在傳統無線網路的運作方式中，行動裝置必須先找尋最近的熱點(Hop Spot)位置，並與基地台完成連線後，才得以和其他裝置進行資訊交換。然而由於熱點的涵蓋範圍有限，行動裝置並非無時無刻都可享受無線技術所帶來的便利，於是行動隨意網路便油然而生。行動隨意網路最大之特點，在於運作時不必事先佈建基礎建設，行動裝置便可透過彼此間存在的連線，順利達成資訊交流。而現行眾多的無線傳輸技術中，普遍用於取代有線電纜的藍芽技術，由於其成本低、功率低、體積小，故非常適合作為行動隨意網路中節點傳送資訊的媒介。 本研究之目的是為在藍芽Scatternet上設計一套可有效運作的P2P檔案分享機制。為了加快資料取得所需要的時間，避免每次欲獲取檔案前，都需以廣播方式查詢網路中擁有該份檔案的節點為何，藍芽網路內應由某些節點負責記錄其他節點擁有何項資料的記錄清單。在此概念下，本研究利用Master與Slave進行週期性輪詢時可能產生的閒置頻寬，設計由各Master負責記載所管轄的Piconet內所有的Slave，以及相鄰的Piconet，願意分享的資料，以縮短取得資料時的搜尋時間。一旦節點欲取得特定的資料檔案，從資料要求封包如何發送，資料封包如何回傳，乃至資料要求發生逾時時該如何處理，本研究亦提出一完整的運作方法。 由於現行藍芽技術的連線機制，可能會產生不必要的Piconet，而造成封包於傳輸上的延遲；當節點不斷於場景中進行移動後，連線路徑可能出現暫時或永久性的分離，導致資料要求發生失敗。本研究亦提出了續傳機制、拓撲最佳化及封包繞路機制，來因應上述各種不利於P2P檔案分享運行的問題。根據模擬實驗之結果，改良後的運作模式都可有效提升資料取得的成功機率。 In traditional wireless networks, a mobile device must search the nearest hot spot to access the internet. A mobile device can exchange data with other devices after connecting with the base station. However, due to the limited coverage of hot spot, it’s difficult for the mobile devices to connect to the wireless network anytime in need. MANET is a mechanism to deal with these issues. The most important feature of MANET is that it does not require any infrastructure. Two near mobile devices can communicate with each other through the connection between them. Thanks to the characteristics of low cost, low power and small volume, Bluetooth is a suitable wireless technology to construct MANET. The objective of this study is to propose an efficient P2P file sharing mechanism on Bluetooth scatternet. To shorten the file seek time and reduce opportunity of broadcasting query to the whole network, some devices should be responsible for maintain file list. The list records information about sharing files in other devices. With this concept, this study takes advantages of the possible bandwidth idle during the periodic polling between Master and Slave. Each Master would maintain file list about all sharing files in internal piconet and all neighbor piconets. Besides, this study also deals with these issues: (1) How to issue and forward the request packet to data owner? (2) How to return data packets? (3) How to handle the exception if response time is up? Additionally, in the current Bluetooth standards, unnecessary piconets may be constructed. The temporary or permanent disconnection may occur when nodes move frequently. These problems may result in delay or failure of the requested data transmission. To deal with these issues, the mechanisms of resume transmission, topology optimization and packet bypass are also proposed in this study. According to the simulation result, the improved operation models can lead higher success rate.
