QoS Metrics Research Articles

High-Speed Satellite Mobile Communications: Technologies and Challenges

Central features of future 4G mobile communication systems are high-speed data transmission (up to 1 Gb/s) and interactive multimedia services. For effective delivery of these services, the network must satisfy some stringent QoS metrics, defined typically in terms of maximum delay and/or minimum throughput. Mobile satellite systems will be fully integrated with the terrestrial cellular systems to provide ubiquitous global coverage to diverse users. The challenges for future broadband satellite systems, therefore, lie in the proper deployment of state-of-the-art satellite technologies to ensure seamless integration of the satellite networks into the cellular systems and its QoS frameworks, while achieving, as far as possible, efficient use of satellite link resources. The paper presents an overview of future high-speed satellite mobile communication systems, the technologies deployed or planned for deployment, and the challenges. Focusing in particular on nonlinear downlink channel behavior, shadowing and multipath fading, various physical channel models for characterizing the mobile satellite systems are presented. The most prominent technologies used in the physical layer, such as coding and modulation schemes, multiple-access techniques, diversity combining, etc., are then discussed in the context of satellite systems. High-speed and QoS-specific technologies, such as onboard processing and switching, mobility and resource management, IP routing and cross-layer designs, employed in the satellite systems are also discussed.

Distributed mechanisms for quality of service in wireless LANs

Wireless local area networks are gaining popularity at an unprecedented rate, at home, at work, and in public hot spot locations. As these networks become ubiquitous and an integral part of the infrastructure, they will increasingly be used for multimedia applications. There is limited QoS support in WLANs, which will become an impediment in deploying multimedia applications. We present a tutorial on QoS support in IEEE 802.11 WLANs with a focus on the distributed MAC protocol of 802.11. Most QoS support mechanisms proposed for 802.11 use well-known techniques such as priority assignment and fair scheduling, and map QoS metrics into some existing 802.11 MAC parameter, thereby avoiding a redesign of the MAC protocol. We provide a taxonomy of the mechanisms and describe the essential concepts, problems, and advantages of each mechanism. From our study, we conclude that choosing the right set of MAC parameters and the QoS mechanism itself to provide predictable QoS in 802.11 networks is still an open problem.

Proportional differentiation: A scalable QoS approach

The proportional service model has gained attention as an effective solution for quantitative service differentiation in IP networks. In particular, this differentiation scheme is controllable, consistent, and scalable. Thus, it gives network operators convenient management of services and resources even in a large-scale network. We give an overview of research efforts on this QoS model. Details about implementation strategies for various QoS metrics are provided. We also discuss how to achieve absolute service bounds in this relative differentiation model with different approaches. Several problems such as feasibility in differentiation are mentioned as open research issues at the end.

A survey of adaptive bandwidth control algorithms

In packet-switched network traffic management and control, efficiently allocating bandwidth to provide quantitative packet-level QoS to aggregate traffic has been difficult due to unpredictable, unknown statistical characteristics of the aggregate traffic. With inaccurate traffic information, using static bandwidth allocation results in the network being underutilized, or the QoS requirement not being satisfied. An alternative is to use adaptive bandwidth control (ABC), whereby the allocated bandwidth is regularly adjusted over the packet-level time scale to attain a given QoS requirement. This paper provides a literature review of ABC algorithms that guarantee aggregate traffic packet-level QoS metrics, such as the average queue length, packet loss, and packet delay. We describe different ABC algorithms, identify their advantages and shortcomings, and provide some comparative performance evaluation results. Open issues in ABC for future research directions are also discussed.

Performance measure sensitive congruences for Markovian process algebras

The modeling and analysis experience with process algebras has shown the necessity of extending them with priority, probabilistic internal/external choice, and time while preserving compositionality. The purpose of this paper is to make a further step by introducing a way to express performance measures, in order to allow the modeler to capture the QoS metrics of interest. We show that the standard technique of expressing stationary and transient performance measures as weighted sums of state probabilities and transition frequencies can be imported in the process algebra framework. Technically speaking, if we denote by n ∈ N the number of performance measures of interest, in this paper we define a family of extended Markovian process algebras with generative master–reactive slaves synchronization mechanism called EMPA gr n including probabilities, priorities, exponentially distributed durations, and sequences of rewards of length n. Then we show that the Markovian bisimulation equivalence ∼ MB n is a congruence for EMPA gr n which preserves the specified performance measures and we give a sound and complete axiomatization for finite EMPA gr n terms. Finally, we present a case study conducted with the software tool TwoTowers in which we contrast the average performance of a selection of distributed algorithms for mutual exclusion modeled with EMPA gr n .

