Lower Priority Classes Research Articles

A base-stock inventory model with service differentiation and response time guarantees

In response to customer specific service time guarantee requirements, service providers can offer differentiated services. Although response time agreements offer more flexibility, most of the theoretical models for customer differentiation are based on fill rates, due to the difficulty of calculating the response time distribution in the presence of priorities. In this paper we focus on the (S−1,S,K) model with two customer classes, in which low priority customers are served only if the inventory level is above K. For this model, we derive the exact distribution of the response time (within lead time) for the lower priority class and provide a new closed-form approximation for the fill rate for high priority customers. Via numerical experiments, we show that the fill rate approximation performs comparable to the best approximations in the literature, while its implementation requires only elementary operations.

Comprehensive bandwidth utilization and polling mechanism for XGPON

SummaryFor an efficient utilization of the upstream bandwidth in passive optical network, a dynamic bandwidth assignment mechanism is necessary as it helps the service providers in provisioning of bandwidth to users according to the service level agreements. The scheduling mechanism of existing schemes, immediate allocation with colorless grant and efficient bandwidth utilization (EBU), does not assign the surplus bandwidth to a specific traffic class and only divides it equally among the optical network units (ONUs). This results in overreporting of ONU bandwidth demand to the optical line terminal and causes wastage of bandwidth and increase in delays at high traffic loads. Moreover, the EBU also assigns the unused bandwidth of lightly loaded ONU queues to the overloaded queues through an Update operation. This Update operation has a flaw that it borrows the extra bandwidth to a queue in the current service interval, if the queue report is higher than its service level agreement and refunds in next service interval. This borrow‐refund operation causes reduced bandwidth allocation to the lower priority classes and increases their delay and frame loss. This study improves both these weaknesses. The simulation results show that the proposed scheme uses bandwidth efficiently and reduces mean upstream delay of type‐2 (T2) traffic class by 38% and type‐3 (T3) up to 150% compared to immediate allocation with colorless grant at a cost of up to 10% higher delay for T2. However, T4 performance improves by 400% compared to EBU with slight increase in delay for T2 traffic class. Overall, it shows a balanced performance for all the traffic classes and minimizes the bandwidth waste per cycle as well as the frame loss rate.

Performance Evaluation of Ethernet Network for Mobile Fronthual Networks

<p>Increasing mobile data traffic due to the rise of both smartphones and tablets has led to high-capacity demand of mobile data network. To meet the ever-growing capacity demand and reduce the cost of mobile network components, Cloud Radio Access Network (C-RAN) has emerged as a promising solution. In such network, the mobile operator’s Remote Radio Head (RRH) and Base Band Unit (BBU) are often separated and the connection between them has very tight timing and latency requirements imposed by Common Public Radio Interface (CPRI) and 3rd Generation Partnership Project (3GPP). This fronthaul connection is not yet provided by packet based network. To employ packet-based network for C-RAN fronthaul, the carried fronthaul traffic are needed to achieve the requirements of fronthaul streams. For this reason, the aim of this paper is focused on investigating and evaluating the feasibility of Ethernet networks for mobile fronthaul. The fronthaul requirements used to evaluate and investigate this network are maximum End to End (E2E) latency, Packet Loss Ratio (PLR) and Packet Delay Variation (PDV). The simulated results and numerical analysis confirm that the PDV and PLR of High Priority (HP) traffic in Ethernet network meet the requirements of mobile fronthaul using CPRI. However, the PDV of HP traffic meets the fronthaul network when the number of nodes in the Ethernet network is at most four. For Ethernet network, the number of nodes in the network limits the maximum separation distance between BBU and RRH (link length); for increasing the number of nodes, the link length decreases. Consequently, Radio over Ethernet (RoE) traffic should receive the priority and Quality of Service (QoS) HP can provide. On the other hand, Low Priority (LP) classes are not sensitive to QoS metrics and should be used for transporting time insensitive applications and services.</p>

