臺灣博碩士論文加值系統

由於能提供沒有地點限制與不需要事先建構好固定基礎結構的無線通訊，無線行動 ad hoc 網路獲得越來越多的研究注意。因為沒有任何靜態的支持架構，ad hoc 網路有易於發生連線失敗的傾向。這種傾向已變成導致在無線行動 ad hoc 網路上使用TCP協定時產量下降的嚴重因素。目前已經有許多研究顯示出在高移動性下TCP產量下降的現象，並且也指出了一個繞路協定若要提高TCP產量則須改進的地方。有些研究選擇了動態源繞路協定作為主題並且顯示出當不直接使用快取來回覆一個路徑時會有較好的結果。在這篇論文中我們介紹一種新的有效的快取管理機制，不但可以提昇當動態源繞路協定使用快取回覆路徑時的TCP產量，並且還能做到當節點本身發生失敗時快取的恢復。我們用模擬軟體在因節點移動性而容易產生連線失敗的環境下，比較我們的機制與原來動態源繞路協定的表現。我們也提供了在無線行動 ad hoc 網路上當有節點壞掉情況發生時，各種協定的模擬結果。

Mobile ad hoc networks have gained more and more research attentions by provisions of wireless communications without location limitations and pre-built fixed infrastructure. Because of the absence of any static support structure, ad hoc networks are prone to link failure. This has become the most serious cause of throughput degradations when using TCP over ad hoc networks. There have been a lot of researches that have confirmed the phenomenon of TCP throughput decrease under high mobility and indicated which aspects of a routing protocol should be modified to improve the throughput. Some of them chose Dynamic Source Routing (DSR) protocol and showed that disabling the assigning of a route directly from cache gives better performance. In this paper, we introduce an efficient cache management mechanism to increase the TCP throughput by replying with a route directly from the cache of DSR and perform the cache recovery when a host failure has occurred. We use simulations to compare the performance of our algorithm with the original DSR under the link failure prone environment due to mobility. We also provide the simulation results when host failures are considered in the ad hoc networks.

Chapter 1.Introduction ……………………………………………….1
Chapter 2.Dynamic Source Routing Protocol……………………….4
2.1 Overview……………………………………………………………………..4
2.2 Route Discovery……………………………………………………………...5
2.3 Route Maintenance…………………………………………………………...7
2.4 Full Use of the Route Cache…………………………………………………8
Chapter 3.Cache Management Problem…….……………………11
3.1 Replying a Route from the Cache…………………………………………..11
3.2 Stale Route Problem…………….…………………………………………..12
3.3 Host Failures…………………….………………………………………….13
Chapter 4. A New Cache Management Protocol for
Fault Tolerance……………………………………………14
4.1 Protocol Overview…………………………………………………………..14
4.2 CacheManagement Protocol ……………………………………………….15
4.2.1 Signal Strength…………..…………………………………………..16
4.2.2 Control Messages………..…………………………………………..17
4.2.3 Implementation Details.…………………………………………..21
4.3 Advantages and Disadvantages……………………………………………..22
4.4 Examples…………………………………………………………………..23
4.4.1 Link Failure……………...…………………………………………..23
4.4.2 Host Failure……………...…………………………………………..24
Chapter 5. Simulation Environment and Methodology ……….……27
5.1 Simulation Environment……......…………………………………………..27
5.1.1 Mobilenode: Creating Wireless Topology…………………………..28
5.1.2 Creating Node Movements…………………………………………..30
5.1.3 Network Components in a Mobilenode……………………………..31
5.1.4 DSR in Mobile Networking………………………………………..35
5.1.5 Trace Support……………………………………………………..36
5.1.6 Generation of Node-Movement and Traffic-Generation for Wireless
Scenarios……….………………………….………………………..37
5.2 Simulation Methodology……...…………………………………………..38
5.3 Implementation Details….……...…………………………………………..39
5.3.1 Program Structure…..…...…………………………………………..39
5.3.2 The Parts Need to be Modified in the Original DSR………………..41
5.3.3 Things Must be Noted...…………………………………………..43
Chapter 6. Simulation Results and Discussions ……….……….……45
6.1 Analysis of Simulation Results……………………………………………..45
6.2 Simulation with Link Failures…..…………………………………………..49
6.3 Simulation with Host Failures…..…………………………………………..53
Chapter 7. Conclusions ………………………………………….……58
References ……………………………………………………….……59

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