Cyclic Queuing and Forwarding (CQF) is a key Time-Sensitive Networking (TSN) shaping mechanism that ensures bounded latency using a simple gate control list (GCL). Recently, variants of CQF, including Cycle Specific Queuing and Forwarding (CSQF) and Multi Cyclic Queuing and Forwarding (MCQF), have emerged. While popular TSN mechanisms such as the Time-Aware Shaper (TAS), Asynchronous Traffic Shaper (ATS), Credit-Based Shaper (CBS), and Strict Priority (SP) have been extensively studied, cyclic shapers have not been thoroughly evaluated. This paper presents a comprehensive analysis of CQF, CSQF, and MCQF, providing insights into their performance. We quantify delays through simulations and quantitative analysis on both synthetic and realistic networks. For the first time, we introduce an open-source OMNeT++ and INET4.4 based framework capable of modeling all three cyclic shaper variants. Our tool facilitates the validation of new algorithms and serves as a benchmark for cyclic shapers. Our evaluations reveal that MCQF supports diverse timing requirements, whereas CSQF, with its additional queue, often results in larger delays and jitter for some TT flows compared to CQF. Additionally, CSQF does not demonstrate significant advantages in TSN networks where propagation delays are less critical than in wide-area networks (WANs).

Time-Sensitive Networking (TSN) supports multiple traffic types with diverse timing requirements, such as hard real-time (HRT), soft real-time (SRT), and Best Effort (BE) within a single network. To provide varying Quality of Service (QoS) for these traffic types, TSN incorporates different scheduling and shaping mechanisms. However, assigning traffic types to the proper scheduler or shaper, known as Traffic-Type Assignment (TTA), is a known NP-hard problem. Relying solely on domain expertise to make these design decisions can be inefficient, especially in complex network scenarios. In this paper, we present a proof-of-concept highlighting the advantages of a learning-based approach to the TTA problem. We formulate an optimization model for TTA in TSN and develop a Proximal Policy Optimization (PPO) based Deep Reinforcement Learning (DRL) model, called “TTASelector”, to assign traffic types to TSN flows efficiently. Using synthetic and realistic test cases, our evaluation shows that TTASelector assigns a higher number of traffic types to HRT and SRT flows compared to the state-of-the-art Tabu Search-based metaheuristic method.

Cyclic Queuing and Forwarding (CQF) is an increasingly adopted mechanism in Time-Sensitive Networking (TSN) for bounding end-to-end delays through fixed-length cycles with alternating transmission queues. While timing guarantees for CQF flows are well established under both time-triggered (TT) and event-triggered (ET) implementations, the worst-case interference that CQF may impose on other traffic classes in mixed-criticality TSN networks remains an open problem. This challenge is exacerbated by the structured, non-work-conserving behavior of CQF and the complexity of its interaction with heterogeneous TSN scheduling mechanisms such as TAS, CBS, and SP. This paper presents the first formal framework for quantifying the worst-case interference caused by CQF on other schedulers under both TT- and ET-based implementations. We propose a network-calculus-based CQF real-time interface abstraction that models the residual service available to coexisting traffic. We formally derive closed-form upper bounds on CQF-induced interference, explicitly capturing bidirectional interactions between CQF and both higher- and lower-priority traffic classes. These bounds can be modularly and seamlessly integrated into existing schedulability analyses, enabling scalable and compositional timing verification in hybrid TSN architectures. Extensive evaluations on synthetic benchmarks and realistic TSN configurations demonstrate the analytical effectiveness, scalability, and practical applicability of the proposed framework in certifying end-to-end guarantees in mixed-criticality TSN systems.

Different scheduling mechanisms in Time Sensitive Networking (TSN) can be integrated together to design and support complex architectures with enhanced capabilities for mixed critical networks. Integrating Frame Preemption (FP) with Credit-Based Shaper (CBS) and Gate Control List (GCL) opens up different modes and configuration choices resulting in a complex evaluation of several possibilities and their impact on the Quality of Service (QoS). In this paper, we implement and quantify the integration of preemptive CBS with GCL by incorporating FP into the architecture. Our experiments show that the end-to-end delay of Audio Video Bridging (AVB) flows shaped by CBS reduces significantly (up to 40%) when AVB flows are set to preemptable class. We further show that the jitter of Time Triggered (TT) traffic remains unaffected in "with Hold/Release" mode. Furthermore, we propose to introduce Guardband (GB) in the "without Hold/Release" to reduce the jitter of the TT flow. We compare all the different integration modes, starting with CBS with GCL, extending it further to FP. We evaluate all feasible combinations in both synthetic and realistic scenarios and offer recommendations for practical configuration methods.