Mobile Video Qos Metrics

Video is an important issue in the latest generation of mobile networks that can provide enough bandwidth for video streaming and mobile video telephony applications. An adequate and accurate QoS evaluation of video is therefore needed. This article presents a practical set of QoS metrics for both objective and subjective measurement of video. Some of the objective metrics described is available in the ANSI and ITU standards, but they are here enriched by a set of nonstandard methods for QoS evaluation. Also included are standard subjective metrics for video quality assessment, as they complement the objective techniques. All of these methods can be used when implementing real-time mobile video applications, such as mobile videophones.

Earliest Deadline First Scheduling with Active Buffer Management for Real-Time Traffic in the Internet

We studied the problem of QoS guarantee for differentiated services. A two-level hierarchical scheduling framework was deployed to separate QoS metrics. Due to its desirable property of minimizing the maximum packet lateness, the Earliest Deadline First (EDF) scheduling was adopted to provide the in-class scheduling for the time-sensitive traffic. We employed an EDF scheduler combined with an active buffer management scheme (CHOKe) to improve the fairness of resource allocation and to maintain a good delay performance for real-time applications. Simulation results showed that the proposed scheme can achieve a better delay performance and make a more fair bandwidth allocation between the real-time TCP and UDP connections than the First Come First Served (FCFS) scheduling with the drop-tail buffer management which is commonly deployed in traditional IP routers.

Service-specific resource allocation in WDM networks with quality constraints

The need to establish wavelength-routed connections in a service-differentiated fashion is becoming increasingly important due to a variety of candidate client networks (e.g., IP, SDH, ATM) and the requirements for QoS-delivery within transport layers. The multiservice operation changes the way we deal with wavelength-routed paths, as they are now being characterized by manifold properties, such as transmission quality, restoration, network management, and policies. We propose a generic approach to service-differentiated connection accommodation in wavelength-routed networks where, for the network state representation, the supplementary network graphs are defined and referred to as service-specific wavelength-resource graphs. These graphs are used for the appropriate allocation of wavelengths on concatenated physical resources building a wavelength route, along which the necessary transmission quality is achieved and the required management and surveillance functions are provided. By considering twofold wavelength routing metrics, i.e., QoS metrics (service requirements) and resource metrics (quality constraints), these graphs can yield the solution to the QoS-routing problem, i.e., the provision of service-specific guarantees under quality constraints-a feature that is still missing from the existing architectures. The numerical analysis of dynamically reconfigurable multiservice WDM networks is presented for regular network operation as well as for optical network service restoration.

Sojourn-time analysis on nodal congestion in broadband networks

In this paper, we study the sojourn-time statistics and the temporal behavior of nodal congestion in integrated broadband networks. The node is modeled as a finite quasi-birth-death (QBD) process with level-dependent transitions. By formulating the problem as one which is amenable to the generalized folding algorithm (GFA), we are, for the first time, able to analyze realistic systems with large buffer and complex input traffic. The dynamics of the system under realistic traffic environment and different operating regimes are studied. The effects of various modeling artifacts such as fluid-flow and infinite-buffer approximations are also investigated. The potential of statistical multiplexing in reducing bursty cell loss is demonstrated. The trade-offs between different system design alternatives, e.g., buffering vs. statistical multiplexing, are discussed. We also investigate the controlling effect of preemptive cell discarding on steady-state and transient system performance. Both single-level and two-level overload control with hysteresial-switching mechanisms are considered. The use of sojourn-time based QoS metrics to supplement long-term steady-state metrics is also discussed.

Impact of ATM switch architectures on CBR video performance

Asynchronous Transfer Mode (ATM) has become one of the leading high-speed networking technologies in the local and wide area environments. ATM offers great promise to meet the real-time requirements of emerging multimedia applications. In the last few years, many ATM networks have been deployed and use different types of ATM switches, many of which differ in their implementations. In this paper, we explore the impact of two ATM switches, namely DEC GIGAswitch/ATM and IBM 8265 on the performance delivery of real-time digital video over native ATM connections. We also demonstrate experimentally the effects of different types of cross-traffic (delivered over both UDP/IP and native ATM) network loads on end-user application performance using QoS metrics such as jitter and packet loss.

