Transcript AFDX Tutorial

AFDX Tutorial
Session One : AFDX background
Aerospace
Introduction
This Session One is built around four main topics:
 General principle about "modern" communication
 The background of airborne data communication
 AFDX standard
 AFDX and A380
Aerospace
Part 1 : Communication principles
The key driver for the definition of the Network layering is the
implementation of independance between application and
communication means.
Application
Application
Application
communication
serives
communication
serives
Network driver
Application
Communication
services
Network driver
Specialization
communication layers
Factorization
Aerospace
Object Oriented
paradigm
Usual communication layers
OSI
reference
Model
Application
IEEE
std
IETF Internet
std
POP
SMTP
...
SNMP
FTP
HTTP
ITU
std
Application services
Presentation
Communication
services
Session
Transport
TCP/UDP
Network
IP
ATM
DataLink/MAC
Physical connection
Aerospace
IEEE 802.3
"Ethernet"
IEEE 802.11
"WI-FI"
G992.1
"ADSL"
Part 2 : Aircraft communication
Internal Aircraft communication
External Aircraft communication :
out of this tutorial scope
Aerospace
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" area not in the "information" area.
Aerospace
Digital transmission
Two kind of digital usage on-board:
 Processus Control

based on sampling system techniques and data transmission


data : the digital value of an analogical parameter (e.g. speed;
heigth, attitude,....)
transmission : no response is expected
 Information systems

based of information exchanges



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information : a complex set of abtract values (e.g. digital map, flight
plan, list of passenger duty free purchase, failure log book....)
exchange : a response is generaly expected, at least to indicated that
the information is received.
This "complex set of abstract values" gives usually a huge amount of
bytes.... This is one reason that calls for higher speed data link
Processus control requirements
As the transmitted data are involved in processus control , the
transmission must be done with a minimum bounded delay.
The stability of the flight relies on this transmission
Time, integrity and availability are the key driver.
Some principles:
 no common shared resource (limited risk of common failure)

one source, one ligne, 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
Aerospace
ARINC 429 reminder
 Each line has only one source and is connected to every
equipment that need the data transmitted by the source
 Each data in individually identified (by a label) and sent
Application
label
data
Application
Presentation
Session
Transport
Network
DataLink/MAC
Physical connection
A429
32 bit
label
Aerospace
data
parity
Information System requirement
In Information system, the major requirement is to insure that the
information is transmitted without any 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
Transport
A429 williamsburg
Network
DataLink/MAC
Physical connection
Aerospace
A429
Avionics market evolution
The evolution of the avionics market is exposed to a great
pressure for reducing cost.
In the same time, mature concepts arised:
 Electronics Modularity
 Operating System
 Decision to re-use and share common resource
Aerospace
AFDX : a real challenge
The key driver for AFDX design choices must answer to
lot of 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
component (COTS: commercial off-the-shelf) under
certification constraint
Aerospace
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
->Best candidate :
 ATM (backbone telecom and ADSL) and cell switching
ITU
std
IEEE
std
IETF Internet
std
POP
SMTP
...
SNMP
FTP
HTTP
TCP/UDP
ATM
G992.1
"ADSL"
Aerospace
IP
IEEE 802.3
"Ethernet"
IEEE 802.11
"WI-FI"
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
Aerospace
Part 3 : 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 definiton 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.
Aerospace
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.
Aerospace
AFDX : an Open Standard
OSI
reference
Model
IETF Internet
std
SNMP
IEEE
std
ARINC 664 Part 7 : AFDX
SNMP
TFTP
TFTP
ARINC 653
Application
Presentation
Session
Transport
TCP/UDP
Network
IP
TCP
UDP
optional
IP
AFDX special features
DataLink/MAC
Physical connection
IEEE 802.3
"Ethernet"
IEEE 802.3 Ethernet MAC + PHY
ARINC 600
Aerospace
AFDX : basic network architecture
AFDX is based on the
Ethernet switched network.
It is built with:
modular avionocs
modular
avionocs
LRU
RDC
ES
ES
ES
ES
 Switches, network devices in
SW
charge of data forwarding
ES
 End System, network devices in
charge of data
SW
SW
SW
transmission/reception
SW
SW
Aerospace
ES
ES
LRU
modular
avionocs
ES
ES
modular
avionocs
RDC
AFDX key feature : Resource Sharing
The main resources shared by AFDX are
 the wiring and
 the attached network devices
IMA/IME
module
ES
IMA/IME
module
LRU
RDC
ES
ES
ES
SW
SW
SW
SW
SW
Aerospace
ES
ES
LRU
IMA/IME
module
ES
ES
RDC
IMA/IME
module
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 needed
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
ES
ES
ES
SW
AFDX
Ethernet data link
Virtual Link
Aerospace
ARINC 429
N/A
twisted pair copper wire
ES
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
Ethernet data link
Virtual Link
Aerospace
ES
Traffic filtering
Traffic filtering
+ forwarding
ES
ES
AFDX key feature : Redundancy
In response to the "Availability" requirement AFDX network is basicaly
redundant.
Each End-System has the capability to send twice each message toward to
independant set of switches.
network A
ES
SW
SW
ES
SW
SW
ES
network B
Key Feature : Redundancy Management
=> each frames are numbered when
transmitted.
Aerospace
Key Feature : Redundancy Management
=> each frames are sorted when received.
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
End System traffic shaping
BAG
Aerospace
BAG
delayed
frame
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
Key Feature : Traffic policing
the traffic is generated according to bandwidth contract
the traffic is monitored according to bandwidth contract
ES
ES
SW
ES
ES
Aerospace
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 evaluated the worst
case filling level of shared output queue and, hence to estimate the
message delay
ES
ES
SW
ES
ES
Ethernet data link
shared output message queue
Virtual Link
Aerospace
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
Aerospace
AFDX "counterpart" : Latency management
 The latency computation is based on the worst case
that can happens.
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....

Aerospace
This gives a certifiable network configuration that
under-uses the true Ethernet capability
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
Aerospace
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 need to have trusted
development that commercial components can not
provide
 The result is that the material itself is still developped
specifically for aeronautical market
(...with the cost associated to certification compliance...)
Aerospace