Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/6610
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dc.contributor.advisor廖俊睿zh_TW
dc.contributor.advisorJan-Ray Liaoen_US
dc.contributor.author黃柏承zh_TW
dc.contributor.authorHuang, Bo-Chengen_US
dc.date2005zh_TW
dc.date.accessioned2014-06-06T06:38:36Z-
dc.date.available2014-06-06T06:38:36Z-
dc.identifier.urihttp://hdl.handle.net/11455/6610-
dc.description.abstract802.11無線區域網路可大致分為無基礎架構網路與有基礎架構網路,無基礎架構網路指的是基本服務區內沒有擷取點與其他的區域網路聯結,反之則為有基礎架構的網路。在802.11無線區域網路中的工作站必須經由802.11 媒介存取控制協定來取得無線傳輸媒介的傳送權以傳送資料,802.11 媒介存取控制協定包含有分散式協調機制與集中式協調機制。分散式協調機制就是載波感測多重存取及衝撞避免機制,工作站必須感測傳輸媒介閒置了一段特定時間後才能傳送資料,每個工作站都有相同的機會競爭到傳輸媒介的傳送權。而集中式協調機制則是由一個稱為集中協調者的裝置經由輪詢的方式決定那個工作站何時有權利傳送資料。 集中式協調機制提供工作站傳送有時限性的資料,但是802.11的集中式協調機制在傳送路徑上並非最佳,多餘的封包轉傳使得整體效能大幅下降。所以我們使用名為直接集中式協調機制的方法去除不必要的封包轉傳,如此可以使得集中式協調機制的效能獲得顯著的改善。我們利用NS2實際的模擬來比較直接集中式協調機制與集中式協調機制的效能差異。zh_TW
dc.description.abstractThe IEEE 802.11 Wireless Local Area Network (WLAN) specification defines two ways to configure a wireless network: ad-hoc mode and infrastructure mode. Ad-hoc networks do not connect to other LAN's wireless stations while infrastructure networks have an access point connecting to other networks. Wireless stations in IEEE 802.11 WLAN should use IEEE 802.11 Medium Access Control (MAC) protocol to access wireless medium to transfer data. IEEE 802.11 MAC protocol incorporates two access methods: Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF is based on the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol. In this mode, a station must sense the medium before sending a packet. If a station(STA) finds the medium idle for a specific time, it can transmit a packet. PCF uses a Point Coordinator (PC) to determine which STA currently has the right to transmit. The operation is essentially that of polling, with the PC performing the role of the polling master. PCF provides STA to transmit delay-limited data. However, PCF doesn't transmit packets by the optimum path. Packets which are forwarded by non-optimal path lead to reduced performance. We use a mechanism called Direct Point Coordination Function (DPCF) that PC can choose if packet need to be forwarded or not. So, the performance will improve greatly. We use Network Simulator Version 2 (NS2) to simulate DPCF and PCF. The results show that DPCF outperforms PCF at high load conditions.en_US
dc.description.tableofcontents致謝……………………………………………………………...………….i 摘要………..……………………...…………………………………….….ii ABSTRACT..…...………………………………………………………...iv 目錄………………………………………………………………………..vi 表目錄……………………………………………………………………..ix 圖目錄………………………………………………………….………..…x 第一章 緒論……………………………………………………………….1 1.1動機與目的………………………………………………………….1 1.2 論文架構……………………………………………………………3 第二章 802.11無線區域網路架構………………………………………..4 2.1 無線區域網路硬體架構……………………………………………8 2.2 無線區域網路軟體架構…………………………………………..11 2.3 總結………………………………………………………………..16 第三章 802.11 MAC協定……………………………………………….18 3.1 分散式協調機制(DCF)…..………………………………………..19 3.1.1 訊框間隔……………………………………………………...20 3.1.2 碰撞偵測與虛擬載波偵測…………………………………...22 3.1.3 退後機制……………………………………………………...24 3.2集中式協調機制(PCF)……..……………………………………...26 3.2.1 免競爭週期的結構與時序…………………………………...27 3.2.2 PCF機制的運作程序…………………………………………30 3.2.3 PCF傳輸程序…………………………………………………32 3.2.4 輪詢名單的建立與維護……………………………………...36 3.3 總結………………………………………………………………..37 第四章 Direct PCF介紹………………………………………………..39 4.1 802.11標準的PCF在傳輸路徑上的缺點..................39 4.2 直接集中式協調機制(DPCF)…………………………………….41 4.2.1 DPCF的傳輸路徑...............................51 4.2.2 DPCF的傳輸程序...............................42 4.2.3 PCF與DPCF傳輸程序的比較.......................43 4.2.4 DPCF的使用時機...............................47 4.3 總結………………………………………………………………..50 第五章 DPCF與PCF模擬結果比較…………...………………………51 5.1 模擬平台介紹……………………………………………………..51 5.2 模擬結果與討論…………………………………………………..52 5.2.1 模擬拓樸……….……………………………………………...52 5.2.2 DPCF和PCF在傳輸CBR資料上的表現..………………...53 5.2.3 模擬結果討論….……………………………………………..59 5.3 總結………………………………………………………………..61 第六章 結論與未來展望………………………………………………...62 參考文獻………………………………………………………………….63zh_TW
dc.language.isoen_USzh_TW
dc.publisher電機工程學系zh_TW
dc.subjectWLANen_US
dc.subject802.11無線區域網路zh_TW
dc.subjectad-hoc networksen_US
dc.subjectmedium access controlen_US
dc.subjectpoint coordination functionen_US
dc.subjectdistributed coordination functionen_US
dc.subjectinfrastructure networksen_US
dc.subject無基礎架構網路zh_TW
dc.subject集中式協調機制zh_TW
dc.subject分散式協調機制zh_TW
dc.subject媒介存取控制zh_TW
dc.subject有基礎架構網路zh_TW
dc.title802.11無線區域網路之直接集中式協調機制zh_TW
dc.titleDirect Point Coordination Function in 802.11 Wireless LANen_US
dc.typeThesis and Dissertationzh_TW
item.openairecristypehttp://purl.org/coar/resource_type/c_18cf-
item.openairetypeThesis and Dissertation-
item.cerifentitytypePublications-
item.fulltextno fulltext-
item.languageiso639-1en_US-
item.grantfulltextnone-
Appears in Collections:電機工程學系所
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