Power-over-Ethernet for avionic networks

Avionic networks are to an increasing extent based on Ethernet physical layer implementations due to economical and technical motivations. While conventional Ethernet-based systems are built up in star topologies, the physical layer can also be used to establish linear networks. Power-over-Ethernet (PoE) uses Ethernet data cabling for the transmission of power. Existing technology however is not able to transmit sufficient power for many avionic applications, particularly for such implemented in a linear topology. With a customized PoE approach, the power capabilities of PoE links can significantly be increased to more than 100 W. With an adequate fail-safe concept, the reliability of a linear Ethernet implementation can be increased, reducing the immanent safety drawback of a linear topology. The presented methods offer the potential to significantly reduce cost, complexity and weight of Ethernet-based system installations, aiming at greener avionics for future aircraft.

Introduction

Ethernet is about to become the new standard physical layer solution for networks in many fields of industry. This trend also applies to the aeronautic industry, where AFDX as an Ethernet based protocol is already widely used in modern avionic systems [1], and where growing interest can be observed to use either commercial off-the-shelf protocols (e.g. IP [2]) or upcoming real-time protocols (e.g. TTEthernet [3]), which are all based on Ethernet physical layer implementations. Much of the motivation for this trend stems from the prevalence of the standard in consumer and information technology, resulting in low component prices, widely available tools and knowledge support. Since also the automotive industry nowadays is about to introduce Ethernet in next generation cars [4], components for extended operating temperature ranges and with qualified¹

According to automotive standards, such as AECQ-100

robustness are available at low costs. Currently the most widespread Ethernet implementation is Fast Ethernet on twisted pair cables (IEEE 802.3 Clause 25). If not otherwise stated, this document therefore refers to this implementation. With data rates of 100 Mbit/s in a full-duplex communication scheme, Fast Ethernet satisfies the bandwidth requirements of many use cases. Fast Ethernet thus can be used from control data exchange in simple sensor-actuator networks up to audio/video streaming in multimedia applications.