1. ARINC 664V7 / AFDX Workshop

2. Introduction Willem Braat Teacher/Instructor AM&TS Woensdrecht
ACC Maastricht

3. ARINC 664V7 / AFDX Analysis ARINC 664V7/AFDX analysis is twofold:
Analysing systems (including OSI layers)
Analysing data and compile into information
Intelligent in-depth data analysis is being addressed by several firms (in alphabetical order):
General Electric (
Vector (
RealTime-at-Work (
Techsat (

4. Workshop Goals This Session is built around these topics:
Analysing systems
General principles about "modern" communication
The background of airborne data communication
AFDX standard
Future of AFDX: Holy Grail or necessary basic (expandable) platform?

5. Communication principles
The key driver for the definition of the Network Layering is the implementation of independence between application and communication means.
Factorization
Network driver
Application
Communication services
Application
Application
Specialization
communication layers
communication
serives
communication
serives
Network driver
Object Oriented paradigm

6. Usual communication layers
OSI
reference
Model
IETF Internet
std IP
TCP/UDP
SNMP
IEEE
IEEE 802.3
"Ethernet"
FTP
IEEE
"WI-FI"
HTTP
POP
SMTP
ITU
...
G992.1
"ADSL"
ATM
Application
Application services
Communication services
Presentation
Session
Transport
Network
DataLink/MAC
Physical connection

7. Aircraft communication
Internal Aircraft communication
External Aircraft communication : out of this workshop’s scope

8. Historical survey
Until recently, there was never a strong need for networking inside an aircraft.
When digital technologies were introduced, the communication was limited to digital data link.
The introduction of digital technologies was done in the "control of platform" domain and not in the "information" domain.

9. Digital Transmission Two kinds of digital usage on-board:
Process Control
based on sampling system techniques and data transmission
data: the digital value of an analog parameter (e.g. speed, height, altitude)
transmission : only sending data; no response is expected
Information systems
based on information exchanges
information : a complex set of abstract values (digital map, flight plan, list of passenger duty free purchase, failure log book....)
exchange : a response is generally expected, at least to indicate that the information has been received.
This "complex set of abstract values" gives usually a huge amount of bytes. This is one reason for a higher speed data link

10. Process Control Requirements
As the transmitted data are involved in process control , the transmission must be done with a minimum delay (jitter).
The stability of the flight relies on this transmission
Time, integrity and availability are the key drivers.
Some principles:
no common shared resource (limited risk of common failure)
one source, one line, several receivers
the transmitter does not need to know who receives data
no time synchronisation between transmitter and receiver
common shared time is a kind of common resource
Aeronautical response :
ARINC 429 Digital Information Transfer System

11. ARINC 429 reminder
Each line has only one source and is connected to every equipment that needs the data transmitted by the source
Each data is individually identified (by a label) and sent
Application
label
data
A429
Application
Presentation
Session
Transport
Network
DataLink/MAC
Physical connection
label
data
parity
32 bit

12. Information System Requirements
In Information systems, the major requirement is to ensure that the information is transmitted and received without error.
Some principles:
the information should be acknowledged
delay is not critical and messages can be sent again in case of error
The former aircraft generation still used A429 but added acknowledged data block
Application
A429 williamsburg
Transport
Network
A429
DataLink/MAC
Physical connection

13. Avionics market evolution
The evolution of the avionics market is exposed to a high pressure for reducing cost.
At the same time, mature concepts have arisen:
Electronics Modularity
Operating System
Decision to re-use and share common resource

14. AFDX : a real challenge
The key driver for AFDX design choices must satisfy many contradictory objectives:
To transmit data under strong time constraint
To guarantee information exchange according to client/server model
To reduce cost by using/reusing commercial components (COTS: commercial off-the-shelf) under certification constraints

15. Technological choices
Communication technologies from desktop computing market
Best candidate :
Ethernet for Physical layer
Internet for upper protocol layer
Communication technologies from multimedia telecom market
ATM (backbone telecom and ADSL) and cell switching
IEEE
std
IEEE 802.3
"Ethernet"
IEEE
"WI-FI"
IETF Internet
std IP
TCP/UDP
SNMP
FTP
HTTP
POP
SMTP
...
ITU
std
G992.1
"ADSL"
ATM

16. AFDX : Avionics Full DupleX switched Ethernet
Final choice
Key drivers:
Heavy aeronautical background:
time constraint
safety
Arrival of Switched Ethernet (from ATM concept)
Low cost, market size of desktop computing versus small telco market
.... and the winner is...
Switched full duplex Ethernet with some specific deviations to cope with real time/certification constraints
AFDX : Avionics Full DupleX switched Ethernet

17. AFDX standard The standardisation body
AFDX is undertaken by the civil aviation usual standardisation body: ARINC/AEEC ADN working group
ARINC: Aeronautical Radio Inc. funded by airlines, in charge of the definition of Aeronautical standards that ensure interchangeability and interoperability.
AEEC: Airlines Electronic Engineering Committee
ADN: Aircraft Data Network working group
The standard
AFDX is described as ARINC specification 664 part 7
The ARINC 664 covers in general, the usage of Ethernet as an airborne communication system, extended to the confidentiality issues and future IPv6 extensions.

18. Key features of AFDX
AFDX is the common communication system used for modular avionics architecture.
It is compliant with the following design key features:
It is based on Open Standard
as required by cost and commercial standard reuse objective
It provides "Resource Sharing"
as required by modularity, reuse, and cost objective
It provides "Robust Partitioning"
as required by resource sharing and safety, certification constraints
It provides "Determinism" and "Availability"
as required by safety, certification constraints
The AFDX key features are mainly concentrated on the Data Link Layer.

