首先,XMPP 是一种协议(protocol),而不是客户端或服务器。使用它的好处之一是可以广泛使用 XMPP 客户端和服务器实现。 Wikipedia article解决了您的大部分问题。
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The architecture of the XMPP network is similar to email; anyone can run their own XMPP server and there is no central master server.
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XMPP could use HTTP in two ways: polling[21] and binding.[22] The polling method, now deprecated, essentially implies messages stored on a server-side database are being fetched (and posted) regularly by an XMPP client by way of HTTP 'GET' and 'POST' requests. With HTTP binding, the client uses longer-lived HTTP connections to receive messages as soon as they are sent. This push model of notification is more efficient than polling, where many of the polls return no new data.