Priority Classes Research Articles

A Two-Dimensional Diffusion Approximation for a Loss Model with Trunk Reservation

We consider a loss model with C servers, and arriving customers are split into two classes. Of the C servers, R may be used only by the high priority class. Thus if a high priority customer sees all C servers occupied, then that customer is lost, while a low priority customer is lost if $\geq C-R$ servers are occupied. Assuming Poisson arrivals of both customer types and exponential service, we study the problem asymptotically, with $C\to\infty$ and the arrival rates comparably large. We assume that the total load is roughly equal to the number of servers, and we obtain a two-dimensional diffusion equation satisfied by the joint steady state probability distribution of the numbers of servers occupied by the two customer classes. We analyze this equation by a combination of analytic and numerical methods. Our singular perturbation analysis makes certain assumptions about not only the forms of various asymptotic expansions but also the asymptotic matching between different scales.

Analysis of a finite buffer model with two servers and two nonpreemptive priority classes

In this paper, we analyze a finite buffer queueing model with two servers and two nonpreemptive priority service classes. The arrival streams are independent Poisson processes, and the service times of the two classes are exponentially distributed with different means. One of the two servers is reserved exclusively for one class with high priority and the other server serves the two classes according to a nonpreemptive priority service schedule. For the model, we describe its dynamic behavior by a four-dimensional continuous-time Markov process. Applying recursive approaches we present the explicit representation for the steady-state distribution of this Markov process. Then, we calculate the Laplace–Stieltjes Transform and the steady-state distribution of the actual waiting times of two classes of customers. We also give some numerical comparison results with other queueing models.

Guard-Channel-Based Incremental and Dynamic Optimization on Call Admission Control for Next-Generation QoS-Aware Heterogeneous Systems

Next-generation communication systems are expected to be highly integrated heterogeneous networking environments. Supporting multimedia services with different quality-of-service (QoS) requirements over such highly heterogeneous environments is a very challenging task, and a unified call admission control (CAC) optimization mechanism is needed to allow resources to be efficiently utilized. In this paper, we propose an optimal CAC mechanism, i.e., the guard-channel-based incremental and dynamic optimization (GUIDO), which is a threshold-based CAC scheme that is designed based on the Markov decision process (MDP) and sensitivity analysis (SA) techniques. The MDP is used to derive the optimal CAC policy for predetermined goals, whereas the use of SA can greatly reduce the effort of unnecessary recomputation of the CAC policy when the traffic condition varies. Through the use of system capacity estimation and QoS mapping techniques, GUIDO allows the CAC operation to be performed in a general framework, even with various underlying communication systems and different access/core networks. GUIDO can be implemented dynamically (online optimization) and statically (lookup table). Homogeneous and heterogeneous systems with multiple service priority classes are studied in this paper. We have considered comprehensive objective functions, and each characterizes a different interest of the service provider. The performance is evaluated via an event-driven simulator, and the results are compared with those of the complete sharing scheme and conventional guard channel schemes under constant call-arrival rates as well as time-varying call-arrival-rate traffic scenarios.

Mean sojourn times for phase-type discriminatory processor sharing systems

In a discriminatory processor sharing (DPS) queueing model, each job (or customer) belongs to one out of finitely many classes. The arrival processes are Poisson. Classes differ with respect to arrival rates and service time distributions. Moreover, classes have different priority levels. All jobs present are served simultaneously but the fraction of the server’s capacity allocated to each one of them is proportional to their class priority parameter (while the total capacity is of course fixed). For the case of exponential service requirements, we find the mean sojourn times of various job classes, conditioning on the system’s state, namely how many of each class are present. Next we derive the well-known system of linear equations solved by the unconditional values. We then switch to the much weaker assumption of phase-type service requirements, different across classes, where additionally the priority parameters may depend both on class and phase (and not only on class as assumed in existing papers). We determine mean sojourn times for a job belonging to any class, firstly conditional on the numbers of jobs from all classes present (which are shown to be affine functions) and secondly, unconditionally (as solutions of a system of linear equations).

The influence of QoS routing on the achievable capacity in TDMA based Ad hoc wireless networks

The issue of providing QoS guarantees in an ad hoc wireless network is a challenging problem. Irrespective of the nature of the routing and reservation protocol used in the QoS scheme, there is an inherent limitation on the kind of QoS guarantees that can be provided. Unlike existing studies which analyze the transport capacity, we focus on the achievable capacity. The framework that we assume is that of a TDMA-based network. In this paper, we investigate the achievable capacity and the influence of routing protocols on it. The metrics that we consider are the call acceptance probability and the system saturation probability. We derive general bounds for the case of multiple-classes of users in the network. These bounds indicate the number of calls of the highest priority class that can be admitted into the network. Simulation studies were performed to study the effect of load, hopcount, and the routing protocol on the call acceptance. The increase of the call acceptance with the introduction of load-balancing highlights the importance of load-balancing in enhancing the system performance.

