High Priority Class Research Articles

Traffic Control Based on Contention Resolution in Optical Burst

Traffic control based on contention resolution process (TCCR) is proposed in this study as a quality of service (QoS) mechanism to offer service level agreement (SLA) for optical burst switch (OBS). QoS of the high and the low priority classes are issued upon their SLA. The first one is defined for real time application as Internet protocol television (IP TV) and voice over Internet protocol (VoIP) while the other is for soft real–time service as Internet protocol remote terminal unit (IP RTU) based on IEC 86070–5–101/104 protocol. A combination of burst aggregation (BA), extra offset time, and fiber delay line (FDL) are utilized in TCCR to offer absolute service differentiation QoS to the high priority class. The experiments show TCCR can offer the high priority class of its satisfied SLA for both blocking probability and delay. It also relatively improves the performances of the low priority class bounded in its SLA because TCCR does not force to drop this class. The performances of TCCR are compared with the other techniques such as no class isolation and bandwidth allocation processes. The comparisons show TCCR gives the best solution of the defined SLA which enhances OBS performances and properly differentiates class of services.

Discouraging Traffic Remapping Attacks in Local Ad Hoc Networks

Quality of Service (QoS) is usually provided in ad hoc networks using a class-based approach which, without dedicated security measures in place, paves the way to various abuses by selfish stations. Such actions include traffic remapping attacks (TRAs), which consist in claiming a higher traffic priority, i.e., false designation of the intrinsic traffic class so that it can be mapped onto a higher-priority class. In practice, TRAs can be executed in IEEE 802.11 ad hoc networks using the Enhanced Distributed Channel Access (EDCA) function. This attack is easy to perform yet hard to prevent. We propose a distributed discouragement scheme based on the threat of TRA detection and punishment. The scheme does not rely on station identities or a trusted third party, nor does it require tampering with the MAC protocol. We analyze an arising non-cooperative TRA game and find that under certain realistic assumptions it only incentivizes TRAs if they are harmless to other stations; otherwise the selfish stations are induced to learn that TRAs are counterproductive.

Spatial Decision Analysis on Wetlands Restoration in the Lower Reaches of Songhua River (LRSR), Northeast China, Based on Remote Sensing and GIS

Wetlands in the Lower Reaches of Songhua River (LRSR), Northeast China, are rich in biodiversityand natural resources, which provide crucial staging and wintering habitats for various endangered species.However, in the past five decades, the size of this wetland area has decreased, and its quality has deteriorated because of increased natural and human activities. Wetland restoration is critical to improve these conditions. In this study, hydrological regulation and habitat suitability, the most important wetland functions, were selected and analyzed to identify suitable wetland restoration sites. By using these two function layers, together with the geographic information system (GIS) spatial analysis function and remote sensing (RS) image data, we identified and prioritized suitable sites for wetland restoration in the LRSR. Areas with high hydrological regulation and good or fair waterbirds’ habitat suitability can support wetland restoration. The potential sites were prioritized in terms of patch size and proximity to natural wetlands and water bodies. Finally, we obtained two priority classes (high and low) of wetland restoration in a spatial scale. The results from this study showed that the areas with high and low priority classes for wetland restoration are 82,628 and 247,039 ha, respectively, which account for 1.23% and 3.67% of the total study area. The high-priority class areas would be used for the wetland restoration.

THE ISRAELI QUEUE WITH INFINITE NUMBER OF GROUPS

The so called “Israeli Queue” is a single server polling system with batch service of an unlimited size, where the next queue to be visited is the one in which the first customer in line has been waiting for the longest time. The case with finite number of queues (groups) was introduced by Boxma, Van der Wal and Yechiali [3]. In this paper we extend the model to the case with a (possibly) infinite number of queues. We analyze the M/M/1, M/M/c, and M/M/1/N—type queues, as well as a priority model with (at most) M high-priority classes and a single lower priority class. In all models we present an extensive probabilistic analysis and calculate key performance measures.

