本論文針對無線網際網路上傳輸即時串流視訊的相關應用發展了一套運用數據壅塞控制協定(datagram congestion control protocol; DCCP)的影像傳送系統，並採用MPEG-4視訊以實現整體系統的開發。設計此套基於DCCP的影像系統主要的挑戰在於須將傳統的影像系統元件如影像來源編碼、通道錯誤編碼和封包轉換與包含有TCP友好速率控制（TCP-friendly rate control; TFRC）以及局部檢查碼覆蓋（partial checksum coverage）的新型DCCP特性此兩者做ㄧ功能整合以完成影像視訊在無線網路上的編碼及傳輸。在DCCP所提供的新型特性中，TFRC為一針對多媒體應用所設計的壅塞控制機制，其旨在藉由採用與TCP相似的傳輸量調整方式以期減少可能發生的封包遺失與傳輸延遲而能有助於串流視訊在網際網路上的傳輸。另ㄧ方面，封包的局部檢查碼覆蓋則是允許接收端的DCCP傳遞已被錯誤損壞的封包到應用程式而非直接將損壞的封包丟棄; 此類包含有損壞資料的封包可以進ㄧ步由抗錯性編碼方式（error-resilient　coding）所加以利用而增加影像在接收端的有效資料量。為了解決上述整合應用層的影像系統元件與傳輸層的DCCP所產生的實際困難，本論文提出了ㄧ個在無線網際網路上運用DCCP的影像傳輸架構並且著重在適應性速率控制以及高效能的封包轉換這兩種解決方案。
在無線網際網路上傳送基於DCCP傳輸架構的串流視訊最主要的需求就是原始影像經由影像來源編碼及通道錯誤編碼後的影像資料量必須要跟TFRC所得出的網路傳輸資料量吻合以確保TCP友好的特性。除了速率吻合的需求外，觀看網路視訊的使用者通常要求在各種不同的網路狀況下必須保持ㄧ個高品質而流暢的影像輸出。因此，我們首先在論文裡提出一個整合式的速率控制機制，此機制所達成的速率吻合具備了可受控制的傳輸緩衝延遲並且能夠減少影像壓縮在輸出速率限制下所造成的畫面跳躍情況。此外，DCCP/TFRC的資料流使用變動的封包長度可以在無線環境中達到較為堅實可靠的視訊傳輸，但是不固定大小的封包在網路上傳輸時卻不利於保持TCP友好的特性。因此，在不改變傳輸封包大小的條件下，我們提出了一個封包內分段的機制將DCCP封包虛擬的切割成數個資料段，並且利用媒體存取控制層（medium access control; MAC）會因傳輸錯誤而觸發的封包重送來回復先前損壞的資料段。基於這種方式，此封包內分段的機制可以在無線傳輸上提供更有效率的資料回復功能，同時也能夠保留住DCCP資料流所應具備的TCP友好特性。經由廣泛的實驗結果已驗證了本論文所提出的整合性速率控制機制與封包內分段的封包轉換機制在各種網路情況下的有效性。最後，在我們成功的系統整合之下，本論文所發展出的基於DCCP架構之視訊傳輸系統可以保有較佳的畫面流暢度並且大幅提升了在無線網際網路下的視訊傳輸品質進而能夠帶給使用者兼具順暢以及高品質的影像觀賞經驗。

This dissertation develops a video transmission system based on datagram congestion control protocol (DCCP) to transport real-time streaming video over wireless Internet and focuses on MPEG-4 video in realizing the system design. The main challenge of the DCCP-based video system is to integrate the system components such as the source coding, channel coding and packetization strategy, with new DCCP features including TCP-friendly rate control (TFRC) and partial checksum coverage for wireless video coding and transmission. TFRC is a congestion control mechanism designed for multimedia flows and aims to benefit the Internet-based video streaming by adapting the system transmission rate to the network congestion level in a TCP-friendly manner to reduce the potential packet loss and delays. On the other hand, the partial checksum coverage allows DCCP to forward the error-corrupted packets instead of dropping them and accordingly facilitates the error-resilient source coding to increase video goodput. In addressing the practical difficulties involved in integrating video system components in the application domain with DCCP in the transport domain, this dissertation presents a DCCP-based video transport architecture for wireless video with emphasis on adaptive source coding and efficient packetization.
Delivering DCCP-based video over the wireless Internet primarily requires the rate matching between the source/channel coding and TFRC transport service to ensure TCP-friendliness. In addition to the rate matching requirement, users demand a high-quality, smooth media output under the varying network conditions. Accordingly, an integrated rate control scheme is first proposed to meet the rate matching with the controlled transmission buffering delay and reduce the frame skipping. Also, DCCP/TFRC flows with variable packet size are beneficial to robust video transmission in the wireless environment but adversely affect the TCP-friendliness feature. Without adapting packet size to the varying channel errors, we present an in-packet segmentation scheme to virtually divide the DCCP packet into segments, and recover the erroneous segments through the MAC-level retransmissions. As a result, the proposed in-packet segmentation scheme is more efficient in data recovery over wireless channels while preserving the TCP-friendliness of DCCP-based video flows. The extensive experiment results have demonstrated the utility of the two proposed schemes under the varying network conditions. Through the successful system integration, the developed DCCP-based video system better preserves the motion smoothness, and improves the overall perceptual quality for wireless video transmissions to obtain a smooth, high visual quality video experience.

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