are transmitted over virtual link are provided with a 1-byte sequence number field that occurs just before the FCS field. Here a sequence number field is added to each frame, and the sequence numbers are incremented on each successive frame.
The sequence number is added to enable the receive function to reconstruct a single ordered stream of frames without duplication before delivery to the receiving partition.
In default mode each frame is sent across both of two networks. When the second frame is received with this sequence number, it is simply discarded. RM is active : This is default mode. The same frames are sent through both network A and B and it should deliver the first of the redundant frames received.
RM is inactive : The frames are sent through either network A or B RM configuration is generally based on the Skewmax parameter Skewmax is nothing but the maximum time between the reception of two redundant frames. System integrator will provide this value in milliseconds which depends on number switches crossed by a frame.
Tutorials - ARINC
AFDX is based on Ethernet technology and adapted to the avionics environment. This interface exports an API to these subsystems, thereby enabling them to communicate with each other through a simple message interface. Each Address is 48 bits wide. The Destination Address identifies the Virtual Link. The source address is a unicast address. The Destination address is a multicast address.
In one abstraction, it is possible to visualise the VLs as an ARINC style network each with one source and one or more destinations. Virtual links are unidirectional logic paths from the source end-system to all of the destination end-systems. The virtual link ID is a bit unsigned integer value that follows a constant 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.