The Research Of Several Key Techs On File Transfer Based On Petri Net

Design of large scale system should apply formal methods. Formal method is based onstrict mathematical basis, and s a development method that has precise mathematicalsemantics. Formal methods can improve the quality of software system development and theefficiency of project potentially, which plays an important role in the process of softwaresystem development.Petri net is suitable for representing the sequence, concurrent, conflicts andsynchronization phenomenon of the system. As a kind of system description tool, not only thestatic structure of system could be depicted by Petri net, but also the dynamic behavior of thesystem. Petri net contains an intuitive graphical representation and the profound connotationand the foundation of mathematics, the model verification can be realized by using manymathematical methods. So, Petri net is an effective tool for formalized large-scale systemdevelopment.Concurrency is a basic characteristic for the computer network, the nodes within thenetwork may transmit file data frequently, the order of file transfer cannot be determined, theresources scheduling of file transfer is a meaningful work. In this paper, two feasible solutionsare proposed for the Gnutella file sharing system and the parallel file transmissionrespectively:(1) We construct a model of Gnutella file sharing system by the extended colored Petrinet and realized the message deal and data deal for the one-to-one and the one-to-many modelcommendably. Then, CPN Tools is applied for simulating the process of the service, and thebehavior of system is also analyzed. Finally, as the situation of the several nodes own thesame file and the node out of line frequently, considered the bandwidth of nodes and thenode’s quality of transfer service we proposed a transfer method which used to handle parallelfiles with priority level to decrease the influence of the node’s off line effectively and the timethat the transfer spend, furthermore it can also balance the load and improve the performanceof the system efficaciously.(2) Petri net is used for modeling the process of parallel file transmit, time becoming aconsumable resource that transition firing required and describe the time that file transmit costintuitively, so it can be helpful for the analysis of the file transmit. Finally, the article useS-Invariants analyze the dynamic behavior of the model, and verify the reasonableness andaccuracy of the model.