| With the enormous application foreground at the aspect of resource share for P2P system, it becomes one of key problems in the academic community. In P2P system, each node is both a client and a server, and all data interchange can be finished among the nodes. P2P lead network calculate mode from concentrate type inclinable to distributed type, so that the core of network application spread from central authorities server to terminal device, which always locate on the edge of network.Gnutella is a kind of complete distributed, P2P network model without rank structure, it can fit the natural characteristic that the node frequently joins and leaves in P2P network .It has character of robusticity, real-time, dependability, and balanced load. More and more software based on the Gnutella protocols had been developed. A large number of users use the such kind of software to search message, download files, and share the data in Internet. However, some kinds of problem we describe as follow have been existed in Gnutella network:1. Too many redundant messages, engulf the bandwidth. The mechanism of flooding message had been introduced into Gnutella network: This kind of messages propagating mechanism produces redundant messages which increase at the rate of index magnitudes. The statistics show, P2P software accounts for 40% — 70%of the operating bandwidth on Internet in the daytime, and sometimes can be up to 80% in the evening.2. Low search efficiency, poor scalability. In Gnutella network, search mechanism treat all nodes uniformly and the difference performance of nodes are unconsidering, it doesn't t utilize successful inquire historical experience too, which lead to low search efficiency. For the same reason of the nodes' difference performance, the network may become division because those specific nodes may have not enough CPU time block, memory and bandwidth to complete the transmitting of messages.3. Reachability question. In Gnutella network, to cope with messages diffusion unlimitedly among network, and reduce redundant, message control mechanism is introduced into Gnutella protocol. However the network heterogeneous latencies and message control mechanism lead to shortcut effect together. Shortcut effect can influence the arrival rate of messages seriously, and result in low inquiry efficiency4. Validity of the network protocol. The protocol is blood and life of the network. Any mistake and defect in the protocol can bring enormous danger to distributed system in the aspect of stability, reliability, tightness, security, fault-tolerant, and communication in different system. However, there are not relevant reports about the validity of P2P protocols, the security of these protocols, the formal specification and protocol verification to P2P protocols ,and whether P2P protocols was developed according to the demand of the project protocol.Focus on above mentioned problems, some research work in this paper, its main contribution is as follows.1. GFB: A system with message feedback mechanism, scalable P2P systemGFB is the improvement of Gia system by author. Gia system keeps terseness of Gnutella while improves the expansion performance of the network. Within any period, demands for resources are not all homogeneous. According with feature of small world and power law, author propose to duplicate the index of the content inquired successfully to some high performance nodes, because these content always prevail on the network near future. In addition we substitute mdfRM search protocol for protocol in Gia system, and achieve better flexibility and search efficiency.2. Connection management in Gnutella networkIt is a key problem that flooding broadcast messages mechanism can cause redundant messages which engulf the bandwidth. In this paper, the necessity and feasibility of discarding some connections is pointed out on the basis of analyzing Gnutella network messages broadcast mechanism, and divide of messages PRI is proposed according to transmit bandwidth and machine time of disposing various kinds of message in Gnutella network. The F-Measure parameters which is used to evaluate the performances of search engine is introduced into connection of control management. We can abandon some redundant connections through calculating those parameters while keep the messages' reachable rate. This solution is realized by the discarding connection management algorithm (DCMA). We provide the instance of algorithms and discussion to the algorithm also. This paper still provides two kinds of measures to assist DCMA to carry network management. Both measures can enhance the connection management in Gnutella network effectively.3. Solve the effect of shortcut effect, improve the message reachabilityIn of the P2P network of the structure, the reachability of news is the key to ensuringinquiring about successfully. It is redundant in a large amount that it causes information of the network that the inundation type of news is broadcast, introduce two kinds of controlling mechanisms for this reason: News survives and news only show that agrees with (UID) the time (TTL ), very effective reduction is redundant. However, the associations of two kinds of mechanisms and the constructing to delay differently of large-scale network, make some nodes in the network unable to arrive, namely the so-called short circuit effect. Find through studying, R _ TTL ring is a basic reason which produces redundant news in the network. This literary grace uses two kinds of solutions: Last controlling mechanism each, store by TTL value that reach first, with and then TTL value that reach compare, make the nodes taking TTL as radius all can be reached; Another kind revises Gnutella agreement, has increased such news as hello , bad ,etc, used to find that combines R in the disconnection network _ TTL ring . The experiment indicate that uses Gnutella procotol after improving, the redundant news in Gnutella network reduces, short out effect reduce, news can the up toing rate raise.4. Verify the method and theory on the basis of the time agreement of automatic machine Protocols are artery of computer networks. The technology of formal specification canprovide unambiguous descriptions, and can formally analyze and refine them. The finite automaton is one of the most significant formal specification techniques. However, there exists state-explosion problem during the verification of systems. We analyzed the algorithm of constructing region automata of R. Alur and D.L. Dill, and found that there were many unreachable states and some reachable but unavailable states in the region automata. After studying further the clock constraints, we eliminated some unreachable and unavailable states when seeking clock regions and timed successors. Thus we optimized the method of constructing region automata and efficiently improved the algorithm of R. Alur.5. Gnutella protocol, construct no RTTL ring network protocol formal specification and protocol verificationA large amount of P2P software have been developed in Gnutella protocol 0.4, and the network protocol of constructing no R_TTL ring was introduced in order to solve the shortcut effect by author. UPPAAL is selected to carry on modeling, simulation, and automatically verification .it's a tool for the formal specification and protocol verification to both protocols. We design and structure the automaton to such process as servent, channels, user's environment, etc. Then combine these automatons into one network to simulating function of whole Gnutellanetwork through synchronized operation. Also such a series of nature as the exactness, security, liveness of the protocol have been verified in this paper.Because the formal specification and protocol verification to P2P protocols have not been found in domestic and international researches, the job of this paper should be initiative, and must play an important role, no matter in the theoretical research or practical application.
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