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Formal Worst-Case Performance Analysis of Time-Sensitive Ethernet with Frame Preemption
Abstract
One of the key challenges in future Ethernet-based
automotive and industrial networks is the low-latency transport
of time-critical data. To date, Ethernet frames are sent non-
preemptively. This introduces a major source of delay, as, in
the worst-case, a latency-critical frame might be blocked by a
frame of lower priority, which started transmission just before the
latency-critical frame. The upcoming IEEE 802.3br standard will
introduce Ethernet frame preemption to address this problem.
While high-priority traffic benefits from preemption, lower-
priority (yet still latency-sensitive) traffic experiences a certain
overhead, impacting its timing behavior. In this paper, we present
a formal timing analysis for Ethernet to derive worst-case latency
bounds under preemption. We use a realistic automotive Ethernet
setup to analyze the worst-case performance of standard Ethernet
and Ethernet TSN under preemption and also compare our
results to non-preemptive implementations of these standards.
... This standard establishes two distinct classes of queues: an "express frames" queue class and a "preemptable frames" queue class. In the "express frames" queue class, frames are promptly transmitted upon readiness and have the ability to fragment preemptable frames currently in transmission, unless frame's length is less than or equal to 143 bytes [20]. However, this process does introduce some overhead in relation to preemptable frames. ...
... A key aspect that sets the TRex generator apart is its utilization of DPDK components, which allows for the bypass of performance bottlenecks in the Linux network stack. DPDK is a whole set of libraries and drivers that are used for fast packet processing by allowing the system to exclude the Linux network stack from the packet processing algorithms so that the tool can interact directly with the network device that is being tested 19,20 . ...
... TRex Frequently Asked Questions. Accessed in May 2024 (https: //trex-tgn.cisco.com/trex/doc/trex\_faq.html#\_general).20 Cisco TRex Traffic Generator: Running Load Tests on a Network. ...
As cities transition into interconnected hubs of technology, the need for efficient time management across diverse interconnected devices becomes a requirement for supporting critical services for emergency, traffic, and other use cases. Time-sensitive network (TSN) emerges as a promising solution, offering standards and mechanisms to synchronize and regulate time-critical traffic in smart city infrastructures. This study researches the main use cases, key standards and mechanisms of TSN, evaluating their feasibility and adaptability to the heterogeneous equipment present in an urban environment of a smart city infrastructure. Through experimental assessments, this article demonstrates the efficacy of TSN-based solutions and also discusses hardware enhancements that complement time-sensitive network (TSN) protocols, improving precision and resource utilization to ensure criticality in urban connectivity, enabling precise control over traffic conditions and service delivery towards the future smart city, as an environment of interconnected things. Moreover, we propose a classification of nine traffic categories to encompass the various traffic flows in a smart city deployment, and validate the application of time-aware and credit-based shaping of all nodes in the network according to the type of service. Results show that TSN is a valid choice to manage mixed-criticality of services in a smart city.
... For Ethernet TSN, the worst-case end-to-end delay of network traffic is usually computed based on either network calculus [109,108] or compositional performance analysis [101,100]. These analyses focus on the effects of the various standardized features of TSN on the worst-case end-to-end delay. ...
... For example, [101] analyzes the worst-case latency when the time-aware shaper (802.1Qbv) or the peristaltic shaper (802.1Qch) is used. [100] analyzes the impact of frame preemption (802.1Qbu) on the worst-case delay. ...
... Thiele et al. [100] proposed a worst-case latency analysis for Ethernet TSN with the frame preemption. The analysis leverages the compositional performance analysis (CPA) framework, and models egress ports as the major resources. ...
Automakers keep adding new functions to their products to attract more customers. Since such newly-introduced functions usually require communication with other electronic control units (ECUs) to acquire & deliver sensor (e.g., speedometer, radar, etc.) data, the amount of in-vehicle network traffic keeps rising. To deal with this ever-increasing trend, automakers have re-designed in-vehicle network architecture and adopted high-bandwidth protocols such as controller area network with flexible data-rate (CAN-FD), switched-Ethernet, etc. However, since the complexity and cost related to in-vehicle networks increases with this change, optimizing the in-vehicle network to minimize the cost becomes a major challenge to the automakers. To tackle such a challenge, we propose a suite of design optimization methods for modern in-vehicle network architectures. First, we present PAMT, an optimal priority-assignment algorithm for a single mixed CAN and CAN-FD bus. By clustering messages based on their type, PAMT minimizes the timing overhead for mode transitions. Second, we propose EACAN to relax the pessimistic assumptions used in the formal verification for CAN communication. Third, we identify configurable parameters for standardized frame preemption of Ethernet Time-Sensitive Networking (TSN) and present DOFP, a genetic algorithm based optimization for the frame preemption. Fourth, we propose OPMB, an optimal priority assignment algorithm for multi CAN/CAN-FD buses with a central gateway. Finally, we propose PRMB which finds a schedulable priority assignment and generates routing tables to use signal-based routing at the central gateway while meeting the timing requirements of in-vehicle data.
... Otherwise, a TSN switch discards the broken fragments which drastically reduces the throughput of the networks. To preserve the IEEE 802.3 MAC (2015) frame format and make frame preemption transparent to Ethernet's physical layer, three MAC frame formats are defined as shown in Figure 3 (Thiele et al., 2016). ...
... Formats for MAC, express and preemptable frames for transmission in PON systems (Thiele et al., 2016) The format of express frames in this work is similar to 802.3 frame format except that SMD (start mframe delimiter) is replaced with SFD-E (start of frame delimiter-express) to identify the beginning of the express frames. As shown in Figure 3, a preemptable frame is split into three fragments, the first fragment has the frame format similar to express frame except FCS is replaced with mCRC, and SFD with SMD-Sx (SMD-start fragment) that identify the starting of a preemptable frame. ...
