Quartz: A QoS Architecture for Open Systems

Abstract

The term `QoS architecture? is used to describe middleware that provides applications with mechanisms for specification and enforcement of quality of service (QoS) requirements. These architectures administer the resources provided by the underlying system with the intent of fulfilling the QoS requirements imposed by applications. Substantial work on QoS architectures can be found in the literature. However, the architectures proposed so far consider only part of the overall problem of delivering QoS in open systems. The QoS architectures currently available are able to provide applications in a particular application area with the guarantees supported by the specific network architecture and the operating system to which they are bound. Most of these architectures, moreover, require QoS to be specified by using a low-level format that is not appropriate for applications that have a more high-level notion of QoS. Due also to their close integration with the underlying system, these architectures cannot be deployed over multiple computing platforms. Since they target a specific area of application, the area in which these architectures can be used is limited. In most cases the underlying system is not made completely transparent for the application, which still has to deal with lowlevel issues. In addition, most QoS architectures ignore dynamic resource adaptation, which can occur due to factors such as resource failure or system reconfiguration. This thesis describes the design and implementation of Quartz, a QoS architecture for QoS specification and enforcement in open systems, designed with the aim of solving

the limitations of previous proposals in this area. Quartz is able to handle the differences between the multiple platforms that may be present in open systems due to its flexible and extensible structure based on replaceable components. Quartz can also adapt itself by rearranging its internal components, in order to provide mechanisms for QoS specification and enforcement suitable for different areas of application. These requirements are interpreted by Quartz and used to enforce QoS by employing the resource reservation mechanisms provided by the network and operating system. By adopting this strategy, Quartz makes the underlying resource reservation mechanisms transparent to applications requiring QoS enforcement. Furthermore, Quartz provides support for QoS adaptation by tracking resource adaptations that occur at lower levels and initiating QoS adaptation whenever needed. This thesis presents a prototype implementation of the Quartz architecture and a series of applications built on top of it, including a complete framework for the development of multimedia applications based on the CORBA architecture. The experience gained by writing these applications shows the usefulness and efficiency of Quartz as a tool for supporting QoS specification and enforcement for diverse areas of application in open, heterogeneous environments.