Analysis of forward approach for upper bounding end-to-end transmission delays over distributed real-time avionics networks

2020 ◽  
Vol 124 (1279) ◽  
pp. 1399-1435
Author(s):  
Q. Xu ◽  
X. Yang
Keyword(s):  
Real Time ◽  
Upper Bound ◽  
Data Exchange ◽  
Direct Consequence ◽  
Transmission Delay ◽  
Worst Case ◽  
Engineering Research ◽  
Transmission Delays ◽  
Global Clock ◽  
End To End

ABSTRACTDistributed real-time avionics networks have been subjected to a great evolution in terms of functionality and complexity. A direct consequence of this evolution is a continual growth of data exchange. AFDX standardised as ARINC 664 is chosen as the backbone network for those distributed real-time avionics networks as it offers high throughput and does not require global clock synchronisation. For certification reasons and engineering research, a deterministic upper bound of the end-to-end transmission delay for packets of each flow should be guaranteed. The Forward Approach (FA) is proposed for the computation of the worst-case end-to-end transmission delay. This approach iteratively estimates the maximum backlog (amount of the pending packets) in each visited switch along the transmission path, and the worst-case end-to-end transmission delay can be computed. Although it is pessimistic (overestimated), the Forward Approach can provide a tighter upper bound of the end-to-end transmission delay while considering the serialisation effect. Recently, our research finds the computation of the serialisation effect might induce an optimistic (underestimated) upper bound. In this paper, we analyse the pessimism in the Forward Approach and the optimism induced by the computation of the serialisation effect, and then we provide a new computation of the serialisation effect. We compare this new computation with the original one, the experiments show that the new computation reduces the optimism and the upper bound of the end-to-end transmission delay can be computed more accurately.

scholarly journals Phasing of Periodic Tasks Distributed over Real-time Fieldbus

2017 ◽  
Vol 12 (5) ◽  
pp. 645 ◽  
Author(s):  
Sang-Hun Lee ◽  
Hyun-Wook Jin ◽  
Kanghee Kim ◽  
Sangil Lee
Keyword(s):  
Real Time ◽  
Search Time ◽  
Periodic Tasks ◽  
Worst Case ◽  
Real Time System ◽  
Delay Bound ◽  
End To End Delay ◽  
Global Clock ◽  
End To End ◽  
Hard Real Time

In designing a distributed hard real-time system, it is important to reduce the end-to-end delay of each real-time message in order to ensure quick responses to external inputs and a high degree of synchronization among cooperating actuators. In order to provide a real-time guarantee for each message, the related literature has focused on the analysis of end-to-end delays based on worst-case task phasing. However, such analyses are too pessimistic because they do not assume a global clock. With the assumption that task phases can be managed by using a global clock provided by emerging real-time fieldbuses, such as EtherCAT, we can try to calculate the optimal task phasing that yields the minimal worst-case end-to-end delay. In this study, we propose a heuristic to manage the phase offsets in the distributed tasks to reduce the theoretical end-to-end delay bound. The proposed heuristic reduces the search time for a solution by identifying time intervals where actual communication occurs among inter-dependent tasks. Furthermore, to analyze the distribution of endto- end delays in different phases, we implemented a simulation tool. The simulation results showed that the proposed heuristic can reduce worst-case end-to-end delay as well as jitter in end-to-end delays.

scholarly journals Recorp: Receiver-oriented Policies for Industrial Wireless Networks

2021 ◽  
Vol 17 (4) ◽  
pp. 1-32
Author(s):  
Ryan Brummet ◽  
Md Kowsar Hossain ◽  
Octav Chipara ◽  
Ted Herman ◽  
David E. Stewart
Keyword(s):  
Real Time ◽  
Salient Feature ◽  
Link Quality ◽  
Worst Case ◽  
Control Loops ◽  
High Data ◽  
Industrial Wireless Networks ◽  
Run Time ◽  
End To End ◽  
The Coordinator

Future Industrial Internet-of-Things (IIoT) systems will require wireless solutions to connect sensors, actuators, and controllers as part of high data rate feedback-control loops over real-time flows. A key challenge in such networks is to provide predictable performance and adaptability in response to link quality variations. We address this challenge by developing RECeiver ORiented Policies (Recorp), which leverages the stability of IIoT workloads by combining offline policy synthesis and run-time adaptation. Compared to schedules that service a single flow in a slot, Recorp policies share slots among multiple flows by assigning a coordinator and a list of flows that may be serviced in the same slot. At run-time, the coordinator will execute one of the flows depending on which flows the coordinator has already received. A salient feature of Recorp is that it provides predictable performance: a policy meets the end-to-end reliability and deadline of flows when the link quality exceeds a user-specified threshold. Experiments show that across IIoT workloads, policies provided a median increase of 50% to 142% in real-time capacity and a median decrease of 27% to 70% in worst-case latency when schedules and policies are configured to meet an end-to-end reliability of 99%.

End-to-End Reservation Services in Real-Time Mach

2001 ◽  
Author(s):  
Raj Rajkumar ◽  
K. Juvva ◽  
A. Molano ◽  
S. Oikawa ◽  
C. Lee
Keyword(s):  
Real Time ◽  
End To End

Effective Model for Real Time End to End Secure Communication Over GSM Voice Channel

2021 ◽  
Author(s):  
Mobeen Ur Rehman ◽  
Muhammad Adnan ◽  
Mouazma Batool ◽  
Liaqat Ali Khan ◽  
Ammar Masood
Keyword(s):  
Real Time ◽  
Secure Communication ◽  
Effective Model ◽  
End To End

scholarly journals Network Calculus-Based Latency for Time-Triggered Traffic under Flexible Window-Overlapping Scheduling (FWOS) in a Time-Sensitive Network (TSN)

2021 ◽  
Vol 11 (9) ◽  
pp. 3896
Author(s):  
Khaled M. Shalghum ◽  
Nor Kamariah Noordin ◽  
Aduwati Sali ◽  
Fazirulhisyam Hashim
Keyword(s):  
Real Time ◽  
Connected Vehicles ◽  
Network Calculus ◽  
Timing Constraints ◽  
Traffic Scheduling ◽  
Worst Case ◽  
Continuous Increase ◽  
Scheduled Traffic ◽  
Support Time ◽  
New Framework

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.

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