Achieving differentiated services through multi-class probabilistic priority scheduling

In high speed networks, the strict priority (SP) scheduling discipline is perhaps the most common and simplest method to schedule packets from different classes of applications, each with diverse performance requirements. With this discipline, however, packets at higher priority levels can starve packets at lower priority levels. To resolve this starvation problem, we propose to assign a parameter to each priority queue in the SP discipline. The assigned parameter determines the probability with which its corresponding queue is served when the queue is polled by the server. We thus form a new packet scheduling discipline, referred to as the probabilistic priority (PP) discipline. By properly setting the assigned parameters, service differentiation as well as fairness among traffic classes can be achieved in PP. In addition, the PP discipline can be easily reduced to the ordinary SP discipline or to the reverse SP discipline.

In computer networks, the Strict Priority (SP) discipline is perhaps the most common and simplest method to schedule packets from different classes of applications, each with diverse performance requirements. With this discipline, however, packets at higher priority levels can starve packets at lower priority levels. To resolve this starvation problem, we propose to assign a parameter to each priority queue in the SP discipline. The assigned parameter determines the probability or extent by which its corresponding queue is served when the queue is polled by the server. We thus form a new packet service discipline, referred to as the Probabilistic Priority (PP) discipline. By properly adjusting the assigned parameters, not only is the performance of higher priority classes satisfied, but also the performance of lower priority classes can be improved. This paper analyzes the delay performance of the PP discipline. A decomposition approach is proposed for calculating the average waiting times and their bounds are studied. Two approximation approaches are proposed to estimate the waiting times. Simulation results that validate the numerical analysis are presented and examined. A numerical example which demonstrates the use of the PP discipline to achieve service differentiation is presented. This example also shows how the assigned parameters can be determined from the results of analysis mentioned above.

The paper proposes two IP packet aggregation techniques, called DAT (Deterministic Aggregation Technique) and WATT (Work-conserving Aggregation Technique with Timer), to adapt IP traffic to a multi-service optical slotted network. To perform aggregation, IP packets belonging to different classes of service (CoS) are polled according to the strict priority (SP) or to an hybrid version of the probabilistic priority (PP) scheduling discipline originally proposed in [1, 2]. An approximate analytical model is given in the case of DAT under the SP discipline. In addition, extensive simulations are used to study the impact of self-similar traffic on the aggregation processes. Finally, performance comparisons between the aggregation techniques and the standard approach (where no aggregation is performed) are carried out in the context of a slotted dual bus optical ring network (SDBORN) which is a candidate viable solution for metropolitan area networks (MAN).

Low cost broadband services used widely in the recent years increased the demand for multimedia applications. Many of these applications require different quality of service (QoS) in terms of throughput and delay. In the current resource constrained wireless networks, resource management plays a vital role. In order to handle the resources effectively and to increase the QoS, proper packet scheduling algorithms need to be developed. Low latency queuing (LLQ) is a packet scheduling algorithm which combines strict priority queuing (SPQ) to class-based weighted fair queuing (CBWFQ). In this paper, an enhanced low latency queuing (ELLQ) algorithm is proposed in which an additional SPQ is introduced along with the existing SPQ. Further, the QoS is improved by integrating congestion avoidance algorithm with ELLQ. Simulation results using the OPNET modeller show that the proposed algorithm outperforms the existing algorithm in terms of throughput and delay for the multimedia applications.

Defending against fake VIP in scant-transparency information systems with QoS differentiation

This paper studies the design and performance of the Probabilistic Priority (PP) packet scheduling algorithm to schedule packets. Unlike an earlier design that uses fractional arithmetic and prohibits large number of classes, we present an integer PP algorithm and show that PP is a special scheme of applying lottery scheduling to bandwidth allocation in a strict priority sense. We then propose a Multi-winner PP (MPP) scheduler using multi-winner lottery scheduling to improve the throughput and response time accuracy and a flexible ticket transfer algorithm to improve the deadline violation probability in probabilistic scheduling. Finally, we investigate the issue of parameter assignment for an MPP scheduler and use our techniques to implement a prototype Assured Forwarding (AF) mechanism in a network processor.

