aircraft data network

Air Craft Data NetworkPrepared by : Nour El-Din safwat

List of contents •ADN (Aircraft Data Network) Overview

▫ADN types▫ADN characteristics▫Old ADN (ARINC 429,629) ▫ ETHERNET

•AFDX (Avionics Full Duplex Switched Ethernet)▫AFDX Characteristics▫AFDX Network Architecture▫AFDX Communication Concept▫AFDX Network Protocol▫AFDX Network Reliability

Overview

Types of Aircraft data networks:

• Control Network– Real-time communication among sensors,

actuators, and LRUs– Wired-network

• Crew Network– Wireless network between a crew and an

infrastructure

• Passenger Network– LAN for infotainment in a cabin– Internet

Overview

Aircraft Data Network (ADN) Characteristics:•Quality of Service (QoS)

▫ A guaranteed bandwidth, limited jitter▫ a low BER ▫ a reliable and deterministic ADN.

•Available bandwidth ▫ New generation aircraft are required to feature more

sophisticated functions, so high bandwidths are needed.

•Weight▫ the less wiring weight leads to a more fuel efficient aircraft

• The cost of its development and deployment.▫ Make benefit from the lower costs of COTS equipment

ARINC 429 (A320,A330)

• Unidirectional communication

• connections are mostly “point-to-point” (or point-to-several, at best)

• One transmitter and up to 2o receivers • limited in bandwidth (100 kbps)• They result in (too) many wires because

ARINC 629 (B777)

• Bidirectional communication

• connect multiple

LRU to a single digital bus. •  up to 128 units can share the same bus.

• supports a data rate of 2 Mbps.•  complex to implement and more expensive

EHTERNET

• Speeds of ≥ 10 Mbps

• Readily available low cost parts

• Well established Softwareprotocols

But,• Probabilistic• Non-redundant

Which not meet the ADN characteristics :• deterministic • Reliability

AFDX

•Avionics Full Duplex Switched Ethernet

•ARINC 664 Aircraft Data Network, Part 7

AFDX Characteristics• AFDX is based on conventional Ethernet.• AFDX allows for transfer rates of either 10 or

100 Mbps over either a copper or fiber transmission medium.

• AFDX ensures a deterministic behavior through traffic control.

• Traffic control is achieved by guaranteeing the bandwidth of each logical communication channel, called a Virtual Link (VL), thereby limiting the jitter and transmit latency.

• To improve reliability, the AFDX standard requires each AFDX channel to be a dual redundant channel, i.e. two channels transmitting the same data stream and at the same time.

AFDX Network Architecture

The most important elements of an AFDX network are:

• AFDX End System: The end system is the interface between the subsystems (for example flight control computer) and the network.• AFDX Switch: A full-duplex switch. The switch forward Ethernet frames to the correct destination.

• AFDX Virtual Links: A virtual link is a unidirectional virtual connection from one-to-one or one-to-many End Systems

Physical Topology

each channel of an ES is connected to a switch port via a cable containing two twisted pair wires interconnecting the input and output ports of the ES and switch.

Logical Topologyan example of the logical topology of two ESs communicating witheach other. ES 1 transmits the messages 1, 2 and 3 to ES 2 using a common virtual link (VL) which is encoded in the destination MAC address.

AFDX Communication ConceptThe Virtual Link (VL):• the communication

between two AFDX ESs takes place over a single physical communication link.

• However ,it is possible to establish many logical communication links, called Virtual Links (VL).• AFDX implements transmit VLs as well as

receive VLs.• Each transmit VL can only be assigned to one

(1) ES.• receive VLs, however, can be assigned to several

Ess.

AFDX Communication ConceptThe Virtual Link (VL):The virtual link has two parameters:• Bandwidth Allocation Gap (BAG) , a timeslot

confining the VL's bandwidth by defining the minimum gap time between two consecutive frames. The BAG value must be in the range 1 - 128ms and must be a power of 2.

• Lmax is the largest Ethernet frame size the virtual link can transmit (IP layer takes care of segmentation and reassembly).

AFDX Communication ConceptVirtual Link Scheduling• The AFDX traffic shaping is managed by the ES's

VL scheduler which multiplexes the frames of all transmit VLs of an AFDX ES onto the physical link

• The multiplexing is regulated by the Bandwidth Allocation Gap (BAG) which is unique to each VL.

• The jitter is an upper bounded transmit latency appearing as a frame time offset within the BAG.

AFDX Network ProtocolAFDX Protocol Stack

•the AFDX Media Access Control (MAC) data link layer is almost identical to the Ethernet MAC layer.•AFDX implements the Internet Protocol (IP) layer which manages frame fragmentation and re-assembly.•The last protocol layer of the AFDX protocol stack is the User Datagram Protocol (UDP).

AFDX Network ProtocolAFDX Frame Structure

Network Reliability• in order to improve reliability even further, the AFDX

network has a double, i.e. a redundant network transmitting the exact same data.

• The purpose of the redundant network is to mitigate the consequences of potential network failures caused by e.g. damaged cables and connectors or devices (e.g. switches) generating babbling data.

• the ES implements Integrity Checking (IC) and Redundancy Management (RM) to ensure data integrity and that only one data stream is forwarded to the upper protocol layers and from there to the application

Network Reliability

•

Network Reliability•Integrity Checking (IC)

is applied on the MAC layerThe SN (sequence number) is the basis for the IC algorithm

•Redundancy Management (RM)•discard possible duplicate frames by

applying a "first-valid-wins" policy on the two

•Frames forward only one copy of each frame to the upper protocol layers.

List of references

•[1] ARINC SPECIFICATION 664P7, June 27, 2005

• [2] AFDX/ARINC 664Concept, Design, Implementation and Beyond,By Detlev Schaadt, CTO, SYSGO AG

• [3] AFDX/ARINC 664 Protocol Tutorial, GE Fanuc Embedded Systems