Priority Scheme Research Articles

Investigating Flash memory wear levelling and execution modes

The impact of wear levelling on a Flash storage package and its access operations’ execution modes is investigated. First, a simple, static logical-to-physical mapping function is proposed and its implied wear levelling is assessed for different distributions of addresses, covering both uniform access and hotspots, as well as the Flash chip utilization within the whole package. Second, for each access mode, different preemptive and non-preemptive priority schemes are considered with a range of IO arrival rates, using Poisson-, Erlang- and Pareto-based arrival processes. The analysis of the impact of the execution modes on the performance of the Flash memory is undertaken using a hardware simulator. The results show clearly the good wear levelling obtained by the mapping functions, even in the presence of hotspots. In addition, the impact of the chosen execution mode on the whole storage package for each IO workload type is assessed, both qualitatively and quantitatively.

Wireless Sensor Networks for an Extended City Intelligent Transportation System

Due to development and extension of city, we propose an extended city intelligent transportation system based on new concept: transport priority schemes and emergency response scheme. In this paper, we propose an extended collaborative traffic information collection, fusion and storage framework for city intelligent transportation system based on wireless sensor technology. The proposed framework not only solved data fusion and storage problem in transport priority schemes and emergency response scheme, but also has higher reliability and flexibility compare with the traditional city intelligent transportation system.

Link layer solutions for supporting real‐time traffic over CDMA wireless mesh networks

AbstractWith recent advances in the development of wireless communication networks, wireless mesh networks (WMNs) have been receiving considerable research interests in recent years. The need to support integrated services and ensure quality of service (QoS) satisfaction for various applications is one of the fundamental challenges for successful WMN deployment. In order to provide differentiated services, medium access control (MAC) should have priority management at the link layer. In code division multiple access (CDMA)‐based WMNs, the interference phenomenon and simultaneous transmissions must be considered. We propose two priority schemes for MAC in a distributed CDMA‐based WMN, taking into account interference, multimedia services, QoS requirements, and simultaneous transmissions. The first priority scheme is within a node. Each node has an independent queue for each traffic class. According to QoS requirements, the queue that should be served first is determined. The second priority scheme is among neighbor nodes. It is proposed for multiple simultaneous transmissions in the CDMA network. This scheme gives a larger chance of correct transmission to high priority traffic than low priority traffic. In addition, we propose to use adaptive spreading gain and a frame structure to achieve high resource utilization. Simulation results demonstrate that the proposed schemes can achieve effective QoS guarantee. Copyright © 2009 John Wiley & Sons, Ltd.

Priority scheduling of requests to web portals

Web portals work as a point of access to a large volume of information on the web. This paper focuses on the performance of Web portals in an E-commerce environment which involves the processing of a large number of users’ requests. It proposes a class-based priority scheme which classifies users’ requests into high and low priorities. In E-commerce, some requests (e.g. buy) are generally considered more important than others (e.g. search or browse). We contend that the requests received from a Web portal should generally get higher priority as such requests are more likely to lead to purchases. We believe that assigning such priorities at multiple service levels can improve the performance of Web portals’ requests of higher priority. The proposed scheme is formally specified and implemented, and performance results are obtained and compared to a server that does not prioritise requests. The results show significant performance improvements in the processing of high priority requests.

RACOON: A Multiuser QoS Design for Mobile Wireless Body Area Networks

In this study, Random Contention-based Resource Allocation (RACOON) medium access control (MAC) protocol is proposed to support the quality of service (QoS) for multi-user mobile wireless body area networks (WBANs). Different from existing QoS designs that focus on a single WBAN, a multiuser WBAN QoS should further consider both inter-WBAN interference and inter-WBAN priorities. Similar problems have been studied in both overlapped wireless local area networks (WLANs) and Bluetooth piconets that need QoS supports. However, these solutions are designed for non-medical transmissions that do not consider any priority scheme for medical applications. Most importantly, these studies focus on only static or low mobility networks. Network mobility of WBANs will introduce unnecessary inter-network collisions and energy waste, which are not considered by these solutions. The proposed multiuser-QoS protocol, RACOON, simultaneously satisfies the inter WBAN QoS requirements and overcomes the performance degradation caused by WBAN mobility. Simulation results verify that RACOON provides better latency and energy control, as compared with WBAN QoS protocols without considering the inter-WBAN requirements.