... In the last preemptable fragment, mCRC is replaced with FCS. The SMD-Sx/Cx and FCnt are used to perform the detection of lost fragments in the network (Thiele et al., 2016). Because of these frame formats, successful identification and transmission of high-priority express frames and low-priority preemptable frames in packet-switched Ethernet-based TDM-PON systems can be realized and thus, implemented in this paper. ...
... Few examples of well-established solutions include the Controller Area Network (CAN) protocol [1], the Local Interconnect Network (LIN) protocol [2], the FlexRay protocol [3], and TTEthernet [4] that mainly focus on the automotive domain; the Avionics Full Duplex Switched Ethernet (AFDX) [5] that targets the avionic domain; and the so called field buses such as SERCUS III [6], EtherCAT [7], and PROFINET [8] that address the industrial domain. Most of these solutions now struggle to keep up with the growing bandwidth and performance demands of emerging applications in their respective domains [9]. On another front, with the convergence of Operation Technology (OT) and Information Technology (IT) [10,11], yet another challenge has settled on the table, justifying the need for new communication technologies that would facilitate the handling of heterogeneous traffic (real-time, non realtime, long and short frames) on the same network infrastructure. ...
... The total overhead associated to the occurrence of each preemption is equivalent to the time taken to transmit 24 bytes of data (i.e., 0.19 μs and 1.9 μs, assuming a 1 and 100 speed Ethernet, respectively). Experimental studies show that this approach improves the performance of express frames [9,13]. Specifically, Thiele and Ernst [9] show that the performance of Standard Ethernet with frame preemption is comparable to that of IEEE 802.1Qbv [15], thus making it an interesting alternative. ...
... Experimental studies show that this approach improves the performance of express frames [9,13]. Specifically, Thiele and Ernst [9] show that the performance of Standard Ethernet with frame preemption is comparable to that of IEEE 802.1Qbv [15], thus making it an interesting alternative. ...
To achieve low latency transmission of time-sensitive flows in Ethernet networks, the IEEE introduced the IEEE 802.1Qbu Standard, which specifies a 1-level preemption scheme for IEEE 802.1 networks. The specification allows the suspension of a preemptable frame prior to its completion for the speedy transmission of an express frame; but any other preemptable frame cannot be transmitted before the completion of the already preempted frame. While this approach improves the performance of express frames, the performance is negatively impacted in scenarios where the number of express frames is high. Another limitation is the fact that preemptable frames with timing requirements can suffer long blocking periods due to the non-preemptive service of frames in the same category. This is irrespective of the individual priority level of each frame.
Recently, a multi-level preemption scheme has been proposed to circumvent these limitations. The work focused on the feasibility and implementation requirement of such an approach, but a formal analysis of the worst-case performance guarantees under the proposed scheme was not provided. In this paper, we fill this gap by presenting the aforementioned analysis of the TSN IEEE 802.1Qbu networks under the multi-level preemption assumption. Evaluation is performed with a realistic automotive use-case and the results showcase an improvement up to 53.07% for preemptable frames with firm timing requirements.
... Several works in the literature addressed the suitability of the TSN standards for industrial and automotive contexts [8]- [10]. In particular, as in these scenarios the timing constraints of the real-time traffic flows have to be guaranteed, a number of research works focused on schedulability analysis and schedule generation algorithms for traffic flows in TSN-based networks [11]- [15]. Some works [16]- [18] proposed offline EDF scheduling of periodic traffic flows over TSN. ...
... Consequently, when u is greater than or equal to 50µs the maximum E2EDelays show a fluctuating trend. This result is more significant for the flows with shorter relative deadlines, i.e., the flows [0-4], [5][6][7][8][9], and [10][11][12][13][14]. ...
The Time-Sensitive Networking (TSN) set of standards allows to support on the same channel the different kinds of traffic flows that are typically found in automotive scenarios. This work proposes the introduction of online Earliest Deadline First-based scheduling in TSN to provide support for event-driven real-time traffic. The proposed approach, called Deadline-TSN, is an online approach and therefore, unlike other approaches in the literature, it does not require complex offline schedule calculations. Moreover, Deadline-TSN is able to uniformly deal with real-time periodic and event-driven traffic flows. The paper presents Deadline-TSN and provides both a worst-case response time analysis and simulative assessments in realistic automotive scenarios.
... Nevertheless, simulation results cannot be used for the schedulability analysis as the corner cases cannot be covered. Thiele et al. [31] presents the formal worst-case timing analysis for frame preemption supporting TSN/GCL+SP. In [40], authors propose the Network Calculus (NC)-based method to support both the non-preemption and the preemption without HOLD/RELEASE modes for the TSN/GCL+CBS architecture. ...
... This is due to the non-frozen behavior described in the 802.1Q [14] standard (c.f. Figure 3), which has already been considered for the performance analysis with the non-preemption integration mode in [39]. A preemption overhead [31] will be added to each fragment of a preempted frame. As described before, the preemption with HOLD/RELEASE mechanism will prevent the ST window from being interfered with by the preemptible traffic while reducing the impact of the GB+ST duration on the link bandwidth that is available to preemptible traffic. ...
The Time-Sensitive Network (TSN) amendments and protocols add capabilities on top of standard 802.1 Ethernet for guaranteeing the timeliness of both (isochronous) scheduled traffic (ST) and shaped (audio-video) communication (AVB) in distributed applications. ST streams are guaranteed via an offline computed schedule controlling the time-aware gate mechanism of IEEE 802.1Qbv, while AVB real-time streams are shaped via a credit-based shaper (CBS) and scheduler with lower-priority than ST. Although the two traffic classes use different TSN mechanisms, they are interrelated as the ST traffic class schedule influences the latency of AVB traffic.
In this paper, we propose a method for the integration of the ST schedule synthesis with an analysis for the AVB class featuring IEEE 802.1Qbu frame preemption under different configurations to reduce the interference between the two classes. We first present a new worst-case response-time (WCRT) analysis for the AVB traffic class in TSN networks with preemption, considering an arbitrary number of AVB queues and different configurations for the CBS credit behavior. Then, we integrate the creation of ST schedule tables with the schedulability analysis of AVB traffic using a heuristic algorithm featuring frame preemption and a novel routing mechanism aimed at maximizing AVB schedulability. Finally, we evaluate our approach using both real-world and synthetic use cases showing the efficiency both in terms of schedule creation runtime and in terms of increasing the schedulability of lower-priority AVB traffic.
