aerospace afdx tutorial session one : afdx background
Post on 20-Dec-2015
299 views
TRANSCRIPT
Aerospace
AFDX Tutorial
Session One : AFDX background
FLS
/04/
005 6
09 IR
00
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
FLS
/04/
005 6
09 IR
00
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.
Network driver
Specializationcommunication layers
Factorization
Network driver
Application Application
Communication services
communication serives
Application
communication serives
Application
Object Oriented paradigm
FLS
/04/
005 6
09 IR
00
Aerospace
Usual communication layers
OSIreference
Model
Physical connection
DataLink/MAC
Network
Transport
Session
Presentation
Application services
IETF Internetstd
IP
TCP/UDP
SNMP
IEEEstd
IEEE 802.3"Ethernet"
FTP
IEEE 802.11"WI-FI"
HTTP
POP SMTP
ITUstd
...
G992.1"ADSL"
ATM
Application
Communication services
FLS
/04/
005 6
09 IR
00
Aerospace
Part 2 : Aircraft communication
Internal Aircraft communication
External Aircraft communication : out of this tutorial scope
FLS
/04/
005 6
09 IR
00
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 platformcontrol of platform" area not in the "informationinformation" area.
FLS
/04/
005 6
09 IR
00
Aerospace
Digital transmission
Two kind of digital usage on-board: Processus ControlProcessus 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 systemsInformation systems based of information exchanges
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
FLS
/04/
005 6
09 IR
00
Aerospace
Processus control requirements
As the transmitted data are involved in processus controlprocessus control , the transmission must be done with a minimum bounded delay. The stability of the flight relies on this transmissionTime, 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
FLS
/04/
005 6
09 IR
00
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
Physical connection
DataLink/MAC
Network
Transport
Session
Presentation
Application
Application
label data
A429
label data parity32 bit
FLS
/04/
005 6
09 IR
00
Aerospace
Information System requirement
In Information systemInformation 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
errorThe former aircraft generation still used A429 but added acknowledged data block
Physical connection
DataLink/MAC
Network
Transport
Application
A429 williamsburg
A429
FLS
/04/
005 6
09 IR
00
Aerospace
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
FLS
/04/
005 6
09 IR
00
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
FLS
/04/
005 6
09 IR
00
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 switchingIEEE
std
IEEE 802.3"Ethernet"
IEEE 802.11"WI-FI"
IETF Internetstd
IP
TCP/UDP
SNMP FTP HTTP
POP SMTP ...
ITUstd
G992.1"ADSL"
ATM
FLS
/04/
005 6
09 IR
00
Aerospace
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
FLS
/04/
005 6
09 IR
00
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.
FLS
/04/
005 6
09 IR
00
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.
FLS
/04/
005 6
09 IR
00
Aerospace
AFDX : an Open Standard
OSIreference
Model
IETF Internetstd
IP
TCP/UDP
SNMP
IEEEstd
IEEE 802.3"Ethernet"
TFTP
Physical connection
DataLink/MAC
Network
Transport
Session
Presentation
Application
ARINC 664 Part 7 : AFDX
IEEE 802.3 Ethernet MAC + PHY
IP
UDP TCPoptional
SNMP TFTP
AFDX special features
ARINC 600
ARINC 653
FLS
/04/
005 6
09 IR
00
Aerospace
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
AFDX : basic network architecture
ESES
SWSW
modular avionocs
ESES
modularavionocs
ESES
LRU
ESES
RDC
ESES
SWSW
SWSW
SWSW
modularavionocs
ESES
SWSW SWSW
modularavionocs
ESES
LRU
ESES
RDC
ESES
FLS
/04/
005 6
09 IR
00
Aerospace
IMA/IMEmodule
RDC
AFDX key feature : Resource Sharing
The main resources shared by AFDX are
the wiring and
the attached network devices
IMA/IMEmodule
ESES
IMA/IMEmodule
ESES
LRU
ESES
RDC
ESES
SWSW
SWSW
SWSW
ESES
SWSW
SWSW
IMA/IMEmodule
ESES
LRU
ESES ESES
FLS
/04/
005 6
09 IR
00
Aerospace
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 addresschannels are merged together on one Ethernet data link
ESESESES
ESES
ESESAFDX
Ethernet data link
Virtual Link
ARINC 429
N/A
twisted pair copper wire
SWSW
FLS
/04/
005 6
09 IR
00
Aerospace
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.
SWSW
ESES
Ethernet data link
Virtual Link
ESES
ESES
ESES
Traffic filtering : Restricted access for only configured VL
Traffic filtering : Restricted access for only configured VL
Tra
ffic
filt
erin
g+
fo
rwa
rdin
g
Tra
ffic
filt
erin
g
FLS
/04/
005 6
09 IR
00
Aerospace
network B
network A
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.
ESES
SWSW SWSW
SWSW SWSW
ESES
ESES
Key Feature : Redundancy Management=> each frames are sorted when received.
Key Feature : Redundancy Management=> each frames are numbered when transmitted.
FLS
/04/
005 6
09 IR
00
Aerospace
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
Source Application
End System traffic shaping
sent fralme
delayed frame
BAG BAG
delayed frame
determinism reason
FLS
/04/
005 6
09 IR
00
Aerospace
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.
SWSW
ESES
ESES
ESES
ESES
Key feature : Traffic shapingthe traffic is generated according to bandwidth contract
Key Feature : Traffic policingthe traffic is monitored according to bandwidth contract
FLS
/04/
005 6
09 IR
00
Aerospace
SWSW
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.
ESES
Ethernet data link
shared output message queue
Virtual Link
ESES
ESES
ESES
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
FLS
/04/
005 6
09 IR
00
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 systeminformation system"
Leads to create large number of VL even if the VL is not used continuously
FLS
/04/
005 6
09 IR
00
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.... This gives a certifiable network configuration that
under-uses the true Ethernet capability
FLS
/04/
005 6
09 IR
00
Aerospace
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
FLS
/04/
005 6
09 IR
00
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...)