Skype的存在如何运作 - 推或拉？ [英] How does Skype presence work -- Push or Pull?

问题描述

有谁知道Skype的存在在技术上是如何工作的，这些状态更新究竟如此快速地完成？所有客户端是否都在不断地轮询服务器以获取其联系人的状态，或者当联系人状态中的某人变为
时，是否会从服务器推送到所有客户端。

Does anyone know how the Skype presence technically works regarding how exactly are those status updates done so fast? Are all the clients constantly polling a server to get status on their contacts or is there a push from the server to all clients when someone in their contacts' status changes.

推荐答案

它可以是两者。

It can be both.

如果为用户创建持久订阅，则服务器会跟踪该用户，并且当该用户更改其存在时，服务器将使用新的状态信息发送通知。 这提供了最快的更新速度，通常具有第二个
或两个存在更改。

If you create a persistent subscription for a user, then the server tracks that and when that user changes their presence, the server will send a notify with the new presence information.  This provides the fastest update speed, generally with a second or two of the presence change.

用户只能订阅一定数量的用户，同样用户也可以只能由一定数量的用户订阅。 该数字默认为200. 对这些订阅有性能影响，并且
对服务器的影响越大。

A user can only subscribe to a certain number of users, and likewise a user can only be subscribed to by a certain number of users.  That number is 200 by default.  There are performance implications for these subscribes and the more there are the greater impact it has on the server.

在某些情况下，客户端只进行轮询订阅，这意味着它会查询定期为用户提供服务。 它之所以这样做是因为它超过了允许的持久订阅数量，或者在某些情况下因为预期不需要持续订阅
，例如Outlook电子邮件中的状态点或搜索结果。轮询间隔通常为5分钟，这意味着在这种情况下，状态信息可能已过时。

In some cases the client only does a polling subscription, meaning it queries periodically for the users presence.  It does this either because it is exceeding the number of permitted persistent subscriptions, or in some cases because it is not expected that a persistent subscription is needed, such as for presence dots in outlook emails, or in search results. The polling interval is generally 5 minutes, so that means presence information can be outdated in this case.

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