Dynamic quality of session control of real-time video multicast

The paper presents a framework for dynamic control of the quality of real time video multicast applications. In such applications, there is a need for introducing the concept of "Quality of Session (Qoss)", beyond the Qos received by individual receivers. The Qoss can be best determined by the end application, depending on the application semantics and the actual Qos seen by each receiver. The control of Qoss is achieved by employing a Qoss monitoring mechanism at the application level and a sender receiver combination control mechanism to react to bottlenecks in the network or end systems. Each receiver performs local control, measures the stream quality offered to the end user and feedback the measurement to the sender using extended RTP receiver reports. According to the feedbacks and multiviewer synchronization requirement, the sender assesses the overall Qoss and adjusts the encoding and/or sending rate. The mechanism can be further enhanced if layered codecs are adopted. Policies of the Qos measurement and Qoss assessment were defined, algorithms of the source rate control were proposed, and the mechanisms of adaptive video encoding is described.