行動隨意網路中合作快取之研究

無線隨意網路中，傳遞資料的內容主要分為兩大類，一種是在伺服器更新的資料，譬如天氣預報、新聞、車況、股票等等的情況，這些資料有些特性，就是普遍具有高度的熱門性，又依更新程度可以分為兩種，一種是如天氣預報以及新聞，這種熱門程度高更新情況低，一種如股票，更新較頻繁。另一類是經由伺服端認證的用戶端可以修改的資料，例如facebook等，由用戶端上傳資料給伺服器，這類的資料就不一定屬於熱門或是冷門的資料。基於2004年Yin等學者提出快取路徑與快取檔案機制， 2010年由Zhao等學者提出每次Query都必須向伺服器做認證，做出需向伺服器認證的快取檔案機制，另外2007年的GroupCache是讓每個節點能夠周期性廣播快取路徑封包，不過跟Zhao’s Method不一樣的是GroupCache會直接回傳檔案給需求的節點，因此正確性不夠，如果資料更新率增高，效能也會降低得很快。我們的方法區域性維護之合作快取機制(Regional Maintained Cooperative Cache ; RMCC)，擷取了Zhao’s Method裡強調的檔案正確性，以及GroupCache的概念，利用經伺服器確認過的回傳封包當作觸發，將快取路徑插入歡迎訊息廣播，鄰居節點收到訊息後，會紀錄發送歡迎訊息節點擁有該筆資料這條路徑，當有需要時可以經由快取路徑向鄰居節點取得。 RMCC與對比的方法相比，在命中率的部分，RMCC因為快取路徑的命中量增加，而有最好的效能，在傳輸總量的部分，，GroupCache因為命中失誤要付出的成本以及維護成本都較高所以封包量也比較多，RMCC因為維護成本比GroupCache低，且快取失誤付出的代價較小，因此整個模擬中封包總量，RMCC是優於其他方法的。經由以上的研究模擬，無線網路快取由有相同目的的一群人群聚在一起(軍方野外進行作戰或是觀光名勝地區分享旅遊導覽)，因此如果這些節點可以各自提供一塊可以互相分享的平台，對於節點電量、頻寬的利用上都能有更好的效率，尤其是鄰近伺服器的節點封包碰撞的機率也是最高，藉由我們的方法可以減低伺服器的負擔平衡整個網路的負載，更可以提高節點的續航力，對於使用者可以提供更好的無線網路的品質。

關鍵字

行動隨意網路；快取

並列摘要

Some recent studies have shown that cooperative cache can improve the system performance in ad hoc networks , mesh networks, and sensor networks. In this paper, In the mobile ad hoc network, a node can communicate with others anywhere and anytime. Cooperative caching scheme can improve the accessibility of data objects. However, the cache hit ratio is reduced and access latency becomes longer significantly due to the mobility of nodes, energy consumption in battery, and limited wireless bandwidth. In this paper, we propose a novel cooperative caching scheme called Regional Maintained Cooperative Cache (RMCC) which allows each Node and its 1-hop neighbors form a group. The caching status is exchanged and maintained when any Node received a data reply message. For a data miss in the CacheData space, each Node searches the data in its CachePath table before forwarding the request to the next node that lies along routing path towards server. We evaluate the performance of the RMCC by using NS2 and compare it with the existing schemes such as SimpleCache , GroupCache and Zhao’s method. Simulation experiments show that the RMCC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies.

並列關鍵字

MANET ； cooperative cache

參考文獻

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[3] Liangzhong Yin and Guohong Cao, “Supporting cooperative caching in ad hoc networks”, Twenty-third AnnualJoint Conference of the IEEE Computer and Communications Societies , Vol. 4, Jan. 2004, PP. 2537 – 2547.

[6] Jing Zhao, Ping Zhang, Guohong Cao and C.R. Das ,“Cooperative Caching in Wireless P2P Networks : Design, Implementation, and Evaluation”, IEEE Transactions on Parallel and Distributed Systems, Vol. 21, Issue 2, PP. 229-241, Feb. 2010.

[7] Yi-Wei Ting and Yeim-Kuan Chang , “A Novel Cooperative Caching Scheme for Wireless Ad Hoc Networks: GroupCaching”, International Conference on Networking, Architecture, and Storage, 2007. July 2007, PP. 62-68.

[8] H. Artail, H. Safa, K. Mershad, Z. Abou-Atme and N. Sulieman , “COACS: A Cooperative and Adaptive Caching System for MANETs” , IEEE Transactions on Mobile Computing, Vol. 7, Issue: 8, PP. 961-977, Aug. 2008.

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行動隨意網路中合作快取之研究

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