Comparing Admission Control Architectures for Real-Time Ethernet

Industry 4.0 and Autonomous Driving are emerging resource-intensive distributed application domains that deal with open and evolving environments. These systems are subject to stringent resource, timing, and other non-functional constraints, as well as frequent reconfiguration. Thus, real-time behavior must not preclude operational flexibility. This combination is motivating ongoing efforts within the Time Sensitive Networking (TSN) standardization committee to define admission control mechanisms for Ethernet. Existing mechanisms in TSN, like those of AVB, its predecessor, follow a distributed architecture that favors scalability. Conversely, the new mechanisms envisaged for TSN (IEEE 802.1Qcc) follow a (partially) centralized architecture, favoring short reconfiguration latency. This paper shows the first quantitative comparison between distributed and centralized admission control architectures concerning reconfiguration latency. Here, we compare AVB against a dynamic real-time reconfigurable Ethernet technology with centralized management, namely HaRTES. Our experiments show a significantly lower latency using the centralized architecture. We also observe the dependence of the distributed architecture in the end nodes' performance and the benefit of having a protected channel for the admission control transactions.This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI), in part by the Fondo Europeo de Desarrollo Regional (FEDER) [AEI/FEDER, Unión Europea (UE)] under Grant TEC2015-70313-R, in part by the European Regional Development Fund (FEDER) through the Operational Programme for Competitivity and the Internationalization of Portugal 2020 Partnership Agreement (PRODUTECH-SIF) under Grant POCI-01-0247-FEDER-024541, and in part by the Research Centre Instituto de Telecomunicações under Grant UID/EEA/50008/2013.info:eu-repo/semantics/publishedVersio

Pre-Shaping Bursty Transmissions under IEEE802.1Q as a Simple and Efficient QoS Mechanism

International audienceThe automotive industry is swiftly moving towards Ethernet as the high-speed communication network for in-vehicle communication. There is nonetheless a need for protocols that go beyond what standard Ethernet has to offer in order to provide additional QoS to demanding applications such as ADAS systems or audio/video streaming. The main protocols currently considered for that purpose are IEEE802.1Q, AVB with the Credit Based Shaper mechanism (IEEE802.1Qav) and TSN with its Time-Aware Shaper (IEEE802.1Qbv). AVB/CBS and TSN/TAS both provide efficient QoS mechanisms and they can be used in a combined manner, which offers many possibilities to the designer. Their use however requires dedicated hardware and software components, and clock synchronization in the case of TAS. Previous studies have also shown that the efficiency of these protocols depends much on the application at hand and the value of the configuration parameters. In this work, we explore the use of "pre-shaping" strategies under IEEE802.1Q for bursty traffic such as audio/video streams as a simple and efficient alternative to AVB/CBS and TSN/TAS. Pre-shaping means inserting on the sender side "well-chosen" pauses between successive frames of a burst (e.g., a camera frame), all the other characteristics of traffic remaining unchanged. We show on an automotive case-study how the use of pre-shaping for audio/video streams leads to a drastic reduction of the communication latencies for the best-effort streams while enabling to meet the timing constraints for the rest of the traffic. We then discuss the limitations of the pre-shaping mechanism and future works needed to facilitate its adoption

Design Optimization of Cyber-Physical Distributed Systems using IEEE Time-sensitive Networks (TSN)

In this paper we are interested in safety-critical real-time applications implemented on distributed architectures supporting the Time-SensitiveNetworking (TSN) standard. The ongoing standardization of TSN is an IEEE effort to bring deterministic real-time capabilities into the IEEE 802.1 Ethernet standard supporting safety-critical systems and guaranteed Quality-of-Service. TSN will support Time-Triggered (TT) communication based on schedule tables, Audio-Video-Bridging (AVB) flows with bounded end-to-end latency as well as Best-Effort messages. We first present a survey of research related to the optimization of distributed cyber-physical systems using real-time Ethernet for communication. Then, we formulate two novel optimization problems related to the scheduling and routing of TT and AVB traffic in TSN. Thus, we consider that we know the topology of the network as well as the set of TT and AVB flows. We are interested to determine the routing of both TT and AVB flows as well as the scheduling of the TT flows such that all frames are schedulable and the AVB worst-case end-to-end delay is minimized. We have proposed an Integer Linear Programming (ILP) formulation for the scheduling problem and a Greedy Randomized Adaptive Search Procedure (GRASP)-based heuristic for the routing problem. The proposed approaches have been evaluated using several test cases