Time-sensitive networking (TSN) is an evolving set of Ethernet standards designed to ensure deterministic communication. Several schedulers can be applied in TSN to support the transmission of mixed time-critical traffic, among which deficit round robin (DRR) is a potential candidate since it can achieve fair queuing with very low complexity. The real-time quality of service (QoS) performance of DRR is determined by the quantum assigned to each queue, yet obtaining configurations with QoS guarantess at the network level is challenging due to the complex interactions of traffic flows. Conventional configuration methods typically adopt the framework based on ex-post schedulability verification, using heuristic algorithms to search for feasible configurations. However, these methods incur significant time overhead during the solution searching and performance verification stage and often lead to bandwidth wastage. This paper proposes an innovative DRR quantum assignment method that maximizes bandwidth utilization while providing prior realtime QoS guarantees. We use network calculus (NC) to build the optimization model and develop a numerical approximation approach based on local analytic solutions to solve for the optimal solution, making our method efficient and scalable. The correctness and optimality of our method are formally proven. Through experiments with network cases of various scales, we comprehensively evaluate the performance of our method. The results show that our method exhibits significant advantages over the conventional methods in terms of both bandwidth utilization and time complexity. In industrial-sized cases, our method saves around 31% of transmission bandwidth compared to the state-of-the-art with a runtime within milliseconds, which is several orders of magnitude faster.

Time-sensitive networking (TSN) has emerged as a promising standard for real-time domains. Efficiently determining critical configuration parameters for latency guarantees for time-critical flows remains an open question. Current configuration approaches rely on optimization methods with real-time performance analysis feedback to ensure deadline quality-of-service requirements. However, the ex-post verification-based optimization methods require exhaustive traversal of the entire network search space, leading to significant time consumption. This article proposes a novel, fast, and scalable deadline-aware method for configuring minimum bandwidth allocation for stream reservation (SR) classes in the TSN network, while guaranteeing deadline requirements for all time-critical traffic. We provide formal proof of our approach, which configures critical parameters in a real-time network with prior performance guarantees, thus reducing computational complexity. The analytical method is evaluated on synthetic cases, comparing it with state-of-the-art solutions to demonstrate validity and correctness. Moreover, an adapted real-world case shows the method's scalability, and minimum bandwidth reservations with guaranteed local deadlines for SR classes on all egress ports of the network can be achieved in seconds.

Time-sensitive networking (TSN) has great potential as an airborne network to interconnect modules in integrated modular avionics (IMA) system. For TSN-based IMA system, the hybrid scheduling of processing in modules and communication in TSN can guarantee its real-time performance. However, traditional task-message scheduling methods still lack applicability and scalability due to their incompatibility with the partition-task hierarchical architecture in modules and high complexity brought by the tight coupling of tasks and messages. Partition-message scheduling methods can ensure this applicability and scalability, but cannot coordinate tasks with messages well, thus sacrificing real-time guarantee capabilities. Namely, existing methods cannot comprehensively ensure the scheduling performance, including applicability, real-time, and scalability. Therefore, we propose a novel loosely coupled partition-(task)-message scheduling framework. It takes partitions and messages as scheduling objects and uses tasks as their coordination medium, to overcome the dependencies of existing methods on time-triggered tasks and guarantee applicability. Besides, it can also enhance real-time performance by analyzing task execution boundaries and application-layer end-to-end delays, and improve scalability through parallel optimizing and the incremental solving with block identification and adaptive adjustment. Experiments validate that it can schedule complex systems with up to 150 partitions, 1000 tasks, and 600 messages. Compared with the existing methods, it can accelerate the solving speed by 41% and reduce end-to-end delays by 27%.