QoS Performance of Integrated Hybrid Optical Network in Mobile Fronthual Networks

<p>Cloud Radio Access Network (C-RAN) has emerged as a promising solution to meet the ever-growing capacity demand and reduce the cost of mobile network components. In such network, the mobile operator’s Remote Radio Head (RRH) and Base Band Unit (BBU) are often separated and the connection between them has very tight timing and latency requirements. To employ packet-based network for C-RAN fronthaul, the carried fronthaul traffic are needed to achieve the requirements of fronthaul streams. For this reason, the aim of this paper is focused on investigating and evaluating the feasibility of Integrated Hybrid Optical Network (IHON) networks for mobile fronthaul. TransPacket AS (www.transpacket.com) develops a fusion switching that efficiently serves both Guaranteed Service Transport (GST) traffic with absolute priority and packet switched Statistical Multiplexing (SM) best effort traffic. We verified how the leftover capacity of fusion node can be used to carry the low priority packets and how the GST traffic can have deterministic characteristics on a single wavelength by delaying it with Fixed Delay Line (FDL). For example, for L<sub>1GE </sub><sup>SM</sup> =0.3 the added SM traffic increases the 10GE wavelength utilization up to 89% without any losses and with SM PLR=1E<sup>-03</sup> up to 92% utilization. The simulated results and numerical analysis confirm that the PDV and PLR of GST traffic in Ethernet network meet the requirements of mobile fronthaul using CPRI. For Ethernet network, the number of nodes in the network limits the maximum separation distance between BBU and RRH (link length); for increasing the number of nodes, the link length decreases. Consequently, Radio over Ethernet (RoE) traffic should receive the priority and Quality of Service (QoS) HP can provide. On the other hand, Low Priority (LP) classes are not sensitive to QoS metrics and should be used for transporting time insensitive applications and services.</p>

Priority Scheduling for Heterogeneous Workloads: Tradeoff Between Evictions and Response Time

Nowadays, large computing clusters are executing highly heterogeneous bursty workloads with different priorities, resource demands, and performance objectives. As the schedulers control the class-specific performance by evictions, a noteworthy amount of the computing resources are wasted by the lost executions of the evicted tasks. This paper presents a system model with a slot-based priority scheduler that captures the execution progress, evictions, and response times when executing complex workloads on heterogeneous systems. To better understand the impact of evictions, we first analyze simple eviction policies and wasted resources associated with evictions by using trace-driven simulation of Google cluster trace. Our key finding is that evictions severely increase system load, which leads to a significant increase in response times, particularly of low-priority classes, due to repetitive evictions. Furthermore, by exploiting the heterogeneity of the workload, we propose a workload-aware slot configuration and task assignment methodology incorporated with slot-based priority scheduling to improve class-based response time and resource efficiency. Our experimental results show that we are able to achieve up to 29% improvement in response times by choosing the right eviction policy, namely, MRS (most recently started), and integrating workload awareness to the slot configuration and task assignment.

Performance modeling of QoS differentiation in optical packet switching via FDL access limitation

We present an exact analytical model for single-wavelength quality of service (QoS) differentiation in a two-class optical packet switch. In this system, QoS differentiation is achieved by limiting the set of fiber delay lines (FDLs) to the low-priority class, whereas the high-priority class is allowed to access the entire FDL bank. The analytical model is based on multi-regime Markov fluid queues and is extensible to multi-class systems with more than two classes. Markovian arrival process packet arrivals and phase-type distributed packet sizes are considered for the purpose of generality. The proposed analytical model is validated through simulations. The numerical results provide insight into determining appropriate subsets of FDLs allowed for the access of the low-priority class. The results also show that it is possible to direct almost all the packet losses to the low-priority class under moderate loads.

