Time-Sensitive Networking (TSN) is a collection of mechanisms to enhance the realtime transmission capability of Ethernet networks. TSN combines priority queuing, traffic scheduling, and the Time-Aware Shaper (TAS) to carry periodic traffic with ultra-low latency and jitter. That is, so-called Talkers send periodic traffic with highest priority according to a schedule. The schedule is designed such that the scheduled traffic is forwarded by the TSN bridges with no or only little queuing delay. To protect that traffic against other frames, the TAS is configured on all interfaces such that lower-priority queues can send only when high-priority traffic is not supposed to be forwarded. In the literature on scheduling algorithms for the TAS there is mostly the explicit or implicit assumption that the TAS also limits transmission slots of high-priority traffic. In this paper we show that this assumption can lead to tremendous problems like very long queuing delay or even packet loss in case of faulty frames. A faulty frame arrives too early or too late according to the schedule, it is missing or additional. We construct minimal examples to illustrate basic effects of faulty frames on a single link and demonstrate how this effect can propagate through the networks and cause remote problems. We further show using simulations that a single slightly delayed frame may lead to frame loss on multiple links. We show that these problems can be alleviated or avoided when TAS-based transmission slots for high-priority traffic are configured longer than needed or if they are not limited at all.

翻译：时间敏感网络（TSN）是一系列增强以太网实时传输能力的机制集合。TSN通过结合优先级队列、流量调度与时间感知整形器（TAS），能够以超低延迟和抖动承载周期性流量。具体而言，所谓的发送端按照预定调度表以最高优先级发送周期性流量。调度表的设计使得被调度的流量在通过TSN网桥时仅产生极少或无需排队延迟。为保护此类流量免受其他帧干扰，TAS在所有接口上配置为仅当无需转发高优先级流量时才允许低优先级队列发送。在现有关于TAS调度算法的文献中，普遍存在一个显性或隐性的假设：TAS同时也会限制高优先级流量的传输时隙。本文通过理论分析与仿真实验证明，该假设在出现故障帧时可能导致严重问题，例如极长的排队延迟甚至丢包。故障帧指相对于调度表过早到达、过晚到达、缺失或额外出现的帧。我们构建了最小示例以说明故障帧在单条链路上的基础影响，并论证了这种影响如何通过网络传播引发远端问题。进一步通过仿真表明，单个轻微延迟的帧可能导致多条链路上的帧丢失。研究最后指出，若将基于TAS的高优先级流量传输时隙配置为比实际需求更长或完全不设限制，上述问题可得到缓解或避免。