在MANET中以負載平衡為基礎的路由協定研究

Mobile Ad hoc Network (MANET) 是由許多具有移動與無線通訊能力的節點所組成，不需無線通訊的基礎建設即可隨意組成網路。而Ad hoc On-demand Distance Vector (AODV)路由協定為目前最熱門的MANET路由協定之一，其優點是能適應高節點密度與重負載的網路環境。不過AODV挑選路徑的標準是考量來源節點到目的節點的最短距離，也就是路徑的最少跳躍數。這種方法所選擇的路徑容易集中在網路中央區域，使網路中央區域的節點必須承擔大部分的負載，增加節點之間的通道競爭，造成網路擁塞。在這種情況下，隨著網路的節點密度與負載越來越高，通道競爭也越來越激烈，網路的效能會劇烈地下降。除此之外，AODV在路徑搜尋程序中產生的控制封包，造成網路多餘的負載，也是造成網路擁塞的主因之一。針對這兩個議題，本論文分別提出Bandwidth-aware AODV (B-AODV)與p-persistent AODV (p-AODV)兩種以負載平衡為基礎的方法來改善AODV。在B-AODV中，每個節點會使用CCA機制估測頻寬利用率，利用指數權重移動平均(EWMA)來消弭偶發性封包氾濫的影響，然後根據不同的頻寬利用率給予不同的權重。當來源節點有資料要傳送時，B-AODV會利用RREQ封包來收集路徑中每個節點的權重資訊，而目的節點收到RREQ封包後，會選擇權重最低，也就是負載最低的路徑回傳RREP封包。在p-AODV中，利用調整RREQ封包轉送機率的方法，減少RREQ封包在路徑搜尋時不必要的氾濫，可以有效解決網路廣播封包過多的問題。本論文的模擬結果顯示，B-AODV 與p-AODV分別在重負載與高節點密度的環境下，充分利用網路頻寬，可以有效改善AODV，增加網路的效能。

關鍵字

路由協定； MANET ； p-AODV ；負載平衡； AODV ； B-AODV

並列摘要

Mobile Ad hoc NETwork (MANET) is a collocation of wireless mobile nodes (MNs) that communicate with each other without fixed infrastructure. Ad hoc On-demand Distance Vector routing protocol (AODV) is one of the most popular MANET routing protocols, it can adapt to the network with high node density and high traffic load. However, AODV chooses the shortest path from the source to the destination for data transportation, this method leads paths to be placed in the central area of the network. Some nodes, therefore, carry traffic more than others and it causes the network congestion. AODV also produces a lot of overhead and causes the capacity of MANET to be overrun by these overhead. In order to solve these two problems, this thesis proposes two schemes called Bandwidth-aware AODV (B-AODV) and p-persistent AODV (p-AODV) to improve AODV. B-AODV estimates available bandwidth by the function on Channel Clear Assessment (CCA) which is supported by PHY and then chooses a path with maximum available bandwidth. p-AODV adjusts the forwarding probability of RREQ to reduce unnecessary overhead. The result of the simulation shows that B-AODV and p-AODV improve AODV, they efficiently utilize the network capacity and enhance the performance.

並列關鍵字

p-AODV ； MANET ； Routing Protocol ； AODV ； Load-balance ； B-AODV

參考文獻

[1]. R. Ramanathan and J. Redi, “A Brief Overview of Ad Hoc Networks: Challenges and. Directions,” IEEE Commun. Mag., vol. 40, no. 5, May. 2002, pp. 20-22.

[2]. C. E. Perkins, E. M. Royer, S. R. Das, and M. K. Marina, “Performance comparison of Two On-Demand Routing Protocols for Ad Hoc Networks,” IEEE Personal Communications, vol. 8, no. 1, Feb. 2001, pp.16-28.

[5]. D. Johnson, Y. Hu and D. Maltz, “The Dynamic Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4,” RFC4728.

[8]. M. R. Pearlman, Z. J. Haas, P. Sholander, and S. S. Tabrizi, “On the impact of alternate path routing for load balancing in mobile ad hoc networks,” in proc. 2000 First Annual Workshop on Mobile and Ad Hoc Networking and Computing, 2000 MobiHOC, Boston, Massachusetts, USA, Aug. 2000, pp. 3 – 10.

[9]. Y. Ganjali and A. Keshavarzian, “Load balancing in ad hoc networks: Single-path routing vs. multi-path routing,” in proc. IEEE infocom 2004, Hong Kong, March 7-11, 2004, pp.352-355.

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在MANET中以負載平衡為基礎的路由協定研究

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