A Multiple Access Protocol for Multimedia Transmission over Wireless Networks

This paper develops and evaluates the performance of an advanced multiple access protocol for transmission of full complement of multimedia signals consisting of various combinations of voice, video, data, text and images over wireless networks. The protocol is called Advanced Multiple Access Protocol for Multimedia Transmission (AMAPMT) and is to be used in the Data Link Layer of the protocol stack. The principle of operation of the protocol is presented in a number of logical flow charts. The protocol grants permission to transmit to a source on the basis of a priority scheme that takes into account a timeto-live (TTL) parameter of all the transactions, selectable priorities assigned to all the sources and relevant channel state information (CSI) in this order. Performance of the protocol is evaluated in terms of quality of service parameters like packet loss ratio (PLR), mean packet transfer delay (MPTD) and throughput. Using a simulation model based on an OPNET simulation software package does the evaluation. under various traffic loads with constant distributions with various mean arrival rates and transaction sizes results obtained show that the performance is improved when this priority scheme is used than when it is not used. The results for AMAPMT are compared with that of the best currently available multiple access protocol called Adaptive Request Channel Multiple Access (ARCMA). AMAPMT protocol out performs ARCMA protocol.

On the PATHGROUPS approach to rapid small phylogeny.

We present a data structure enabling rapid heuristic solution to the ancestral genome reconstruction problem for given phylogenies under genomic rearrangement metrics. The efficiency of the greedy algorithm is due to fast updating of the structure during run time and a simple priority scheme for choosing the next step. Since accuracy deteriorates for sets of highly divergent genomes, we investigate strategies for improving accuracy and expanding the range of data sets where accurate reconstructions can be expected. This includes a more refined priority system, and a two-step look-ahead, as well as iterative local improvements based on a the median version of the problem, incorporating simulated annealing. We apply this to a set of yeast genomes to corroborate a recent gene sequence-based phylogeny.

Gateway Strategies for VoIP Traffic over Wireless Multihop Networks

When supporting both voice and TCP in a wireless multihop network, there are two conflicting goals: to protect the VoIP traffic, and to completely utilize the remaining capacity for TCP. We investigate the interaction between these two popular categories of traffic and find that conventional solution approaches, such as enhanced TCP variants, priority queues, bandwidth limitation, and traffic shaping do not always achieve the goals. TCP and VoIP traffic do not easily coexist because of TCP aggressiveness and data burstiness, and the (self-) interference nature of multihop traffic. We found that enhanced TCP variants fail to coexist with VoIP in the wireless multihop scenarios. Surprisingly, even priority schemes, including those built into the MAC such as RTS/CTS or 802.11e generally cannot protect voice, as they do not account for the interference outside communication range. We present VAGP (Voice Adaptive Gateway Pacer) - an adaptive bandwidth control algorithm at the access gateway that dynamically paces wired-to-wireless TCP data flows based on VoIP traffic status. VAGP continuously monitors the quality of VoIP flows at the gateway and controls the bandwidth used by TCP flows before entering the wireless multihop. To also maintain utilization and TCP performance, VAGP employs TCP specific mechanisms that suppress certain retransmissions across the wireless multihop. Compared to previous proposals for improving TCP over wireless multihop, we show that VAGP retains the end-to-end semantics of TCP, does not require modifications of endpoints, and works in a variety of conditions: different TCP variants, multiple flows, and internet delays, different patterns of interference, different multihop topologies, and different traffic patterns.

The performances study of IEEE 802.11e to support QoS in channel error environment

ABSTRACTOne of the most important functions in IEEE 802.11e is enhanced distributed coordination function (EDCF). EDCF is an enhanced version of IEEE 802.11 distributed coordination function (DCF) which provides a priority scheme by differentiating the inter‐frame space and the initial window size. We proposed a modified Markov chain model to study the EDCF priority scheme. We have theoretically analyzed the saturation throughput and delay by using the modified Markov chain model in non‐ideal channel scenario. We also have compared it with the Markov chain model that exists under ideal channel scenario. Simulations are also conducted to validate analytical results. Our study shows that the modified model under ideal channel scenario is better than that in channel error scenario. Copyright © 2011 John Wiley & Sons, Ltd.

