網路多媒體服務應用在最近已經越來越受到歡迎，許多服務甚至已成為我們生活中不可或缺的一部分，例如線上遊戲、網路電視、影像電話等等。在這些服務中，影像傳輸品質會直接影響到應用服務的品質，尤其是在即時多媒體服務上，很容易受到端點與端點間的延遲、抖動、訊框錯誤和封包遺失等影響，進而產生延遲或中斷的情形。
無線網路的種類繁多，從IEEE 802家族到UMTS網路，甚至是3GPP LTE，無不增強其網路對多媒體影音傳輸的服務能力。因此使用者或應用程式會透過訊號強度、價錢、服務品質和網路涵蓋範圍等來選擇最佳的網路傳輸影像。當一個可以移動的傳輸設備移動時，可能會面臨到經常換手的情況。而為了解決異質網路換手過程中產生的各種問題，IEEE組織提出了IEEE 802.21標準。IEEE 802.21定義了一個中介層函式來讓換手過程更加順利，而該中介層被稱作Media Independent Handover (MIH) function。
當一個移動節點試圖要換手進入另外的網路當中，多媒體串流必定會被中斷直到新的連線已經被建立到新的網路連結點。在換手的過程中，資料連結層的連線過程可能會花費最多的時間。在本研究當中，本文提出一套新的緩衝區管理方式，儲存足夠的影像封包來讓影像串流能夠在換手時維持播放，透過這套新的方法，多媒體服務就能夠在異質網路間達成無縫式換手。
為了讓緩衝區能夠應用在各種應用程式的換手過程中，本文提出將緩衝區建置在MIH層中，並且透過Service Specific Layer (SSL)層讓MIH層可以和上層的應用程式溝通，因此MIH就可以針對不同的應用程式有不同的緩衝區管理機制。之後本文提出了完整的影像緩衝區管理機制來解決異質網路換手的問題。本文首先闡述異質網路換手的流程，並且以frame-based觀點來討論影像傳輸遭遇換手會產生的影響。最後本文討論了如何動態調整緩衝區上下限以降低換手時影像停止的機率。
隨著通訊技術的迅速蓬勃發展，透過手機、PDA等產品無線上網的機率大增，網路換手也隨之難以避免。而透過網路傳輸的各項影音串流服務也有越來越多的趨勢，尤其數據也顯示目前網路上的影音封包數量，已經成為網路傳輸的最大宗。因此本研究提供減少異質網路換手對影音傳輸影響的方法，將可使多媒體影像品質有所提升。

The Internet multimedia applications are more and more popular at the present age. A lot of applications become parts of our life such as online game, network TV, video phone and etc. In these services, the network transmission arrive rate will affect the video streaming quality directly. Multimedia service will be delayed or interrupted by end-to-end time delay, jitter, frame error, and packet loss. However, these facts would also happen during handover.
There are many kinds of wireless, from IEEE 802 families to UMTS network, even more 3GPP LTE. These networks enhance the ability of multimedia services as good as possible. The user or application will choose the best network from signal strength, price, QoS, network coverage, and so on. When the mobile device moves, the handover between different networks will happen frequently. In order to perform seamless handover between heterogeneous wireless network, IEEE group propose the IEEE 802.21 standard. IEEE 802.21 defines a middleware function to make handover smoothly, which is called Media Independent Handover (MIH) function.
When a mobile host (MH) tries to handover into another network, the media streaming must be interrupted until the new connection is established to new point-of-attachment (POA) or base station (BS). We propose a novel buffer management and frame rate control to provide enough frame packets for streaming. By this method, the multimedia service can make handover seamlessly between heterogeneous wireless networks.
In order to satisfy all application during handover, we add a buffer in MIH. We also use Service Specific Layer (SSL) to bridge the MIH and Upper applications. Therefore, the different applications can fit different buffer management mechanism according MIH. Then we expound the procedure of heterogeneous handover, and talk about the effect of video transmission during handover in frame-based viewpoint. Finally, we discuss how to dynamically adjust buffer to reduce the probability of video disruption.
With the development of communication technology, we can use mobile phone and PDA to access internet. Therefore, network handover is hard to avoid. Multimedia streaming services by network transmitting are also growing fast. Video and audio data have become the most data in network packets. This research gives a solution to reduce influence of handover between heterogeneous networks, especially in streaming transmission. By this method, the quality of streaming service will be better.