... Many automotive embedded systems are constrained by stringent timing requirements. Hence, developers of these systems have to not M. Ashjaei et al. 100 Mbit/s to 10 Gbit/s a The recommended maximum data-rate for CAN XL in the data phase is 10 Mbit/s. However, the datarate can be higher depending upon the CAN transceiver capabilities and characteristics of physical layer components [6,7]. ...
... However, there is currently no analysis technique considering the proposed novel preemption models. The work in [100] proposes a technique to perform an analysis considering the preemption support under the IEEE802.3br standard. ...
The functionality advancements and novel customer features that are currently found in modern automotive systems require high-bandwidth and low-latency in-vehicle communications, which become even more compelling for autonomous vehicles. In a recent effort to meet these requirements, the IEEE Time-Sensitive Networking (TSN) task group has developed a set of standards that introduce novel features in Switched Ethernet. TSN standards offer, for example, a common notion of time through accurate and reliable clock synchronization, delay bounds for real-time traffic, time-driven transmissions, improved reliability, and much more. In order to fully utilize the potential of these novel protocols in the automotive domain, TSN should be seamlessly integrated into the state-of-the-art and state-of-practice model-based development processes for automotive embedded systems. Some of the core phases in these processes include software architecture modeling, timing predictability verification, simulation, and hardware realization and deployment. Moreover, throughout the development of automotive embedded systems, the safety and security requirements specified on these systems need to be duly taken into account. In this context, this work provides an overview of TSN in automotive applications and discusses the recent technological developments relevant to the adoption of TSN in automotive embedded systems. The work also points at the open challenges and future research directions.
... Moreover, the work presented in [18] proposed an analysis for time-aware shaper and peristaltic shaper, while a very recent work in [4] presented an analysis based on network calculus. Moreover, the work in [19] presents a timing analysis considering frame preemption in TSN networks. The work in [20] complements the previous analysis by considering various modes in combination with the Hold/Release mechanism as well as the delay analysis for ST frames. ...
... According to Annex S of the IEEE 802.1Q-2018 standard, when the preemption mechanism is used in combination with the scheduled traffic two modes can be implemented, being ''with'' or ''without'' Hold/Release mechanism. In most of the TSN performance studies, including the timing analysis of the network, (e.g., [4,5,19,30]), this mode is considered explicitly as using Hold/Release. The very recent work in [20] considers both modes in the worst-case delay analysis of classes A and B. Nevertheless, selection of this mode can have a considerable effect on the performance of both the SR and ST traffic. ...
This paper identifies a limitation in the frame preemption model in the TSN standard (IEEE 802.1Q-2018), due to which high priority frames can experience significantly long blocking delays, thereby exacerbating their worst-case response times. This limitation can have a considerable impact on the design, analysis and performance of TSN-based systems. To address this limitation, the paper presents a novel and more efficient frame preemption model in the TSN standard that allows over 90% reduction in the maximum blocking delay leading to lower worst-case response times of high priority frames compared to the frame preemption model used in the existing works. The paper also shows that the improvement becomes even more significant in multi-switch TSN networks. In order to evaluate the effects of preemption, the paper performs simulations by enabling and disabling preemptions as well as enabling and disabling the Hold/Release mechanism supported by TSN. Furthermore, the paper performs a comparative evaluation of the two models of frame preemption in TSN using simulations. The evaluation shows that the maximum response times of high priority frames can be significantly reduced with very small impact on the response times of lower priority frames. The paper also shows the improvement in the maximum response times of higher priority frames using an automotive industrial use case that employs a multi-hop TSN network for on-board communication.
... Since the forwarding delay and propagation delay of packets are related to the physical characteristics of switches and links and typically in the order of a few clock cycles [31], to simplify the implementation of the simulation in this study, we assume that these parameters ( f d and p d ) in the network are fixed to zero. Therefore, the E2E latency of frames can be represented by Equation (5). ...
The development of the automotive industry and automation has led to a growing demand for time-critical systems to have low latency and jitter for critical traffic. To address this issue, the IEEE 802.1 Time-Sensitive Networking (TSN) task group proposed the Time-Aware Shaper (TAS) to implement Time-Triggered (TT) communication, enabling deterministic transmission by assigning specific time windows to each stream. However, the deployment of TAS requires a solution for the particular deployment scenario. Scheduling algorithms with Fixed-Routing and Waiting-Allowed (FR-WA) mechanisms while providing flexible solutions still have room for optimization in terms of their solution time, reducing network design efficiency and online scheduling deployment. Firstly, the paper overviews the key mechanisms to implement TT communication in TSN, including TAS and FR-WA scheduling algorithms. Secondly, building on this overview of these mechanisms, potential problems with the current implementation of the TAS mechanism are analyzed, including the increasing constraint number as the network scales and potential issues that may arise in traffic anomalies. Then, a method for implementing TT communication using Urgency-Based Scheduler (TT-UBS) is proposed to improve solution efficiency and deterministic transmission in the presence of traffic anomalies. The effectiveness of this method is also analyzed. We propose a scheduling algorithm for solving the parameters of the TT-UBS mechanism. Finally, a simulation-based assessment of the TT-UBS mechanism and the scheduling algorithm is presented. In addition, we extend the method of modifying the scheduling algorithm to other scheduling algorithms and explore the solution efficiency of the extended algorithms.
... Frame preemption allows express frame to preempt preemptable frame, which can provide a reduced latency transmission for scheduled, time-critical frames. Since preemption can change the frame transmission timing, the schedulability analysis for this mechanism is also necessary [131]. Most other timing analyses are based on this research, such as [72] and [127]. ...
