P 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 compromise 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 self-configuring, 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 DHT-based P2P. While centering on the issue of routing enhancement, the aut无忧论文 【http://www.uklunwen.com】hor has conducted an in-depth research on how to extract topology information and how to utilize that information to construct topology-aware 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 wide-area file-sharing 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 |
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论文题目：
基于DHT的P2P研究 
