TO PROVIDE a standard real-time data network, the IEEE Time-Sensitive Networking (TSN) working group has defined several extensions to Ethernet. Among them, Cyclic Queuing and Forwarding (CQF), inspired by the "stop-and-go" queuing discipline [1] , has been introduced to provide bounded delay and limited jitter [2] . Briefly (see Section II ), CQF assumes a common time cycle T and uses two queues per output port to alternately store and forward packets. It guarantees that the delay experienced by a packet traversing h nodes lies between ( h −1) T and ( h +1) T .

Time-Sensitive Networking (TSN) provides deterministic guarantees and bounded latency for safety-critical applications across different domains. While the IEEE 802.1 TSN standards provide a comprehensive set of mechanisms for time synchronization, shaping, scheduling, resource reservation, and reliability, deploying TSN in real-world applications remains a complex, multi-step engineering task. Existing research primarily focuses on optimizing individual objectives, such as increasing schedulability, reducing latency, accelerating solution generation, or improving performance analysis. However, whether these extensively researched solutions can be deployed in real-world systems remains unanswered, as the assumptions made in these methodologies often differ from practical hardware constraints. Therefore, a broader, holistic view of end-to-end TSN deployment and management remains an open research question. Currently, there is a lack of a unified perspective, consensus, and coordinated research efforts focusing on a comprehensive end-to-end TSN deployment workflow. We present a comprehensive overview of the TSN deployment lifecycle, current challenges, limitations of existing tools, and future research directions for TSN deployment and management. Lastly, we identify key research gaps from a deployment perspective and provide guidance for the development of next-generation deployable TSN networks.

Cyclic Queuing and Forwarding (CQF) is a mechanism defined by IEEE Time-Sensitive Networking (TSN) for providing low jitter in a deterministic network. CQF uses a common time cycle and two buffers per node output port. During one cycle, incoming packets are stored in one buffer while packets in the other buffer are being transmitted. At the end of a cycle, the roles of the two buffers are exchanged. CQF provides very simple bounds on latency and jitter. Its correct operation requires a large enough cycle duration so that all packets received by a node in one cycle can be forwarded during the next cycle. We give a necessary and sufficient condition for this to hold. Our condition depends on the link properties and the flow characteristics at the network input.We apply the condition to obtain the minimal admissible cycle duration. We observe that the minimal cycle duration is not always margin-safe, i.e., larger values might be non-admissible, which suggests replacing the minimal cycle duration with the minimal margin-safe cycle duration.

The sets of Ethernet extensions known as "Time Sensitive Networking" (TSN) is a promising candidate as the next backbone of real-time distributed systems. The flexibility of TSN is also an opportunity to reconfigure the network in presence of faults. This white paper presents an avionic case study for a TSN reconfiguration.

Faults may appears in embedded networks: vibrations, temperature conditions, cybersecurity attacks, etc. may cause a port to stop sending frames, requiring a network reconfiguration. In real-time networks, the new configuration must continue ensuring real-time guarantees. In the French Resilient Time-Sensitive Networks (ResTSN) project, ONERA and THALES are developing a solution to enable the reconfiguration of embedded Time-Sensitive Networks. This paper presents the core ideas driving the development of the architecture and associated algorithms of TSN reconfiguration. The approach will ultimately be applied on a Multi-Role Armoured Vehicle (MRAV) use-case. This paper also presents our cybersecurity risk assessment approach to the use of TSN on this MRAV use-case.

Real-time systems often consist of numerous sub-systems engaged in extensive data exchange. Despite their complexity, a critical challenge lies in effectively incorporating real-time constraints within these systems. To address this challenge, designers typically conduct analyses to establish upper bounds on delays, ensuring they remain within the deadlines of incoming requests. However, adopting a pessimistic approach often results in over-dimensioning the systems. Then, to reduce the pessimism, we want to take into account the fact that a subsystem cannot propagate more requests/data than it can execute. This phenomenon is well-known in network analysis as it reduces the burst of data. As a consequence, this notion is easier to grasp in theories developed to compute delay bounds in networks. That is why we choose, in this paper, to perform the analysis using the Network Calculus theory, since it offers the possibility to easily aggregate flows (i.e. sum flows) and then take into account the phenomenon of smoothing the traffic. To handle tasks and networks, our model relies on packetization and workload scaling. In this paper, we improve some results regarding the already existing elements of Network Calculus and the aggregation. Also, we update and complete definitions and results related to workload scaling.

The Asynchronous Traffic Shaping (ATS) has been designed by the Time Sensitive Networking (TSN) group as a reshaping mechanism for real-time data flows, based on the initial proposition of the Urgency Based Shaper (UBS). Several studies have exhibited properties and limitations of this solution, but most of them are based on the model presented in the UBS definition [Specht and Samii, 2016], whereas the implementation described in the standard uses a different architecture and algorithm. This paper presents an equivalence proof between the model and the standard specification.