Differentiated waiting time management according to patient class in an emergency care center using an open Jackson network integrated with pooling and prioritizing

Unlike ordinary outpatient clinics, an emergency care center sees a variety of patients with diverse diseases and injuries of different levels of severity. Since patients who are in a critical condition face serious consequences, target waiting times must be determined based on patient acuity levels. To reflect the special situation in emergency care centers included in this study, patient flows are formulated using an open Jackson network with multiple patient classes. This paper is unique because of the integration of pooling and prioritizing patient classes with the open Jackson network. In particular, a hybrid priority model is presented in which a first-come-first-served discipline is applied in some processes and a priority discipline is applied in other processes in the open Jackson network, in order to minimize waiting times for patients with more urgent concerns. A case study based on actual data from an emergency care center demonstrates that the proposed model of pooling and prioritizing patient classes is effective in decreasing waiting times for higher-priority classes without substantially sacrificing those for lower-priority classes.

A heuristic for rationing inventory in two demand classes with backlog costs and a service constraint

We study the rationing policy in an inventory system with two demand classes and different service criteria for backorders. Due to the difference of customer values, system performance sometimes has to be measured with a mixture of penalty cost and service level in managing inventory. With a continuous review (r,Q) system, we develop a critical level rationing policy in which a threshold mechanism is adopted to allocate backorders when multiple outstanding orders exist. Due to the complexity of the problem, a heuristic is developed based on the principle that both demand classes are served with respective target service levels. We also introduce bounds so that the search ranges of decision variables become restrictive. The numerical examples indicate an excellent performance of our heuristic. In addition, when ordering cost is medium or high, the threshold clearing mechanism has the same results as the optimal one. When ordering cost is small (set to zero), different clearing mechanisms should be used depending on the priorities of demand classes. Further analysis indicates that transforming the service constraint into a cost parameter and then applying the existing algorithm will not be a good approach for this problem with mixed performance criteria. It either increases the costs or violates the service constraint. This study also shows the importance of applying rationing policy when high priority class has a low demand volume, target service levels between two classes have a large gap, or replenishment lead time is long. The results of this study should enhance our understanding of how to implement rationing policies in practice.

Average waiting time of customers in a new queue system with different classes

PurposeIt is very complicated to keep the business processes under control since the business processes change rapidly and thus flexibility is an important attribute which businesses should possess in order to respond to rapid changes in the business environment. The purpose of this paper is to divide the companies' customers into different priority groups to be served according to their payment history and feedback in order to increase the companies' performance and profit and save the time of customers within high priority class which may lead to increase their satisfaction.Design/methodology/approachThe paper proposes a requirements engineering‐based approach for business process modelling to assist businesses maintain their performance in such an environment. The paper proposes a new numerical model to improve customer satisfaction in relation to delivery or service waiting time according to their priority class, particularly customers in the high priority class. A call centre at the selected telecommunication company is used as a case study to validate the proposed numerical model.FindingsThe customers' satisfaction in the area of the time to be served according to their priority group classes can be improved using the proposed model.Research limitations/implicationsThe paper has some limitations as the paper only tested the numerical model on one real business organisation and one business process service.Originality/valueTo date, no research has been conducted in the area of separating customers into different priority groups to provide services according to their required delivery time, payment history and feedback which will increase the company's performance and profit and provide prompt service to customers in the high priority class which in turn, will increase their satisfaction.

