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研究生(外文):Jhao-Wei Deng
論文名稱(外文):Cost-Effective Caching for Mobility Support in IEEE 802.11 Networks
指導教授(外文):Kuang-Hui Chi
中文關鍵詞:LRU預先主動儲存快取IEEE 802.11快速換手
外文關鍵詞:LRUIEEE 802.11Fast HandoffProactive Caching
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本論文是針對IEEE 802.11無線網路工作站與基地台Access Point (AP)間快速換手,所提出的快取管理方法。目前一般的技術是預先與行動工作站Mobile Station (MS)作認證(preauthentication)或預先主動存放工作站的安全認證資料於鄰近的基地台。若工作站與目標基地台連結(reassociate)建立起連線,基地台的快取記憶體會存有與工作站完成訊息交換後所得到安全認證資訊,當下一次再次連線時基地台可以從快取記憶體中,得到這些事先保留下來的訊息,不用再執行繁複的訊息交換動作。但是快取記憶體空間為有限的,所以這些資料無法永久的被滯留於快取記憶體中。因此本論文提出一個基於Least Recently Used (LRU)策略有效管理快取記憶體的方法,我們考慮到工作站拜訪基地台的頻率;以及當工作站與基地台連線時,因基地台的快取記憶體內沒有存放連線工作站所對應的資料,而須執行完整連線訊息交換的延遲時間(latency)。而本論文所提的方法是企圖讓對整體系統效能會造成高損失的這些資訊在有限的儲存空間條件下,可以有效地留於基地台的快取記憶體中,不會在LRU置換決策下給輕易的置換掉,因此達到提升整體網路效能。
In IEEE 802.11 networks, the handoff process occurs when a station moves its association from one access point (AP) to another. Handoff involves AP discovery, authentication, reassociation establishment, and possible inter-AP transfer of physical connectivity and context like quality of service parameters or credentials specific to the mobile station. For secure context exchanges along with authentication and cryptographic key management, the IEEE 802.1X framework has been adopted as mandatory part of Robust Security Networks. Provided IEEE 802.1X transactions at a remote site, internetwork operations account for another potentially prohibitive handoff delay.
For the provisioning of fast handoff support, current schemes preauthenticate a mobile station or distribute the context of the station proactively to neighboring APs. Each target AP caches the station’s context a priori and can thus bypass IEEE 802.1X authentication if the station reassociates. We present an approach independent of any well-known schemes to improving caching effectiveness that allows for both recency information and distinct cache miss penalty indicative of authentication delay. These metrics form a means to assess the relative importance of each context among all the contending contexts. We assign longer cache lifetime (called Time-to-Live value in this text) to high-penalty contexts such that these contexts become less volatile, whereas low-penalty data shorter lifetime. In consequence, low-penalty contexts are more likely to expire and can thus make room for caching other new contexts without overriding the storage space of high penalty contexts. This enables high-penalty stations to receive fewer cache misses upon reassociations. An underlying idea is that frequent high-penalty cache misses by reassociating stations impairs the handoff process and hence should be avoided. Performance results show that our approach outperforms counterpart schemes generally by over 15%~35% in terms of handoff delays when the ratio of cache capacity to station population is small. Our development lends itself to the emerging IEEE 802.11r standard in support of fast Basic Service Set transitions.
中文摘要 i
英文摘要 ii
誌 謝 iv
目 錄 v
圖目錄 vii

第一章 緒論 1
1.1問題描述與研究動機 1
1.2本論文架構 2
第二章 背景知識 3
2.1 在無線網路中換手機制 3
2.2 IEEE 802.1X的架構 5
2.3 實體認證埠 6
2.4 IEEE 802.11網路中的EAPOL交換程序 7
2.5 預先儲存技術(Proactive caching scheme) 9
2.6 LRU頁面替換法則 11
2.7 80-20法則 13
第三章 相關參考文獻 14
3.1針對IEEE 802.11無線網路為達快速換手使用有選擇性的鄰近預先快取技 術(SNC:A Selective Neighbor Caching Scheme for Fast Handoff in IEEE 802.11 Wireless Networks) 14
3.2針對IEEE 802.1X認證機制有效利用快取技術達到快速換手(Caching Effectiveness for Fast Handoff Schemes in IEEE 802.1X Frameworks) 16
3.3在行動環境中方位察覺快取替換機制(Location-Aware Cache Replacement for Mobile Environments) 18
3.4針對代理伺服快去記憶體存取機制延伸LRU機制優先置換延遲時間短者(LRU based Small Latency First Replacement (SLFR) algorithm for the proxy cache.20
3.5在無先區域網路系統使用行動預測實現快去換手技術(Fast Handoff scheme based on mobility prediction in public wireless LAN systems) 22
第四章 方法實現 24
4.1實現應用之相關設定 26
4.2 方法(一)TTL過時者為優先替換對象 29
4.3 方法(二)TTL為該快取資料的壽命 32
第五章 效能模擬 35
5.1.1效能模擬方法(一)-FP=1/3 36
5.1.2效能模擬方法(一)-Fp=1/6 44
5.2.1效能模擬方法(二)-Fp=1/3 51
5.2.2效能模擬方法(二)-Fp=1/6 58
第六章 結論 67
參考文獻 68
作者簡歷 70
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