传统Web通信系统多采用轮询拉取方式，此种方式存在实时性低、网络资源消耗大、扩展性差等缺点。针对上述问题，本文研究了WebSocket中的长连接技术，结合MQTT协议，提出了基于pub/sub模型的Web端即时通信解决方案，以推送取代传统拉取方式。文中重点阐述了 IM 与通知类消息格式设计，并针对通知类消息提出了 agent 代理模型，同时为了进一步减少网络资源消耗，提出了预订阅模式。最后将该解决方案与现流行的bosh+xmpp方式在时延、带宽消耗方面做了对比分析，以验证该方案的性能优势。%Polling pull strategy, which is widely used in traditional web communication system, has some problems, such as low real-time, heavy consumption of network resource and poor scalability. To solve these problems, much research about long connection technology in WebSocket has been done in the paper. Combining WebSocket with MQTT protocol, a new web instant messaging solution based on pub/sub model was proposed to replace polling strategy with push strategy. The formation design of IM and notification message was described in detail. And agent model was proposed for notification message. Meanwhile, a pre-subscription scheme was put forward to decrease net resource consumption further. Moreover, a comparative analysis on delay, bandwidth consumption between the solution and a current popular way bosh+xmpp was done to verify the advantages of the solution.
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