含行動主機之網際網路群播管理

Abstract

在本論文中，我們討論在行動計算環境中提供群播路由給行動主機之問題。在行動計算環境中，群播路由最大的挑戰在於會員的可能移動。以往的方法著重於在會員之母網路間建立一群播樹，當會員離開其母網路時，則利用行動網際網路協定通道來傳送群播訊息。然而當傳送會員和其他會員都離開其母網路時，這些方法會導致無效率地群播傳送和難以接受的群播延遲。為了解決這些缺點，我們提出一個啟發式群播路由演算法，以提供有效率地群播傳送和更小地群播延遲。其主要的觀念是將群播樹的根固定在傳送會員之母網路上，並根據接收會員所在的網路動態地調整群播樹。為了減少動態調整群播樹所產生的成本，對於哪些在網路間頻繁來回移動的會員，我們採用行動網際網路協定通道來傳送群播訊息。除此之外，在一個區域網路內，我們使用一個區域群播路由機制，這個機制只會傳送群播訊息至會員所在的基地台及其相鄰基地台而非所有的基地台。如此一來，當一個區域網路只有極少數的會員時，這個機制可以避免群播訊息充斥於區域網路內。我們發展了一個模擬模式來作效能分析，並和一個知名的動態群播路由演算法比較。模擬結果顯示當會員移動越頻繁時，我們的方法可以減少9% - 79% 加入時間和9% - 60% 傳輸延遲，而調整群播樹的額外成本低於14%。

In this thesis, we discuss the problems of providing multicast routing to mobile hosts in mobile computing environments. In such an environment, the main challenge of multicast routing is group member mobility. Previous approaches focused on setting up a multicast tree among the home networks of group members and used Mobile IP to tunnel multicast packets when any group member is away from its home network. These approaches led to inefficient multicast deliveries and unacceptable multicast latency when both of the source and other group members are not in their home networks. To overcome these drawbacks, we propose a heuristic multicast routing algorithm that aims at delivering multicast packets efficiently and reduces multicast latency. The key idea of our approach is to set up an efficient multicast tree rooted at the home network of the source and to adjust the tree according to the current locations of other group members. To reduce reconstruction overhead of the multicast tree, we eliminate the reconstruction overhead caused by frequently to-and-fro movements of group members between networks by using Mobile IP tunneling. In addition, we use a local multicast routing mechanism that only delivers multicast packets to the base stations that group members currently dwell and their surrounding base stations instead of all base stations in a local network. This can avoid flooding a local network that only has few group members. A simulation model has been developed for performance evaluation. A well known dynamic multicast routing algorithm in mobile computing environments acts as a reference to compare with our proposed heuristic multicast routing algorithm through a series of experiments. Simulation results show that our proposed method outperforms the well known method by reducing 9% - 79% join time and 9% - 60% multicast latency as mobility increases, and causes less than 14% reconstruction overhead.