臺灣博碩士論文加值系統

現今的無線網路系統的設計中，因為提供了高頻寬，使的更多的功能能夠在無線網路上應用。最明顯的需求有影像方面的服務，例如有視訊會議，緊急的醫療救助或是定位系統等等。
在這篇論文中，提出了利用將封包的優先權來分級的架構來使的在無線網路中傳輸影像能夠非常的流暢，並且希望在傳送端及接收端能夠減輕負載。在這個優先權分級架構中包含了兩個部分，第一個部分是將影像資料利用H.263的編碼以及優先權來做分級，第二個部分則是將分級完的封包做丟棄的決策。在影像分級部份中，先把影像依照I-frame或是p-frame來決定高低優先權，所有的I-frames及每三張p-frams中取出一張來設定為高優先權，其餘剩下的全部設定為低優先權。在封包丟棄決策中，所有的高優先權的封包一律不丟棄。在這樣的前提下，我們出了兩種方式，一是依據緩衝儲存器的門檻來決定是否丟棄，只要緩衝儲存器內資料量的長度超過了我們設定的門檻則進行低優先權封包的丟棄。第二種方式則是依據目前的頻道傳輸率來決定。越高的頻道傳輸率丟棄越低的比例的低優先權封包，反之，越低的頻道傳輸率則丟棄越高比例的低優先權封包。
利用模擬的實驗中可以得知，沒有使用任何機制來處理封包傳輸狀況的效果最差，影像會因網路壅塞產生嚴重的延遲，再則比較這篇論文中所提出的兩中方式中，利用目前頻道的傳輸率來丟棄封包的機制所顯示出來的影像比依據緩衝儲存器的門檻來丟棄封包的效果要佳。

1 Introduction 2
2 The Hierarchical Video Codec and the Packet Discarder 5
2.1 Hierarchical Video Codec 5
2.2 Packet Discard Policies 7
3 Fluid Analysis 9
4 Experimental and Numerical Results 16
5 Conclusion 20

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