臺灣博碩士論文加值系統

網路電話(Voice over IP, VoIP)的應用隨著網際網路的普及越來越廣泛，尤其是結合企業內部網路通訊系統應用最為普遍；無線區域網路(Wireless Local Area Network, WLAN)的傳輸速率(Data Rate)隨著調變技術改良及採用多重輸入與多重輸出天線技術(Multiple Input Multiple Output, MIMO)而快速提升；然而，如何確保語音封包與其它資料於同一傳輸平台同時間傳送時的品質是最大的問題。影響VoIP品質的主要因素有封包遺失(Packet Loss)、封包延遲(Packet Delay)及抖動率(Jitter)等。
本研究以實際建置兩組實驗環境及四種量測架構，將VoIP系統應用於有線及無線網路混合環境下，依據ITU-T對語音品質之標準E模型(E-Model)和平均意見得分(Mean Opinion Score, MOS)來測量VoIP語音品質之等級，分析VoIP於不同WLAN系統環境下之效能，並以實作應用IP網路之低延遲佇列(Low Latency Queuing , LLQ)機制提供確保VoIP 服務品質QOS (Quality Of Service)建議架構。

Voice over IP becomes more and more popular due to the widespread use of the internet. Besides, Wireless Local Area Network can achieve higher speed via using the multiple input multiple output technique. However, it is an important issue to guarantee the Quality of Service of the VoIP through the internet. Three major factors that influence the Quality of Service; i.e., Packet Loss, Packet Delay and Jitter.
The purpose of this study is to measure the QoS of the VoIP in a hybrid wireline and wireless communication environment according to the E-Model and MOS. The influences of these three factors to the QoS are also investigate. Meanwhile, the QoS measurement of a LLQ QoS scheme is also given in the study.

摘要 V
Abstract VI
圖目錄 IX
表目錄 XII
第一章 緒論 1
1.1 前言……………………………………………..………………………… 1
1.2 研究動機與目的 2
1.3 各章內容概要 4
第二章 背景及相關研究 5
2.1 IEEE 802.11之制定標準簡介 5
2.1.1 無線區域網路的基本架構 6
2.1.2 802.11b 7
2.1.3 802.11a 8
2.1.4 802.11g 8
2.1.5 802.11n ( Draft 2.0 ) 9
2.2 VoIP的基本架構原理 10
2.2.1 H.323簡介 10
2.2.2 SIP簡介 12
2.2.3 語音封包壓縮/解壓縮格式 ( Coder/Decoder, CODEC ) 15
2.2.4 網路電話頻寬之計算 17
2.2.5 即時傳輸協定( Real-Time Transport Protocol, RTP ) 18
2.3 影響VoIP品質之因素 21
2.3.1 封包延遲 ( Packet Delay ) 21
2.3.2 封包遺失 ( Packet Loss ) 23
2.3.3 抖動率 (Jitter) 24
2.4 VoIP品質量測方法 25
2.4.1 平均意見得分(Mean Opinion Score, MOS) 26
2.4.2 E-模型 (E-Model) 27
2.5 網路壅塞管理機制 30
2.5.1 類別基礎的加權公平佇列(Class Base Weighted Faire Queue, CBWFQ) 31
2.5.2 優先佇列(Priority Queue, PQ) 32
2.5.3 低延遲佇列(Low Latency Queue, LLQ) 33
第三章 測量的方法及架構 34
3.1 實際量測環境 34
3.1.1 環境 (一) 34
3.1.2 環境 (二) 38
3.2 實驗設備及量測的工具 42
3.2.1 Cisco Aironet 1250 Access Point 42
3.2.2 D_Link DWA-645無線網卡 43
3.2.3 訊舟無線基地台 EDIMAX Access Point BR6204 44
3.2.4 Cisco Router 1841 45
3.2.5 OCTTEL ITG MS-2040 46
3.2.6 IxChariot 5.4 47
3.2.7 Network Stumbler 48
3.2.8 VQManager 49
3.2.9 Wireshark 50
第四章 實驗方法與結果分析 51
4.1 實驗方法重點說明 51
4.2 實驗(一)量測方法與結果分析 53
4.2.1 (A-1)各種無線區域網路系統之傳輸效能比較 54
4.2.2 (A-2)AP使用不同天線數之Data Rate實際量測 58
4.2.2 (A-3)不同無線區域網路系統於接收端移動下之效能比較 61
4.2.4 (A-4)無線區域網路系統之頻寬共享特性量測 63
4.2.5 (B-1)語音封包壓縮格式與網路電話品質之影響 65
4.2.6 (B-2)封包延遲(Delay)對於VoIP語音品質影響 66
4.2.7 (B-3)測量抖動率(Jitter)對於VoIP語音品質的影響 69
4.2.8 (B-4)VoIP於不同無線區域網路系統之容量評估 71
4.3 實驗(二) (三) (四)量測方法及結果分析 72
4.3.1 實驗（二）於無線區域網路下之QOS機制量測 72
4.3.2 實驗（三）於無線及有線區域網路混合環境下之QOS機制量 測.. 80
4.3.3 實驗（四）透過廣域網路連結兩不同無線區域網路之QOS機制量測 85
第五章 結論與建議 92
參考文獻 94

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