檔案分享是大多數應用程式最基本也最常用到的功能操作。近年來，人們對於檔案分享的議題研究已經從有線網路轉移到無線行動隨意網路﹝MANETs﹞上頭。在此種網路環境下，使用者可以任意自由的在任何時間、任意地點建構出無基礎建設的無線網路。然而，要在高封包遺失率的MANET環境中完成可靠檔案廣播不是一件容易的事。我們著重在研究可靠檔案廣播議題，並且收集許多關於如何增進可靠廣播效能的文獻，最終發現大多數的人解決此問題是朝向設計新的路由協定﹝routing protocols﹞或改善媒體存取控制層﹝MAC-layer﹞、傳輸層﹝Transport-layer﹞的功能方向走。我們認為要完成可靠檔案廣播最基本的方法就是使用像肯定應答﹝ACK﹞或否定應答﹝NACK﹞的控制封包。在此篇論文中，我們研究NACK封包在MANET環境中對可靠檔案廣播所造成的影響。我們列出七種使用NACK封包的方式：其中兩種的目的在增加NACK封包的有效性﹝S1, S2﹞，有一種的目的在減少網路內封包的數量﹝S3﹞，有三種的目的在減少重傳封包的數量﹝S4, R1, R2﹞，最後一種的目的在減少NACK封包的數量﹝R3﹞。模擬結果顯示每一種方法都有它們對可靠檔案廣播獨特的影響，而且對於上述七種不同的方法，不同的組合使用也有不一樣的效能結果。網路的頻寬消耗並不如我們在模擬前所預期的那麼和平均完成時間有相關性。

File sharing is a basic and popular operation of most applications. Recent years, people have study file sharing issues from wired network to wireless Mobile Ad Hoc networks (MANETs). In which, users can construct the network by them self in an infrastructure-less, any time, any where manner. However, it is not easy to finish a reliable file transmission under such inefficient wireless network condition that have high packet loss rate. We focus on the study of reliable file broadcasting and survey several topics about how to improve the performance of reliable broadcasting, finally we find that people almost solve this problem by designing routing protocols or enhanced MAC-layer, Transport-layer functionality. We think the basic solution to finish reliable file broadcasting is to use control messages like Acknowledge (ACK) or Negative Acknowledge (NACK). In this thesis, we study the effects of NACK packets on reliable file broadcasting in MANETs. We set up seven approaches to use NACK packets: Two are aim at increase the NACK validity (S1, S2), one is aim at reducing packets number in the network (S3), three are aim at reducing the requested packets (S4, R1, R2), and last one is aim at reducing the numbers of NACK packets (R3). The simulations show that each approach has its own special effects on reliable file broadcasting, and different combinations of above seven approaches also have diverse performance results. The bandwidth consumption is not related to average finish time so closely as our imagination before simulation results carries out.

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