Transient behaviour of queueing systems with correlated traffic

In this paper, we present the time-dependent solutions of various stochastic processes associated with a finite Quasi-Birth-Death queueing system. These include the transient queueing solutions, the transient departure and loss intensity processes and certain transient cumulative measures associated with the queueing system. The focus of our study is the effect of the arrival process correlation on the queueing system before it reaches steady-state. These time-dependent solutions require the computation of the exponential of the stochastic generator matrix G which may be of very large order. This precludes the use of known techniques to solve the matrix exponential such as the eigenvalue decomposition of G. We present a numerical technique based on the computation of the Laplace Transform of the matrix exponential which may then be numerically inverted to obtain the time-dependent solutions. We also propose new QoS metrics based on transient measures and efficient techniques for their computation.

Transient behaviour of queueing systems with correlated traffic

In this paper, we present the time-dependent solutions of various stochastic processes associated with a finite Quasi-Birth-Death queueing system. These include the transient queueing solutions, the transient departure and loss intensity processes and certain transient cumulative measures associated with the queueing system. The focus of our study is the effect of the arrival process correlation on the queueing system before it reaches steady-state. These time-dependent solutions require the computation of the exponential of the stochastic generator matrix G which may be of very large order. This precludes the use of known techniques to solve the matrix exponential such as the eigenvalue decomposition of G. We present a numerical technique based on the computation of the Laplace Transform of the matrix exponential which may then be numerically inverted to obtain the time-dependent solutions. We also propose new QoS metrics based on transient measures and efficient techniques for their computation.

Transient behaviour of queueing systems with correlated traffic

In this paper, we present the time-dependent solutions of various stochastic processes associated with a finite Quasi-Birth-Death queueing system. These include the transient queueing solutions, the transient departure and loss intensity processes and certain transient cumulative measures associated with the queueing system. The focus of our study is the effect of the arrival process correlation on the queueing system before it reaches steady-state. With the aid of numerous examples, we investigate the strong relationship between the time scales of variation of the arrival process and those of the transient queueing, loss and departure processes. These time-dependent solutions require the computation of the exponential of the stochastic generator matrix G which may be of very large order. This precludes the use of known techniques to solve the matrix exponential such as the eigenvalue decomposition of G. We present a numerical technique based on the computation of the Laplace Transform of the matrix exponential which may then be numerically inverted to obtain the time-dependent solutions. In this paper, we also propose new QoS metrics based on transient measures and efficient techniques for their computation.

Transient behaviour of queueing systems with correlated traffic

Abstract In this paper, we present the time-dependent solutions of various stochastic processes associated with a finite Quasi-Birth-Death queueing system. These include the transient queueing solutions, the transient departure and loss intensity processes and certain transient cumulative measures associated with the queueing system. The focus of our study is the effect of the arrival process correlation on the queueing system before it reaches steady-state. With the aid of numerous examples, we investigate the strong relationship between the time scales of variation of the arrival process and those of the transient queueing, loss and departure processes. These time-dependent solutions require the computation of the exponential of the stochastic generator matrix G which may be of very large order. This precludes the use of known techniques to solve the matrix exponential such as the eigenvalue decomposition of G . We present a numerical technique based on the computation of the Laplace Transform of the matrix exponential which may then be numerically inverted to obtain the time-dependent solutions. In this paper, we also propose new QoS metrics based on transient measures and efficient techniques for their computation.

QoS mapping scheme and a model for MAN-ATM internetworking

Integrated service networks like Asynchronous Transfer Mode (ATM) and Distributed Queue Dual Bus (DQDB) are designed to support various applications. Meeting QoS requirements is dependent on the bandwidth allocated to them. Hence, resource sharing becomes a key factor in such an environment. In the case of internetworking between networks, a QoS mapping must be defined in order to meet the requirements of all the applications. In this paper, we focus on the support of real-time applications and classify them into three traffic classes. For these applications, delay is the most important QoS metric. In particular, we present an architecture for ATM-DQDB internetworking, dedicated to the integrated services. This includes an admission control scheme and a signaling protocol. In that framework, we propose a dynamic renegotiation scheme for applications with flexible bandwidth requirements.