隨著無線網狀網路的快速發展與大量佈建，應用於無線網狀網路服務的傳輸需求也越來越大。然而無線網狀網路(Wireless Mesh Network)容易受到網路壅塞而導致無法提供有效的連線品質，因此網路連線的強韌性已成為非常重要的議題。對於傳統TCP而言，壅塞控制機制大多是採用單層最佳化或底層對上層的連線通告方式，因此其運作在無線網狀網路上時，TCP流率調節容易因為往返時間的增加而延遲，造成傳輸效率不佳。而對於媒體存取層，逐跳(Hop-by-Hop)壅塞控制法不但有通道偵測問題，監控流量所造成的負擔也不容小覷。
有鑑於此，本篇論文提出一種跨層式的替代路徑建立機制來解決連線壅塞問題，我們稱之為"基於替代性路徑之吞吐量調節器"。此機制主要減緩流率的調節與減免太多的底層監控負擔，以強韌端點對端點的TCP連線品質。此機制主要由三種元件組成:基於領域建立法之多路徑路由、應用流量估測之壅塞偵測法與替代路徑切換法。藉由所取得的領域建立法之多路徑路由機制，我們可以找出多條可替代路徑以供其一路徑壅塞時之切換，再利用壅塞偵測法判斷壅塞的發生與替代路徑的切換時機，最後用替代路徑法在路徑發生壅塞時做路徑切換以增加連線強韌性並保持連線品質。
最後，我們設計了網格與隨機拓樸的無線網狀網路環境來驗證此機制的效能。經由模擬結果我們能證明此機制的正確性與可行性，相信此替代路徑建立機制將能大大增加無線網狀網路上TCP連線的強韌性，以提供無線網狀網路服務更可靠的傳輸環境。

With the rapid growth and considerable deployment of wireless mesh networks, there are high demands on the robustness of transmission quality over wireless mesh networks. However, a wireless mesh network suffers from sudden congestions due to channel instability and burst traffic, so that it is arduous to support quality connection. Therefore, the robustness of connections has become a significant issue in wireless mesh networks. The congestion control of traditional TCP connections is only focused on single-layer optimization or supported by lower-layer to upper-layer notifications. For instance, a congestion detected by TCP layer cannot change the route configuration managed by MAC layer in a mesh network. Therefore, the rate reduction is the only way to mitigate congestion rather than a better path applicability of a TCP connection, which suffers from serious congestion and long round-trip-time. Moreover, the non-aggressive behavior of flow-rate adaptation also causes non-effectiveness of TCP performance. For a congestion control in wireless mesh MAC, only the channel access of the neighborhood is detectable. No end-to-end connection information is available for MAC. Besides, it is not neglected the high overhead of traffic monitoring.
We propose a cross-layer alternative-path approach to prevent the congestion problems above. The approach demonstrates good regulation performance and low overhead of traffic monitoring. The mechanism is named “Path-alternation-based throughput regulator (PATR)”, and it consists of three components: Region-established Multipath based on Radio-Metric Ad Hoc on demand Distance Vector (M-RMAODV), Rate-based Congestion Detection and Mesh Path-alternation. First, we acquire multiple paths by Region-established M-RMAODV for alternative-path choosing. Second, Rate-based Congestion Detection discovers congestion according to the estimations of flow rate and its variation. Finally, the mesh path-alternation is helpful to the robustness of TCP connections by reliable path-switching during congestion periods.
At the end, both grid and random topologies are designed to verify the correctness and feasibility of PATR. From simulation results, we are convinced that the mechanism dramatically improves the robustness of TCP connections and supplies a reliable environment for transmission in wireless mesh networks.

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