A buffered-bandwidth approach for supporting real-time video streaming over cellular networks

In this paper, we study the admission and bandwidth allocation problems in real-time video streaming in a cellular network. Admission control in a cellular network is a complex issue due to the mobility of the clients, and the additional workload imposed by incoming clients could exceed the network capacity of a cell and seriously degrade the quality of services provided to the resident clients. To minimize the number of forced terminations of real-time video playback, we incorporate the notion of buffered bandwidth in the admission test for handoff client. Using this approach, we can balance the video workload among adjacent cells to minimize the impact of overloading as the result of handoff operations. We also examine techniques to maintain fairness in services especially under overload situations even though the requested videos from various types of clients could generate very different workload. Simulation experiments confirm the effectiveness of our approach compared to widely used schemes.     

A buffered-bandwidth approach for supporting real-time video streaming over cellular networks

In this paper, we study the admission and bandwidth allocation problems in real-time video streaming in a cellular network. Admission control in a cellular network is a complex issue due to the mobility of the clients, and the additional workload imposed by incoming clients could exceed the network capacity of a cell and seriously degrade the quality of services provided to the resident clients. To minimize the number of forced terminations of real-time video playback, we incorporate the notion of buffered bandwidth in the admission test for handoff client. Using this approach, we can balance the video workload among adjacent cells to minimize the impact of overloading as the result of handoff operations. We also examine techniques to maintain fairness in services especially under overload situations even though the requested videos from various types of clients could generate very different workload. Simulation experiments confirm the effectiveness of our approach compared to widely used schemes.     

PID feedback for load-balanced parallel gridless DSMC

Parallel code presents a non-trivial problem of load balancing computational workload throughout a system of hardware and software resources. The task of load balancing is further complicated when the number of allowable processors changes through time. This paper presents a two-component load-balancing mechanism using optimal initial workload distribution and dynamic load maintenance. The initial guess is provided by inversion of the workload distribution function. Workload distribution inversion enables efficient domain decomposition for arbitrary workloads and easily compensates for changes in system resources. Dynamic load balancing is provided by process feedback control as used, for example, in control mechanisms of physical processes. Proportional, integral, and differential (PID) feedback readily allows controls to compensate for runtime-changes of the workload distribution function. This paper demonstrates a one-dimensional realization of the ideas presented here. We apply this load-balancing technique to our gridless direct simulation Monte Carlo algorithm. We demonstrate that the method does indeed maintain uniform workload distribution across available resources as the workload and usable system resources undergo change through time.     

A core stateless bandwidth broker architecture for scalable support of guaranteed services

We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed recently. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the per-hop behaviors of core routers and the end-to-end properties of their concatenation. We focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both per-flow end-to-end guaranteed delay services and class-based guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on a per domain basis instead of on a "hop-by-hop" basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of dynamic flow aggregation in providing guaranteed delay services and devise a new apparatus to effectively circumvent this problem. We conduct detailed analyses to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.     

Cataclysm: Scalable overload policing for internet applications

In this paper we present the Cataclysm server platform for handling extreme overloads in hosted Internet applications. The primary contribution of our work is to develop a low overhead, highly scalable admission control technique for Internet applications. Cataclysm provides several desirable features, such as guarantees on response time by conducting accurate size-based admission control, revenue maximization at multiple time-scales via preferential admission of important requests and dynamic capacity provisioning, and the ability to be operational even under extreme overloads. Cataclysm can transparently trade-off the accuracy of its decision making with the intensity of the workload allowing it to handle incoming rates of several tens of thousands of requests/second. We implement a prototype Cataclysm hosting platform on a Linux cluster and demonstrate the benefits of our integrated approach using a variety of workloads.     

