The Workload Model

 
Figure 1: Architectural View : Components of a QoS Based Architecture

Selection criteria for video QoS metrics come from two perspectives - the end-user and the service provider. With a VOD application, the end-user requirements are dominant and stringent, the QoS is prespecified and is expected to be met accurately. In an unconstrained environment such as the Internet, both user and service-provider factors are variable. The end-user desires that the best approximation to the QoS criteria be satisfied while the service provider wants to ensure cost-effective utilization of resources. In order to satisfy the dual requirements of user-satisfaction and cost effectiveness, we need integrated metrics for determining the best possible QoS.

To determine measures of cost-effectiveness and user satisfaction, we must define a workload model. Our workload model consists of three elements (see Figure 1 )

• Customer description: description of expected workloads and classes of customer requests and the correspondence of the workload components to customer classes. This information is typically obtained from empirical studies by observing customer request patterns and analyzing them.
• Service demands: description of interaction b/w customers and service (resource) centers (e.g. QoS requirements). This involves the translation of abstract customer descriptions obtained from empirical studies into more tangible parameters in an analytical model.
• Service Center description: a baseline description of the set of services that serve user requests and the correspondence of resources to service centers.

From the workload model it follows that selecting a unified metric will involve a choice of multiple parameters. This choice is based on empirical and statistical data which provides a base for analytical models with user requirements and resource allocations.