Time-sensitive networking (TSN) has been considered as a promising networking candidate for avionics systems due to its capability of deterministic communication. In such TSN-based avionics systems, the network scheduling enables the timely transmission of messages. However, this is insufficient to satisfy the real-time requirements of functions since functions involve the chain execution of several tasks where messages only serve for the inter-task communication. In order to enhance the functionality of TSN-based avionics systems, scheduling should be extended from the network level to the system level to coordinate message transmission with task execution. Then, how to efficiently implement the hybrid scheduling of tasks and messages becomes an important issue. In this article, we construct a novel hybrid scheduling framework for TSN-based avionics systems, which consists of system consistency constraints, in-loop function delay calculation, and two hybrid scheduling algorithms. Consistency constraints restrict the unexpected interaction of messages and tasks for hybrid scheduling to guarantee the system-level determinism. Function delay is the end-to-end delay of the task chain, and its calculation provides the optimization objective for hybrid scheduling indicated by two metrics. Scheduling algorithms improve solving efficiency and functional performance through the incremental strategies of message dynamic ordering and task-message rescheduling. Experimental results verify that, compared with existing scheduling work that considers the dependency of messages on tasks, our work can complete complex scheduling for large systems even with hundreds of functions and can reduce function delays by 69% in reaction delay and 37% in age delay.

IEEE 802.1 Time-Sensitive Networking (TSN) comprises a set of real-time sub-standards that are rapidly becoming the de facto standard in numerous safety-critical domains. Nevertheless, existing TSN standards face challenges when encountering runtime reconfigurations, such as the efficient and safe real-time reconstruction of networks, which has become a current focal point of research. Although certain studies have commenced on dynamic scheduling and routing for TSN networks, a research gap persists in the online schedulability verification of mixed-critical messages. The present real-time performance analysis method is oriented toward assessing the schedulability of entire network flows. Consequently, even minor alterations made during reconfiguration necessitate the re-evaluation of all flows to verify their adherence to deadlines. In the paper, we propose an incremental performance analysis method (iPAM) to mitigate the cost of schedulability re-verification when reconfiguring the network of the TSN/TAS+CBS hybrid architecture. Extensive experiments conducted on a large-scale adapted realistic test case, demonstrate that, in comparison to the state-of-the-art full-performance analysis method, our iPAM substantially reduces evaluation time by approximately 75%-95% for large-scale networks. This advantage becomes increasingly pronounced as the scale of the network expands.

The selection of a Time-Sensitive Networking (TSN) shaping mechanism is a crucial design decision that impacts the Quality of Service (QoS) of applications and configuration complexity. However, current research has mainly evaluated TSN shapers individually, despite them being designed to work together in an egress port. Hence, the lack of investigation of the mixed TSN shaping mechanism is a major limitation of the current state of the art. Combined TSN traffic shaping provides greater flexibility to improve QoS than individual shapers, making it particularly beneficial for real-time applications. This paper aims to bridge this research gap by implementing the Asynchronous Traffic Shaper (ATS) in a plug-and-play manner, enabling its use individually or in combination with other TSN shapers. We propose various models of mixed TSN shaper architectures and implement the frozen and non-frozen credit behavior of the Time Aware Shaper (TAS) + Credit Based Shaper (CBS) during the guard band (GB) using OMNeT++. Furthermore, we compare the simulation results of ATS and CBS with the Network Calculus (NC) upper bounds. Our results indicate that the simulated delays (SMDs) were significantly lower than the theoretical worst-case delays (WCDs) obtained from the NC, indicating the need for tighter theoretical upper bounds, particularly for higher network loads. To the best of our knowledge, we are the first to provide simulation-based performance analysis of the combined$\text{TAS}+\text{ATS}+\text{CBS}$and$\text{TAS}+\text{ATS}+\text{Strict}$Priority (SP) architecture. Overall, this paper highlights the benefits of combining TSN shapers and encourages further research into the potential advantages of utilizing multiple shapers simultaneously to decrease reliance on TAS and CBS.

