即时通讯系统的设计与实现

【作者】 杨烜会；

【导师】 吉国力；

【作者基本信息】 厦门大学 ， 系统工程， 2002， 硕士

【摘要】 新兴的即时通信(Instant Messaging)是目前互联网应用的一大热点。即时通信系统通过建立网络虚拟社区，为用户提供了实时有效的沟通手段。随着即时通讯系统向综合通讯媒体的演化、向企业应用领域的进军，这一领域的研究也日益重要，然而国内外关于即时通讯的研究还不够系统和深入。 在承担定向即时通讯系统研发的过程中，我们通过调查研究解决了几个基础问题： 1．即时通讯系统需要做什么? 2．如何设计即时通讯协议? 3．如何实现即时通讯服务器? 继而又引发了以下的思考： 1．即时通讯系统发展的趋势是什么? 2．如何设计应用层通讯协议? 3．如何构造网络服务器框架? 围绕这几个问题，基于项目实践，我们对即时通信系统的概念、服务模式、通讯协议、服务器原理和实现方式等诸多层面做了系统总结。文中提出的应用层协议设计原则在开发应用层协议方面具有基础性的参考价值；我们设计的面向对象服务器框架是应用框架技术的新颖实例。 在本文中，通过对即时通信系统基本功能——出席信息和即时消息服务的剖析，我们描述了即时通讯抽象模型和与实际即时通信系统的映射关系；我们从TCP／IP协议研究中总结出若干应用层协议设计原则，并应用它们完整设计了一个即时通讯系统协议。我们比较了众多的服务器设计策略，提出了特殊的伴生端口机制和状态检测算法，给出了一个较好的服务器设计方案。通过吸收面向对象技术的最新思想——设计模式，我们提炼出一个即时通讯服务器的框架，它良好的扩展特性是我们讨论的重点。最后，通过产业调研，我们梳理了即时通信系统的发展脉络，同时也指出了即时通讯研究中亟待解决的问题。更多还原

【Abstract】 Instant Messaging (IM) is the highlight of current Internet applications, which provides web users with real-time, effective communications by organizing virtual Internet community. With the evolvement of IM to integrated web portal, and the advancement of IM to enterprise applications, studies on IM systems become more and more important. However, little result has been documented yet.In practice of our Directed IM Project, we encountered some fundmental problems: i. WHAT can IM provide for users?ii. HOW to design an IM protocol?iii. HOW to implement an IM system, especially an IM server? When resolving these problems, some other questions raise: i. HOW can IM system be employed in other form?ii. HOW to design application protocols? iii. HOW to construct general network server frameworks?The formal questions are engineering whereas the latter are more theoretical. Focusing on these topics, we present our solutions and thinking in this paper. Application protocol designing and application framework constructing solutions are innovated. Together with these two, issues that cover almost all facets of IM systems, including conceptual model, protocol designing, server algorithms analysis and implementation, are addressed in detail in this paper.Following contents can be found in this paper:First, the mapping between IM abstract model and IM systems in practice is described. Secondly, by using some application protocol designing laws extracted from TCP/IP protocol family, the round-trip IM protocol designing is demonstrated. After subtle comparisons of algorithms for network server constructing, a schema for an effective IM server is brought out. By introducing Design Pattern, the most newly developed Objected-Oriented technique, an application framework with remarkable flexibility and extensibility is concluded from the Directed IM Project programming. At last, the tendency of IM systems and problems to be conquered are listed out.更多还原