Worst-case backlpg for AFDX network with n-priorities

International audienceIn most recent avionics systems, AFDX (Avionics Full Duplex Switched Ethernet) is the network used to replace the previously employed point-to-point networks. AFDX guarantees bandwidth reservations by means of virtual links which can be classified with two priority levels. AFDX compliant switches implement output buffers at each switch output port. The stored frames leave each output port according to a fixed priority FIFO policy. Overflow of these buffers must be avoided at all cost to prevent data loss. Although the AFDX standard determines the minimum buffer size dedicated to an output port, the actual length of each priority buffer, is a designer decision. Previous works address the worst case backlog of ADFX buffers of one and two priorities. In this work we assume an extended AFDX network in which virtual links can be classified into n-priorities and present the problem statement to compute an upper bound on the worst case backlog faced by each buffer of each output port in each switch of the network

Priority assignment on an avionics switched Ethernet network (QoS AFDX)

International audienceAFDX (Avionics Full Duplex Switched Ethernet) standardised as ARINC 664 is a major upgrade for avionics systems. For current aircrafts, it implements a FIFO scheduling policy and allows the transmission of sporadic flows between avionics functions distributed on a set of end systems. The certification imposes to guarantee that the end-to-end delay of any frame transmitted on the network is upper-bounded and that no frame is lost due to buffer overflow. This guarantee is obtained thanks to a worst-case analysis which is based on either network calculus or trajectory approach. However it leads to an over-dimensioning of the network. For future aircraft, it is envisioned to use a Fixed Priority scheduling policy in order to better use network resources (QoS AFDX). Existing AFDX switches implement two priority levels. A worst-case analysis of such a network exists, based on the Trajectory approach. Thus, the remaining issue is to assign efficiently the available priorities to the flows. The contribution of this paper deals with this issue. It proposes to assign the priorities to the flows using the well-know Optimal Priority Assignment algorithm (OPA) which was first defined for monoprocessor preemptive systems. The proposed solution is applied on two case studies. The overall worst-case delay is reduced by 30 % on a small configuration and 20 % on a realistic one

QoS-aware AFDX: Benefits of an efficient priority assignment for avionics flows

International audienceAFDX (Avionics Full Duplex Switched Ethernet) standardised as ARINC 664 is a major upgrade for avionics systems. The certification imposes to guarantee that the end-toend delay of any frame transmitted on the network is upperbounded and that no frame is lost due to buffer overflow. This guarantee is obtained thanks to a worst-case analysis assuming a FIFO scheduling policy of flows on each output port. For future aircraft, it is envisioned to modify AFDX switch and to use a Fixed Priority scheduling policy of flows (QoS AFDX using IEEE 802.p mechanisms). A worst-case analysis of such a network has been proposed, based on the Trajectory approach. But the remaining issue is to efficiently assign available priorities to the avionics flows inside the network without modifying the application knowledge. The objective is then to minimise overall the worst case end to end delay of flows and consequently to minimise needed buffer size at switch level. The main contribution of this paper deals with the assignment of priorities to the flows using the well-know Optimal Priority Assignment algorithm (OPA) which was first defined for monoprocessor preemptive systems. The schedulability test is then based on the worst case delay analysis of each flow allocated on the AFDX QoS network computed by the trajectory approach. The proposed mechanisms have been applied on an industrial AFDX case study using two priority levels and the overall worstcase delay could be reduced by 20 %

Applying Trajectory approach with static priority queuing for improving the use of available AFDX resources

International audienceAFDX (Avionics Full Duplex Switched Ethernet) standardized as ARINC 664 is a major upgrade for avionics systems. The mandatory certification implies a worst-case delay analysis of all the flows transmitted on the AFDX network. Up to now, this analysis is done thanks to a tool based on a Network Calculus approach. The more recent Trajectory approach has been proposed for the computation of worst-case response time in distributed systems. This paper shows how the worst-case delay analysis of an AFDX network can be improved using an optimized Trajectory approach. This approach, which implements static priority QoS policies, provides bound needed for deterministic avionics flows (high priority) and allows addition of (lower priority) non avionics flows

Trends in avionics switched Ethernet networks

The AFDX (Avionics Full DupleX switched Ethernet) which has been standardized as ARINC 664 is based on Ethernet Technology

Managing temporal allocation in Integrated Modular Avionics

International audienceRecent civil airborne platforms are produced using Integrated Modular Avionics (IMA). IMA promotes both sharing of execution and communication resources by the avionics applications. Designs following IMA decrease the weight of avionics equipment and improve the whole system scalability. However, the price to pay for these benefits is an increase of the system's complexity, triggering a challenging system integration process. Central to this integration step are the timing requirements of avionics applications: the system integrator has to find a mapping of applications and communications on the available target architecture (processing modules, networks, etc.) such as end-to-end delay constraints are met. These challenges stress the need for a tool capable of evaluating different integration choices in the early design stages of IMA. In this paper, we present and formalize the problem of spatial and temporal integration of an IMA system. Then, we focus on the temporal allocation problem which is critical to ensure a proper timely behavior of the system. Two main properties are presented to ensure perfect data transmission for hard real-time flows. To quantify the quality of a set of valid temporal allocations, CPM utilization and communication robustness performance criteria are defined. We show on an example that both criteria are antagonist and that they can be leveraged to choose an allocation that either improves the system computing performance or the robustness of the network

End-to-end delay analysis in an Integrated Modular Avionics architecture

National audienceRecent modular avionics architectures have been designed to share computation and communication resources. However, such an approach creates new challenges to master the temporal properties of avionics applications. In the context of IMA (Integrated Modular Avionics), it is crucial to investigate the performance gains that future integration platforms and software will propose. This paper brings to light the impact of spatial and temporal integration choices on the communication performance (e.g. message loss rate, latencies, ...). The conclusion of this investigation is that it is necessary to conduct a thorough modeling and simulation study of an IMA architecture integrating several applications during its early design stages

Extending CAN over the air: an interconnection study through IEEE802.11

International audienceThe flexibility of wireless connectivity is appealing in the context of industrial networks. This paper discusses the use of a wireless protocol to interconnect remotely located fieldbuses. The focus of this paper is to analyze the feasibility and design issues related to this type of hybrid network architecture. Therefore, we concentrate on deriving appropriate bridging strategies for a network topology composed of remotely located CAN buses interconnected through a wireless local area network following the IEEE802.11g protocol. Using this very simple and cost-effective architecture, we show in this study that by intelligently leveraging the features of CAN and IEEE802.11g in the interconnection policies employed, the missed deadlines can be limited for the CAN frames carried by the wireless network