On a general mixed priority queue with server discretion

ABSTRACTWe consider a single-server queueing system which attends to N priority classes that are classified into two distinct types: (i) urgent: classes which have preemptive resume priority over at least one lower priority class, and (ii) non-urgent: classes which only have non-preemptive priority among lower priority classes. While urgent customers have preemptive priority, the ultimate decision on whether to interrupt a current service is based on certain discretionary rules. An accumulating prioritization is also incorporated. The marginal waiting time distributions are obtained and numerical examples comparing the new model to other similar priority queueing systems are provided.

TCP-LP: Fair and Friendly Congestion Control Approach

Internet users always seek service prioritization. This service can be defined as“Give importanceto important network traffic over unimportant network traffic”.Conventional methods can be categorization of traffic by considering the existing traffic as“best-effort” class can be named as low-priority (LP) class, and keen to develop mechanisms which will give “better-than-best-effort” service. It is worth mentioning thatthis paper is going to mention the ides of developing a Low Priority distributed algorithm whose objective is to utilize only the rest bandwidth and give priority to other delay sensitive traffic generated by interactive applications or media streaming application and interested in devising a efficient approach or algorithm called novel distributed algorithm to implement a LP service which work as against existing best effort traffic service from the communication endpoints. Keywords-AQM, drop-tail, fairness, reno, SFQ, vegas.

Avoiding class warfare: managing continuous queries with differentiated classes of service

Data stream management systems (DSMSs) offer the most effective solution for processing data streams by efficiently executing continuous queries (CQs) over the incoming data. CQs inherently have different levels of criticality and hence different levels of expected quality of service (QoS) and quality of data (QoD). Adhering to such expected QoS/QoD metrics is even more important in cases of multi-tenant data stream management services. In this work, we propose DILoS, a framework that, through priority-based scheduling and load shedding, supports differentiated QoS and QoD for multiple classes of CQs. Unlike existing works that consider scheduling and load shedding separately, DILoS is a novel unified framework that exploits the synergy between scheduling and load shedding. We also propose ALoMa, a general, adaptive load manager that DILoS is built upon. By its design, ALoMa performs better than the state-of-the-art alternatives in three dimensions: (1) it automatically tunes the headroom factor, (2) it honors the delay target, (3) it is applicable to complex query networks with shared operators. We implemented DILoS and ALoMa in our real DSMS prototype system (AQSIOS) and evaluate their performance for a variety of real and synthetic workloads. Our experimental evaluation of ALoMa verified its clear superiority over the state-of-the-art approaches. Our experimental evaluation of the DILoS framework showed that it (a) allows the scheduler and load shedder to consistently honor CQs' priorities, (b) significantly increases system capacity utilization by exploiting batch processing, and (c) enables operator sharing among query classes of different priorities while avoiding priority inversion, i.e., a lower-priority class never blocks a higher-priority one.

M/M/c Queue with Two Priority Classes

This paper provides the first exact analysis of a preemptive M/M/c queue with two priority classes having different service rates. To perform our analysis, we introduce a new technique to reduce the two-dimensionally infinite Markov chain (MC), representing the two class state space, into a one-dimensionally infinite MC, from which the generating function (GF) of the number of low-priority jobs can be derived in closed form. (The high-priority jobs form a simple M/M/c system and are thus easy to solve.) We demonstrate our methodology for the c = 1, 2 cases; when c > 2, the closed-form expression of the GF becomes cumbersome. We thus develop an exact algorithm to calculate the moments of the number of low-priority jobs for any c ≥ 2. Numerical examples demonstrate the accuracy of our algorithm and generate insights on (i) the relative effect of improving the service rate of either priority class on the mean sojourn time of low-priority jobs; (ii) the performance of a system having many slow servers compared with one having fewer fast servers; and (iii) the validity of the square root staffing rule in maintaining a fixed service level for the low-priority class. Finally, we demonstrate the potential of our methodology to solve other problems using the M/M/c queue with two priority classes, where the high-priority class is completely impatient.