Time-Sensitive Networking (TSN) is a set of standards that provide low-latency, high-reliability guarantees for the transmission of traffic in networks, and it is becoming an accepted solution for complex time-critical systems such as those in industrial automation and the automotive. In time-critical systems, it is essential to verify the timing predictability of the system, and the application of scheduling mechanisms in TSN can also bring about changes in system timing. Therefore, schedulability analysis techniques can be used to verify that the system is scheduled according to the scheduling mechanism and meets the timing requirements. In this paper, we provide a clear overview of the state-of-the-art works on the topic of schedulability analysis in TSN in an attempt to clarify the purpose of schedulability analysis, categorize the methods of schedulability analysis and compare their respective strengths and weaknesses, point out the scheduling mechanisms under analyzing and the corresponding traffic classes, clarify the network scenarios constructed during the evaluation and list the challenges and directions still needing to be worked on in schedulability analysis in TSN. To this end, we conducted a systematic literature review and finally identified 123 relevant research papers published in major conferences and journals in the past 15 years. Based on a comprehensive review of the relevant literature, we have identified several key findings and emphasized the future challenges in schedulability analysis for TSN.
... With the introduction of the TSN family of standards, many works addressed schedulability analysis and scheduling algorithms for traffic flows on time-sensitive networks [34][35][36][37][38][39][40]. The work in [41] proposed a heuristic scheduling approach for time-driven flows while the work in [42] presented a solution to statically schedule time-driven flows according to an EDF-based policy. ...
Recent work on automotive communications based on the Time-Sensitive Networking (TSN) standards proposed an approach to handle all the real-time frames in a uniform way regardless of their arrival pattern. According to such an approach, instead of binding all the frames of the same flow to a traffic class, each periodic or event-driven frame is scheduled based on its absolute deadline according to the Earliest Deadline First (EDF) algorithm. The approach does not impose additional frame overhead and does not require complex offline configurations that would be unsuitable for event-driven traffic. However, EDF scheduling cannot support time-driven communications. To solve this problem, this paper proposes a framework that combines the flexibility of online EDF frame scheduling for both periodic and event-driven traffic with the ability to guarantee temporal isolation to time-driven traffic. The paper describes the design of the proposed approach and the performance obtained using the OMNeT++ simulation environment.
... Still, two frames in the same class cannot preempt one another, thus some blocking remains. Several studies have shown that such a scheme significantly improves flows' schedulability and that its performance is comparable to that of TAS, which is more complex and expensive to implement [16,18,45]. Recently, Ojewale et al. [32,33]; Gogolev and Bauer [16]; Ashjaei et al. [2]; and Lo Bello et al. [6] pointed out several limitations of the 1-level preemption scheme as specified in the standards. ...
... Nonetheless, preemption also may cause overhead when other flows are interrupted by the guardband; therefore, [18] propose a mechanism to calculate and reduce the guardband size and, consequently, the overhead. As the usage of preemption is an important research topic, many works have studied timing analysis from frame preemption in TSN networks alongside other traffic shaping mechanisms and scheduled traffic [19,20]. ...
Ultra-low latency (ULL) is a challenging but nonetheless important network requirement to achieve in many contexts. Industrial automation (IEC/IEEE 60802), in vehicle communications (IEEE P802.1DG), audio and video bridging (IEEE Std 802.1BA), aerospace and 5G fronthall (IEEE 802.1CM) applications demand a low network latency in the order of few milliseconds or even microseconds. ULL services target a more controlled latency for end-to-end device communication and, in critical environments, near real-time connections. Time-Sensitive Networks (TSN) aim at providing deterministic connectivity over IEEE 802 networks guaranteeing packet transport with bounded latency, low packet delay variation, and low packet loss. This work analyzes TSN latency mechanisms and examines the way they influence E2E latency. Moreover, it builds a regression-based surrogate model enabling next the creation of optimization models used to find optimal configurations for a given TSN network. Our findings span the discussion of the characteristics of each individual TSN latency mechanism to the benefits achieved by the proposed optimization models and using these to achieve optimal E2E latency.
... Thiele and Ernst [19] proposed an analysis method to calculate worst-case latencies under preemptive scheduling in TSN. Lo Bello et al. [2] extended the analysis with preemptive credit-based shaping and time-aware shaping. ...
... Hence, before each TT window, 802.1Qbv sets a large enough guard band during which no new packet is scheduled at the cost of bandwidth waste. Frame preemption solves this problem by a dedicated and complex MAC sub-layer for splitting and reassembling AVB and BE packets, with a guard band up to 143 bytes [29]. Furthermore, a packet scheduling algorithm, PAS [30], is proposed to utilize the guard band efficiently by modeling the problem as a Knapsack Problem [31]. ...
Time Sensitive Networking (TSN) is an emerging Ethernet technology for real-time systems. To address different Quality-of-Service (QoS) requirements of applications, IEEE 802.1 TSN Task Group has standardized several packet scheduling and shaping algorithms. The software implementation of these algorithms is hard to meet the performance requirements, while the hardware implementation in Application-Specific Integrated Circuit (ASIC) is inflexible. A hardware-programmable scheduler is necessary to deal with this dilemma. Among the existing primitives, the most expressive one is Push-In-Extract-Out (PIEO), but its complexity makes the implementation very expensive. A relatively lower-cost implementation of PIEO cannot guarantee the scheduling correctness for the most critical Time-Triggered (TT) traffic in TSN. As a remedy, in this paper we propose a new Push-In-Pick-Out (PIPO) primitive under a TSN programmable scheduling framework. Composed of simple priority queues, PIPO can express all existing TSN scheduling and shaping algorithms, and is flexible enough to support future ones.
Our PIPO implementation guarantees the TT traffic scheduling correctness. The simulation results corroborate the theoretical analysis that the low-cost PIPO can closely approximate PIEO and sustain a high bandwidth utilization. The prototype on Xilinx
FPGA shows that, with 2,048 inputs, the PIPO-based scheduler achieves a throughput of 70 Mpps, which is 1.64x higher than the PIEO-based one, but using only 14.7% Look-Up Tables (LUTs) and 40.5% Block RAMs of the latter.
