AFDX Tutorial

1. AFDX Tutorial Session One : AFDX background Aerospace

2. 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

3. Application Application Communication services Network driver Specialization communication layers Factorization 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 communication serives communication serives Network driver Object Oriented paradigm Aerospace

4. IEEE std IETF Internet std ITU std POP SMTP ... SNMP FTP HTTP TCP/UDP IP ATM IEEE 802.3 "Ethernet" IEEE 802.11 "WI-FI" G992.1 "ADSL" Usual communication layers OSI reference Model Application Application services Communication services Presentation Session Transport Network DataLink/MAC Physical connection Aerospace

5. Part 2 : Aircraft communication Internal Aircraft communication External Aircraft communication : out of this tutorial scope Aerospace

6. 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

7. Digital transmission • Two kind of digital usage on-board: • Processus Control • based on sampling system techniques and datatransmission • data : the digital value of an analogical parameter (e.g. speed; heigth, attitude,....) • transmission : no response is expected • Information systems • based of informationexchanges • 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 Aerospace

8. 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

9. Application label data 32 bit A429 label data parity 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 Presentation Session Transport Network DataLink/MAC Physical connection Aerospace

10. Application A429 williamsburg A429 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 Transport Network DataLink/MAC Physical connection Aerospace

11. 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 • OperatingSystem • Decision to re-use and share common resource Aerospace

12. 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

13. IEEE std IETF Internet std ITU std POP SMTP ... SNMP FTP HTTP TCP/UDP IP ATM IEEE 802.3 "Ethernet" IEEE 802.11 "WI-FI" G992.1 "ADSL" Technological choices • Communication technologies from desktopcomputing market • ->Best candidate : • Ethernet for Physical layer • Internet for upper protocol layer • Communication technologies from multimediatelecom market • ->Best candidate : • ATM (backbone telecom and ADSL) and cell switching Aerospace

14. Finalchoice • 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

15. 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

16. 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

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

18. AFDX : basic network architecture modular avionocs • 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 RDC modular avionocs LRU ES ES ES ES SW SW SW ES SW SW SW ES ES ES ES LRU modular avionocs RDC modular avionocs Aerospace

19. 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 RDC IMA/IME module Aerospace

20. 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 SW ES ES ES ES AFDX Ethernet data link Virtual Link ARINC 429 N/A twisted pair copper wire Aerospace

21. 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 Aerospace

22. 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 ES network B SW SW Key Feature : Redundancy Management => each frames are sorted when received. Key Feature : Redundancy Management => each frames are numbered when transmitted. Aerospace

23. sent fralme delayed frame delayed frame 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 End System traffic shaping BAG BAG Aerospace

24. 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 policing the traffic is monitored according to bandwidth contract Key feature : Traffic shaping the traffic is generated according to bandwidth contract SW ES ES ES ES Aerospace

25. 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 SW ES ES ES Ethernet data link shared output message queue Virtual Link Aerospace

26. 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

27. 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 Aerospace

28. 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

29. 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