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How does Skype presence work -- Push or Pull?

    Question

  • 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.
    Tuesday, September 4, 2018 10:54 PM

All replies

  • It can be both.

    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.

    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.

    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 The polling interval is generally 5 minutes, so that means presence information can be outdated in this case.

    Thursday, September 20, 2018 7:51 PM