Adaptive SLA-Aware Algorithms for Provisioning Shared Mesh Optical Networks

 Abstract—The paper proposes a novel SLA-aware mechanism to improve the performance of the networks with huge traffic volume of high priority connection requests with long holding time for optical shared mesh networks. The proposed mechanism consists of two parts, a novel re- provisioning algorithm which buffers and further processes the potentially blocked high priority connection requests, and a new time-aware path constraint which takes advantage of availability and holding-time as two crucial SLA connection parameters. The proposed mechanism benefits from dynamic service level agreement negotiation between a customer and service providers. The simulation results show reduced blocking probability, increased availability satisfaction rate, decreased resource overbuild, and better resource utilization to preserve the high priority class of traffic compared to other SLA-aware algorithms and protection schemes in shared mesh optical networks. proposing a new time-aware path metric, introducing a novel re-provisioning algorithm based on the proposed metric, and applying a huge volume of high-priority traffic with long duration to the introduced algorithm. As discussed in (1), (2), based on SLA contracts or bandwidth-leasing markets between network operators and customers, it is reasonable to assume that the connection holding time can be known in advance while the algorithm is serving online type of traffic in which the algorithm has no knowledge about the coming request. As the first part of the contribution in this paper, we take advantage of a combination of the connection availability, the connection holding-time, and the maximum path availability (3) of the request to introduce a novel path metric. The proposed re- provisioning algorithm presented in this paper as the second part of the contribution benefits from the new path metric to better serve high-priority connection requests. To achieve this goal, we have assumed that the period during which a connection is valid, holding-time, is known a priori. The second part of the contribution is to introduce a novel re-provisioning mechanism by which some of those high- priority connection requests which were blocked in other SLA-aware algorithms or protection schemes are preserved. The paper focuses on specific type of traffic which is of dynamic type and mainly high priority class with long duration while the majority of the existing algorithms either take small portion of the traffic as high priority into account or consider short connection holding times. The proposed re-provisioning mechanism is typically a dynamic provisioning algorithm including a time-aware buffering mechanism which is working based on the new metric presented in this paper. The re-provisioning algorithm employs three algorithms, an algorithm to calculate the maximum path availability reviewed from previous work (3), an algorithm to find the matrix of time-aware maximum path availability of each connection, and an algorithm by which the potentially blocked connections are buffered and served based on the connections holding time. The paper compares the performance of the proposed algorithm to

Queuing system for different classes of customers

Flexibility is an important attribute, which businesses should possess in order to respond to rapid changes in the business environment. The literature shows that customers now have the power to influence companies and manufacturers by conveying their requirements, hence, companies can use this information to attract the best customers to their business. In this paper, we propose a requirements engineering-based approach for business process modelling to assist businesses maintain their performance in such an environment. We propose a new mathematical model to improve customer satisfaction in relation to delivery or service waiting time according to their priority class, particularly customers in the high priority class.

Enhanced Adaptive SLA-aware Algorithms for Provisioning Shared Mesh Optical Networks

The paper deploys an adaptive provisioning algorithm to the traffic with huge volume of high priority connection requests with long holding time by proposing a novel SLA-aware mechanism over optical shared mesh networks. The contribution presented in this paper follows three main characteristics: i) Proposing a new time-aware traffic engineering path constraint considering holding time of connections in addition to the availability, ii) Introducing a novel provisioning algorithm considering the proposed path attribute, and iii) Applying a high volume of high- priority dynamic traffic with long duration to the introduced mechanism in a new simulation environment to prove its effectiveness. The proposed mechanism benefits from dynamic service level agreement negotiation between a customer and service providers to buffer and further process the potentially blocked high priority connection requests. The simulation results show reduced blocking probability, increased availability satisfaction rate, decreased resource overbuild, and better resource utilization to preserve the high priority class of traffic compared to other SLA-aware algorithms and protection schemes in shared mesh optical networks.

