本論文之主要目的為提出一個以階層式視訊編碼為主的多重播放系統設計法則。該系統可達成單點對多點的傳送，並具有下列特性：
1.傳送端結構簡單：傳送端僅負責執行階層式視訊編碼及通道編碼，並不需要考慮不同接收端的網路環境。
2.接收端具有彈性：接收端可根據個別之網路特性選擇適當的傳送資料以最佳化其效能。
3.結合FEC及ARQ：在封包流失率很高時FEC的保護效能可能不佳，而ARQ則有較長傳送延遲之缺點，本計畫使用Hybrid Pseudo-ARQ技術將FEC及ARQ結合以去除二者之缺點同時保留其優點。
在執行Hybrid Pseudo-ARQ時傳送端將FEC封包分階段傳送至不同的多重播放群組，而接收端則在檢視其封包流失情況後至後續階段的FEC多重播放群組抓取適量的FEC封包進行還原。
在設計Hybrid Pseudo-ARQ時我們需要一個最佳的Policy來協助接收端判斷應抓取的FEC封包數。然而由於Policy的個數很多，所以我們使用動態規劃法來尋找最佳Policy，跟全搜尋法比較起來，動態規劃法降低了許多的計算複雜度。
最後本論文考慮網路環境變化的問題。通常網路的封包流失率、以及傳送的視訊內容常會不斷的變化，而Hybrid Pseudo-ARQ需要這些參數來訂定Policy。在網路環境變化快速時，雖然使用動態規劃法決定Policy會得到最佳的效能，但是會造成計算上的沉重負擔。所以我們提出一個快速搜尋Table法來降低此負擔同時滿足即時Policy最佳化之需求。
本論文所提出之架構及演算法，預期可增進多重播放系統在複雜網路環境下的傳送及容錯能力，並進而提升多媒體通訊之應用範圍。

A novel error control algorithm for robust video transmission is presented in this paper. In the algorithm, both the source packets and parity packets are delivered in layers. Each receiver, in accordance with its available bandwidth and packet loss rate, employs the optimal policy for subscribing source layers and parity layers minimizing the average distortion of the reconstructed frames. The algorithm is able to perform fast policy adaptation for the location and time-varying network environments. The implementation of the fast adaptive algorithm is based on a novel table look-up process, in which the tables are constructed using a dynamic programming technique. Our experiments show that the algorithm is an effective alternative for the video broadcast applications where the robust transmissions over the heterogeneous network environment are desired.

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