这是依赖于浏览器。
默认情况下，IE浏览器有两分钟一分钟的附加限制因素（ServerInfoTimeout）的KeepAliveTimeout值。任何一个设置都可导致Internet Explorer重置套接字。 - 从IE浏览器的支持 http://support.microsoft.com/kb/813827

Firefox是围绕着相同的值，我认为也是如此。

Firefox is around the same value I think as well.

虽然通常服务器超时设置比浏览器超时低，但至少你可以控制，并设置较高的。

Usually though server timeout are set lower than browser timeouts, but at least you can control that and set it higher.

您宁愿处理超时的，所以这样你可以在这样的事件采取行动。
看到这个主题：How在浏览器的AJAX（XmlHtt prequest）调用检测超时？

You'd rather handle the timeout though, so that way you can act upon such an event. See this thread: How to detect timeout on an AJAX (XmlHttpRequest) call in the browser?