Schedulability analysis of Ethernet Audio Video Bridging networks with scheduled traffic support

Abstract

The IEEE Audio Video Bridging (AVB) technology is nowadays under consideration in several automation domains, such as, automotive, avionics, and industrial communications. AVB offers several benefits, such as open specifications, the existence of multiple providers of electronic components, and the real-time support, as AVB provides bounded latency to real-time traffic classes. In addition to the above mentioned properties, in the automotive domain, comparing with the existing in-vehicle networks, AVB offers significant advantages in terms of high bandwidth, significant reduction of cabling costs, thickness and weight, while meeting the challenging EMC/EMI requirements. Recently, an improvement of the AVB protocol, called the AVB ST, was proposed in the literature, which allows for supporting scheduled traffic, i.e., a class of time-sensitive traffic that requires time-driven transmission and low latency. In this paper, we present a schedulability analysis for the real-time traffic crossing through the AVB ST network. In addition, we formally prove that, if the bandwidth in the network is allocated according to the AVB standard, the schedulability test based on response time analysis will fail for most cases even if, in reality, these cases are schedulable. In order to provide guarantees based on analysis test a bandwidth over-reservation is required. In this paper, we propose a solution to obtain a minimized bandwidth over-reservation. To the best of our knowledge, this is the first attempt to formally spot the limitation and to propose a solution for overcoming it. The proposed analysis is applied to both the AVB standard and the AVB ST. The analysis results are compared with the results of several simulative assessments, obtained using OMNeT++, on both automotive and industrial case studies. Real-Time Syst (2017) 53:526-577 527 between the results of the analysis and the simulation ones shows the effectiveness of the analysis proposed in this work.

Impact on credit freeze before gate closing in CBS and GCL integration into TSN

“…The credit evolution rule is the one of AVB: when a CBS queue waits, its credit increases, whether this waiting is due to any guard band or a ST slot. A worst case response time AVB ST is done in [4], making clear distinction between the standard behaviour of TSN and the AVB ST proposal.…”

“…It can be upper bounded: each close-gate event may generate only one pre-close interval, and its length is at most the duration of one frame of maximal length. Let MaxPreCloseTime be its maximal value on a GCL cycle 4 .…”

“…We chose the term "pre-closing" time for these intervals, instead of "guard band" which is more commonly used, because depending on the authors, the "guard band" is this dynamic pre-closing time, whereas for others, the "guard band" is a static interval before the gate-close event, whose length must be large enough to prevent any encroaching. In the standard itself, the term "guard band" is used only in an informative appendix [1, Appendix Q], and without any exact definition 4. The terms portTransmitRate, OperCycleTime, GateOpenTime operIdleSlope, are from the standard, the terms GateCloseTime, PreCloseTime and MaxPreCloseTime have been introduced to ease the discussion.…”

Performance enhancement of extended AFDX via bandwidth reservation for TSN/BLS shapers

“…We perform a set of experiments to assess the efficiency of our introduced methods, with reference to an intuitive bandwidth reservation method. Similar works have been conducted to define bandwidth reservation methods for Credit Based Shaper (CBS) of AVB networks [2], [1]. However, to the best of our knowledge, this issue has not been handled yet in the literature for TSN/BLS shapers in avionics domain.…”

A Calibrated Test-Set for Measurement of Access-Point Time Specifications in Hybrid Wired/Wireless Industrial Communication †

“…The demanding requirements of this communication environment, briefly summarized in Table 1, have been largely addressed by wired networks such as field-busses (e.g., Profibus DP [3], CANopen [4] and DeviceNet [5] to mention some) and Real-Time Ethernet (RTE), which is an effective family of communication systems for factory automation developed in the last decade [6][7][8][9]. Moving to the wireless domain, although dedicated industry standard solutions are currently available for process automation scenarios, such as WirelessHART and ISA 100.11a [10][11][12], so far stand-alone wireless networks have not been widely considered at the field level in factory automation applications.…”