Control/Network Codesign Basics for IP‐Based Shared Networks

Network and control relationship is an essential aspect in the design of networked control systems (NCSs). The design parameters are mainly centered in the transmission rate and in the packet structure, and some studies have been made to determine how transmission rate affects the network delay and consequently the stability of the control. In Internet, these analysis are mathematically complex due to the large number of different potential scenarios. Using empirical methods, this work deduces that the transmission scheduling problem of an NCS can be solved by designing an appropriate transport protocol, taken into account high and periodic sampling rates. The transport protocol features are determined by simulation, using a new test platform based on the NS2 network simulation suite, to develop control/network codesign solutions. Conclusions of this paper are that the transport features are packet‐loss‐based flow control, best effort, and fairness, supplemented by a packet priority scheme.

Handoff Priority Schemes in Wireless Mobile Cellular System

Handoff Priority Schemes in Wireless Mobile Cellular System

Concordance of freshwater and terrestrial biodiversity

Efforts to set global conservation priorities have largely ignored freshwater diversity, thereby excluding some of the world's most speciose, threatened, and valuable taxa. Using a new global map of freshwater ecoregions and distribution data for about 13,300 fish species, we identify regions of exceptional freshwater biodiversity and assess their overlap with regions of equivalent terrestrial importance. Overlap is greatest in the tropics and is higher than expected by chance. These high-congruence areas offer opportunities for integrated conservation efforts, which could be of particular value when economic conditions force conservation organizations to narrow their focus. Areas of low overlap—missed by current terrestrially based priority schemes—merit independent freshwater conservation efforts. These results provide new information to conservation investors setting priorities at global or regional scales and argue for a potential reallocation of future resources to achieve representation of overlooked biomes.

Regular User Priority Scheme for Performance Improvement in 4G Network

Wireless network are growing rapidly, leading to overloaded systems, unacceptable delays and increasing computational costs due to inefficient channel allocation strategy. Handoff call is more important over new call so it must provide some priority; this is the prime objective of all channel allocation strategy. In this paper we propose regular users priority scheme to better utilization of channel and reduce handover blocking probability. We have analyzed a particular path for several users and assign a symbol for regular, medium and normal users. These symbols are also inserted with other related information of user in HLR. Some channels are reserve for regular and medium users over normal users. Strategy of channel reservation schemes provides priority to regular and medium user over normal user. The aim of proposed scheme will use to increase user loyalty by reducing handover blocking probability. Now-a-days it is important not only to acquire new mobile users for mobile companies but also retain them. We can retain mobile users by providing them good channel facility as described in proposed scheme.

Aggregation convergecast scheduling in wireless sensor networks

We consider the problem of scheduling in wireless sensor networks for the purposes of aggregation convergecast. We observe that existing schemes adopt essentially a two phase approach, consisting of, first, a tree construction and, second, a scheduling phase. Following a similar approach, we propose two new improvements, one to each of the two phases. Starting with a new lower bound on the schedule length, we make use of it in the tree construction phase. The tree construction phase consists of solutions to instances of bipartite graph semi-matchings. The scheduling phase is a weight-based priority scheme that obeys dependency (tree) and interference constraints. Our extensive experiments show that, overall, our proposed solution not only outperforms all previously proposed solutions in terms of schedule length, but it also significantly extends the network's lifetime.

A dynamic priority-based approach to concurrent toolpath planning for multi-material layered manufacturing

This paper presents an approach to concurrent toolpath planning for multi-material layered manufacturing (MMLM) to improve the fabrication efficiency of relatively complex prototypes. The approach is based on decoupled motion planning for multiple moving objects, in which the toolpaths of a set of tools are independently planned and then coordinated to deposit materials concurrently. Relative tool positions are monitored and potential tool collisions detected at a predefined rate. When a potential collision between a pair of tools is detected, a dynamic priority scheme is applied to assign motion priorities of tools. The traverse speeds of tools along the x -axis are compared, and a higher priority is assigned to the tool at a higher traverse speed. A tool with a higher priority continues to deposit material along its original path, while the one with a lower priority gives way by pausing at a suitable point until the potential collision is eliminated. Moreover, the deposition speeds of tools can be adjusted to suit different material properties and fabrication requirements. The proposed approach has been incorporated in a multi-material virtual prototyping (MMVP) system. Digital fabrication of prototypes shows that it can substantially shorten the fabrication time of relatively complex multi-material objects. The approach can be adapted for process control of MMLM when appropriate hardware becomes available. It is expected to benefit various applications, such as advanced product manufacturing and biomedical fabrication.