The Effective Bandwidth Problem Revisited

This article studies a single-server queueing system with autonomous service and ℓ priority classes. Arrival and departure processes are governed by marked point processes. There are ℓ buffers corresponding to priority classes, and upon arrival a unit of the kth priority class occupies a place in the kth buffer. Let N (k), k = 1,2,…, ℓ denote the quota for the total kth buffer content. The values N (k) are assumed to be large, and queueing systems both with finite and infinite buffers are studied. In the case of a system with finite buffers, the values N (k) characterize buffer capacities. This article discusses a circle of problems related to optimization of performance measures associated with overflowing the quota of buffer contents, particularly buffers models. Our approach to this problem is new, and the presentation of our results is simple and clear for real applications.

Prioritizing veterinary pharmaceuticals for aquatic environment in Korea

Pharmaceutical residues may have serious impacts on nontarget biological organisms in aquatic ecosystems, and have therefore precipitated numerous investigations worldwide. Many pharmaceutical compounds available on the market need to be prioritized based on their potential ecological and human health risks in order to develop sound management decisions. We prioritized veterinary pharmaceuticals in Korea by their usage, potential to enter the environment, and toxicological hazard. Twenty compounds were identified in the top priority class, most of which were antibiotics. Among these compounds, 8 were identified as deserving more immediate attention: amoxicillin, enramycin, fenbendazole, florfenicol, ivermectin, oxytetracycline, tylosin, and virginiamycin. A limitation of this study is that we initially screened veterinary pharmaceuticals by sales tonnage for veterinary use only. However, this is the first attempt to prioritize veterinary pharmaceuticals in Korea, and it provides important concepts for developing environmental risk management plans for such contaminants in aquatic systems.

Customer segmentation, allocation planning and order promising in make-to-stock production

Modern advanced planning systems offer the technical prerequisites for an allocation of “available-to-promise” (ATP) quantities—i.e. not yet reserved stock and planned production quantities—to different customer segments and for a real time promising of incoming customer orders (ATP consumption) respecting allocated quota. The basic idea of ATP allocation is to increase revenues by means of customer segmentation, as it has successfully been practiced in the airline industry. However, as far as manufacturing industries and make-to-stock production are concerned, it is unclear, whether, when, why and how much benefits actually arise. Using practical data of the lighting industry as an example, this paper reveals such potential benefits. Furthermore, it shows how the current practice of rule-based allocation and consumption can be improved by means of up-to-date demand information and changed customer segmentation. Deterministic linear programming models for ATP allocation and ATP consumption are proposed. Their application is tested in simulation runs using the lighting data. The results are compared with conventional real time order promising with(out) customer segmentation and with batch assignment of customer orders. This research shows that—also in make-to-stock manufacturing industries—customer segmentation can indeed improve profits substantially if customer heterogeneity is high enough and reliable information about ATP supply and customer demand is available. Surprisingly, the choice of an appropriate number of priority classes appears more important than the selection of the ATP consumption policy or the clustering method to be applied.

Fuzzy logic packet scheduling approach for QoS provision of delay-constrained traffic in synchronous optical packet switched networks

We describe a fuzzy-logic-based scheduling algorithm for synchronous optical packet switches that provides quality of service for delay-constrained traffic. The proposed method considers both packet importance as well as delay constraints. One of the advantages of a fuzzy controller is the fact that, regardless of the design complexity, it can be implemented as a simple look-up table. This makes it ideal for high-speed optical switches. We have used two fuzzy controllers: one to select a packet to be forwarded to an output port and another to decide which packet(s) should be buffered or dropped. In a simulation example, video traffic with three priority classes is considered. The results show up to 3dBs of improvement in the quality of the received video, resulting from the packet loss differentiation achieved by employing the proposed fuzzy packet scheduling approach.

Statistical delay control scheme for DiffServ networks with self-similar traffic

A statistical traffic control scheme is proposed, which computes the expected queue-length boundary conditions for self-similar traffic priority classes and can adapt the traffic class service level to provide practical and effective guaranteed quality of service control support in DiffServ networks.

