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

Abstract

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.

Worst-Case Latency Analysis for AVB Traffic Under Overlapping-Based Time-Triggered Windows in Time-Sensitive Networks

“…Accordingly, allowing TT to overlap will undoubtedly improve the unscheduled traffic performance [6]. But strict constraints must be applied to bound the overlapping ratio that guarantees TT requirements, as discussed in [8], [7]. Shalghum et al [7] proposed an analytical model for the worst-case end-to-end latency of TT traffic based on flexible window-overlapping scheduling (FWOS) algorithm, which was used to determine the VOLUME 10, 2022 maximum allowable overlapping ratio (OR) that guarantees TT latency deadlines.…”

“…Shalghum et al [7] proposed an analytical model for the worst-case end-to-end latency of TT traffic based on flexible window-overlapping scheduling (FWOS) algorithm, which was used to determine the VOLUME 10, 2022 maximum allowable overlapping ratio (OR) that guarantees TT latency deadlines. More latency-based optimizations for FWOS model were introduced in [8] as an optimized FWOS (OFWOS) algorithm, resulting in a complete view for the overlapping effect on the TT latency performance. As the TT overlapping was proposed to support soft real-time flows (AVB), a complete view for the worst-case AVB latency under these overlaps is essential to make critical tradeoffs with TT evaluations and implement the most appropriate GCL designs.…”

“…Only one guard band is required during the hyper-period. In [7] and [8], all overlapping situations are considered to express and evaluate the worst-case TT latency behavior with both configuration methods. Nevertheless, the worst-case end-to-end latency for AVB traffic under those overlapping situations is critically essential to provide critical optimizations and tradeoffs.…”

“…One of the attractive design ideas is to allow TT windows to overlap in each node leading to more available bandwidth for unscheduled traffic, as suggested in [5], [6]. The TT overlaps have been optimized in [7], [8] to ensure worst-case TT latency requirements. Together with the TT QoS needs, the worst-case performance evaluations for AVB traffic are essential under considering TT impacts.…”

“…Accordingly, the presented forms are evaluated under porosity (one-sided overlapping) and back-to-back (two-sides overlapping) configurations. These evaluations (AVB latencies under variable OR) with those in [8] (TT latencies under variable OR) can be considered as a complete helpful guide for TSN designers to implement more appropriate and trusted GCL schedules that guarantee worstcase latency deadlines for hard/soft real-time traffic. Thus, the main contributions of this paper can be summarized as:…”