Towards Quality of Service Provision with Avionics Full Duplex Switching

Avionics Full-Duplex Switched Ethernet (AFDX) has been designed to carry exclusively time-critical flows dictated by the severe real-time constraints of avionics. Certification methods ensure end-to-end communication delays are upper bounded at the cost of an over-provision of network bandwidth. This paper investigates the issues related to the efficient use of such wasted communication capacity. The basic idea is to push additional Ethernet flows of lower priority into the network with the goal of offering different quality of service levels to them. This addition should of course be transparent to real-time flows. Different scheduling policies, enforced at the end system and at the switches, can provide such features. This paper questions i) their impact on the real-time flow end-to-end delay and ii) the quality of service non real-time flows can expect in terms of end-to-end delay distribution. The ultimate goal of this study is to decide if such a network configuration offers the opportunity to deploy multimedia applications such as VoIP traffic, live video streaming over an AFDX industrial configuration. A first study investigates the use of static priority queuing and traffic scheduling tables on an industrial A350 AFDX configuration. Traffic scheduling tables are shown to be promising as they can spread non-critical traffic more evenly over time, reducing congestion peaks at switches. I. APPLICATION DOMAIN & CHALLENGE A. Application domain Avionics Full DupleX switching (AFDX) networks have become the de-facto technology for commercial avionics embedded networks in the last decade. AFDX follows ARINC664 Part 7 norm [1] and is currently deployed by the biggest aircraft manufacturers. A complex industrial ecosystem has been created around this technology to efficiently design, prototype and certify such networks. Even though alternative solutions are being investigated, this protocol will remain in use for couple of decades in the industry. AFDX is a switched Ethernet network where network interface cards (the so-called end systems) can only emit frames following a pre-defined virtual link (VL) setting. A VL is defined by minimum and maximum frame sizes, together with a BAG duration (Bandwidth Allocation Gap) that expresses the minimum duration that separates two consecutive frames of the VL. A given bandwidth is as such associated to a VL. BAG durations are selected within the discrete power set of {1, 2, 4, 8, 16, 32, 64, 128} milliseconds. AFDX switches are configured statically with VL routes that can be set as multicast. For each egress port, two queues with different priority levels exist. Fig. 1: Example of an A350-like AFDX network topology. Switches are given by red vertices, other nodes representing end systems. Figure 1 represents an example network similar to the ones deployed on an A350 aircraft. It is composed of 126 end systems interconnected by two redundant AFDX networks composed of 7 switches each. End systems generate 1106 VLs.