【作者】 李彬；

【导师】 王芙蓉；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2006， 硕士

【摘要】 VoIP已经成为如今语音通信发展的趋势,但是随着其商用范围的不断扩大,一系列安全管理问题随之而生,其中就包括VoIP合法监听问题。本文主要针对VoIP合法监听问题进行深入研究,并给出了具体解决方案,实现了其关键实体——监听接入点IAP(Interception Access Point)。论文介绍了VoIP的基本原理及实现方式,以及会话初始化协议SIP(Session Initiation Protacol)和SIP基本呼叫流程,并详细探讨了网络监听关键技术,包括监听原理、包过滤技术和协议分析技术。针对网络监听问题,引入欧洲电信标准委员会(ETSI)提出的软交换系统监听模型,详细讨论了该模型中各实体的功能及接口。在此基础上结合会话边缘控制器SBC(Session Border Controller)接入组网的VoIP部署方式,给出了分别基于业务逻辑、旁路媒体流、设置监听器和信令中转的四种监听系统部署方案,通过对比分析监听需求、设计原则和系统性能要求,选取设置监听器为最佳部署方案。其次,在对SBC工作机制深入分析的基础上,结合监听数据需求以及监听系统部署方案,提出了IAP的总体设计,详细描述了IAP的功能结构和工作机制,并通过使用libpcap函数库给出了IAP的关键模块——捕获分析模块的具体实现。IAP的主要设计思想是通过INVITE消息中携带的电话号码触发监听,通过分析SIP消息,得到信道信息,更新过滤规则,从而完整获得该通话的所有呼叫相关信息和通话内容。它有三个特点:第一能够捕获会话中动态分配的媒体端口和信令端口;第二依据端口,快速更新过滤器规则,缩短过滤时间;第三是通过构造状态机准确把握呼叫相关信息对应的会话状态。最后对模式匹配算法进行了研究,改进了Boyer-Moore-Horspool(BMH)算法,通过采用多线程处理和线程池技术,减少了线程开销,提高了IAP监听效率。更多还原

【Abstract】 VoIP has already been the trend of voice communication. Yet, along with the expending of its business scope, a series of security and management problems occurs, including the Lawful Interception (LI) problem. This paper mainly researches in the lawful interception of VoIP, and proposes a concrete solution of it as well as implementation of its interception access point (IAP).This paper introduces the basic theory of VoIP and its deployment, as well as the Session Initiation Protocol (SIP) and its basic callflow. It discusses the key technology of the network interception, including the interception theorem, packet filtering and protocol analyzing technology. Then, it introduces a LI model which was designed by IETF for the softswitch system, in addition, it introduces the function of each functional entity and the interfaces between them. Then, it raises four solutions of the LI system’s deployment on the basis of the network involving the Session Border Controller (SBC). The four solutions are making use of conference service, changing the route of media stream, setting packet filter and forwarding the signals.Whereafter, the advantages and disadvantages of each solution are discussed, and the setting packet filter method is chosen as the best LI network deployment solution according to the acquirement of interception and the principles of designing.After the analyzing of the SBC’s mechanism, this paper designs the IAP on the basis of the requirement of interception data and the deployment of the LI system, and describes its architecture and mechanism in detail. Then it uses the libpcap functions and gives the implementation of the filtering and analyzing module which is the key inner module of IAP.According to the main design consideration of IAP, the interception is triggered by the INVITE message with the phone number, the filter’s rule code is refreshed with the message type and the call related information which is derived from the SIP message. There are three features of the implementation, The first one is that, the media stream ports and the signal ports can be captured during the session, the second one is the filter’s rule code is refreshed with the ports captured, which results in the reduction of the time of filtering. The last feature is that, it can correlate the session’s state and the interception infomaion with the help of the state machine. At the end, the string pattern matching is researched, and a new algorithm derived from Boyer-Moore-Horspool(BMH) algorithm is raised. In addition, muti-thread processing and thread-pool technology are introduced in the system to increase the efficiency of the IAP.更多还原