长时间轮询：也就是所谓的异步轮询，这种方式是纯服务器端推送方式和客户端拉取方式的混合。
Long Polling: Also known as Asynchronous Polling, this method is a hybrid of pure server push and client pull.
Facebook聊天功能提供了关于AJAX一个有意思的问题案例：把数据从服务器端推送到客户端。
Facebook chat provides an example of an interesting problem with AJAX: pushing data from server to client.
另一种通信形式就是消息，这样应用就可以推送来自于服务器端的消息并进行近乎实时的通信。
The other type of communication is messaging. This can be used to create applications that push messages from the server and perform near real time communication.
RTMP的一个主要好处是可以一直打开与客户端的连接，这样就可以推送服务器端的数据了。
One of the primary benefits of RTMP is the connection with the client stays open so it can be used to push data from the server.
DWR不仅省去了大量客户端和服务器端编码，而且ReverseAjax还从代码中将完整的服务器-推送机制抽象出来。
Not only does DWR save you much client - and server-side coding, but Reverse Ajax also abstracts the whole server-push mechanism away from your code.
DWR不仅省去了大量客户端和服务器端编码，而且ReverseAjax还从代码中将完整的服务器-推送机制抽象出来。
Not only does DWR save you much client - and server-side coding, but Reverse Ajax also abstracts the whole server-push mechanism away from your code.
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