Analysis and development of new queue draining mechanisms for IEEE 802 standards-based bridged real-time ethernet networks

One of the major trends in current times is the fast growing number of interconnections between smart electronic devices. Such interconnections between devices impose more stringent specification requirements on the underlying communication networks. Often these growing requirements result in an increase of the required network bandwidth; furthermore, the emerging real-time applications’ demands on network latency time specifications are growing. However, these requirements on network latency time cannot always be solved with an increase of bandwidth.

In the past, the standard IEEE Std 802.1Q based Ethernet networks, without any special additions, offered a best effort type of service for networked electronic devices. The only supported prioritization mechanism was strict priority. Strict priority follows the simple concept ’highest priority first’. Such a mechanism is not capable of providing latency guarantees in converged Ethernet networks that are required by many applications. Furthermore, the ’highest priority first’ scheme is beneficial in networks with a small amount of high priority traffic, but it is not suitable for net?works with a high amount of high priority traffic.

Audio Video Bridging (AVB) was the first approach of the IEEE 802.1 Working Group to add a real-time mechanism to standard IEEE 802.1 bridging for high bandwidth streams with a defined upper bound of latency. This is the starting point of this research work. The resulting achievable worst-case latency time is analysed and compared with defined goals for industrial and automotive Ethernet network specifications. In order to perform an in-depth analysis of the latency timing, a latency simulator is created, which allows for a graphical analysis of the different occurring latency components.

Based on this analysis, new mechanisms are developed, investigated and analysed in order to achieve the best latency requirements for automotive and industrial applications using bridged real-time Ethernet networks. This includes queue draining mechanisms to reduce the interference between low and high priority traffic as well as the interference between different high priority traffic streams. One essential component required by these mechanisms is time synchronization. Hence the impact of networks using these mechanisms, especially time synchronization, on automotive measurement and development tools is investigated. In addition it is shown how a time-aware end station, which is necessary to apply these mechanisms, can be built.