... There is a plethora of research that compares the TSN traffic control approaches from a performance standpoint. On this [8] also compare the performance of TAS and frame preemption and conclude that the two approaches achieve very similar end-to-end delays. The authors go further to suggest, that standard Ethernet with frame preemption is a viable alternative to TAS. ...
The IEEE Time-Sensitive Networking (TSN) Task Group specifies a set of standards that enables real-time communication with predictable and bounded delays over the Ethernet. Specifically, TSN introduces a new set of so-called shapers, which regulate traffic arrival and transmission in the networks. Prominent among those are the IEEE 802.1 Qbv Time-Aware Shaper (TAS) and IEEE 802.1Qav Credit-Based Shaper (CBS). Another traffic control mechanism is the IEEE 802.1Qbu Frame Preemption. Most works in the literature have focused on the quantitative performance comparison between these mechanisms. However, the discussion on how they compare in terms of implementation cost has received less attention. In this paper, we provide a comprehensive comparison of the implementation cost of the aforementioned TSN traffic control mechanisms. This comparison can help system designers in choosing which of the mechanism(s) to deploy for their applications.
... Frame preemption mechanism[48], being BE: Best-effort frame, and TS: Time-sensitive frame. ...
A short time after the official launch of WiFi 6, IEEE 802.11 working groups along with the WiFi Alliance are already designing its successor in the wireless local area network (WLAN) ecosystem: WiFi 7. With the IEEE 802.11be amendment as one of its main constituent parts, future WiFi 7 aims to include time-sensitive networking (TSN) capabilities to support low latency and ultra-reliability in license-exempt spectrum bands, enabling many new Internet of Things scenarios. This article first introduces the key features of IEEE 802.11be, which are then used as the basis to discuss how TSN functionalities could be implemented in WiFi 7. Finally, the benefits and requirements of the most representative Internet of Things low-latency use cases for WiFi 7 are reviewed: multimedia, healthcare, industrial, and transport.
... based, which cannot express all pessimistic transmission cases and, then, leads to unsafe latency evaluations [37]. As known, critical time applications have hard and soft real-time traffic. ...
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.
... According to the TSN standards, IEEE802.3br/IEEE802.1Qbu states that pre-emption de¯nes a mechanism that ensure high priority tra±c arrives at a destination with a¯xed latency by break-up frames into smaller pieces (Thiele and Ernst, 2016). Pre-emption allows unscheduled tra±c to be prioritised to have a¯xed latency. ...
IEEE802.1 Time-Sensitive Networking (TSN) makes it conceivable to convey the data traffic of time as well as critical applications using Ethernet shared by different applications having diversified Quality of Service (QoS) requirements for both TSN and non-TSN. TSN assures a guaranteed data delivery with limited latency, low jitter, and amazingly low loss of data for time-critical traffic. By holding networking resources for basic traffic, and applying different queuing and traffic shaping strategies, TSN accomplishes zero congestion loss for basic time-critical traffic. In proposed system, backpropagation algorithm is used to train the training set and fuzzy inference system methodologies such as Mamdani fuzzy inference system which has fuzzy inputs and fuzzy outputs, Sugeno FIS which has fuzzy inputs and a crisp output and adaptive-network-based fuzzy inference system has obtained from the neural network and fuzzy logic. The proposed system uses neuro-fuzzy techniques to handle frame pre-emption and reduces the time taken for decision making. It presents a decision making process using the traffic class.
The Credit-Based Shaping (CBS) algorithm is a traffic scheduling technique commonly used in Time-Sensitive Networking (TSN) to manage audio and video streams. CBS is designed to solve the problem of continuous blocking of low-priority data streams caused by high-bandwidth data streams occupying communication resources for long durations. However, in certain application scenarios with stringent jitter requirements, CBS may fall short in meeting the demands of real-time control data streams. In this paper, we improve the CBS algorithm by introducing a frame preemption mechanism and propose a time-sensitive scheduling algorithm to ensure real-time transmission of critical traffic. Additionally, we conduct worst-case response time (WCRT) analysis of the proposed scheduling scheme under both preemptive and non-preemptive scenarios. Finally, we validated our design through a vehicular network scenario. The results indicate that this method not only resolves the real-time transmission issues of critical traffic but also reduces the overall traffic transmission delay.
div class="section abstract"> The current automotive industry has a growing demand for real-time transmission to support reliable communication and for key technologies. The Time-Sensitive Networking (TSN) working group introduced standards for reliable communication in time-critical systems, including shaping mechanisms for bounded transmission latency. Among these shaping mechanisms, Cyclic Queuing and Forwarding (CQF) and frame preemption provide deterministic guarantees for frame transmission. However, despite some current studies on the performance analysis of CQF and frame preemption, they also need to consider the potential effects of their combined usage on frame transmission. Furthermore, there is a need for more research that addresses the impact of parameter configuration on frame transmission under different situations and shaping mechanisms, especially in the case of mechanism combination. Firstly, this paper comprehensively reviews the schedulability analysis of the combined usage of CQF and frame preemption based on Compositional Performance Analysis (CPA). This paper summarizes the Worst-Case Responses (WCRs) of streams of each class under CQF with preemption. Secondly, this paper analyses the WCR under CQF with preemption. This analysis identifies the factors that influence the transmission latency for streams of each class and proposes several guidelines in parameter configuration under this mechanism combination. Then, this paper develops a scheduler named CQFP scheduler, enabling the computation of the WCR for all streams under CQF with preemption in different network scenarios. Finally, the paper conducts simulations to obtain the WCR under various configurations, validating the guidelines and the results obtained from the CQFP scheduler. This evaluation provides insights into the performance of the combination of CQF and preemption. The results can provide the network designers detailed guidelines in traffic class assignment and parameter configuration under CQF with preemption.