Analysis of M/M/1 queueing system with two priority classes

The present paper investigates the two-class priority M/M/1 queueing system, where the prioritized first class customers are served under first-come , first served (FCFS) preemptive resume discipline and have finite room capacity. The second class customers have infinite waiting space and low priority i.e. during the service of a low priority customer, if a high priority customer joins the system, then the low priority customer’s service is interrupted and will be resumed again when there is no high priority customer present in the system. Our aim is to get explicit expressions for the generating functions of the steady state probabilities in terms of Chebyshev’s polynomial of second kind have obtained. A recursive method is employed to solve the steady-state equations governing the model. Moreover, the expressions for the mean queue length, the marginal distributions of high and low priority customers are also given. The derivation is based only on the general structure of the system and the generating function involved, and thus is simpler than previous methods. We examine the effect of number of high priority customers, input and output rates on the average queue lengths of low and high priority classes by looking at a numerical illustration.

Scheduler design for multiple traffic classes in OFDMA networks

This paper considers some scheduler structures that are executable in the environments of multiple traffic classes and multiple frequency channels. To design a scheduler structure for multiple traffic classes, we first propose a scheduler selection rule that uses the priority of traffic class and the urgency level of each packet. Then we relax the barrier of traffic class priority when a high priority packet has some room in waiting time. This gives us a chance to exploit multiuser diversity, thereby giving more flexibility in scheduling. Our considered scheduler can achieve higher throughput compared to the simple extension of conventional modified largest weighted delay first (MLWDF) scheduler while maintaining the delay performance for QoS class traffic. We also design a scheduler structure for multiple frequency channels that chooses a good channel for each user whenever possible to exploit frequency diversity. The simulation results show that our proposed scheduler increases the total system throughput by up to 50% without degrading the delay performance. Our schedulers are suited to be deployed for OFDMA systems like IEEE 802.16 systems that have plenty of frequency channels and use the adaptive modulation and coding (AMC) scheme.

On the unfairness in IEEE 802.11e networks: Desynchronization of its medium access mechanism

Since the advent of the first IEEE 802.11 standard, several papers have proposed means of providing QoS to IEEE 802.11 networks and evaluate various traffic-prioritization mechanisms. Nevertheless, studies on the assignment of AIFS times defined in IEEE 802.11e reveal that the various priority levels work in a synchronized manner. The studies show that, under large loads of high-priority traffic, EDCA starves low-priority frames, which is undesirable. We argue that QoS traffic needs to be prioritized, but users sending best-effort frames should also obtain the expected service. High-priority traffic can also suffer performance degradation when using EDCA because of heavy loads of low-priority frames. Thus, we have proposed a mechanism based on desynchronizing the IEEE 802.11e working procedure. It prevents stations that belong to different priority classes from attempting simultaneous transmission, prioritizes independent collision groups and achieves better short-term and long-term channel access fairness. We have evaluated the proposal based on extensive analytical and simulation results. It prevents the strangulation of low-priority traffic, and, moreover, reduces the degradation of high-priority traffic with the increased presence of low-priority frames.

Informationally Decentralized Video Streaming Over Multihop Wireless Networks

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Various packet scheduling, dynamic routing, error-protection, and channel adaptation strategies have been proposed at different layers of the protocol stack to address multi-user video streaming over multihop wireless networks. However, these cross-layer transmission strategies can be efficiently optimized only if they use accurate information about the network conditions and hence, are able to timely adapt to network changes. Due to the informationally decentralized nature of the multihop wireless network, performing centralized optimization for delay-sensitive video streaming application based on global information about the network status is not practical. Distributed solutions that adapt the transmission strategies based on timely information feedback need to be considered. To acquire this information feedback for cross-layer adaptation, we deploy an overlay infrastructure, which is able to relay the necessary information about the network status and incurred delays across different network “horizons” (i.e., across a different number of hops in a predetermined period of time). In this paper, we propose a distributed streaming approach that is optimized based on the local information feedback acquired from the various network horizons. We investigate the distributed cross-layer adaptation at each wireless node by considering the advantages resulting from an accurate and frequent network information feedback from larger horizons as well as the drawbacks resulting from an increased transmission overhead. Based on the information feedback, we can estimate the <emphasis emphasistype="italic">risk</emphasis> that packets from different priority classes will not arrive at their destination before their decoding deadline expires. Subsequently, the various transmission strategies such as packet scheduling, retransmission limit and dynamic routing policies are adapted to jointly consider the estimated risk as well as the impact in terms of distortion </para>

Providing differentiated services for multi-class traffic in IP/MPLS over WDM networks

Providing differentiated services in IP/MPLS over WDM networks has attracted a lot of recent attention. This article extends the Path Inflation Control (PIC) policy recently proposed by us to provide differentiated services in IP/MPLS over WDM networks with traffic grooming. Three different algorithms are considered for provisioning differentiated services. The simulation results show that, with two of the three algorithms, the network cannot only provide differentiated services when the traffic load is high but also gives significantly lower blocking for the lower priority class traffic and for the overall traffic at low traffic loads.

