Over the past several years there has been a considerable amount of research within the field of quality-of-service (QoS) support for distributed multimedia systems. To date, most of the work has been within the context of individual architectural layers such as the distributed system platform, operating system, transport subsystem and network layers. Much less progress has been made in addressing the issue of overall end-to-end support for multimedia communications. In recognition of this, a number of research teams have proposed the development of QoS architectures which incorporate QoS-configurable interfaces and QoS driven control and management mechanisms across all architectural layers. This paper examines the state-of-the-art in the development of QoS architectures. The approach taken is to present QoS terminology and a generalized QoS framework for understanding and discussing QoS in the context of distributed multimedia systems. Following this, we evaluate a number of QoS architectures that have emerged in the literature.

https://www.cs.dartmouth.edu/~campbell/papers/multimediaa.pdf

A survey of QoS architectures

For applications relying on the transfer of multimedia, and in particular continuous media, it is essential that quality of service (QoS) is guaranteed system-wide, including end-systems, communications systems and networks. Although researchers have addressed many isolated areas of QoS provision, little attention has so far been paid to the definition of an integrated and coherent framework that incorporates QoS interfaces, management and mechanisms across all architectural layers. To address this deficiency, we are developing a Quality of Service Architecture (QoS-A) which offers a framework to specify and implement the required performance properties of multimedia applications over high-performance ATM-based networks. The QoS-A incorporates the notions of flow, service contract and flow management. Flows characterise the production, transmission and eventual consumption of single media streams, service contracts are binding agreements between users and providers and flow management provides for the monitoring and maintenance of the contracted QoS levels. This paper provides an overview of the QoS-A and focuses particularly on the role of the transport service and protocol in the architecture. We describe a multimedia enhanced transport service (METS), flow management and transport layer service contract. We show how QoS levels contracted at the transport service interface can be assured in the context of our local ATM environment.

https://cs.dartmouth.edu/~campbell/papers/thesis.pdf

A quality of service architecture

Questioning whether layering is still an adequate foundation for networking architectures, this paper investigates non-layered approaches to the design and implementation of network protocols. The goals are greater flexibility and control with fewer feature interaction problems. The paper further proposes a specific non-layered paradigm called role-based architecture.

From protocol stack to protocol heap: role-based architecture

Many application domains (e.g., avionics, telecommunications, and multimedia) require real-time guarantees from the underlying networks, operating systems, and middleware components to achieve their quality of service (QoS) requirements. In addition to providing end-to-end QoS guarantees, applications in these domains must be flexible and reusable. Requirements for flexibility and reusability motivate the use of object-oriented middleware like the Common Object Request Broker Architecture (CORBA). However, the performance of current CORBA implementations is not yet suited for hard real-time systems (e.g., avionics) and constrained latency systems (e.g., teleconferencing). This article describes the architectural features and optimizations required to develop real-time ORB end systems that can deliver end-to-end QoS guarantees to applications. While some operating systems, networks, and protocols now support real-time scheduling, they do not provide integrated solutions. The main thrust of this article is that advances in real-time distributed object computing can be achieved only by systematically pinpointing performance bottlenecks; optimizing the performance of networks, ORB end systems, common services, and applications; and simultaneously integrating techniques and tools that simplify application development.

/pdf/a-high-performance-end-system-architecture-for-real-time-roajzuvr9a.pdf

A high-performance end system architecture for real-time CORBA

The ADAPTIVE Service eXecutive (ASX) is a highly modular and extensible object-oriented framework that simplifies the development and configuration of distributed applications on shared memory multi-processor platforms. This paper describes the structure and functionality of the ASX framework's object-oriented architecture. In addition, the paper presents the results of performance experiments conducted using ASX-based implementations of connection-oriented and connectionless protocols from the TCP/IP protocol family. These experiments measure the performance impact of alternative methods for parallelizing communication protocol stacks. Throughout the paper, examples are presented to indicate how the use of object-oriented techniques facilitate application extensibility, component reuse, and performance enhancement.

https://www.dre.vanderbilt.edu/~schmidt/PDF/C++-USENIX-94.pdf

ASX: an object-oriented framework for developing distributed applications

A function-based communication model that allows applications to request individually tailored services from the communication subsystem is presented. Based on service requirements and available resources, suitable protocol machines are configured to serve the application. This configuration is done using a proper combination of functional modules. The concept of layering is therefore abandoned for both flexibility and efficiency reasons. >

A model for flexible high-performance communication subsystems

A framework containing a number of resources, languages, and tools for generating customized protocols that support diverse multimedia applications running on high-performance networks is described. The framework facilitates the configuration of application-tailored, function-based communication protocols that are automatically synthesized from high-level specifications.

Language support for flexible, application-tailored protocol configuration

Many emerging applications require very diverse services from the underlying communication subsystem. Future communication nodes will have to offer some flexibility in selecting service characteristics and efficiency in implementing them. In this paper, we present a model that allows each application to request the communication service that it needs. Based on service requirements and available resources, a suitable protocol machine is configured to serve the application. This configuration is done using the proper combination of protocol functions. The concept of layering is therefore abandoned for both flexibility and efficiency.

Application-Driven Flexible Protocol Configuration

Transport systems as they are known today will not be suited for the environment of high speed networks and future applications as e.g. multi-media applications. First of all, concepts to overcome the protocol processing bottleneck are necessary. They lead to a design of a transport oriented component within a network as a conglomeration of protocol functions without internal layering. This results in an impressive reduction of functions to be realized. Moreover, the transport service interface must be designed in a way that allows an easy and efficient support of various service requirements. Therefore, the transport service interface can be classified into four transport service classes, which are derived from the application requirements on performance and functional criteria. Each service class is associated with an individual protocol stack. The paper discusses these topics with special regards to flexible high speed transport systems. The flexibility, which is the possibility to adapt the transport system to the specific application dynamically, will be obtained by using an underlying multi-processor architecture, where the processing of different functions in parallel will be supported.

A Concept for a Flexible High Performance Transport System

Emerging ATM networks accompanied by an increasing variety of application service requirements may change future transport subsystem design in order to provide enhanced service characteristics and improved performance. System designs integrating proper architectures, services and protocols are increasingly required. This paper gives a survey of some research work dealing with transport subsystem issues for ATM network. A framework for an ATM transport system is presented providing an enhanced service interface and supporting application-driven flexible protocol configurations. The framework uses a non-hierarchical, fine granular function-based decomposition of the communication task in order to efficiently provide these features.

Burkhard Stiller

Papers

A model for flexible high-performance communication subsystems

Language support for flexible, application-tailored protocol configuration

Application-Driven Flexible Protocol Configuration

A Concept for a Flexible High Performance Transport System

On Transport Systems for ATM Networks