Network Calculus-Based Latency for Time-Triggered Traffic under Flexible Window-Overlapping Scheduling (FWOS) in a Time-Sensitive Network (TSN)

Abstract

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.

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.…”

“…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. 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.…”

“…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.…”

Joint Scheduling and Routing Optimization for Deterministic Hybrid Traffic in Time-Sensitive Networks Using Constraint Programming

“…Additionally, they enable real-time synchronization and allow for effective management of different traffic types [5]. The TSN framework is designed to handle hybrid traffic encompassing three types, each with distinct priorities for mixed-criticality applications [6]. The highest priority class, which requires bounded latency and zero-jitter, is the TT traffic.…”