A Dynamic QoS Control Scheme for Videoconferencing in a Heterogenous Internet
Conference Paper
Overview
Overview
abstract
Multicasting is a bandwidth-efficient approach to transmitting real-time audio and video to multipoint receivers over the current Internet. The heterogeneous nature of the Internet, however, can cause a conflict between receivers in multiparty videoconferencing. In a real-time videoconferencing session with many participants, some receivers could suffer congestion when their link bandwidths are very limited or congested with heavy traffic. Because of different link capacities, a single multicast stream cannot always provide good service to all receivers. If the source transmits high-quality video data, receivers with low bandwidth will suffer from high packet loss, which causes a degradation in quality. If the source adapts the video quality to support receivers with low bandwidth, the participants with high bandwidth links will complain about the lower quality. Layered multicast has been proposed as an effective solution to cope with the heterogeneity of network bandwidth for multiparty videoconferencing over the Internet. In layered multicast, a source transmits layered video streams through multiple channels. By adjusting the subscription level of layers, each receiver can dynamically adapt to its own capacity. In layered coding, a video source is divided into several sub-streams where a lower layer must be received before a higher layer can be decoded. Adding incremental layers in order increases the quality of the representation. In order to utilize a higher layer, all of the lower layers must be received. Although significant research on layered multicast has been conducted, problems in scalability and implementation remain. Therefore, we are proposing a dynamic quality-of-service (QoS) control scheme based on a new architectural feature to support layered multicast videoconferencing over the current best-effort and heterogeneous Internet. The receiver adds and drops layers to reduce the packet-loss rate by reacting quickly to network congestion. Some other important issues, including information sharing and bandwidth fairness, are also considered in designing the architecture and QoS control scheme. The new approach is implemented on a videoconferencing tool, CafeMocha, which has been developed in the Texas A&M University Multimedia and Networking Laboratory. We will show the soundness of the proposed concepts through the experimental results.