Analytical modeling of an integrated priority and WFQ scheduling scheme in multi-service networks

The provisioning of differentiated Quality-of-Service (QoS) is a key objective in the design and deployment of convergent multi-service communication networks. Integrated traffic management schemes that combine various fundamental scheduling principles have been proposed for the QoS differentiation in cellular and IEEE 802.16/WiMAX-based broadband wireless networks. In this paper, cost-effective analytical performance models are devised for a new hybrid scheduling scheme based on the integration of the well-known Priority Queueing (PQ) and Weighted Fair Queueing (WFQ) scheduling principles. In these models, traffic arrival processes are represented, respectively, by non-bursty Poisson process and bursty-correlated Markov-Modulate Poisson Process (MMPP) and new closed-form expressions of main performance metrics are derived including system fairness, mean number of packets in each buffer, system throughput, mean queueing delay and packet loss probability of individual traffic flows. The accuracy of the analytical models is validated through extensive comparisons between analytical results and those obtained from simulation experiments. Finally, these models are adopted to investigate the impact of the weights of traffic flows served by WFQ and assess the adverse effects of the traffic burstiness and correlation on the performance of the integrated scheduling scheme.

Pathgroups, a dynamic data structure for genome reconstruction problems

Ancestral gene order reconstruction problems, including the median problem, quartet construction, small phylogeny, guided genome halving and genome aliquoting, are NP hard. Available heuristics dedicated to each of these problems are computationally costly for even small instances. We present a data structure enabling rapid heuristic solution to all these ancestral genome reconstruction problems. A generic greedy algorithm with look-ahead based on an automatically generated priority system suffices for all the problems using this data structure. The efficiency of the algorithm is due to fast updating of the structure during run time and to the simplicity of the priority scheme. We illustrate with the first rapid algorithm for quartet construction and apply this to a set of yeast genomes to corroborate a recent gene sequence-based phylogeny. http://albuquerque.bioinformatics.uottawa.ca/pathgroup/Quartet.html chunfang313@gmail.com Supplementary data are available at Bioinformatics online.

Split algorithm of binary tree with priority and its simulation under free access channel

A modified binary-tree based algorithm with priority scheme was proposed in this paper.The algorithm can guarantee the priority service to access channel in high probability while avoiding congestion.The main factors that affect the grouping measure for priority services and its transmission efficiency were analyzed also in the paper.Computer simulation experiments were carried out under the condition of two priorities,while set different arrival rate,initial access probability,the proportion of high priority service among whole traffic and the retransmission probability,to analyze the delay and throughput of blocked and free access channel.The result indicates that the algorithm is efficent and reliable.

A review of coastal risk management in the UK

This paper reviews the approaches that have been developed in the UK in order to deliver sustainable policies for managing risks from coastal erosion and flooding. One of the most important facilitators has been the adoption of a strategic framework at a national scale. This framework involves several scales of plans (shoreline management plans and strategy plans) as well as schemes. The recognition that funding sources are finite, and therefore need to be spent wisely, has also encouraged the development of more sustainable schemes. This has necessitated the development of a national appraisal methodology under which only the highest priority schemes achieve central government funding. The government also funds a national research programme to support flood and coastal erosion risk management. This paper gives examples of some of the outputs of this programme, which have included studies that have led to an improved understanding of coastal processes, coastal evolution, and risk levels, as well as the development of national data sets and management tools. The paper suggests some further improvements that could be made to the research programme. The discussion focuses on the likelihood of increasing choice of ‘managed realignment’ and ‘no active intervention’ policies in the future, their potential unpopularity with local stakeholders, and the current work under way to deal with these issues. The paper concludes with some thoughts on the priorities for coastal management over the next decade.

Performance Analysis of Priority Scheme in ATM Network

The asynchronous Transfer Mode (ATM) is the widely used packet switching and connection oriented technology that meets diverse services and performance requirements of real time applications using the broadcast . An ATM network is suitable for multimedia services with different traffic flow characteristics and quality of services (QoS ) requirements. In order to meet the required QoS of each traffic type, some types of priority disciplines are needed in packet switching to increase the utilization of switches in ATM networks. This paper describes a buffer management scheme using two different prioritized service disciplines in order to improve the QoS in terms of cell delay time for each traffic class and to reduce the cell loss rate of loss sensitive class in an ATM network. The performance analysis and comparative study of these priority schemes have been presented.