目錄
第一章  緒論	- 1 -
1.1	前言	- 1 -
1.2	動機與目的	- 2 -
1.3	論文章節架構	- 4 -
第二章  異質網路換手的相關研究	- 6 -
2.1	異質網路間的換手	- 6 -
2.1.1	換手的種類	- 7 -
2.1.2	換手的相關技術	- 8 -
2.1.3	異質網路換手的挑戰	- 9 -
2.2	IEEE 802.21 MIH架構	- 10 -
2.2.1	Service Access Point服務存取點	- 12 -
2.2.2	MIH的三種服務	- 14 -
2.3	異質網路的換手流程	- 21 -
2.4	Service Specific Layer服務決策層	- 25 -
第三章  群播影像傳輸與緩衝區管理技術	- 28 -
3.1	群播的特性	- 28 -
3.2	影像串流服務的緩衝區管理機制	- 29 -
3.2.1	根據緩衝區限制調整傳輸速率	- 30 -
3.2.2	針對換手的影像緩衝區管理機制	- 31 -
3.3	緩衝區下限	- 32 -
3.4	緩衝區上限	- 33 -
第四章  換手時動態調整群播的畫面更新率	- 35 -
4.1	MIH架構整合畫面更新率調整機制	- 37 -
4.2	影像存量計算與換手時間預測	- 39 -
4.2.1	影像存量計算	- 39 -
4.2.2	換手時間預測	- 41 -
4.3	畫面更新率動態調整機制	- 41 -
4.3.1	不調整畫面更新率	- 44 -
4.3.2	漸進式調整畫面更新率	- 46 -
4.3.3	直線式調整畫面更新率	- 50 -
4.3.4	恢復畫面更新率	- 52 -
4.4	群播對影像傳輸換手的影響	- 56 -
第五章  模擬環境及模擬結果分析	- 60 -
5.1	模擬環境架構	- 60 -
5.2	三種畫面更新率調整機制比較	- 61 -
5.3	恢復畫面更新率比較	- 66 -
5.4	群播畫面更新率調整與換手時間比較	- 68 -
5.5	三種調整機制的特性	- 70 -
第六章  結論與未來展望	- 72 -
參考文獻	- 74 -

圖目錄
圖2.1 換手交遞示意圖	- 6 -
圖2.2 SAP示意圖	- 13 -
圖2.3 MIH Function基本架構圖	- 15 -
圖2.4 Remote MIH示意圖	- 21 -
圖2.5 異質網路換手流程圖(以802.11與802.16為例)	- 22 -
圖2.6 802.11換手至802.16的訊息交握過程	- 25 -
圖2.7 SSL元件架構圖	- 27 -
圖3.1 群播概念圖	- 29 -
圖3.2 影像傳輸率最佳化	- 31 -
圖3.3 換手的緩衝區狀態	- 32 -
圖4.1 改良的SSL元件架構圖	- 37 -
圖4.2 換手時影像存量與緩衝區上下限的關係	- 40 -
圖4.3 調整畫面更新率的範例	- 42 -
圖4.4 不調整畫面更新率	- 45 -
圖4.5 不調整畫面更新率的變化量	- 46 -
圖4.6 漸進式調整畫面更新率	- 49 -
圖4.7 漸進式調整畫面更新率的變化量	- 50 -
圖4.8 直線式調整畫面更新率	- 51 -
圖4.9 直線式調整畫面更新率的變化量	- 52 -
圖4.10 恢復畫面更新率	- 55 -
圖4.11 恢復畫面更新率的變化量	- 56 -
圖4.12 群播換手使用畫面更新率調整機制	- 58 -
圖4.13 群播換手示意圖	- 59 -
圖5.1 模擬網路架構圖	- 60 -
圖5.2 Tend = 45，三種機制的畫面更新率比較	- 62 -
圖5.3 Tend = 45，三種機制的畫面存量比較	- 63 -
圖5.4 FO = 10，三種機制的延長播放時間比較	- 64 -
圖5.5 漸進式機制的延長播放時間比較	- 65 -
圖5.6 漸進式機制的畫面存量比較	- 65 -
圖5.7 恢復機制的所需時間比較	- 66 -
圖5.8 恢復機制的畫面存量比較	- 67 -
圖5.9 群播時的畫面更新率和換手時間比較	- 69 -
圖5.10 群播時的畫面存量比較	- 70 -

表目錄
表2.1 MIES Link Event	- 16 -
表2.2 MIES MIH Event	- 17 -
表2.3 MICS MIH Command	- 18 -
表2.4 MICS Link Command	- 19 -
表5.1 三種調整機制的比較	- 71 -

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