Class Based and Shared Resources Access Control for Distributed Video-on-Demand System

We are proposing an efficient admission control policy for Video-on-Demand (VOD) system. Traditional Admission control system uses either threshold or resource capacity to accept or reject any incoming request. The distinction of the proposed scheme from the previous work includes: (1) a new concept of integrating the both schemes (shared resource admission control and class base admission control) into one system, is introduced (2) another new concept of Probability, is introduced to access the shared resource (Ports, Bandwidth). In the proposed system, total capacity of VOD server (ports) is partitioned equal to the number of classes plus shared area. When a request arrives at VOD server, it will be admitted if there is capacity to its corresponding partition, otherwise we will check the capacity of shared area and admit it with some probability. If there is no capacity in shared area or no probability, the request will be rejected. The evaluation of the proposed system is done by the simulation model. Numbers of blocked requests are calculated for performance measure. It is observed from the simulation results that proposed admission control policy not only improves the performance of high-priority classes but also reduces a lot the total number of rejected requests.

QoSatAr: a cross-layer architecture for E2E QoS provisioning over DVB-S2 broadband satellite systems

This article presents QoSatAr, a cross-layer architecture developed to provide end-to-end quality of service (QoS) guarantees for Internet protocol (IP) traffic over the Digital Video Broadcasting-Second generation (DVB-S2) satellite systems. The architecture design is based on a cross-layer optimization between the physical layer and the network layer to provide QoS provisioning based on the bandwidth availability present in the DVB-S2 satellite channel. Our design is developed at the satellite-independent layers, being in compliance with the ETSI-BSM-QoS standards. The architecture is set up inside the gateway, it includes a Re-Queuing Mechanism (RQM) to enhance the goodput of the EF and AF traffic classes and an adaptive IP scheduler to guarantee the high-priority traffic classes taking into account the channel conditions affected by rain events. One of the most important aspect of the architecture design is that QoSatAr is able to guarantee the QoS requirements for specific traffic flows considering a single parameter: the bandwidth availability which is set at the physical layer (considering adaptive code and modulation adaptation) and sent to the network layer by means of a cross-layer optimization. The architecture has been evaluated using the NS-2 simulator. In this article, we present evaluation metrics, extensive simulations results and conclusions about the performance of the proposed QoSatAr when it is evaluated over a DVB-S2 satellite scenario. The key results show that the implementation of this architecture enables to keep control of the satellite system load while guaranteeing the QoS levels for the high-priority traffic classes even when bandwidth variations due to rain events are experienced. Moreover, using the RQM mechanism the user’s quality of experience is improved while keeping lower delay and jitter values for the high-priority traffic classes. In particular, the AF goodput is enhanced around 33% over the drop tail scheme (on average).

Traffic management strategy for delay-tolerant networks

Messages in delay-tolerant networks (DTNs) are generally classified by relative priority into low, medium, and high priority classes, thus creating challenges in structuring scheduling and drop policies of a traffic management system. This study proposes a novel traffic management strategy for DTNs. The proposed scheme improves message deliveries of different priority classes by utilizing message properties such as estimated total number of replicas, elapsed time, and remaining time-to-live. A delete mechanism of delivered messages is also incorporated to use buffer space efficiently. The performance of the proposed strategy is verified via implementation of a simulation model along with existing scheduling and drop policies and is tested with two well-known real-world trace datasets. The results demonstrate that the proposed strategy yields improved message deliveries of high priority as well as medium and low priority classes.

PERFORMANCE ANALYSIS OF ULTRA WIDEBAND MEDIA ACCESS CONTROL PROTOCOL PROVIDING TWO CLASS TRAFFIC

UWB (Ultra wideband) technology has a huge potential for revolutionizing the world of digital communications, particularly wireless communications that based primarily on the impulse radio paradigm. UWB technology was originally seen purely as a physical layer technology, with no or little protocol to control the communication. It is now clear that Media Access Control (MAC) features play a major role in UWB communication systems. In this paper, a communication system is considered with a small number of geographically separated nodes in UWB ad hoc networks. An active node can be in one of two possible classes (H,L); high priority or low priority class, depending on its nature and / or the type of information that it desires to transmit. Nodes in class-H are given some priority over those in class-L. The motivation comes from the observation that, in the absence of a sophisticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the Delay Spread of the channel which amounts to 60 ns in indoor environments. Therefore, using a wider frequency band to shorten the transmission time for each pulse may not increase the data rate in proportion to the available bandwidth. Thus, a multiband approach is considered to better utilize the available spectrum, where each transmitter sends longer pulses in one of many narrower frequency bands. Measures of system performance including throughput, average delay and bit error rate will be presented in single band and multiband approaches. Additionally, there is a comparison between numerical results and how they are achieved by simulation of the entire system providing two priority classes.

