57 research outputs found
Impact of AS6802 Synchronization Protocol on Time-Triggered and Rate-Constrained Traffic
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
Quantitative Performance Comparison of Various Traffic Shapers in Time-Sensitive Networking
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 in 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 two novel hybrid
architectures of combined traffic shapers, i.e., TAS+ATS+SP and TAS+ATS+CBS. 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
A Fast Iterative Pursuit Algorithm in Robust Face Recognition Based on Sparse Representation
A relatively fast pursuit algorithm in face recognition is proposed, compared to existing pursuit algorithms. More stopping rules have been put forward to solve the problem of slow response of OMP, which can fully develop the superiority of pursuit algorithm—avoiding to process useless information in the training dictionary. For the test samples that are affected by partial occlusion, corruption, and facial disguise, recognition rates of most algorithms fall rapidly. The robust version of this algorithm can identify these samples automatically and process them accordingly. The recognition rates on ORL database, Yale database, and FERET database are 95.5%, 93.87%, and 92.29%, respectively. The recognition performance under various levels of occlusion and corruption is also experimentally proved to be significantly enhanced
Total-effect Test May Erroneously Reject So-called "Full" or "Complete" Mediation
The procedure for establishing mediation, i.e., determining that an
independent variable X affects a dependent variable Y through some mediator M,
has been under debate. The classic causal steps require that a "total effect"
be significant, now also known as statistically acknowledged. It has been shown
that the total-effect test can erroneously reject competitive mediation and is
superfluous for establishing complementary mediation. Little is known about the
last type, indirect-only mediation, aka "full" or "complete" mediation, in
which the indirect (ab) path passes the statistical partition test while the
direct-and-remainder (d) path fails. This study 1) provides proof that the
total-effect test can erroneously reject indirect-only mediation, including
both sub-types, assuming least square estimation (LSE) F-test or Sobel test; 2)
provides a simulation to duplicate the mathematical proofs and extend the
conclusion to LAD-Z test; 3) provides two real-data examples, one for each
sub-type, to illustrate the mathematical conclusion; 4) in view of the
mathematical findings, proposes to revisit concepts, theories, and techniques
of mediation analysis and other causal dissection analyses, and showcase a more
comprehensive alternative, process-and-product analysis (PAPA)
Latency Analysis of Multiple Classes of AVB Traffic in TSN with Standard Credit Behavior using Network Calculus
Time-Sensitive Networking (TSN) is a set of amendments that extend Ethernet
to support distributed safety-critical and real-time applications in the
industrial automation, aerospace and automotive areas. TSN integrates multiple
traffic types and supports interactions in several combinations. In this paper
we consider the configuration supporting Scheduled Traffic (ST) traffic
scheduled based on Gate-Control-Lists (GCLs), Audio-Video-Bridging (AVB)
traffic according to IEEE 802.1BA that has bounded latencies, and Best-Effort
(BE) traffic, for which no guarantees are provided. The paper extends the
timing analysis method to multiple AVB classes and proofs the credit bounds for
multiple classes of AVB traffic, respectively under frozen and non-frozen
behaviors of credit during guard band (GB). They are prerequisites for
non-overflow credits of Credit-Based Shaper (CBS) and preventing starvation of
AVB traffic. Moreover, this paper proposes an improved timing analysis method
reducing the pessimism for the worst-case end-to-end delays of AVB traffic by
considering the limitations from the physical link rate and the output of CBS.
Finally, we evaluate the improved analysis method on both synthetic and
real-world test cases, showing the significant reduction of pessimism on
latency bounds compared to related work, and presenting the correctness
validation compared with simulation results. We also compare the AVB latency
bounds in the case of frozen and non-frozen credit during GB. Additionally, we
evaluate the scalability of our method with variation of the load of ST flows
and of the bandwidth reservation for AVB traffic
Effect of Vent Mode on the Differential Pressure Pre-cooling Efficiency of Layered Peaches
The objective of this study was to explore the effect of the vent mode of corrugated boxes universally used in the market on the precooling performance of layered peaches and to determine the functional relationship between the precooling environmental parameters and the precooling efficiency and the optimal vent mode under different differential pressure pre-cooling working conditions in order to realize the rapid energy-saving precooling of peaches after harvest. A numerical model of heat and mass transfer during differential pressure precooling with circular and rectangular vents (abbreviated as CV and RV, respectively) was established based on computational fluid dynamics. By comparing and analyzing the experimental and simulated data, it was found that the maximum root mean square error and mean absolute percentage error between the two vent designs were 0.799 ℃ and 6.6%, respectively, which fully verified that this numerical model had high prediction accuracy. Through in-depth exploration of the temperature and flow field distribution in different vent modes, it was found that CV exhibited inferior precooling uniformity when compared with RV. Nevertheless, CV demonstrated a notable reduction in precooling time by 30%–40% and a decrease in fan energy consumption by 50%. Additionally, their relationships with differential pressure were described by. Based on these obtained results, the precooling quality of peaches could be improved by using RV, and the precooling cost could be reduced by using CV. To simultaneously achieve these two goals, the diameter of CV should be greater than 35 mm. This study provides a theoretical reference for the reasonable selection of vent parameters and accurate monitoring of fruit precooling performance in small and medium-sized orchards
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