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Higher levels of automated driving also require a more sophisticated environmental perception. Therefore, an increasing number of sensors transmit their data samples as frame bursts to other applications for further processing. As a vehicle has to react to its environment in time, such data is subject to safety-critical latency constraints. To keep up with the resulting data rates, there is an ongoing transition to a Time-Sensitive Networking (TSN)-based communication backbone. However, the use of TSN-related industry standards does not match the automotive requirements of large timely sensor data transmission, nor it offers benefits on time-critical transmissions of single control data packets. By using the full data rate of prioritized IEEE 802.1Q Ethernet, giving time guarantees on large data samples is possible, but with strongly degraded results due to data collision. Resolving such collisions with time-aware shaping comes with significant overhead. Hence, rather than optimizing the parameters of the existing protocol, we propose a system design that synchronizes the transmission times of sensor data samples. This limits network protocol complexity and hardware requirements by avoiding tight time synchronization and time-aware shaping. We demonstrate that individual sensor data samples are transmitted without significant interference, exclusively at full Ethernet data rate. We provide a synchronous event model together with a straightforward response time analysis for synchronous multi-frame sample transmissions. The results show that worst-case latencies of such sample communication, in contrast to non-synchronized approaches, are close to their theoretical minimum as well as to simulative results while keeping the overall network utilization high.
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.
Time-sensitive networking (TSN) standards can provide high bandwidth and low latency for communication. Schedulability analysis under mechanism combinations needs to be studied. Under cyclic queuing and forwarding (CQF) with preemption, this letter analyzes the traffic transmission process and defines the traffic classes. Then, this letter provides a schedulability analysis on streams of all traffic classes. The results can provide the network designers with guidelines in the configuration under CQF with preemption and accelerate the usage of TSN for safety-critical communication scenarios.
With the continued evolution of autonomous driving, the communication demand for in-vehicle networks has dramatically increased, and the traditional in-vehicle network solutions have become ineligible for the needs of new in-vehicle applications. Time-Sensitive Network(TSN) with the characteristics of determinism, low latency, high reliability, large bandwidth, and open industry standards, has been considered as the most promising technology for the next-generation in-vehicle networks(IVN). This paper summarizes the current state and methodologies of in-vehicle TSN research through the following five aspects: QoS(Quality of Service) strategy, reliability, clock synchronization, network planning, and network management. The corresponding research priorities and technical challenges are also addressed respectively.
Recently, there has been an interest from the automotive industry in a novel single-pair, half-duplex Ethernet multidrop provision (i.e., 10BASE-T1S), which relies on a coordinated channel access method provided by Physical Layer Collision Avoidance (PLCA). PLCA avoids frame collisions and provides bounded latency, while guaranteeing fairness among nodes and optimal bandwidth utilization. However, despite these advantageous features, PLCA is not aware of flow priorities and, consequently, does not provide priority-based Quality of Service (QoS). Thus, there is an opportunity for integrating QoS-aware schemes, such as the Time-Sensitive Networking (TSN)-based Time-Aware Shaper (TAS) algorithm, into PLCA. In this paper, we present modeling and analysis strategies using Network Calculus for integrating TAS with PLCA to support scheduled traffic, and we compare our modeling and analysis with a baseline work which previously modeled TAS for full-duplex point-to-point Ethernet only. We show that replacing full-duplex point-to-point links with half-duplex PLCA multidrop links still complies with end-to-end delay deadlines, while leading to a reduction of system costs due to the fewer number of Ethernet transceivers in a PLCA multidrop. Moreover, we also show that our results for TAS, when applied only on full-duplex point-to-point links, outperform the results of the baseline work in most use cases.
Ultra-low latency (ULL) is a challenging but nonetheless essential network requirement to achieve in many contexts. Industrial automation (IEC/IEEE 60802), in-vehicle communications (IEEE P802.1DG), audio and video bridging (IEEE Std 802.1BA), aerospace, and 5G fronthall (IEEE 802.1CM) applications demand a low network latency in the order of few milliseconds or even microseconds. ULL services target a more controlled latency for end-to-end device communication and, in critical environments, near real-time connections. Time-Sensitive Networks (TSN) aim at providing deterministic connectivity over IEEE 802 networks guaranteeing packet transport with bounded latency, low packet delay variation, and low packet loss. This work analyzes TSN latency mechanisms and examines how they influence E2E latency. Moreover, it builds a regression-based surrogate model that enables the creation of optimization models to find optimal configurations for a given TSN network. Our findings span the discussion of the characteristics of each individual TSN latency mechanism to the benefits achieved by the proposed optimization models and using these to achieve optimal E2E latency.
Time-Sensitive Networking (TSN) is being widely investigated to provide Ethernet capabilities for in-vehicle backbone communication. However, the gate control list (GCL), as a simple mechanism for achieving timing determinism for safety-critical traffic (ST) frames with hard deadlines, is too rigid to handle the intrinsic timing uncertainty of automated driving systems (ADS). Due to the complexity and the unpredictable operating environment, there can be delayed ST frames that can disrupt the solidly fixed timing behaviour. In this work, we present one novel approach to effectively use bandwidth resources to deal with delayed ST frames, which cannot be handled by a traditional fixed GCL, and the discarding of them should be reduced to improve system’s integrity. An acceptance test is implemented to report to the application layer when an ST frame will miss its deadline and hence be rejected, i.e. prevented from entering the switch. To further improve the efficiency of bandwidth usage, we investigate how to improve the performance of the more important Class A frames in an audio-video-bridging (AVB) switch, which adopts a credit-based shaper mechanism, and we propose a constant bandwidth server to replace the credit-based shaper, while taking fairness into consideration. Evaluation with extensive experiments shows that both resilience and efficiency of the TSN are significantly enhanced compared with a credit-based shaper, especially when the traffic load is relatively high. For the delayed ST frames and event-triggered traffic, our approach is able to schedule more than the solution using the AVB switch even with high network load.
