QoS-enabled middleware

by Saltanat Mashirova

Distributed applications

Distributed applications have distinctly different characteristics than conventional desktop or back office applications in that the right answer delivered too late can become the wrong answer, i.e., failure to meet key QoS requirements can lead to catastrophic consequences. Middleware that can satisfy stringent quality of service (QoS) requirements, such as predictability, latency, efficiency, scalability, dependability, and security, is increasingly being applied to DRE application development.

Limits of Conventional Middleware

- Lack of functional boundaries

- Lack of generic server standards

- Lack of software configuration and deployment standards

Component Middleware

Component middleware is a class of middleware that enables reusable services to be composed, configured, and installed to create applications rapidly and robustly.

How component middleware overcome those limitations

Creating a virtual boundary around larger application component implementations that interact with each other only through well-defined interfaces

Defining standard container mechanisms needed to execute components in generic component servers

Specifying the infrastructure to assemble, package, and deploy components throughout a distributed environment

Component Middleware

CORBA Component Model (CCM) is an example of component middleware

The CCM specification extends the CORBA object model to support the concept of components and establishes standards for implementing, packaging, assembling, and deploying component implementations.

Component is an implementation entity that exposes a set of ports, which are named interfaces and connection points that components use to collaborate with each other

Client View of CCM Components

Overview of the CCM Run-time Architecture

Limitations of Component Middleware

It doesn’t give us:

Ways to specify end-to-end QoS requirements, i.e. QoS Characteristics and QoS Values

Ways to specify adaptation strategies for how Resource Consuming Components can coordinate with other entities in order to meet QoS requirements

Ways to specify QoS management which cross multiple system and application level boundaries

QoS

Due to the limitations described above, it is necessary to extend standard middleware specifications so that they provide better abstractions for controlling and managing both functional and QoS aspects of DRE systems. What is needed is QoS-enabled component middleware that preserves existing support for heterogeneity in standard component middleware.

CIAO

CIAO supports Lightweight CCM mechanisms that enable the specification, validation, packaging, configuration, and deployment of component assemblies and integrates these mechanisms with TAO’s Real-time CORBA features, such as thread-pools, lanes, and client-propagated and server-declared policies.

DAnCE

DAnCE is a middleware framework for CIAO based on the OMG’s Deployment and Configuration specification which standardizes many deployment and configuration aspects of component-based distributed applications, including component configuration, assembly, and packaging; package configuration and deployment; and resource configuration and management