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to implement as much functionality as possible in avionics. This leads to more
complex avionics systems that need to process more data than legacy systems, and
consequently a need for ADNs with higher available bandwidths arises.
Another important attribute of an ADN is the required wiring. The less wiring
required, the less its weight which leads to a more fuel efficient aircraft.
Finally, the cost of an ADN's development and deployment is an important factor as
well. Traditionally, ADNs have been based on new technologies specifically
developed for the purpose, thereby making the ADN development very expensive.
Meanwhile, it has become much more desirable to utilize already existing commercial
technologies more or less adapted to the requirements of ADNs. The purpose of this is
not only to benefit from the lower costs of COTS equipment, but also to take
advantage of the fact that COTS equipment is already field-proven.
Emerging of AFDX
Prior to the Airbus 380 Aircraft, the three main ADNs were ARINC 429, MIL-STD-
1553 and ARINC 629 with a max bandwidth of 100 Kbps, 1 Mbps and
2 Mbps, respectively. For the new generation A380, none of these ADNs would fulfill
the aircraft's demanding requirements to a high available bandwidth, minimum wiring
to reduce the weight and low development cost. As a consequence, the Avionics Full
Duplex Switched Ethernet (AFDX) was conceived by Airbus and first implemented
on the A380.
Meanwhile AFDX is not only used on the A380 but also on the Airbus 400M military
transport aircraft and the Boeing 787 Dreamliner, the latter, however, with some
minor extensions to the standard. Furthermore, AFDX is foreseen as the ADN
backbone in the planned Airbus A350. This shows a broad appliance and acceptance
of the AFDX technology leading to reduced cost of AFDX equipment, thus making it
even more attractive to deploy this technology.
Overview
10/30 􀁟 700008_TUT-AFDX-EN_1000
AFDX Characteristics
The AFDX standard was originally defined by Airbus in the "AFDX Detailed
Functional Specification (DFS)" standard. Meanwhile the same standard also exists as
an ARINC standard which is called "ARINC 664".
As mentioned earlier, Boeing has based the ADN backbone of their 787 aircraft on
the ARINC 664 standard, however with some minor extensions. The Boeing AFDX
standard is called "Interoperability Specification for the 787 End System".
AFDX is a serial data transfer method based on conventional Ethernet defined in the
standard IEEE802.3. AFDX allows for transfer rates of either 10 or 100 Mbps over
either a copper or fiber transmission medium. Since conventional Ethernet is not a
deterministic network, AFDX had to be extended to ensure a deterministic behavior
and a high reliability in order to comply with the stringent requirements to ADNs.
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. At any one time AFDX will only forward one data stream to the upper
layers, and automatically exclude an erroneous data stream from being forwarded.
With these characteristics AFDX ensures a BER as low as 10-12 while providing a
bandwidth up to 100 Mbps thereby fulfilling the requirements of new generation
aircraft avionics in terms of reliability and available bandwidth.
AFDX® / ARINC 664 Tutorial 􀁠 11/30
AFDX Network Architecture
End
System
# 1
Switch
Switch
End
System
# 2
Network A (red)
Network B (blue)
End
System
# 3
End
System
# 4
End
System
# n
…
As depicted in Figure 1 each AFDX ES is connected to two independent networks
namely network A (red) and network B (blue). The heart of each AFDX network is
the switch which establishes physical links between all the ESs connected to the
switch. The switch is capable of forwarding data from any connected ES to one or
more other ESs connected to the switch. However, which incoming data will in fact
be forwarded to which ESs depends on the switch configuration which establishes the
logical communication links between ESs.
Based on its configuration, the switch also polices that the bandwidth allocated to
each communication link is not exceeded. If the switch detects that the bandwidth of a
communication link is exceeded, data is dropped (i.e. discarded and therefore not
　
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