Reservation and allocation policies for influenza vaccines

This research investigates the impact of alternative allocation mechanisms that can be employed in the context of vaccine inventory rationing. Available vaccine inventory can be allocated to arrivals from high priority (target groups such as healthcare professionals) and low priority (non-target groups) demand classes using Partitioned Allocation (PA), Standard Nesting (SN), and Theft Nesting (TN). In any one of the mechanisms, a part of the available inventory is reserved for the exclusive use of the high priority demand class. They differ, however, in how the unreserved portion of the inventory is utilized: Under PA, demand from the high (low) priority class consumes only the reserved (unreserved) quantity. Under SN, demand from the high priority class first consumes the reserved quantity; once and if this quantity is exhausted, high priority demand competes with low priority demand for the remaining inventory. Under TN the sequence of allocation is reversed: both demand classes first compete for the unreserved inventory. Once this portion of inventory is exhausted, high priority demand is fulfilled from the reserved inventory and low priority demand is rejected. We develop service level (probability of fulfilling the entire demand) and fill rate (fraction of demand fulfilled) expressions for all three allocation mechanisms. Based on these expressions, numerical analyses are conducted to illustrate which allocation mechanism a health planner should choose depending on the availability of vaccines, and how the health planner should set the reserved quantity for the high priority class. We observe that (1) there exist certain conditions under which one of the allocation mechanisms outperforms the others and (2) this effect is determined by the decision maker’s choice of the performance measure.

A Mathematical Optimization Model for Locating Telecenters

Telecommuting is a Transportation Demand Management strategy to partially or completely replace the daily commute with telecommunication technologies. Research has revealed that telecommuting can be effectively done from special places provided for this purpose called telecenters. In telecenter-based telecommuting, trip lengths are shortened due to change in the location of work places. Thus suitable locations of telecenters play an important role in increasing the beneficial impacts of telecommuting in the transportation systems. In this research, a mathematical optimization model for finding optimal location and capacity of telecenters is proposed. This model is a bi-objective linear program, and a Fuzzy Goal Programming method with a preemptive structure is used to solve it. Telecommuting demand is classified into three groups of telecommuters and a priority structure that assigns the higher priority class to the closer telecenters is also incorporated into the model. The proposed model is implemented in a case study of finding optimal location of telecenters for government employees in Tehran (capital of Iran) metropolitan area. The base model is solved and its sensitivity to different parameters has been analyzed based on which, an optimal model is selected. The solution of this model is an optimal pattern for distribution of telecommuting capacities and yields the most system-wide benefits from implementation of telecommuting.

Optimal multi-class rescheduling of railway traffic

During real-time traffic management, the railway system suffers perturbations. The task of dispatchers is to monitor traffic flow and to compute feasible rescheduling solutions in case of perturbed operations. The main objective of the infrastructure manager is delay minimization, but the dispatchers also need to comply with the objectives of the train operating companies. This paper presents an innovative optimization framework in order to reschedule trains with different classes of priority, that can be computed statically or dynamically in order to include the needs of different stakeholders. An iterative train scheduling procedure is proposed in order to compute feasible train schedules for an ordered set of priority classes, from the highest one to the lowest one. At each step, the procedure focuses on the current priority class, preserving solution quality from the higher priority classes and neglecting lower priority classes in the optimization of train orders and times. The multi-class rescheduling problem is formulated via alternative graphs that are able to model precisely train movements at the microscopic level of block sections and block signals. Each step of the iterative train scheduling procedure is solved to optimality by a state-of-the-art branch and bound algorithm. The results show an interesting gap between single-class and multi-class rescheduling problems in terms of delay minimization. Each priority class is also evaluated in order to assess the performance of the different rescheduling solutions.

