Latency Analysis of Multiple Classes of AVB Traffic in TSN With Standard Credit Behavior Using Network Calculus

Abstract

Time-Sensitive Networking (TSN) is a set of amendments that extend Ethernet to support distributed safety-critical and real-time applications in the industrial automation, aerospace and automotive areas. TSN integrates multiple traffic types and supports interactions in several combinations. In this paper we consider the configuration supporting Scheduled Traffic (ST) traffic scheduled based on Gate-Control-Lists (GCLs), Audio-Video-Bridging (AVB) traffic according to IEEE 802.1BA that has bounded latencies, and Best-Effort (BE) traffic, for which no guarantees are provided. The paper extends the timing analysis method to multiple AVB classes and proofs the credit bounds for multiple classes of AVB traffic, respectively under frozen and non-frozen behaviors of credit during guard band (GB). They are prerequisites for non-overflow credits of Credit-Based Shaper (CBS) and preventing starvation of AVB traffic. Moreover, this paper proposes an improved timing analysis method reducing the pessimism for the worst-case end-to-end delays of AVB traffic by considering the limitations from the physical link rate and the output of CBS. Finally, we evaluate the improved analysis method on both synthetic and real-world test cases, showing the significant reduction of pessimism on latency bounds compared to related work, and presenting the correctness validation compared with simulation results. We also compare the AVB latency bounds in the case of frozen and non-frozen credit during GB. Additionally, we evaluate the scalability of our method with variation of the load of ST flows and of the bandwidth reservation for AVB traffic.

A Comprehensive Review on Time Sensitive Networks with a Special Focus on Its Applicability to Industrial Smart and Distributed Measurement Systems

“…The relation between the IEEE 802.1Qbu and IEEE 802.3br amendments is represented in Figure 8, where it is possible to notice that two different MAC layers are introduced, eMAC and pMAC, to handle, respectively, express and preemptable traffic. The effect of the preemption capability was evaluated in several works [106][107][108][109][110]. Conversely, authors of [111] underlined the importance to study the impact of the preemption activity also on the delay introduced in the Best Effort (BE) traffic communication.…”

Critical Offset Optimizations for Overlapping-Based Time-Triggered Windows in Time-Sensitive Network

“…Zhang et al [29] reduced the effect of higher priority flows on the lower priority traffic by selecting an appropriate transmission cycle and proper scheduling unit. On the other hand, the researchers in [4], [30]- [32] presented formal AVB latency analysis based on predefined TT schedules. The authors demonstrated some improvements in the CBS limitations.…”

“…Designing appropriate GCLs in all selected nodes while guaranteeing the quality-of-service (QoS) requirements for critical time flows is a complex and vital problem. The designer has to pay the highest attention to two significant aspects; the TT latency requirements, and the impact on unscheduled real-time traffic [4]. Although several safe analytical models have been proposed to speed TT scheduling, they still have a degree of pessimism in latency evaluations.…”

Quantitative Performance Comparison of Various Traffic Shapers in Time-Sensitive Networking

“…Since the standard 802.1Q [1] now supports multiple number of AVB classes, we extend the previous analysis work of supporting two classes [28] and three classes [29] to arbitrary number of AVB classes. The extension proof of credit bounds for arbitrary number of AVB classes can be found in our previous work [34]. Although [34] is the NC-based performance analysis for combined TAS and CBS, and TT transmission delays AVB traffic, AVB credits will not be affected by TT traffic if credit frozen during TT window and the protection interval ("guard band" (GB)), which is one of the cases discussed in [34].…”

“…Zhao et al [33] propose the performance analysis of AVB traffic under the coexistence of CBS and TAS. The same authors [34] extend the timing analysis for arbitrary number of AVB classes under the same architecture of TAS+CBS, considering both standard credit behavior and more generally assumed credit behavior but deviating from the standard 802.1Q [1]. Mohammadpour et al [35] consider the combination of non-time-triggered control-data traffic (CDT), CBS and ATS, and give the latency and backlog bounds for the traffic of CBS affected by ATS.…”