The automotive E/E architecture has undergone a paradigm shift in the past century. Particularly, the new requirements of automated driving are severely challenging the existing architecture, which has led to ongoing revolutionary innovation in E/E architecture. In this paper, we reviewed the evolution of E/E architecture and outlined the requirements-driven developments. We illustrated the state-of-the-art E/E architecture, including network topology, standards, simulator and software platform. We also discussed the next generation of E/E architecture from the perspective of different OEMs and suppliers. The analysis shows that software-defined, hierarchical, reconfigurable and customized E/E architecture is universally accepted. Furthermore, the automotive industry has been experiencing several transitions related to OEMs and suppliers. With the emergence and maturation of automated driving, we analyzed the new requirements on E/E architecture and proposed prospective development trends.
Proprietary field buses such as PROFINET IRT, EtherNet/IP, and EtherCAT are currently used to ensure realtime communication in industrial automation appliances. Despite the fact that they are mostly Ethernet-based, interoperability between them is limited or not feasible at all. In the Industry 4.0 context, the goal is to enable real-time communication with ultralow latencies, while also permitting non-critical traffic and ensuring interoperability between devices from different manufacturers. Time-Sensitive Networking (TSN) is a promising candidate to meet these requirements on layer 2 of the OSI reference model in conjunction with a suitable higher-level protocol. The IEEE 802.1 TSN Task Group has been developing extensions to the Ethernet technology to make it more deterministic and reliable since 2012. In this paper, we have evaluated the TSN mechanisms (1) Time-Aware Shaper (TAS) and (2) frame preemption (FP) and compared them to the existing strict priority scheduling (ST) mechanism in exemplary setups. The chosen comparison criteria are latency guarantee, jitter, and the influence on noncritical traffic. Since the support of TSN devices on the market is low, we have carried out the evaluation using the simulation framework OMNeT++ and the NeSTiNg library. Our evaluation shows that, all in all, TAS performs the best, but it introduces a great configuration overhead. FP and ST can keep up in certain scenarios and their performance can even be improved.
In this paper, we apply IEEE 802.1Qbu Preemptive Priority Frame Forwarding mechanism to the IEEE 802.3z Gigabit Ethernet networks, and compare its performance with non-frame-preemption queuing schemes for various traffic patterns. A feasible implementation of the proposed solutions is addressed. The FPF effectively reduces the forwarding delay as well as jitter, so as to enhance response time of real-time services in GbE networks. Through simulations, we show that the FPF achieves superior and precise QoS control compared to existing non-preemptive-based priority scheduling schemes.
The paper addresses performance modelling of safety critical Ethernet networks with special attention to in-car networks. A specific Ethernet/IP based in-car network is considered as use-case. The modelling is based on the analytical method Real-Time Calculus (RTC), providing hard bounds on delay and buffer utilization. We show how RTC can be applied on the use-case network. Furthermore, we develop a network simulation, used to evaluate the overestimation. It is found that the delays from RTC is significantly overestimated. The bounds from RTC, however, are guaranteed bounds, which is not the case for the simulated.
Controller Area Network (CAN) is used extensively in automotive applications, with in excess of 400 million CAN enabled microcontrollers manufactured each year. In 1994 schedulability analysis was developed for CAN, showing how worst-case response times of CAN messages could be calculated and hence guarantees provided that message response times would not exceed their deadlines. This seminal research has been cited in over 200 subsequent papers and transferred to industry in the form of commercial CAN schedulability analysis tools. These tools have been used by a large number of major automotive manufacturers in the design of in-vehicle networks for a wide range of cars, millions of which have been manufactured during the last decade.
This paper shows that the original schedulability analysis given for CAN messages is flawed. It may provide guarantees for messages that will in fact miss their deadlines in the worst-case. This paper provides revised analysis resolving the problems with the original approach. Further, it highlights that the priority assignment policy, previously claimed to be optimal for CAN, is not in fact optimal and cites a method of obtaining an optimal priority ordering that is applicable to CAN. The paper discusses the possible impact on commercial CAN systems designed and developed using flawed schedulability analysis and makes recommendations for the revision of CAN schedulability analysis tools.
AFDX (Avionics Full Duplex Switched Ethernet) standardized as ARINC 664 is a major upgrade for avionics systems. The mandatory certification implies a worst-case delay analysis of all the flows transmitted on the AFDX network. Up to now, this analysis is done thanks to a tool based on a Network Calculus approach. The more recent Trajectory approach has been proposed for the computation of worst-case response time in distributed systems. It has been shown that the worst-case delay analysis of an AFDX network can be improved using an optimized Trajectory approach. This paper extends this optimized approach with the integration of static priority QoS policies. This extension makes possible to compute the bounds needed for deterministic avionics flows (high priority) when (lower priority) non avionics flows are added. Moreover, the paper provides an analysis of the pessimism of the obtained bounds.
Ethernet is considered as a future communication
standard for distributed embedded systems in the automotive
and industrial domains. A key challenge is the deterministic
low-latency transport of Ethernet frames, as many safety-critical
real-time applications in these domains have tight timing requirements. Time-sensitive networking (TSN) is an upcoming set of
Ethernet standards, which (among other things) address these
requirements by specifying new quality of service mechanisms in
the form of different traffic shapers. In this paper, we consider
TSN’s time-aware and peristaltic shapers and evaluate whether
these shapers are able to fulfill these strict timing requirements.
We present a formal timing analysis, which is a key requirement
for the adoption of Ethernet in safety-critical real-time systems,
to derive worst-case latency bounds for each shaper. We use a
realistic automotive Ethernet setup to compare these shapers to
each other and against Ethernet following IEEE 802.1Q.
Ethernet is currently explored as the upcoming network standard for distributed control applications in many different industries such as automotive, avionics and industrial automation. It offers higher performance and flexibility over traditional control bus systems such as CAN and ProfiBus. For distributed control applications, predictable communication timing is highly important which can be problematic using standard Ethernet. The new Ethernet AVB standard aims to improve this by a new scheduling algorithm based on traffic shaping. However, the current AVB standard lacks a formal timing guarantee which is important for safety-critical control applications. As a solution to this, we present a model for Ethernet AVB networks and a transformation into a timing analysis model. Based on the timing model, we apply a compositional performance analysis approach known from the analysis of distributed real-time systems to derive worst-case timing properties and hence timing guarantees of the original Ethernet AVB network. For this, we provide the required formalism for the analysis of the scheduling of Ethernet AVB.
