Priority Assignment Technique Research Articles

Partition window assignment in hierarchically scheduled time-partitioned distributed real-time systems with multipath flows

Time and space partitioning techniques are implemented in the development of safety-critical applications to ensure isolation among components. A suitable arrangement of the execution of such partitions is a key challenge so that applications meet the timing requirements imposed to software. In this work, the effect of window sizes and context switch overheads in the partition window configuration is studied, with the aim of analyzing their impact when the response-time analysis and priority assignment techniques are applied. Then, a heuristic algorithm is proposed, in order to obtain a partition window configuration that enables the schedulability of partition-based safety critical systems. This algorithm is evaluated in synthetic test scenarios and it is also applied to a safety-critical use-case in the railway domain.

PDMAC: A Priority-Based Enhanced TDMA Protocol for Warning Message Dissemination in VANETs.

Vehicular ad hoc networks (VANETs) are the key enabling technology for intelligent transportation systems. Carrier-sense multiple access with collision avoidance (CSMA/CA) is the de facto media access standard for inter-vehicular communications, but its performance degrades in high-density networks. Time-division multiple access (TDMA)-based protocols fill this gap to a certain extent, but encounter inefficient clock synchronization and lack of prioritized message delivery. Therefore, we propose a priority-based direction-aware media access control (PDMAC) as a novel protocol for intra-cluster and inter-cluster clock synchronization. Furthermore, PDMAC pioneers a three-tier priority assignment technique to enhance warning messages delivery by taking into account the direction component, message type, and severity level on each tier. Analytical and simulation results validate the improved performance of PDMAC in terms of clock synchronization, channel utilization, message loss rate, end-to-end delays, and network throughput, as compared with eminent VANET MAC protocols.

Data Priority Assignment Technique for Opportunistic Routing

Data Priority Assignment Technique for Opportunistic Routing

Pre-channel scheduling and Priority-based reservation in medium access control for industrial wireless sensor network applications

Numerous technical advancements and the pervasive controlling schemes in the Industrial Wireless Sensor Network (IWSN) with the capability of interoperability among the nodes facilitate the reliable communication. With the increase of participating sensors size, the memory and energy consumption reduce the lifetime adversely. To alleviate these issues, this paper creates an energy efficient data management and routing architecture based on the data fusion techniques in IEEE 802.15.4. The data classification through proposed Multi-Stage Classification (MSC) prior to priority assignment techniques makes the immediate decision regarding the controlling actions. The split up of data using Reservation-based Medium Access Control (RMAC) raises the resource allocation requests according to the data type. The built up of the relationship between the number of slots and the data arrival enhances the resource utilization performance for each slot. The guarantee of transfer of immediate transmission with the priority supports the critical conditions with high energy efficiency.

A review of priority assignment in real-time systems

It is over 40 years since the first seminal work on priority assignment for real-time systems using fixed priority scheduling. Since then, huge progress has been made in the field of real-time scheduling with more complex models and schedulability analysis techniques developed to better represent and analyse real systems. This tutorial style review provides an in-depth assessment of priority assignment techniques for hard real-time systems scheduled using fixed priorities. It examines the role and importance of priority in fixed priority scheduling in all of its guises, including: pre-emptive and non-pre-emptive scheduling; covering single- and multi-processor systems, and networks. A categorisation of optimal priority assignment techniques is given, along with the conditions on their applicability. We examine the extension of these techniques via sensitivity analysis to form robust priority assignment policies that can be used even when there is only partial information available about the system. The review covers priority assignment in a wide variety of settings including: mixed-criticality systems, systems with deferred pre-emption, and probabilistic real-time systems with worst-case execution times described by random variables. It concludes with a discussion of open problems in the area of priority assignment.

