【正文】 □ 不及格三、論文（設(shè)計）水平論文（設(shè)計）的理論意義或?qū)鉀Q實際問題的指導(dǎo)意義□ 優(yōu) □ 良 □ 中 □ 及格 □ 不及格論文的觀念是否有新意？設(shè)計是否有創(chuàng)意？□ 優(yōu) □ 良 □ 中 □ 及格 □ 不及格論文（設(shè)計說明書）所體現(xiàn)的整體水平□ 優(yōu) □ 良 □ 中 □ 及格 □ 不及格評定成績：□ 優(yōu) □ 良 □ 中 □ 及格 □ 不及格（在所選等級前的□內(nèi)畫“√”）教研室主任（或答辯小組組長）： （簽名）年 月 日教學(xué)系意見：系主任： （簽名）年 月 日摘要隨著個人計算機性能的提高和互連網(wǎng)用戶的急劇增長，在網(wǎng)絡(luò)邊緣出現(xiàn)了大量的閑散計算和存儲資源，而網(wǎng)絡(luò)帶寬的大幅提高也使得開發(fā)和利用這些潛在的計算資源成為可能。在大規(guī)模的P2P系統(tǒng)中，如何高效地查找到指定的數(shù)據(jù)是一個非常關(guān)鍵的問題。為了解決P2P系統(tǒng)中可擴展的數(shù)據(jù)檢索問題，國際上幾個研究小組獨立地提出了Chord、CAN、Pastry和Tapestry等基于DHT的結(jié)構(gòu)化P2P系統(tǒng)。但是目前DHT還面臨許多問題，最大的問題之一就是DHT在初始設(shè)計時忽略了參與節(jié)點在物理網(wǎng)絡(luò)上的鄰近性，導(dǎo)致重疊網(wǎng)絡(luò)和物理網(wǎng)絡(luò)脫節(jié)，即DHT未能充分利用底層物理網(wǎng)絡(luò)的拓撲信息，從而造成實際的尋路效率低下。DHT具有廣闊的應(yīng)用前景，國際上許多著名的研究機構(gòu)都在開展基于DHT的大規(guī)模P2P系統(tǒng)研制工作。本文的主要工作和創(chuàng)新點如下：1. 提出了從IPv6地址前綴中提取節(jié)點位置信息的方法。我們創(chuàng)造性的提出節(jié)點標(biāo)識符可以分段構(gòu)造，標(biāo)識符的前綴可以通過哈希同一個域中節(jié)點共同的位置信息得到，從而使得物理網(wǎng)絡(luò)上臨近的節(jié)點在重疊網(wǎng)絡(luò)上也互為近鄰。本文創(chuàng)新性的提出把節(jié)點的位置信息也存儲到DHT系統(tǒng)中，新加入的節(jié)點可以通過DHT查詢到具有相同位置信息的全部節(jié)點列表，從而在物理網(wǎng)絡(luò)上臨近的節(jié)點之間構(gòu)造內(nèi)嵌于全局DHT中的本地DHT。仿真的結(jié)果證明該方案的有效性。關(guān)鍵字：P2P，DHT，Chord，查找，尋路，IPv6，拓撲，層次化，文件共享５７中國科學(xué)技術(shù)大學(xué)碩士學(xué)位論文 AbstractAbstractWith the great improvement of PC performance and the fast growth of Internet users, there emerges a vast quantity of puting and storage resources on the Internet edge. P2P (peertopeer) technology can be an effective means to harness these resources, which accounts for the fact that P2P applications are being more and more popular these days. In a P2P system, all peers are identical regarding functionality. Unlike the traditional C/S (client/server) model, there are no dedicated servers and peers can directly municate with each other for data transmission. P2P can solve the problems of single point failure and performance bottle encountered by C/S model. A fundamental problem that confronts a largescale P2P system is the efficient location of the node that stores the desired date item. However, the first generation of P2P systems did not address the problem well. Napster has a centralized index server where scalability can be limited by the machine power and the network bandwidth of the central point. Gnutella employs a messaging mechanism that is based on flooding, which can impose heavy burden on networks and thus promise its scalability. To address the problem, several research groups independently proposed DHT (distributed hash table) systems, which include Chord, CAN, Pastry and Tapestry. DHTs reorganize peers into an overlay in the application level, distribute file indexes into the network, and route queries through the overlay. DHTs are robust in the face of failures, attacks and unexpectedly high loads. They are scalable, achieving large system sizes without incurring undue overhead. They are selfconfiguring, automatically incorporating new nodes without manual intervention or oversight. They provide a simple and flexible interface and are simultaneously usable by many applications.However, DHTs are still faced with many problems, one of which is the fact that most DHTs do not take into account physical network topology in their original design, thus resulting in high routing latency and low efficiency. Therefore, to improve routing performance is an important direction for research on DHTbased P2P. While centering on the issue of routing enhancement, the author has conducted an indepth research on how to extract topology information and how to utilize that information to construct topologyaware DHT systems. In Chapter 3, we propose three solutions, which are called DHT with hierarchical identifiers, embedded DHT and hierarchical DHT. To illustrate our solutions, we build Chord6, eChord and hChord all upon the original Chord system. Analysis and simulation results prove that our solutions can greatly improve routing efficiency in Chord.Currently, a new generation of applications has been proposed on top of DHTs. In this paper, we also design a widearea filesharing system based on Chord6, validating the effectiveness of our research work on DHT routing enhancement. The major contributions of this paper are listed as follows:1. Propose a novel method to extract topology information from IPv6 address prefixes. We notice that IPv6 addresses are assigned in a hierarchical way so that nodes with the same prefix are in the same autonomous domain. Therefore peers in a DHT system can learn their location information from their own IPv6 addresses.2. Devise a smart scheme to exploit the IPv6 address hierarchical feature, so as to construct an efficient version of Chord dubbed Chord6. We propose that node identifiers can be divided into several parts and thus be produced separately. For a node identifier divided into two parts, the higher bits can be obtained by hashing the shared address prefix among all nodes within the same AS, and the lower bits are the hash result of the rest of the IPv6 address. As a result, topologically close peers shall also be adjacent in the overlay. An important advantage of our scheme is that it is very simple and barely modifies the original Chord. Simulation results have shown that our method can significantly reduce interdomain traffic that causes the long routing latency.3. Devise a novel scheme to construct embedded DHT, which can not only improve the routing efficiency, but also inherit the loadbalancing feature of the original DHT. First, nodes independently insert their location information into DHT systems as they do with file indexes. Then, a newly joined node can utilize DHT to get a plete list of all nodes that are close to it in the underlying physical networks. Finally, nodes within the same domains are organized into many local DHTs which are then embedded into a global DHT prised of all nodes. Thus, routing can be conducted in local DHTs first, and pass through each other (if necessary) with the aid of the global DHT, which means that interdomain traffic can be minimized to the extreme. To illustrate the feasibility and effectiveness of the s