Giovanni Pacifici

Real-time scheduling with quality of service constraints

Whether or not the introduction of traffic classes improves upon the performance of ATM networks is discussed within the framework provided by a class of networks that guarantees quality of service. To provide a meaningful comparison the authors define the concept of a schedulable region, a region in the space of loads for which the quality of service is guaranteed. The authors show the dependence of the schedulable region on the scheduling algorithm employed, quality of service parameters, and traffic statistics. An efficient real-time scheduling algorithm is introduced that substantially increases the schedulable region without incurring prohibitive complexity costs. The schedulable region associated with this algorithm is compared with the ones generated by the static priority scheduling algorithm and a variant of the minimum laxity threshold algorithm. The size and shape of the schedulable region is explored by means of simulations. >

Control of resources in broadband networks with quality of service guarantees

The design principles of resource control algorithms based on asynchronous time-sharing (ATS) are addressed, together with their interaction and cooperation in a wide area network environment, and a framework for evaluating the overall performance of the system is presented. The basic concepts of the ATS framework are presented, along with an overview of an architecture for joint scheduling and admission control. Scheduling mediates the low-level competition for service between cells of different classes; admission control regulates the acceptance or blocking of incoming traffic on a call-by-call basis. The performance of the scheduling algorithms is evaluated and the interaction between scheduling and admission control is quantified. A reference model for broadband networks is presented. >

A separation principle between scheduling and admission control for broadband switching

A framework for joint scheduling and admission control in broadband switching systems based on a principle of separation between these two levels of control is developed. It is shown that an admission control strategy can be tailored to a particular mix of traffic by using high-level information from the scheduler. This principle is presented in the context of asynchronous time-sharing (ATS) in which explicit guarantees of cell-level and call-level quality of service (QOS) are given to several traffic classes. The separation principle allows the formulation of an optimal admission control policy that maximizes the expected system utility and maintains all QOS guarantees. Several heuristic admission control policies are considered and compared with the optimal policy. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time traffic are used to illustrate the effects of different scheduling and admission control policies on both the expected utility and the admissable load region. >

Modeling video sources for real-time scheduling

What is the impact of the autocorrelation of variable-bit-rate (VBR) sources on real-time scheduling algorithms? Our results show that the impact of long term, or interframe, autocorrelation is negligible, while the impact of short term, or intraframe, autocorrelation can be significant. Such results are essentially independent of the video coding scheme employed. To derive these results, video sequences are modeled as a collection of stationary subsequences called scenes. Within a scene, a statistical model is derived for both the sequence of frames and of slices. The model captures the distribution and the autocorrelation function of real-time video data. In previous work, the pseudoperiodicity of the slice level auto-correlation function made it difficult to develop a simple yet accurate model. We present a generalization of previous methods that can easily capture this pseudoperiodicity and is suited for modeling a greater variety of autocorrelation functions. By simply tuning a few parameters, the model reproduces the statistic behavior of sources with different types and levels of correlation on both the frame and the slice level.

Joint scheduling and admission control for ATS-based switching nodes

A joint scheduling and admission control algorithm is presented for Asynchronous Time-Sharing (ATS)-based switching nodes carrying real-time traffic. Systems based on ATS guarantee quality of service, at both the levels of cells and calls, for three well-defined traffic classes. A mechanism is outlined by which an admission control strategy can be tailored to a particular mix of traffic classes. A mechanism is outlined by which an admission control strategy can be tailored to a particular mix of traffic by making use of high-level information from the scheduler. This mechanism is based on a principle of separation between scheduling and admission control. A linear programming formulation is used to find the admission control policy which will maximize the expected system utility while maintaining the guaranteed quality of service. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time traffic are used to illustrate the effects of different scheduling and admisssion control policies on both the expected utility and the admissible load region.

Real-time traffic measurement on MAGNET II

Real-time traffic measurements on MAGNET II, an integrated network testbed based on asynchronous time sharing, are reported. The quality of service is evaluated by monitoring the buffer-occupancy distribution, the packet time-delay distribution, the packet loss, and the gap distribution of the consecutively lost packets. The experiments show that both time-delay and buffer-occupancy distributions of multiplexed video sources display a marked bimodal behavior, which does not seem to depend on the buffer size. The reliance of the network designer on traffic sources that do not exhibit substantial correlations can lead to implementations with serious congestion problems. For asynchronous-time-sharing-based networks with different traffic classes, the impact of a traffic class on the performance of the other classes tends to be diminished when compared to single-class-based asynchronous transfer mode (ATM) networks. >

An architecture for performance management of multimedia networks

A principal requirement for multimedia networks is the ability to allocate resources to network services with different quality-of-service demands. The objectives of achieving efficient resource utilization, providing quality-of-service guarantees, and adapting to changes in traffic statistics make performance management for multimedia networks a challenging endeavor. In this paper, we address the following questions: what is the respective role of the real—time control system, the performance management system, and the network operator, and how do they interact in order to achieve performance management objectives? We introduce an architecture for performance management, which is based on the idea of controlling network performance by tuning the resource control tasks in the traffic control system. The architecture is built around the L-E model, a generic system-level abstraction of a resource control task. We use a cockpit metaphor to explain how a network operator interacts with the management system while pursuing management objectives.

Integration of Internet and telecommunications: an architecture for hybrid services

We propose an architecture for hybrid services, i.e., services that span many network technologies, such as the public switched telephone network (PSTN), cellular networks, and networks based on IP. These services will play an important role in the future because they leverage on the existing infrastructures rather than requiring new and sophisticated mechanisms to be deployed. We explore a few issues related to hybrid services and propose a platform as well as a set of components to facilitate their creation and deployment. The existing infrastructure is only required to generate specific events when requests for hybrid services are detected. We present the design of a service layer, based on Java, that handles the treatment of these special requests. Our service layer is provided with a set of generic components realized according to the JavaBeans model. We illustrate the strength of our architecture by discussing two hybrid-service examples: a calendar service and a call forwarding service.

An architecture for the integration of Internet and telecommunication services

We propose an architecture for hybrid services, i.e., services that span many network technologies, especially the PSTPN and the Internet. These services will play an important role in the future, because they leverage on the existing infrastructures, rather than requiring brand new and sophisticated mechanisms to be deployed. We explore a few issues related to hybrid services and propose a platform, as well as a set of components, to facilitate their creation and deployment. The existing infrastructure is only required to generate specific events when requests for hybrid services are detected. We present the design of a service layer based on Java that handles the treatment of these special requests. Our service layer is provided with a set of generic components realized as Java Beans. Hence, we can provide hybrid services without changing the existing infrastructure. We illustrate this strength of our architecture by discussing the call forwarding service.

Modeling VC, VP and VN Bandwidth Assignment Strategies in Broadband Networks

We introduce a methodology for establishing a connection between two nodes of a broadband network, that allows for securing sufficient resources at every intermediate node along the selected route, and thereby guarantee Quality of Service. We describe how a Virtual Path (VP) mechanism may be implemented within our framework, and compare the performance achieved by such a scheme with that of a Virtual Circuit (VC) approach.