臺灣博碩士論文加值系統

隨著無線傳輸技術的蓬勃發展與寬頻網路的普及，多媒體透過網路傳輸的相關應用日趨豐富。由於目前的網際網路大多為盡力傳送式的環境，其變動的可用頻寬和網路的延遲變異等問題，均對具有叢集特性的視訊訊務其接收品質造成嚴重的影響，速率控制便成為多媒體傳輸系統中的關鍵機制。但現行廣用的壅塞控制協定，如TCP與TFRC在應用於無線環境時，往往存在著效能低落的問題。
在本論文中，根據上述問題提出一套在無線區域網路下具有正確分辨封包遺失成因之錯誤分離機制，減低壅塞控制協定因無線通道傳輸錯誤而調降傳輸率的機會，提升整體頻寬利用率效能。論文首先利用無線區域網路標準中各層次間定義之控制訊息，上傳給錯誤分離機制作判斷使用。另外，當無線網路啟動自動重送機制時，可能因為重傳封包導致基地台緩衝區溢滿進而引發壅塞事件，無線傳輸錯誤訊息亦表示某種程度的壅塞警訊。因此我們將部分傳輸錯誤視為壅塞封包遺失，調整其判斷比例並且在不同競爭程度的網路中進行實驗分析。
模擬結果顯示，在未啟動自動重送機制的無線網路中，具錯誤分離機制的協定其有效接收率較原始協定至少提升了9倍；於啟動自動重送機制的無線網路中，適度調整錯誤分離機制之判斷比例可將有效接收率變化維持在容許範圍內，但大幅降低壅塞封包遺失率與傳輸延遲時間，提升整體傳輸效能。

With the technology advances in wireless and broadband Internet technology, multimedia communications over network are dramatically boosted. However, a best-effort network with variable available bandwidth and delay may result in degradation of received video quality drastically. Hence, Rate Control plays a key role in transmission systems, but wireless networks with many non-congestion losses may bring huge performance reduction to current TCP and TFRC.
This thesis proposes a Loss Differentiation Algorithm (LDA) over WLAN environment, which could distinguish between packet losses due to buffer overflow or those due to bit errors. It avoids treating wireless losses as congestive, which leads to unnecessary rate reduction and poor performance. We try to notice wireless transmission error to upper layers by exploiting the signaling messages from the standard. Besides, data retransmission may put the incoming packets to be dropped due to buffer overflow when the common used technique ARQ is turned on. In certain circumstances, wireless transmission error message could be translated into congestion warning. Therefore, we try to modify the separation ratio in the algorithm and observe its behavior in different network conditions.
Simulation results show that, the receiving rate of the protocol with LDA is 9 times higher when ARQ is turned off; tuning the separation ratio properly would not degrade the rate but improves congestion loss rate and delay time massively.

附圖索引 V
附表索引 IX
第1章 緒論 1
1.1 研究背景與動機 1
1.2 相關研究 2
1.3 提出之機制與主要貢獻 4
1.4 論文架構 5
第2章 TFRC在無線網路之相關研究介紹 7
2.1 TFRC壅塞控制協定 8
2.1.1 TCP流量模型 9
2.1.2 TFRC規範內容 11
2.1.3 TFRC的行為模式 15
2.2 TCP於無線網路之相關研究 18
2.2.1 無線環境傳輸議題 19
2.2.2 TCP於無線環境之改進方法 21
2.3 TFRC於無線網路之相關研究 29
2.3.1 端點式錯誤分離機制 30
2.3.2 集中式錯誤分離機制 35
2.3.3 非錯誤分離之改善機制 37
第3章 應用於無線區域網路錯誤分離機制 41
3.1 IEEE 802.11錯誤分離機制 41
3.1.1 資料傳輸子層區交換的詳細訊息-MAC層 42
3.1.2 資料傳輸子層區交換的詳細訊息-實體層 45
3.2 具錯誤分離之TFRC機制 50
3.3 效能與問題分析 54
第4章 應用於自動重送機制下的探討 64
4.1 自動重送機制 64
4.2 應用於自動傳送機制之TFRC機制 66
4.2.1 IEEE 802.11錯誤回復機制 66
4.2.2 系統架構 66
4.3 效能與問題分析 69
第5章 實驗結果與討論 89
5.1 模擬環境架構說明 89
5.1.1 模擬用之視訊序列統計資料說明 90
5.1.2 網路模擬環境說明及其參數設定 91
5.2 使用錯誤分離機制的TFRC視訊串流分析 93
5.2.1 無自動重送機制 93
5.2.2 自動重送次數為一次 97
5.2.3 自動重送次數為二次 101
第6章 結論與未來工作 105
參考文獻 107
附錄A 其他數據資料 111

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