Integration of admission,congestion, and peak power control in QoS-aware clusters

Admission, congestion, and peak power control mechanisms are essential parts of a cluster network design for supporting integrated traffic. While an admission control algorithm helps in delivering the assured performance, a congestion control algorithm regulates traffic injection to avoid network saturation. Peak power control forces to meet pre-specified power constraints while maintaining the service quality by regulating the injection of packets. In this paper, we propose these control algorithms for clusters, which are increasingly being used in a diverse set of applications that require QoS guarantees. The uniqueness of our approach is that we develop these algorithms for wormhole-switched networks, which have been used in designing clusters. We use QoS-capable wormhole routers and QoS-capable network interface cards (NICs), referred to as Host Channel Adapters (HCAs) in InfiniBand™ Architecture (IBA), to evaluate the effectiveness of these algorithms. The admission control is applied at the HCAs and the routers, while the congestion control and the peak power control are deployed only at the HCAs. A mixed workload consisting of best-effort, real-time, and control traffic is used to investigate the effectiveness of the proposed schemes.     

Dynamic CPU provisioning for self-managed secure web applications in SMP hosting platforms

Overload control mechanisms such as admission control and connection differentiation have proven effective for preventing overload of application servers running secure web applications. However, achieving optimal results in overload prevention is only possible when some kind of resource management is considered in addition to these mechanisms.In this paper we propose an overload control strategy for secure web applications that brings together dynamic provisioning of platform resources and admission control based on secure socket layer (SSL) connection differentiation. Dynamic provisioning enables additional resources to be allocated to an application on demand to handle workload increases, while the admission control mechanism avoids the server’s performance degradation by dynamically limiting the number of new SSL connections accepted and preferentially serving resumed SSL connections (to maximize performance on session-based environments) while additional resources are being provisioned.Our evaluation demonstrates the benefit of our proposal for efficiently managing the resources and preventing server overload on a 4-way multiprocessor Linux hosting platform, especially when the hosting platform is fully overloaded.     

Dynamic adaptation of response-time models for QoS management in autonomic systems

In transactional systems, the objectives of quality of service regarding are often specified by Service Level Objectives (SLOs) that stipulate a response time to be achieved for a percentile of the transactions. Usually, there are different client classes with different SLOs. In this paper, we extend a technique that enforces the fulfilment of the SLOs using admission control. The admission control of new user sessions is based on a response-time model. The technique proposed in this paper dynamically adapts the model to changes in workload characteristics and system configuration, so that the system can work autonomically, without human intervention. The technique requires no knowledge about the internals of the system; thus, it is easy to use and can be applied to many systems. Its utility is demonstrated by a set of experiments on a system that implements the TPC-App benchmark. The experiments show that the model adaptation works correctly in very different situations that include large and small changes in response times, increasing and decreasing response times, and different patterns of workload injection. In all this scenarios, the technique updates the model progressively until it adjusts to the new situation and in intermediate situations the model never experiences abnormal behaviour that could lead to a failure in the admission control component.     

视频点播服务器的服务质量控制框架

视频点播服务器工作于开放的网络环境中,系统负载难以预测,其运行时资源瓶颈依赖于实时服务类型.基于性能模型和实时负荷估计方法,本文提出视频点播服务器的服务质量控制框架,提供系统负荷监控、准入控制和区分服务等三种服务质量控制.实际系统的验证实验表明,本文的方法可以有效的对系统负荷进行监控,确保系统负荷稳定在服务提供商希望的水平线以下,向不同级别的用户提供不同质量级别的服务.     

Linux下区分服务逐跳行为的设计与实现

区分服务为不同数据流提供了不同方式和级别的服务，可以为重要性不同的应用提供不同的带宽和优先级保证。Linux平台具备功能强大的带宽管理工具集，为应用的分类和带宽保证提供有效手段。通过结合区分服务规范定义的加速转发、保证转发，以及传统尽力而为的转发方式，在Linux平台上使用流量控制工具集TC，设计并实现了不同类数据流的区分和带宽保证，建立了区分服务逐跳行为在Linux下的映射模型。