【作者】 张泽鹏；

【导师】 温向明；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2010， 硕士

【摘要】 近年来随着P2P技术的日益成熟与发展,以Maze, PPLive, Skype为代表的P2P文件共享软件和即时通信软件受到了越来越多用户的青睐。P2P是一种要求端到端的对等的连接与通信的技术,然而网络上存在的NAT设备却阻止来自外部未知网络主机的连接,这样就造成了P2P技术应用与发展的瓶颈。因为NAT设备隐藏了构建P2P网络的节点信息,因此如何使得位于NAT设备后面的节点在P2P网络中查找对方建立连接成为P2P技术发展过程中亟待解决的问题之一。本文首先介绍了P2P技术的特点与应用场景,重点分析了本课题研究中涉及到的三种P2P模型。本文对NAT穿越理论的基础做了全面研究,包括NAT的原理,类型与应用,并对基于TCP的NAT穿越技术做了全面介绍,通过测试分析了目前基于TCP的NAT穿越的各种解决方案,并比较了这些技术的优缺点。本文在研究了NUTSS协议的基础上,基于NUTSS协议应用的局限性提出了改进的NAT穿越模型CNUTS,并且提供了相关设计方案及核心实现代码。CNUTS模型的突出之处在于提出了两种全新的穿越模式：SYN/ACK生成模式和“同时打开”模式以及端口预测功能,这样建立了穿越行为与网络环境之间的关系,使得对于不同的NAT类型以及不同的网络架构,CNUTS能选择最优化的穿越行为建立TCP连接。本文的重点集中在穿越模型的设计和实现。采取了模块化思想,在客户端以及服务器端实现了用户信息注册,类型检查,端口扫描,穿越选择,穿越通信模块以及维护注册信息的更新等功能。通过理论分析和仿真试验,新的穿越模型不但克服了目前穿透机制的对对称性NAT设备以及高安全性网络的不支持,而且提高了穿越的性能以及成功率,大大增强了P2P网络的通信效率。本文最后对NAT穿越技术进行了展望。更多还原

【Abstract】 With the development of P2P (Peer-to-Peer) technologies, some software in file sharing and instance message, for instance, Maze, PPLive and Skype, has been used more and more online. P2P is a technology which enables connection and telecommunication between peers, while some NAT equipment disables unknown outer connections, which prevent the development of p2P. So how to discover other peers behind NAT and make a connection is one of the problems in P2P networks.First of all, the paper introduces the concept of P2P networks, and analysis three P2P modular covered in this paper. Also introduce NAT traversal theories over TCP, including NAT technology, types and implementation. And compares the advantages and disadvantages of approaches on the NAT traversal over TCP.Then the paper introduces the optimized mechanism based on NUTSS protocol, CNUTS, and provides the design framework, core coding implantation. The principle method is proposed two traversal modes:SYN/ACK mode and "simultaneously open"mode, which make a optimized mode selection based on the net conditions and NAT types to enhance the traversal success rates effectively.The paper emphasize on the design and implantation of traversal modular. At client and server point, user register, NAT type detection and selection of NAT traversal methods, updated messages modular are achieved in our system. And the test results identified the system can not only access to symmetric NAT, but also reach a high successful rates.Finally the paper gives summarizations and prospect to NAT traversal.更多还原