A New Two‐Bin Policy for Inventory Systems with Differentiated Demand Classes

We consider an inventory system under continuous review with two demand classes that are different in terms of service level required (or penalty cost incurred for backordering of demand). Prior literature has proposed the critical level rationing (CLR) policy under which the demand from the lower priority class is backordered once inventory falls below the critical level. While this reduces the penalty cost for the higher demand class, the fill rate achieved for the lower priority demand class gets compromised. In this study, we propose a new class of two‐bin (2B) policy for the problem. The proposed 2B policy assigns separate bins of inventory for the two demand classes. The demand for each class is fulfilled from its assigned bin. However, when the bin intended for the higher demand class is empty, the demand from the higher class can still be fulfilled with the inventory from the other bin. The advantage of the 2B policy is that better fill rates are achieved, especially for the lower demand class. Computational results show that the proposed policy is able to provide a much higher service level for the lower priority class demand without increasing the total cost too much and without affecting the service level for the higher priority class. When a service level constrained optimization problem is considered, the 2B policy dominates the CLR policy when the service level difference for the two classes is not too high or the service levels required for both the classes are relatively lower.

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.

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.

Analysis of a prioritized contention model for multimedia wireless sensor networks

Emerging multimedia applications for sensor networks require the co-existence of different types of traffic with different QoS provisions in terms of latency and throughput. Prioritization-based service differentiation mechanisms are applied in all layers of communication to satisfy the QoS requirements of each traffic class. The prioritization in the contention is one of these differentiation methods applied in the medium access layer. In this article, we propose an analytical model for the contention latencies and energy expenditures of different classes in a prioritized contention structure with uniform backoff scheme. The contention window is divided into three partitions which are allocated for the use of only high-priority, both priorities, and only low-priority classes. We further generalize the model for binary exponential backoff schemes and for more than two priority classes. In the analysis, we explore the optimum sizes of these partitions in terms of contention latency and the total energy expenditure for each priority class. Our model is also useful for the evaluation of various recent contention prioritization schemes in WSNs.

Performance Modeling in Multi-Service Communications Systems with Preemptive Scheduling

This paper presents two separate Markov models to investigate blocking probabilities in multi-service communications systems, when preemptive scheduling is adopted to implement service differentiation. One is the generalized model, which is built as a multi-dimensional Markov chain, based on a variant of the multi-dimensional Erlang loss model. The other is the hierarchical model, which is constructed as a multi-level Markov chain, based on a combination of one-dimensional Erlang loss models. A detailed comparison when applying these two models to a general R- service communications system is presented. This validates the major advantages of the proposed hierarchical model: the closed form expressions of blocking probabilities; the dramatically reduced computational complexity; and the excellent scalability for analyzing larger systems. Furthermore, the analytical values are compared with simulation results for two- and three-service systems. Results show that the proposed hierarchical model provides a high degree of accuracy in the blocking probabilities under different scenarios, especially when the relative arrival rates of the lower priority classes are high.

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.

Multiple Downlink Fair Packet Scheduling Scheme in Wi-Max

IEEE 802.16 is standardization for a broadband wireless access in network metropolitan area network (MAN). IEEE 802.16 standard (Wi-Max) defines the concrete quality of service (QoS) requirement, a scheduling scheme and efficient packet scheduling scheme which is necessary to achieve the QoS requirement. In this paper, a novel waiting queue based on downlink bandwidth allocation architecture from a number of rtps schedule has been proposed to improve the performance of nrtPS services without any impaction to other services. This paper proposes an efficient QoS scheduling scheme that satisfies both throughput and delay guarantee to various real and non-real applications corresponding to different scheduling schemes for k=1,2,3,4. Simulation results show that proposed scheduling scheme can provide a tight QoS guarantee in terms of delay for all types of traffic as defined in WiMax standards. This process results in maintaining the fairness of allocation and helps to eliminate starvation of lower priority class services. The authors propose a new efficient and generalized scheduling schemes for IEEE 802.16 broadband wireless access system reflecting the delay requirements.

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.