Performance Based Improvement of the CPU by reducing the Real-Time Interrupt Latency using the PPTS Algorithm

The main objective of the research is to improve the performance of the CPU at software level by reducing the Interrupt Latency of the Real time systems. Interrupt Latency provides an important metric in increasing the performance of the Real Time Kernal. So far the research has been investigated with respect to real-time interrupt latency reduction using non-pre-emptive task scheduling algorithms. A general disadvantage of the non-preemptive discipline is that it introduces additional blocking time in higher priority tasks, so reducing schedulability. If the interrupt latency is increased, the task switching delay shall be increasing with respect to each task. Hence most of the research work has been focussed to reduce interrupt latency by using the Pre-emptive Task scheduling algorithm. Based on the literature survey, A Deadline Monotonic Priority Assignment technique is used to reduce the latency with respect to the deadline. Deferred pre-emption scheduling and Fixed pre-emptive scheduling algorithm are used to reduce the interrupt latencies based on the queue fixed to the priority of the tasks to be handled. Here we suggest a new algorithm named “Priority Preemptive task scheduling algorithm” which preempts and serve the task with highest priority and also concentrates on the low priority tasks during the buffering time of the higher priority tasks.

On new scheduling policy for the improvement of firm RTDBSs performances

Earliest deadline first (EDF) is one of the main scheduling policies used in real-time database systems (RTDBSs) for transactions processing. With EDF, prioritized transactions are not necessarily the most important in the system. Moreover, it is well-known that EDF is not efficient in overload conditions. In this paper, we introduce the notion of transaction importance and present a new priority assignment technique based on both transactions importance and deadlines. This assignment policy leads to a new scheduling policy, called generalized earliest deadline first (GEDF). In order to show the benefits of using GEDF for managing real-time transactions, we have designed an RTDBS simulator and carried out Monte Carlo simulations.

Utilization of execution histories in scheduling real-time database transactions

Real-time database systems support data processing needs of real-time systems where transactions have time constraints. Here we consider repetitively executed transactions, and assume that execution histories are logged. A well-known priority assignment technique called earliest-deadline-first is biased towards short transactions in which short transactions have better chances of completing their executions within their deadlines. We introduce the notion of “fair scheduling” in which the goal is to have “similar” completion ratios for all transaction classes (short to long in sizes). We propose priority assignment techniques that overcome the biased scheduling and show that they work via extensive simulation experiments.

A multiclass priority-based slotted-ring network for LAN-ATM interworking

Interworking LANs with an ATM backbone network is considered a cost-effective and most promising solution for bringing ATM into the mainstream. To sustain delay-sensitive applications (e.g., video or voice) and loss-sensitive applications (e.g., data transfer), this paper presents a slotted-ring network (SRN) with spatial reuse. In order to provide nonpreemptive multipriority services over SRN, a simple priority-based media access protocol, called the check requested before send (CRBS), is proposed. A dynamic priority assignment technique is described to assign priorities based on their delay and loss requirements. An analytical model is presented to analyze CRBS protocol under Poisson input traffic and uniform output traffic. Extensive simulations are run to assess the performance of CRBS protocol for two classes of cells with priorities 0 and 1.

A dynamic priority assignment technique for streams with (m, k)-firm deadlines

The problem of scheduling multiple streams of real-time customers, is addressed in this paper. The paper first introduces the notion of (m, k)-firm deadlines to better characterize the timing constraints of real-time streams. More specifically, a stream is said to have (m, k)-firm deadlines if at least m out of any k consecutive customers must meet their deadlines. A stream with (m, k)-firm deadlines experiences a dynamic failure if fewer than m out of any k consecutive customers meet their deadlines. The paper then proposes a priority-based policy for scheduling N such streams on a single server to reduce the probability of dynamic failure. The basic idea is to assign higher priorities to customers from streams that are closer to a dynamic failure so as to improve their chances of meeting their deadlines. The paper proposes a heuristic for assigning these priorities. The effectiveness of this approach is evaluated through simulation under various customer arrival and service patterns. The scheme is compared to a conventional scheme where all customers are serviced at the same priority level and to an imprecise computation model approach. The evaluation shows that substantial reductions in the probability of dynamic failure are achieved when the proposed policy is used.

A Communications System Which Prioritizes the Queues, Service Channels, and Traffic

A new priority communications protocol has been defined and analyzed. This <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M/M/C/K</tex> system is unique because priorities are assigned not only to the incoming traffic, but also to the queues and the service channels (which may process calls only of an equal or higher priority). This nonpreemptive priority assignment technique significantly improves the grade of service and reduces the average waiting time for high priority calls while reducing only slightly the system's utilization factor.