Cyclic Queuing and Forwarding (CQF) is a mechanism defined by IEEE TSN for providing low jitter in a deterministic network. CQF uses a common time cycle and two buffers per node output port: during one cycle incoming packets are stored in one buffer while packets in the other buffer are being transmitted; at the end of a cycle, the roles of the two buffers are exchanged. The cycle start times are determined by a time offset that may be different for every output buffer. A guard band at both cycle ends is devised in order to compensate for misalignment and timing inaccuracies. The proper operation of CQF requires that the guard band and the offsets are computed such that nodes are sufficiently time-aligned. First, we give necessary and sufficient conditions for this to be guaranteed. The sufficient conditions lend themselves to tractable computations and we show that they are close to optimal. Our conditions account for nonideal clocks and non-zero propagation times; we show that accounting for these two elements does matter. Second, we give a method for computing the minimal duration of the guard band, given prior choices of time offsets. Third, a judicious choice of time offsets can considerably decrease the required duration of the guard band: we give a practical algorithm, based on a Mixed Integer Linear Program, for computing offsets that minimize the guard band. We illustrate our results on several CQF network topologies with or without cyclic dependencies.

The Network Calculus theory has been designed to compute upper bounds on delay and backlog in data networks. A lot of results have been developed to address different aspects. However, they are not all compatible with each other since they make different assumptions on the continuity of a core aspect of the model (the cumulative curves). However, real systems may mix several mechanisms. When modeling such a system, one has to choose one continuity hypothesis and limit the analysis to a subset of existing results. This paper addresses the continuity problem and argues formally that continuity issues are mathematical details that can be solved as long as the min-plus properties are used (minimal and maximal service, shaping). Conversely, it gives a counter-example for properties based on strict service, requiring a generalisation of the backlogged interval notion.

Network calculus is a well established method for computing guaranteed delay bounds in networks. When a network element is shared between several flows, its aggregate capacity is shared with regards to a scheduling policy. In this case, network calculus can compute a residual service curve for each flow, based on scheduling information. In most systems, when a frame is selected for transmission, it is transmitted at full (constant) line rate up to completion or preemption. In this letter, we propose a generic approach that can enhance any residual service curve by taking this effect into account.

We introduce a new paradigm for synthesizing time-triggered schedules that guarantees the correct temporal behavior of time-triggered (TT) tasks and the schedulability of sporadic event-triggered (ET) tasks with arbitrary deadlines at design time. The approach first expresses a constraint for the TT task schedule in the form of a maximal affine envelope that ensures that as long as the schedule generation respects this envelope, all sporadic ET tasks meet their deadline. The second step consists of modeling this envelope as a burst limiting constraint (BLC) and building the schedule. The BLC constraint can be added to any existing TT schedule generation method as an additional constraint on the TT slot positioning. Here, we propose an efficient TT schedule generation method that integrates the BLC constraint via simulating a modified Least-Laxity-First (LLF) scheduler. We show via synthetic and real-world test cases that our novel method achieves better schedulability and a faster schedule generation for most use cases compared to other approaches inspired by, e.g., hierarchical scheduling. Moreover, we present an extension to our method that finds the most favorable schedule for TT tasks with respect to ET schedulability, thus increasing the probability that the system remains feasible when ET tasks are later added or changed.

Total Flow Analysis (TFA) is a method for the worst-case analysis of time-sensitive networks. It uses service curve characterizations of the network nodes and arrival curves of flows at their sources; for tractability, the latter are often taken to be linear functions. For periodic flows, which are common in time-sensitive networks, linear arrival curves are known to provide less good bounds than ultimately pseudo-periodic (UPP) arrival curves, which exactly capture the periodic behaviours. However, in existing tools, applying TFA with many flows and UPP curves quickly becomes intractable because when aggregating several UPP curves, the pseudo-period of the aggregate might become extremely large. We propose a solution to this problem, called Finite-Horizon TFA. The method computes finite horizons over which arrival and service curves can be restricted without affecting the end-results of TFA. It can be applied to networks with cyclic dependencies. We numerically show that, while remaining computationally feasible, the method significantly improves the bounds obtained by TFA when using linear curves.

. The network calculus theory is widely used to check that a network satis-fies its real-time requirements. Such checking involves a lot of computations in the min-plus dioid. This paper shows how such computations can be formally checked us-ing the Coq proof assistant in a realistic industrial context.

Latency and jitter are two main requirements when controlling cyber-physical systems, especially in case of remote control through a network. When jitter is a major concern, one can either control the jitter all along the path, or compensate it by buffering at reception. This is usually done by the destination host, but it can also be done by the last network node. We call this approach Egress TT. This paper presents Egress TT, its benefits in terms of configuration time and applicative constraints. It also presents two possible implementations within a Time Sensitive Networking context.

—The Network Calculus theory allows to compute upper bounds on delays and memory usage in data networks. The mathematical foundations rely on piecewise-continuous functions being, depending on the authors, either left-or right-continuous. It is then impossible to use all existing results in a single analysis, since the hypotheses are incompatibles. This paper shows how, under some reasonable assumptions, it is possible to project property from left-continuous word to right-continuous world, and vice-versa.

Classical Response Time Analysis (RTA) and Network Calculus (NC) are two major formalisms used for the verification of real-time properties. We offer mathematical links between these two different theories. Based on these links, we then prove the equivalence of various key notions in both frameworks. This enables specialists of both formalisms to get increase confidence on their models, or even, like the authors, to discover errors in theorems by investigating apparent discrepancies between some notions expected to be equivalent. The presented mathematical results are all mechanically checked with the interactive theorem prover Coq, building on existing formalizations of RTA and NC. Establishing such a link between NC and RTA paves the way for improved real-time analyses obtained by combining both theories to enjoy their respective strengths (e