Methods for bounding end-to-end delays on an AFDX network Hussein Charara, Jean-Luc Scharbarg, J´ erˆ ome Ermont, Christian Fraboul IRIT - ENSEEIHT 2, rue Camichel 31000 Toulouse - France Hussein.Charara@enseeiht.fr Abstract Architectures of avionics networks, such as that of the Airbus A380, currently know important evolutions. This is principally due to the increase in the complexity of the embedded systems, in term of rise in number of inte- grated functions and their connectivity. The evolution of Switched Ethernet technologies allows their implementa- tion as an avionics architecture (AFDX: Avionics Full Du- plex Switched Ethernet). The problem is then to prove that no frame will be lost by the network (no switch queue will overflow) and to evaluate the end-to-end transfer delay through the network. The objective of this paper is to present and shortly com- pare three methods for the evaluation of end-to-end delays: network calculus, queuing networks simulation and model checking. 1. Introduction The evolution of avionics embedded systems and the am- plification of the integrated functions number in the current aircraft imply a huge increase in the exchanged data quan- tity and thus in the number of connections between func- tions. To control this complexity, we can benefit from the tech- nological developments based on the concept of modular architecture [2, 3]. But the growth of the number of multi point communication, such as the setting in motion of em- bedded networks, constitutes one of the major stakes of new generation architectures. Several avionics architec- tures were developed but the most of them rest on rather old means of communication, like the ARINC 429 data busses which are mono transmitter buses with limited per- formances (100 Kbits/s) [6]. The solution adopted by Airbus for the new A 380 gen- eration consists on the utilization of a recognized standard which allows a re-use of development tools as well as of existing material components while achieving better per- formance. It consist of the Switched Ethernet technology which benefits from a long industrial experiment [4], that allows to have confidence in the reliability of the material and on the facility of its maintenance. Hence aeronautical system can profit of a much more powerful technology than the traditional avionics bus (Switched Ethernet / 100 Mbps). The disadvantage of Ethernet, opposite to an avionics application, is the non intrinsic determinism of its access method to the physical support, CSMA/CD (which induces possible collisions on the point-to-point links level) [5]. The solution is thus to use bi-directional links and so Full Duplex Switched Ethernet (AFDX) [7], where each equip- ment, in this architecture is only connected to a switch by the means of a Full Duplex link [8]. This way, there can- not be any more collisions on the physical support, and the CSMA/CD is no more necessary [24]. This standardized solution via the ARINC 664, elimi- nates the inherent indeterminism of the traditional Ethernet and the collision frame losses. But, the ARINC 664 shifts in fact the problem to the switch level where various flows will enter in competition for the use of the resources of the switch. This problem results in: • Congestion on the output ports of the switch, if at a given time too much traffic moves towards one port only, there will be frame losses by overflow of it queues. • Moreover, a burst of traffic, due to a passenger obstruc- tion on a switch port, can likely encumber the neigh- bor switch. Thus, congested switches can lead to loss of frames. • In the same way, the storage of frames in the switches queues can involve latency and important jitter. In order to understand if such congestions can occur in the network, it is necessary to study the performance of the net- work. The objective is to measure: Proceedings of the 18th Euromicro Conference on Real-Time Systems (ECRTS’06) 0-7695-2619-5 /06 $20.00 © 2006 IEEE