New hard real-time Advanced Driver Assistance Systems such as the Collision-Avoidance System push the bandwidth requirements of the communication infrastructure to a new level. Controller Area Network (CAN) and FlexRay are reaching their limits. Ethernet-based automotive networks such as Ethernet AVB are capable of addressing these requirements. However, designing predictable Ethernet networks is more complex than the design of a traditional CAN bus. Formal real-time performance characteristics are key to a successful Ethernet integration. In this paper we present an improved Ethernet AVB performance analysis which exploits traffic-stream correlations. The results are significantly tighter compared to related work.
The real-time performance of control network between process control system(PCS) in a nuclear power plant is an important factor to ensure safety and reliability of power plant. Ethernet network is widely adopted in modern PCS even though it does not guarantee hard real-time performance in the non-safety region of a nuclear power plant. To achieve better real-time performance and QoS(Quality of Service), PCS usually uses switched Ethernet with the priority feature, which is based on the IEEE 802.1Q/p protocol. However, the IEEE 802.1Q/p protocol also has a priority inversion problem when transmission of a higher-priority frame is requested during transmission of a lower-priority frame. To resolve this problem, this paper proposes Preemptive Switched Ethernet(PSE) that is based on the IEEE 802.1Q/p protocol with a preemption mechanism. This paper shows that PSE provides better real-time performance than the standard IEEE 802.1Q/p protocol especially when non-real-time and real-time traffics are mixed together. This paper also implements PSE controller using the FPGA (Virtex-4) and MicroBlaze processor. From the implementation results, PSE controller shows an improved latency and jitters of transmission period compare to the normal Ethernet controller. Experiment result shows that the jitter of real-time packet is 50% less than the standard 802.1Q/p protocol.
Ethernet is increasingly recognized as the future communication standard for distributed embedded systems in multiple domains such as industrial automation, automotive and avionics. A main motivation for this is cost and available data rate. A critical issue in the adoption of Ethernet in these domains is the timing of frame transfers, as many relevant applications require a guaranteed low-latency communication in order to meet real-time constraints. Ethernet AVB is an upcoming standard which addresses the timing issues by extending the existing strict-priority arbitration. Still, it needs to be evaluated whether these mechanism suffice for the targeted applications. For safety-critical applications, this can not only be done using intuition or simulation but requires a formal approach to assure the coverage of all worst-case corner cases. Hence, we present in this paper a formal worst-case analysis of the timing properties of Ethernet AVB and strict-priority Ethernet. This analysis mathematically determines safe upper bounds on the latency of frame transfers. Using this approach, we evaluate different topologies for a typical use-case in industrial automation.
Ethernet could be a promising solution to satisfy the increasing bandwidth requirements of future automotive systems. While the non-deterministic timing behavior of standard Ethernet makes its application unsuitable for time critical systems, different real-time Ethernet solutions which ensure bounded communication delays exist and are also already employed in the industry. A common aspect of the existing solutions is the full duplex switched Ethernet network architecture on which they are based. This makes it possible to guarantee the existence of an upper bound of the message latency, but the determination of this bound is far from trivial in most cases. For the determination of the message latency, the behavior of all sources of traffic on the network has to be taken into account. Specifically, one must consider the maximum frame size transmitted by any device, the scheduling parameters of the frames (e.g. Class of Service (CoS) priorities), and the time distribution and rate of frames. In this paper, we present how the concepts used in compositional system level performance analysis can be adapted to analyze full duplex switched based network architectures. We also demonstrate the feasibility of the formal approach by analyzing a system based upon a prominent real time Ethernet solution, namely AFDX, and compare the obtained results with results obtained by simulation.
TT Ethernet is a communication architecture which allows the integration of the standard Ethernet traffic and real-time Ethernet traffic in the same network without invalidating the real-time properties of the real-time traffic. The TT Ethernet switch distinguishes between two classes of traffic. The standard Ethernet traffic is handled in conformance with the existing (standard) Ethernet, whereas the real-time traffic is transmitted with a constant transmission delay. In order to guarantee a constant message transmission delay, the TT Ethernet switch preempts, if necessary, the transmission of standard Ethernet messages, and retransmit the preempted Ethernet message as soon as the transmission of the real-time Ethernet message is finished. The message can be preempted several times before it is successfully transmitted, which decreases the throughput of standard Ethernet messages. In this paper, we propose a segmentation mechanism for standard Ethernet frames in order to increase the throughput. The segmentation mechanism does not change the format of Ethernet frame and is transparent to higher levels of a protocol stack such as TCP/IP.
This paper establishes a link between three areas, namely Max-Plus
Linear System Theory as used for dealing with certain classes of
discrete event systems, Network Calculus for establishing time bounds in
communication networks, and real-time scheduling. In particular, it is
shown that important results from scheduling theory can be easily
derived and unified using Max-Plus Algebra. Based on the proposed
network theory for real-time systems, the first polynomial algorithm for
the feasibility analysis and optimal priority assignment for a general
task model is derived
SymTA/S is a system-level performance and timing analysis approach based on formal scheduling analysis techniques and symbolic simulation. The tool supports heterogeneous architectures, complex task dependencies and context aware analysis. It determines system-level performance data such as end-to-end latencies, bus and processor utilisation, and worst-case scheduling scenarios. SymTA/S furthermore combines optimisation algorithms with system sensitivity analysis for rapid design space exploration. The paper gives an overview of current research interests in the SymTA/S project.
Real-time Ethernet on IEEE 802.3 Networks
- winkel
This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 644080
- L Winkel
- M J Teener
L. Winkel and M. J. Teener, "Real-time Ethernet on IEEE 802.3
Networks," in IEEE 802.3 Plenary Meeting, Berlin, Germany, 2015.
This work has received funding from the European Union's
Horizon 2020 research and innovation programme under grant
agreement No 644080.