The deployment of new 5G services and future demands for 6G make it necessary to increase the performance of access networks. This challenge has prompted the development of new standardization proposals for Passive Optical access Networks (PONs) that offer greater bandwidth, greater reach and a higher rate of aggregation of users per fiber, being Time- and Wavelength-Division Multiplexing (TWDM) a promising technological solution for increasing the capacity by up to 40 Gbps by using several wavelengths. This solution introduces tunable transceivers into the Optical Network Units (ONUs) for switching from one wavelength to the other, thus addressing the ever-increasing bandwidth demands in residential broadband and mobile fronthaul networks based on Fiber to the Home (FTTH) technology. This adds complexity and sources of inefficiency, such as the laser tuning time (LTT) delay, which is often ignored when evaluating the performance of Dynamic Bandwidth Allocation (DBA) mechanisms. We present a novel DBA algorithm that dynamically handles the allocation of bandwidth and switches the ONUs’ lasers from one wavelength to the other while taking LTT into consideration. To optimize the packet delay, we introduce a scheduling mechanism that follows the Longest Processing Time first (LPT) scheduling discipline, which is implemented over the Interleaved Polling with Adaptive Cycle Time (IPACT) DBA. We also provide quality of service (QoS) differentiation by introducing the Max-Min Weighted Fair Share Queuing principle (WFQ) into the algorithm. The performance of our algorithm is evaluated through simulations against the original IPACT algorithm, which we have extended to support multi-wavelengths. With the introduction of LPT, we obtain an improved performance of up to 73% reduction in queue delay over IPACT while achieving QoS differentiation with WFQ.

We consider a priority queue with a dynamic, queue-length-threshold scheduling policy. Customers are classed into two types (type-1 and type-2), and the service order of the two classes depends on the queue length of the type-1 queue. The high priority (type-2) class (e.g., voice) is served until the low priority (e.g., data) queue exceeds the threshold L, at which time service is given to the low priority class until its queue length decreases to L. The arrivals of the two classes follow independent Poisson processes, and the service time of each customer has an exponential distribution with parameter $\mu$. We derive the balance equations in the steady state, and explicitly obtain the joint probability generating function for the queue lengths of the two customer classes. This gives the joint queue length distribution as an integral. We then obtain detailed asymptotic results for the joint distribution. In particular, we study the tail behavior. We also discuss heavy traffic diffusion approximations for this model.

To provide Quality of Service (QoS) and data rate differentiation, we investigate in this paper a 2 dimensional optical code division multiple access (OCDMA) technique. A 2D multi-weight coding scheme with parallel mapping technique is developed. The system enhancement is assessed thanks to the use of Forward Error Correction (FEC) based on Low Density Parity Check (LDPC) codes. In order to have an efficient correction power, we develop an adaptation of the LDPC decoding algorithm to the specific multiple access interference distribution in a multimedia OCDMA network. The proposed network permits a high number of users to communicate with high data rates adapted to a multimedia transmission (voice, data and video) with corresponding QoS (10-3, 10-6, 10-9).

The software is created and constructed to address particular issues in the applied field. In this context, there is a need to be aware of the crucial characteristics to assess the quality of software. But not all software requires checking all the quality-of-service parameters, resulting in effort loss and time consumption. Therefore, it is required to develop software quality characteristics recommendation model to address and resolve the issue. The proposed work involved in this paper can be subdivided into three main parts (1) a review of popular software quality models and their comparison to create a complete set of predictable, and (2) the design of an ML-based recommendation model for recommending the software quality model and software quality characteristics (3) performance analysis. The proposed recommendation system utilizes the different software quality of service attributes as well as the software attributes where these models are suitably applied to satisfy the demands. Profiling of applications and their essential requirements have been performed Based on the different quality of service parameters and the requirements of applications. These profiles are learned by machine learning algorithms for distinguishing the application-based requirement and recommending the essential attributes. The implementation of the proposed technique has been done using Python technology. The simulation aims to demonstrate how to minimize the cost of software testing and improve time and accuracy by utilizing the appropriate quality matrix. Finally, a conclusion has been drawn and the future extension of the proposed model has been reported.

