Streaming audio and video applications are becoming increasingly popular on the Internet, and the lack of effective congestion control in such applications is now a cause for significant concern. Layered video is one good solution for the heterogeneous Internet. But the problem is how to utilize the layered video to adapt to the time varying channel condition. A rapid fluctuation in quality will be disturbing to the users, and it should be minimized.
In this thesis, we present a layer selection mechanism for layered video in the context of unicast congestion control. For improved decision for rebuffering at receiving data buffer, a display time buffer is introduced after the receiving buffer. It is shown that the layer selection control by the display time buffer(DTB) is better than by the channel bandwidth or simple buffer fullness. The oscilation between two layers is also reduced by the control with two thresholds in DTB. These quality adaptation mechanism adds or drops the enhancement layer to perform long-term quality adaptation.