| 摘要: | 無線通訊技術的進步，讓無線接取網路的頻寬日漸增大，過去一般的資料傳輸服務已無法滿足使用者需求，即時性的多媒體影音語音服務已成為下一代的應用服務的主流。但在一般多媒體的群播的應用中，視訊編碼器很難同時針對異質性用戶之不同需求(頻寬、畫面大小、畫面速率)，讓音視訊內容能因網路傳輸特性及因行動載具的不同，而進行視訊內容之動態調適。因此，研究動態地調整網路傳輸參數及轉換視訊內容，使得在變動之異質性環境中，視訊傳輸能夠保持順暢、低延遲及高畫質，讓使用者能方便地使用多樣化之視訊應用，是現今網路技術快速發展下應被深入探討與研究的議題。另外，在移動式的網路環境之下，如何在不同的網域間進行換手也是重要的議題。除了在換手時，要顧及群播連線通道品質，封包延遲的時間外，也要考慮在異質的網路環境下，如何進行有效率的同步與溝通，讓換手能夠順利的進行，並節省網路資源。本子計畫以考量網路通道品質、網路服務品質保證的前題下，將進行異質行動網路群播連線相關議題之研究，並將透過擬似系統的設計整合相關研究成果。本子計畫預計在第一年度進行網路群播協定之研究。主要概念是透過對使用者不同服務與品質需求加以分類至不同的群組，以方便群播連線之安排，提升傳輸品質，進而節省網路頻寬等資源。此外針對不同的群組可依其對服務品質要求之不同，給予不同的優先權、及不同的編碼方式。在不同的通道環境品質下，透過此方式彈性地管理網路元件，以提高整體網路效能。除此之外，將以NS2 核心為基礎，規劃實作一共通但音視訊專用之異質網路擬似環境，透過模擬的方式作為各子計畫所開發各種演算法效能分析與參考。第二年度，將延續第一年度群播協定的演算法上，進行換手議題的相關研究。在移動式的網路環境下，網路的通道品質會因時因地而產生變化，造成音視訊的多媒體品質低落。而由於各種不同接取網路傳輸特性各不相同，因此如何選擇適當的接取網路換手也是影響品質的重要議題。除通道狀況影響品質外，換手過程中所需之安全機制認證及連線改接，所需之煩雜的控制訊息流程，也是影響換手品質的重要因素之一，尤其是在異質網路架構下，影響情況將更為嚴重。因此透過研究流程的簡化，將能有效的改良換手品質。此外，換手可能發生在異質性的網路環境下，如何在不同的網路環境下進行換手溝通，互相先協商換手的程序，也是研究的重要方向。除此之外，也將延續第一年度的擬似平台，將IEEE 802.21 的MIH(Medium Independent Handover)加入擬似系統中，提供效能模擬分析所需之環境。在本子計畫的最後(第三)年度，將把所發展的擬似平台與其他子計畫進行整合與測試。多媒體服務的品質將可透過動態調整平台上通道調變及相關參數，進行密集之性能模擬，以驗證音視訊資料在不同的網路環境下的效能。本子計畫在三年的執行期限內，將深入探討以下各議題：異質無線網路群播換手、跨服務/網路層的網路管理與控制技術、異質網路QoS 技術之整合等。除此之外，上述各議題之研究成果將具體反應落實在擬似系統之開發上，以支援異質無線網路上多媒體服務效能之研究。 ; The progress of wireless network technology enlarges the bandwidth of wireless access networks. The traditional data service is not satisfied in human life, the real time multimedia service has become the application trend of network environment. However, current video coding and decoding technologies can not well performed in accordance with different kinds requirements (such as bandwidth, screen size, and frame speed) in multicast applications. Therefore, in order to maintain the quality of services, such as smooth delivery and low delay, dynamic adjustment of transmission parameters and content is a quite critical issue toward the provision of various applications for users. In addition, as the channel condition of wireless network may vary from time to time, the issue of selection of appropriate access network for handover is also an important topic. It shall not only consider the quality of communication channel and delay constraint, but also the synchronization and communications between devices so that the connection can be smoothly handover. This subproject focuses on the issue of multicast multimedia services for device and content handover in mobile environment by considering the QoS guaranteed over various channel condition and access networks. The issue of multicast protocol related issues is scheduled to be studied in the first year. The users can be categorized into groups in accordance with users’ types and their Qos constraints of the receiving contents so as to efficiently utilize network resources by using priority concept. Although the channel condition may vary from time to time, properly and flexibly arrange network resources can increase overall network throughput. The NS2 will be adopted as the basic tool for the development of the emulation environment. The emulation environment will act as the common but specific environment for the performance simulation of algorithms developed by other subprojects. In the second year, the handover mechanism of multicast connections will be studied. The service quality, especially for the multimedia applications, will be decreased when the channel quality changes due to the movement of the mobile device. The selection of a proper base station or wireless access network is also a very critical issue in the heterogeneous wireless network environment. The emulation platform developed in the first year will be extended to integrate with IEEE 802.21 medium independent handover (MIH) component to support the environment for the performance study. In the third year, the developed emulation platform will be tightly integrated with other subprojects to support the integration test and system emulations. The performance of multimedia services will be exhaustively tested and verified by adaptively changing the channel condition and related parameters of the emulation platform. During the three-year research, the following topics will be deeply studied in this subproject: the handover of multicast connection in heterogeneous mobile environment, the cross service/network layers control and management, and the QoS integration technology for heterogeneous network architectures. In addition, the above researches will be fed back for the design of the emulation platform to support the performance study for applications of multimedia services over heterogeneous wireless network. ; 研究期間 9808 ~ 9907 |
