本論文針對網路上傳輸的語音封包，其冗長的Header，會造成網路頻寬花費過高，提出一套動態MUX/DEMUX機制，用來壓縮VoIP封包多餘的Header資訊，並針對多條VBR語音通話，在不同的時間延遲和不同封包長度的情況下，動態的調整其壓縮過後的IP封包長度，並儘可能減少WiMAX網路的頻寬花費。並且在還原語音封包時，維持其QoS，不讓使用者覺得語音品質下降。
為了驗證本論文的機制，我們在中山大學WiMAX網路環境中(採用IEEE 802.16a)，在其BS (Base Station)的兩側，利用Linux平台建置了兩部WiMAX VoIP閘道器(Gateway)。針對VBR的語音封包，提出兩種不同的迷你壓縮標頭格式並且撰寫了壓縮語音封包的機制、Multiple Buffers機制，動態的調整不同來源的語音通話在MUX Gateway的等待時間，已達到節省頻寬花費且不讓語音品質降低的目的。最後再經由Linux平台的實作，以實驗來證明，使用動態MUX/DEMUX機制，可以顯著的節省VoIP在WiMAX網路上的頻寬花費，並且驗證語音通話受到干擾時，透過我們的機制，可以使Packet Arrival Interval達到穩定，而進一步提升語音串流品質。

Because the relatively long headers in voice packets may cause unnecessary waste in network bandwidth, in this Thesis, we propose a dynamic MUX/DEMUX mechanism to compress the overhead headers in the VoIP packets. The proposed mechanism can dynamically adjust the length of the compressed VoIP packets for multiple VBR voice connections in a mixed WLAN and WiMAX environment. QoS in terms of voice jitter can be guaranteed after the multiplexed voice packets are de-multiplexed.
To validate the proposed mechanism, we implement two VoIP MUX/DEMUX gateways on Linux platform and place them in a mixed WLAN and WiMAX (IEEE 802.16a) network at NSYSU campus. On the VoIP MUX/DEMUX gateways, we implement four functions; (i) the header formats of two different mini compressions, (ii) the mechanism of compressing voice packets, (iii) multiple waiting buffers, and (iv) the mechanism of dynamically adjusting waiting time of voice packets from different sources. According to the experimental results, the proposed VoIP MUX/DEMUX mechanism has shown that it can substantially save WiMAX bandwidth and consistently stabilize packet arrival interval (PAI) of voice packets under different levels of background traffic (constant or burst). Thus, the QoS of voice communications are guaranteed through our proposed mechanism.

第一章 導論 1
1.1 研究動機 1
1.2 研究方向與方法 1
1.3 章節介紹 3
第二章 無線網路上的語音通話 4
2.1 VOIP (VOICE OVER IP) 4
2.1.1 SIP (Session Initiation Protocol) 5
2.1.2 RTP (Real-Time Transport Protocol) 6
2.2 WLAN與WIMAX 6
2.2.1 WLAN (Wireless Local Area Network) 6
2.2.2 WiMAX 7
2.3 語音通話多工的相關研究 8
2.3.1 Video Multiplexing 8
2.3.2 Voice Multiplexing 9
2.4 本論文的動態語音通話多工機制 12
第三章 MUX/DEMUX調整機制 13
3.1 在WIMAX網路上的MUX/DEMUX 13
3.2 MUX封包的HEADER設計 14
3.2.1 MUX Table欄位設計 14
3.2.2 Miniheader設計 17
3.3 動態MUX/DEMUX的調整機制 19
3.3.1 測量RTT 20
3.3.2 Multiple Buffers 23
第四章 LINUX實作與結果分析 27
4.1 LINUX平台上的實作 27
4.1.1 VoIP MUX Gateway新增的核心模組 27
4.1.2 VoIP DEMUX Gateway新增的核心模組 31
4.1.3 SIP Phone User新增的核心模組 33
4.2 實驗拓樸與環境設定 35
4.3 實驗結果與分析 38
4.3.1 實驗一：網路頻寬的節省 38
4.3.2 實驗二：PAI on WLAN 42
4.3.3 實驗三：PAI on WiMAX 44
4.3.4 實驗四：MUX/DEMUX on Burst Traffic 46
第五章 結論與未來工作的方向 48
5.1 結論 48
5.2 實作經驗 49
5.3 未來工作 50
參考文獻（REFERENCES） 51
附錄A 55
ACRONYMS 58
索引 (INDEX) 59

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[38] Speex - http://www.speex.org/

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