Periodic GATE Optimization (PGO): A New Service Scheme for Long-Reach Passive Optical Networks

In this paper, we present a new service scheme, Periodic GATE Optimization (PGO) for long-reach passive optical networks. PGO is based on a previously proposed service scheme where the optical line terminal (OLT) generates multiple threads to poll the bandwidth requests of the optical network units (ONUs). In PGO, OLT periodically builds an ILP formulation by using the collected requests of the ONUs, and solves the model for the overloaded ONUs. Based on the outputs, it determines how to credit the ONUs until the next ILP formulation whenever they are overloaded. We evaluate the performance of PGO by simulation, and show that it introduces further decrease in average packet delay until the heavy loads. Average queue length at the ONUs is also shortened by PGO. The results imply that PGO achieves these enhancements without increasing the packet drop probability. In the paper, we also present the quality-of-service (QoS) aware version of PGO, namely PGO-QoS. PGO-QoS consists of two modules such as intra-ONU scheduling where the dequeuing proportion of the QoS classes is determined and reported to OLT, and dynamic bandwidth allocation module where mostly PGO runs. We evaluate the performance of PGO-QoS for each QoS class and for the overall network in terms of average packet delay, average queue size, and packet drop probability under different scenarios. Based on the simulation results, PGO-QoS is shown to introduce further decrease in delay, queue length, and packet loss probability for the high priority class requests that are granted by multithread polling in Long-Reach PON.

Selecting Sites for Converting Farmlands to Wetlands in the Sanjiang Plain, Northeast China, Based on Remote Sensing and GIS

Wetlands in the Sanjiang Plain are rich in biodiversity and natural resources in the northeast of China. However, this wetland area has decreased in size and deteriorated in quality owing to expanded agricultural activities since the 1950s. Converting farmlands to wetlands is necessary to improve these conditions. Using Remote Sensing (RS) and Geographic Information Systems (GIS) technologies, we derived farmland productivity data and hydrology data for the Sanjiang Plain. The farmland productivity data were derived from land use and net primary productivity (NPP) data of the MODIS products. We obtained three productivity farmland classes (low, medium, and high) through the NPP anomaly percentage method. We were only concerned with the low-productivity farmland. Hydrology data were modeled with a wetness index, which was derived from Digital Elevation Model (DEM) data. Based on these two data layers, we identified and prioritized sites for the conversion of farmlands to wetlands. The areas with low farmland productivity and medium or high wetness values have potential to support the conversion of farmlands to wetlands. Potential sites were prioritized in terms of patch size and proximity to natural wetlands and water bodies. We obtained three priority classes, among which the high-priority class would be used as the areas for the recent conversion of farmlands to wetlands. The area of this class was 75,888ha and accounted for 1.3% of the total farmland area.

Optical MAN ring performance with traffic aggregations

We propose to study end to end delays in slotted optical MAN (Metropolitan Area Networks) ring networks. Edge nodes interconnect the fibre of the MAN and the client layer. We propose a mechanism based on IP traffic aggregations with QoS requirements in order to build optical packets. IP packet aggregation is performed in a loop manner by always beginning the aggregation cycle with the highest priority class. In order to overcome the drawbacks of the strict priority discipline, an algorithm depicting a probabilistic priority discipline is presented. The aggregation technique leads to increasing the filling ratio of an optical packet, and consequently, the bandwidth efficiency of an optical network. We present an analytical model in order to evaluate the performance of the aggregation mechanism. Secondly, we study the performance of the optical MAN ring with different packet formats. The MAC protocol is based on the “empty slot” procedure. Different queueing models based on the GI/G/1 queues with server interruptions are presented in order to compute mean packet delays according to the rank nodes.