QoS specification and enforcement

Typical application QoS parameters for images and video include image size, frame rate, startup delay, reliability etc. The application QoS profile can also include subjective factors such as the degree of importance of the information to the user and the overall cost-quality metric that the user desires. Network QoS parameters include bandwidth, delay, jitter and loss rate. End-system parameters include CPU load, utilization, buffering mechanisms and storage related parameters. Users express dynamic preferences for media quality through benefit functions,  [22], for e.g.

1. frame rate benefit function which indicates that beyond a threshold frame rate, there is no additional benefit,
2. synchronization benefit function which indicates that the benefit is high only when the audio/video synchronization skew is low.

There are several challenges in delivering the specified QoS to video applications. The mapping between different sets of parameters at different levels in the system, the QoS translation process is one of the challenges in meeting end-to-end performance bounds. QoS parameters at the user level must be translated to quantitative parameters at the network and system level. This translation is required during the admission control process where resource availability at different levels must be queried and negotiated for. The admission control process represents a second challenge and consists of a variety of tests such as EED(end-to-end delay), buffer allocation and schedulability tests [17].

Since network and system conditions are likely to be dynamic, the optimal operating point is not constant and this represents yet another challenge in QoS enforcement. Several QoS parameters such as deadlines and packet losses [7, 3] must dynamically adapt during processing and communication. Violation of the QoS bounds portrays itself as flickering video, distorted audio, blanks and frozen images.