Quality of service (QoS) in wireless 802.11 networks cannot be achieved without the support for service differentiation at the medium access layer. IEEE802.11 suffers from QoS limitations that have often been summarized in the literature. We present simulation results to show the effectiveness of several proposed techniques of improving the QoS in the IEEE802.11 protocol. Specifically, we closely examine the sliding contention window (SCW) technique and present a performance study that augments the work done by the original authors, by considering the determinism of QoS achieved. We find that simple approaches such as priority queuing and differential inter-frame spacing provide service differentiation at a single station but are not successful in providing it across a number of stations. Further, we find that the SCW approach provides a high service differentiation and deterministic QoS guarantees. It achieves these by a strict separation of the contention window range of different priority classes. Further, it measures and reacts to losses suffered by high priority flows at the MAC layer and to the increase in network load. These cross layer design techniques help SCW maintain good performance even at high network load. However, this strict service differentiation comes at the cost of reduced performance of low priority flows at heavy load.

The conventional medium access control (MAC) protocols assume that only one packet (frame) can be received at a given time. However, with the advent of spread spectrum, antenna arrays, and sophisticated signal processing techniques, it is now possible to achieve multiple-packet reception (MPR) in wireless networks. With MPR, the network capacity can be remarkably increased, but so far, how to achieve fair bandwidth allocation for the stations with different quality of service (QoS) requirements in such networks is still a problem. To solve this problem, we propose a distributed method that can support multiple priority classes in the MPR-capable wireless networks with weighted fair share. In particular, this method assigns each class a frame transmission probability to reflect its relative weight among the different data traffic flows. A closed-form expression of system throughput is derived for each class in the environment, and it is numerically evaluated with different simulation scenarios. The results show that the method can achieve the weighted fairness under different numbers of priority classes and different numbers of stations in the networks.