Owning to the sub-standards being developed by IEEE Time-Sensitive Networking (TSN) Task Group, the traditional IEEE 802.1 Ethernet is enhanced to support real-time dependable communications for future time- and safety-critical applications. Several sub-standards have been recently proposed that introduce various traffic shapers (e.g., Time-Aware Shaper (TAS), Asynchronous Traffic Shaper (ATS), Credit-Based Shaper (CBS), Strict Priority (SP)) for flow control mechanisms of queuing and scheduling, targeting different application requirements. These shapers can be used in isolation or combination and there is limited work that analyzes, evaluates, and compares their performance, which makes it challenging for end-users to choose the right combination for their applications. This paper aims at (i) quantitatively comparing various traffic shapers and their combinations, (ii) summarizing, classifying, and extending the architectures of individual and combined traffic shapers and their Network calculus (NC)-based performance analysis methods, and (iii) filling the gap in the timing analysis research on handling ATS and CBS used for different priority queues, and two novel hybrid architectures of combined traffic shapers, i.e., TAS+ATS+SP and TAS+ATS+CBS when ATS and CBS used at the same queue. A large number of experiments, using both synthetic and realistic test cases, are carried out for quantitative performance comparisons of various individual and combined traffic shapers, from the perspective of upper bounds of delay, backlog, and jitter. To the best of our knowledge, we are the first to quantitatively compare the performance of the main traffic shapers in TSN. The paper aims at supporting the researchers and practitioners in the selection of suitable TSN sub-protocols for their use cases.

Time-sensitive networking (TSN) is an upcoming set of Ethernet standards designed for real-time and safety-critical Internet-of-Things (IoT) applications in automotive, aerospace, and industrial automation domains. With the combination, complexity, and flexibility of flow control mechanisms in TSN connected systems, the performance analysis for mixed-critical messages is becoming a difficult challenge. The flexible window-based gate control list (GCL) scheduling model has been proposed as a relaxation to assumptions on frames-to-window allocation, mutually exclusive gates opening, and scheduled end systems and switches, which offers more flexibility in the configuration of GCLs. In this article, we are interested in providing a reliable verification method based on the network calculus theory to drive GCL configurations for TSN networks. To the best of our knowledge, this is the first performance analysis method suitable for the general flexible window-based GCLs in entire TSN networks, by reflecting the relative positional relationships of windows for same priority queues on consecutive nodes and constructing the window limitations into the shaper curve, in order to reduce the pessimism of the latency bounds. We validate the proposed method through Industrial IoT synthetics test cases and two large realistic cases, showing the significant reduction in pessimism on delay bounds, and the correctness and scalability by comparing with results from the previous work and simulation results.

TTEthernet is an Ethernet-based synchronized network technology compliant with the AFDX standard. It supports safety-critical applications by defining different traffic classes: Time-Triggered (TT), Rate-Constrained (RC), and Best-Effort traffic. The synchronization is managed through the AS6802 protocol, which defines so-called Protocol Control Frames (PCFs) to synchronize the local clock of each device. In this paper, we analyze the synchronization protocol to assess the impact of the PCFs on TT and RC traffic. We propose a method to decrease the impact of PCFs on TT and a new Network Calculus model to compute RC delay bounds with the influence of both PCF and TT traffic. We finish with a performance evaluation to i) assess the impact of PCFs, ii) show the benefits of our method in terms of reducing the impact of PCFs on TT traffic and iii) prove the necessity of taking the PCF traffic into account to compute correct RC worst-case delays and provide a safe system.

Time-Sensitive Networking (TSN) introduces standardized mechanisms that add real-time capabilities to IEEE 802.1 Ethernet networks. In particular, the Time-Aware Shaper (TAS) can be used to send frames in a deterministic fashion according to a predefined global schedule. Existing methods for generating the global communication schedule enforce isolation either in the time or in the space domain. This extended abstract presents a novel, more flexible window-based scheduling algorithm which removes the previously required isolation constraints for Scheduled Traffic (ST) by integrating worst-case delay analysis to guarantee bounded latency.

Time-Sensitive Networking (TSN) is a collection of standards that extend Ethernet to support safety-critical and real-time applications. TSN integrates multiple traffic types, i.e., Time-Triggered (TT) traffic scheduled based on Gate-Control-Lists (GCLs), Audio-Video-Bridging (AVB) traffic that requires bounded latencies, and Best-Effort (BE) traffic, for which no guarantees are provided. This paper proposes a Network Calculus-based approach to determine the worst-case end-to-end delays of AVB traffic in a TSN network with both non-preemption and preemption modes. We consider the effects of TT traffic due to GCLs, "guard bands", i.e., time windows that block other traffic from transmitting, and preemption overhead on the service for AVB traffic. We provide a proof of non-overflow condition for AVB credit, which is used to control the AVB traffic transmission. The analysis method is evaluated on realistic test cases, and compared to related work.