To achieve low latency transmission of time-sensitive flows in Ethernet networks, the IEEE introduced the IEEE 802.1Qbu Standard, which specifies a 1-level preemption scheme for IEEE 802.1 networks. The specification allows the suspension of a preemptable frame prior to its completion for the speedy transmission of an express frame; but any other preemptable frame cannot be transmitted before the completion of the already preempted frame. While this approach improves the performance of express frames, the performance is negatively impacted in scenarios where the number of express frames is high. Another limitation is the fact that preemptable frames with timing requirements can suffer long blocking periods due to the non-preemptive service of frames in the same category. This is irrespective of the individual priority level of each frame.

Recently, a multi-level preemption scheme has been proposed to circumvent these limitations. The work focused on the feasibility and implementation requirement of such an approach, but a formal analysis of the worst-case performance guarantees under the proposed scheme was not provided. In this paper, we fill this gap by presenting the aforementioned analysis of the TSN IEEE 802.1Qbu networks under the multi-level preemption assumption. Evaluation is performed with a realistic automotive use-case and the results showcase an improvement up to 53.07% for preemptable frames with firm timing requirements.

为了实现以太网中对时间敏感的流的低延迟传输，IEEE引入了IEEE 802.1Qbu标准，该标准为IEEE 802.1网络规定了一种1级抢占方案。该规范允许可抢占帧在完成之前暂停，以快速传输快速帧; 但在已被抢占的帧完成之前，无法发送任何其他可抢占的帧。尽管此方法提高了快速帧的性能，但在快速帧数较多的情况下，性能受到负面影响。另一个局限性是由于具有相同类别的帧的非抢先服务，具有定时要求的可抢占帧会遭受较长的阻塞时间。这与每个帧的优先级无关。

近来，已经提出了一种多级抢占方案来规避这些限制。该工作侧重于这种方法的可行性和实施要求，但未对提议的方案中的最坏情况下的性能保证进行正式分析。在本文中，我们通过提出在多级抢占假设下对TSN IEEE 802.1Qbu网络的上述分析来填补这一空白。评估是基于实际的汽车用例进行的，结果显示，对于具有固定时间要求的可抢占式框架，改进幅度高达53.07％。