With the onset of multimedia applications, Quality of Service (QoS) in 802.11-based wireless ad hoc networks has been an essential area to look into. Standard wireless protocols such as IEEE 802.11b and IEEE 802.11e have been deemed unsuitable for multimedia traffic transmission in an ad hoc (multihop) network environment due to the unique network characteristics. As an ad hoc network is infrastructureless and distributed in nature, it gives rise to several challenges in QoS provisioning. In this thesis, we focus on the research of three key areas on QoS in ad hoc networks namely, buffer management in the medium access control (MAC) layer, cross-layer design and flow admission control. Firstly, we study MAC layer buffer management in the IEEE 802.11e protocol. The IEEE 802.11e MAC protocol provides QoS for multimedia traffic by probabilistic priority queueing. Ad hoc networks tend to generate a large volume of network control packets for route maintenance and these control packets are typically queued in the highest priority queue. As a result, higher priority control traffic is always being served, consuming most of the bandwidth and results in poor network performance for data traffic. We examine this problem and propose a dynamic buffer management scheme to mitigate it. By setting different threshold levels in different priority queues, we allow lower priority data traffic to be served when the higher priority control traffic is deemed to be excessive. Simulation of our proposed scheme has shown that our approach yielded better network performance compared to the standard protocol in terms of packet delivery ratio and average delay. Secondly, we study the cross-layer interaction between the MAC and Network layers to identify its impact on QoS. We select the IEEE 802.11e MAC protocol and Ad-hoc On Demand Distance Vector (AODV) routing protocol in our study since they are standardized protocols for wireless networks. In IEEE 802.11e MAC protocol, lower priority traffic has a higher probability of being blocked. Hence, the MAC layer will inform the Network layer of a broken link through the link notification function. In this case, AODV will re-route the paths that traverse this link. As a result, higher priority traffic which shares the same link as the lower priority traffic will undergo the same re-routing procedures. We termed this phenomenon path correlation effect. Under high traffic load, the path correlation effect will be more intense and hence degrade the QoS of higher priority traffic. To break the path correlation effect, we propose a cross-layer design called the Bundled Virtual Circuit (BVC). Our proposed BVC scheme not only addresses the path correlation issues, but also provides priority treatment from the Network layer to the MAC layer. Through our simulations, our proposed cross-layer design approach is proven to provide better network performance than the 802.11e/AODV protocols in terms of packet delivery ratio and delay. Finally, we examine flow admission control at the routing layer in ad hoc networks. Standard routing protocols such as AODV performs routing on a shortest path basis. In the presence of multiple routes, hotspots are likely to form among the intermediate nodes and thus lead to network congestion. In addition, existing routes are not well-protected from the introduction of new routes. We propose a flow admission control algorithm to be used with AODV. Our algorithm allows routes to be created through available bandwidth and congestion estimation. During the route discovery phase, each node will be gauged on its estimated available bandwidth and its backlog of packets in the MAC buffer. If a node does not have sufficient bandwidth, or has too many backlogged packets compared to the requested flow rate, it will not participate in the route discovery process. From simulations, our new scheme is able to provide better network performance than the standard AODV protocol in terms of delay. Our work in this thesis focuses on QoS provisioning in ad hoc networks from the MAC and network layer perspectives. By studying the network characteristics and protocols’ behavior, we investigate the various problems of providing QoS in an ad hoc network environment and propose three different schemes to improve the QoS provisioning at the MAC and network layers. We believe that our work is able to provide some insights to the research area on QoS in ad hoc networks.

Trust is one of the most critical quality factors for service requestors when they select the services from a large pool of Web services. However, existing web service trust models either do not focus on satisfying user's preferences for different quality of service (QoS) attributes, or do not pay enough attention to the impact of malicious ratings on trust evaluation. To address these gaps, a user-oriented trust model considering user's preferences and false ratings is proposed in this paper. The model introduces an approach to automatically mine user's preferences from their requirements, the preferences are used to determine the weights of each QoS attribute when integrating local trust into the multi-dimensional QoS attributes. The local trust on a service for the user is derived by combining the trust on QoS attributes and the trust on user's ratings. In this model, the users are classified into different groups according to their preferences, the honesty of each group is assessed by filtering out dishonest users using a hybrid approach which combines rating consistency clustering and an average method. To calculate the global trustworthiness of a service for the users group, the weight of ratings is dynamically adjusted according to the results of honesty assessment. The simulation results indicate that the model works well on personalized evaluation of trust, and it can effectively dilute the influence of malicious ratings.

This paper addresses the problem of real-time multimedia transmission in fiber-optic networks using code division multiple access (CDMA). We present a multirate optical fast frequency hopping CDMA (OFFH-CDMA) system architecture using fiber Bragg gratings (FBGs). In addition, we argue that, in multimedia applications, different services have different quality of service (QoS) requirements; hence, the user only needs to use the minimum required power to transmit the signal, such that the required signal-to-interference ratio (SIR) is met. We show that a variable bit rate optical communication system with variable QoS can be implemented by way of power control with great efficiency. Present-day multirate optical CDMA systems concentrate on finding the code structure that supports a variable rate system, neglecting the importance of the transmission power of active users on the multiple access interference (MAI) and, therefore, on the system capacity. We assign different power levels to each rate through a power control algorithm using variable optical attenuators, which minimizes the interference and, at the same time, provides variable QoS constraints for different traffic types. Although we are using a code family that preserves good correlation properties between codes of different lengths, simulations show a great improvement in the system capacity when power control is used.