摘要
即时消息(IM)就是一种实时发送简短信息到在线用户的一种手段。即时消息结合了两个关键的技术—即时消息传递和存在信息—已经在互联网上很流行，并且产生了许多有趣的服务和特色。现在，即时消息服务正朝着移动领域发展，移动的即时消息增添了许多更吸引用户的特色。移动的即时消息主要的好处是访问即时消息服务变得更普遍，意味着用户能够交互即时消息和存在信息，不只是在电脑前。
作者在本文中引入了即时消息系统如何支持移动性。设计了一个支持移动的即时消息系统原型—Jchat，它具有新的特点和功能。开源软件Jabber和它的开放的XML消息协议作为一个基本的即时消息的框架。在这个框架上，增加了支持无线设备用户的重要功能。Jchat为移动电话和桌面电脑提供客户端应用程序，它们分别是用Java 2 Micro Edition和Java 2 Standard Edition作为开发工具的。
Jchat原型的基本特点是提供给用户具有扩展的感知信息。在存在的系统中，移动用户在不同的环境和设置中可能不能获得感知信息。在Jchat原型中，感知信息沿着三个不同的轴—存在，设备和内容。扩展的感知信息对于在移动环境中的用户改进通信是重要的。
系统使用Jabber设计和实现，扩展Jabber支持移动性。
研究了如下几个方向：
·真正的瘦客户端的处理，通过减少客户端的处理和通信
·单用户的多个同时活动的客户端
·在存在／感知协议里位置信息的集成
·对接收者，目标设备和位置的透明和不透明的消息的支持
Instant Messaging(IM) is a way of sending short,simple messages that are delivered immediately to online users.Instant Messaging combines two key technologies-instant message delivery and presence information-instant messaging services have proven popular on the Internet and have given birth to a range of other interesting services and features. Now,instant messaging services are moving to the mobile domain.The benefits of mobility adds a number of features to make it even more attractive to the user. The main added benefits is that access to IM services becomes ubiquitous,meaning that a user can access presence information and exchange IM messages ,not only when seated in front of a desktop PC
In this thesis,the author has studied how support for mobility can be introduced in IM systems.New features and functionality is demonstrated in a prototype implementation of an EVI system with mobility support-Jchat.The open source software Jabber and its open XML message protocol is used as a framework for basic IM functionality.Upon this framework we added this functionality found important to support users on wireless devices. Jchat provides client applications for mobile phones and desktop PCs,developed with Java 2 Micro Edition and Java 2 Standard Edition,espectively
Providing users with extended awareness information is a fundamental feature of the Jchat prototype, mobile users can be in different environments and settings not captured by the awareness information available in existing systems.The awareness information in Jchat is structured along three independent axes-presence,devices and context.Extended awareness information is important to improve communication between users in mobile environments.
The system is designed and implemented using Jabber, extended to jabber support mobility.
Several areas are to be investigated:
handling of very thin clients, by reducing client processing and communication
multiple simultaneously active clients for single person
integration of location information in presence/awareness protocol
support for both transparent and opaque messaging with respect to recipient, target device and location
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