Extending an open media-streaming platform to support Differentiated Services

Abstract – In this paper, architectural extensions for enhancing an open media-streaming platform with differentiated services mechanisms are studied, implemented, and experimentally evaluated. Towards this end, an appropriate layering is adopted in order to enable 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

A Priority Dropping Mechanism for the Multicast Delivery of Layered Video in a DiffServ Environment

Abstract:- In this paper a network-based, open loop mechanism for the multicast delivery of layered video streams is specified and experimentally evaluated for a DiffServ environment. Network oriented mechanisms for delivering layered multicast video offer simplicity and efficiency. Before the emergence of the Differentiated Services (DiffServ) framework a solid and feasible set of network mechanisms supporting such functionalities did not exist. The central idea is that once the application flow provides indications of how to scale in cases of losses, it is task of the network to manage packet drops according to their importance. The application defines priority layers within the video stream through packet marking, while the DiffServ is exploited to provide layer aware packet dropping together with a complete QoS provisioning framework. In this sense, each video stream is delivered in a single multicast group, without the need for extensive group management functions. During congestion at multicast tree nodes, packets corresponding to a lower priority layer are dropped first, thus protecting the most precious entities of the stream. In this context, congestion is handled at the node it occurs as soon as it occurs. Experiments with a DiffServ aware MPEG-4 streaming platform, were conducted over a laboratory platform validating the mechanism’s applicability. Experimental results are exposed. Key-Words:- Multicast, DiffServ, priority dropping, video, MPEG4IP, experiments