Optimal offset-time decision for QoS in optical burst switching networks

In this paper, we propose the optimal offset-time decision (OOD) algorithm which can effectively reduce the pre-transmission delay compared to the perfect isolation model, and can also be extended to general n priority classes while the target loss probability of each class is guaranteed for the variable offered load. In order to drive the OOD algorithm, we first analyze the loss probability of each priority class through class aggregation and iteration method; the analytic results obtained through the proposed algorithm are then validated with results garnered from extensive simulation tests.

Introducing a Relative Priority for the Shared-Protection Schemes

One the of major challenges of optical network operators is ensuring the stringent levels of availability required by their highest class clients. To achieve this, we introduce relative priorities among the different primary connections contending for access to the shared-protection paths. In this paper, we provide an analytical model for the proposed priority-enabled scheme. As a key distinguishing feature from existing literature, we derive explicit analytic expressions for average the availability and service disruption rate for the different priority classes.

Land register of contaminated sites in an industrial chilean region: Identification and evaluation of suspected sites

This work introduces the outcomes of the first process for the identification and evaluation of sites potentially contaminated in the Region of the Bio Bio, Chile. The methodology combined qualitative and quantitative elements from Austrian and German risk assessment procedures, calibrated and adapted to the Chilean reality. The developed process consists of collecting historical and current registers on soil use, effects of materials handling on the population's health, and the description of the site conditions. The first analytical step corresponds to an image algebra analysis, through which the most vulnerable areas of the region are established. The sites identified inside the most vulnerable areas are classified into five priority classes, giving an approximate degree of endangerment from these sites. Through the experience, from a total of 507 sites identified as suspicious of contamination, five sites were classified under the highest priority. The results of this analysis have allowed Chilean authorities to focus their resources on the detailed investigations to be carried out in the five priority locations, whilst planning the future strategy to follow for the practical management of all sites found as currently posing a risk to the environment and to the society.

OCGRR: A New Scheduling Algorithm for Differentiated Services Networks

We propose a new fair scheduling technique, called OCGRR (Output Controlled Grant-based Round Robin), for the support of DiffServ traffic in a core router. We define a stream to be the same-class packets from a given immediate upstream router destined to an output port of the core router. At each output port, streams may be isolated in separate buffers before being scheduled in a frame. The sequence of traffic transmission in a frame starts from higher-priority traffic and goes down to lower-priority traffic. A frame may have a number of small rounds for each class. Each stream within a class can transmit a number of packets in the frame based on its available grant, but only one packet per small round, thus reducing the intertransmission time from the same stream and achieving a smaller jitter and startup latency. The grant can be adjusted in a way to prevent the starvation of lower priority classes. We also verify and demonstrate the good performance of our scheduler by simulation and comparison with other algorithms in terms of queuing delay, jitter, and start-up latency.

Dynamic Spectrum Access with QoS and Interference Temperature Constraints

Spectrum is one of the most precious radio resources. With the increasing demand for wireless communication, efficiently using the spectrum resource has become an essential issue. With the Federal Communications Commission's (FCC) spectrum policy reform, secondary spectrum sharing has gained increasing interest. One of the policy reforms introduces the concept of an interference temperature - the total allowable interference in a spectral band. This means that secondary users can use different transmit powers as long as the sum of these power is less than the interference threshold. In this paper, we study two problems in secondary spectrum access with minimum signal to interference noise ratio (quality of service (QoS)) guarantee under an interference temperature constraint. First, when all the secondary links can be supported, a nonlinear optimization problem with the objective to maximize the total transmitting rate of the secondary users is formulated. The nonlinear optimization is solved efficiently using geometric programming techniques. The second problem we address is, when not all the secondary links can be supported with their QoS requirement, it is desirable to have the spectrum access opportunity proportional to the user priority if they belong to different priority classes. In this context, we formulate an operator problem which takes the priority issues into consideration. To solve this problem, first, we propose a centralized reduced complexity search algorithm to find the optimal solution. Then, in order to solve this problem distributively, we define a secondary spectrum sharing potential game. The Nash equilibria of this potential game are investigated. The efficiency of the Nash equilibria solutions are characterized. It is shown that distributed sequential play and an algorithm based on stochastic learning attain the equilibrium solutions. Finally, the performances are examined through simulations