臨機網路中基於Erasure Coding之路由與資料傳輸

Abstract

隨著無線科技的發展與普及，許多超越以往有線網路能力所及的挑戰，在近幾年紛紛浮現出來。雖然無線網路擴展了Internet的服務，它們還是有許多限制。具體地說，在傳送資料前，發送端與接收端之間必須存在至少一條完整路徑，否則傳統的路由方法會宣告失敗。但在很多情況之下，這樣的限制是很難符合的。在臨機網路中，點跟點之間會間歇性且臨機性地作連結。在這種網路下，排程式或預測式的路由方法將很難被應用。如果能解決這些的問題，我們將可以大大地擴展無線資料網路的功能。 在這篇論文中，我們提出了一個有效的路由方法，稱作H-EC。它是個結合erasure coding和複製的傳送方法。H-EC比先前的方法在較小延遲的成績上更進步，同時也保留了其在最糟延遲下的傑出表現。我們也提出了在H-EC上的三種排程演算法，並比較其表現成果。從模擬結果我們發現，即使在臨機網路上傳送資料非常困難，我們提出的方法仍然可使其具有實用性。在了解到要完整的傳送資料非常困難後，我們更進一步將Layered Multiple Description Coding應用到臨機網路上作影片檔案的傳輸，以期許能讓終點端的使用者能讀取未完 成的檔案。利用基於LMDC的方法，終點端的使用者可在尚未接收完資料前'預覽'影片檔。此外，基於LMDC的方法還能降低每張畫面間品質的差異。

With the development and popularity of wireless technologies, many challenges beyond the capability of wired networks have been emerging in recent years. Although wireless data networks extend the service of Internet, they still have many constraints. Specifically, at least one complete path between the source and the destination pair should be found before transferring data. But in many scenarios, this constraint is hard to conform. In opportunistic networks, nodes connect to each other intermittently and opportunistically. Neither scheduled routing nor predicted routing can be utilized in such networks. If we can deal with these problems, we can greatly extend the utility of wireless data networks. In this thesis, we propose an efficient routing approach called H-EC. It is a hybrid forwarding scheme based on erasure coding and replication methods. H-EC improves the performance of previous works in small delay performance cases while still keep excellent results in worst delay performance cases. We also propose three message scheduling algorithms of H-EC and compare their different performances. From simulation results, we find that although transferring data in opportunistic networks is difficult, our proposed approaches make it practical. Being conscious that successful delivery is very hard, we further apply Layered Multiple Description Coding (LMDC) for transferring video file in opportunistic networks in order to let end users can read incomplete video file. By LMDC based schemes, end users can 'preview' the video before completely receiving data. Moreover, LMDC based schemes decline the heavy variance in per frame quality.