19. AFDX : an Open Standard OSI reference Model IETF Internet std IEEE std
ARINC 664 Part 7 : AFDX
IEEE Ethernet MAC + PHY IP
UDP
TCP
optional
SNMP
TFTP
SNMP
TFTP
ARINC 600
ARINC 653
Application
Presentation
Session
Transport
TCP/UDP
Network IP
IEEE 802.3
"Ethernet"
AFDX special features
DataLink/MAC
Physical connection

20. AFDX : basic network architecture
AFDX is based on the Ethernet switched network.
It is built with:
Switches, network devices in charge of data forwarding
End System, network devices in charge of data transmission/reception
modular avionocs
modular
avionocs
LRU
RDC ES ES ES ES SW SW SW ES SW SW SW ES ES ES ES
LRU
modular
avionocs
modular
avionocs
RDC

21. AFDX key feature : Resource Sharing
The main resources shared by AFDX are
the wiring and
the attached network devices
IMA/IME
module
IMA/IME
module
LRU
RDC ES ES ES ES SW SW SW SW SW ES ES ES ES
LRU
IMA/IME
module
IMA/IME
module
RDC

22. AFDX key feature : Virtual Link
The robust partitioning for networking is applied on bandwidth allocated to "communication channel".
The VL model is ARINC429 "single wire" and the ATM "Virtual Channel"
one wire/channel for one data source, distributed to all who need it
The AFDX response is:
one channel (named VL "Virtual Link") for one data source, distributed with multicast Ethernet address channels are merged together on one Ethernet data link SW ES ES ES ES
AFDX
Ethernet data link
Virtual Link
ARINC 429
N/A
twisted pair copper wire

23. AFDX key feature : "Firewalling"
Another feature related to robust partition and safety is the integrated "firewall" provided by the AFDX.
This firewall is implemented by Access Control List (ACL) mechanism.
Traffic filtering : Restricted access for only configured VL
Traffic filtering : Restricted access for only configured VL ES SW ES ES
Traffic filtering
+ forwarding ES
Ethernet data link
Virtual Link
Traffic filtering

24. AFDX key feature : Redundancy
In response to the "Availability" requirement AFDX network is basically redundant.
Each End-System has the capability to send each message twice toward independent set of switches.
network A ES SW SW ES ES
network B SW SW
Key Feature : Redundancy Management
=> each frame is sorted when received.
Key Feature : Redundancy Management
=> each frame is numbered when transmitted.

25. AFDX key feature : Latency management(1/3)
The VL receive a "Bandwidth contract".
This contract is expressed in terms of:
Maximum Frame Size (MFS)
Minimum time between two frames
named Bandwidth Allocation Gap (BAG)
Max contractual bandwidth[kbit/s] = MFS[bit]/BAG[ms]
Single VL max bandwidth = c.a. 12Mb/s
determinism reason
Source Application
sent fralme
delayed frame
delayed frame
End System traffic shaping
BAG
BAG

26. AFDX key feature : Latency management(2/3)
The robust partitioning relies on "Bandwidth contract" granted to each Virtual Link.
The ES has Bandwidth Contract for each Virtual Link and must comply with this contract
The Switches know the term of the contract for each Virtual Link and monitor the traffic to check if contract is respected.
Key feature : Traffic shaping
the traffic is generated according to bandwidth contract
Key Feature : Traffic policing
the traffic is monitored according to bandwidth contract SW ES ES ES ES

27. AFDX key feature : Latency management (3/3)
In AFDX context the determinism is defined as the control of maximum transmission delay through the network.
The enabler of such control is precisely the bandwidth contract.
Ethernet Switch provides better capability for determinism than usual Ethernet Hub because there is no collision and no transmission random retry.
Key feature : Bounded latency
The knowledge of bandwidth contract allows to evaluate the worst case filling level of shared output queue and, hence to estimate the message delay ES SW ES ES ES
Ethernet data link
shared output message queue
Virtual Link

28. AFDX "counterpart" : Virtual Link
Fit perfectly usual "non shared" aeronautical communication (ARINC429) like in "process control" where the bandwidth is continuously used.
Difficult to manage bi-directional communication like in modern "information system"
Leads to create large number of VL even if the VL is not used continuously

29. AFDX "counterpart" : Latency management
The latency computation is based on the worst case that can happen. This is a certification concern not a performance concern!!
As far as we can not state on the actual source traffic, the latency is systematically majored....
This gives a certifiable network configuration that under-uses the true Ethernet capability

30. Part 4 : The AFDX and the A380 Requested performance
Airbus requirements impose a strong constraint on time and "proof of determinism"
Computation of UDP message, IP fragmentation, traffic shaping, redundancy generation, Ethernet frame building < 150µs
Reception of continuous "back to back" Ethernet, traffic filtering, redundancy management, IP reassembly < 150µs
Frame forwarding, traffic policing, multicast management < 100µs
AFDX suppliers
Two AFDX suppliers:
Rockwell-Collins : Switches and End System
Thales : End System

31. Open Standard benefits
The use of "Open standard" such as Ethernet reduces the development cost in the following areas:
Laboratory Instrumentation.... Ethernet standard tools are used, no need to develop specific tools
Design and development.... the definition of the standard relies on existing data and expertise
However, this benefit should be mitigated because the use of equipment in an aircraft needs to have trusted development that commercial components can not provide
The result is that the material itself is still developed specifically for the aeronautical market (...with the cost associated to certification compliance...)