Abstract
In this paper, architectural extensions for enhancing an open media-streaming platform with Differentiated Services (DiffServ) mechanisms are studied, implemented, and experimentally evaluated. Towards this end, an appropriate layering is adopted in order to enable the definition of Quality of Service (QoS) specifications and their mapping to network parameters during transmission. Furthermore, a component dedicated to the off-line study of quality requirements is specified and integrated into the QoS aware platform. This component enables to preview the effects of quality violations on media streams, before they are transmitted to the network, by simulating packet losses/delays during the packetization process. Based on this component, a suitable quality metric is introduced for video streams, which is sensitive both to spatial and temporal distortion effects and can be easily applied to other types of streams, or to groups of related streams (e.g. synchronized audio-video). The aforementioned extensions are implemented on the open source MPEG4IP platform. The applicability of certain QoS policies is experimentally evaluated over a laboratory-based DiffServ testbed. In this case, QoS specifications are mapped to DiffServ compliant Type of Service (ToS) values during transmission. Experiments are conducted with an MPEG-4 encoded video stream under different network configurations, QoS policies, and error resilience mechanisms. The performance of the stream is evaluated based on the proposed quality metric.
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