Deterministic and low latency communications are increasingly becoming essential requirements for several safety-critical applications, such as automotive and automation industries. The timesensitive networking (TSN) is an element of the new IEEE 802.1 standards that introduced Ethernet-based amendments to support these applications. One of these enhancements was presented in IEEE 802.1Qbv to define time-aware shaping (TAS) technique for time-triggered (TT) traffic scheduling. The TAS mechanism is a window-based scheduling using a gating system controlled by the gate control list (GCL) schedules in all nodes. Although several scheduling algorithms have been proposed to investigate the effects of windowrelated parameters on network performance, the offset difference ( ) between the same-class windows in the adjoining nodes has not been optimized yet. These optimizations are extremely crucial to implement less pessimistic latency schedules. In this paper, we propose an optimized flexible window-overlapping scheduling (OFWOS) algorithm that optimizes TT window offsets based on latency evaluations considering the overlapping between different priority windows at the same node. First, we formulate the GCL timings as mathematical forms under variable s between the same-priority windows. Then, an analytical model is implemented using the network calculus (NC) approach to express the worst-case end-to-end delay ( ) for TT flows and evaluated using a realistic vehicular use case. The OFWOS model optimizes under all overlapping situations between TT windows at the same node. In comparison with latest works of 3-hop and 30-hop TSN connections, the OFWOS reduces the bounds by 8.4% and 32.6%, respectively which accomplishes less pessimistic end-to-end latency bounds.
Deterministic latency is an urgent demand to pursue the continuous increase in intelligence in several real-time applications, such as connected vehicles and automation industries. A time-sensitive network (TSN) is a new framework introduced to serve these applications. Several functions are defined in the TSN standard to support time-triggered (TT) requirements, such as IEEE 802.1Qbv and IEEE 802.1Qbu for traffic scheduling and preemption mechanisms, respectively. However, implementing strict timing constraints to support scheduled traffic can miss the needs of unscheduled real-time flows. Accordingly, more relaxed scheduling algorithms are required. In this paper, we introduce the flexible window-overlapping scheduling (FWOS) algorithm that optimizes the overlapping among TT windows by three different metrics: the priority of overlapping, the position of overlapping, and the overlapping ratio (OR). An analytical model for the worst-case end-to-end delay (WCD) is derived using the network calculus (NC) approach considering the relative relationships between window offsets for consecutive nodes and evaluated under a realistic vehicle use case. While guaranteeing latency deadline for TT traffic, the FWOS algorithm defines the maximum allowable OR that maximizes the bandwidth available for unscheduled transmission. Even under a non-overlapping scenario, less pessimistic latency bounds have been obtained using FWOS than the latest related works.
Deterministic and low end-to-end latency communication is an urgent demand for many safety-critical applications such as autonomous vehicles and automated industries. The time-sensitive network (TSN) is introduced as Ethernet-based amendments in IEEE 802.1 TSN standards to support timetriggered (TT) traffic in these applications. In the presence of TT flows, TSN is designed to integrate Audio/Video Bridging (AVB) and Best Effort (BE) traffic types. Although AVB traffic has a lower priority than TT, it still requires low and deterministic latency performance, which may not be guaranteed under strict predefined TT scheduling constraints. For this reason, a window-overlapping scheduling algorithm is recently proposed in different works as analytical forms for TT latency under overlapping-windows based. But worst-case AVB latency evaluation under overlapped TT windows is also essential for critical optimizations and tradeoffs. In this paper, a worst-case end-to-end delay (WCD) for AVB traffic under overlapping-based TT windows (AVB-OBTTW) algorithm is proposed. Separate analytical models are derived using the network calculus (NC) approach for AVB-OBTTW with both non-preemption and preemption mechanisms. Using an actual vehicular use case, the proposed models are evaluated with backto-back and porosity configurations under light and heavy loading scenarios. For specific AVB credit bounds, a clear WCD reduction has been achieved by increasing the overlapping ratio (OR), especially under back-to-back configuration. Preemption and non-preemption modes are compared under different loading conditions, resulting in lower WCDs using preemption mode than non-preemption, especially with porosity style. Compared to the latest related works, AVB-OBTTW reduces WCD bounds and increases unscheduled bandwidth, leading to the highest enhancements with the maximum allowable OR.INDEX TERMS Safety-critical real-time systems, time-sensitive network (TSN), network calculus, worstcase latency analysis, AVB traffic, credit-based shaping (CBS).
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