行動隨意網路是一種自組性的網路，它是由許多個行動節點組合而成的，形成一種動態的網路拓樸，每個行動節點都是行動路由器和行動用戶端，封包的傳送是藉著節點之間多點跳躍的方式傳送封包，而且不具有任何固定式基礎建設或是中央集權管理者，所以它可快速的部署完成，適合運用在緊急事故上，例如：緊急救難、軍事用途等，所使用的網路不再是只有兩點之間的溝通，而是群體的通訊，群播網路在此環境下扮演著極重要的角色。由於手持式裝置的計算能力有限，以樹狀式拓撲較佳，可是樹狀式的拓樸常因節點的移動性，使得路徑失效而降低傳送率。
本論文提出以調變式緩衝區間的主動路由維護策略，探討如何在群播行動隨意網路以樹狀式的拓樸之下，利用調變式緩衝區間維護路由，以減少移動性之影響。在需求式群播距離向量路由策略的路徑維護方面，若在一段時間內沒有接收到上游節點所傳送出來的任何封包時，節點才會發現路由已經失效，並開始啟動區域修補路由，如此被動式路由維護的方法，容易遺失封包而降低傳送率。本文提出的調變式緩衝區間的主動路由維護策略係藉由節點之間傳送訊息時，感測出對方節點的所發出訊息之信號強度，計算兩節點之間的距離和背離速度，再以背離速度來控制緩衝區間，若上游節點移動到節點的緩衝區之內，則開始啟動區域修補路由，以減少路由失效。
經由模擬結果，本文提出之調變式緩衝區間的主動路由維護策略，改善了需求式群播距離向量路由的維護策略，減少路由失效的機率、提升傳輸效率和降低傳輸封包成本。

Mobile Ad Hoc Network (MANET) is a self configuring network of nodes that consists of mobile routers and mobile users. The mobile nodes are programmed to instantly self-organize into a network topology without support from network infrastructure or centralized control. Packets are routed via multi-hop peer-to-peer protocol between nodes to transmit the data. MANETs are ideal in advanced applications such as emergency rescue operations, instant urban wireless coverage, temporary social event networks, and military digitized battlefields. In such events, nodes are expected to collaborate and communicate as a group rather than as pairs of point-to-point. The multicast characteristic of MANETs serves as a critical functionality to support these applications. Because the capability of each mobile device is limited, the tree-based topology of multicast network delivers better performance. However, the mobility of mobile nodes often break links in the tree-based topology which cause lower data packet ratio.
In this paper, we propose “Pro-active Route Maintenance with Adaptive Buffer Zone” to reduce link breakage for the tree-based topology of multicast network in MANET. The Multicast Ad hoc On-demand Distance Vector (MAODV) method of route maintenance detects link breakage when the node does not receive any packets from the upstream node after certain time. This kind of re-active route maintenance does not initiate local tree repair until the node loses packets and reduces data packet delivery ratio. This paper proposes adding a link breakage prediction algorithm to the MAODV. The node would use signal power strength from the received packets to compute the distance and the deviating speed of the upstream node. The deviating speed of upstream node is used to compute the range of the buffer zone. When the upstream node enters the buffer zone, the node initiates local tree repair to reduce potential route failure.
According to the simulation results, the usage of Pro-active Route Maintenance with Adaptive Buffer Zone in MAODV improves the route maintenance of the MAODV. We analyze the six strategies with six matrices. Experiments demonstrate that adding link breakage prediction to the MAODV can increase data packet delivery ratio and reduce control overhead cost.

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